JP2004201111A - Multicast packet distribution system, method and program - Google Patents

Abstract

A multicast distribution system for receivers distributed on networks having different packet error conditions, wherein each receiver receives necessary redundant data as much as necessary without imposing a special load on the sender.
A multicast packet distribution system for distributing a multicast packet to a packet communication network, comprising: a receiving unit for receiving the multicast packet by a plurality of receiving addresses on a receiving side; A monitoring unit 17, an address selection unit 20 for selecting an address to be used from reception addresses based on a monitoring result by the monitoring unit 17, and a reception address selected by the address selection unit 20 on the transmission side. And a transmission unit 14 for allocating and transmitting a multicast packet.
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a multicast distribution technique requiring reliability, and relates to a multicast packet distribution system, method, and program for improving reliability based on a reception situation.
[0002]
[Prior art]
In packet communication in a wireless LAN or the like, multicast distribution for simultaneously distributing data to a plurality of specific receiver groups identified by addresses assigned to individual terminals is possible. This multicast distribution is a one-to-many communication in which the same packet is transmitted to a plurality of recipients simultaneously by a process in which the sender transmits one packet.
[0003]
FIG. 8 is a diagram showing a configuration of a conventional multicast distribution. As shown in FIG. 1, a conventional multicast distribution system includes a transmission host 101 that transmits original data and FEC redundant data, and a multicast router 102 that transfers or duplicates a multicast packet of the original data and FEC redundant data according to a destination multicast address. And the receiving hosts 105 to 107 for receiving the original data and the FEC redundant data are connected to the IP networks 111 to 116.
[0004]
By the way, in this conventional multicast distribution, it is an effective distribution means for stream distribution and the like, but since it is non-confirmation type communication, if a packet is lost on a communication system, the receiver must receive the corresponding packet. Can not.
[0005]
Conventionally, various error correction techniques have been developed as techniques for dealing with this distribution error. FIG. 9 shows an example of Reed-Solomon encoding among FEC techniques applied to packets.
[0006]
As shown in the drawing, in steps S201 to S204, the original content is divided into k packets (original data) of a fixed length, and r pieces of redundant data of the same size are generated by an encoding process. By the multicast transmission processing in 206, (k + r) packets are transmitted to the multicast address G1.
[0007]
The receiver selects k different packets from the (k + r) packets and restores k original data. In other words, this is a technique that can restore original data if any k packets can be received even if a maximum of r packets are lost among (k + r) packets.
[0008]
The transmitting host applies the error correction technique as described above, and performs multicast transmission together with the original data and redundant data that can be applied to packet loss on a communication path that is expected in advance.
[0009]
As a result, the receiver can expect to receive a packet enough to recover the packet loss expected to occur on the communication path, and can receive and restore the transmitted original data.
[0010]
[Non-patent document 1]
Thomas Mauffer, translated by Hiroyuki Kusumoto, "Introduction to IP Multicast", First Edition, Kyoritsu Shuppan Co., Ltd., November 2001
[Non-patent document 2]
Dave Kosiur, translated by Yukio Kanda, "Mastering TCP / IP Multicast", 1st edition, 2nd print, November 2000.
[Non-Patent Document 3]
Beau Williamson, Translated by Comsus, Translated by Cisco Systems, "IP Multicast Network Development Guide, Vol. 1," First Edition, July 2001.
[Problems to be solved by the invention]
However, the above-described conventional error correction technique has a problem that a communication load increases due to redundant data that is unnecessarily distributed.
[0014]
That is, in the multicast distribution, since the receivers having different packet error conditions are distributed on the network, in the case of the conventional method, when the transmitting host 101 performs the multicast distribution, the worst reception condition among the receivers is considered. The redundant data is generated and transmitted in conformity with the receiving host 107 connected to the wireless LAN 116 having a high error rate.
[0015]
Therefore, in the conventional method, in the wireless LAN 114 where no error occurs, the receiving host 105 always receives an extra packet, and communication resources are consumed by the distribution of the unnecessary redundant data. May be
[0016]
In view of the above, the present invention has been made in view of the above points. In multicast distribution in a wireless LAN or the like, each receiver sets a necessary minimum amount of redundant data so that a special It is an object of the present invention to provide a multicast packet distribution system, method, and program capable of reducing the influence of packet loss without imposing a load.
[0017]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention monitors a reception status on a receiving side when a multicast packet is distributed to a packet communication network, and based on the monitoring result, stores a plurality of addresses for reception on the receiving side. , An address to be used is selected, a multicast packet is allocated to the selected receiving address on the transmitting side and transmitted, and the multicast packet is received on the receiving side by the selected receiving address.
[0018]
In the above invention, redundant data of a multicast packet is generated, and the generated redundant data is allocated to a receiving address and distributed.
[0019]
According to the present invention, when the receiving condition is improved on the receiving side due to a change in the communication environment, the number of necessary redundant data is reduced. The number of receiving addresses) can be reduced. On the other hand, when the reception situation is deteriorated due to a change in the reception environment, the number of necessary redundant data increases, and accordingly, the number of selected multicasts is increased. As a result, the receiving host having a good receiving environment does not need to receive unnecessary redundant data, and can reduce the communication load.
[0020]
In the above invention, it is preferable that the selected receiving address is notified to the transmitting side, and the transmitting side allocates redundant data to the notified receiving address. In this case, the transmitting side can also adjust the amount of redundant data to be transmitted or transferred in accordance with the receiving environment of the receiving side, thereby avoiding unnecessary data congestion and reducing the communication load of the entire network. Can be reduced.
[0021]
In the above invention, it is preferable to monitor the error rate of the received packet on the receiving side and determine the number of receiving addresses to be used based on the error rate. In this case, appropriate monitoring of the reception environment can be performed based on the error rate of the reception side.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of a multicast distribution system according to the present invention will be described. FIG. 1 is an explanatory diagram schematically showing an outline of the multicast distribution system according to the present embodiment.
[0023]
(Overview of multicast distribution system)
As shown in FIG. 1, a multicast packet distribution system according to the present embodiment includes a transmission host 301 that is a source of multicast distribution, reception hosts 305 to 307, and routers 302 to 304. In this embodiment, the receiving hosts 305 to 307 having different receiving conditions on the network receive the same original data and receive the respective necessary redundant data. Here, it is assumed that the reception status of the networks 315 and 316 to which the reception hosts 306 and 307 are connected is worse than that of the network 314 to which the reception hosts 305 are connected.
[0024]
Here, in FIG. 1, different multicast distributions are indicated by different arrows 317 to 319, indicating that there are three types of multicast distribution. Here, the reception host 305 receives only the multicast distribution of the original data because the reception status is good. Also, the receiving host 306 selects multicast distribution of original data and multicast distribution of another redundant data according to the receiving situation, and the receiving host 307 similarly distributes redundant data. Two multicast distributions are selected.
[0025]
As a result, the receiving host 305 can receive the necessary redundant data by the multicast distribution selected by the receiving host 305 itself without being affected by the multicast distribution selected by the receiving hosts 306 and 307. . By using a multicast routing protocol such as PIM or IGMP, the router 302 transfers the transmission packets 318 and 319 from the transmission host 301 to the reception hosts 306 and 307 to the networks 312 and 314 on the reception host 305 side. Therefore, the network load on the networks 312 and 314 is reduced.
[0026]
(Configuration of multicast distribution system)
FIG. 2 is a block diagram showing an internal configuration of the transmission host 301 and the reception hosts 305 to 307. As shown in the drawing, the transmission host 301 includes a packet generation unit 11, a redundant data generation unit 12, a distribution processing unit 13, a database 15, and a transmission unit 14. On the other hand, the receiving hosts 305 to 307 include a receiving unit 16, a monitoring unit 17, a determining unit 19, a storage unit 18, and an address selecting unit 20.
[0027]
The transmission host 301 is a communication module that allocates redundant data to reception addresses and distributes the data. The packet generation unit 11 is a module that divides the original content into k packets (original data) of a fixed length and generates a packet. The generated packet is output to the redundant data generation unit 12.
[0028]
The redundant data generation unit 12 is a module that generates redundant data of a multicast packet on the transmission side. In the present embodiment, r pieces of redundant data having the same size as the packet generated by the packet generation unit 11 are generated by the encoding process, and the packet (original data) input from the packet generation unit 11 and the redundant data generation unit The redundant data generated in step 12 is output to the distribution processing unit 13.
[0029]
The distribution processing unit 13 is a module that distributes the original data and the redundant data to the multicast address of the receiving host, and refers to the multicast address information T1 stored in the database 15 when performing the distribution.
[0030]
The database 15 is a storage device for storing the multicast address information T1 as shown in FIG. 4, and collates the multicast address information T1 in response to a request from the distribution processing unit 13, and outputs the collation result to the distribution processing unit 13. I do. The multicast address information T1 is table data in which a reception address item 501 and a type address item 502 are associated with each other. The reception address item 501 indicates a destination IP multicast address to which a multicast packet is transmitted. The address item 502 indicates the type of the original data or the redundant data by FEC encoding.
[0031]
The multicast address information T1 is shared by the sending host 301 and the receiving hosts 305 to 307. As a method of sharing, the transmission host 301 and the reception hosts 305 to 307 may be fixedly determined in advance, or the reception address selected from the reception hosts 305 to 307 may be transmitted to the transmission host 301. The information may be reported to 301. When the selected receiving address is reported to the transmitting host, the transmitting side can also adjust the amount of redundant data to be transmitted or transferred in accordance with the receiving environment of the receiving side, so that unnecessary data can be adjusted. Can be avoided, and the communication load of the entire network can be reduced.
[0032]
The transmitting unit 14 is a module that allocates and transmits a multicast packet to the receiving address selected by the address selecting unit 20 on the transmitting side. In particular, in the present embodiment, the transmitting unit 14 has a function of allocating redundant data to the receiving address notified from the receiving host side.
[0033]
The receiving unit 16 is a communication module that receives a multicast packet using a plurality of receiving addresses on the receiving side. The monitoring unit 17 is a module that monitors a reception state (for example, an error rate of a received packet) in the receiving unit 16. The determining unit 19 is a module that determines the number of receiving addresses to be used based on the error rate.
[0034]
The address selecting unit 20 includes means for selecting an address to be used from among the receiving addresses based on the monitoring result by the monitoring unit 17 and notifying the transmitting side of the selected receiving address.
[0035]
(Operation of the multicast packet distribution system)
The operation of the multicast packet distribution system according to the present embodiment having the above-described configuration will be described with reference to FIGS. FIG. 3 is a flowchart showing the operation in the transmission host.
[0036]
As shown in the figure, in the transmission host 301, the packet generation unit 11 generates an original content (S401) and divides the packet into k packets (original data) of a fixed length (S402). Next, the redundant data generation unit 12 performs an encoding process (S403) to generate r pieces of redundant data having the same size (S404). Next, the original data and the redundant data are distributed to each reception address by the distribution processing unit 13 (S405).
[0037]
When the multicast address is allocated in step S405, each packet is allocated to a predetermined number of multicast addresses with reference to the multicast address information T1. The number of multicast addresses set at this time is determined by a request on the system. Here, the original data is transmitted at the multicast address G1, and the redundant data is transmitted at ten types of multicast addresses G2 to G10.
[0038]
Then, the transmission unit 14 allocates and transmits the original data to the multicast address G1 (S406), and transmits the redundant data at the multicast addresses G2 to G10 as indicated by 407 (S407). That is, (k + r) packets are transmitted to the multicast address G1, and the receiving host selects k different packets from the (k + r) packets and restores k original data.
[0039]
In the example shown in FIG. 3, the number of redundant data transmitted at each multicast address is one, but the number of redundant data may be two or more.
[0040]
(Example of change)
In the above-described embodiment, the case where the content is divided into an arbitrary number of data has been described as an example. However, in the above-described step S402, k pieces of original data can be associated with image frames. For example, when the frame is composed of an intra frame (one frame) and an inter frame (B, P frame) as in mpeg, the intra frame and the inter frame are transmitted using different multicast addresses even if the data is original data. be able to.
[0041]
Further, if the data is independent in units of frames as in the case of motion JPEG, for example, odd frames and even frames can be transmitted using different multicast addresses.
[0042]
FIG. 5 shows such a receiving process in the receiving host according to this modification. First, the receiving host selects reception of a multicast for original data (S601). In the receiving hosts 305 to 307, the monitoring status of the original data is monitored by the monitoring unit 17 (S602). FIG. 6 shows an example of basic data of the reception status used by the reception hosts 305 to 307 at this time.
[0043]
As shown in the figure, the sender manages the original content divided into k pieces as one reception block by adding a reception block number thereto. The number of received packets of redundant data is used as data and stored for each received block number. In this example, the required number k is four.
[0044]
Next, the monitoring result is determined (S603). That is, the current number of received packets is counted, and it is determined whether the count value is appropriate, insufficient, or excessive. If the result of the determination in step S603 is that the required number of k packets cannot be received, a new selection is made to receive a multicast address for transmitting redundant data (S604). If more than k packets have been received, the multicast address for transmitting the redundant data is deleted (S605). If k packets have been received, it is determined to be appropriate. Note that this determination is not always performed every time a reception block is received, but can be determined through two or more reception block receptions.
[0045]
FIG. 7 shows a process of receiving redundant data by the above method. In the figure, when four pieces of original data are distributed from the sending host 301 at the multicast address G1 (S801 and S805), for example, one packet loss occurs between the multicast router and the receiving host 304 (S806). This shows a case where not all packets have been delivered to the receiving host 304.
[0046]
The receiving host 304 determines that the reception is insufficient in the reception determination (S807), and performs additional selection of multicast distribution (S808). The information of the IP multicast address is shared with the transmission host 301, and the multicast address G2 is selected.
[0047]
As a result, the multicast router is notified of the multicast membership report message of the added multicast address G2 (S809). Based on this, the multicast router performs processing S810 for transferring the multicast address G2, and transmits a multicast membership report between routers to the multicast router (S811).
[0048]
Based on this, the multicast router transfers the multicast packet addressed to the multicast address G2 to the multicast router (S814). The multicast router transfers this to the receiving host (S815). The receiving host 305 performs a receiving determination S816. Through the above procedure, the receiving host 305 can receive the redundant data distributed by the multicast address G2.
[0049]
(Multicast packet distribution program)
Note that the multicast packet distribution system and method in the above-described embodiment and its modified example can be a program described in a predetermined computer language. That is, by installing this program on a computer or an IC chip provided in the transmission host 301, the routers 302 to 304, the reception hosts 305 to 307, etc., the transmission host, router or reception host having the above-described functions can be easily implemented. Can be built. This program can be, for example, an application that runs on a communication service and a standalone computer.
[0050]
(Effect)
According to the multicast packet distribution system and the distribution method according to the embodiment and the modification described above, when the reception situation on the receiving host 305 to 307 side is improved due to a change in the communication environment, the necessary number of redundant data is reduced. Accordingly, the number of multicasts (reception addresses) for which reception has been selected can be correspondingly reduced.
[0051]
On the other hand, when the reception condition is deteriorated due to a change in the reception environment, the number of necessary redundant data increases, and accordingly, the number of selected multicasts can be increased. Thereby, for example, the reception host 305 having a favorable reception environment shown in FIG. 1 does not need to receive unnecessary redundant data, and can reduce the communication load.
[0052]
In the above embodiment, the error rate of the received packet on the receiving host side is monitored by the monitoring unit 17, and the number of receiving addresses to be used is determined by the determining unit 19 and the address selecting unit 20 based on the error rate. Since the judgment and the selection are made, it is possible to appropriately monitor the reception environment based on the error rate of the receiving side.
[0053]
【The invention's effect】
As described above, according to the present invention, in a multicast distribution system configured on networks having different packet error conditions, without applying a special load on the sender side, an optimal network is provided according to the reception status of each network. Multicast numbers can be received.
[0054]
In a network with good reception conditions, unselected multicast packets are not transferred from the multicast router to the network, so that redundant redundant data transfer is reduced and the network load is reduced.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram schematically showing an outline of a multicast distribution system according to an embodiment.
FIG. 2 is a block diagram showing an internal configuration of a transmission host 301 and reception hosts 305 to 307 according to the embodiment.
FIG. 3 is a flowchart illustrating an operation of the transmission host according to the embodiment.
FIG. 4 is an explanatory diagram showing a data structure of multicast address information T1 according to the embodiment.
FIG. 5 is a flowchart showing a receiving process in a receiving host according to a modified example.
FIG. 6 is an explanatory diagram showing a data structure of basic data of reception status used by reception hosts 305 to 307.
FIG. 7 is a sequence diagram showing a process of receiving redundant data in a modified example.
FIG. 8 is a diagram showing a configuration of a conventional multicast distribution.
FIG. 9 is an explanatory diagram showing an example of Reed-Solomon encoding among FEC techniques applied to a conventional packet.
[Explanation of symbols]
G2 to G10 Multicast address T1 Multicast address information 4 Original data 11 Packet generating unit 12 Redundant data generating unit 13 Processing unit 14 Transmitting unit 15 Database 16 Receiving unit 17 Monitoring unit 18 Storage unit 19 ... Judging section 20... Address selecting section 301... Sending hosts 302 to 304... Routers 305 to 307.

Claims (15)

A multicast packet delivery system for delivering a multicast packet to a packet communication network,
On the receiving side, a receiving unit that receives the multicast packet with a plurality of receiving addresses,
A monitoring unit that monitors a reception state in the receiving unit,
An address selection unit that selects an address to be used from among the reception addresses based on a monitoring result by the monitoring unit;
A transmission unit that allocates and transmits the multicast packet to a reception address selected by the address selection unit on a transmission side. On the transmitting side, a redundant data generating unit that generates redundant data of the multicast packet is provided,
The multicast packet distribution system according to claim 1, wherein the transmission unit allocates the redundant data to the reception address and distributes the redundant data. The address selecting unit includes means for notifying the selected receiving address to the transmitting side,
The multicast packet distribution system according to claim 2, wherein the transmission unit allocates the redundant data to the notified reception address. 4. The apparatus according to claim 1, wherein the monitoring unit includes a determination unit that monitors an error rate of a received packet and determines the number of receiving addresses to be used based on the error rate. Multicast packet distribution system. The packet communication network is configured by connecting a plurality of networks having different error conditions to each other, and the transmitting unit is provided in a router installed at a connection point of the plurality of networks. Item 5. The multicast packet distribution system according to any one of Items 1 to 4. A multicast packet delivery method for delivering a multicast packet to a packet communication network,
(1) monitoring the reception status on the receiving side;
(2) selecting an address to be used from a plurality of receiving addresses on the receiving side based on the monitoring result in the step (1);
(3) on the transmitting side, allocating and transmitting the multicast packet to the receiving address selected in the step (2);
(4) receiving the multicast packet transmitted in step (3) by the receiving address selected in step (2) on the receiving side. 7. The multicast packet distribution method according to claim 6, wherein in the step (3), redundant data of the multicast packet is generated, and the generated redundant data is allocated to the reception address and distributed. In the step (2), the selected receiving address is notified to the transmitting side,
The multicast packet distribution method according to claim 7, wherein in the step (3), the redundant data is allocated to the notified receiving address. 9. The multicast packet distribution method according to claim 6, wherein in the step (1), the error rate of the received packet is monitored, and the number of receiving addresses to be used is determined based on the error rate. . The packet communication network is configured by connecting a plurality of networks having different error conditions to each other, and the step (3) is performed by a router installed at a connection point of the plurality of networks. The multicast packet distribution method according to claim 6. A multicast packet distribution program for distributing multicast packets to a packet communication network, comprising: a computer installed on the packet communication network;
(1) monitoring the reception status on the receiving side;
(2) selecting an address to be used from a plurality of receiving addresses on the receiving side based on the monitoring result in the step (1);
(3) on the transmitting side, allocating and transmitting the multicast packet to the receiving address selected in the step (2);
Receiving the multicast packet transmitted in the step (3) by the receiving address selected in the step (2) on the receiving side, and executing the processing (4). . The multicast packet distribution program according to claim 11, wherein, in the step (3), redundant data of the multicast packet is generated, and the generated redundant data is allocated to the reception address and distributed. In the step (2), the selected receiving address is notified to the transmitting side,
13. The multicast packet distribution program according to claim 12, wherein in the step (3), the redundant data is allocated to the notified receiving address. 14. The program according to claim 11, wherein in the step (1), an error rate of a received packet is monitored, and the number of receiving addresses to be used is determined based on the error rate. . The packet communication network is configured by connecting a plurality of networks having different error conditions to each other, and the step (3) is performed by a router installed at a connection point of the plurality of networks. The multicast packet distribution program according to claim 11.

Images