JP3987903B2 - Non-geostationary orbit satellite communication network and its relay device - Google Patents

Description

表１は、第一の実施形態に関するものである。第一の実施形態ではハンドオーバに関しては、新たなサービス衛星が、その隣接衛星にハンドオーバ通知を行ない、さらに、端末が旧サービス衛星にサービス衛星の変更通知を行う。転送方路切替えでは、個別のハンドオーバに関する情報の授受を行わない。このような方法を採った場合に、ハンドオーバ方向と、転送規則の切替え方向によって、前述のようなロスの可能性があるケースを×で、そのようなことが起きないケースを○で示す。
【００５５】
図１８ではパケットロスが生じないケースとして、衛星１７０１へハンドオーバが生じ状態で、衛星１７０２へ切替えが生じる場合の転送方路の変化を示す。図１９では、パケットロスが生じるケースとして、衛星１７０９へハンドオーバが生じ状態で、衛星１７０２へ切替えが生じる場合の転送方路の変化を示す。
【００５６】
基本的には、切替え後の本来のサービス衛星と新サービス衛星が２リンク以上になる位置にハンドオーバしている場合、前述の第二のケースに該当し、パケットロスの可能性がある。なお、表１のようなハンドオーバと転送規則切替えの組は同一の確率で生じるわけでない。端末の動きが衛星および地球の動きに対して遅い場合は、先行衛星へのハンドオーバの発生確率は、後続衛星へのハンドオーバに比べる発生確率は低いと思われる。
また、そのような衛星へハンドオーバしたまま通信を継続する時間も、後続衛星へハンドオーバした場合に比べると小さくならざるを得ない。前述のように切替え後２リンク以上になるのは、このような先行衛星へのハンドオーバが起きた状態で切替えが発生する場合である。
【００５７】
本発明の第二の実施形態の場合も同様の結果となる。例えば、ハンドオーバ通知を新サービス衛星だけでなく、旧サービス衛星も通知する場合には、本来の新サービス衛星が旧サービス衛星の隣接衛星であることから、表２のようになり、ロスするケースを減らすことができる。
【００５８】
なお、旧サービス衛星による通知は、新サービス衛星がどの衛星であるかを通知するものとする。
【００５９】
この情報は、通常、旧サービス衛星と新サービス衛星が隣接する関係にあること、あるいは端末からの通知などに基づいて設定することが可能である。
【００６０】
【表２】

図２０は、図１９で示した新サービス衛星しか通知しない場合にはロスが発生するケースにおいて、旧サービス衛星も通知を行う場合を示す。図からわかるように転送規則切替え後に本来サービス衛星となるべきであった衛星１７０２には、ハンドオーバ時にすでに旧サービス衛星からハンドオーバ通知がなされているので、転送規則切替え後も、自分がサービス衛星とならず、旧サービス衛星に転送すればよいことを知ることができる。
【００６１】
また、旧サービス衛星も隣接衛星にハンドオーバ通知を行なう代わりに、転送規則の切替え時に、本来の転送規則だけでなく、バッファ上にあるハンドオーバ端末の転送規則も後続衛星に転送することでも、同様な効果を得ることができる。
【００６２】
次に本発明の第三の実施形態を、図８以降を用いて説明する。
本発明の第三の実施形態では、端末８０１がサービス衛星を衛星８０２から衛星８０３にハンドオーバした際、第一の実施形態では新たなサービス衛星が直接通信可能な隣接衛星のみにハンドオーバ通知を出していたのに対し、ハンドオーバがあった方向と垂直で、元のサービス衛星８０２を含む衛星８０２を中心とした地球一周分のパス８０５と新たなサービス衛星８０３を含む衛星８０３を中心とした地球一周分のリンク集合８０４上の全衛星にハンドーバ通知を行うことを特徴としている。
【００６３】
本実施形態の詳細を説明する前に、本実施形態を用いない場合の課題、すなわち第一あるいは第二の実施形態の場合の問題点に関して、図９を用いて説明する。端末９０１に対するハンドオーバ前のサービス衛星を衛星９０２、ハンドオーバ後のサービス衛星を衛星９０３とする。第一および第二の実施形態の場合、図７の説明と同様にして、ハンドオーバ検知が行われ、ハンドオーバおよびそれに対する隣接衛星の転送規則の修正が行われる。この間の手順は、図７の７０1から７０９を図９の９０１から９０９に読み替えることで、図７の説明を参照して欲しい。ハンドオーバ直後の状態では、衛星９１１を経由するパケットはパス９１２のようになり、理想的な経路と比べると２リンク分余計なリンクを通ることとなる。
【００６４】
このような余計なリンクにより伝送遅延時間、ネットワーク負荷、ロス率などが若干増加するものと考えられる。
【００６５】
第三の実施形態はこのような第一および第二の実施形態の持つ課題に鑑みてなされたものである。
【００６６】
新しいサービス衛星８０３上で転送規則を、ハンドオーバに対応して変更する手順は、図３と全く同様である。ただし、ステップ３０５で行う隣接衛星への通知はハンドオーバが起きたリンクの先行衛星８０２とそのリンクと垂直なリンク上の隣接衛星８０６，８０７に対してのみ実施する。
また、ハンドオーバが起きたリンクと垂直なリンクへの通知には、単に対象となる端末のアドレスだけでなく、通知を転送する回数を設ける。
転送回数は、該通知方向が軌道面間に跨る方向で、軌道面数が奇数であれば、数３によって決まる値とする。
転送回数＝（軌道面数−１）／２ ・・・（数３）
また軌道面数が偶数の場合は、数４と数５によって定める。
転送回数＝ｆｌｏｏｒ（（軌道面数−１）／２） ・・・（数４）
＝ｆｌｏｏｒ（（軌道面数−１）／２）＋1 ・・・（数５）
なお、数４と数５はそれぞれ別の方向への転送回数として使用し、数４だけあるいは数５だけで決まる数を両方の転送方向に出力することはしない。
【００６７】
なお、ｆｌｏｏｒ（実数引数）は実数引数を超えない最大の整数を返す関数を示す。
【００６８】
一方、通知方向が軌道面方向で、軌道面あたりの衛星数が奇数であれば、数３の軌道面数を軌道面あたりの衛星数に置き換えた値を、軌道あたり衛星数が偶数の場合は数４および数５の軌道面数を軌道面あたりの衛星数に置き換えた値を利用する。
【００６９】
なお、隣接軌道面の斜め後ろの衛星にハンドオーバがおきる場合は、軌道面に垂直な方向へのハンドオーバと水平な方向へのハンドオーバが同時に発生したものとする。
【００７０】
次に図１０を用いて、ハンドオーバが起きたリンクの先行衛星８０２の動作アルゴリズムを説明する。
【００７１】
ハンドオーバが起きたリンクの先行衛星８０２は、ハンドオーバの通知を待ち（ステップ１００１）、受信した場合（ステップ１００２）には、ハンドオーバ通知を受信した方路を当該アドレスの転送方路として転送規則を変更し（ステップ１００３）、続いて、ハンドオーバ通知を受信した方路と直交する方向へ転送回数付きハンドオーバ通知を送信する（ステップ１００４）。
【００７２】
次に図１１を用いて、リンク集合８０４あるいはリンク集合８０５上の、新たなサービス衛星８０３とそのハンドオーバ方向の先行衛星８０２を除く衛星における、転送回数付きハンドオーバ通知の受信時の動作アルゴリズムを説明する。
【００７３】
前述の条件に合致する衛星は、転送回数付きハンドオーバ通知の受信待ちを行う（ステップ１１０１〜１１０２）。該通知を受けた場合、事前方路保存要否フラッグがＴＲＵＥの場合は、受信時点の転送規則上の当該アドレスに対する転送方路をバックアップ情報に記録する（ステップ１１０３）。続いて、該通知を受信した方向へ該宛先への転送方路を変更する（ステップ１１０４）。受信した転送回数が１以上の場合（ステップ１１０５）は、該通知を受信した方路と反対の方路へ、通知を転送する。ただし、ここでは転送回数を１減らしたものにする（ステップ１１０６）。
【００７４】
なお、ハンドオーバ通知とは無関係にタイマ割込みを受けた場合の処理は、第一の実施形態あるいは第二の実施形態と同様の動作とする。
【００７５】
以上のようなアルゴリズムに基づく転送規則の転送処理を、再び図８に戻って説明する。
【００７６】
ハンドオーバにより衛星８０３が新たなサービス衛星となると、直前までのサービス衛星との関係から、ハンドオーバ方向と直交する衛星間リンク集合８０４，８０５を特定することができる。そこで、新たなサービス衛星８０３は、直交方向へのハンドオーバ通知とハンドオーバ方向へのハンドオーバ通知を作成し、隣接衛星へ送信する。ハンドオーバ方向の先行衛星である衛星８０２は転送回数なしのハンドオーバ通知を受け取るので、図１０のアルゴリズムに従って、当該アドレスに対する転送方向を修正すると供に、転送回数付きのハンドオーバ通知をリンク集合８０５上に送出する。一方、新たなサービス衛星に対してハンドオーバ方向と垂直な方向にある隣接衛星８０６および隣接衛星８０７と、旧サービス衛星８０２の同方向への隣接衛星８０８と隣接衛星８０９は、転送回数付きのハンドオーバ通知を受信し、図１１のアルゴリズムに従って、当該宛先アドレスに対する転送方路を修正するとともに、ハンドオーバ通知の再転送を行う。
【００７７】
この後、タイマ割込みによる転送規則の切替え処理が発生すると、衛星８１０から衛星８０９のように先行衛星上の転送規則が後続衛星に移行し変えられるので、図９の転送規則の切替え後で示すような状態となり、サービス衛星に対する相対的な転送規則の配置は領域８１４に示すようにハンドオーバ前と同じ状態になる。
【００７８】
次の図１３を用いて、２πコンスタレーションの地球非静止軌道衛星ネットワークシステムを前提とした本発明の実施形態を説明する。
【００７９】
２πコンスタレーションでは、図１３に示すようにほぼ直交する進行方向を持つ衛星郡が同一の地域の上空に位置することになる。端末１３０１が始め北西から南東へ進む軌道上の衛星１３０２をサービス衛星としていたが、衛星の移動あるいは端末の移動で、南西から北東へ進む軌道上の衛星１３０３へハンドオーバする場合を考える。
【００８０】
衛星は図１４に示すような軌道上を周回しているため、図１４で地球１４０１の表側では南西から北東へ進む軌道１４０２が、地球の裏側では北西から南東に向かう軌道になっている。地球の自転方向で半日ずれた軌道面１４０３上の衛星は赤道上で軌道面１４０２と直交する軌道上にいることになるが、それら軌道面１４０２，１４０３上の衛星同士の相対速度は、隣接軌道面や同一軌道面の衛星と比べると非常に速く、通信が出来ない場合が多い。従って、前述のように進行方向の異なる衛星間でコネクションハンドオーバが発生すると、例えば、一旦地球の裏側へ転送し、そこから隣接軌道面間を転送して戻してくるような転送手順が必要となり、経路１４０５のように地理的には近いにも係わらず、非常に伝送経路の距離が長くなり、遅延時間やそのジッタが大きくなるため、通信品質が低下するという問題あった。
【００８１】
またこのような状況で転送規則をＯＳＰＦアルゴリズムなどで調整する場合には、全地球ネットワーク規模での転送規則の再構成が必要となるため、公知例のような方式では、セッションを継続することは出来ない。
【００８２】
このような状況で転送規則の更新のための通信量や計算処理を最小化すると供に、転送規則の変更に要する時間を少なくする本発明の第四の実施形態について図１３と図１５を用いて説明する。
【００８３】
第四の実施形態は、図１５に示すように２πコンスタレーションの地球非静止軌道衛星１５０１の他、地上に複数配置された進行方向の異なる軌道面（以下ではシームと呼ぶ）間の通信を中継する中継ノード１５０２からなる。
【００８４】
また、各衛星では、北東向きに進んでいる時に使用する転送規則と、南東向きに進んでいる時に使用するものの２通りを持つものとする。
元のサービス衛星１３０２と新たなサービス衛星１３０３は、各々端末からハンドオーバ通知とハンドオーバ要求を受ける。ハンドオーバ通知は、少なくとも当該端末のアドレスと新たなサービス衛星１３０３の識別子とを含み、ハンドオーバ要求は少なくとも当該端末のアドレスと元のサービス衛星１３０２の識別子を含むものとする。このようなハンドオーバ通知およびハンドオーバ要求により、お互いが同一軌道面内あるいは隣接軌道面間でハンドオーバが起きたのか、シーム間でハンドオーバが起きたのかを判定できる。異なるシーム間でハンドオーバが発生したと考えられる場合、元のサービス衛星１３０２は、自分の位置から最寄りのシーム間中継局１３０４を割り出し、そことコネクションを持つ同一シーム上の衛星の識別子を最寄りのシーム間中継局１３０４に問い合わせる。問い合わせは、少なくともハンドオーバを行った端末１３０１のアドレスと元のサービス衛星１３０２の識別子および新しいサービス衛星の識別子１３０３を含む構成とし、シーム間中継局１３０４では、この端末１３０１のアドレスに関する転送規則を保持していなければ、問い合わせに含まれる元サービス衛星の識別子を用いて、同一シームの直接通信可能な衛星１３０５の識別子を返送する。
【００８５】
また、該宛先に対する転送規則を記憶する。さらに該直接通信可能な衛星１３０５に対してサービス衛星として振舞うよう端末と同様なハンドオーバ要求を行う。旧サービス衛星はこのようにして見つけたシーム間中継局１３０４とコネクションを持つ衛星１３０５を新たなサービス衛星として前述の第一あるいは第二あるいは第三の実施形態に基づき、元のサービス衛星としての転送規則の更新処理を実施する。
【００８６】
シーム間中継局１３０４は当該アドレス宛てのパケットを受信すると、別のシーム上の直接通信可能な衛星１３０６に転送する。転送されたパケットを受信した衛星１３０６は、その所属するシーム上の転送規則に基づき、新たなサービス衛星１３０３へパケットを転送する。
【００８７】
また、問い合わせ中の端末アドレスに対する転送規則を既に保持していた場合には、問い合わせに含まれる新たなサービス衛星のアドレスを返信し、該中継局１３０４上の転送規則から当該端末アドレスに対するデータを削除する。また、該中継局１３０４と直接通信可能な衛星で、新たなサービス衛星と同一のシーム上の衛星に対して、元サービス衛星に対して端末が行うハンドオーバ通知と同様の通知を実施する。
【００８８】
従って逆に、始めに異なるシーム間でシーム間中継局１３０４経由で通信していた場合、元のサービス衛星１３０３と新たなサービス衛星１３０２は端末からハンドオーバ通知とハンドオーバ要求を受ける。この中にある相互の情報によりお互いが隣接軌道面でハンドオーバが起きたのか、シーム間でハンドオーバが起きたのかを判定できる。異なるシーム間でハンドオーバが発生したと考えられる場合は、最寄りのシーム間中継局１３０４に、当該アドレスに関する転送規則をもっているか否かを問い合わせる。当該アドレスに対する転送規則を持っている場合は、既にシーム間での通信に当該シーム間中継局を使っていたことが判るので、使っていたと判断される場合は、シーム間中継局とコネクションを持つ衛星１３０５から新たなサービス衛星１３０２にハンドオーバしたものとして、前述の第一あるいは第二あるいは第三の実施形態に基づく転送規則の更新処理を実施する。
【００８９】
なお、シーム間中継局は、各々のシームに関して、少なくとも１つの衛星と通信が可能で無ければならない。このため、各シーム用の２個のアンテナ以外に、ダイバーシティ用に予備のアンテナを物理的に離した位置に設置するなどの構成的な特徴をもつ。
【００９０】
異なるシームへのハンドオーバが起きた場合、元のサービス衛星１３０２と同一シームで、シーム間中継局と直接通信可能な衛星１３０５は、必ずしも隣接衛星あるいは、隣接衛星の隣接衛星であるとは限らないので、本発明の第一あるいは第二の実施形態を用いて、ハンドオーバにともなう転送規則の更新処理を行った場合、元のサービス衛星から、シーム間中継局までの転送方路を決定できない可能性がある。すなわち、このような場合には、図５のステップ５０８により、問い合わせが行われるが、図１６のアルゴリズムでは応答が返ってこない可能性がある。そこで、本実施形態に第一あるいは第二の実施形態を適用する場合は、図１６のアルゴリズムのように目的のアドレスに関する情報が無い場合は問い合わせを無視するのではなく更に隣接衛星に問い合わせを行うようにすればよい。
【００９１】
ただし、問い合わせには識別番号と転送回数などの情報を付与し、同一の問い合わせへの重複解答や問い合わせの無限の転送を回避する必要がある。また、応答に関しても、問い合わせもとまで転送して戻す処理を行う必要あがる。
【００９２】
このような方式を実現するためには、問い合わせを行う元のサービス衛星が、問い合わせに宛先アドレス、識別番号および最大転送回数を設定して、隣接衛星に問い合わせを送信する。送信に際しては、問い合わせの識別番号と宛先アドレスのペアを記録しておく。隣接衛星では、問い合わせを受信した方路と問い合わせの識別番号および宛先アドレスの組を記録し、当該アドレスへの方路情報を持っていれば、返信を行い、登録内容を削除する。持っていなければ、問い合わせを受信した以外の方路へ問い合わせを転送する。ただし、この際は最大転送回数を１つ小さな値に変更する。
【００９３】
また返信には、問い合わせの識別番号を設定する。なお、問い合わせを受信した際には、同一識別番号の問い合わせを受けているかどうかを、前述の組の記録から確認し、既に問い合わせを受けていれば、この問い合わせを無視するものとする。
【００９４】
応答を受信した場合は、前記記録済み組をチェックし、当該識別番号の記録を削除すると供に、当該アドレスに対する転送方路を応答を受信した方路へ変更する。また、応答を要求のあった方路へ転送する。
【００９５】
問い合わせに応答が届くと、問い合わせ元では、当該アドレスの転送方路を、応答を受信した方路に変更し、当該識別番号に関するペアの記録を削除する。
【００９６】
【発明の効果】
本発明の請求項１によれば、中継ノードが移動するネットワークにおけるルーティング情報の維持管理を容易にすることが出来る。
【００９７】
本発明の請求項２によれば、ルーティング情報の維持管理の制御を容易にすることが出来る。
【００９８】
本発明の請求項３と請求項８の組み合わせあるいは請求項４と、請求項６および請求項７によれば、宛先ステーションへのサービスステーションの隣接中継ノードになった後、サービスステーションの隣接中継ノードで無くなった後も、以前、その位置の中継ノードが利用していたルーティング情報を復元できる。
【００９９】
本発明の請求項５によれば、宛先アドレスに対するサービスステーションが変化したことを、最適なタイミングでネットワークに反映し、該宛先アドレスへのメッセージ転送を継続させることが出来る。
【０１００】
本発明の請求項９によれば、宛先アドレスに対するサービスステーションが変化した際、該宛先へのメッセージの転送経路をホップ数の観点で最適に維持することが出来る。
【０１０１】
本発明の請求項１０によれば、移動する中継ノードが複数のグループに分かれていて、それらの間で直接通信が出来ない場合で、宛先ステーションが第一のグループから第二のグループに移動した場合にも、メッセージの転送が可能となる。
【０１０２】
本発明の請求項１１によれば、第一のグループからのメッセージを第二のグループに属するサービスステーションで宛先ステーションに転送している状況から、宛先ステーションが第一のグループの中継ノードをサービスステーションに変更した時も、該宛先ステーションへのメッセージの転送が可能となる。
【０１０３】
本発明の請求項１２および請求項１３によれば地球非静止軌道衛星によって前述のようなネットワークを構成できる。
【０１０４】
本発明の請求項１４および請求項１５によれば、地球非静止軌道衛星によって構成した上述の特徴を持つネットワークにおけるルーティング情報の転送タイミングを適切に決定できる。
【０１０５】
本発明の請求項１５によれば、地球非静止軌道衛星によって構成した請求項９の特徴を持つネットワークにおいて、サービスステーション変更通知の転送回数を最適に決定できる。
【図面の簡単な説明】
【図１】図１は第一の実施形態のコンセプトを説明するための説明図である。
【図２】図２は本発明における衛星の通信処理部の基本構成図である。
【図３】図３はハンドオーバ時における新たなサービス衛星の動作アルゴリズムを説明するための説明図である。
【図４】図４はハンドオーバ通知を受けた隣接衛星の動作アルゴリズムを説明するための説明図である。
【図５】図５はハンドオーバでサービス衛星でなくなる衛星の動作アルゴリズムを説明するための説明図である。
【図６】図６はハンドオーバとは無関係に実施される転送方路情報の引継ぎ処理アルゴリズムを説明するための説明図である。
【図７】図７は転送規則の更新の概要を説明するための説明図である。
【図８】図８は第三の実施形態のコンセプトを説明するための説明図である。
【図９】図９は第一あるいは第二の実施形態の問題点を説明するための説明図である。
【図１０】図１０はハンドオーバが起きたリンクの先行衛星の動作アルゴリズムを説明するための説明図である。
【図１１】図１１は新たなサービス衛星とそのハンドオーバ方向の先行衛星に対して垂直なリンク上に位置し、それら以外の衛星における、転送回数付きハンドオーバ通知の受信時の動作アルゴリズを説明するための説明図である。
【図１２】図１２は転送方路の問合せ処理に対する応答アルゴリズムを説明するための説明図である。
【図１３】図１３は本発明の第四の実施形態のコンセプトを説明するための説明図である。
【図１４】図１４は２πコンスタレーションの地球非静止軌道衛星ネットワークシステムの特徴を説明するための説明図である。
【図１５】図１５は第四の実施形態の構成説明図である。
【図１６】図１６は転送方路不明の場合の問い合わせへの対応アルゴリズムを説明するための説明図である。
【図１７】図１７はハンドオーバが起こる可能性のある衛星と転送規則切替えの起こる可能のある衛星の組み合わせの説明図である。
【図１８】図１８はハンドオーバ後の転送規則切替えの説明図（パケットロスが起きない場合）である。
【図１９】図１９はハンドオーバ後の転送規則切替えの説明図（パケットロスが起きる場合）である。
【図２０】図２０はハンドオーバ後の転送規則切替えの説明図（旧サービス衛星も通知し、新サービス衛星の通知の方が新サービス衛星の通知より優先度が低い場合）である。
【符号の説明】
１０１ 端末
１０２〜１０６ 衛星の進行方向（軌道面）
１０７、１０８、１０９、１１０、１１１ 衛星[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a data communication network and system such as the Internet, and more particularly to a communication network involving movement of a network device, such as a communication network using a low earth orbit satellite or a medium orbit satellite.
[0002]
[Prior art]
As for communication networks using medium and low orbit satellites, as disclosed in Japanese Patent Laid-Open No. 2000-224237, connection-oriented services such as IRIDIUM (registered trademark) and GLOBALSTAR (registered trademark), and no connection as in the known example There is an oriented service. The Internet is widely used as a connection-oriented communication system. A communication procedure used for data transfer between terminals that communicate on this network is called an Internet protocol (hereinafter referred to as IP). It is supposed to solve the problems in using it for orbiting satellites.
[0003]
In this known example, the main problem is that the Inter-Satlite link lacks toughness compared to the terrestrial link. In response to this problem, it is said that the robustness of communication can be maintained by transferring packet copies through a plurality of routes. Also, in the satellite network system, the transmission delay tends to increase because the physical distance until the packet arrives at the receiving end from the transmitting end is long. For this reason, the delay when a packet is lost and resent is doubled. Therefore, the influence on the communication quality is a characteristic issue for the satellite network system. Is transmitted in advance, so that it is possible to save the trouble of twice from the retransmission request to the retransmission, and to eliminate the delay at the time of retransmission that has occurred in the conventional IP communication technology.
[0004]
By the way, as described in the known example, the IP is a communication system that can be compared with a postal system as a model. A packet to be transferred corresponds to a postal matter, and IP address information for specifying a destination is added. Based on this address, the router device corresponding to the post office judges the transfer direction one by one, and at least one or more (strictly zero or more because terminals under the same network can communicate directly without going through the router device) The packet is transferred to the final destination via the router device. For example, when mails written as Japan and AirMail are handled at a post office in the United States, they are sorted to be placed on air mail to Japan. Similarly, the router device also needs to determine the transfer direction according to the IP address, and holds data called a routing table in order to manage the correspondence.
[0005]
In the postal system, addresses are set according to the hierarchical structure of the government such as country and state, but in the IP network, as described on the website of the Japan Network Information Center, the network infrastructure It is determined by network addresses that are distributed as hierarchically as possible along the topology.
[0006]
When using a low earth orbit mobile satellite as a router device, it is like a post office flying over the sky, and it is necessary to change the sorting method, ie the contents of the routing table, according to the position of the corresponding ground surface .
[0007]
Even in the known example, the following problems are mentioned in the examples regarding the above-described problems. “The router 4 must know which available routes it has and which routes can be supported (at least at the moment)”. On the other hand, in the known example, it is possible to cope with the following two methods.
[0008]
1) “The satellites in the orbital array 2 can be predicted in these orbits, and since the gateway 5 has not moved relative to the ground surface, it is possible to maintain a database of addresses of these routers. , Map IP addresses to satellites in orbital array 2 according to a computational algorithm based on time geography and system availability. "
2) “Each router 4 (and 6) is to broadcast its address periodically, and each router that receives the broadcast distribution information is given its destination route list. Revise according to the distribution "
In this way, it is said that routers can continue to update the latest information on routers on satellites and terrestrial routers that can communicate with each other. A router mounted on a mobile satellite can always determine an appropriate transfer direction for an IP packet of an arbitrary destination.
[0009]
[Problems to be solved by the invention]
In the above conventional example, regarding the update method of the routing table of the router mounted on the low earth orbit mobile satellite that has been raised as a problem, in addition to the above-mentioned quotation, the latest information is notified to other satellites by broadcast delivery, It only states that OSFP can be used as a means for changing the destination route list of each satellite, that is, the routing table, and there is no discussion as to whether this is practically possible.
[0010]
Unlike the terrestrial network, the satellite network has a flat hierarchical structure, so if the network below the terrestrial gateway that has a link with the satellite is successfully aggregated, it should be delivered to the router on the gateway (aggregated Even if there is only one supernet address, it is necessary to provide a service to multiple gateways with a single satellite, and that the network is usually composed of about 100 to 300 satellites. Considering that satellites can no longer be seen in 5 to 10 minutes at orbital altitude of about 1000 km even if the minimum elevation angle that can be communicated is 20 °, information about networks that is several times the number of all satellites is updated every 5 to 10 minutes. Information to always manage the routing table. It is envisioned to be a situation such as trotting over the satellite network.
[0011]
In routing protocols such as OSFP and BGP (Border Gateway Protocol), once the routing table on each router is formed, the communication load and CPU load to form it are large. In order to reduce the number of information exchanges for maintaining the system, functions such as monitoring of life and death and notification of only the changed part are incorporated. However, in a low earth, medium orbit mobile satellite communication system, the relative position of the router on the satellite and the ground gateway is constantly changing, which is a big difference from the situation where all information must be exchanged even if it is a changed part. It is considered that there is no such state, and the situation is greatly different from the assumed operating conditions such as OSFP, and it is considered that these methods cannot be used in practice.
[0012]
The present invention relates to a routing table management method associated with satellite movement, which is a problem when performing communications using the Internet protocol in a low earth, medium orbit mobile satellite communication system, and reduces the CPU load and network load due to routing table management accompanying satellite movement. The purpose is to do.
[0013]
[Means for Solving the Problems]
In order to achieve the above object, the relay apparatus according to the present invention includes, for example, a routing table that stores information on a route to be transferred to a destination network address similar to that of a normal router apparatus as a satellite-mounted router apparatus. And means for transferring information (destination and route pair) in the routing table to adjacent satellites as a specific configuration, and means for updating the routing table with the transferred information, To do.
[0014]
Further, when the satellite-mounted router device of the present invention becomes a service satellite to the terminal or the gateway according to a request from the ground terminal or the ground gateway, the destination of the network in the routing table is set to the ground-satellite link of the own satellite. Means for switching and notifying the adjacent satellite router device that the service satellite for the network has changed. The adjacent satellite router apparatus that has received the notification includes means for updating a routing table so as to forward a packet to the network in a direction in which the notification is received.
[0015]
Furthermore, the satellite-mounted router device of the present invention transfers information in the routing table of the own satellite to a satellite capable of direct communication on an adjacent orbital plane in the same direction as the rotation of the earth at a timing determined by the rotation period of the earth. Routing information transfer means is provided for transferring information in the routing table of the own satellite to a subsequent satellite on the same orbital plane at a timing determined by the revolution period of the satellite. The satellite that has received the notification includes means for executing a procedure for taking over routing information (destination, that is, a pair of a network address of the network and a transfer direction path).
[0016]
According to another configuration of the present invention, a service satellite change notification is transmitted by a link of the original service satellite to a link orthogonal to the link connecting the original service satellite and the new service satellite. The satellite that has received the notification from the former service satellite has a transfer route for the address as a link that has received the notification, and includes a means for transferring to a link opposite to the link that has received the notification. This means is characterized in that the number of transfers is set so that the transfer ends in a half-earth globe. Assuming that the direction in which the notification is transferred is the direction between the track surfaces, the number of times of transfer is the smallest integer exceeding (N-1) / 2 when the number of track surfaces is N.
[0017]
In another configuration of the present invention, an inter-seam relay station capable of communicating simultaneously with satellites in different traveling directions in a 2π type orbital plane arrangement and installed from several to a dozen or so on the global scale, And a satellite that carries such a device and flies on a 2π-type orbital plane.
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described with reference to FIG.
[0018]
In FIG. 1, a packet transfer rule destined for the terminal 101, that is, a packet transfer direction is represented by an arrow from each satellite. Broken lines 102 to 106 with arrowheads indicate the traveling direction of the satellite, that is, the orbital plane. The satellite 107 is a satellite that directly transfers a packet to the terminal 101, and such a satellite is called a service satellite.
[0019]
The satellite is flying in the direction of the arrowhead on the orbital plane, and goes around the orbital plane in about 109 minutes at an orbital altitude of 1200 meters. Due to the rotation of the earth, the orbital plane moves in the direction of arrow 112 at a speed of one revolution per day.
[0020]
When the satellite moves in the orbital plane direction, the elevation angle of the service satellite 107 as viewed from the terminal 101 gradually decreases, and communication with the satellite 107 becomes difficult, but communication with the satellite 108 becomes easy. For this reason, when a communication system is constructed with a non-geostationary orbit satellite, service satellite switching, also known as connection handover, occurs.
[0021]
In the first embodiment of the present invention, when the terminal 101 hands over the service satellite from the satellite 107 to the satellite 108, the transfer direction for the address of the terminal 101 is changed to the adjacent satellite 109, 110, 111, 107 of the new service satellite 108. Then, the service satellite 108 notifies. The satellite that has received this notification switches the transfer direction for the address of the terminal 101 to the route that has received the notification. The transfer rules for the addresses of other terminals are handed over to the following satellites on the same orbital plane or adjacent satellites on the orbital plane in the rotation direction at a constant cycle. The delivery cycle on the same track surface is a cycle determined by the following equation (1).
Delivery cycle within the same orbital plane = orbiting time of satellites / number of satellites per orbital plane (1)
In addition, the delivery process between the raceway surfaces has a cycle determined by the following equation 2.
Delivery cycle between raceways = 24 hours / number of raceways ... (Equation 2)
The transfer rule change from the new service satellite 108 may be notified to at least the satellites 109, 110, 111, and 107 that are adjacent to the new service satellite for the following reason. In all satellites, packets to the handed over terminal are transferred to the service satellite 107 before the handover, via the satellite other than the new service satellite 108 and its adjacent satellites 109, 110, 111, 107. Even when a packet is transferred to the old service satellite 107, it is finally transferred to the old service satellite 107. Since the old service satellite knows that the satellite 108 is the new service satellite, the packet can be forwarded to the new service satellite 108.
[0022]
FIG. 2 shows a basic configuration of the communication processing unit of the satellite according to the present invention. The satellite is provided with a plurality of interfaces 201 and 202 for inter-satellite communication with adjacent satellites and an interface 203 for communication with the ground, each having a reception unit and a transmission unit, and the received data is processed by data processing. The processing is performed by the unit 204 and the control data processing 205. In the case of the communication data requested in Step 301, Step 307, Step 401, Step 501, and Step 601, among the algorithms shown in FIG. 3, FIG. 4, FIG. 5, FIG. In the section, the transfer rule 208, the backup information 209, and the temporary storage area 210 are updated according to the algorithm shown in FIG. 3, FIG. 4, FIG. 5, and FIG. The transfer rules 208, the backup information 209, and the temporary storage area 210 are also updated by the algorithm shown in FIG. 6 by the interruption of the timers 206 and 207 driven at the periods shown in the equations 1 and 2.
[0023]
If the received data is not the communication data requested in step 301, step 307, step 401, step 501, or step 601, the received route is determined based on the destination address information of the data packet and the transfer rule 208. The data packet is transferred to a different path or downlink through a transmission unit corresponding to each physical interface.
[0024]
Hereinafter, the operation algorithm of the new service satellite 108 at the time of handover will be described with reference to FIG. 3, and the operation algorithm of the adjacent satellites 109, 110, 111, and 107 that have received the handover notification will be described with reference to FIG.
[0025]
As a satellite, the operations in FIGS. 3, 4 and 6 are performed in parallel. When a handover request is received from a terminal, step 302 and subsequent steps in FIG. 3 are received. When a handover notification is received from an adjacent satellite, step 405 and subsequent steps in FIG. 4 are received. When switching information from a preceding satellite is received or a timer interruption occurs Performs step 604 and subsequent steps in FIG. As an operation as a service satellite for the terminal, the processes shown in FIGS. 5 and 12 are performed in parallel. When a service satellite switching notification is received from the terminal, step 503 and subsequent steps in FIG. 5 are performed. When a request for transfer route information is received from an adjacent satellite, step 1203 and subsequent steps in FIG. 12 are performed.
[0026]
As shown in FIG. 3, the new service satellite 108 first waits for detection of a handover request (step 301). At the time of detection (step 302), the new service satellite 108 uses the address of the handover target terminal at that time. The transfer route information is stored in the backup information as an address / route pair (step 303). Subsequently, the transfer route for the address is switched to the downlink (step 304). Next, a handover notification indicating that the service satellite to the address is the own satellite 108 is sent to the adjacent satellites 109, 110, 111, and 107 (step 305). Next, an inquiry is made to the preceding satellite on the same orbital plane for the transfer route for the address (step 306). The system waits for a response to this (step 307), and if there is a response within a certain time, it overwrites the backup route backup information for the address created in step 303 with the received information (step 308). .
[0027]
It should be noted that the preceding satellite that receives the inquiry in step 306 is the old service satellite 107 in most cases. If the old service satellite receives a transfer rule from the preceding satellite by the procedure described in FIG. 6 during the service period, the rule is stored in the temporary storage area or the backup information. Therefore, the procedure described in FIG. The information on the temporary storage area or the backup is returned.
[0028]
If there is no information in the backup or temporary storage area of the preceding satellite, or if the transfer route is downlink, no reply will be made.
[0029]
In satellites other than the service satellite and its adjacent satellites, packets can be transferred to the service satellite by periodically updating the transfer route information as the satellite moves. Therefore, backup information is not registered for such a destination. However, since the satellite itself is a service satellite or an adjacent satellite to another terminal, the operation described above and the operation as an adjacent satellite of the service satellite described later are not necessarily performed.
[0030]
On the other hand, as shown in FIG. 4, the satellites 109, 110, 111, and 107 that receive the handover notification first wait for reception of the handover notification (step 401), and when received (step 402), After storing the transfer route as backup information (step 403), the route that received the handover notification is set as the transfer direction for the address (step 404).
[0031]
In the present embodiment, detection of a handover notification or the like is described as a non-block type process. However, if these notifications and request events can be detected by a hardware detection unit or the like, No in step 402 In this case, a loop returning to step 401 is not necessary.
[0032]
Next, the operation algorithm of the satellite 107 that is no longer a service satellite due to handover will be described with reference to FIG. The terminal waits for reception of a service satellite switching notification from the terminal (step 501), and if received (step 502), the satellite 107 checks whether or not there is a handover notification to the terminal (step 506). Ignores the service satellite switching notification and follows the handover notification. Otherwise, the presence / absence of backup information for the address is checked (step 507), and if there is, the transfer route for the address is switched to the path stored in the backup information (step 503). If there is no backup information, an inquiry is made to an adjacent satellite (step 508). Finally, the data corresponding to the address is deleted from the backup information (step 504).
[0033]
In response to the inquiry in step 508, as shown in FIG. 16, in the adjacent satellite, when the inquiry is received (step 1602), the presence / absence of information on the transfer route to the destination is checked (step 1603). In that case, a reply is made to the inquiry source (step 1604). The inquiry occurs when a handover occurs to a satellite that can directly communicate with the adjacent orbital plane, so as to establish the transfer route information to the new service satellite by making an inquiry to the adjacent satellite as described above. Can do.
[0034]
Next, a transfer route information takeover processing algorithm executed regardless of handover will be described with reference to FIG.
[0035]
This process is performed so that the service satellite or a satellite other than its neighboring satellites makes the transfer route information for the terminal 101 performing the connection handover almost stationary with respect to the earth.
[0036]
In the following description, it is assumed that such transfer route information takeover processing is asynchronously started by an internal timer of each satellite or a ground position detection means such as GPS. In addition, the temporary storage area that appears in the following description is a transfer route included in the switching information received from the preceding satellite without transmitting the transfer route information of the own satellite to the subsequent satellite in such asynchronous processing. This is for temporarily storing transfer route information received from a preceding satellite when it cannot be overwritten with information.
[0037]
The transfer route information takeover process irrelevant to the connection handover starts with the switching information from the preceding satellite or the timer interruption shown in Equation 1 and Equation 2 (step 601). When a timer interrupt or switching information reception occurs (step 602), an event determination is made as to whether the switching information is received or the timer interrupt occurs (step 604). If the timer interrupt is received, it is determined whether there is backup information (step 604). 605) If there is no backup information, the transfer rule is transmitted to the following satellite (step 607). If there is backup information, the transfer route on the backup information is transmitted to the destination satellite on the backup information, and the route on the transfer rule is transmitted to the subsequent satellite for the other addresses (step 606). Subsequently, it is determined whether or not the switching information from the preceding satellite has been received (step 608). If it has not been received, the process returns to step 601 to wait for the reception of the switching information.
[0038]
On the other hand, if the determination result in step 604 is reception of switching information, the received data is saved in the temporary storage area (step 609). Subsequently, it is determined whether or not the switching information has been transmitted to the subsequent satellite (step 610), and if it has been transmitted, the process proceeds to step 611 and subsequent steps. If it has not been transmitted, the process returns to step 601 to wait for a timer interrupt.
[0039]
If the timer interrupt has advanced to step 603 and subsequent steps and the switching information has already been received from the preceding satellite in the determination of step 606, or if the switching information has been received from the preceding satellite, the processing proceeds to step 603 and subsequent steps. If the switching information has already been transmitted to the succeeding satellite, it is determined whether or not there is backup information (step 611). If there is backup information, for the address stored in the backup information, the transfer route on the backup information is replaced with the received information on the transfer route of the preceding satellite. For the transfer route to an address not included in the backup information, the received information on the transfer route of the preceding satellite is adopted as a transfer rule (step 612). On the other hand, if there is no backup information, the information on the transfer route received from the preceding satellite is adopted as the transfer rule (step 613).
[0040]
When taking over the entire satellite network in order, for example, when the switching information is received from the preceding satellite, the transfer route information of the own satellite is sent to the succeeding satellite as the switching information. It is possible to jump directly from step 601 to step 611 and subsequent steps.
[0041]
Finally, a response algorithm for the transfer route inquiry processing performed in step 306 will be described with reference to FIG.
[0042]
The transfer route information request waiting (step 1201) is always performed, and when this is received (step 1202), it is first checked whether there is transfer route information for the destination address in the temporary storage area (step 1202). 1203) If this exists, a transfer route information response for the address is created and returned based on the information in the temporary storage area, and the information about the address is deleted from the temporary storage area (step 1204). If the information of the address is not in the temporary storage area, the backup information is checked (step 1205). If there is, the transfer route information response is created from the transfer route for the address of the backup information and returned, The information about the address is deleted from the backup information (step 1206). If there is no information about the address in the backup information, a transfer route information response to the address is sent from the transfer route of the address in the transfer rule. Create and reply (step 1207).
[0043]
By performing the above processing, the transfer rule is updated as shown in FIG. When time elapses from the situation in which the service satellite for the terminal 701 is the satellite 702 and the service satellite hands over to the satellite 703, the algorithms shown in FIG. 3 and FIG. The transfer route is changed. The arrowheads of the route information determined by this algorithm are indicated by diamonds. The route information stored in the backup information by this algorithm is indicated by a dashed arrow. Subsequently, the transfer rule switching process is started over time, and the transfer rules of other satellites (706, 707, etc.) are replaced with the transfer rules of the preceding satellites by the algorithm of FIG.
[0044]
For example, the switching information passed from the satellite 704 to the satellite 706 is transferred on the backup route in step 606 of the algorithm of FIG. On the other hand, for switching from the satellite 705 to the satellite 704, even if the transfer rule is received from the preceding satellite 705 on the satellite 704, the route is determined by the algorithm of FIG. Only the backup information is updated. Further, when switching between the satellite 706 and the satellite 707, all of the determination units in step 603, step 605, and step 611 are No, so that the transfer rule of the satellite 706 that is the preceding satellite is taken over to the satellite 707 as it is.
[0045]
In FIG. 7, the orbital plane of the satellite is indicated by thick dotted lines 709 and 708.
[0046]
By following such an algorithm, the transfer rule before the handover can be stored after the handover in the sense that the satellites having the same relative position to the service satellite have the same transfer rule. FIG. 7 shows that the transfer rule held by the service satellite 702 and its vicinity 710 and the transfer rule stored in the service satellite 703 and its vicinity 711 after the handover are stored.
[0047]
It should be noted that, according to the identifier of the timer that is started in the cycle shown in Equations 1 and 2, in the case of the timer corresponding to Equation 1, the preceding satellite is the satellite of the same orbital plane, and in the case of corresponding to Equation 2, the east side A satellite on the adjacent orbital plane.
[0048]
Next, a second embodiment of the present invention will be described. In the first embodiment, it is assumed that a notification is made to the original service satellite at the time of handover, and the algorithm shown in FIG. 5 is used as a process for this notification. This corresponds to the case where no notice is sent. When the service satellite is handed over to a satellite capable of direct communication on the adjacent orbital plane and when it is handed over to a succeeding satellite on the same orbital plane, it becomes the adjacent satellite of the new service satellite, and therefore receives the notification of step 305 in FIG. Therefore, an error that the transfer route is a downlink does not occur, but such a situation occurs when handing over to a satellite obliquely behind the adjacent orbital plane. In this case, the service satellite before the handover is not notified to the service satellite, and the service satellite before the handover is not a satellite that can directly communicate with the new service satellite. It will be said that. In this case, since there is no corresponding terminal beyond the downlink, an error is detected in data transfer to the downlink. In the present invention, when such an error is found, the packet is transferred to a succeeding satellite on the same orbital plane. This is the case when the service satellite is switched to a satellite obliquely behind the adjacent orbital plane. Thus, by transferring the packet to the succeeding satellite on the same orbital plane, the new adjacent satellite The packet can be transferred to the satellite, and as a result, the packet can be transferred to the target terminal.
[0049]
Next, such a handover direction and transfer rule switching pattern will be described with reference to FIG.
[0050]
First, assume that the service satellite of the terminal 1710 is the satellite 1705. FIG. 17 shows a satellite that may cause a handover due to movement of the terminal 1710 or movement of the satellite.
[0051]
It is desirable to avoid the occurrence of packet loss due to the handover notification or transfer rule switching algorithm. Examples of packet loss due to transfer rule switching or handover notification algorithm include the following cases. In the first case, a certain satellite X does not know that a handover has been performed to the new service satellite, and transfers the packet to the old service satellite, and the old service satellite forwards the packet to the new service satellite. This is a case in which a transfer to the satellite X occurs again. In such a case, the packet is repeatedly transferred to the satellite between the old service satellite and satellite X, and is lost due to a limit on the maximum number of transfers.
[0052]
The second case is a case where a transfer rule indicating that a satellite that has not been notified of a handover should become a service satellite by switching the transfer rule is received. Packets destined for the terminal via the satellite are transferred to the downlink, but are lost because the terminal uses another satellite as a service satellite.
[0053]
Table 1 below shows the presence or absence of such a possibility as parameters of the handover notification range and the transfer rule switching method.
[0054]
[Table 1]

Table 1 relates to the first embodiment. In the first embodiment, with regard to handover, a new service satellite notifies the adjacent satellite of the handover, and the terminal notifies the service satellite of the old service satellite. In transfer route switching, information related to individual handover is not exchanged. When such a method is adopted, a case where there is a possibility of loss as described above depending on the handover direction and the switching direction of the transfer rule is indicated by x, and a case where such a case does not occur is indicated by ◯.
[0055]
FIG. 18 shows a change in the transfer route when the switching to the satellite 1702 occurs when the handover to the satellite 1701 occurs and the packet loss does not occur. FIG. 19 shows a change in transfer route when a packet loss occurs and a handover to the satellite 1709 occurs and a switch to the satellite 1702 occurs.
[0056]
Basically, when the original service satellite after switching and the new service satellite are handed over to a position where there are two or more links, this corresponds to the second case described above, and there is a possibility of packet loss. Note that the combinations of handover and transfer rule switching as shown in Table 1 do not occur with the same probability. When the movement of the terminal is slow relative to the movement of the satellite and the earth, the occurrence probability of the handover to the preceding satellite is considered to be lower than the occurrence probability of the handover to the succeeding satellite.
In addition, the time for continuing communication while handed over to such a satellite is inevitably reduced as compared with the case of handing over to a subsequent satellite. As described above, there are two or more links after switching when switching occurs in a state where handover to the preceding satellite occurs.
[0057]
Similar results are obtained in the second embodiment of the present invention. For example, when notifying not only the new service satellite but also the old service satellite, the handover notification is as shown in Table 2 because the original new service satellite is an adjacent satellite of the old service satellite. Can be reduced.
[0058]
Note that the notification by the old service satellite indicates which satellite the new service satellite is.
[0059]
This information can usually be set based on the fact that the old service satellite and the new service satellite are adjacent to each other, or notification from the terminal.
[0060]
[Table 2]

FIG. 20 shows a case where the old service satellite is also notified when a loss occurs when only the new service satellite shown in FIG. 19 is notified. As can be seen from the figure, the satellite 1702, which should originally be a service satellite after switching the transfer rule, has already received a handover notification from the old service satellite at the time of handover. It is possible to know that it is only necessary to transfer to the old service satellite.
[0061]
In addition, the old service satellite does not send the handover notification to the adjacent satellite, but when the transfer rule is switched, not only the original transfer rule but also the transfer rule of the handover terminal on the buffer is transferred to the succeeding satellite. An effect can be obtained.
[0062]
Next, a third embodiment of the present invention will be described with reference to FIG.
In the third embodiment of the present invention, when the terminal 801 hands over the service satellite from the satellite 802 to the satellite 803, in the first embodiment, the handover notification is issued only to the adjacent satellite with which the new service satellite can directly communicate. On the other hand, a path 805 for one round of the earth centered on the satellite 802 including the original service satellite 802 and one round of the earth centered on the satellite 803 including the new service satellite 803 are perpendicular to the direction in which the handover occurred. It is characterized in that a handover notification is sent to all the satellites on the link set 804.
[0063]
Before describing the details of the present embodiment, problems when the present embodiment is not used, that is, problems with the first or second embodiment will be described with reference to FIG. A service satellite before handover to the terminal 901 is a satellite 902, and a service satellite after handover is a satellite 903. In the case of the first and second embodiments, handover detection is performed in the same manner as described with reference to FIG. 7, and handover and the transfer rules of adjacent satellites corresponding thereto are corrected. For the procedure during this period, refer to the explanation of FIG. 7 by replacing 701 to 709 in FIG. 7 with 901 to 909 in FIG. In the state immediately after the handover, a packet passing through the satellite 911 is like a path 912, and passes an extra link by two links compared to an ideal route.
[0064]
Such extra links are thought to slightly increase transmission delay time, network load, loss rate, and the like.
[0065]
The third embodiment has been made in view of the problems of the first and second embodiments.
[0066]
The procedure for changing the transfer rule on the new service satellite 803 corresponding to the handover is exactly the same as in FIG. However, the notification to the adjacent satellite in step 305 is performed only for the preceding satellite 802 of the link where the handover has occurred and the adjacent satellites 806 and 807 on the link perpendicular to the link.
In addition, for the notification to the link perpendicular to the link where the handover has occurred, not only the address of the target terminal but also the number of times the notification is transferred is provided.
The number of transfers is a value determined by Equation 3 if the notification direction is a direction straddling between the track surfaces and the number of track surfaces is an odd number.
Number of transfers = (number of track surfaces−1) / 2 (Equation 3)
Further, when the number of raceway surfaces is an even number, it is determined by Equations 4 and 5.
Number of transfers = floor ((number of track surfaces-1) / 2) (Equation 4)
= Floor ((number of raceway surfaces-1) / 2) +1 (Equation 5)
Equations 4 and 5 are used as the number of transfers in different directions, respectively, and the numbers determined by Equation 4 or Equation 5 are not output in both transfer directions.
[0067]
The floor (real argument) indicates a function that returns the maximum integer that does not exceed the real argument.
[0068]
On the other hand, if the notification direction is the orbital plane direction and the number of satellites per orbital plane is odd, the value obtained by replacing the number of orbital planes in Equation 3 with the number of satellites per orbital plane is A value obtained by replacing the number of orbital surfaces in Equations 4 and 5 with the number of satellites per orbital surface is used.
[0069]
When a handover is performed on a satellite obliquely behind an adjacent orbital plane, it is assumed that a handover in a direction perpendicular to the orbital plane and a handover in a horizontal direction occur simultaneously.
[0070]
Next, the operation algorithm of the preceding satellite 802 of the link where the handover has occurred will be described with reference to FIG.
[0071]
The preceding satellite 802 of the link where the handover has occurred waits for the notification of the handover (step 1001), and when received (step 1002), changes the transfer rule with the route that received the handover notification as the transfer route of the address. Then (step 1003), a handover notification with the number of transfers is transmitted in a direction orthogonal to the path that received the handover notification (step 1004).
[0072]
Next, with reference to FIG. 11, an operation algorithm at the time of receiving a handover notification with the number of transfers in a satellite other than the new service satellite 803 and the preceding satellite 802 in the handover direction on the link set 804 or the link set 805 will be described. .
[0073]
A satellite that meets the above-described conditions waits for reception of a handover notification with the number of transfers (steps 1101 to 1102). When the notification is received and the advance route storage necessity flag is TRUE, the transfer route for the address in the transfer rule at the time of reception is recorded in the backup information (step 1103). Subsequently, the transfer route to the destination is changed in the direction in which the notification is received (step 1104). If the received transfer count is 1 or more (step 1105), the notification is transferred to a path opposite to the path that received the notification. However, here, the number of transfers is reduced by 1 (step 1106).
[0074]
Note that the processing when a timer interrupt is received regardless of the handover notification is the same operation as in the first embodiment or the second embodiment.
[0075]
The transfer process of the transfer rule based on the algorithm as described above will be described again with reference to FIG.
[0076]
When the satellite 803 becomes a new service satellite by the handover, the inter-satellite link sets 804 and 805 orthogonal to the handover direction can be specified from the relationship with the service satellite up to immediately before. Therefore, the new service satellite 803 creates a handover notification in the orthogonal direction and a handover notification in the handover direction, and transmits them to the adjacent satellite. Since the satellite 802, which is the preceding satellite in the handover direction, receives the handover notification without the number of transfers, the handover notification with the number of transfers is sent on the link set 805 while correcting the transfer direction for the address according to the algorithm of FIG. To do. On the other hand, the adjacent satellite 806 and the adjacent satellite 807 that are perpendicular to the handover direction with respect to the new service satellite, and the adjacent satellite 808 and the adjacent satellite 809 in the same direction of the old service satellite 802 are notified of handover with the number of transfers , And the transfer route for the destination address is corrected and the handover notification is retransmitted according to the algorithm shown in FIG.
[0077]
Thereafter, when the transfer rule switching process by the timer interrupt occurs, the transfer rule on the preceding satellite is changed from the satellite 810 to the succeeding satellite as in the satellite 809. Therefore, as shown after the transfer rule switching in FIG. As shown in a region 814, the arrangement of the transfer rule relative to the service satellite is the same as before the handover.
[0078]
The embodiment of the present invention based on a 2π constellation earth non-geostationary orbit satellite network system will be described with reference to FIG.
[0079]
In the 2π constellation, as shown in FIG. 13, satellite groups having traveling directions almost orthogonal to each other are located above the same region. The satellite 1302 in the orbit that the terminal 1301 starts and moves from northwest to southeast is used as the service satellite. However, a case is considered in which handover is performed to the satellite 1303 in the orbit that proceeds from southwest to northeast by the movement of the satellite or the movement of the terminal.
[0080]
Since the satellite orbits the orbit as shown in FIG. 14, the orbit 1402 traveling from southwest to northeast on the front side of the earth 1401 in FIG. 14 is the orbit from northwest to southeast on the back side of the earth. The satellites on the orbital plane 1403 deviated by half a day in the rotation direction of the earth are on the orbit perpendicular to the orbital plane 1402 on the equator. Compared to satellites with the same plane or the same orbital plane, it is very fast and communication is often impossible. Therefore, when a connection handover occurs between satellites with different traveling directions as described above, for example, a transfer procedure is required in which the transfer is once transferred to the back side of the earth and then transferred between adjacent orbital planes. In spite of being geographically close like the route 1405, the distance of the transmission route becomes very long, and the delay time and its jitter become large, so that there is a problem that the communication quality deteriorates.
[0081]
In addition, when the transfer rule is adjusted by the OSPF algorithm or the like in such a situation, it is necessary to reconfigure the transfer rule on a global network scale. I can't.
[0082]
In this situation, FIGS. 13 and 15 are used for the fourth embodiment of the present invention that minimizes the communication amount and calculation processing for updating the transfer rule and reduces the time required for changing the transfer rule. I will explain.
[0083]
In the fourth embodiment, as shown in FIG. 15, in addition to a 2π constellation earth non-geostationary orbit satellite 1501, a plurality of orbital planes (hereinafter referred to as seams) having different traveling directions arranged on the ground are relayed. Relay node 1502 to be used.
[0084]
In addition, each satellite has two types, a transfer rule that is used when traveling northeast and a satellite that is used when traveling southeast.
The original service satellite 1302 and the new service satellite 1303 receive a handover notification and a handover request from the terminals, respectively. The handover notification includes at least the address of the terminal and the identifier of the new service satellite 1303, and the handover request includes at least the address of the terminal and the identifier of the original service satellite 1302. With such a handover notification and a handover request, it is possible to determine whether a handover has occurred within the same track surface or between adjacent track surfaces, or a handover has occurred between seams. When it is considered that a handover has occurred between different seams, the original service satellite 1302 determines the nearest inter-seam relay station 1304 from its own position, and uses the identifier of the satellite on the same seam that has a connection therewith as the nearest seam. The inter-relay station 1304 is inquired. The inquiry includes at least the address of the terminal 1301 that has performed the handover, the identifier of the original service satellite 1302, and the identifier 1303 of the new service satellite. The inter-seam relay station 1304 holds a transfer rule regarding the address of the terminal 1301. If not, the identifier of the satellite 1305 capable of direct communication with the same seam is returned using the identifier of the original service satellite included in the inquiry.
[0085]
Also, the transfer rule for the destination is stored. Further, a handover request similar to that of the terminal is issued to the satellite 1305 capable of direct communication so as to behave as a service satellite. The old service satellite uses the satellite 1305 having the connection with the inter-seam relay station 1304 thus found as a new service satellite, and transfers it as the original service satellite based on the first, second, or third embodiment. Implement rule update processing.
[0086]
When the inter-seam relay station 1304 receives a packet addressed to the address, the inter-seam relay station 1304 transfers the packet to a satellite 1306 that can directly communicate with another seam. The satellite 1306 that received the transferred packet transfers the packet to the new service satellite 1303 based on the transfer rule on the seam to which it belongs.
[0087]
If the transfer rule for the terminal address being inquired is already held, the address of the new service satellite included in the inquiry is returned, and the data for the terminal address is deleted from the transfer rule on the relay station 1304. To do. In addition, a satellite that can directly communicate with the relay station 1304 performs a notification similar to the handover notification that the terminal makes to the original service satellite to a satellite on the same seam as the new service satellite.
[0088]
Therefore, conversely, when communication is first performed between different seams via the inter-seam relay station 1304, the original service satellite 1303 and the new service satellite 1302 receive a handover notification and a handover request from the terminal. It is possible to determine whether a handover has occurred on the adjacent orbital plane or whether a handover has occurred between the seams based on the mutual information. If it is considered that a handover has occurred between different seams, the nearest inter-seam relay station 1304 is inquired as to whether or not it has a transfer rule for the address. If you have a transfer rule for the address, you can see that the inter-seam relay station has already been used for communication between seams. As a result of handover from the satellite 1305 to the new service satellite 1302, the transfer rule update processing based on the first, second, or third embodiment described above is performed.
[0089]
It should be noted that the inter-seam relay station must be able to communicate with at least one satellite for each seam. Therefore, in addition to the two antennas for each seam, there is a structural feature such that a spare antenna for diversity is installed at a physically separated position.
[0090]
When a handover to a different seam occurs, the satellite 1305 that can communicate directly with the inter-seam relay station with the same seam as the original service satellite 1302 is not necessarily an adjacent satellite or an adjacent satellite of an adjacent satellite. When using the first or second embodiment of the present invention to perform transfer rule update processing associated with handover, there is a possibility that the transfer route from the original service satellite to the inter-seam relay station cannot be determined. is there. That is, in such a case, an inquiry is made in step 508 of FIG. 5, but there is a possibility that no response is returned by the algorithm of FIG. Therefore, when the first or second embodiment is applied to this embodiment, if there is no information about the target address as in the algorithm of FIG. 16, the inquiry is further made to the adjacent satellite instead of ignoring the inquiry. What should I do?
[0091]
However, it is necessary to give information such as an identification number and the number of times of transfer to the inquiry to avoid duplicate answers to the same inquiry and infinite transfer of the inquiry. Also, regarding the response, it is necessary to perform a process of transferring back to the inquiry source.
[0092]
In order to realize such a method, the original service satellite that makes an inquiry sets the destination address, the identification number, and the maximum number of transfers in the inquiry and transmits the inquiry to the adjacent satellite. At the time of transmission, a pair of inquiry identification number and destination address is recorded. In the adjacent satellite, a set of the route that received the inquiry, the identification number of the inquiry, and the destination address is recorded, and if there is route information to the address, a reply is made and the registered content is deleted. If not, forward the query to a route other than the one that received the query. However, in this case, the maximum transfer count is changed to one smaller value.
[0093]
An inquiry identification number is set in the reply. When an inquiry is received, it is confirmed whether or not an inquiry for the same identification number has been received from the above-mentioned set of records. If an inquiry has already been received, the inquiry is ignored.
[0094]
When a response is received, the recorded set is checked, the record of the identification number is deleted, and the transfer route for the address is changed to the route that received the response. It also forwards the response to the requested route.
[0095]
When a response to the inquiry arrives, the inquiry source changes the transfer route of the address to the route that received the response, and deletes the record of the pair related to the identification number.
[0096]
【The invention's effect】
According to claim 1 of the present invention, it is possible to facilitate maintenance and management of routing information in a network in which a relay node moves.
[0097]
According to the second aspect of the present invention, it is possible to easily control the maintenance and management of the routing information.
[0098]
According to claim 3 and claim 8 of the present invention or claim 4, claim 6 and claim 7, after becoming the adjacent relay node of the service station to the destination station, the adjacent relay node of the service station The routing information that was previously used by the relay node at that position can be restored even after it disappears.
[0099]
According to claim 5 of the present invention, the change of the service station for the destination address can be reflected on the network at the optimum timing, and the message transfer to the destination address can be continued.
[0100]
According to the ninth aspect of the present invention, when the service station for the destination address changes, the message transfer route to the destination can be optimally maintained in terms of the number of hops.
[0101]
According to claim 10 of the present invention, when the moving relay node is divided into a plurality of groups and direct communication is not possible between them, the destination station moves from the first group to the second group. Even in this case, the message can be transferred.
[0102]
According to the eleventh aspect of the present invention, since the message from the first group is transferred to the destination station by the service station belonging to the second group, the destination station sends the relay node of the first group to the service station. The message can be transferred to the destination station even when it is changed to.
[0103]
According to the twelfth and thirteenth aspects of the present invention, the above-described network can be constituted by a non-geostationary orbit satellite.
[0104]
According to the fourteenth and fifteenth aspects of the present invention, it is possible to appropriately determine the transfer timing of the routing information in the network having the above-described characteristics constituted by the non-geostationary orbiting satellite.
[0105]
According to the fifteenth aspect of the present invention, in the network having the feature of the ninth aspect constituted by a non-geostationary orbiting satellite, the number of transfer times of the service station change notification can be optimally determined.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram for explaining a concept of a first embodiment.
FIG. 2 is a basic configuration diagram of a communication processing unit of a satellite according to the present invention.
FIG. 3 is an explanatory diagram for explaining an operation algorithm of a new service satellite at the time of handover.
FIG. 4 is an explanatory diagram for explaining an operation algorithm of an adjacent satellite that has received a handover notification;
FIG. 5 is an explanatory diagram for explaining an operation algorithm of a satellite that is no longer a service satellite by handover.
FIG. 6 is an explanatory diagram for explaining a transfer route information takeover processing algorithm performed irrespective of handover.
FIG. 7 is an explanatory diagram for explaining an outline of update of a transfer rule.
FIG. 8 is an explanatory diagram for explaining the concept of the third embodiment;
FIG. 9 is an explanatory diagram for explaining a problem of the first or second embodiment.
FIG. 10 is an explanatory diagram for explaining an operation algorithm of a preceding satellite of a link where a handover has occurred.
FIG. 11 is a diagram illustrating an operation algorithm when receiving a handover notification with the number of transfers in a satellite that is positioned on a link perpendicular to a new service satellite and a preceding satellite in the handover direction; It is explanatory drawing of.
FIG. 12 is an explanatory diagram for explaining a response algorithm with respect to a transfer route inquiry process;
FIG. 13 is an explanatory diagram for explaining a concept of a fourth embodiment of the present invention.
FIG. 14 is an explanatory diagram for explaining the features of a 2π constellation non-geostationary orbit satellite network system.
FIG. 15 is an explanatory diagram of a configuration of a fourth embodiment.
FIG. 16 is an explanatory diagram for explaining an algorithm for responding to an inquiry when a transfer route is unknown;
FIG. 17 is an explanatory diagram of a combination of a satellite in which handover may occur and a satellite in which transfer rule switching may occur.
FIG. 18 is an explanatory diagram of transfer rule switching after handover (when packet loss does not occur).
FIG. 19 is an explanatory diagram of transfer rule switching after handover (when packet loss occurs).
FIG. 20 is an explanatory diagram of transfer rule switching after handover (when the old service satellite is also notified, and the notification of the new service satellite is lower in priority than the notification of the new service satellite).
[Explanation of symbols]
101 terminal
102-106 Satellite travel direction (orbital plane)
107, 108, 109, 110, 111 satellites

Claims (14)

Routing information comprising a set of identifiers of destination stations and a route to which messages of the identifiers should be transferred is retained for a plurality of identifiers, and a plurality of messages including the identifiers of destination stations are relayed based on the routing information. A network composed of moving relay nodes, wherein the routing information is transmitted to adjacent relay nodes in a direction before the relay node moves in a certain cycle as the relay node moves sequentially in a certain direction on the track surface. If the adjacent node capable of direct communication is a service node for the destination station, the data related to the destination station in the routing information transmitted to the relay node is stored internally, and the destination The transfer to the station is relayed to the service node for the destination station. Service node to the destination station when no longer can communicate directly neighboring nodes, relay apparatus characterized by relaying on the basis of the internal to the stored data. Routing information comprising a set of identifiers of destination stations and a route to which messages of the identifiers should be transferred is retained for a plurality of identifiers, and a plurality of messages including the identifiers of destination stations are relayed based on the routing information. A network composed of moving relay nodes, wherein the routing information is transmitted to adjacent relay nodes in a direction before the relay node moves in a certain cycle as the relay node moves sequentially in a certain direction on the track surface. If the adjacent node capable of direct communication is a service node for the destination station, the data related to the destination station in the routing information transmitted to the relay node is stored internally, and the destination The transfer to the station is relayed to the service node for the destination station. Service node to the destination station when a predetermined time has elapsed from when the communicable adjacent nodes directly, the relay apparatus characterized by relaying on the basis of the internal to the stored data. Routing information comprising a set of identifiers of destination stations and a route to which messages of the identifiers should be transferred is retained for a plurality of identifiers, and a plurality of messages including the identifiers of destination stations are relayed based on the routing information. A network composed of moving relay nodes, which relays the routing information to adjacent relay nodes in the direction before the relay nodes move in accordance with the movement of the relay nodes that sequentially move in a fixed direction on the track surface. When a service node that can directly communicate with a destination station is changed in a network composed of devices , a new service node sends a message to the destination station to an adjacent relay node that can directly communicate with the service node. Requesting that the transfer route be the service node. Network. 4. The relay apparatus constituting the network according to claim 3, wherein when the transfer route change request is received from a new service node, the transfer route to the destination station is changed to the route that has received the request. In addition, the relay apparatus is characterized in that it internally stores information on the destination station and transfer route used immediately before receiving the request. 5. The relay apparatus according to claim 4 , wherein when the information on the destination station and the transfer route stored therein is stored, the routing information is transmitted to the adjacent relay node in the direction before the relay node is moved. In this case, the relay apparatus transmits the information stored internally with respect to the destination address. Routing information comprising a set of identifiers of destination stations and a route to which messages of the identifiers should be transferred is retained for a plurality of identifiers, and a plurality of messages including the identifiers of destination stations are relayed based on the routing information. A network composed of moving relay nodes, which relays the routing information to adjacent relay nodes in the direction before the relay nodes move in accordance with the movement of the relay nodes that sequentially move in a fixed direction on the track surface. When a service node that can directly communicate with a destination station changes in a network composed of devices , the original service node becomes an adjacent relay node that can directly communicate with the service node, and the service node is a service node. A network characterized by notification that it has been lost. Routing information comprising a set of identifiers of destination stations and a route to which messages of the identifiers should be transferred is retained for a plurality of identifiers, and a plurality of messages including the identifiers of destination stations are relayed based on the routing information. A network composed of moving relay nodes, which relays the routing information to adjacent relay nodes in the direction before the relay nodes move in accordance with the movement of the relay nodes that sequentially move in a fixed direction on the track surface. When a service node that can directly communicate with a destination station is changed in a network composed of devices , a new service station is connected to a relay node in a direction orthogonal to the direction of the original service node. Notification of the change, and the relay node that has received the notification A notification is further transferred to an adjacent relay node in a direction opposite to the relay node in the direction in which the notification is received, and the relay node that has received the notification corresponds to the destination address used before receiving the notification. The forwarding route information is stored internally, and the forwarding route to the address is changed to the route that received the notification. Furthermore, the original service node has a new service node The relay node in the direction orthogonal to the direction is notified of the change of the service node, and the relay node that has received this notification is parallel to the direction in which the notification is received and adjacent in the direction opposite to the relay node in the received direction. The relay node further forwards the notification to the relay node, and the relay node that has received the notification deletes the information on the forwarding route to the destination station that is stored internally, and Networks and changes the transfer route of the dress, the route that has received the notification. The network according to any one of claims 3, 6 and 7 , wherein the moving relay nodes can be divided into two or more groups and direct communication between the groups is not possible. When multiple relay nodes that can communicate and do not move are arranged, have different routing information for the same station in both groups, and the destination station changes from the first group to the second group The original service node in the first group requests the non-moving relay node in the shortest distance to transfer the message to the destination station to the second group, and the non-moving relay in the first group A network characterized by updating routing information with a node as a new service node. 9. The non-moving relay apparatus on the network according to claim 8, wherein when a message from the first group to the second group is requested to be transferred to the destination station, the message is already transferred to the destination station. If not, the mobile node can communicate directly with the non-moving relay node, and notifies the moving relay node belonging to the second group that it is no longer a service node for the destination address. Relay device. A communication satellite in which the function of the relay device according to any one of claims 1, 2, 4, and 5 is implemented. The non-geostationary orbit satellite network according to any one of claims 3, 6, and 7 , wherein a moving relay node constituting the network is realized by an earth non-geostationary orbit satellite. 12. The network according to claim 11 , wherein a communication satellite having the function of the relay node according to claim 2 is used, wherein the orbital lap time is divided by the number of satellites per orbital plane in the routing table update period. A non-geostationary orbit satellite communication network characterized by using a period less than the value. 12. The network according to claim 11 , wherein a communication satellite having the function of the relay device according to claim 2 is used, wherein a period equal to or less than a value obtained by dividing 24 hours by the number of orbital planes is set as an update period of the routing table. A non-geostationary orbit satellite communication network characterized by using. The network according to claim 7 or 8 , wherein the communication satellite according to claim 10 is used as a relay device. A non-geostationary orbit satellite communication network characterized in that the number of times of transfer is set to the maximum number of satellites per orbit minus 1 when the transfer direction is in the orbital plane.

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