JP2002314601A - Method for notifying receiving state, node device and receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a receiving state notifying method, etc., capable of contributing to the relaxation of transmission line congestion due to a retransmission request and also surely supplying information showing the receiving state of a receiver being in a worst receiving state to a transmitter. SOLUTION: A NAK (negative acknowledge character) detecting part 23 detects a NAK supplied to a buffer 22. A deciding part 24 decides whether or not to be the first NAK for a multicast packet having a sequence number in response to the sequence number in the extracted NAK, makes a NAK transmitting part 26 generate a NAK obtained by replacing the receiving state in the NAK with the worst receiver information held by a NAK holding part 25 for the first NAK, and discards the NAK if the NAK is not the first NAK.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reception status reporting method in a communication system that performs multicast, a node device that relays multicast, and a reception device that receives multicast packets.

[0002]

2. Description of the Related Art ICMP (Internet Control Message P)
rotocol), IGMP (Interior Gateway Routing Prot)
In a network (IP network) using a broadly-defined IP (Internet Protocol) protocol including, for example, an ocol), multicast for distributing data such as a moving image to a plurality of receiving apparatuses can be performed. The procedure for this is described in the IETF (Internet Engineering Task Forc
e) RFC (Request For Comments) 1112 and the like.

In such multicast communication, a receiving device is connected to a transmitting device that performs multicasting via a multicast router, and when a receiving request from the receiving device is supplied to the transmitting device via the multicast router, A transmission path of the multicast packet is formed between the transmission device, the multicast router, and the reception device.
In multicast, UDP (User Datagram Prot
ocol) protocol, so the transmission path is T
This is a concept different from the connection of CP (Transmission Control Protocol).

[0004] When such a transmission path is formed, when a multicast packet is supplied from the transmitting device to the multicast router on the transmission path, the multicast router becomes a plurality of subordinates (downstream from the transmitting device). If there are transmission paths, the supplied multicast packet is copied and transmitted for each transmission path. As described above, when there are a plurality of transmission paths under the control, that is, when the transmission path branches, the multicast packet is copied and transmitted, so that the traffic on the transmission path is not increased more than necessary, and the congestion of the network is reduced. Can contribute to mitigation.

[0005] By the way, an IP network such as the Internet basically has a best effort.
Because of this type of network, the transmission conditions of the multicast packet on the transmission path to each receiving device may not be uniform. In such a case, if the transmission rate or the like is not properly controlled, a packet loss, an unacceptable delay, or the like may occur, and a problem such as a partial loss of an image may occur.

For this reason, there is known a multicast (reliable multicast) in which the reliability is improved so that the multicast packet is reliably delivered to all the destinations. In such a multicast, each receiving device receives an acknowledgment (AC
K) and a retransmission request (N
AK: Negative ACK). However, in the former case, when the number of receiving devices increases, the number of acknowledgments transmitted to the transmitting device increases, causing network congestion.
The latter is often used in terms of scalability.

[0007] In the reliable multicast by NAK,
In the transmitting device, a continuous number (Seq: sequence number) is assigned to each multicast packet to be transmitted. The receiving device monitors the sequence number Seq of the received multicast packet, and upon detecting a packet loss or the like according to the sequence number Seq, transmits a retransmission request message (NAK) to the transmitting device. This N
The AK may have information indicating a reception state such as a throughput to the receiving apparatus and a delay time.

[0008] When such a NAK is supplied, the transmitting apparatus adjusts a transmission rate and the like according to information indicating a reception state such as a throughput in the NAK and has a sequence number Seq indicated in the NAK. Send the multicast packet again.

At this time, if the transmission rate or the like is adjusted so that even the receiving device that has transmitted the NAK has the worst transmission condition, the multicast packet is reliably delivered to all the receiving devices. be able to.

[0010]

SUMMARY OF THE INVENTION However, NAK
Also, in the reliability multicast according to the above, when the number of receiving devices increases, the number of NAKs transmitted to the transmitting device increases, which may be a cause of network congestion.

[0011] For this reason, it is conceivable to reduce the NAK supplied to the transmitting device by integrating the NAKs to reduce network congestion. However, simply integrating the NAKs may reduce the receiving device in the worst reception state. Since the reception state may not be transmitted to the transmission device, it is not possible to appropriately control the transmission rate and the like.

The present invention has been made in view of the above-mentioned problems, and has as its object to provide a reception status reporting method, a node device, and a reception device that can improve the reliability of multicast.

[0013]

In order to solve the above-mentioned problem, a reception status reporting method according to the present invention has reception status information indicating a reception status of a multicast packet in each of a plurality of receiving devices. A method for transmitting a retransmission request for requesting retransmission of a multicast packet, and causing the transmitting device to control the transmission of the multicast packet in accordance with the reception status information in any of the retransmission requests. Extracting the reception state information during the retransmission request from the receiving apparatus, holding the reception state information from the reception apparatus having the worst reception state according to the extracted reception state information, and transmitting the received reception state information to the transmission apparatus. And supplying to the

Here, the reception status information indicating the reception status of the multicast packet includes, for example, information such as a sequence number indicating a multicast packet that could not be received by the receiving device, throughput to the receiving device, and information on the receiving device. Information or the like indicating the delay time can be used.

In this receiving state reporting method, the receiving state information during the retransmission request from each receiving apparatus is extracted, the receiving state information from the receiving apparatus having the worst receiving state is held, and the held receiving state information is transmitted. Supply to equipment.

Further, the node device according to the present invention has reception status information indicating a reception status of the multicast packet in each of the plurality of reception devices with respect to the multicast packet from the transmission device, and performs retransmission of the multicast packet. A node device for supplying a requested retransmission request to the transmitting device, the extracting device extracting reception state information in the retransmission request received from each of the plurality of receiving devices, and a receiving device according to the receiving state information extracted by the extracting device. It is characterized by comprising a holding unit for holding reception state information from a reception device having the worst reception state, and a transmission unit for supplying the reception state information held by the holding unit to the transmission device.

In this node device, the extracting means extracts the receiving state information during the retransmission request from each receiving apparatus, and the holding means holds the receiving state information from the receiving apparatus having the worst receiving state. The transmitting means supplies the receiving state information to the transmitting device.

Further, the receiving apparatus according to the present invention provides a transmitting apparatus for controlling transmission of a multicast packet in accordance with a receiving state of a multicast packet in a receiving apparatus of a transmission destination, from a retransmission request from a subordinate receiving apparatus to a receiving state. A receiving device connected via a node device that provides the transmitting device with the receiving status of the worst receiving status by extracting the receiving status information shown in FIG. A retransmission request transmitting means for transmitting a retransmission request having reception state information indicating a reception state of the multicast packet in the apparatus is provided.

In this receiving apparatus, when the retransmission request unit detects a packet loss of the multicast packet,
The receiving apparatus transmits a retransmission request having reception state information indicating the reception state of the multicast packet.

[0020]

FIG. 1 is a block diagram showing a configuration of a communication system according to a first embodiment of the present invention.

This communication system includes a transmitting device 10 for forming and transmitting a predetermined packet (multicast packet) from data such as a moving image and a sound, and a transmitting device 10.
Device 20 for relaying multicast data from
Receiving device 30a that receives the multicast data,
30b.

The transmitting device 10 is composed of an information processing device such as a personal computer or a work station, and is, for example, an HDD in which data such as moving images and sounds is stored.
11, a packet generation unit 12 that reads data stored in the HDD 11 and generates multicast data,
A communication interface (I / F) 13 for communicating with the node device 20 and a control unit 14 for controlling a transmission rate of a multicast packet generated by the packet generation unit 12 and the like are provided.

The control of the transmission rate and the like by the control unit 14 is as follows.
This is performed by interrupting the packet generation unit 12 at a predetermined interval to generate a packet of a predetermined length. As a result, the transmission rate of the multicast packet is controlled to be constant. Alternatively, for example, a window for several packets may be set, an acknowledgment (ACK) is transmitted to the transmitting device only from the receiving device having the worst reception state (worst receiving device), and the acknowledgment is transmitted before the ACK is returned. The number of possible packets may be limited within the window.
As a result, the number of multicast packets transmitted can be limited within a range that the worst receiving device can receive.

The node device 20 comprises, for example, a so-called multicast router, and the receiving devices 30a, 30
0b, and a buffer 22
And a NAK detecting unit 23 for detecting retransmission request messages (NAK: Negative Ack) from the receiving devices 30a and 30b
A determination unit 24 for determining whether or not to relay the NAK to the transmission device 10; a NAK holding unit 25 for holding information indicating reception information in the NAK from the reception device having the worst reception state of the multicast packet; A NAK addressed to the transmitting device 10 is generated and transmitted according to an instruction from the determination unit 24.
An AK transmitting unit 26, a buffer 27, a communication I / F 28 for communicating with the transmitting device 10, and an IGMP (Inte
and a routing control unit 29 for controlling transmission of multicast packets according to a protocol (rior Gateway Routing Protocol).

Although the node device 20 can be configured as dedicated hardware having such a function, a personal computer that realizes the NAK detecting unit 23, the determining unit 24, the NAK transmitting unit 26, and the like by software. , And a general-purpose information processing device such as a workstation.

The receiving device 30a is composed of an information processing device such as a personal computer and a workstation, and includes a communication I / F 31 for communicating with the node device 20,
The system includes a buffer 32, a Web browser 33 that executes processing such as displaying a moving image on a monitor 34 in response to a received multicast packet, and an analysis unit 35 that analyzes a reception state of the multicast packet. The receiving device 30b is configured similarly to the receiving device 30a.

In FIG. 1, for simplification of description, one node device 20, two receiving devices 30a,
Although a communication system including 30b has been shown, for example, as shown in FIG. 2, more terminal devices 30a to 30d and a plurality of hierarchically connected node devices 20a, 20b, 2
0c may be provided.

In the communication system configured as described above, before the transmitting device 10 starts the multicast, a multicast group including the receiving device 30 of the multicast destination is set. When the multicast group is set, a transmission path of the multicast packet is set from the transmitting device 10 to each of the receiving devices 30a and 30b, and N is transmitted from the node device 20 to each of the receiving devices 30a and 30b.
The address of the upper node (node device 20 in the case of FIG. 1) transmitting the AK is notified.

In response, each of the receiving devices 30a, 30b
Is an RTT (round-trip time) between the transmitting apparatus 10
Is measured. This measurement is performed until each of the receiving devices 30a and 30b transmits a predetermined packet to the transmitting device 10 and a packet transmitted from the transmitting device 10 is supplied to each of the receiving devices 30a and 30b in response to the packet. The time is measured by each of the receiving devices 30a and 30b. When the RTT is measured in this manner, each of the receiving devices 30a, 30b
Determines that the packet loss rate is 0 in the initial state, and determines the throughput between the transmitting apparatus 10 and the RTT from the loss rate. Thereafter, each of the receiving devices 30a and 30b transmits a status report packet having information indicating the received status such as the obtained throughput to the transmitting device 10. Note that this status report packet may be integrated in the same manner as NAK described later, and only the status report packet from the receiving device with the worst reception status may be supplied to the transmitting device 10.

This packet is transmitted to the node device 20, the communication I /
It is supplied to the control unit 14 via F13. Control unit 14
According to the supplied information indicating the throughput and the like in the status report packets from each of the receiving devices 30a and 30b, conditions such as the transmission rate of the multicast packet and the like are set so that the receiving device in the worst receiving condition can also receive it. Set.

When the setting of the conditions is completed, the control unit 14
In response, the transmission rate of the multicast packet generated by the packet generation unit 12 is controlled.

In response to this, the packet generation unit 12
Start reading the data held in DD11,
For each predetermined length, a multicast packet including information indicating a multicast destination group (multicast address), a continuous number (Seq: sequence number) for identifying individual packets in a series of multicast packets, and the like is generated and transmitted. The data is transmitted via the I / F 13.
The timing at which the packet generation unit 12 generates a multicast packet is controlled by the control unit 14 as described above, for example, according to information indicating a reception state (for example, throughput or the like) during NAK. This multicast packet includes, for example, the above-mentioned multicast address in a header,
It is composed of an IP packet having a sequence number and the like. In the payload portion of the IP packet, for example, a UDP packet having a predetermined UDP port number in a header portion is stored. In the payload portion of the UDP packet, for example, data such as moving image and audio divided into a predetermined length is stored. By the way, when TCP is used instead of UDP as a transport layer protocol, a sequence number (Seq) is added to the TCP header. However, in the case of UDP, a sequence number is not added to the UDP header. For example, a sequence number is added to the data of the payload portion.

The multicast packet transmitted from the transmitting device 10 is supplied to the communication I / F 28 via a transmission path. Upon receiving the multicast packet, the reception I / F 28 sequentially stores the received multicast packet in the reception buffer 27. The routing control unit 29 transmits the multicast packet stored in the buffer 27 to the multicast destination connected to the node device 20 (the receiving device 30a,
30b), and supplies them sequentially to the buffer 22. When a multicast packet is supplied to the buffer 22, the communication I / F 21 sequentially reads out the multicast packet,
The data is transmitted to the receiving devices 30a and 30b.

The communication I / F 31 of the receiving device 30a receives the multicast packets from the node device 20 and sequentially stores them in the buffer 32. The stored multicast packet is provided with a destination port number in, for example, a UDP header. The destination port number is, for example, I
When the receiving device 30 joins the multicast group according to the GMP protocol, the application software (the Web browser 33 in the case of FIG. 1) that receives the multicast packet is notified from the node device 20 or the like. When the multicast packet having the port number is stored in the buffer 32, the Web browser 33 acquires the packet from the buffer 32 and reproduces the data of the payload.

Further, the Web browser 33 displays, for example, a moving image on the monitor 34 according to the reproduced data. In a similar procedure, the multicast packet is also supplied to the receiving device 30b, and a moving image corresponding to the multicast packet is displayed on the monitor 34 of the receiving device 30b.

In this communication system, the analyzing unit 35 of each of the receiving devices 30a and 30b monitors the receiving state of the received multicast packet, and generates a retransmission request message (NAK) when there is a packet loss. To the upstream device. In the case shown in FIG. 1, each of the receiving devices 30a and 30b is a node device 2 that is an upstream device.
Since the address 0 is known, N is sent to the node device 20.
Send AK. However, there is a case where the address of the node device 20 is not known, for example, a receiving device that has joined the multicast group after the start of the multicast. Therefore, in such a case, the NAK is transmitted to the transmitting device 10.

As shown in FIG. 5, for example, the NAK contains information indicating the receiving state such as the IP address of the receiving apparatus, the sequence number (Seq) of the lost multicast packet, the throughput in the receiving apparatus, and the multicast. The number of NAK transmissions for the packet is included. Since the NAK is transmitted as data of the payload portion of the IP packet, if the node device 20 appropriately manages the IP address in the header of the IP packet, the IP address of the receiving device is included in the NAK. Is not necessary. Thus, IP
By using the IP address in the header, the size of the NAK can be reduced, which can further contribute to alleviation of congestion due to the NAK.

Instead of using the IP addresses of the receiving devices 30a and 30b, an identification number (id) may be assigned to each of the receiving devices, and the receiving device may be indicated by the identification information.

As described above, the multicast packet transmitted from the transmitting device 10 includes the sequence number (Se
q) is attached. The analysis unit 35 determines whether or not the sequence numbers (Seq) of the received multicast packets are consecutive, and if there are any missing packets,
NAK including the sequence number (Seq) of the packet
Is generated and transmitted to the transmission device 10 (or to the node device 20 when the address of the node device 20 up to the transmission device 10 is known).

As described above, the throughput can be obtained from, for example, the packet loss rate and the RTT. However, in addition to the throughput, other parameters such as a delay time and a loss rate can be used for the reception state in the receiving apparatus. However, only the throughput will be described below as an example.

As shown in FIG. 3, for example, as shown in FIG. 3, information indicating the reception state of the receiving apparatus (worst receiving apparatus) having the worst receiving state of the multicast packet supplied from the determining unit 24 (worst receiving apparatus) Information) is retained.

In the NAK holding unit 25, as shown in FIG. 4, for example, a table (NAK number) in which the number of NAK receptions (NAK number) for each multicast packet is associated with each multicast packet sequence number Seq. (Reception number table).

If the number of NAK transmissions in the NAK is larger than the number of NAKs in the NAK reception number table for the NAK for the same multicast packet, Of the transmitting device 10
(If there is a node device up to the transmitting device 10, transfer it to the node device.) If the number of NAK transmissions in the NAK is equal to or smaller than the number of NAKs in the NAK reception number table, the NAK is discarded. I do.

FIG. 6 is a flowchart showing such NAK integration processing. When the NAK is supplied to the buffer 22 and the NAK is supplied from the NAK detection unit 23 to the determination unit 24, the processing from step S1 in FIG. 6 is started.

First, in step S1, the judgment unit 24
Indicates that the address (Addr) in the supplied NAK is NA
A comparison is made with the address (Nomaddr) in the worst receiving device information held in the K holding unit 25. If it is not a NAK from the worst receiving device, the process proceeds directly to step S3. If it is a NAK from the worst receiving device, the process proceeds to step S2.
, The state in the supplied NAK (State) is changed to the state in the worst receiving device information of the NAK holding unit 25 (Nom
After the worst receiving device information is updated as (state), the process proceeds to step S3.

Next, in step S3, the received N
The state in AK (State) and the state in worst receiving device information (Nomstate) are compared. NAK received
If the middle state is worse (for example, the throughput is lower), the receiving state of the receiving apparatus that transmitted the NAK is worse than the receiving apparatus held as the current worst receiving apparatus information. The determination unit 24 proceeds to step S4, and sets the address (Addr) and state (State) in the received NAK as the address (Nomaddr) in the worst receiving device information, and proceeds to step S5. on the other hand,
If the state in the received NAK is not worse, the process directly proceeds to step S5.

Further, in step S5, the NAK
Is transmitted to a more upstream device (the transmitting device 10 in the case of FIG. 1, but if there is a node device further upstream as shown in FIG. 2).
Specifically, the number of NAKs in the received NAK (Count
t) is the NAK count (Na) in the NAK reception count table corresponding to the sequence number Seq in the NAK.
kCount [seqNum]).

The number of NAKs in the received NAK (Count
If t) is larger than the NAK count (NakCount [seqNum]) in the NAK reception count table, the process proceeds to step S6, where the information indicating the reception status in the NAK is replaced with the worst reception device information described above. To the transmission device 10 (if applicable, a further upstream node device), and ends the processing for one NAK. On the other hand, the number of NAKs (Count) in the received NAKs corresponds to the number of NAKs (NakCount [s
eqNum]), and terminates as it is if it is smaller or equal. As a result, the NAK is discarded without being transmitted to the transmitting device 10 (if applicable, a further upstream node device).

Hereinafter, the determination in step S5 will be described. The judging unit 24 determines in advance that the NAK detecting unit 23
The number of NAKs transmitted by the NAK transmitting unit 26 is counted for each sequence number (Seq) in the NAK supplied from. This count value (NakCount [se
qNum]) is 0, and is incremented by 1 each time the NAK transmitting section 26 transmits a NAK having the corresponding sequence number Seq.

If only the first NAK for the same multicast packet is simply detected, the determination may be made based on whether or not the number of NAKs (NakCount [seqNum]) is zero. However, even when the multicast packet is retransmitted in response to the NAK, packet loss or the like may occur again. For this reason, when the receiving device 30 cannot receive the corresponding multicast packet within a predetermined time after transmitting the NAK, the receiving device 30 transmits the NAK again. The NAK in such a case needs to be supplied to the transmitting device 10 even when the NAK has the same sequence number Seq.

The receiving apparatus 30 counts the number of times NAKs having the same sequence number Seq have been transmitted, and uses this number as the number of NAKs (Count).
It is added inside.

Therefore, the number of NAKs (Count) in the received NAK is larger than the number of NAKs (NakCount).
[SeqNum]), the NAK again
Therefore, the NAK is supplied to the transmitting apparatus 10 as described above. Conversely, the number of NAKs in received NAKs (Cou
nt) is the NAK count (NakCount [seq
Num]), the corresponding NAK has already been transmitted to the transmitting device 10, and the received NAK has already been transmitted.
Discard the AK.

In this communication system, as described above, even if the worst receiving device information is updated in step S2 or step S4 in order to alleviate the NAK congestion, the judgment result in step S5 is used. All but the first NAK are discarded.

However, the worst receiving device information updated as described above is used when the next NAK is transmitted.
Since the information indicating the reception state of the worst reception device is supplied to the transmission device 10 as the information indicating the middle state, the transmission device 10 can be reliably supplied with the information indicating the reception state of the worst reception device.

FIG. 7 is a sequence diagram showing transmission and reception of multicast packets and NAKs in this communication system.

In FIG. 7, 1 is assigned to the receiving device 30a (receiving device A) as the identification number (id), 2 is assigned to the receiving device 30b (receiving device B) as the identification number (id), and the sequence number ( x), an NAK having an identification number (y) and information (z) indicating throughput
(X, y, z).

When a multicast packet is supplied from the transmitting device at a predetermined interval, the node device 20 copies the multicast packet to each of the receiving devices 30a and 30a.
0b.

Each of the receiving devices 30a and 30b receives the sequence number (Se) in the received multicast packet.
q) is monitored, and if the sequence numbers (Seq) are not continuous, it is determined that the multicast packet between them is lost, and the address of the node device 20 to the transmission device 10 (the address of the node device 20 up to the transmission device 10 is known). If there is, the NAK is transmitted to the node device).

For example, if the sequence number Seq in FIG.
, Does not reach the receiving device 30a or the receiving device 30b.
30b each transmit a NAK. These NAKs
Although supplied to the node device 20, for example, the receiving device 30a
(2, 1, 64 kbps) from the first device reaches the node device 20, the NAK becomes the sequence number Seq.
The first NA for multicast packets with
Since it is K, it is transferred to the transmitting device 10 as it is,
NAK (2, 2, 48 kbps) from the receiving device 30b
Is the second or later N for the multicast packet
It is discarded as AK.

As a result, only NAK (2, 1, 64k) is supplied to the transmitting device 10 as information indicating the receiving state, the transmitting device 10 determines that the receiving device 10a is the worst receiving device, and A multicast packet is transmitted at a transmission rate according to the throughput 64k during NAK.

In this case, NAK (2, 2, 48 kbp
Although s) is discarded, information indicating the reception state in the NAK (for example, id of the worst receiving device = 2, throughput = 48 kbps) is held in the NAK holding unit 25 as the worst receiving device information.

Therefore, after this, another sequence number S
NAK for multicast packets with eq
(For example, a NAK for a multicast packet whose sequence number Seq is 4)
0b, the receiving devices 30a, 30b
Of the NAKs supplied from the receiving device 30 (in the case of FIG.
ps)) is the worst receiving device information held in the NAK holding unit 25 (that is, the receiving condition in the NAK supplied from the receiving device 30b for the multicast packet having the sequence number Seq of 2). NAK (4,2,48 kbps)
Is supplied to the transmission device 10 as The transmitting device 10 determines that the receiving device 10b is the worst receiving device according to the NAK, and transmits a multicast packet at a transmission rate according to the throughput 48k in the NAK.

FIG. 8 is a diagram conceptually showing transmission and reception of the NAK shown in FIG. As described above, in this communication system, even if NAK integration is performed, information indicating the reception state of the receiving device that is the worst receiving device can be reliably supplied to the transmitting device.

As described above, in this communication system, N
Since the AKs are integrated, the number of NAKs transmitted between the transmitting device 10 and the node device 20 can be reduced, which can contribute to alleviation of network congestion.

When the NAK does not include the reception information of the worst receiving device, in order to reduce the number of NAKs transmitted between the transmitting device 10 and the node device 20, for example, as shown in FIG. Thus, N is simply used for multicast packets having the same sequence number Seq.
It seems that it is sufficient to transfer the earliest AK to the transmitting device 10 and discard the second and subsequent NAKs.

However, if the received information of the worst receiving apparatus is included in the NAK, the NAK is simply used as the earliest NAK.
If only the NAK is supplied to the transmitting apparatus 10 and the second and subsequent NAKs are discarded, the receiving state of the worst receiving apparatus may not be supplied to the transmitting apparatus 10 as shown in FIG. 10, for example.

On the other hand, in this communication system, as described above, the updated worst
When transmitting K to the transmission device 10, the transmission device 10 transmits the information indicating the reception state of the transmission device 10 addressed to the transmission device 10.
Supplied to That is, in this communication system, as long as NAKs from the receiving device 30 occur at appropriate intervals, although there is a slight delay, the information indicating the receiving condition of the receiving device with the worst true receiving condition can be reliably obtained. It can be supplied to the transmission device 10.

Therefore, if the transmission of the multicast packet is controlled according to the reception state of the worst receiving apparatus, the transmission of the multicast packet can be controlled in accordance with the actual transmission conditions. As described above, in this communication system, NAK integration can be performed to contribute to alleviation of network congestion, and by controlling transmission of multicast packets in accordance with actual transmission conditions, the reliability of multicast can be improved. It can contribute to improvement.

Further, in this communication system, as described above, it is possible to contribute to alleviation of network congestion, and therefore, it is possible to improve affinity with other protocols on the network, for example, TCP and the like.

In the above description, the retransmission request (N
AK) is transmitted, but when the transmission state is good, NAK may not be transmitted for a long time. In this case, it takes time until the worst receiving device information held in the NAK holding unit 25 is supplied to the transmitting device 10.

For this reason, in consideration of such a case, a timer for measuring a predetermined time is provided in the receiving apparatus, and if NAK is not transmitted at all within the predetermined time, the receiving apparatus is provided with a timer. May be transmitted to the node device 20 having information indicating the reception status of the node device 20. As a result, at least once within a predetermined time period, the node device 2 can receive either the NAK or the status report packet.
0 is supplied with the reception status of each receiver.

When the status report packet is supplied as described above, the node device 20 executes the same processing as that of FIG. 6 described above, and the status having the reception status of the worst receiving device held in the NAK holding unit 25 is obtained. A report packet is generated and supplied to the transmitting device 10. Thereby, similarly to the NAK, the status report packet is also integrated and supplied to the transmitting device 10.

As a result, even if the NAK is not transmitted for a long time, the worst receiving device information is supplied to the transmitting device 10 once every predetermined time. Therefore, it is possible to control the transmission of the multicast packet in accordance with more actual transmission conditions, and it is possible to contribute to further improving the reliability of the multicast.

Further, a buffer for holding the multicast packet is provided in the node device 20, and when the multicast packet corresponding to the NAK supplied from the receiving device is held in the buffer, the node device 2
0 retransmits the multicast packet to the receiver, N
If the multicast packet corresponding to the AK is not held in the buffer, the node device 20 may transmit the NAK to an upstream device (the node device 20, the transmitting device 10, etc.).

In the communication system described above, at least one NAK from the receiving device for a multicast packet having the same sequence
0, and the transmitting device 10 retransmits the multicast packet.

On the other hand, as described above, the node device 20
NAK only when the multicast packet corresponding to the NAK from the receiving device is not held in the buffer of
Is transferred to the upstream device, the NAK supplied to the transmitting device 10 is reduced, so that the time until the receiving device of the worst receiving device in the NAK is supplied to the transmitting device 10 becomes longer, Considering the entire network, the number of transmitted NAK packets is reduced, which can contribute to further alleviation of network congestion.

If all the multicast packets are to be stored in the buffer of the node device 20, a large storage capacity is required for the buffer. However, the first multicast packet is not stored in the buffer, and the retransmitted multicast packet is not stored. Only the buffer may be held. Thereby, the NAK for the first multicast packet is supplied to the transmitting device 10 and the transmitting device 1
Although the retransmission is performed from 0, the node device 2 does not respond to the NAK for the retransmitted multicast packet.
The multicast packet held in the buffer No. 0 is retransmitted.

As a result, compared to the case where no buffer is provided, the NAK transmitted to the transmitting device 10 is reduced, and it is possible to contribute to alleviation of network congestion.
Further, compared to the case where all the multicast packets are held in the buffer, the time until the receiving device of the worst receiving device is supplied to the transmitting device 10 can be reduced.

[0079]

According to the receiving state reporting method of the present invention, the receiving state information during the retransmission request from each receiving apparatus is extracted, the receiving state information from the receiving apparatus having the worst receiving state is held, and the held receiving state is held. The state information is supplied to the transmitting device.

As a result, it is possible to reliably supply the transmitting device with the receiving status information indicating the receiving status of the multicast packet in the receiving device having the worst receiving status. Therefore, the transmitting device, according to the received reception state information,
It is possible to perform appropriate multicast packet transmission control according to the receiving state of the receiving device having the worst receiving state,
Multicast with high certainty in accordance with actual transmission conditions can be performed.

Further, in the node device according to the present invention, the extracting means extracts the receiving state information during the retransmission request from each receiving apparatus, and the holding means holds the receiving state information from the receiving apparatus having the worst receiving state. The transmitting means transmits the held reception state information to the transmitting device. As a result, similarly to the reception state reporting method according to the present invention, the reception state information of the multicast packet from the reception apparatus having the worst reception state can be reliably supplied to the transmission apparatus. As a result, the transmitting apparatus can perform highly reliable multicasting in accordance with actual transmission conditions.

In the receiving apparatus according to the present invention, when the retransmission request means detects a packet loss of the multicast packet, the retransmission request means transmits a retransmission request having reception state information indicating a reception state of the multicast packet in the receiving apparatus. . The reception status information during the retransmission request is extracted by the node device, and the reception status information indicating the reception status of the reception device in the worst reception status is provided to the transmission device.

Thus, the transmitting apparatus can control the transmission of the multicast packet in accordance with the receiving state of the receiving apparatus in the worst receiving state, and perform highly reliable multicasting in accordance with the actual transmission conditions. it can.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a communication system according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of a transmission device configuring the communication system.

FIG. 3 is a diagram illustrating a case where a node device constituting the communication system is an NA device;
FIG. 9 is a diagram illustrating worst receiving device information held in a K holding unit.

FIG. 4 is a diagram illustrating a case where a node device constituting the communication system is an NA device;
FIG. 9 is a diagram illustrating a NAK reception count table held in a K holding unit.

FIG. 5 is a diagram showing an example of a format of a NAK transmitted by a receiving device constituting the communication system for a packet loss or the like.

FIG. 6 is a flowchart showing NAK integration processing in the node device.

FIG. 7 is a sequence diagram showing transmission and reception of a multicast packet and a NAK in the communication system.

FIG. 8 is a diagram conceptually showing NAK transmission and reception in the communication system.

FIG. 9 is a diagram conceptually showing NAK transmission and reception in another communication system.

FIG. 10 is a diagram conceptually showing NAK transmission / reception in another communication system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Transmission apparatus 12 ... Packet generation part 14 ... Control part 20, 20a, 20b, 20c ... Node apparatus 21, 28 ... Communication I / F 22, 27 ... Reception buffer 23 ... NAK detection part 24 ... Judgment part 25 ... NAK holding | maintenance Unit 26 NAK transmission unit 29 Routing control unit 30, 30a, 30b, 30c, 30d Receiving device 35 Analysis unit

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5K014 AA01 DA02 FA05 5K030 GA11 HA08 HB01 HB02 JA11 LA01 LA02 LD06

Claims (12)

[Claims] 1. A retransmission request requesting retransmission of a multicast packet is transmitted from each of a plurality of reception devices, the reception device having reception status information indicating a reception status of a multicast packet in each reception device. A receiving state reporting method for causing a transmitting apparatus to control transmission of a multicast packet in accordance with receiving state information, comprising: extracting receiving state information during a retransmission request from each of the receiving apparatuses; A receiving state reporting method, comprising: holding the receiving state information from the receiving apparatus having the worst receiving state in response thereto; and supplying the held receiving state information to the transmitting apparatus. 2. The reception status reporting method according to claim 1, wherein the step of supplying the reception status information to the transmission device comprises: receiving a first retransmission request for the same multicast packet; Receiving the received reception state information in the received reception state information and supplying the received reception state information to the transmitting apparatus. 3. The reception status reporting method according to claim 1, wherein the step of supplying the reception status information to the transmission device includes a step of discarding a second or subsequent retransmission request for the same multicast packet. A reception status reporting method. 4. The reception status reporting method according to claim 1, wherein the receiving device transmits the retransmission request when detecting a packet loss of a multicast packet. 5. The reception status reporting method according to claim 1, wherein the reception device transmits the packet including the reception status information when the retransmission request has not been transmitted for a predetermined time or more. And the reception status reporting method. 6. The reception status reporting method according to claim 1, wherein the reception status information includes information indicating a throughput to the reception device or a delay time to the reception device. Reporting method. 7. The reception status reporting method according to claim 6, wherein the step of holding the reception status information from the reception device having the worst reception status includes: A receiving state reporting method, comprising the step of determining according to the information indicating the throughput or delay time in the receiving state information from the server. 8. A transmission apparatus according to claim 8, wherein each of the plurality of receiving apparatuses has reception status information indicating a reception state of the multicast packet in each of the plurality of receiving apparatuses in response to the multicast packet from the transmitting apparatus. Extraction means for extracting reception state information in a retransmission request received from each of the plurality of reception apparatuses, and a reception apparatus having the worst reception state according to the information extracted by the extraction means. A node device comprising: holding means for holding the receiving state information of the above; and transmitting means for supplying the receiving state information held by the holding means to the transmitting device. 9. The node device according to claim 8, wherein the transmitting unit, when receiving a first retransmission request for the same multicast packet, stores reception state information in the retransmission request in the holding unit. A node device, which replaces the received reception state information with the received reception state information and supplies the information to the transmission device. 10. The node device according to claim 8, wherein the reception status information of the reception device includes at least information indicating a throughput or a delay time to the reception device, and the holding unit determines that the reception status is A node device that determines a worst receiving device according to information indicating a throughput or a delay time in reception status information from each of the receiving devices. 11. A transmitting apparatus for controlling transmission of a multicast packet in accordance with a receiving state of a multicast packet in a provided receiving apparatus, by extracting receiving state information indicating a receiving state from a retransmission request from a subordinate receiving apparatus. A receiving apparatus connected via a node device that provides a receiving state of a receiving apparatus having the worst receiving state to the transmitting apparatus, wherein the receiving apparatus receives the multicast packet when a packet loss of the multicast packet is detected. A receiving apparatus comprising: a retransmission request transmitting unit that transmits a retransmission request having reception state information indicating a state. 12. The receiving apparatus according to claim 11, wherein said retransmission request transmitting means transmits a packet including said reception state information when said retransmission request transmitting means has not transmitted said retransmission request for a predetermined time or more. A receiving device comprising: