JPWO2003028314A1 - COMMUNICATION METHOD, TRANSMISSION DEVICE, RECEPTION DEVICE, COMMUNICATION PROGRAM, COMPUTER-READABLE RECORDING MEDIUM CONTAINING THE COMMUNICATION PROGRAM, AND NETWORK SYSTEM - Google Patents

Abstract

In the communication method of the present invention, acknowledgment information for a plurality of transmission packets (1 to 20) is collectively notified from the receiving station to the transmitting station via the acknowledgment packets (Dly ACK packets a to d). The delivery confirmation packet includes reception information about a packet that may not yet be received. This provides a communication method that avoids delaying retransmission due to packet loss, expiration of a packet, and packet rearrangement.

Description

送信状況リストは送信するストリーム毎に作成され、当該ストリームを格納する各パケットの送信状況を示す。受信状況には「未送信」、「送信済」、「再送要」の３種類がある。「未送信」は送信局２０１が当該パケットをまだ送信していないことを示す。「送信済」は送信局２０１が当該パケットを送信したが、再送が必要か否かが不明なことを示す。「再送要」は受信局３０１が当該パケットの受信に失敗したため再送が必要なことを示す。
パケット送信前の初期状態は「未送信」で、送信局２０１がパケットを送信すると当該パケット番号の送信状況が「送信済」となる。送信局２０１が受信局３０１からのＤＥＬＡＹＥＤ−ＡＣＫを受信した際、あるパケットのパケット番号が受信されていないことを示している場合に当該パケット番号の送信状況が「再送要」となる。
表２に受信局３０１の受信状況管理部３０６が管理する受信状況リストの一例を示す。
【表２】

受信状況リストは受信するストリーム毎に作成され、当該ストリームを格納する各パケットの受信状況を示す。状況には「未受信」、「受信済」の２種類がある。「未受信」は受信局３０１が当該パケットをまだ受信していないことを示す。「受信済」は受信局３０１が当該パケットを受信したことを示す。
パケット受信前の初期状態は「未受信」で、受信局３０１がパケットを受信すると当該パケット番号の受信状況が「受信済」となる。
図１３に本実施の形態における送信局２０１の動作のフローチャートを示す。
ここには図示していないが、送信局２０１はストリームデータを送信する前に、ストリームデータの種類、データサイズ、ストリームデータを識別するためのＩＤ、受信確認の方法（通常のＡＣＫがＤＥＬＡＹＥＤ−ＡＣＫか）などの情報について、受信局３０１の間でネゴシエーションを行う。このネゴシエーションが完了したら、送信局２０１は当該ストリームデータ用の送信準備を行う（例えば送信済みパケットの最大パケット番号を格納する変数Ｓｍａｘの初期化、送信状況リストの初期化など）。
引き続いて送信アプリケーション２０５が何らかの方法で送信要求を受信すると、送信アプリケーション２０５はストリームデータを送信パケット作成部２０６へ出力する。送信パケット作成部２０６はストリームデータを無線パケットに格納する形式に加工し、送信パケット管理部２０７へ送信する。送信パケット管理部２０７は受信したデータを自らのバッファに格納し、無線回線への送信権が得られるのを待つ。
またパケットに付番されるパケット番号は、同一ストリームデータ（ストリームデータ毎に各ストリームデータを識別するためのＩＤを持つが、そのＩＤが同一のパケット群）において０から昇順に１ずつ増加するよう付番される。
送信局２０１がパケット受信部２０２にて自局宛てのパケットを受信すると（ステップ４０１）、パケット受信部２０２はそのパケットが正常に受信されたか否かを判定する（ステップ４０２）。正常な場合、そのパケットを受信パケット判定部２０３に送信し、受信パケット判定部２０３はパケットの種類を判定する（ステップ４０３）。
受信パケット判定部２０３の受信したパケットがパケットを受信局３０１へ送信するための送信権を与えるポーリング用パケットである場合、受信パケット判定部２０３は送信パケット管理部２０７へ対象ストリームデータのＩＤを通知する。
通知を受けた送信パケット管理部２０７は、まず送信状況管理部２０４の管理するパケット送信状況リストを参照し、再送が必要なパケットをパケット送信部２０８経由で送信し、送信状況リストの当該パケットの欄を「送信済」と書き替える（ステップ４０４）。続いて新規送信するパケットを順に送信し、同様に送信状況リストの当該パケットの欄を「送信済」と書き換える（ステップ４０５）。
受信パケット判定部２０３の受信したパケットがＤＥＬＡＹＥＤ−ＡＣＫである場合、受信パケット判定部２０３は送信状況管理部２０４に受信したＤＥＬＡＹＥＤ−ＡＣＫに記されているストリームデータのＩＤと各パケットの受信状況を通知する。送信状況管理部２０４は送信されたＩＤから対象となるストリームデータを判定し（ステップ４０６）、当該ストリームデータの送信状況リストの更新を行う（ステップ４０７から４１２）。詳細な手順は次の通りである。
まずＤＥＬＡＹＥＤ−ＡＣＫで通知された最小のパケット番号Ｄｍｉｎを変数Ｘに代入し（ステップ４０７）、送信状況管理部の管理する送信済みパケットの最大パケット番号Ｓｍａｘとの大小を比較する（ステップ４０８）。もしＸが送信済みパケットの最大パケット番号Ｓｍａｘより大きい場合、以後のＤＥＬＡＹＥＤ−ＡＣＫに格納された情報は送信局２０１がまだ送信していないパケットに対するもののため無視する。Ｘが送信済みパケットの最大パケット番号Ｓｍａｘと等しいか小さい場合、すでに送信局２０１が送信したパケットに対する情報のため、パケット番号Ｘが受信済みか否かを確認する（ステップ４０９）。パケット番号Ｘが未受信の場合、送信状況リストのパケット番号Ｘの欄を「再送要」と設定する（ステップ４１０）。パケット番号Ｘが受信済みの場合何もしない。最後にパケット番号ＸがＤＥＬＡＹＥＤ−ＡＣＫに含まれている最大のパケット番号Ｄｍａｘ以上か否かを判定する（ステップ４１１）。パケット番号ＸがＤｍａｘより小さければ、次のパケット番号について同様な処理を行う（ステップ４１２以降）。パケット番号ＸがＤｍａｘ以上であれば、処理を終了する。そして次のパケットの受信を待つ。
受信パケット判定部２０３の受信したパケットがその他の種類のパケットである場合、受信パケット判定部２０３はそのパケットの種類に応じた処理を行う（ステップ４１３）。
図１４に本実施の形態における受信局３０１の動作のフローチャートを示す。
ここには図示していないが、送信局２０１からのストリームデータを受信する前に、ストリームデータの種類、データサイズ、ストリームデータを識別するためのＩＤ、受信確認の方法（通常のＡＣＫかＤＥＬＡＹＥＤ−ＡＣＫか）などの情報について送信局２０１と受信局３０１の間でネゴシエーションを行う。このネゴシエーションが完了したら、受信局３０１は当該ストリームデータ用の受信準備を行う（例えば受信済みパケットの最大パケット番号を格納する変数Ｒｍａｘの初期化など）。
またパケットに付番されているパケット番号は、同一ストリームデータにおいて０から昇順に１ずつ増加するよう付番されているものとする。
受信局３０１がパケット受信部３０２にて自局宛てのパケットを受信すると（ステップ５０１）、パケット受信部３０２はそのパケットが正常に受信されたか否かを判定する（ステップ５０２）。正常な場合、そのパケットを受信パケット判定部３０３に送信し、受信パケット判定部３０３はパケットの種類を判定する（ステップ５０３）。
受信パケット判定部３０３の受信したパケットがＤＥＬＡＹＥＤ−ＡＣＫで受信状況が伝達されるパケットである場合、受信パケット判定部３０３は当該パケットを受信パケット管理部３０４へ送信する。受信パケット管理部３０４はどのストリームを受信したかをＩＤから判定し（ステップ５０４）、自らの持つ当該ＩＤに対応するバッファへ当該パケットを蓄積する（ステップ５０５）。バッファに蓄積されたパケットに格納されたストリームデータは時刻などの出力条件が揃ったら受信アプリケーション３０５へ出力される。受信パケット管理部３０４はまた、受信状況管理部３０６に受信したストリームデータのＩＤとパケット番号を通知する。
受信状況管理部３０６は通知されたストリームデータのＩＤとパケット番号について、当該ストリームデータの受信状況リストに当該パケット番号が受信済であることを記録する（ステップ５０６）。そして当該パケット番号が受信済みパケットの最大パケット番号Ｒｍａｘより大きいなら（ステップ５０７）、Ｒｍａｘに当該パケット番号を代入する（ステップ５０８）。そして次のパケットの受信を待つ。
受信パケット判定部３０３の受信したパケットがＤＥＬＡＹＥＤ−ＡＣＫを送信局２０１へ返送するためのポーリング用パケットである場合、受信パケット判定部３０３はＤＥＬＡＹＥＤ−ＡＣＫ作成部３０７へ対象ストリームデータのＩＤを通知する。通知を受けたＤＥＬＡＹＥＤ−ＡＣＫ作成部３０７は、受信状況管理部３０６の管理するパケット受信状況リストを参照し、ＤＥＬＡＹＥＤ−ＡＣＫパケットを作成する（ステップ５０９）。そして作成したＤＥＬＡＹＥＤ−ＡＣＫパケットをパケット送信部３０８経由で送信局２０１へ送信する。
受信パケット判定部３０３の受信したパケットがその他の種類のパケットである場合、受信パケット判定部３０３はそのパケットの種類に応じた処理を行う（ステップ５１１）。
図１５に、本実施の形態における図１４のステップ５０９に係るＤＥＬＡＹＥＤ−ＡＣＫ作成手順の一例を示す。まず始めに、受信済みパケットの最大パケット番号Ｒｍａｘより大きなパケット番号を持つパケットが、いくつ送信されている可能性があるかを推定する（推定方法の例は図３〜図６に基づいて詳細に後述する。）。この推定した数をＰｌｏｓｓとする。
後述の推定方法でＰｌｏｓｓを推定した後、Ｄｍａｘ＝Ｒｍａｘ＋ＰｌｏｓｓとしてＤＥＬＡＹＥＤ−ＡＣＫに含める最大パケット番号Ｄｍａｘを定める（ステップ６０２）。
そして、受信状況リストのパケット番号Ｒｍａｘ＋１〜Ｄｍａｘまでの受信状況を「未受信」に設定する。もっとも、初期処理によって「未受信」と設定されている場合、この処理は不要である。
最後に、パケット番号Ｄｍａｘから通知が必要なパケットまでの受信状況を順にＤＥＬＡＹＥＤ−ＡＣＫパケットに格納する（ステップ６０３）。
本実施の形態ではステップ６０１〜６０３で示したように、受信局３０１が実際に受信したパケットよりも新しい、すなわち送信局２０１が未だ送信していないかも知れないパケットについてパケット受信状況を「未受信」としてＤＥＬＡＹＥＤ−ＡＣＫを送信している。
これを受信した送信局２０１は、ステップ４０７から４１２で示した処理を実行するため、受信したＤＥＬＡＹＥＤ−ＡＣＫ中のパケット番号が送信済みのものであれば、通常の未受信のケースと同様にしてそれらのパケットは再送される。
また、受信したＤＥＬＡＹＥＤ−ＡＣＫ中のパケット番号が未送信のものである場合は、送信局２０１がそれらの情報を無視して予定通りにパケットを送信するため、通常の処理と同様の順序でパケットを送信できる。
すなわち受信局３０１が、まだ送信されていない可能性があるパケットについてのパケット受信状況を「未受信」として送信局２０１に返送することにより、ＤＥＬＡＹＥＤ−ＡＣＫ送信直前に送信されたパケット（パケット群）が紛失している場合も、ステップ４０４に示したようにそれらのパケット（パケット群）は次のＴＸＯＰで再送することが可能となる（ＤＥＬＡＹＥＤ−ＡＣＫ送信後であって、当該ＴＸＯＰ内で上記パケット（パケット群）を再送してもよい。）。また受信局においては送信側の意図した本来のパケット順での受信が可能となる。
本発明は、上記の場合に限定されるものではなく、次のように処理してもよい。すなわち、受信局の返送するＤＥＬＡＹＥＤ−ＡＣＫに含まれているパケット番号より新しいパケットは受信失敗したと送信局が解釈する場合の例を以下に示す。なお、機器構成、メッセージシーケンス、送信局および受信局のブロック図、および受信局動作のフローチャートは上述の場合と同一のため記述を省略する。
図１６に本実施の形態における送信局２０１の動作のフローチャートを示す。なお、送信局２０１の動作のうち図１３における動作と同じところは記述を省略し、当該ストリームの送信状況リストの更新を行う部分（ステップ７０７〜７１３）のみ記載する。
まずＤＥＬＡＹＥＤ−ＡＣＫで通知された最小のパケット番号Ｄｍｉｎを変数Ｘに代入し（ステップ７０７）、パケット番号Ｘが受信済みか否かを確認する（ステップ７０８）。パケット番号Ｘが未受信の場合、送信状況リストのパケット番号Ｘの欄を「再送要」と設定する（ステップ７０９）。パケット番号Ｘが受信済みの場合何もしない。続いてパケット番号ＸがＤＥＬＡＹＥＤ−ＡＣＫに含まれている最大のパケット番号Ｄｍａｘ以上か否かを判定する（ステップ７１０）。パケット番号ＸがＤｍａｘより小さければ、次のパケット番号について同様な処理を行う（ステップ７１１以降）。パケット番号ＸがＤｍａｘ以上であれば、以下の処理へ進む。以下の処理に進む時点でＤＥＬＡＹＥＤ−ＡＣＫに含まれているパケット情報についての送信情報リストへの反映は終了している。
次に送信済みパケットの最大パケット番号ＳｍａｘとＤＥＬＡＹＥＤ−ＡＣＫに含まれている最大のパケット番号Ｄｍａｘとの大小を比較する（ステップ７１２）。もしＳｍａｘがＤｍａｘより大きい場合、ＤＥＬＡＹＥＤ−ＡＣＫに含まれていない送信済パケット情報が存在することを意味する。この場合、それらのパケットは受信失敗したものと解釈し、送信状況リストのパケット番号Ｄｍａｘ＋１からＳｍａｘについて「再送要」と設定する（ステップ７１３）。ＳｍａｘがＤｍａｘと等しいか小さい場合は何もしない。そして次のパケットの受信を待つ。
図１７に、本実施の形態における図１４のステップ５０９に係るＤＥＬＡＹＥＤ−ＡＣＫ作成手順の一例を示す。
まずＤｍａｘ＝ＲｍａｘとしてＤＥＬＡＹＥＤ−ＡＣＫに含める最大パケット番号を定める（ステップ８０１）。次にパケット番号Ｄｍａｘから通知が必要なパケットまでの受信状況を順にＤＥＬＡＹＥＤ−ＡＣＫパケットに格納する（ステップ８０２）。
本実施の形態ではステップ７１３で示したように、受信したＤＥＬＡＹＥＤ−ＡＣＫで通知されたパケット情報の最新のものより、送信局２０１が新しいパケットを送信していた場合に、送信局２０１がＤＥＬＡＹＥＤ−ＡＣＫで通知されなかったそれらのパケットは受信失敗したとみなして再送するよう設定している。
これにより、ＤＥＬＡＹＥＤ−ＡＣＫ送信直前に送信されたパケット（パケット群）が紛失している場合も、ステップ７０４に示したようにそれらのパケット（パケット群）は次のＴＸＯＰで再送される（ＤＥＬＡＹＥＤ−ＡＣＫ送信後であって、当該ＴＸＯＰ内で上記パケット（パケット群）を再送してもよい。）。また受信局においては送信側の意図した本来のパケット順での受信が可能となる。
ここで、本実施の形態において、パケット紛失に伴う再送が遅れてしまうこと、パケットの有効期限が切れてしまうこと、及びパケットの並べ替えをそれぞれ回避するために、講ずるべき措置（次の何れかの措置▲１▼又は▲２▼）についてより具体的に説明する。
▲１▼受信局では、受信済の最新パケットの順序番号にある数を加えた順序番号まで送信されたものとみなす。そして、ＤＥＬＡＹＥＤ−ＡＣＫに、その番号のパケットまでの受信情報を含める。最新パケットとは、送信局が再送を行わない場合のパケット順において、最後に受信されたパケットを意味し、順序番号がシーケンシャルに増加し続ける場合において、受信されたパケットのうち最大の順序番号を持つもの。
▲２▼送信局におけるＤＥＬＡＹＥＤ−ＡＣＫの解釈方法に、『ＤＥＬＡＹＥＤ−ＡＣＫに、送信済かつ受信成功の通知を受信していないパケットについての受信情報が含まれていない場合、当該パケットの送信は失敗したものとみなされる』という解釈を導入する。以下に、詳細に説明する。
従来においては、ＤＥＬＡＹＥＤ−ＡＣＫは、既に受信したパケットまたは受信していないことがはっきりしているパケットに対して、その受信状態を送信局へ通知するものである。
これに対して、本実施の形態の上記措置▲１▼によれば、受信局において、未だ送信局が送信しているかどうか不明のパケットの受信情報（受信状況）までをＤＥＬＡＹＥＤ−ＡＣＫに含めるようにしている。
このように、未だ送信局が送信しているかどうか不明のパケット（未だ送信局が送信していない可能性のあるパケット）の受信情報までをＤＥＬＡＹＥＤ−ＡＣＫに含めることによって、送信局は、これら不明のパケットを適宜、次のＴＸＯＰにおいて、再送することが可能となる（ＤＥＬＡＹＥＤ−ＡＣＫ送信後であって、当該ＴＸＯＰ内で上記パケット（パケット群）を再送してもよい。）。
ここで、図１を参照しながら、上記措置▲１▼の具体例を説明する。なお、図１８等と同じ機能を有するものについては、同一の参照符号を付記し、詳細な説明は省略する。
図１に示すように、まず、ＴＸＯＰ−１において、パケット群Ａ内のパケット１〜５が送信局から受信局へ送信される。受信局は、前述のように、ＤＥＬＡＹＥＤ−ＡＣＫパケットａを介して、パケット１〜５及び以前のＴＸＯＰで送信されたパケット−４〜０を送信局へ通知する。
送信局は、このＤＥＬＡＹＥＤ−ＡＣＫに基づいて、パケット１〜５が無事に受信局で受信されたと判断し、次のＴＸＯＰ−２において、パケット群Ｂのパケット６〜１０を受信局へ送信する。このとき、何らかの原因でパケット群Ｂのパケット１０が受信局で受信および検出されなかったとする。
本実施の形態によれば、このような状況下では、受信済の最新パケットの順序番号『９』に、ある数（図１の場合、『１』）を加えた順序番号までのパケット（つまり、パケット１０まで）が送信されたと推定し、その旨をＤＥＬＡＹＥＤ−ＡＣＫパケットｂに受信情報として含める。なお、上記のある数は、後述の方法などを用いて決定すればよい。
つまり、受信局では、パケット群Ｂのパケット６〜１０の全てが送信されたとみなし、これらパケット６〜１０の各受信情報が送信局へ通知されることになる。図１によれば、受信済のパケット６〜９（最新パケット）と未受信のパケット１０とに係る受信情報がＤＥＬＡＹＥＤ−ＡＣＫに含められる。
送信局は、ＤＥＬＡＹＥＤ−ＡＣＫパケットｂを介して、パケット群Ｂ内のパケット１０が受信局により受信されていないこと（パケット６〜９については受信済、パケット１０については未受信とそれぞれ通知されるため、受信情報から判明する。）をＤＥＬＡＹＥＤ−ＡＣＫに基づいて判断し、次のＴＸＯＰ−３において、パケット１０の再送を受信局に対して行う。結局、ＴＸＯＰ−３において、再送すべきパケット１０以外に、パケット群Ｃのパケット１１〜１４が併せて、受信局へ送信される。
受信局では、パケット１０〜１４に係る受信情報をＤＥＬＡＹＥＤ−ＡＣＫに含め、ＤＥＬＡＹＥＤ−ＡＣＫパケットｃを介して送信局へ通知する。送信局では、この通知（ｃ２参照）により、再送したパケット１０に加えてパケット１１〜１４が無事に受信局により受信されたと判断し、次のＴＸＯＰ−４において、パケット群Ｄのパケット１５〜１９が受信局へ送信される。受信局では、パケット１５〜１９に係る受信情報をＤＥＬＡＹＥＤ−ＡＣＫに含め、ＤＥＬＡＹＥＤ−ＡＣＫパケットｄを介して送信局へ通知する。
なお、図１の例では、既に送信しているパケットについては、受信した受信状況を参照して必要ならば再送処理が行われる。また、未送信のパケットについては、当該情報は無視される。
以上のように、ＴＸＯＰ−２で受信に失敗したパケット１０は、次の送信機会であるＴＸＯＰ−３において迅速に再送されることになる。したがって、パケット紛失に伴う再送が遅れてしまうこと、パケットの有効期限が切れてしまうこと、及びパケットの並べ替えを行うことをそれぞれ確実に回避できる。
ここで、図２を参照しながら、上記措置▲１▼を講ずる他の例を以下に説明する。
図２に示す例は、パケット群Ｂの全てのパケット６〜１０が、何らかの原因で受信局により受信および検出されなかった場合を示す。なお、図１等と同じ機能を有するものについては、同一の参照符号を付記し、詳細な説明は省略する。
図２に示すように、まず、ＴＸＯＰ−１において、パケット群Ａ内のパケット１〜５が送信局から受信局へ送信される。受信局は、前述のように、ＤＥＬＡＹＥＤ−ＡＣＫパケットａを介して、パケット１〜５及び以前のＴＸＯＰで送信されたパケット−４〜０を送信局へ通知する。
送信局は、このＤＥＬＡＹＥＤ−ＡＣＫに基づいて、パケット１〜５が無事に受信局で受信されたと判断し、次のＴＸＯＰ−２において、パケット群Ｂのパケット６〜１０を受信局へ送信する。このとき、何らかの原因でパケット群Ｂのパケット６〜１０が受信局で受信および検出されなかったとする。
上記のように、最新パケットは、パケット５であるので（パケット１〜５までは、受信局により受信済であるので）、受信済の最新パケットの順序番号『５』に、ある数（図２の場合、『５』（つまり、一つのＴＸＯＰで送信されるパケット数の最大値）を加えた順序番号までのパケット（つまり、パケット１０まで）が送信されたと推定し、その旨をＤＥＬＡＹＥＤ−ＡＣＫパケットｂに受信情報として含める。ＤＥＬＡＹＥＤ−ＡＣＫパケットｂには、パケット６〜１０に係る受信情報が含められる。
つまり、受信局では、パケット群Ｂのパケット６〜１０の全てが送信されたとみなし、これらパケット６〜１０の各受信情報が送信局へ通知されることになる。図２によれば、パケット６〜１０に係る受信情報がＤＥＬＡＹＥＤ−ＡＣＫに含められる。
送信局は、ＤＥＬＡＹＥＤ−ＡＣＫパケットｂを介して、パケット群Ｂ内のパケット６〜１０が受信局により受信されていないことをＤＥＬＡＹＥＤ−ＡＣＫにより判断し、次のＴＸＯＰ−３において、パケット６〜１０の再送を受信局に対して行う。その結果、ＴＸＯＰ−３において、再送すべきパケット６〜１０が受信局へ送信される。
受信局では、パケット６〜１０に係る受信情報をＤＥＬＡＹＥＤ−ＡＣＫに含め、ＤＥＬＡＹＥＤ−ＡＣＫパケットｃを介して送信局へ通知する。送信局では、この通知（ｃ２の内容参照）により、再送したパケット６〜１０が無事に受信局により受信されたと判断し、次のＴＸＯＰ−４において、パケット群Ｄのパケット１１〜１５が受信局へ送信される。受信局では、パケット１１〜１５に係る受信情報をＤＥＬＡＹＥＤ−ＡＣＫに含め、ＤＥＬＡＹＥＤ−ＡＣＫパケットｄを介して送信局へ通知する。
以上のように、ＴＸＯＰ−２で送信に失敗したパケット６〜１０は、次の送信機会であるＴＸＯＰ−３において迅速に再送されることになる。したがって、パケット紛失に伴う再送が遅れてしまうこと、パケットの有効期限が切れてしまうこと、及びパケットの並べ替えを行うことをそれぞれ確実に回避できる。
図１及び図２は、パケット群の最後のパケット又はパケット群のパケット全体が、何らかの原因により、受信局により受信されなかった場合に、受信済の最新パケット以降、当該ＴＸＯＰ終了までに送信され得るパケット数を推定し、最後に受信したパケットの順序番号に、その推定パケット数を加えた数を推定送信済パケット順序番号とする。本発明は、これらの場合（図１及び図２の場合）に限定されるものではない。
ここで、上記の『ある数』の決定例について以下に説明する。
図３は、受信済の最新パケット以降、当該ＴＸＯＰの終了までに送信される可能性のあるパケット数を推定する。最後に受信したパケットの順序番号に、その推定パケット数を加えた数を推定送信済パケット順序番号とする。
この場合、図３に示すように、たとえば、パケット群Ｂのパケット９が何らかの原因により受信局により受信されなかった場合、１送信機会内で送信可能なパケット数が５であり、受信済の最新パケットの順序番号が『１０』であるので、推定送信済パケット順序番号は、１０となる。
以下、同様に、パケット群Ｂのパケット１０が何らかの原因により受信局により受信されなかった場合（図１の場合）、受信済の最新パケットの順序番号が『９』であり、ＴＸＯＰ−２終了までに送信され得るパケット数は『１』であるので、推定送信済パケット順序番号は、９＋１＝１０となる。
パケット群Ｂのパケット９及び１０が何らかの原因により受信局により受信されなかった場合、受信済の最新パケットの順序番号が『８』であり、ＴＸＯＰ−２終了までに送信され得るパケット数は『２』であるので、推定送信済パケット順序番号は、８＋２＝１０となる。パケット群Ｂのパケット７、９、及び１０が何らかの原因により受信局により受信されなかった場合、受信済の最新パケットの順序番号が『８』であり、ＴＸＯＰ−２終了までに送信され得るパケット数は『２』であるので、推定送信済パケット順序番号は、８＋２＝１０となる。
ここで、図４を参照しながら、送信パケット数の推定方法について、以下に説明する。
図４は、１パケットサイズ、及び一つのＴＸＯＰにおいて受信済の最新パケットの受信後から当該ＴＸＯＰの終了までの時間（受信済最新パケットの受信後におけるＴＸＯＰの残り時間）に基づいて、受信済最新パケットの送信から当該ＴＸＯＰ終了までにいくつのパケットの送信が可能かを推定する場合を示す。
一般に、ＴＸＯＰの期間は、予め設定されているので、受信局が最後のパケットを受信した時刻、ＴＸＯＰの終了する時刻、及びパケットのサイズが所定の長さを有していることに基づいて、最新パケットの送信以降、いくつのパケットの送信が可能かを推定できる。
例えば、図４に示す場合、パケット群Ｂのパケット１０が何らかの原因により受信局により受信されなかった場合、受信済の最新パケットの順序番号が『９』であるので、このパケット９受信後に送信可能なパケット数は、（ＴＸＯＰの終了するまでの残り時間／１パケット送信に要する時間）により推定できる。このように算出されるので、推定結果の精度は高くなる。
図４で示す例は、時刻の管理や演算等が必要なため、煩雑化の傾向にある。これに対して、図５に示す例によれば、受信パケット毎の受信時刻の管理を行わずに、いくつのパケットの送信が可能かを容易に短時間で推定できる。
つまり、図５の推定方法によれば、推定送信パケット数は、一つのＴＸＯＰで送信可能なパケット数から、受信されたパケット数と受信に失敗したことが判明しているパケット数とを差し引いたものに等しい。
例えば、図５の場合、パケット群Ｂのパケット７、９、及び１０が何らかの原因により受信局により受信されなかった場合、最新パケットの順序番号が『８』であり、ＴＸＯＰ−２において送信され得るパケット数は『５』であり、受信済のパケット数が２（即ち、パケット６及び８）であり、パケット７が受信に失敗していることが判明しているので、推定送信パケット数は、８＋｛５−（２＋１）｝＝１０となる。つまり、推定送信済パケットの順序番号は、『１０』と推定できる。
具体的な例について図６を参照しながら、以下に説明する。
図６に示すように、例えば、パケット群Ｂのパケット９が何らかの原因により受信局により受信されなかった場合、受信済の最新パケットの順序番号が『１０』であり、ＴＸＯＰ−２で送信可能なパケット数が５であり、パケット９が受信に失敗していることが判明しているので（なぜなら、パケット９が受信済のパケット８と１０の間に位置するため）、推定送信済パケット順序番号は、１０＋｛５−（４＋１）｝＝１０となる（この場合、推定送信パケット数は０である。）。
パケット群Ｂのパケット１０が何らかの原因により受信局により受信されなかった場合、受信済の最新パケットの順序番号が『９』であり、ＴＸＯＰ−２で送信可能なパケット数が５であり、受信に失敗していることが判明しているパケットが存在しないので、推定送信済パケット順序番号は、９＋｛５−（４＋０）｝＝１０となる（この場合、推定送信パケット数は１である。）。
パケット群Ｂのパケット９及び１０が何らかの原因により受信局により受信されなかった場合、受信済の最新パケットの順序番号が『８』であり、ＴＸＯＰ−２で送信可能なパケット数が５であり、受信に失敗していることが判明しているパケットが存在しないので、推定送信済パケット順序番号は、８＋｛５−（３＋０）｝＝１０となる（この場合、推定送信パケット数は２である。）。
パケット群Ｂのパケット７、９、及び１０が何らかの原因により受信局により受信されなかった場合、受信済の最新パケットの順序番号が『８』であり、ＴＸＯＰ−２で送信可能なパケット数が５であり、パケット７が受信に失敗していることが判明しているので、推定送信済パケット順序番号は、８＋｛５−（２＋１）｝＝１０となる（この場合、推定送信パケット数が２である。）。
パケット群Ｂのパケット６〜１０が何らかの原因により受信局により受信されなかった場合、受信済の最新パケットの順序番号が『５』であり、ＴＸＯＰ−２で送信可能なパケット数が５であり、受信に失敗していることが判明しているパケットが存在しないので、推定送信済パケット順序番号は、５＋｛５−（０＋０）｝＝１０となる（この場合、推定送信パケット数が５である。）。
ここで、上記措置▲２▼について以下に説明する。
上記措置▲２▼によれば、送信局においてＤＥＬＡＹＥＤ−ＡＣＫを解釈する際、ＤＥＬＡＹＥＤ−ＡＣＫに、送信済かつ受信成功の通知を受信していないパケットについての受信情報が含まれていない場合、当該パケットの送信は失敗したものとみなされる。
この場合、受信局は、受信に成功したパケットのパケット番号までを含むＤＥＬＡＹＥＤ−ＡＣＫを送信局へ返送する。送信局は、上記の解釈に基づいて判断し、必要ならばパケットの再送を行う。
図７を参照しながら、具体例を挙げて以下に説明する。なお、図１等と同じ機能を有するものについては、同一の参照符号を付記し、詳細な説明は省略する。
図７に示すように、まず、ＴＸＯＰ−１において、パケット群Ａ内のパケット１〜５が送信局から受信局へ送信される。受信局は、前述のように、ＤＥＬＡＹＥＤ−ＡＣＫパケットａを介して、パケット１〜５及び以前のＴＸＯＰで送信されたパケット−４〜０を送信局へ通知する。
送信局は、このＤＥＬＡＹＥＤ−ＡＣＫに基づいて、パケット１〜５が無事に受信局で受信されたと判断し、次のＴＸＯＰ−２において、パケット群Ｂのパケット６〜１０を受信局へ送信する。このとき、何らかの原因でパケット群Ｂのパケット１０が受信局で受信および検出されなかったとする。
本実施の形態によれば、このような状況下では、ＤＥＬＡＹＥＤ−ＡＣＫパケットｂには、送信局が送信済であって、しかも受信局により受信済のパケットのうち最新パケットである順序番号（９）までのパケットに係る受信情報が含められる。図７の場合、ｂ２に示すように、パケット０〜９までが受信済のパケットである旨の受信情報が送信局へ通知される。
この際、送信局は、上記通知に基づいて、パケット１０については送信済且つ受信成功に係る受信情報が含まれていなかったことを検出し、パケット１０が何らかの原因で受信局により受信されなかったと判断し、次のＴＸＯＰ−３において、パケット１０の再送を受信局に対して行う。結局、ＴＸＯＰ−３において、再送すべきパケット１０以外に、パケット群Ｃのパケット１１〜１４が併せて、受信局へ送信される。
受信局では、パケット１０〜１４に係る受信情報をＤＥＬＡＹＥＤ−ＡＣＫに含め、ＤＥＬＡＹＥＤ−ＡＣＫパケットｃを介して送信局へ通知する。送信局では、この通知（ｃ２の内容を参照）により、再送したパケット１０に加えてパケット１１〜１４が無事に受信局により受信されたと判断し、次のＴＸＯＰ−４において、パケット群Ｄのパケット１５〜１９が受信局へ送信される。受信局では、パケット１５〜１９に係る受信情報をＤＥＬＡＹＥＤ−ＡＣＫに含め、ＤＥＬＡＹＥＤ−ＡＣＫパケットｄを介して送信局へ通知する。
以上のように、ＴＸＯＰ−２で送信に失敗したパケット１０は、その次の送信機会であるＴＸＯＰ−３において迅速に再送されることになる。したがって、パケット紛失に伴う再送が遅れてしまうこと、パケットの有効期限が切れてしまうこと、及びパケットの並べ替えを行うことを確実に回避できる。
ここで、図８を参照しながら、ＴＸＯＰ−２中のパケットの全てが受信局により受信および検出されなかった場合について説明する。なお、図７等と同じ機能を有するものについては、同一の参照符号を付記し、詳細な説明は省略する。
図８に示すように、まず、ＴＸＯＰ−１において、パケット群Ａ内のパケット１〜５が送信局から受信局へ送信される。受信局は、前述のように、ＤＥＬＡＹＥＤ−ＡＣＫパケットａを介して、パケット１〜５及び以前のＴＸＯＰで送信されたパケット−４〜０を送信局へ通知する。
送信局は、このＤＥＬＡＹＥＤ−ＡＣＫに基づいて、パケット１〜５が無事に受信局で受信されたと判断し、次のＴＸＯＰ−２において、パケット群Ｂのパケット６〜１０を受信局へ送信する。このとき、何らかの原因でパケット群Ｂの全てのパケット（パケット６〜１０）が受信局で受信および検出されなかったとする。
本実施の形態によれば、このような状況下では、ＤＥＬＡＹＥＤ−ＡＣＫパケットｂには、受信済の最新パケットの順序番号（５）までの受信情報が含められる。図８の場合、ｂ２に示すように、パケット５までが受信済のパケットである旨の受信情報が送信局へ通知される。
この際、送信局は、上記通知に基づいて、パケット６〜１０については送信済且つ受信成功に係る受信情報が含まれていなかったことを検出し、パケット６〜１０が何らかの原因で受信局により受信されなかったと判断し、次のＴＸＯＰ−３において、パケット６〜１０の再送を受信局に対して行う。結局、ＴＸＯＰ−３において、ＴＸＯＰ−２において送信すべきすべてのパケットが受信局へ再送される。
受信局では、パケット６〜１０に係る受信情報をＤＥＬＡＹＥＤ−ＡＣＫに含め、ＤＥＬＡＹＥＤ−ＡＣＫパケットｃを介して送信局へ通知する。送信局では、この通知（ｃ２の内容を参照）により、再送したパケット６〜１０が無事に受信局により受信されたと判断し、次のＴＸＯＰ−４において、パケット群Ｄのパケット１１〜１５が受信局へ送信される。受信局では、パケット１１〜１５に係る受信情報をＤＥＬＡＹＥＤ−ＡＣＫに含め、ＤＥＬＡＹＥＤ−ＡＣＫパケットｄを介して送信局へ通知する。
以上のように、ＴＸＯＰ−２で送信に失敗したパケット６〜１０は、次の送信機会であるＴＸＯＰ−３において迅速に再送されることになる。したがって、パケット紛失に伴う再送が遅れてしまうこと、パケットの有効期限が切れてしまうこと、及びパケットの並べ替えを行うことを確実に回避できる。
なお、上記説明においては、検出された受信失敗パケットを送信局がＤＥＬＡＹＥＤ−ＡＣＫの次の送信機会に再送する場合を例示しているが、本発明は、これに限定されるものではなく、上記ＤＥＬＡＹＥＤ−ＡＣＫ後の直近の送信機会に再送する場合も含む。
すなわち、後述するように、本発明は、或る送信機会における送達確認情報送信後であって当該送信機会内に上記再送処理を行っても良いし（ＤＥＬＡＹＥＤ−ＡＣＫが送信機会の最初や中間で送信される場合に該当する。）、次の送信機会に上記再送処理を行っても良いし、又は複数個の送信機会毎に上記再送処理を行っても良い。
また、本発明においては、各パケット群は、５個のパケットを含む場合に限定されるものではなく、他の数、例えば１６の倍数単位である（１６個、３２個、…）のパケットを含む場合にも適用できる。
また、上記説明においては、指定した順序番号からシーケンシャルにパケット受信状況を通知している場合を示すが、本発明はこれに限定されるものではない。要は、一括して複数のパケットに係る受信状況が通知できればよい。
さらに、ＤＥＬＡＹＥＤ−ＡＣＫパケットａ〜ｄの通知すべきパケット数については、通信路の状況や送信するデータの種類に応じて決定すればよい。例えば、通信路におけるエラー発生率が小さい場合には、少ないパケット数でよく、エラー発生率が大きい場合には、多いパケット数とすればよい。
また、上記説明においては、受信済の最新パケット以降当該ＴＸＯＰの終了までに送信される可能性のあるパケット数を推定することによって、送信局へ通知するパケットを決定していたが、通知するパケットの決定方法はこれに限定されるものではない。
ここで、図２２を参照しながら、通知するパケットの決定方法に係る他の例を説明する。なお、図１等と同じ機能を有するものについては、同一の参照符号を付記し、詳細な説明は省略する。
図２２に示すように、まず、ＴＸＯＰ−１において、パケット群Ａ内のパケット１〜５が送信局から受信局へ送信される。受信局は、前述のように、ＤＥＬＡＹＥＤ−ＡＣＫパケットａを介して、パケット１〜５、以前のＴＸＯＰで送信されたパケット−２〜０、及び受信済最新パケットの順序番号『５』に、一定値（この例では２）を加えた順序番号（この例では順序番号『７』）を送信局へ通知する。
送信局は、このＤＥＬＡＹＥＤ−ＡＣＫに基づいて、パケット１〜５が無事に受信局で受信されたと判断し、次のＴＸＯＰ−２において、パケット群Ｂのパケット６〜１０を受信局へ送信する。このとき、何らかの原因でパケット群Ｂのパケット１０が受信局で受信および検出されなかったとする。
ここで示す例によれば、このような状況下では、パケット９まで受信したので、パケット１０及び１１については未受信として送信局に通知する。つまり、順序番号『９』に、一定値『２』を加えた順序番号までのパケット（つまり、パケット１１まで）をＤＥＬＡＹＥＤ−ＡＣＫパケットｂに受信情報として含める。
送信局は、ＤＥＬＡＹＥＤ−ＡＣＫパケットｂを介して、パケット群Ｂ内のパケット１０が受信局により受信されていないこと（パケット６〜９については受信済、パケット１０については未受信とそれぞれ通知されるため、受信情報から判明する。）をＤＥＬＡＹＥＤ−ＡＣＫに基づいて判断し、次のＴＸＯＰ−３において、パケット１０の再送を受信局に対して行う。結局、ＴＸＯＰ−３において、再送すべきパケット１０以外に、パケット群Ｃのパケット１１〜１４が併せて、受信局へ送信される。
受信局では、パケット１０〜１４に係る受信情報をＤＥＬＡＹＥＤ−ＡＣＫに含め、ＤＥＬＡＹＥＤ−ＡＣＫパケットｃを介して送信局へ通知する。送信局では、この通知（ｃ２参照）により、再送したパケット１０に加えてパケット１１〜１４が無事に受信局により受信されたと判断し、次のＴＸＯＰ−４において、パケット群Ｄのパケット１５〜１９が受信局へ送信される。受信局では、パケット１５〜１９に係る受信情報をＤＥＬＡＹＥＤ−ＡＣＫに含め、ＤＥＬＡＹＥＤ−ＡＣＫパケットｄを介して送信局へ通知する。
このように、ＴＸＯＰ−２で受信に失敗したパケット１０は、次の送信機会であるＴＸＯＰ−３において迅速に再送されることになる。したがって、パケット紛失に伴う再送が遅れてしまうこと、パケットの有効期限が切れてしまうこと、及びパケットの並べ替えを行うことをそれぞれ確実に回避できる。
以上のように、送信済最新パケットの順序番号の推定を行わず、各ＤＥＬＡＹＥＤ−ＡＣＫにおいて常に受信済最新パケットの順序番号に一定値（図２２の場合は『２』）を加えたパケットの情報を送信局に通知すると、ＴＸＯＰごとの推定が行われないので、その分、受信局の処理を簡素化できる。
図２２に示すように、すべてのＴＸＯＰにおいて受信済の最新パケットまでの受信情報に、その後に続くと予想される一定個数（図２２の場合には２個）のパケットの受信情報を加えたものを送信局へ通知してもよい。これにより、受信局が行う送信パケットの推定処理を簡素化することが可能となる。なお、図２２においては、パケット番号が昇順に付番される場合を例示しているが、本発明はこれに限定されるものではなく、降順に付番される場合にも適用可能である。
また、本実施の形態においては、各ＴＸＯＰの長さがほぼ同一、すなわち、或るＤＥＬＡＹＥＤ−ＡＣＫから次のＤＥＬＡＹＥＤ−ＡＣＫまでの期間においてパケットを最大５個送信可能な長さに揃えられているが、各ＴＸＯＰの長さが受信局へ通知されるなどの方法でこの間に送信されるパケット数を推定可能であれば、図２３のように異なったＴＸＯＰ長であってもよい。
図２３の例では、ＴＸＯＰ−１にはパケット１〜４の合計４個のパケットを送信する時間が、ＴＸＯＰ−２にはパケット５〜１０の合計６個のパケットを送信する時間が、ＴＸＯＰ−３及びＴＸＯＰ−４にはパケット１０〜１４及び１５〜１９のそれぞれ合計５個のパケットを送信する時間が割り当てられている。
各ＴＸＯＰの時間は、送信局にＴＸＯＰを割り当てる制御局（ＨＣ）が送信局に送信権を割り当てる際に送信するパケット（図示しない）に含めるなどの方法により、送受信局を含む各局へ通知することが可能となる。
図２３の場合、まず、ＴＸＯＰ−１において、パケット群Ａ内のパケット１〜４が送信局から受信局へ送信される。受信局は、前述のように、ＤＥＬＡＹＥＤ−ＡＣＫパケットａを介して、パケット１〜４及び以前のＴＸＯＰで送信されたパケット−５〜０を送信局へ通知する。
送信局は、このＤＥＬＡＹＥＤ−ＡＣＫに基づいて、パケット１〜４が無事に受信局で受信されたと判断し、次のＴＸＯＰ−２において、パケット群Ｂのパケット５〜１０を受信局へ送信する。このとき、何らかの原因でパケット群Ｂのパケット１０が受信局で受信および検出されなかったとする。
このような状況下では、受信済の最新パケットの順序番号『９』に、ある数（図２３の場合、『１』）を加えた順序番号までのパケット（つまり、パケット１０まで）が送信されたと推定し、その旨をＤＥＬＡＹＥＤ−ＡＣＫパケットｂに受信情報として含める。
つまり、受信局では、パケット群Ｂのパケット５〜１０の全てが送信されたとみなし、これらパケット５〜１０の各受信情報が送信局へ通知されることになる。図２３によれば、受信済のパケット５〜９と未受信のパケット１０とに係る受信情報がＤＥＬＡＹＥＤ−ＡＣＫに含められる。
送信局は、ＤＥＬＡＹＥＤ−ＡＣＫパケットｂを介して、パケット群Ｂ内のパケット１０が受信局により受信されていないこと（パケット５〜９については受信済、パケット１０については未受信とそれぞれ通知されるため、受信情報から判明する。）をＤＥＬＡＹＥＤ−ＡＣＫに基づいて判断し、次のＴＸＯＰ−３において、パケット１０の再送を受信局に対して行う。結局、ＴＸＯＰ−３において、再送すべきパケット１０以外に、パケット群Ｃのパケット１１〜１４が併せて、受信局へ送信される。
受信局では、パケット１０〜１４に係る受信情報をＤＥＬＡＹＥＤ−ＡＣＫに含め、ＤＥＬＡＹＥＤ−ＡＣＫパケットｃを介して送信局へ通知する。送信局では、この通知（ｃ２参照）により、再送したパケット１０に加えてパケット１１〜１４が無事に受信局により受信されたと判断し、次のＴＸＯＰ−４において、パケット群Ｄのパケット１５〜１９が受信局へ送信される。受信局では、パケット１５〜１９に係る受信情報をＤＥＬＡＹＥＤ−ＡＣＫに含め、ＤＥＬＡＹＥＤ−ＡＣＫパケットｄを介して送信局へ通知する。
なお、図２３の例では、既に送信しているパケットについては、受信した受信状況を参照して必要ならば再送処理が行われる。また、未送信のパケットについては、当該情報は無視される。
以上のように、ＴＸＯＰ−２で受信に失敗したパケット１０は、次の送信機会であるＴＸＯＰ−３において迅速に再送されることになる。したがって、パケット紛失に伴う再送が遅れてしまうこと、パケットの有効期限が切れてしまうこと、及びパケットの並べ替えを行うことをそれぞれ確実に回避できる。
さらに、上記説明においては、送信するパケットの順序番号が連続する場合を例示したが、本発明は、これに限定されるものではなく、図２４のように、パケットの順序番号が不連続な場合にも適用可能である。
なお、このように不連続な場合として、たとえば、送信局が無線ＬＡＮにおけるアクセスポイント（ＡＰ）であり、インターネットから送信されてくる複数のストリームを無線局へ中継する際に、アクセスポイントから出力するストリーム毎に異なる順序番号を付番するのではなく、アクセスポイントへ入力されるストリームすべてに共通な順序番号を付番する際などに生じる。
ここで、図２４を参照しながら、具体例を説明する。なお、図１等と同じ機能を有するものについては、同一の参照符号を付記し、詳細な説明は省略する。
図２４に示すように、まず、ＴＸＯＰ−１において、パケット群Ａ内のパケット１、３、４、５、及び７が送信局から受信局へ送信される。受信局は、前述のように、ＤＥＬＡＹＥＤ−ＡＣＫパケットａを介して、パケット１、３、４、５、及び７、並びに以前のＴＸＯＰで送信されたパケット−２〜０及び未受信のパケット２・６を送信局へ通知する。
送信局は、このＤＥＬＡＹＥＤ−ＡＣＫに基づいて、パケット３、４、５、及び７が無事に受信局で受信されたと判断し、次のＴＸＯＰ−２において、パケット群Ｂのパケット８〜１１及び１３を受信局へ送信する。このとき、何らかの原因でパケット群Ｂのパケット１３が受信局で受信および検出されなかったとする。
本実施の形態によれば、このような状況下では、受信済の最新パケットの順序番号『１１』に、ある数（図２４の場合、『２』）を加えた順序番号までのパケット（つまり、パケット１３まで）が送信されたと推定し、その旨をＤＥＬＡＹＥＤ−ＡＣＫパケットｂに受信情報として含める。
つまり、受信局では、パケット群Ｂのパケット８〜１１及び１３の全てが送信されたとみなし、これらパケットの各受信情報が送信局へ通知されることになる。図２４によれば、受信済のパケット８〜１１（最新パケット）と未受信のパケット１２及び１３とに係る受信情報がＤＥＬＡＹＥＤ−ＡＣＫに含められる。
送信局は、ＤＥＬＡＹＥＤ−ＡＣＫパケットｂを介して、パケット群Ｂ内のパケット１３が受信局により受信されていないこと（パケット８〜１１については受信済、パケット１３については未受信とそれぞれ通知されるため、受信情報から判明する。）をＤＥＬＡＹＥＤ−ＡＣＫに基づいて判断し、次のＴＸＯＰ−３において、パケット１３の再送を受信局に対して行う。結局、ＴＸＯＰ−３において、再送すべきパケット１３以外に、パケット群Ｃのパケット１４、１６、１７、及び１８が併せて、受信局へ送信される。
受信局では、パケット１３、１４、１６、１７、及び１８に係る受信情報をＤＥＬＡＹＥＤ−ＡＣＫに含め、ＤＥＬＡＹＥＤ−ＡＣＫパケットｃを介して送信局へ通知する。送信局では、この通知（ｃ２参照）により、再送したパケット１３に加えてパケット１４、１６、１７、及び１８が無事に受信局により受信されたと判断し、次のＴＸＯＰ−４において、パケット群Ｄのパケット２０、２１、２３、２４、及び２６が受信局へ送信される。受信局では、パケット２０、２１、２３、２４、及び２６に係る受信情報をＤＥＬＡＹＥＤ−ＡＣＫに含め、ＤＥＬＡＹＥＤ−ＡＣＫパケットｄを介して送信局へ通知する。
なお、図２４の例では、既に送信しているパケットについては、受信した受信状況を参照して必要ならば再送処理が行われる。また、未送信のパケットについては、当該情報は無視される。また、上記説明では、ビットマップ方式の場合について例示しているが、本発明はこれに限定されるものではなく、パケット番号を伝える方式でもよい。また、上記説明では昇順の場合について例示したが、降順の場合についても本発明は適用でき、この場合、或る値を減算すればよい。
以上のように、ＴＸＯＰ−２で受信に失敗したパケット１３は、次の送信機会であるＴＸＯＰ−３において迅速に再送されることになる。したがって、パケット紛失に伴う再送が遅れてしまうこと、パケットの有効期限が切れてしまうこと、及びパケットの並べ替えを行うことをそれぞれ確実に回避できる。
パケット順序番号が不連続な場合、受信局は受信済最新パケットの順序番号に一定数を加えたり、受信済パケットの順序番号のパターンを解析したりなどして推定送信済パケット順序番号を算出し、送達確認情報にそのパケットの受信状況まで含めて送信することが有効である。
受信済パケットの順序に一定数を加える場合、パケットの順序番号が連続する場合に比べて大きな値を加えることが有効である。推定送信済パケット順序番号を推定する場合、図２５に示すように、推定送信パケット数に一定数（図２５の場合α）を掛ける、あるいは加えるなどの方法で順序番号の離散に対応することが望ましい。
ここで、図２５を参照しながら、パケットの順序番号が不連続な場合の具体的な推定方法について説明する。
図２５は、受信済の最新パケット以降、当該ＴＸＯＰの終了までに送信される可能性のあるパケット数を推定することを示している。最後に受信したパケットの順序番号（受信済最新パケットの順序番号）に、その推定送信パケット数に一定数αを掛けたものを加えた数を推定送信済パケットの順序番号とする。このαは、パケットの順序番号が連続時には小さく、不連続時には大きくすると有効である。
具体的には、図２５に示すように、例えば、パケット群Ｂのパケット９が何らかの原因により受信局により受信されなかった場合、１送信機会内で送信可能なパケット数が５であり、受信済の最新パケットの順序番号が『１０』であるので、推定送信済パケット順序番号は、１０（＝１０＋０×α）となる。
同様に、パケット群Ｂのパケット１０が何らかの原因により受信局により受信されなかった場合、図２５に示すように、受信済の最新パケットの順序番号が『９』であり、ＴＸＯＰ−２終了までに送信され得るパケット数は『１』であるので、推定送信済パケット順序番号は、９＋α（＝９＋１×α）となる。
パケット群Ｂのパケット９及び１０が何らかの原因により受信局により受信されなかった場合、図２５に示すように、受信済の最新パケットの順序番号が『８』であり、ＴＸＯＰ−２終了までに送信され得るパケット数は『２』であるので、推定送信済パケット順序番号は、８＋２α（＝８＋２×α）となる。
パケット群Ｂのパケット７、９、及び１０が何らかの原因により受信局により受信されなかった場合、受信済の最新パケットの順序番号が『８』であり、ＴＸＯＰ−２終了までに送信され得るパケット数は『２』であるので、推定送信済パケット順序番号は、推定送信済パケット順序番号は、８＋２α（＝８＋２×α）となる。
ところで、以上の説明では、送信局のＴＸＯＰ終了後に受信局が自発的にＤＥＬＡＹＥＤ−ＡＣＫパケットを送信する場合について例示したが、本発明はこれに限定されるものではない。たとえば、ＤＥＬＡＹＥＤ−ＡＣＫパケットを送信局からの要求に応じて送信してもよいし、あるいはその送信する期間が送信局の持つＴＸＯＰ中であってもよい。
以下、図２６を参照しながら、具体例について説明する。なお、図２６は、受信局がＤＥＬＡＹＥＤ−ＡＣＫパケットを返送するタイミングを送信局が指定する場合を示している。
図２６では、送信局が順序番号１〜１０のパケットを送信し、続けてＤＥＬＡＹＥＤ−ＡＣＫ要求パケットを送信している。受信局は、このＤＥＬＡＹＥＤ−ＡＣＫ要求パケットを受けて、ＤＥＬＡＹＥＤ−ＡＣＫパケットを送信している。
この際、受信局はパケット１０の検出、受信に失敗しているが、受信済の最新パケット９に『１』を加えたパケット（１０）の受信情報まで送信しているため、送信局はパケット１０を次のＴＸＯＰ−２で再送することが可能である。この処理は、ＤＥＬＡＹＥＤ−ＡＣＫパケットを送信局のＴＸＯＰ終了後に自発的に送信する例と同様な処理である。
このとき、ＤＥＬＡＹＥＤ−ＡＣＫパケットにどのパケットの受信状況まで含むかをデータ受信局（ＤＥＬＡＹＥＤ−ＡＣＫパケットを送信する局）が決定できることが好ましい。この場合、上記受信局は、送信機会の長さ、パケットサイズ、実際に受信されたパケットの個数などの情報を用いて、あるいはその他の方法で送信済みパケット順序番号を推定し、送信局に対してそれらのパケットの再送を要求することが可能となる。
図２６の例では、ＴＸＯＰの最後にＤＥＬＡＹＥＤ−ＡＣＫ要求パケットとＤＥＬＡＹＥＤ−ＡＣＫパケットとの送信を行う例について説明したが、本発明はこれに限定されるものではなく、この２個のパケットを送信するタイミングはＴＸＯＰの最初でも途中でもよい。
図２７にＴＸＯＰ−１の途中でＤＥＬＡＹＥＤ−ＡＣＫ要求パケットとＤＥＬＡＹＥＤ−ＡＣＫパケットとの送信を行う例を示すが、この場合、再送対象のパケット１０はＤＥＬＡＹＥＤ−ＡＣＫパケットの後、送信局が同一のＴＸＯＰ−１内で再送することが可能である。
また、受信局がどのパケットまでの受信情報を送信するかを決定する際に、送信局が通知するパケットの送信状況のデータを利用してもよい（送信局が通知した送信状況を反映させてもよい）。この場合を図２８に示す。
図２８では、送信局はＴＸＯＰ−１においてパケット１〜１０を送信し、ＤＥＬＡＹＥＤ−ＡＣＫ要求（ＤＥＬＡＹＥＤ−ＡＣＫ ＲＥＱＵＥＳＴ）パケットに「パケット１０まで送信した」という情報を含めて送信している。受信局は、何らかの原因でパケット１０を受信できなかったが、送信局から「パケット１０まで送信した」という情報が送られているため、送信局からの送信状況に基づいてパケット１０までの受信状況を通知することとし、ＤＥＬＡＹＥＤ−ＡＣＫパケットに受信したパケット１〜９を「受信済」、パケット１０を「未受信」と設定して送信局へ送信する。これにより、送信局は、直近の送信機会であるＴＸＯＰ−２においてパケット１０の再送を行うことが可能となる。
また、本実施の形態においてはパケットについて説明しているが、複数のブロックを一つのパケットの中に格納して送信し、それらのブロックの送達確認情報を一括して送達確認パケットを介して受信局から送信局へ通知し、上記送達確認パケットが、未だ上記送信局が送信していない可能性のあるブロックについての受信情報を含んでいるように構成してもよい。この場合でも、上記の通信方法と同様の作用・効果を奏する。
本発明の通信方法は、以上のように、複数個の送信パケットに対する送達確認情報を一括して送達確認パケットを介して受信局から送信局へ通知する通信方法において、次の措置を講じたことを特徴としている。
すなわち、上記通信方法においては、上記送達確認パケットが、未だ送信局が送信していない可能性のあるパケットについての受信情報を含んでいることを特徴としている。
或る送信機会に、複数個のパケットを送信局から受信局へ送信した際、何らかの原因によって、受信局がパケットあるいはパケット群を受信できなかった場合、従来は、送達確認パケットには、受信できなかったパケットに関する受信情報は含まれていなかった。これは、次の理由による。すなわち、従来においては、送達確認パケットに含まれる受信情報は、受信済のパケットに係る受信状況と、受信していないことがはっきりしているパケットに係る受信状況とに限られていた。
このため、未だ送信局が送信していない可能性のあるパケットについての受信情報は、送信局へは通知されることはなかった。その結果、送信局は、送信機会（第１送信機会）の終了直前に送信したパケットあるいはパケット群の受信状態に係る受信情報の通知がこないため、受信に失敗していない（受信に成功した）ものと判断し、後続のパケットを次の送信機会（第２送信機会）に受信局へ送信することになる。
これに対して、受信局は、受信できなかったことが判明したパケットあるいはパケット群に係る受信情報を送信局へ送達確認パケットを介して通知する。そして、更に次の送信機会（第３送信機会）に、送信局は、受信局からの通知結果に基づいて、受信に失敗したパケットの再送を受信局に対して行う。このようにして、複数個のパケットが、すべて、送信局から受信局へ通信される。
以上のように、従来の通信方法によれば、第１送信機会において受信に失敗したパケットの再送は、次の第２送信機会で行われるのではなくて、第３送信機会において行われる。このように、従来技術によれば、受信に失敗したパケットが送信されるタイミングは、本来送信されるべき送信機会（第１送信機会）よりも少なくとも２周期遅れてしまう（第３送信機会）。
この再送の遅れにより、パケット受信時には既に有効期限が切れてしまっていることがある（有効期限切れのパケットは、使用されない）。また、パケットの再送が遅れることに伴って受信局側でパケットの並べ替えが必要になることもある。
これに対して、上記の通信方法によれば、或る送信機会に、複数個のパケットを送信局から受信局へ送信した際、何らかの原因によって、受信局がパケットあるいはパケット群を受信できなかった場合、上記パケットあるいはパケット群についての受信情報を含む上記送達確認パケットが受信局から送信局へ通知され、この送達確認パケットにより、送信局は、未だ送信局が送信していない可能性のあるパケットについての受信情報を得ることになる。
このように、送信局は、受信局からの送達確認パケットを介して、未だ受信していない可能性のあるパケットについての情報を得ることができる。したがって、送信局は、受信局からの上記通知に基づいて、未だ受信していない可能性のあるパケットについて、再送等の適切な措置を迅速に講ずることが可能となる。
再送等の迅速な措置が講じられるので、パケット受信時には既に有効期限が切れてしまっていることや、迅速な措置が講じられないことに伴って受信局側でパケットの並べ替え等の処理が別途必要となることを確実に回避できる。
上記送達確認パケットは、未だ送信局が送信していない可能性のあるパケットについては受信していない旨を示す受信情報を含んでいることが好ましい。この場合、受信局は、未だ受信していない可能性のあるパケットについては受信していないことを示す受信情報を送信局へ通知する。送信局は、この受信情報を受け取り、送信したパケットのうち、受信局により受信されなかったパケットが存在することを知り、該当するパケットの再送を行うことができる。
この場合にも、送信局は、当該送信機会またはその次の送信機会に、受信局からの上記通知に基づいて、未だ受信していない可能性のあるパケットについて、迅速に再送することが可能となる。また、再送が迅速に行われるので、パケット受信時には既に有効期限が切れてしまっていることや、迅速な措置が講じられないことに伴って受信局側でパケットの並べ替え等の処理が別途必要となることを確実に回避できる。
上記受信局は、上記受信情報の対象となる送信パケットを決定することが好ましい。この場合、上記受信局は、送信機会の長さ、パケットサイズ、実際に受信されたパケットの個数などの情報を用いて、あるいはその他の方法で送信済みパケット順序番号を推定し、送信局に対してそれらのパケットの再送を要求することが可能となる。
上記受信情報は、受信済の最新パケットの順序番号に所定数を加えた順序番号までのいずれかのパケットについての受信情報を含むことが好ましい。この場合、送信局は当該順序番号のパケットを送信していたら、その内容に応じた処理を行う一方、当該順序番号のパケットを未だ送信していなかったら、受信通知を無視して、自らのスケジュールどおりに当該パケットの送信を行う。
上記所定数は、各送達確認パケットにおいて同一値であることが好ましい。この場合、ＴＸＯＰ毎に送信済の最新パケットの順序番号の推定を行わないので、その分、受信局の処理を簡素化できる。
上記受信情報における上記所定数は、ある送達確認パケットの送信から次の送達確認パケットの送信までの送信機会において送信されるパケット数の最大値に設定されていてもよい。この場合、ある送達確認パケットの送信から次の送達確認パケットの送信までの送信機会に含まれるパケットの全てが何らかの原因により受信できなかった場合でも、これら全てのパケットの再送が迅速かつ確実に行える。
上記受信情報における上記所定数は、ある送達確認パケットの送信から次の送達確認パケットの送信までの送信機会において、受信済最新パケット以降、上記送信機会終了までに送信される可能性のあるパケット数の推定値であってもよい。
この場合、受信済の最新パケットの順序番号に上記推定値を加えた順序番号のパケットまでが送信されたものとされ、その旨が受信情報に含められる。そして、既に送信しているパケットについては、受信した受信情報（受信状況）に基づいて、適宜、再送処理が送信局から受信局に対して行われる。なお、未受信のパケットについては、当該情報が無視され、本来予定しているタイミングで送信される。
上記の推定値は、上記パケットのサイズと上記最新パケット受信から上記送信機会が終了するまでの間に送信可能なパケット数とに基づいて算出されることが好ましい。
この場合、或るパケットが何らかの原因により受信局により受信されなかった場合、受信済の最新パケットに、この最新パケット受信から上記送信機会が終了するまでの間に送信可能なパケット数が加えられ、この加算結果の順序番号までが送信されたとみなされる。そして、受信した受信情報（受信状況）に基づいて、次の送信機会において受信されていないパケットの再送処理が行われる。
なお、上記の送信可能なパケット数は、最新パケット受信から上記送信機会が終了するまでの時間を、一つのパケットを送信するのに要する時間で除したものとして算出される。このように、除算値に基づいて上記推定値が算出されるので、非常に精度の高い推定を行うことが可能となる。
上記のように送信可能なパケット数を上記のように除算により求める代わりに、減算により求めてもよい。すなわち、上記の推定値は、上記の送信機会において送信可能なパケット数から（受信されたパケット数＋受信に失敗したことが判明しているパケット数）を減算した値に等しいとしてもよい。
このように、上記推定値を時間の測定なしに算出できるので、推定に要する工程及び時間を大幅に短縮できる。
上記受信情報における上記所定数は、上記送信局が通知するパケット送信情報を用いて上記受信局が決定することが好ましい。この場合、受信局は確実に送信局の送信したパケットの情報を入手でき、再送対象となるパケットを確実に再送要求に含めることが可能となる。
また、本発明の他の通信方法は、以上のように、複数個の送信パケットに対する送達確認情報を一括して送達確認パケットを介して受信局から送信局へ通知する通信方法において、次の措置を講じたことを特徴としている。
すなわち、上記の通信方法は、上記送達確認パケットに送信済且つ受信成功に係る情報が含まれていない場合、対応するパケットの送信に失敗したものとみなし、該パケットの再送を行うことを特徴としている。
この場合、受信局は、受信に成功したパケットのパケット番号までを含む送達確認情報を送信局へ通知する。これに対して、送信局は、上記送達確認パケットに、送信済且つ受信成功通知を受信していないパケットについての受信情報が含まれていない場合、このパケットの送信は失敗したものとみなし、適宜、再送処理が行われる。この場合、或る送信機会における送達確認情報送信後であって当該送信機会内に上記再送処理を行っても良いし、次の送信機会に上記再送処理を行っても良いし、又は複数個の送信機会毎に上記再送処理を行っても良い。
このように、パケットの送信に失敗したとみなされたパケットについては、迅速に再送される。これに伴って、パケット受信時には既に有効期限が切れてしまっていることや、迅速な措置が講じられないことに伴って受信局側でパケットの並べ替え等の処理が別途必要となることを確実に回避できる。
本発明の送信装置は、以上のように、上記複数個の送信パケットに対する送達確認情報を一括して送達確認パケットを介して受信装置から受領する送信装置であって、上記送達確認パケットを介して、未だ送信局が送信していない可能性のあるパケットについての受信情報を上記受信装置から受信した場合、送信していないパケットについての受信情報は無視することを特徴としている。
上記の送信装置によれば、複数個のパケットを送信装置から受信装置へ送信した際、何らかの原因によって、受信装置が受信できなかった場合、上記送達確認パケットが受信装置から送信装置へ通知され、この送達確認パケットにより、送信装置は、未だ送信装置が送信していない可能性のあるパケットについての受信情報を得ることになる。
送信装置が今後送信予定のパケットについて未受信という受信情報を受け取っても、それらのパケットは、後に、予定どおり送信されるため、その受信情報は無視してもかまわない。
仮に、この受信情報に今後送信予定のパケットが含まれていたとしても、送信局は、そのパケットの受信情報を無視して本来予定しているタイミングで当該パケットの送信を行うため、過不足の無いパケット送信が可能となる。
再送等の迅速な措置が講じられるので、パケット受信時には既に有効期限が切れてしまっていることや、迅速な措置が講じられないことに伴って受信装置側でパケットの並べ替え等の処理が別途必要となることを確実に回避できる。
また、本発明の他の送信装置は、以上のように、複数個の送信パケットに対する送達確認情報を一括して送達確認パケットを介して受信装置から受領する送信装置であって、送信済のパケットに関する受信情報が上記送達確認パケットを介して上記受信装置から受信されなかった場合、対応するパケットの送信に失敗したものとみなし、上記パケットの再送を上記受信装置に対して行うことを特徴としている。
上記の送信装置によれば、受信装置は受信済のパケット番号までを含む送達確認情報を送信局へ通知する。これに対して、送信装置は、送信済のパケットに関する受信情報が上記送達確認パケットを介して上記受信装置から受信されなかった場合、対応するパケットの送信に失敗したものとみなし、上記パケットの再送を上記受信装置に対して行う。
この場合、或る送信機会における送達確認情報送信後であって当該送信機会内に上記再送処理を行っても良いし、次の送信機会に上記再送処理を行っても良いし、又は複数個の送信機会毎に上記再送処理を行っても良い。
このように、上記のパケットは、迅速に再送されるので、パケット受信時には既に有効期限が切れてしまっていることや、迅速な措置が講じられないことに伴って受信装置側でパケットの並べ替え等の処理が別途必要となることを確実に回避できる。
本発明の受信装置は、以上のように、複数個の送信パケットに対する送達確認情報を一括して送達確認パケットを介して送信装置へ通知する受信装置であって、上記送達確認パケットを介して、未だ送信装置が送信していない可能性のあるパケットについての受信情報を上記送信装置へ通知することを特徴としている。
上記受信装置によれば、複数個のパケットを送信装置から受信装置へ送信した際、何らかの原因によって、受信装置が受信できなかった場合、上記送達確認パケットが受信装置から送信装置へ通知され、この送達確認パケットにより、送信装置は、未だ送信装置が送信していない可能性のあるパケットについての受信情報を得ることになる。
このように、送信装置は、受信装置からの送達確認パケットを介して、未だ送信装置が送信していない可能性のあるパケットについての情報を得ることができる。したがって、送信装置は、受信装置からの上記通知に基づいて、未だ送信装置が送信していない可能性のあるパケットについて、再送等の適切な措置を迅速に講ずることが可能となる。
再送等の迅速な措置が講じられるので、パケット受信時には既に有効期限が切れてしまっていることや、迅速な措置が講じられないことに伴って受信装置側でパケットの並べ替え等の処理が別途必要となることを確実に回避できる。
本発明に係る受信装置は、前記いずれか一つの通信方法を用いて上記受信情報の対象となるパケットを決定することを特徴としている。
上記通信方法において、上記送達確認パケットを、上記送信パケットを送信する局からの要求に応じて送信することが好ましい。これにより、送達確認パケット送信後に送信機会が残っている場合、送信局は再送などの適切な措置を当該送信機会において迅速に講ずることが可能となる。
上記送信装置において、上記送達確認パケットを要求するためのパケットが上記受信装置に送信されることが好ましい。これにより、送達確認パケット送信後に送信機会が残っている場合、送信局は再送などの適切な措置を当該送信機会において迅速に講ずることが可能となる。
上記受信装置は、上記送達確認パケットを、上記送信装置からの要求に応じて送信することが好ましい。この場合、送信装置は、上記送達確認パケットに基づいて、より迅速に且つ適切に必要な措置を講ずることが可能となる。
本発明の通信プログラムは、以上のように、前記のいずれか一つの通信方法の各手順をコンピュータに実現させるための通信プログラムであることが好ましい。
本発明の記録媒体は、以上のように、前記のいずれか一つの通信方法の各手順をコンピュータに実行させるための通信プログラムを記録したコンピュータ読み取り可能な記録媒体であることが好ましい。
上記の通信プログラム及びそれを記録したコンピュータ読み取り可能な記録媒体をコンピュータに実行させることによって、通信方法、送信装置、受信装置において、再送等の迅速な措置が講じられるので、パケット受信時には既に有効期限が切れてしまっていることや、迅速な措置が講じられないことに伴って受信装置側でパケットの並べ替え等の処理が別途必要となることを確実に回避できる。
本発明のネットワークシステムは、前記のいずれか一つの通信方法によって通信を管理することを特徴としている。
上記のネットワークシステムによれば、再送等の迅速な措置が講じられるので、パケット受信時には既に有効期限が切れてしまっていることや、迅速な措置が講じられないことに伴って受信装置側でパケットの並べ替え等の処理が別途必要となることを確実に回避でき、信頼性の高いネットワークシステムを提供することが可能となる。
上記はパケットについて規定しているが、複数のブロックを一つのパケットの中に格納して送信し、それらのブロックの送達確認情報を一括して送達確認パケットを介して受信局から送信局へ通知する通信方法であって、上記送達確認パケットは、未だ上記送信局が送信していない可能性のあるブロックについての受信情報を含んでいることを特徴とする通信方法であっても、上記と同様の作用・効果を奏する。
なお、本発明は、上述した各実施形態に限定されるものではなく、請求項に示した範囲で種々の変更が可能であり、異なる実施形態にそれぞれ開示された技術的手段を適宜組み合わせて得られる実施形態についても本発明の技術的手段に含まれる。
また、発明を実施するための最良の形態の項においてなした具体的な実施態様または実施例は、あくまでも、本発明の技術内容を明らかにするものであって、そのような具体例にのみ限定して狭義に解釈されるべきものではなく、本発明の精神と次に記載する特許請求の範囲内で、いろいろと変更して実施することができるものである。
産業上の利用の可能性
以上のように、本発明の通信方法は、複数の通信装置が一つのネットワーク経路を時分割で共有するネットワークの通信方法として有用であり、特に、パケット紛失に伴う再送が遅れてしまうこと、パケットの有効期限が切れてしまうこと、及びパケットの並べ替えを行うことを回避することが可能なネットワークの通信方法として有用である。
【図面の簡単な説明】
図１は、本発明に係る通信方法において行われる順序番号の推定について説明する説明図である。
図２は、本発明に係る通信方法において行われる順序番号の他の推定について説明する説明図である。
図３は、上記推定の具体的な例を示す説明図である。
図４は、上記推定の具体的な他の例を示す説明図である。
図５は、上記推定の具体的な更に他の例を示す説明図である。
図６は、上記推定の具体的な更に他の例を示す説明図である。
図７は、本発明に係る他の通信方法に係る手順を説明する説明図である。
図８は、本発明に係る他の通信方法に係る他の手順を説明する説明図である。
図９は、本発明の通信方法を説明するための概略構成を示す説明図である。
図１０は、上記通信方法において、送信局と受信局との間で行われるパケット送信と送達確認パケットのメッセージシーケンスを示す説明図である。
図１１は、上記送信局の概略構成を示すブロック図である。
図１２は、上記受信局の概略構成を示すブロック図である。
図１３は、上記受信局が非送信パケットに対する受信情報を返送するときの上記送信局の行う動作のフローを示すフローチャートである。
図１４は、非送信パケットに対する受信情報を返送するときの上記受信局の行う動作のフローを示すフローチャートである。
図１５は、非送信パケットに対する受信情報を返送するときの上記受信局におけるＤＥＬＡＹＥＤ−ＡＣＫ作成のフローを示すフローチャートである。
図１６は、ＤＥＬＡＹＥＤ−ＡＣＫの解釈を変更したときの上記送信局の行う動作のフローを示すフローチャートである。
図１７は、ＤＥＬＡＹＥＤ−ＡＣＫの解釈を変更したときの上記受信局におけるＤＥＬＡＹＥＤ−ＡＣＫ作成のフローを示すフローチャートである。
図１８は、従来の通信方法の手順を示す説明図である。
図１９は、従来の通信方法のＤＥＬＡＹＥＤ−ＡＣＫにおける通知範囲を示す説明図である。
図２０は、図１９の具体例を示す説明図である。
図２１は、従来の通信方法において、パケット紛失の検出における問題点を示す説明図である。
図２２は、本発明において、送信済の最新パケットの順序番号の推定を行わず、各ＤＥＬＡＹＥＤ−ＡＣＫにおいて常に受信済の最新パケットの順序番号に一定値を加えたパケット情報を返送する例を説明する説明図である。
図２３は、本発明においてＴＸＯＰが可変長の例について説明する説明図である。
図２４は、本発明において送信するパケットの順序番号が不連続な例を説明する説明図である。
図２５は、図２４の場合の具体例を説明する説明図である。
図２６は、ＤＥＬＡＹＥＤ−ＡＣＫパケットを送信局からの要求に応じて送信する例について説明する説明図である。
図２７は、ＤＥＬＡＹＥＤ−ＡＣＫパケットを送信局からの要求に応じて送信する他の例について説明する説明図である。
図２８は、ＤＥＬＡＹＥＤ−ＡＣＫパケットが送信局からの送信状況の通知内容を反映している例について説明する説明図である。Technical field
The present invention relates to a delayed delivery confirmation (DELAYED-ACK) system in which delivery confirmation information for received information units is collectively returned after reception of information units in a network in which a plurality of communication devices share one network path in a time division manner, and The present invention relates to a delayed delivery confirmation device.
Background art
Conventionally, in a computer network or the like, data is transmitted and received by a communication method called a packet communication method. The packet communication method is a communication method in which a data packet including one or more series of data serving as a unit of returning acknowledgment information called an information unit is transmitted and received as one data block.
For example, in a network with a high error occurrence rate in a communication path such as wireless communication, a protocol for performing retransmission processing of a data packet that has failed in data transmission is implemented in order to improve data delivery accuracy. For example, when one information unit is included in one packet, retransmission is performed in units of packets. When one packet includes a plurality of error correction blocks as information units, for each error correction block Will be retransmitted.
The above retransmission process is performed as follows. First, the data receiving station that has received the data packet returns delivery confirmation information indicating whether or not the information unit included in the packet has been successfully received to the data transmitting station. The data transmitting station detects an information unit that has failed to be received based on the acknowledgment information returned from the data receiving station, and retransmits the information unit toward the data receiving station.
In order to improve the accuracy of data delivery, when error correction processing is performed, the data transmitting station transmits an error correction code for each information unit, and the data receiving station includes the received data in the received data. It is determined whether the received data is complete based on the error correction code to be received.
When the retransmission process as described above is performed, the data receiving station normally returns delivery confirmation information for each information unit immediately after receiving the data packet. However, if it takes time to perform error correction processing at the data receiving station, the delivery confirmation information may not be returned immediately after receiving the information unit. In such a case, the delivery confirmation information is returned after a certain period of data packet reception.
In such a case, a plurality of communication devices share one network path in a time-sharing manner, and leave the transmission right to the data receiving station during the period from when data communication is completed until delivery confirmation information is returned. In the meantime, the communication device that does not transmit anything holds the transmission right.
As a result, the bandwidth usage efficiency decreases. In order to avoid this, conventionally, when data transmission is completed, the data transmitting station gives up the transmission right, and then the data receiving station reacquires the transmission right and returns delivery confirmation information. .
For example, the HCF (Hybrid Coordination Function) system (in accordance with the IEEE802.11 wireless communication system standardized for a wireless LAN (a system conforming to ANSI / IEEE Std. 802.11, 1999 Edition)) ( The addition of a method for performing bandwidth management of a network path, called a method conforming to IEEE Std 802.11e / D1, March 2001), is under study.
In this HCF system, a packet called DELAYED-ACK (delivery confirmation packet) is provided in order to return acknowledgment information for a plurality of data packets in one packet. This DELAYED-ACK is a collective response system deliberated by IEEE 802.11e. According to DELAYED-ACK, the reception status of each packet in the previous transmission opportunity (TXOP) is returned to the transmitting station and notified. The transmitting station that has received this DELAYED-ACK refers to the notified reception status and retransmits the packet as necessary.
According to the HCF system, a transmission station address, a destination address, a TCID uniquely assigned to each transmission station-destination pair in the transmission station, and a packet number assigned in the order of transmission for all packets are assigned to each packet. It is a specification included in the header part. Therefore, the data packet can be uniquely determined by checking this header portion.
The DELAYED-ACK includes a bitmap in which one bit is assigned to one packet number with respect to a plurality of continuous data packets. In the above bitmap, the data receiving station sets “1” to the bit assigned to the packet number of the data packet that has been successfully received, and “0” to the bit assigned to the packet number of the data packet that has failed to be received. ”Is set. Then, the data receiving station includes the first packet number of the data packet for which the acknowledgment information is to be returned by the DELAYED-ACK including the bitmap in the DELAYED-ACK, and then sends the DELAYED-ACK to the transmitting station. Return it.
Here, with reference to FIG. 18, it will be described that the DELAYED-ACK is returned from the receiving station to the transmitting station.
According to FIG. 18, each packet group A to D includes five packets to be transmitted. For example, the transmitting station transmits packets 1 to 5 of the packet group A to the receiving station during the period of TXOP-1. At this time, the reception status is not returned from the reception station to the transmission station for each packet, but after all of the packets 1 to 5 are transmitted to the reception station, the reception status is determined via the DELAYED-ACK packet a. Notified to the transmitting station.
Similarly, during the next TXOP-2, packets 6 to 10 are transmitted from the transmitting station to the receiving station, and the reception status is notified to the transmitting station via the DELAYED-ACK packet b.
During the next TXOP-3, packets 11 to 15 are transmitted from the transmitting station to the receiving station, and the reception status is notified to the transmitting station via the DELAYED-ACK packet c.
Further, during the next TXOP-4, packets 16 to 20 are transmitted from the transmitting station to the receiving station, and the reception status is notified to the transmitting station via the DELAYED-ACK packet d.
The DELAYED-ACK packet a has contents as shown in a1 in the figure, for example, when notifying the latest five packets. Moreover, according to the condition of a communication channel, as shown to a2 in the figure, the structure which notifies the 10 latest packets may be sufficient. In a2, the left half (“−4” to “0”) indicates a packet transmitted in the previous TXOP, and the right half (“1” to “5”) indicates a packet transmitted in the previous TXOP. . Note that the DELAYED-ACK packets b to d are basically the same as the DELAYED-ACK packet a and will not be described.
Further, in DELAYED-ACK, it is not defined which packet the reception status is returned to the transmitting station. This is shown in FIG. In addition, about the thing which has the same function as FIG. 18, the same referential mark is attached and detailed description is abbreviate | omitted.
In FIG. 19, a2 indicates a case including a packet immediately before DELAYED-ACK, a3 indicates a case not including a packet immediately before DELAYED-ACK, and a4 indicates a case not including a packet included in a TXOP immediately before DELAYED-ACK. Show. In a3, six packets from the left indicate packets transmitted in the previous TXOP, and four packets from the right indicate packets transmitted in the immediately preceding TXOP.
By the way, in the above HCF system, a period called CFP (Contention Free Period) and a period called CP (Contention Period) are alternately set. CFP is a period in which a central management device called HC (Hybrid Coordinator) manages the transmission right of all communication devices belonging to the network, and CP is a period in which transmission right management by the central management device is not performed. Of the communication devices belonging to the network, communication devices other than the HC are called ESTA (Enhanced Station).
In CFP, HC grants ESTA a transmission right with a time limit called TXOP (Transmission Opportunity) and sends a packet called QoS CF-POLL to ESTA that gives the transmission right to notify it. . The CF-POLL includes information on a period during which the transmission right is granted, and the ESTA that has received the CF-POLL is permitted to transmit data during this period.
In the CP, transmission rights are managed by a method called DCF (Distributed Coordination Function). When each ESTA that intends to transmit data detects that the wireless medium is idle during a period called DIFS (Distributed Coordination Function Inter Frame Space) after it finally detects the busy state of the wireless medium, A down timer having a random size is started. If the wireless medium is idle when the timer reaches 0, data transmission is started.
In the above-mentioned CFP, allocation of transmission rights is determined by the HC, so that data transmission stations that need to transmit data to some extent continuously, for example, when transmitting real-time data such as moving image data, are used. On the other hand, it is possible to perform management such that a transmission right is preferentially given.
However, if all the periods are allocated to the CFP, there is a problem that normal data transmission is not easily performed. Therefore, by providing the above-described CP, data transmission that performs normal data transmission is performed. The station has increased opportunities to secure transmission rights. The allocation of the period between the CFP and the CP is appropriately set according to the state of the type of data communicated in the network system.
In the case of the specifications related to HCF published at the present time (method conforming to IEEE Std 802.11e / D1, March 2001), DELAYED-ACK cannot be returned by CFP but by CP.
That is, the data transmission station transmits data packets 1 to n (n: natural number) in TXOP1 given by HC in CFP. After the preparation for returning the DELAYED-ACK is completed, the data receiving station participates in the DCF in the CP to acquire the transmission right, and returns the DELAYED-ACK.
In order to perform the retransmission processing as described above, it is first necessary to determine whether or not each packet has been successfully received at the data receiving station.
When sending back acknowledgment information every time data is received, check the continuity with the packet number of the packet received immediately before for the packet that was received correctly on the receiving station side. It is a general technique to detect the latter packet by determining that a packet having a packet number of is not received.
Here, detection of a packet that has failed to be received based on the above continuity will be described below with reference to FIG. In addition, about the thing which has the same function as FIG. 18, the same referential mark is attached and detailed description is abbreviate | omitted.
In TXOP-1, packets 1 to 5 in packet group A are transmitted from the transmitting station to the receiving station. Via the DELAYED-ACK packet a, the reception status of the packets 1 to 5 (see a2 in the figure) is notified to the transmitting station. In this case, the transmitting station confirms that the packets 1 to 5 have been successfully received by the receiving station from the notified DELAYED-ACK.
In the next TXOP-2, packets 6 to 10 of the packet group B are transmitted to the receiving station. At this time, if the transmitting station fails to transmit or the receiving station fails to receive and the packet 7 is not received by the receiving station, it is transmitted that the packet 7 cannot be received via the content of b2. The station is notified. In this case, in the content of b2, because the reception status of the packet 8 is discontinuously arranged next to the packet 6 (that is, based on the lack of continuity), the transmission station failed to receive the packet 7 It can be judged that.
A method for detecting packet loss in DELAYED-ACK is not defined. On the other hand, in communication methods other than DELAYED-ACK (normal ACK or the like), it is common to detect packet loss from the sequence numbers of the preceding and following packets. In this case, even when the header portion of the packet is crushed and the sequence number cannot be identified, it is possible to detect that the packet 7 is lost from the sequence numbers (6, 8) of the preceding and succeeding packets.
If determined in this way, the transmitting station retransmits the packet 7 prior to transmission of the packet 11 in the next TXOP-3. As a result, during the period of TXOP-3, a total of five packets of retransmission packet 7 (packet in packet group B) and packets 11 to 14 (packet in packet group C) are transmitted to the receiving station. Packet.
As a result of the retransmission of the packet 7, the DELAYED-ACK packet c includes the reception status relating to the packets 5 to 14 (see the contents of c2). Thereafter, in TXOP-4, the packets 15 to 19 in the packet group D are transmitted to the receiving station, and the DELAYED-ACK packet d includes the reception status relating to the packets 10 to 19 (see the contents of d2). . In this way, the packets 1 to 19 are transmitted from the transmitting station to the receiving station via the four TXOP-1 to TXOP-4.
However, the prior art has the following problems.
That is, when the delivery confirmation information is collectively notified using the above-described DELAYED-ACK or the like, as shown in FIG. 21, after receiving a series of packet groups B, it is delivered before receiving the next series of packet groups C. Confirmation information may be notified. If the packet 10 transmitted at the end of a series of packet groups B is not received and detected for some reason (if lost), when the delivery confirmation information for the packet group B is collectively notified, A series of packet groups C has not yet been received. For this reason, the receiving station determines that the packet 10 is not lost but has not been transmitted yet, and the delivery confirmation information does not include the information of the packet.
When the transmitting station has transmitted the packet 10, the transmitting station does not receive a notification of the loss of the packet 10, so it is determined that reception has not failed (successful reception), and the packet group C ( Packets 11 to 15) are transmitted to the next transmission opportunity (TXOP-3 in FIG. 21).
On the other hand, the receiving station detects the loss of the packet 10 by receiving the packet group C (see content c2 in FIG. 21), and the packet 10 is lost by the delivery confirmation information after the reception of the packet group C. To the transmitting station.
However, in this case, the timing at which the packet 10 is transmitted is delayed by at least two cycles from the transmission opportunity (TXOP-2 in FIG. 21) that should be transmitted (in TXOP-4 in FIG. 21, the packet 10 Will be resent).
Due to this delay in retransmission, the expiration date may have already expired when the packet is received (that is, the expired packet will not be used). In addition, as the retransmission of packets is delayed, it may be necessary to rearrange the packets on the receiving station side.
The example of FIG. 21 shows the case where the last packet of a certain packet group is not received and detected. However, even when the entire packet group is not received and detected for some reason, the same as in the case of FIG. All packets in the packet group are retransmitted with a delay of two cycles, which causes a similar problem. That is, in this case, if all the packets in the packet group are collectively considered as the last packet, this is equivalent to the case of FIG.
The present invention has been made in view of the above-described conventional problems, and its purpose is to delay retransmission due to packet loss, packet expiration, and packet rearrangement. There is to avoid.
Disclosure of the invention
In order to achieve the above object, the communication method of the present invention provides the following measures in the communication method in which delivery confirmation information for a plurality of transmission packets is collectively notified from the reception station to the transmission station via the delivery confirmation packet. It is characterized by having taken.
In other words, the communication method is characterized in that the delivery confirmation packet includes reception information about a packet that may not yet be transmitted by the transmitting station.
According to the communication method, when a plurality of packets are transmitted from a transmitting station to a receiving station at a certain transmission opportunity, if the receiving station cannot receive the packet or the packet group for some reason, The delivery confirmation packet including the reception information about the packet group is notified from the receiving station to the transmitting station, and by this delivery confirmation packet, the transmitting station receives the reception information about the packet that the transmitting station may not yet transmit. Will get.
In this way, the transmitting station can obtain information about a packet that may not yet be received via the delivery confirmation packet from the receiving station. Therefore, based on the notification from the receiving station, the transmitting station can quickly take an appropriate measure such as retransmission for a packet that may not have been received yet.
Since a quick measure such as retransmission is taken, when the packet is received, the expiry date has already expired, or when the quick measure is not taken, processing such as packet reordering is separately performed on the receiving station side It is possible to reliably avoid the necessity.
In order to achieve the above object, another communication method of the present invention is a communication method in which delivery confirmation information for a plurality of transmission packets is collectively notified from a reception station to a transmission station via a delivery confirmation packet. It is characterized by taking measures.
That is, the above communication method is characterized in that if the delivery confirmation packet has been transmitted and does not include information related to successful reception, it is assumed that transmission of the corresponding packet has failed, and the packet is retransmitted. Yes.
In this case, the receiving station notifies the transmitting station of delivery confirmation information including up to the packet number of the packet that has been successfully received. On the other hand, if the transmission confirmation packet does not include reception information for a packet that has been transmitted and has not received a reception success notification, the transmission station considers that transmission of this packet has failed, A retransmission process is performed. In this case, after the delivery confirmation information is transmitted in a certain transmission opportunity, the retransmission process may be performed within the transmission opportunity, the retransmission process may be performed in the next transmission opportunity, or a plurality of You may perform the said resending process for every transmission opportunity.
In this way, a packet that is deemed to have failed to be transmitted is retransmitted quickly. Along with this, it is certain that the expiration date has already expired at the time of packet reception, and that processing such as packet rearrangement is required separately on the receiving station side due to the fact that prompt measures are not taken. Can be avoided.
In order to achieve the above object, the transmission device of the present invention is a transmission device that collectively receives delivery confirmation information for the plurality of transmission packets from the reception device via a delivery confirmation packet, wherein the delivery confirmation is performed. When reception information about a packet that may not be transmitted by the transmitting station has been received from the receiving device via the packet, the reception information about the packet that has not been transmitted is ignored.
According to the above transmission apparatus, when a plurality of packets are transmitted from the transmission apparatus to the reception apparatus at a certain transmission opportunity, if the reception apparatus cannot be received for some reason, the delivery confirmation packet is transmitted from the reception apparatus. The transmission device is notified, and by this delivery confirmation packet, the transmission device obtains reception information about a packet that may not be transmitted by the transmission device.
Even if the transmission apparatus receives reception information indicating that the packet scheduled to be transmitted in the future has not been received, since the packet is transmitted later as scheduled, the reception information may be ignored.
Even if a packet scheduled to be transmitted in the future is included in this received information, the transmitting station ignores the received information of the packet and transmits the packet at the originally scheduled timing. No packet transmission is possible.
Since a quick measure such as retransmission is taken, when the packet is received, the expiration date has already expired, or when the quick measure is not taken, processing such as packet reordering on the receiving device side is separately performed It is possible to reliably avoid the necessity.
According to another aspect of the present invention, there is provided a transmitting device that collectively receives delivery confirmation information for a plurality of transmission packets from a receiving device via a delivery confirmation packet in order to achieve the above object. When reception information regarding a transmitted packet is not received from the receiving device via the delivery confirmation packet, it is assumed that transmission of the corresponding packet has failed, and the packet is retransmitted to the receiving device. It is characterized by.
According to the above transmission device, the reception device notifies the transmission station of delivery confirmation information including up to the received packet number. On the other hand, if the reception information on the transmitted packet is not received from the reception device via the delivery confirmation packet, the transmission device regards that the corresponding packet has failed to be transmitted and retransmits the packet. To the receiving apparatus.
In this case, after the delivery confirmation information is transmitted in a certain transmission opportunity, the retransmission process may be performed within the transmission opportunity, the retransmission process may be performed in the next transmission opportunity, or a plurality of You may perform the said resending process for every transmission opportunity.
In this way, since the above packet is retransmitted quickly, the packet is rearranged on the receiving device side due to the fact that the expiration date has already expired when the packet is received or that no prompt action is taken. Thus, it is possible to reliably avoid the need for such processing.
In order to achieve the above object, a receiving apparatus according to the present invention is a receiving apparatus that collectively notifies delivery confirmation information for a plurality of transmission packets to the transmitting apparatus via a delivery confirmation packet, wherein the delivery confirmation packet In this case, the transmission apparatus is notified of reception information about a packet that may not have been transmitted yet by the transmission apparatus.
According to the receiving device, when a plurality of packets are transmitted from the transmitting device to the receiving device at a certain transmission opportunity, if the receiving device cannot receive for some reason, the delivery confirmation packet is transmitted from the receiving device. The notification is sent to the device, and by this delivery confirmation packet, the transmission device obtains reception information on a packet that may not be transmitted by the transmission device.
As described above, the transmission device can obtain information on a packet that may not be transmitted by the transmission device yet via the delivery confirmation packet from the reception device. Therefore, based on the notification from the receiving device, the transmitting device can quickly take an appropriate measure such as retransmission for a packet that may not be transmitted by the transmitting device.
Since a quick measure such as retransmission is taken, when the packet is received, the expiration date has already expired, or when the quick measure is not taken, processing such as packet reordering on the receiving device side is separately performed It is possible to reliably avoid the necessity.
Other objects, features, and advantages of the present invention will be fully understood from the following description. The benefits of the present invention will become apparent from the following description with reference to the accompanying drawings.
BEST MODE FOR CARRYING OUT THE INVENTION
An example of a case where it is appropriate to include the reception status of a packet that may not have been transmitted by the transmitting station in the DELAYED-ACK (Dly ACK: delivery confirmation information) returned by the receiving station will be described below. Here, a case will be described as an example in which stream data such as moving images and audio is handled as data transmitted from the transmitting station 201 to the receiving station 301.
FIG. 9 shows a device configuration diagram in the present embodiment. A packet is transmitted from the transmitting station 201 to the receiving station 301 between the transmitting station 201 and the receiving station 301. The receiving station 301 stores the reception status of the stream packet (hereinafter referred to as a packet) in DELAYED-ACK and transmits the packet. Return to 201.
FIG. 10 shows a message sequence of packet transmission and delivery confirmation packet in the present embodiment. The transmitting station transmits packets 1 to 5 without waiting for the reception of the ACK, and the receiving station returns at least the reception status of packets 1 to 5 in DELAYED-ACK1.
FIG. 11 shows a block diagram of a transmitting station in the present embodiment. The transmitting station 201 receives a packet from the wireless channel, receives the packet from the wireless communication line 202, receives the packet determining unit 203 that determines the type of the received packet, and performs packet retransmission based on the DELAYED-ACK packet information received from the received packet determining unit 203. A transmission status management unit 204 for determining and managing necessity of transmission, a transmission application 205 for transmitting wirelessly transmitted stream data, and a transmission packet for processing stream data transmitted by the transmission application 205 into a format for storing in wireless packets Creation unit 206, buffer for transmission created by transmission packet creation unit 206, transmission packet management unit 207 for determining transmission order, and packet transmission unit for sending packets output from transmission packet management unit 207 to the radio line Composed of 208 That.
FIG. 12 shows a block diagram of the receiving station 301 in this embodiment. The receiving station 301 buffers the packets received by the packet receiving unit 302 that receives packets from the wireless line, the received packet determining unit 303 that determines the type of the received packet, and the received packet determining unit 303, and arranges the packet order. The reception packet management unit 304 that outputs stream data, the reception application 305 that uses the received stream data, the reception status management unit 306 that manages the reception status of packets, and the reception status managed by the reception status management unit 306 are also included. And DELAYED-ACK creation unit 307 that creates DELAYED-ACK, and packet transmission unit 308 that sends a packet such as DELAYED-ACK to the wireless line.
Table 1 shows an example of a transmission status list managed by the transmission status management unit 204 of the transmission station 201.
[Table 1]

The transmission status list is created for each stream to be transmitted, and indicates the transmission status of each packet storing the stream. There are three types of reception status: “not transmitted”, “transmitted”, and “retransmission required”. “Not transmitted” indicates that the transmitting station 201 has not yet transmitted the packet. “Transmitted” indicates that the transmitting station 201 has transmitted the packet, but it is unknown whether retransmission is necessary. “Retransmission required” indicates that retransmission is necessary because the receiving station 301 failed to receive the packet.
The initial state before packet transmission is “not transmitted”, and when the transmitting station 201 transmits a packet, the transmission state of the packet number becomes “transmitted”. When the transmitting station 201 receives the DELAYED-ACK from the receiving station 301, it indicates that the packet number of a certain packet has not been received, and the transmission status of the packet number becomes “retransmission required”.
Table 2 shows an example of a reception status list managed by the reception status management unit 306 of the receiving station 301.
[Table 2]

The reception status list is created for each stream to be received, and indicates the reception status of each packet storing the stream. There are two types of situations: “not received” and “received”. “Not received” indicates that the receiving station 301 has not received the packet yet. “Received” indicates that the receiving station 301 has received the packet.
The initial state before receiving the packet is “not received”, and when the receiving station 301 receives the packet, the reception state of the packet number becomes “received”.
FIG. 13 shows a flowchart of the operation of transmitting station 201 in the present embodiment.
Although not shown here, the transmitting station 201 transmits the stream data type, the data size, the ID for identifying the stream data, the reception confirmation method (ordinary ACK is DELAYED-ACK) before transmitting the stream data. Etc.) is negotiated between the receiving stations 301. When this negotiation is completed, the transmitting station 201 prepares for transmission of the stream data (for example, initialization of a variable Smax that stores the maximum packet number of transmitted packets, initialization of a transmission status list, etc.).
Subsequently, when the transmission application 205 receives a transmission request by some method, the transmission application 205 outputs the stream data to the transmission packet creation unit 206. The transmission packet creation unit 206 processes the stream data into a format for storing it in a wireless packet, and transmits it to the transmission packet management unit 207. The transmission packet management unit 207 stores the received data in its own buffer, and waits for the right to transmit to the wireless line.
The packet number assigned to the packet is incremented by 1 in ascending order from 0 in the same stream data (having an ID for identifying each stream data for each stream data, but the ID is the same packet group). Numbered.
When the transmitting station 201 receives a packet addressed to itself at the packet receiving unit 202 (step 401), the packet receiving unit 202 determines whether or not the packet is normally received (step 402). If normal, the packet is transmitted to the received packet determining unit 203, and the received packet determining unit 203 determines the type of the packet (step 403).
When the packet received by the reception packet determination unit 203 is a polling packet that gives a transmission right for transmitting the packet to the reception station 301, the reception packet determination unit 203 notifies the transmission packet management unit 207 of the ID of the target stream data To do.
Upon receiving the notification, the transmission packet management unit 207 first refers to the packet transmission status list managed by the transmission status management unit 204, transmits a packet that needs to be retransmitted via the packet transmission unit 208, and transmits the packet in the transmission status list. The field is rewritten as “transmitted” (step 404). Subsequently, packets to be newly transmitted are sequentially transmitted, and similarly, the column of the packet in the transmission status list is rewritten as “transmitted” (step 405).
When the packet received by the reception packet determination unit 203 is DELAYED-ACK, the reception packet determination unit 203 displays the ID of the stream data described in the DELAYED-ACK received by the transmission status management unit 204 and the reception status of each packet. Notice. The transmission status management unit 204 determines the target stream data from the transmitted ID (step 406), and updates the transmission status list of the stream data (steps 407 to 412). The detailed procedure is as follows.
First, the minimum packet number Dmin notified by DELAYED-ACK is substituted into a variable X (step 407), and the size is compared with the maximum packet number Smax of transmitted packets managed by the transmission status management unit (step 408). If X is larger than the maximum packet number Smax of the transmitted packet, the information stored in the subsequent DELAYED-ACK is ignored because it is for a packet not yet transmitted by the transmitting station 201. If X is equal to or smaller than the maximum packet number Smax of the transmitted packet, it is confirmed whether or not the packet number X has been received because of information on the packet already transmitted by the transmitting station 201 (step 409). If the packet number X has not been received, the field of the packet number X in the transmission status list is set to “retransmission required” (step 410). If the packet number X has been received, nothing is done. Finally, it is determined whether or not the packet number X is greater than or equal to the maximum packet number Dmax included in the DELAYED-ACK (step 411). If the packet number X is smaller than Dmax, the same processing is performed for the next packet number (step 412 and subsequent steps). If the packet number X is greater than or equal to Dmax, the process ends. It then waits for the next packet to be received.
If the packet received by the received packet determining unit 203 is another type of packet, the received packet determining unit 203 performs processing according to the type of the packet (step 413).
FIG. 14 shows a flowchart of the operation of the receiving station 301 in this embodiment.
Although not shown here, before receiving the stream data from the transmitting station 201, the type of stream data, the data size, the ID for identifying the stream data, the reception confirmation method (normal ACK or DELAYED- Negotiation between the transmitting station 201 and the receiving station 301 is performed for information such as ACK). When this negotiation is completed, the receiving station 301 prepares to receive the stream data (for example, initialization of a variable Rmax that stores the maximum packet number of the received packet).
Further, the packet numbers assigned to the packets are assumed to be increased by 1 in ascending order from 0 in the same stream data.
When the receiving station 301 receives a packet addressed to itself at the packet receiving unit 302 (step 501), the packet receiving unit 302 determines whether or not the packet is normally received (step 502). If normal, the packet is transmitted to the received packet determining unit 303, and the received packet determining unit 303 determines the type of the packet (step 503).
When the packet received by the reception packet determination unit 303 is a packet whose reception status is transmitted by DELAYED-ACK, the reception packet determination unit 303 transmits the packet to the reception packet management unit 304. The received packet management unit 304 determines which stream has been received from the ID (step 504), and accumulates the packet in a buffer corresponding to the ID of its own (step 505). The stream data stored in the packet accumulated in the buffer is output to the reception application 305 when output conditions such as time are met. The reception packet management unit 304 also notifies the reception status management unit 306 of the ID and packet number of the received stream data.
For the notified stream data ID and packet number, the reception status management unit 306 records that the packet number has been received in the reception status list of the stream data (step 506). If the packet number is larger than the maximum packet number Rmax of the received packet (step 507), the packet number is substituted into Rmax (step 508). It then waits for the next packet to be received.
When the packet received by the received packet determining unit 303 is a polling packet for returning a DELAYED-ACK to the transmitting station 201, the received packet determining unit 303 notifies the DELAYED-ACK creating unit 307 of the ID of the target stream data. . Receiving the notification, the DELAYED-ACK creation unit 307 refers to the packet reception status list managed by the reception status management unit 306 and creates a DELAYED-ACK packet (step 509). Then, the created DELAYED-ACK packet is transmitted to the transmission station 201 via the packet transmission unit 308.
When the packet received by the received packet determining unit 303 is another type of packet, the received packet determining unit 303 performs processing according to the type of the packet (step 511).
FIG. 15 shows an example of a DELAYED-ACK creation procedure according to step 509 of FIG. 14 in the present embodiment. First, it is estimated how many packets having a packet number larger than the maximum packet number Rmax of received packets may be transmitted (examples of estimation methods will be described in detail based on FIGS. 3 to 6). (It will be described later.) Let this estimated number be Ploss.
After estimating Ploss by the estimation method described later, the maximum packet number Dmax to be included in DELAYED-ACK is determined as Dmax = Rmax + Ploss (step 602).
Then, the reception statuses of packet numbers Rmax + 1 to Dmax in the reception status list are set to “not received”. However, this processing is not necessary when “not received” is set in the initial processing.
Finally, the reception status from the packet number Dmax to the packet requiring notification is sequentially stored in the DELAYED-ACK packet (step 603).
In this embodiment, as shown in steps 601 to 603, the packet reception status of a packet that is newer than the packet actually received by the receiving station 301, that is, that the transmitting station 201 may not yet transmit, is set to “unreceived”. DELAYED-ACK is transmitted.
The transmitting station 201 that has received this executes the processing shown in steps 407 to 412. Therefore, if the packet number in the received DELAYED-ACK has already been transmitted, the same processing as in a normal unreceived case is performed. Those packets are retransmitted.
Further, when the packet number in the received DELAYED-ACK is an untransmitted packet, the transmitting station 201 ignores the information and transmits the packet as scheduled, so the packet is processed in the same order as in normal processing. Can be sent.
That is, the packet (packet group) transmitted immediately before the DELAYED-ACK transmission by the reception station 301 returning the packet reception status of a packet that may not be transmitted as “not received” to the transmission station 201. Can be retransmitted in the next TXOP as shown in step 404 (after the DELAYED-ACK transmission, the packet is included in the TXOP). (Packet group) may be retransmitted.) In addition, the receiving station can receive in the original packet order intended by the transmitting side.
The present invention is not limited to the above case, and may be processed as follows. That is, an example in which the transmitting station interprets that reception of a packet newer than the packet number included in the DELAYED-ACK returned by the receiving station has failed is shown below. Note that the device configuration, message sequence, block diagram of the transmitting station and receiving station, and the flowchart of the operation of the receiving station are the same as those in the above case, so the description is omitted.
FIG. 16 shows a flowchart of the operation of transmitting station 201 in the present embodiment. Note that the description of the operation of the transmitting station 201 that is the same as the operation in FIG.
First, the smallest packet number Dmin notified by DELAYED-ACK is substituted into a variable X (step 707), and it is confirmed whether the packet number X has been received (step 708). If the packet number X has not been received, the field of the packet number X in the transmission status list is set to “retransmission required” (step 709). If the packet number X has been received, nothing is done. Subsequently, it is determined whether or not the packet number X is greater than or equal to the maximum packet number Dmax included in the DELAYED-ACK (step 710). If the packet number X is smaller than Dmax, the same processing is performed for the next packet number (step 711 and subsequent steps). If the packet number X is equal to or greater than Dmax, the process proceeds to the following process. Reflecting the packet information included in the DELAYED-ACK in the transmission information list is complete when the process proceeds to the following processing.
Next, the maximum packet number Smax of the transmitted packet is compared with the maximum packet number Dmax included in DELAYED-ACK (step 712). If Smax is greater than Dmax, it means that there is transmitted packet information that is not included in DELAYED-ACK. In this case, these packets are interpreted as having failed to be received, and “retransmission required” is set for packet numbers Dmax + 1 to Smax in the transmission status list (step 713). If Smax is equal to or smaller than Dmax, nothing is done. It then waits for the next packet to be received.
FIG. 17 shows an example of a DELAYED-ACK creation procedure according to step 509 of FIG. 14 in the present embodiment.
First, the maximum packet number to be included in DELAYED-ACK is determined as Dmax = Rmax (step 801). Next, the reception status from the packet number Dmax to the packet requiring notification is sequentially stored in the DELAYED-ACK packet (step 802).
In the present embodiment, as shown in step 713, when the transmitting station 201 is transmitting a new packet from the latest packet information notified by the received DELAYED-ACK, the transmitting station 201 transmits the DELAYED- Those packets not notified by ACK are set to be retransmitted on the assumption that reception has failed.
As a result, even when packets (packets) transmitted immediately before DELAYED-ACK transmission are lost, as shown in step 704, these packets (packets) are retransmitted at the next TXOP (DELAYED- (After transmitting the ACK, the packet (packet group) may be retransmitted in the TXOP.) In addition, the receiving station can receive in the original packet order intended by the transmitting side.
In this embodiment, in order to avoid delays in retransmission due to packet loss, expiration of packets, and packet reordering, any measures to be taken (any of the following) Measure (1) or (2)) will be described more specifically.
{Circle around (1)} The receiving station considers that it has been transmitted up to a sequence number obtained by adding a certain number to the sequence number of the latest received packet. Then, the reception information up to the packet of that number is included in the DELAYED-ACK. The latest packet means the last received packet in the packet order when the transmitting station does not retransmit, and when the sequence number keeps increasing sequentially, the maximum sequence number among the received packets is What you have.
(2) In the method of interpreting DELAYED-ACK at the transmitting station, “if the DELAYED-ACK does not contain received information about a packet that has been transmitted but has not received a notification of successful reception, transmission of the packet fails. Introduced the interpretation “ This will be described in detail below.
Conventionally, DELAYED-ACK notifies the transmitting station of the reception state of a packet that has already been received or a packet that is clearly not received.
On the other hand, according to the above measure (1) of the present embodiment, the receiving station includes in the DELAYED-ACK up to the reception information (reception status) of the packet whose transmission station is unknown whether or not it is still transmitting. I have to.
In this way, by including in the DELAYED-ACK the reception information of packets that are unknown whether the transmitting station is still transmitting (packets that may not be transmitted yet by the transmitting station), the transmitting station can identify these unknowns. Can be retransmitted as appropriate in the next TXOP (after the DELAYED-ACK transmission, the packet (packet group) may be retransmitted in the TXOP).
Here, a specific example of the measure (1) will be described with reference to FIG. Note that components having the same functions as those in FIG. 18 and the like are denoted by the same reference numerals, and detailed description thereof is omitted.
As shown in FIG. 1, first, in TXOP-1, packets 1 to 5 in the packet group A are transmitted from the transmitting station to the receiving station. As described above, the receiving station notifies the transmitting station of the packets 1 to 5 and the packets -4 to 0 transmitted by the previous TXOP via the DELAYED-ACK packet a.
Based on this DELAYED-ACK, the transmitting station determines that the packets 1 to 5 have been successfully received by the receiving station, and transmits the packets 6 to 10 of the packet group B to the receiving station in the next TXOP-2. At this time, it is assumed that the packet 10 of the packet group B is not received and detected by the receiving station for some reason.
According to the present embodiment, under such a situation, packets up to a sequence number obtained by adding a certain number (“1” in the case of FIG. 1) to the sequence number “9” of the latest received packet (that is, , Up to packet 10) is transmitted, and the fact is included in the DELAYED-ACK packet b as reception information. In addition, what is necessary is just to determine the said certain number using the below-mentioned method.
That is, the receiving station considers that all of the packets 6 to 10 of the packet group B have been transmitted, and notifies each transmitting information of these packets 6 to 10 to the transmitting station. According to FIG. 1, reception information regarding received packets 6 to 9 (latest packet) and an unreceived packet 10 is included in the DELAYED-ACK.
The transmitting station is notified through the DELAYED-ACK packet b that the packet 10 in the packet group B has not been received by the receiving station (packets 6 to 9 have been received, and packet 10 has not been received). Therefore, based on the DELAYED-ACK, the packet 10 is retransmitted to the receiving station in the next TXOP-3. Eventually, in TXOP-3, in addition to the packet 10 to be retransmitted, the packets 11 to 14 of the packet group C are also transmitted to the receiving station.
The receiving station includes the received information related to the packets 10 to 14 in the DELAYED-ACK and notifies the transmitting station via the DELAYED-ACK packet c. Based on this notification (see c2), the transmitting station determines that the packets 11 to 14 have been successfully received by the receiving station in addition to the retransmitted packet 10, and in the next TXOP-4, packets 15 to 19 of the packet group D are transmitted. Is transmitted to the receiving station. The receiving station includes the reception information related to the packets 15 to 19 in the DELAYED-ACK and notifies the transmitting station via the DELAYED-ACK packet d.
In the example of FIG. 1, for a packet that has already been transmitted, a retransmission process is performed if necessary with reference to the received reception status. For untransmitted packets, this information is ignored.
As described above, the packet 10 that has failed to be received in TXOP-2 is quickly retransmitted in TXOP-3, which is the next transmission opportunity. Therefore, it is possible to reliably avoid delays in retransmission due to packet loss, expiration of packets, and rearrangement of packets.
Here, another example in which the above measure (1) is taken will be described with reference to FIG.
The example shown in FIG. 2 shows a case where all the packets 6 to 10 of the packet group B are not received and detected by the receiving station for some reason. In addition, about the thing which has the same function as FIG. 1 etc., the same referential mark is attached and detailed description is abbreviate | omitted.
As shown in FIG. 2, first, in TXOP-1, packets 1 to 5 in the packet group A are transmitted from the transmitting station to the receiving station. As described above, the receiving station notifies the transmitting station of the packets 1 to 5 and the packets -4 to 0 transmitted by the previous TXOP via the DELAYED-ACK packet a.
Based on this DELAYED-ACK, the transmitting station determines that the packets 1 to 5 have been successfully received by the receiving station, and transmits the packets 6 to 10 of the packet group B to the receiving station in the next TXOP-2. At this time, it is assumed that the packets 6 to 10 of the packet group B are not received and detected by the receiving station for some reason.
As described above, since the latest packet is packet 5 (packets 1 to 5 have already been received by the receiving station), there is a certain number in the sequence number “5” of the received latest packet (FIG. 2). In this case, it is estimated that packets up to the sequence number (that is, up to packet 10) to which “5” (that is, the maximum number of packets transmitted in one TXOP) is added are transmitted. Included as reception information in packet b DELAYED-ACK packet b includes reception information related to packets 6-10.
That is, the receiving station considers that all of the packets 6 to 10 of the packet group B have been transmitted, and notifies each transmitting information of these packets 6 to 10 to the transmitting station. According to FIG. 2, the reception information related to the packets 6 to 10 is included in the DELAYED-ACK.
The transmitting station determines that the packets 6 to 10 in the packet group B are not received by the receiving station via the DELAYED-ACK packet b, and uses the DELAYED-ACK to transmit the packets 6 to 10 in the next TXOP-3. Is retransmitted to the receiving station. As a result, in TXOP-3, packets 6 to 10 to be retransmitted are transmitted to the receiving station.
The receiving station includes the reception information related to the packets 6 to 10 in the DELAYED-ACK and notifies the transmitting station via the DELAYED-ACK packet c. The transmitting station determines that the retransmitted packets 6 to 10 have been successfully received by the receiving station by this notification (refer to the contents of c2), and in the next TXOP-4, the packets 11 to 15 of the packet group D are received by the receiving station. Sent to. The receiving station includes the reception information related to the packets 11 to 15 in the DELAYED-ACK and notifies the transmitting station via the DELAYED-ACK packet d.
As described above, the packets 6 to 10 that have failed to be transmitted in TXOP-2 are quickly retransmitted in TXOP-3 which is the next transmission opportunity. Therefore, it is possible to reliably avoid delays in retransmission due to packet loss, expiration of packets, and rearrangement of packets.
FIG. 1 and FIG. 2 show that when the last packet of the packet group or the whole packet of the packet group is not received by the receiving station for some reason, it can be transmitted after the latest received packet until the end of the TXOP. The number of packets is estimated, and a number obtained by adding the estimated number of packets to the sequence number of the last received packet is set as an estimated transmitted packet sequence number. The present invention is not limited to these cases (FIGS. 1 and 2).
Here, an example of determining the “certain number” will be described below.
FIG. 3 estimates the number of packets that may be transmitted after the latest received packet and before the end of the TXOP. The number obtained by adding the estimated number of packets to the sequence number of the last received packet is set as the estimated transmitted packet sequence number.
In this case, as shown in FIG. 3, for example, when the packet 9 of the packet group B is not received by the receiving station for some reason, the number of packets that can be transmitted within one transmission opportunity is 5, and the latest received Since the packet sequence number is “10”, the estimated transmitted packet sequence number is 10.
Similarly, when the packet 10 of the packet group B is not received by the receiving station for some reason (in the case of FIG. 1), the sequence number of the latest received packet is “9”, and the TXOP-2 ends. Since the number of packets that can be transmitted to is “1”, the estimated transmitted packet sequence number is 9 + 1 = 10.
When the packets 9 and 10 of the packet group B are not received by the receiving station for some reason, the sequence number of the latest received packet is “8”, and the number of packets that can be transmitted before the end of TXOP-2 is “2”. Therefore, the estimated transmitted packet sequence number is 8 + 2 = 10. When the packets 7, 9, and 10 of the packet group B are not received by the receiving station for some reason, the sequence number of the latest received packet is “8”, and the number of packets that can be transmitted before the end of TXOP-2 Since “2”, the estimated transmitted packet sequence number is 8 + 2 = 10.
Here, a method of estimating the number of transmission packets will be described below with reference to FIG.
FIG. 4 shows the latest received based on one packet size and the time from the reception of the latest packet received in one TXOP to the end of the TXOP (the remaining time of the TXOP after receiving the latest received packet). A case where the number of packets that can be transmitted from the transmission of the packet to the end of the TXOP is estimated.
In general, since the period of TXOP is preset, based on the time when the receiving station received the last packet, the time when TXOP ends, and the size of the packet has a predetermined length, It is possible to estimate how many packets can be transmitted after the latest packet is transmitted.
For example, in the case shown in FIG. 4, when the packet 10 of the packet group B is not received by the receiving station for some reason, the sequence number of the latest received packet is “9”. The number of packets can be estimated by (remaining time until the end of TXOP / time required for transmitting one packet). Since it is calculated in this way, the accuracy of the estimation result is increased.
The example shown in FIG. 4 tends to be complicated because it requires time management and calculation. On the other hand, according to the example shown in FIG. 5, it is possible to easily estimate how many packets can be transmitted in a short time without managing the reception time for each received packet.
That is, according to the estimation method of FIG. 5, the estimated number of transmitted packets is obtained by subtracting the number of received packets and the number of packets known to have failed to be received from the number of packets that can be transmitted by one TXOP. Equal to the thing.
For example, in the case of FIG. 5, when the packets 7, 9, and 10 of the packet group B are not received by the receiving station for some reason, the sequence number of the latest packet is “8” and can be transmitted in TXOP-2. The number of packets is “5”, the number of received packets is 2 (that is, packets 6 and 8), and it is known that the packet 7 has failed to be received. 8+ {5- (2 + 1)} = 10. That is, the sequence number of the estimated transmitted packet can be estimated as “10”.
A specific example will be described below with reference to FIG.
As shown in FIG. 6, for example, when the packet 9 of the packet group B is not received by the receiving station for some reason, the sequence number of the latest received packet is “10” and can be transmitted by TXOP-2. Since the number of packets is 5 and it is known that packet 9 has failed to be received (because packet 9 is located between received packets 8 and 10), the estimated transmitted packet sequence number 10+ {5- (4 + 1)} = 10 (in this case, the estimated number of transmission packets is 0).
When the packet 10 of the packet group B is not received by the receiving station for some reason, the sequence number of the latest received packet is “9”, the number of packets that can be transmitted by TXOP-2 is 5, Since there is no packet that is known to have failed, the estimated transmitted packet sequence number is 9+ {5- (4 + 0)} = 10 (in this case, the estimated number of transmitted packets is 1). .
When the packets 9 and 10 of the packet group B are not received by the receiving station for some reason, the sequence number of the latest received packet is “8”, and the number of packets that can be transmitted by TXOP-2 is 5. Since there is no packet that is known to have failed to be received, the estimated transmitted packet sequence number is 8+ {5- (3 + 0)} = 10 (in this case, the estimated number of transmitted packets is 2). .)
When the packets 7, 9, and 10 of the packet group B are not received by the receiving station for some reason, the sequence number of the latest received packet is “8”, and the number of packets that can be transmitted by TXOP-2 is 5. Since it is known that the packet 7 has failed to be received, the estimated transmitted packet sequence number is 8+ {5- (2 + 1)} = 10 (in this case, the estimated number of transmitted packets is 2). .)
When the packets 6 to 10 of the packet group B are not received by the receiving station for some reason, the sequence number of the latest received packet is “5”, and the number of packets that can be transmitted by TXOP-2 is 5. Since there is no packet that is known to have failed to be received, the estimated transmitted packet sequence number is 5+ {5- (0 + 0)} = 10 (in this case, the estimated number of transmitted packets is 5). .)
Here, the above measure (2) will be described below.
According to the measure {circle around (2)}, when the DELAYED-ACK is interpreted at the transmitting station, if the DELAYED-ACK does not include reception information on a packet that has been transmitted and has not received a notification of successful reception, Packet transmission is considered to have failed.
In this case, the receiving station returns a DELAYED-ACK including the packet number of the successfully received packet to the transmitting station. The transmitting station makes a determination based on the above interpretation, and retransmits the packet if necessary.
A specific example will be described below with reference to FIG. In addition, about the thing which has the same function as FIG. 1 etc., the same referential mark is attached and detailed description is abbreviate | omitted.
As shown in FIG. 7, first, in TXOP-1, packets 1 to 5 in packet group A are transmitted from the transmitting station to the receiving station. As described above, the receiving station notifies the transmitting station of the packets 1 to 5 and the packets -4 to 0 transmitted by the previous TXOP via the DELAYED-ACK packet a.
Based on this DELAYED-ACK, the transmitting station determines that the packets 1 to 5 have been successfully received by the receiving station, and transmits the packets 6 to 10 of the packet group B to the receiving station in the next TXOP-2. At this time, it is assumed that the packet 10 of the packet group B is not received and detected by the receiving station for some reason.
According to the present embodiment, in such a situation, the DELAYED-ACK packet b includes a sequence number (9) which is transmitted by the transmitting station and is the latest packet among the packets received by the receiving station. ) Includes reception information related to packets up to. In the case of FIG. 7, as shown in b2, the transmission information is notified to the transmitting station that packets 0 to 9 are already received packets.
At this time, based on the notification, the transmitting station detects that the packet 10 has been transmitted and does not include reception information related to successful reception, and the packet 10 has not been received by the receiving station for some reason. In the next TXOP-3, the packet 10 is retransmitted to the receiving station. Eventually, in TXOP-3, in addition to the packet 10 to be retransmitted, the packets 11 to 14 of the packet group C are also transmitted to the receiving station.
The receiving station includes the received information related to the packets 10 to 14 in the DELAYED-ACK and notifies the transmitting station via the DELAYED-ACK packet c. Based on this notification (refer to the contents of c2), the transmitting station determines that the packets 11 to 14 have been successfully received by the receiving station in addition to the retransmitted packet 10, and in the next TXOP-4, the packet of the packet group D 15 to 19 are transmitted to the receiving station. The receiving station includes the reception information related to the packets 15 to 19 in the DELAYED-ACK and notifies the transmitting station via the DELAYED-ACK packet d.
As described above, the packet 10 that failed to be transmitted in TXOP-2 is quickly retransmitted in TXOP-3, which is the next transmission opportunity. Therefore, it is possible to reliably avoid delays in retransmission due to packet loss, expiration of packets, and rearrangement of packets.
Here, a case where all of the packets in TXOP-2 are not received and detected by the receiving station will be described with reference to FIG. In addition, about the thing which has the same function as FIG. 7 etc., the same referential mark is attached and detailed description is abbreviate | omitted.
As shown in FIG. 8, first, in TXOP-1, packets 1 to 5 in packet group A are transmitted from the transmitting station to the receiving station. As described above, the receiving station notifies the transmitting station of the packets 1 to 5 and the packets -4 to 0 transmitted by the previous TXOP via the DELAYED-ACK packet a.
Based on this DELAYED-ACK, the transmitting station determines that the packets 1 to 5 have been successfully received by the receiving station, and transmits the packets 6 to 10 of the packet group B to the receiving station in the next TXOP-2. At this time, it is assumed that all the packets (packets 6 to 10) of the packet group B are not received and detected by the receiving station for some reason.
According to the present embodiment, under such circumstances, the DELAYED-ACK packet b includes reception information up to the sequence number (5) of the latest received packet. In the case of FIG. 8, as shown in b <b> 2, reception information that the packets up to packet 5 are already received is notified to the transmitting station.
At this time, based on the above notification, the transmitting station detects that the packets 6 to 10 have been transmitted and the reception information related to the reception success is not included, and the packets 6 to 10 are detected by the receiving station for some reason. It is determined that the packet has not been received, and in the next TXOP-3, the packets 6 to 10 are retransmitted to the receiving station. Eventually, in TXOP-3, all packets to be transmitted in TXOP-2 are retransmitted to the receiving station.
The receiving station includes the reception information related to the packets 6 to 10 in the DELAYED-ACK and notifies the transmitting station via the DELAYED-ACK packet c. Based on this notification (see the contents of c2), the transmitting station determines that the retransmitted packets 6 to 10 have been successfully received by the receiving station, and the packets 11 to 15 of the packet group D are received at the next TXOP-4. Sent to the station. The receiving station includes the reception information related to the packets 11 to 15 in the DELAYED-ACK and notifies the transmitting station via the DELAYED-ACK packet d.
As described above, the packets 6 to 10 that have failed to be transmitted in TXOP-2 are quickly retransmitted in TXOP-3 which is the next transmission opportunity. Therefore, it is possible to reliably avoid delays in retransmission due to packet loss, expiration of packets, and rearrangement of packets.
In the above description, the case where the transmission station retransmits the detected reception failure packet at the next transmission opportunity of DELAYED-ACK is exemplified, but the present invention is not limited to this, This includes the case of retransmission at the latest transmission opportunity after DELAYED-ACK.
That is, as will be described later, the present invention may perform the above retransmission processing after transmission confirmation information transmission at a certain transmission opportunity and within the transmission opportunity (DELAYED-ACK is at the beginning or middle of the transmission opportunity). This corresponds to the case of transmission).) The retransmission processing may be performed at the next transmission opportunity, or the retransmission processing may be performed at a plurality of transmission opportunities.
Further, in the present invention, each packet group is not limited to including five packets, but other numbers, for example, 16 (32,...) Packets that are multiples of 16 units. It can also be applied when including.
Moreover, although the case where the packet reception status is sequentially notified from the designated sequence number is shown in the above description, the present invention is not limited to this. In short, it is only necessary to be able to notify the reception status of a plurality of packets at once.
Further, the number of packets to be notified of the DELAYED-ACK packets a to d may be determined according to the state of the communication path and the type of data to be transmitted. For example, when the error occurrence rate on the communication path is small, the number of packets may be small, and when the error occurrence rate is large, the number of packets may be large.
In the above description, the packet to be notified to the transmitting station is determined by estimating the number of packets that may be transmitted after the latest received packet and before the end of the TXOP. However, the determination method is not limited to this.
Here, another example according to a method for determining a packet to be notified will be described with reference to FIG. In addition, about the thing which has the same function as FIG. 1 etc., the same referential mark is attached and detailed description is abbreviate | omitted.
As shown in FIG. 22, first, in TXOP-1, packets 1 to 5 in the packet group A are transmitted from the transmitting station to the receiving station. As described above, the receiving station uses the DELAYED-ACK packet a to set the packets 1 to 5, the packets 2 to 0 transmitted in the previous TXOP, and the sequence number “5” of the latest received packet. The sequence number (sequence number “7” in this example) plus the value (2 in this example) is notified to the transmitting station.
Based on this DELAYED-ACK, the transmitting station determines that the packets 1 to 5 have been successfully received by the receiving station, and transmits the packets 6 to 10 of the packet group B to the receiving station in the next TXOP-2. At this time, it is assumed that the packet 10 of the packet group B is not received and detected by the receiving station for some reason.
According to the example shown here, in such a situation, the packet 9 is received, so the packets 10 and 11 are notified to the transmitting station as not received. That is, packets up to the order number obtained by adding the constant value “2” to the order number “9” (that is, up to the packet 11) are included in the DELAYED-ACK packet b as reception information.
The transmitting station is notified through the DELAYED-ACK packet b that the packet 10 in the packet group B has not been received by the receiving station (packets 6 to 9 have been received, and packet 10 has not been received). Therefore, based on the DELAYED-ACK, the packet 10 is retransmitted to the receiving station in the next TXOP-3. Eventually, in TXOP-3, in addition to the packet 10 to be retransmitted, the packets 11 to 14 of the packet group C are also transmitted to the receiving station.
The receiving station includes the received information related to the packets 10 to 14 in the DELAYED-ACK and notifies the transmitting station via the DELAYED-ACK packet c. Based on this notification (see c2), the transmitting station determines that the packets 11 to 14 have been successfully received by the receiving station in addition to the retransmitted packet 10, and in the next TXOP-4, packets 15 to 19 of the packet group D are transmitted. Is transmitted to the receiving station. The receiving station includes the reception information related to the packets 15 to 19 in the DELAYED-ACK and notifies the transmitting station via the DELAYED-ACK packet d.
Thus, the packet 10 that has failed to be received in TXOP-2 is quickly retransmitted in TXOP-3, which is the next transmission opportunity. Therefore, it is possible to reliably avoid delays in retransmission due to packet loss, expiration of packets, and rearrangement of packets.
As described above, the sequence number of the latest packet that has already been transmitted is not estimated, and in each DELAYED-ACK, packet information that is always added to the sequence number of the latest packet that has already been received ("2" in the case of FIG. 22). Is not estimated for each TXOP, the processing of the receiving station can be simplified accordingly.
As shown in FIG. 22, the reception information up to the latest packet received in all TXOPs plus the reception information of a certain number of packets expected to follow (two in the case of FIG. 22). May be notified to the transmitting station. This makes it possible to simplify the transmission packet estimation process performed by the receiving station. Note that FIG. 22 illustrates the case where the packet numbers are assigned in ascending order, but the present invention is not limited to this and can be applied to the case where the packet numbers are assigned in descending order.
Further, in the present embodiment, the lengths of the TXOPs are almost the same, that is, the lengths are set such that a maximum of 5 packets can be transmitted in a period from a certain DELAYED-ACK to the next DELAYED-ACK. However, as long as the number of packets transmitted during this period can be estimated by a method such as notifying the receiving station of the length of each TXOP, different TXOP lengths may be used as shown in FIG.
In the example of FIG. 23, a time for transmitting a total of 4 packets 1 to 4 is transmitted to TXOP-1, and a time for transmitting a total of 6 packets 5 to 10 is transmitted to TXOP-2. 3 and TXOP-4 are allotted a time for transmitting a total of five packets 10-14 and 15-19.
The time of each TXOP is notified to each station including the transmitting and receiving stations by a method such as being included in a packet (not shown) transmitted when the control station (HC) allocating the TXOP to the transmitting station allocates the transmission right to the transmitting station. Is possible.
In the case of FIG. 23, first, in TXOP-1, packets 1 to 4 in the packet group A are transmitted from the transmitting station to the receiving station. As described above, the receiving station notifies the transmitting station of the packets 1 to 4 and the packets 5 to 0 transmitted by the previous TXOP via the DELAYED-ACK packet a.
Based on the DELAYED-ACK, the transmitting station determines that the packets 1 to 4 have been successfully received by the receiving station, and transmits the packets 5 to 10 of the packet group B to the receiving station in the next TXOP-2. At this time, it is assumed that the packet 10 of the packet group B is not received and detected by the receiving station for some reason.
Under such circumstances, packets up to a sequence number obtained by adding a certain number (“1” in the case of FIG. 23) to the sequence number “9” of the latest received packet (that is, up to the packet 10) are transmitted. And the fact is included in the DELAYED-ACK packet b as reception information.
That is, the receiving station assumes that all of the packets 5 to 10 of the packet group B have been transmitted, and notifies each transmitting information of these packets 5 to 10 to the transmitting station. According to FIG. 23, reception information relating to received packets 5 to 9 and unreceived packet 10 is included in DELAYED-ACK.
The transmitting station is notified that the packet 10 in the packet group B is not received by the receiving station via the DELAYED-ACK packet b (packets 5 to 9 have been received, and packet 10 has not been received). Therefore, based on the DELAYED-ACK, the packet 10 is retransmitted to the receiving station in the next TXOP-3. Eventually, in TXOP-3, in addition to the packet 10 to be retransmitted, the packets 11 to 14 of the packet group C are also transmitted to the receiving station.
The receiving station includes the received information related to the packets 10 to 14 in the DELAYED-ACK and notifies the transmitting station via the DELAYED-ACK packet c. Based on this notification (see c2), the transmitting station determines that the packets 11 to 14 have been successfully received by the receiving station in addition to the retransmitted packet 10, and in the next TXOP-4, packets 15 to 19 of the packet group D are transmitted. Is transmitted to the receiving station. The receiving station includes the reception information related to the packets 15 to 19 in the DELAYED-ACK and notifies the transmitting station via the DELAYED-ACK packet d.
In the example of FIG. 23, for a packet that has already been transmitted, a retransmission process is performed if necessary with reference to the received reception status. For untransmitted packets, this information is ignored.
As described above, the packet 10 that has failed to be received in TXOP-2 is quickly retransmitted in TXOP-3, which is the next transmission opportunity. Therefore, it is possible to reliably avoid delays in retransmission due to packet loss, expiration of packets, and rearrangement of packets.
Furthermore, in the above description, the case where the sequence numbers of the packets to be transmitted are illustrated is exemplified, but the present invention is not limited to this, and the sequence numbers of the packets are discontinuous as shown in FIG. It is also applicable to.
In this case, for example, when the transmitting station is an access point (AP) in a wireless LAN and relays a plurality of streams transmitted from the Internet to the wireless station, the output is output from the access point. This occurs when, for example, a common sequence number is assigned to all streams input to the access point, instead of assigning a different sequence number to each stream.
Here, a specific example will be described with reference to FIG. In addition, about the thing which has the same function as FIG. 1 etc., the same referential mark is attached and detailed description is abbreviate | omitted.
As shown in FIG. 24, first, in TXOP-1, packets 1, 3, 4, 5, and 7 in packet group A are transmitted from the transmitting station to the receiving station. As described above, the receiving station transmits the packets 1, 3, 4, 5, and 7 through the DELAYED-ACK packet a, the packets -2 to 0 transmitted in the previous TXOP, and the unreceived packet 2. 6 is notified to the transmitting station.
Based on this DELAYED-ACK, the transmitting station determines that the packets 3, 4, 5, and 7 have been successfully received by the receiving station, and in the next TXOP-2, packets 8 to 11 and 13 of the packet group B are transmitted. To the receiving station. At this time, it is assumed that the packet 13 of the packet group B is not received and detected by the receiving station for some reason.
According to the present embodiment, under such a situation, packets up to a sequence number obtained by adding a certain number (“2” in the case of FIG. 24) to the sequence number “11” of the latest received packet (that is, , Up to packet 13) is transmitted, and the fact is included in the DELAYED-ACK packet b as reception information.
That is, the receiving station assumes that all of the packets 8 to 11 and 13 of the packet group B have been transmitted, and notifies each transmitting information of these packets to the transmitting station. According to FIG. 24, reception information regarding received packets 8 to 11 (latest packet) and unreceived packets 12 and 13 is included in DELAYED-ACK.
The transmitting station is notified that the packet 13 in the packet group B has not been received by the receiving station via the DELAYED-ACK packet b (packets 8 to 11 have been received, and packet 13 has not been received). Therefore, based on the DELAYED-ACK, the packet 13 is retransmitted to the receiving station in the next TXOP-3. Eventually, in TXOP-3, in addition to packet 13 to be retransmitted, packets 14, 16, 17, and 18 of packet group C are also transmitted to the receiving station.
The receiving station includes the received information related to the packets 13, 14, 16, 17, and 18 in the DELAYED-ACK and notifies the transmitting station via the DELAYED-ACK packet c. Based on this notification (see c2), the transmitting station determines that the packets 14, 16, 17, and 18 have been successfully received by the receiving station in addition to the retransmitted packet 13, and in the next TXOP-4, the packet group D Packets 20, 21, 23, 24, and 26 are transmitted to the receiving station. The receiving station includes the received information related to the packets 20, 21, 23, 24, and 26 in the DELAYED-ACK and notifies the transmitting station via the DELAYED-ACK packet d.
In the example of FIG. 24, for a packet that has already been transmitted, a retransmission process is performed if necessary with reference to the received reception status. For untransmitted packets, this information is ignored. Further, in the above description, the case of the bitmap method is illustrated, but the present invention is not limited to this, and a method of transmitting a packet number may be used. In the above description, the case of ascending order is illustrated, but the present invention can also be applied to the case of descending order. In this case, a certain value may be subtracted.
As described above, the packet 13 that failed to be received in TXOP-2 is quickly retransmitted in TXOP-3, which is the next transmission opportunity. Therefore, it is possible to reliably avoid delays in retransmission due to packet loss, expiration of packets, and rearrangement of packets.
If the packet sequence number is discontinuous, the receiving station calculates the estimated transmitted packet sequence number by adding a certain number to the sequence number of the latest received packet or analyzing the sequence number pattern of the received packet. It is effective to send the delivery confirmation information including the reception status of the packet.
When a certain number is added to the order of received packets, it is effective to add a larger value than when packet order numbers are consecutive. When the estimated transmitted packet sequence number is estimated, as shown in FIG. 25, the estimated number of transmitted packets may be multiplied by a certain number (in the case of FIG. 25, or added) to cope with the discrete sequence number. desirable.
Here, a specific estimation method when the packet sequence numbers are discontinuous will be described with reference to FIG.
FIG. 25 illustrates estimating the number of packets that may be transmitted after the latest received packet and before the end of the TXOP. The number obtained by multiplying the sequence number of the last received packet (the sequence number of the latest received packet) by the estimated number of transmitted packets multiplied by a fixed number α is set as the sequence number of the estimated transmitted packet. This α is effective when the sequence number of the packet is small when it is continuous and large when it is discontinuous.
Specifically, as shown in FIG. 25, for example, when the packet 9 of the packet group B is not received by the receiving station for some reason, the number of packets that can be transmitted within one transmission opportunity is 5, and the reception has been completed. Since the sequence number of the latest packet is “10”, the estimated transmitted packet sequence number is 10 (= 10 + 0 × α).
Similarly, when the packet 10 of the packet group B is not received by the receiving station for some reason, as shown in FIG. 25, the sequence number of the latest received packet is “9”, and the TXOP-2 is completed by the end. Since the number of packets that can be transmitted is “1”, the estimated transmitted packet sequence number is 9 + α (= 9 + 1 × α).
When the packets 9 and 10 of the packet group B are not received by the receiving station for some reason, as shown in FIG. 25, the sequence number of the latest received packet is “8” and transmitted by the end of TXOP-2. Since the number of packets that can be transmitted is “2”, the estimated transmitted packet sequence number is 8 + 2α (= 8 + 2 × α).
When the packets 7, 9, and 10 of the packet group B are not received by the receiving station for some reason, the sequence number of the latest received packet is “8”, and the number of packets that can be transmitted before the end of TXOP-2 Is “2”, the estimated transmitted packet sequence number is 8 + 2α (= 8 + 2 × α).
In the above description, the case where the receiving station spontaneously transmits the DELAYED-ACK packet after the TXOP of the transmitting station is illustrated, but the present invention is not limited to this. For example, the DELAYED-ACK packet may be transmitted in response to a request from the transmission station, or the transmission period may be during TXOP of the transmission station.
Hereinafter, a specific example will be described with reference to FIG. FIG. 26 shows a case where the transmitting station designates the timing at which the receiving station returns the DELAYED-ACK packet.
In FIG. 26, the transmitting station transmits packets with sequence numbers 1 to 10, and subsequently transmits a DELAYED-ACK request packet. The receiving station receives the DELAYED-ACK request packet and transmits a DELAYED-ACK packet.
At this time, the receiving station has failed to detect and receive the packet 10, but has transmitted up to the reception information of the packet (10) obtained by adding “1” to the latest received packet 9, so that the transmitting station 10 can be retransmitted in the next TXOP-2. This process is similar to the example in which the DELAYED-ACK packet is spontaneously transmitted after the TXOP of the transmitting station ends.
At this time, it is preferable that the data receiving station (station transmitting the DELAYED-ACK packet) can determine which packet reception status is included in the DELAYED-ACK packet. In this case, the receiving station estimates the transmitted packet sequence number using information such as the length of the transmission opportunity, the packet size, the number of packets actually received, or other methods, and It is possible to request retransmission of these packets.
In the example of FIG. 26, the example in which the DELAYED-ACK request packet and the DELAYED-ACK packet are transmitted at the end of the TXOP has been described. However, the present invention is not limited to this, and these two packets are transmitted. The timing to perform may be at the beginning or middle of TXOP.
FIG. 27 shows an example in which a DELAYED-ACK request packet and a DELAYED-ACK packet are transmitted in the middle of TXOP-1. In this case, the retransmission target packet 10 has the same transmitting station after the DELAYED-ACK packet. It is possible to retransmit within TXOP-1.
In addition, when determining which packet the reception information is to be transmitted by the receiving station, the packet transmission status data notified by the transmitting station may be used (the transmission status notified by the transmitting station is reflected). Also good). This case is shown in FIG.
In FIG. 28, the transmitting station transmits packets 1 to 10 in TXOP-1, and transmits the DELAYED-ACK REQUEST packet including information “transmitted to packet 10”. Although the receiving station could not receive the packet 10 for some reason, the information “transmitted to the packet 10” is sent from the transmitting station, so the reception status up to the packet 10 based on the transmission status from the transmitting station. The packets 1 to 9 received in the DELAYED-ACK packet are set as “received” and the packet 10 is set as “not received” and transmitted to the transmitting station. As a result, the transmitting station can retransmit the packet 10 in TXOP-2 which is the latest transmission opportunity.
In this embodiment, a packet is described. However, a plurality of blocks are stored in one packet and transmitted, and delivery confirmation information of these blocks is received together via a delivery confirmation packet. A notification may be sent from the station to the transmitting station, and the delivery confirmation packet may include reception information about a block that may not be transmitted by the transmitting station yet. Even in this case, the same operation and effect as the communication method described above can be obtained.
In the communication method of the present invention, as described above, the following measures have been taken in the communication method in which delivery confirmation information for a plurality of transmission packets is collectively notified from the reception station to the transmission station via the delivery confirmation packet. It is characterized by.
In other words, the communication method is characterized in that the delivery confirmation packet includes reception information about a packet that may not yet be transmitted by the transmitting station.
When a plurality of packets are transmitted from a transmitting station to a receiving station at a certain transmission opportunity and the receiving station cannot receive the packet or the packet group for some reason, conventionally, the delivery confirmation packet cannot be received. The reception information about the missing packet was not included. This is due to the following reason. That is, conventionally, the reception information included in the delivery confirmation packet is limited to the reception status related to the received packet and the reception status related to the packet that is clearly not received.
For this reason, reception information about a packet that may not be transmitted by the transmitting station has not been notified to the transmitting station. As a result, the transmitting station has not failed to receive (successfully received) because there is no notification of reception information related to the reception state of the packet or packet group transmitted immediately before the end of the transmission opportunity (first transmission opportunity). Therefore, the subsequent packet is transmitted to the receiving station at the next transmission opportunity (second transmission opportunity).
On the other hand, the receiving station notifies the transmitting station of the reception information related to the packet or the packet group that is found to be unreceivable via the delivery confirmation packet. Then, at the next transmission opportunity (third transmission opportunity), the transmitting station retransmits the packet that failed to be received to the receiving station based on the notification result from the receiving station. In this way, all the plurality of packets are communicated from the transmitting station to the receiving station.
As described above, according to the conventional communication method, retransmission of a packet that failed to be received at the first transmission opportunity is not performed at the next second transmission opportunity, but is performed at the third transmission opportunity. Thus, according to the prior art, the timing at which a packet that has failed to be received is delayed by at least two cycles from the transmission opportunity (first transmission opportunity) that should be transmitted (third transmission opportunity).
Due to this delay in retransmission, the expiration date may have already expired when the packet is received (the expired packet is not used). In addition, as the retransmission of packets is delayed, it may be necessary to rearrange the packets on the receiving station side.
On the other hand, according to the above communication method, when a plurality of packets are transmitted from the transmitting station to the receiving station at a certain transmission opportunity, the receiving station cannot receive the packet or the packet group for some reason. In this case, the delivery confirmation packet including the reception information about the packet or the packet group is notified from the receiving station to the transmitting station, and the sending station may cause the transmitting station to send a packet that the transmitting station may not yet transmit. You will get the received information about.
In this way, the transmitting station can obtain information about a packet that may not yet be received via the delivery confirmation packet from the receiving station. Therefore, based on the notification from the receiving station, the transmitting station can quickly take an appropriate measure such as retransmission for a packet that may not have been received yet.
Since a quick measure such as retransmission is taken, when the packet is received, the expiry date has already expired, or when the quick measure is not taken, processing such as packet reordering is separately performed on the receiving station side It is possible to reliably avoid the necessity.
The delivery confirmation packet preferably includes reception information indicating that a packet that may not have been transmitted by the transmitting station has not been received yet. In this case, the receiving station notifies the transmitting station of reception information indicating that a packet that may not have been received has not been received yet. The transmitting station receives this reception information, knows that there is a packet that has not been received by the receiving station among the transmitted packets, and can retransmit the corresponding packet.
Also in this case, the transmitting station can quickly retransmit a packet that may not have been received yet, based on the notification from the receiving station, at the transmission opportunity or the next transmission opportunity. Become. In addition, since retransmission is performed quickly, additional processing such as packet rearrangement is required on the receiving station side because the expiration date has already expired at the time of packet reception and prompt measures are not taken. It can be avoided reliably.
Preferably, the receiving station determines a transmission packet that is a target of the reception information. In this case, the receiving station estimates the transmitted packet sequence number using information such as the length of the transmission opportunity, the packet size, the number of packets actually received, or other methods, and It is possible to request retransmission of these packets.
The reception information preferably includes reception information on any packet up to a sequence number obtained by adding a predetermined number to the sequence number of the latest received packet. In this case, if the transmitting station has transmitted the packet with the sequence number, the transmitting station performs processing according to the contents. On the other hand, if the transmitting station has not yet transmitted the packet with the sequence number, it ignores the reception notification and The packet is transmitted as expected.
The predetermined number is preferably the same value in each delivery confirmation packet. In this case, since the sequence number of the latest packet that has already been transmitted is not estimated for each TXOP, the processing of the receiving station can be simplified accordingly.
The predetermined number in the reception information may be set to a maximum value of the number of packets transmitted at a transmission opportunity from transmission of a certain delivery confirmation packet to transmission of the next delivery confirmation packet. In this case, even when all the packets included in the transmission opportunity from the transmission of a certain delivery confirmation packet to the transmission of the next delivery confirmation packet cannot be received for some reason, all of these packets can be retransmitted quickly and reliably. .
The predetermined number in the reception information is the number of packets that may be transmitted after the latest received packet and before the end of the transmission opportunity in a transmission opportunity from transmission of a certain delivery confirmation packet to transmission of the next delivery confirmation packet. May be an estimated value.
In this case, it is assumed that the packet up to the sequence number obtained by adding the estimated value to the sequence number of the latest received packet is transmitted, and that fact is included in the reception information. For packets that have already been transmitted, retransmission processing is appropriately performed from the transmitting station to the receiving station based on the received reception information (reception status). For unreceived packets, the information is ignored and transmitted at the originally scheduled timing.
The estimated value is preferably calculated based on the size of the packet and the number of packets that can be transmitted between the reception of the latest packet and the end of the transmission opportunity.
In this case, when a certain packet is not received by the receiving station for some reason, the number of packets that can be transmitted between the latest packet reception and the end of the transmission opportunity is added to the received latest packet, It is considered that up to the sequence number of the addition result has been transmitted. Then, based on the received reception information (reception status), retransmission processing is performed on packets that have not been received at the next transmission opportunity.
The number of packets that can be transmitted is calculated by dividing the time from reception of the latest packet to the end of the transmission opportunity by the time required to transmit one packet. Thus, since the estimated value is calculated based on the division value, it is possible to perform highly accurate estimation.
The number of packets that can be transmitted as described above may be obtained by subtraction instead of being obtained by division as described above. That is, the estimated value may be equal to a value obtained by subtracting (the number of received packets + the number of packets known to have failed to receive) from the number of packets that can be transmitted in the transmission opportunity.
Thus, since the estimated value can be calculated without measuring time, the process and time required for estimation can be greatly shortened.
The predetermined number in the reception information is preferably determined by the receiving station using packet transmission information notified by the transmitting station. In this case, the receiving station can reliably obtain information on the packet transmitted by the transmitting station, and can reliably include the packet to be retransmitted in the retransmission request.
Further, as described above, another communication method of the present invention is a communication method in which delivery confirmation information for a plurality of transmission packets is collectively notified from the reception station to the transmission station via the delivery confirmation packet. It is characterized by having taken.
That is, the above communication method is characterized in that if the delivery confirmation packet has been transmitted and does not include information related to successful reception, it is assumed that transmission of the corresponding packet has failed, and the packet is retransmitted. Yes.
In this case, the receiving station notifies the transmitting station of delivery confirmation information including up to the packet number of the packet that has been successfully received. On the other hand, if the transmission confirmation packet does not include reception information for a packet that has been transmitted and has not received a reception success notification, the transmission station considers that transmission of this packet has failed, A retransmission process is performed. In this case, after the delivery confirmation information is transmitted in a certain transmission opportunity, the retransmission process may be performed within the transmission opportunity, the retransmission process may be performed in the next transmission opportunity, or a plurality of You may perform the said resending process for every transmission opportunity.
In this way, a packet that is deemed to have failed to be transmitted is retransmitted quickly. Along with this, it is certain that the expiration date has already expired at the time of packet reception, and that processing such as packet rearrangement is required separately on the receiving station side due to the fact that prompt measures are not taken. Can be avoided.
As described above, the transmission device of the present invention is a transmission device that collectively receives delivery confirmation information for the plurality of transmission packets from the reception device via the delivery confirmation packet. When receiving information on a packet that may not be transmitted by the transmitting station has been received from the receiving apparatus, the received information on a packet that has not been transmitted is ignored.
According to the above transmission device, when a plurality of packets are transmitted from the transmission device to the reception device, if the reception device cannot be received for some reason, the delivery confirmation packet is notified from the reception device to the transmission device, With this delivery confirmation packet, the transmission apparatus obtains reception information about a packet that may not be transmitted by the transmission apparatus yet.
Even if the transmission apparatus receives reception information indicating that the packet scheduled to be transmitted in the future has not been received, since the packet is transmitted later as scheduled, the reception information may be ignored.
Even if a packet scheduled to be transmitted in the future is included in this received information, the transmitting station ignores the received information of the packet and transmits the packet at the originally scheduled timing. No packet transmission is possible.
Since a quick measure such as retransmission is taken, when the packet is received, the expiration date has already expired, or when the quick measure is not taken, processing such as packet reordering on the receiving device side is separately performed It is possible to reliably avoid the necessity.
Further, as described above, another transmitting apparatus of the present invention is a transmitting apparatus that receives delivery confirmation information for a plurality of transmission packets from the receiving apparatus through the delivery confirmation packet in a lump, and has already transmitted packets. If the reception information on the packet is not received from the reception device via the delivery confirmation packet, it is assumed that transmission of the corresponding packet has failed, and the packet is retransmitted to the reception device. .
According to the above transmission device, the reception device notifies the transmission station of delivery confirmation information including up to the received packet number. On the other hand, if the reception information on the transmitted packet is not received from the reception device via the delivery confirmation packet, the transmission device regards that the corresponding packet has failed to be transmitted and retransmits the packet. To the receiving apparatus.
In this case, after the delivery confirmation information is transmitted in a certain transmission opportunity, the retransmission process may be performed within the transmission opportunity, the retransmission process may be performed in the next transmission opportunity, or a plurality of You may perform the said resending process for every transmission opportunity.
In this way, since the above packet is retransmitted quickly, the packet is rearranged on the receiving device side due to the fact that the expiration date has already expired when the packet is received or that no prompt action is taken. Thus, it is possible to reliably avoid the need for such processing.
As described above, the receiving device of the present invention is a receiving device that collectively notifies the transmitting device of delivery confirmation information for a plurality of transmission packets via the delivery confirmation packet, and through the delivery confirmation packet, It is characterized in that the transmission apparatus is notified of reception information about a packet that may not be transmitted yet by the transmission apparatus.
According to the receiving device, when a plurality of packets are transmitted from the transmitting device to the receiving device, if the receiving device cannot be received for some reason, the delivery confirmation packet is notified from the receiving device to the transmitting device. With the delivery confirmation packet, the transmission apparatus obtains reception information about a packet that may not be transmitted by the transmission apparatus yet.
As described above, the transmission device can obtain information on a packet that may not be transmitted by the transmission device yet via the delivery confirmation packet from the reception device. Therefore, based on the notification from the receiving device, the transmitting device can quickly take an appropriate measure such as retransmission for a packet that may not be transmitted by the transmitting device.
Since a quick measure such as retransmission is taken, when the packet is received, the expiration date has already expired, or when the quick measure is not taken, processing such as packet reordering on the receiving device side is separately performed It is possible to reliably avoid the necessity.
The receiving apparatus according to the present invention is characterized in that a packet to be the target of the reception information is determined using any one of the communication methods.
In the communication method, the delivery confirmation packet is preferably transmitted in response to a request from a station that transmits the transmission packet. As a result, when a transmission opportunity remains after transmission of the delivery confirmation packet, the transmitting station can quickly take appropriate measures such as retransmission at the transmission opportunity.
In the transmitting device, a packet for requesting the delivery confirmation packet is preferably transmitted to the receiving device. As a result, when a transmission opportunity remains after transmission of the delivery confirmation packet, the transmitting station can quickly take appropriate measures such as retransmission at the transmission opportunity.
It is preferable that the receiving device transmits the delivery confirmation packet in response to a request from the transmitting device. In this case, the transmission device can take necessary measures more promptly and appropriately based on the delivery confirmation packet.
As described above, the communication program of the present invention is preferably a communication program for causing a computer to implement each procedure of any one of the communication methods described above.
As described above, the recording medium of the present invention is preferably a computer-readable recording medium that records a communication program for causing a computer to execute each procedure of any one of the communication methods described above.
By causing the computer to execute the communication program and the computer-readable recording medium on which the communication program is recorded, the communication method, the transmission device, and the reception device can take quick measures such as retransmission. Therefore, it is possible to reliably avoid the necessity of separate processing such as packet rearrangement on the receiving apparatus side due to the fact that the packet has been cut off or the prompt action is not taken.
The network system of the present invention is characterized in that communication is managed by any one of the communication methods described above.
According to the above network system, since a quick measure such as retransmission is taken, the packet at the receiving device has already expired when the packet is received, or when a quick measure is not taken. Therefore, it is possible to reliably avoid the necessity of a separate process such as rearrangement, and to provide a highly reliable network system.
Although the above stipulates packets, a plurality of blocks are stored in one packet and transmitted, and delivery confirmation information of these blocks is notified from the receiving station to the transmitting station via the delivery confirmation packet. Even if the communication method is characterized in that the delivery confirmation packet includes reception information about a block that may not have been transmitted by the transmitting station, the same as above Has the effects and effects.
The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims, and the technical means disclosed in different embodiments can be appropriately combined. Embodiments to be described are also included in the technical means of the present invention.
The specific embodiments or examples made in the best mode for carrying out the invention are merely to clarify the technical contents of the present invention, and are limited to such specific examples. The present invention should not be construed as narrowly defined but can be implemented with various modifications within the spirit of the present invention and the scope of the following claims.
Industrial applicability
As described above, the communication method of the present invention is useful as a network communication method in which a plurality of communication apparatuses share one network path in a time-sharing manner, and in particular, retransmission due to packet loss is delayed, This is useful as a network communication method capable of avoiding that the expiration date of the packet expires and performing packet rearrangement.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram for explaining estimation of sequence numbers performed in the communication method according to the present invention.
FIG. 2 is an explanatory diagram illustrating another estimation of sequence numbers performed in the communication method according to the present invention.
FIG. 3 is an explanatory diagram showing a specific example of the above estimation.
FIG. 4 is an explanatory diagram showing another specific example of the above estimation.
FIG. 5 is an explanatory diagram showing still another specific example of the above estimation.
FIG. 6 is an explanatory diagram showing still another specific example of the above estimation.
FIG. 7 is an explanatory diagram illustrating a procedure according to another communication method according to the present invention.
FIG. 8 is an explanatory diagram for explaining another procedure according to another communication method according to the present invention.
FIG. 9 is an explanatory diagram showing a schematic configuration for explaining the communication method of the present invention.
FIG. 10 is an explanatory view showing a message sequence of packet transmission and delivery confirmation packet performed between the transmitting station and the receiving station in the communication method.
FIG. 11 is a block diagram showing a schematic configuration of the transmitting station.
FIG. 12 is a block diagram showing a schematic configuration of the receiving station.
FIG. 13 is a flowchart showing a flow of operations performed by the transmitting station when the receiving station returns reception information for a non-transmitted packet.
FIG. 14 is a flowchart showing a flow of operations performed by the receiving station when returning reception information for a non-transmission packet.
FIG. 15 is a flowchart showing a DELAYED-ACK creation flow in the receiving station when returning reception information for a non-transmission packet.
FIG. 16 is a flowchart showing a flow of operations performed by the transmitting station when the interpretation of DELAYED-ACK is changed.
FIG. 17 is a flowchart showing a DELAYED-ACK creation flow in the receiving station when the interpretation of DELAYED-ACK is changed.
FIG. 18 is an explanatory diagram showing a procedure of a conventional communication method.
FIG. 19 is an explanatory diagram showing a notification range in DELAYED-ACK in the conventional communication method.
FIG. 20 is an explanatory diagram showing a specific example of FIG.
FIG. 21 is an explanatory diagram showing problems in packet loss detection in the conventional communication method.
FIG. 22 illustrates an example of returning packet information obtained by always adding a constant value to the sequence number of the latest received packet in each DELAYED-ACK without estimating the sequence number of the latest transmitted packet in the present invention. It is explanatory drawing to do.
FIG. 23 is an explanatory diagram illustrating an example in which the TXOP has a variable length in the present invention.
FIG. 24 is an explanatory diagram illustrating an example in which the sequence numbers of packets to be transmitted are discontinuous in the present invention.
FIG. 25 is an explanatory diagram for explaining a specific example in the case of FIG.
FIG. 26 is an explanatory diagram illustrating an example in which a DELAYED-ACK packet is transmitted in response to a request from a transmitting station.
FIG. 27 is an explanatory diagram illustrating another example in which a DELAYED-ACK packet is transmitted in response to a request from a transmitting station.
FIG. 28 is an explanatory diagram illustrating an example in which the DELAYED-ACK packet reflects the notification content of the transmission status from the transmission station.

Claims (22)

It is a communication method for notifying the transmission station of the delivery confirmation information for a plurality of transmission packets from the reception station to the transmission station via the delivery confirmation packet,
The communication method according to claim 1, wherein the delivery confirmation packet includes reception information on a packet that may not be transmitted by the transmitting station. It is a communication method for notifying the transmission station of the delivery confirmation information for a plurality of transmission packets from the reception station to the transmission station via the delivery confirmation packet,
The communication method according to claim 1, wherein the delivery confirmation packet includes reception information indicating that a packet that may not be transmitted by the transmitting station has not been received yet. The communication method according to claim 1, wherein the receiving station determines a transmission packet that is a target of the reception information. 4. The communication method according to claim 3, wherein the reception information includes reception information for any packet up to a sequence number obtained by adding a predetermined number to the sequence number of the latest received packet. The communication method according to claim 4, wherein the predetermined number is the same value in each delivery confirmation packet. 5. The communication according to claim 4, wherein the predetermined number in the reception information is a maximum value of the number of packets transmitted at a transmission opportunity from transmission of a certain delivery confirmation packet to transmission of a next delivery confirmation packet. Method. The predetermined number in the reception information is the number of packets that may be transmitted after the latest received packet and before the end of the transmission opportunity in a transmission opportunity from the transmission of a certain delivery confirmation packet to the transmission of the next delivery confirmation packet. The communication method according to claim 4, wherein the communication method is an estimated value. 8. The communication according to claim 7, wherein the estimated value is calculated based on the size of the packet and the number of packets that can be transmitted between the reception of the latest packet and the end of the transmission opportunity. Method. The communication method according to claim 7, wherein the estimated value is equal to a value obtained by subtracting the number of received packets from the number of packets that can be transmitted in the transmission opportunity. The communication method according to claim 4, wherein the predetermined number in the reception information is determined by the receiving station using packet transmission information notified by the transmitting station. It is a communication method for notifying the transmission station of the delivery confirmation information for a plurality of transmission packets from the reception station to the transmission station via the delivery confirmation packet,
A communication method characterized in that if the delivery confirmation packet has not been transmitted and does not contain information related to successful reception, it is considered that transmission of the corresponding packet has failed, and the packet is retransmitted. A transmission device that receives delivery confirmation information for a plurality of transmission packets in a batch from a reception device via a delivery confirmation packet,
A transmission apparatus characterized by ignoring reception information about these packets when receiving reception information about packets not yet transmitted from the reception apparatus via the delivery confirmation packet. A transmission device that receives delivery confirmation information for a plurality of transmission packets in a batch from a reception device via a delivery confirmation packet,
When reception information regarding a transmitted packet is not received from the receiving device via the delivery confirmation packet, it is assumed that transmission of the corresponding packet has failed, and the packet is retransmitted to the receiving device. A transmitter characterized by the above. A receiving device that collectively notifies delivery information to a plurality of transmission packets via a delivery confirmation packet to a transmission device,
A receiving apparatus that notifies the transmitting apparatus of reception information about a packet that may not be transmitted yet by the transmitting apparatus via the delivery confirmation packet. 15. The receiving apparatus according to claim 14, wherein a packet that is a target of the reception information is determined using the communication method according to any one of claims 4 to 9. The communication method according to claim 1, wherein the delivery confirmation packet is transmitted in response to a request from a station that transmits the transmission packet. The transmission device according to claim 12 or 13, wherein a packet for requesting the delivery confirmation packet is transmitted to the reception device. 16. The receiving apparatus according to claim 14, wherein the delivery confirmation packet is transmitted in response to a request from the transmitting apparatus. The communication program for making a computer implement | achieve each procedure of the communication method as described in any one of Claims 1-11, or Claim 16. The computer-readable recording medium which recorded the communication program for making a computer perform each procedure of the communication method as described in any one of Claims 1-11, or Claim 16. A network system, wherein communication is managed by the communication method according to any one of claims 1 to 11. It is a communication method for storing a plurality of blocks in one packet and transmitting them, and sending the acknowledgment information of those blocks in a batch to the transmitting station via a delivery confirmation packet,
The communication method according to claim 1, wherein the delivery confirmation packet includes reception information about a block that may not be transmitted by the transmitting station.

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