JP2016027698A - Data transfer system, relay node, and data transfer method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of distributing datagrams in a small amount of relay mode memory as possible without flowing as unnecessary datagrams as possible to a network.SOLUTION: An upstream node and a downstream node are connected to a data transfer system. The upstream node comprises a parity datagram creation unit which creates and holds a parity datagram and outputs the parity datagram according to a parity datagram transmission request to a switch. The downstream node comprises a parity datagram transmission request unit and a content datagram reconfiguration unit. The parity datagram transmission request unit transmits the parity datagram transmission request to the upstream node when detecting a loss in a predetermined content datagram. The content datagram reconfiguration unit reconfigures the lost content datagram using a parity datagram when receiving the parity datagram from the upstream node.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a data transfer system, a relay node, and a data transfer method for distributing content from a distribution server to one or a plurality of receiving devices.

  Recently, large-capacity content such as 4K video and 8K video has been sent to the back of the earth in real time using an IP network such as the Internet, and it is thought that it will become increasingly popular in the future. However, in an IP network such as the Internet, packet loss occurs due to occasional congestion, and it is also affected by the status of the network used. In general, the larger the content and the longer the distance, The number of packet loss tends to increase.

  Conventionally, several methods have been used as countermeasures against such situations. For example, there is a method using End-to-end FEC (Forward Error Correction) (see Non-Patent Document 1). However, as described above, since the number of packet loss tends to increase as the content to be transmitted increases in capacity and as the distance increases, a packet carrying FEC parity bits (hereinafter referred to as a parity packet). For example, a large amount of parity packets also flow in unnecessary places in the network, such as at the beginning of the passing network. This not only reduces the network utilization efficiency, but may cause further packet loss due to them.

  As another method, there is a re-transmission by End-to-end TCP (Transmission Control Protocol), which re-transmits a lost packet from a transmission server to a receiving apparatus. However, since the lost packet is retransmitted after the retransmission request arrives at the transmission server from the receiving device, the propagation delay time increases when the distance is long, such as several tens of thousands km, and the retransmission may be repeated many times. Therefore, real-time content playback becomes difficult.

  Therefore, instead of resending by the end-to-end TCP protocol, one or more relay nodes are provided in the network, and between the transmission server and the relay node, between the relay node and the relay node, and between the relay node and the receiving device. A method of performing retransmission using the TCP protocol is conceivable.

  In general, this method tends to reduce the number of lost packets in a relay section as the number of relay nodes increases, and retransmission is not performed in a section without loss, so that there is an advantage that delay time due to retransmission can be reduced. is there. However, this method has a problem that a large amount of content must be held in all relay nodes for a certain period of time in order to perform retransmission according to the TCP protocol. That is, there is a problem that the total memory amount increases as the number of relay nodes increases.

JP 2011-199647 A

Supervised by Hideki Imai, Electronics Essentials series "Key points of error correction coding technology", Japan Industrial Technology Center, Chapter 3 Application to communication, 1.1 FEC and ARQ to 1.2 Application form to communication system, pp. 49-51 (1986)

  It is an object of the present invention to provide a method capable of delivering unnecessary datagrams on a network as much as possible and delivering them with as little relay node memory as possible.

  Note that the datagram here is a packet of various communication protocols including an IP packet, an Ethernet (registered trademark) frame, an ATM cell, X. It refers to a batch of bit strings for transferring some information such as 25 packets.

Specifically, the data transfer system according to the present invention includes:
A data transfer system in which a distribution server or an upstream node is connected to an upstream side of a network, and a downstream node or a receiving device is connected to a downstream side of the network,
The distribution server or upstream node is
A parity datagram transmission request receiving unit for receiving a parity datagram transmission request for requesting transmission of a parity datagram from the downstream node or the receiving device;
When a predetermined content datagram is received, a parity datagram for performing forward error correction of the content datagram is created and held using the content datagram, and notified from the parity datagram transmission request receiving unit A parity datagram creating unit that outputs a parity datagram corresponding to the parity datagram transmission request to be sent to the downstream node or a switch that transmits to the receiving device;
With
The downstream node or receiving device is:
A parity datagram transmission requesting unit for transmitting the parity datagram transmission request to the distribution server or the upstream node when a loss is detected in a predetermined content datagram from the distribution server or the upstream node;
When a parity datagram is received from the distribution server or upstream node, a lost content datagram reconstructing unit that reconstructs a lost content datagram using the received parity datagram;
Is provided.

  The parity datagram transmission request unit may transmit a numerical value indicating the degree of content datagram loss to the distribution server or the upstream node in addition to the parity datagram transmission request. In addition, the parity datagram transmission request receiving unit may adjust the amount of parity bits to be transmitted according to the degree of content datagram loss represented by the numerical value and notify the parity datagram creation unit.

  The distribution server or the upstream node may be a distribution server that distributes content datagrams or a relay node that transfers the content datagrams to a receiving device. The downstream node or the reception device may be a relay node that transfers the content datagram to the reception device or a reception device that receives the content datagram.

Specifically, the relay node according to the present invention is:
A relay node that forwards a datagram from a delivery server or upstream node connected upstream to a downstream node or receiving device connected downstream;
A parity datagram transmission request receiving unit for receiving a parity datagram transmission request for requesting transmission of a parity datagram from the downstream node or the receiving device;
When a predetermined content datagram is received, a parity datagram for performing forward error correction of the content datagram is created and held using the content datagram, and notified from the parity datagram transmission request receiving unit A parity datagram creating unit that outputs a parity datagram corresponding to the parity datagram transmission request to be sent to the downstream node or a switch that transmits to the receiving device;
Is provided.

Specifically, the relay node according to the present invention is:
A relay node that forwards a datagram from a delivery server or upstream node connected upstream to a downstream node or receiving device connected downstream;
When a loss is detected in a predetermined content datagram from the distribution server or upstream node, a parity datagram transmission request for requesting transmission of a parity datagram for performing error correction of the content datagram is sent to the upstream node Or a parity datagram transmission request part to be transmitted to the receiving device;
When receiving a parity datagram from the distribution server or upstream node, a lost content datagram reconstructing unit for reconstructing a lost content datagram using the received parity datagram;
Is provided.

Specifically, the data transfer method according to the present invention includes:
A data transfer method in a data transfer system in which a distribution server or an upstream node is connected to an upstream side of a network and a downstream node or a receiving device is connected to a downstream side of the network,
When the distribution server or upstream node receives a predetermined content datagram, a parity datagram that creates and holds a parity datagram for performing forward error correction of the content datagram using the content datagram Creation procedure and
Parity data to request transmission of a parity datagram held by the distribution server or upstream node when the downstream node or receiving device detects a loss in a predetermined content datagram from the distribution server or upstream node A parity datagram transmission request procedure for transmitting a grams transmission request to the distribution server or upstream node;
When the downstream node or the receiving device receives a parity datagram from the distribution server or the upstream node, a lost content datagram reconfiguration procedure for reconstructing a lost content datagram using the received parity datagram;
In order.

  The above inventions can be combined as much as possible.

  ADVANTAGE OF THE INVENTION According to this invention, it can distribute with the memory amount of a relay node as little as possible, without flowing unnecessary datagrams to a network as much as possible.

It is an example of the network where the relay node which concerns on embodiment of this invention is used. It is an example of the functional block structure of the relay node which concerns on embodiment of this invention. It is outline | summary explanatory drawing (description figure about distribution of the content bit sequence CF of one FEC block) of the delivery method which concerns on embodiment of this invention. It is an example of the content data which concerns on embodiment of this invention. It is an example of the content datagram which concerns on embodiment of this invention. It is an example of the parity datagram which concerns on embodiment of this invention. It is an example of the operation of the relay node according to the embodiment of the present invention (description of distribution of content bit string CF of one FEC block). It is an example (description about distribution of the content bit string CF of one FEC block) of the operation | movement of the receiver which concerns on embodiment of this invention. It is an example of the functional block structure of the process part 30 which concerns on embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited to embodiment shown below. These embodiments are merely examples, and the present invention can be implemented in various modifications and improvements based on the knowledge of those skilled in the art. In the present specification and drawings, the same reference numerals denote the same components.

[First Embodiment]
Hereinafter, a first embodiment of the present invention will be described. The invention according to the present embodiment calculates and holds the parity bit of FEC in each relay node, and when a certain relay node detects the loss of a datagram, it holds it in the nearest relay node upstream of the relay node. Request parity bit transmission and use the received parity bit to recover the lost datagram.

  FIG. 1 is an example of a network 0 in which a relay node 1 incorporating the function of the present invention is used. The distribution server 2, the receiving device 3, and the operation device 4 are connected to the network 0. In the network 0, one or more relay nodes 1 are arranged as devices having a datagram transfer function. The relay node 1 includes at least a function as an upstream node (hereinafter referred to as an upstream node function) and a function as a downstream node (hereinafter referred to as a downstream node function). The distribution server 2 has an almost equivalent upstream node function in addition to the functions of the conventional FEC system distribution server, and the receiving apparatus 3 has one function other than the functions of the conventional FEC system reception apparatus. Although it is different, it has a substantially equivalent downstream node function (details will be described later).

  FIG. 3 shows an example of a simple distribution route in which a content bit string CF of one FEC block is distributed from the distribution server 2 to the receiving device 3 via the relay nodes 1a and 1b among the plurality of relay nodes 1. In this case, communication between devices, that is, exchange of datagrams, and main processing in each device are described as time t passes. Hereinafter, it demonstrates in detail in order.

  First, the distribution server 2 constructs a payload portion and adds a header such as a destination to create a datagram. For this purpose, the distribution server 2 creates a content bit string CF by dividing the content data CD to be distributed into a certain bit amount suitable for FEC parity bit calculation, as shown in FIG. To do. If there is a shortage at the end, padding is performed. The distribution server 2 further divides the content bit string CF in accordance with the bit length (for example, 1400 bytes) in the payload of the datagram to create a divided bit string CB.

  Then, as shown in FIG. 5, the distribution server 2 includes at least “FEC block number” indicating which FEC block belongs to each divided bit string CB and “where in the FEC block”. FEC block number "is assigned. The destination of the datagram is the address of the receiving device 3 when performing unicast delivery, that is, one-to-one delivery from the delivery server 2 to one receiving device 3, and multicast delivery, ie, the delivery server 2 When a one-to-many distribution is performed to a plurality of receiving devices 3, a multicast address or the like is used. Hereinafter, the datagram will be referred to as “content datagram GC”.

  The distribution server 2 further creates a predetermined number of FEC parity bit strings PB for the content bit string CF of each FEC block as an upstream node function. Then, as shown in FIG. 6, a datagram is similarly created. In other words, at least a “FEC block number” indicating which FEC block is a parity bit string and a “parity bit string number” indicating which parity bit string is created are assigned to each parity bit string PB. The destination of the datagram is the address of the receiving device 3 when performing unicast delivery, that is, one-to-one delivery from the delivery server 2 to one receiving device 3, and multicast delivery, ie, the delivery server 2 When a one-to-many distribution is performed to a plurality of receiving devices 3, a multicast address or the like is used. When the distribution server 2 creates the parity bit string PB, the distribution server 2 erases the content bit string CF. Hereinafter, the datagram will be referred to as “parity datagram GP”. Up to this point, the operation is similar to that of a conventional FEC distribution server.

  In the conventional FEC method, the content datagram GC is transmitted for each FEC block, and then the parity datagram GP is transmitted. The distribution server 2 according to the embodiment of the present invention receives the transmission request for the parity datagram GP. Unless it is, the parity datagram GP is not transmitted. Further, when the content datagram GC for one FEC block is transmitted, the datagram is immediately deleted.

  The distribution server 2 holds the parity datagram GP as a upstream node function for a preset time. Further, while holding the parity datagram GP, a “parity datagram transmission request” for requesting transmission of the parity datagram GP from the nearest downstream relay node 1 that has received the content datagram GC is received. When it comes, the corresponding parity datagram GP is transmitted. The parity datagram GP that has passed a preset holding time is erased.

FIG. 7 shows a flowchart of an example of the operation of the relay node 1. Hereinafter, an example of the operation of the relay node 1 will be described with reference to FIG.
The relay node 1 receives the content datagram GC sent from the relay node 1 upstream of the relay node 1 or the distribution server 2 as a downstream node function (S101).

  In FIG. 3, the relay node 1a closest to the distribution server 2 receives the content datagram GC transmitted from the distribution server 2 (S101). For example, the relay node 1a receives GC # 1 including CB # 1-1, GC # 2 including CB # 1-2,..., GC # n including CB # 1-n from the distribution server 2. .

  The relay node 1a further functions as a downstream node function from the FEC block number and the FEC block number written in the content datagram GC, in each FEC block, between the distribution server 2 and the relay node 1a. The presence or absence of the content datagram GC that could not be received due to the above loss or the like is checked (S102). This check is performed, for example, after the elapse of a predetermined time after receiving the first content datagram GC # 1 of each FEC block number.

In FIG. 3, if all the content datagrams GC of the corresponding FEC block have been received by the time set in advance (No in S102), the relay node 1a transmits the divided bit string CB from each content datagram GC. Is taken out (S103).
Next, the relay node 1a immediately reads the destination in the header of each content datagram GC and directs the content datagram GC to one or a plurality of destinations in order to deliver the memory amount of the relay node as small as possible. The content datagram GC is immediately deleted (S104).

  At this time, as the downstream node function, it may be notified to the upstream nearest distribution server 2 using the datagram that there is no content datagram that could not be received. The distribution server 2 that has received it deletes it as an upstream node function even before a predetermined time when the held parity datagram should be held. Thereby, the memory usage of the relay node can be reduced.

Next, the relay node 1a reconstructs the content bit string CF of the original FEC block from the extracted divided bit string CB, and erases the extracted divided bit string CB (S105).
Next, the relay node 1a creates a preset number of parity bit sequences PB from the content bit sequence CF and deletes the content bit sequence CF (S106).
Next, the relay node 1a creates a parity datagram GP from each parity bit string PB, and deletes each parity bit string PB (S107).
When each “parity datagram transmission request” is received (Yes in S108), each parity datagram GP is transmitted downstream (S109).
The parity datagram GP is held for a predetermined time, and when the holding time has passed (Yes in S110), the corresponding parity datagram GP is deleted (S111).
The operation of the relay node 1 when all the content datagrams GC of the corresponding FEC block are not received by a preset time will be described in the following relay node 1b.

  In FIG. 3, the relay node 1b immediately downstream of the relay node 1a receives the content datagram GC transmitted from the relay node 1a (S101).

  The relay node 1b further performs the following operation as a downstream node function. That is, from the FEC block number and the FEC block number written in the datagram, the content data that could not be received in each FEC block due to loss on the network path between the relay node 1a and the relay node 1b. The presence or absence of the gram GC is checked (S102).

  In FIG. 3, the relay node 1b that has failed to receive a part or all of the content datagram GC of the corresponding FEC block by a preset time (Yes in S102) executes a procedure for receiving a parity datagram. To do. That is, the relay node 1b transmits a datagram of “parity datagram transmission request” to the nearest upstream relay node 1a (S201). In this datagram, at least the FEC block number and the number of datagrams that could not be received are entered.

  For example, when the relay node 1b has not received the content datagram GC # 2 (Yes in S102), the relay node 1b has at least the necessary for restoring the divided bit string CB included in the content datagram GC # 2. Then, the FEC block number to which the content datagram GC # 2 belongs and the “parity datagram transmission request” in which “1” is entered as the number of datagrams that could not be received are transmitted to the relay node 1a.

  The relay node 1a that has received the “parity datagram transmission request” datagram (S108) immediately transmits the necessary number of parity datagrams GP of the corresponding FEC block as an upstream node function (S109).

  The “necessary number” mentioned here is as follows. In the method using FEC, if there are a number of parity datagrams GP corresponding to the number of lost content datagrams in one FEC block, the lost division in the FEC block is performed using the parity bit string PB in them. The bit string CB can be restored and the content bit string CF of the FEC block can be reconstructed. The number of parity datagrams GP corresponding to the number of lost content datagrams GC is, for example, the same as the number of lost content datagrams GC in the case of the Reed-Solomon code, and LDGM (Low Density Generator Matrix). In the case of a code, for example, it is 10% for a loss of 7% of the content datagram GC, and the number corresponding to the code used for FEC is set in advance in the distribution server 2 and each relay node 1.

  Further, the relay node 1b does not always transmit a “parity datagram transmission request” datagram for the same FEC block, but the parity data on the network path between the relay node 1a and the relay node 1b. Due to the loss of the gram GP, the relay node 1b may transmit the “parity datagram transmission request” datagram again. In such a case, even if the same parity datagram GP that can be received by the relay node 1b is transmitted from the relay node 1a, it does not help to recover the lost divided bit string CB in the FEC block. The number of the already received parity datagram GP is also described in the datagram “datagram transmission request”. The relay node 1a avoids the already received parity datagram GP, and transmits the insufficient number of parity datagrams GP to the relay node 1b.

  Although there is a possibility that the parity datagram GP is lost on the network path between the relay node 1a and the main relay node 1b, the relay node 1b has already been included in the datagram of the “parity datagram transmission request”. Instead of describing the number of the received parity datagram GP, the relay node 1a on the transmission side records the number of the parity datagram GP transmitted by the corresponding FEC block and selects it so as not to overlap. There is also a way to send.

  The relay node 1 receives the parity datagram GP as a downstream node function (S202).

  In FIG. 3, the relay node 1b receives the parity datagram GP transmitted from the relay node 1a (S202).

  The relay node 1b further has a network path between the relay node 1a and the relay node 1b as a downstream node function based on the datagram type and the FEC block number of the parity datagram GP written in the datagram. It is checked whether there is a parity datagram GP that could not be received due to the above loss or the like (S203). This check is performed, for example, after the elapse of a predetermined time after receiving the first parity datagram GP of each FEC block number.

The relay node 1b, which has received the number of parity datagrams GP necessary for the parity calculation of the corresponding FEC block within the preset time (Yes in S203), receives the parity bit string PB from the received parity datagram GP. And the parity datagram GP is immediately deleted (S204).
Further, the divided bit string CB is extracted from each of the plurality of content datagrams GC already held in the corresponding FEC block (S205).
Next, the “lost divided bit string CB” is restored from the divided bit string CB and the parity bit string PB by the parity calculation, and the parity bit string PB is erased (S206).
Next, the lost content datagram GC is reconstructed (S207).
Next, returning to step S104, the operations from S104 to S111 are the same as described above.

  All the relay nodes 1 have the upstream node function and the downstream node function described above, and perform the same operation as described above. The downstream node function is a function realized by the operations of S101 to S103, S105, and S201 to S207 in FIG. 7, and the upstream node function is a function realized by the operations of S104 and S106 to S111 in FIG.

  The distribution server 1 does not have a downstream node function, has an upstream node function substantially equivalent to the relay node 1 described above, creates a datagram from content data, and transmits the datagram to the network 0. The upstream node function of the distribution server 1 is different from the upstream node function of the relay node 1 in that a divided bit string CB is created from the content bit string CF of the FEC block, and a content datagram GC is created from the divided bit string CB. The point is to erase CB. These are because the distribution server 1 already has content data CD.

  The receiving device 3 does not have an upstream node function, has a downstream node function substantially equivalent to the relay node 1 described above, receives a datagram from the network 0, and reproduces the original content data. The downstream node function of the receiving device 3 is different from the downstream node function of the relay node 1 in that the content datagram GC is deleted in S303 corresponding to S103 and S405 corresponding to S205, and there is no operation corresponding to S207. It is. These are because there is no need to transfer the content datagram GC downstream of the receiving device.

FIG. 8 shows an operation algorithm of the receiving device 3. The receiving device 3 has the downstream node function described above. In FIG. 3, when the content datagram GC is received from the network 0 (S301), the receiving device 3 checks the same operation as the downstream node function of the relay node 1, that is, whether or not the received content datagram GC is lost. (S302). This check is performed, for example, after the elapse of a predetermined time after receiving the first content datagram GC of the target FEC block number.
If there is no loss (No in S302), the divided bit string CB is extracted from each content datagram GC and held, and the content datagram GC is erased (S303).

If there is a loss (Yes in S302), a “parity datagram transmission request” is transmitted to the nearest upstream relay node 1b (S401). Thereby, the parity datagram GP is transmitted from the nearest upstream relay node 1b, and the receiving device 3 receives the parity datagram GP (S402).
Next, the receiving device 3 checks whether there is a loss of the parity datagram GP on the network path between the nearest upstream relay node 1 and the receiving device 3. That is, it is checked whether or not the number of parity datagrams GP necessary for restoring the divided bit string CB included in the lost content datagram GC has been received (S403). This check is performed, for example, after the elapse of a predetermined time after receiving the first parity datagram GP of the target FEC block number.
If there is a loss (No in S403), a “parity datagram transmission request” is transmitted again to the nearest upstream relay node 1b (S401). This operation is repeated until the number of parity datagrams GP necessary for restoring the divided bit string CB included in the lost content datagram GC is received.

When the necessary number of parity datagrams GP is received (Yes in S403), the receiving device 3 extracts the parity bit string PB from the parity datagram GP and immediately deletes the parity datagram GP (S404).
Next, the divided bit string CB is extracted from the content datagram GC, and the parity datagram GC is immediately erased (S405).
Next, a parity calculation is performed using the extracted one or more parity bit sequences PB and one or more divided bit sequences CB already held in the receiving apparatus 3, and the division included in the lost content datagram GC is performed. The bit string CB is restored (S406).

Next, the content bit string CF of the FEC block is reconstructed from the restored one or more divided bit strings CB and one or more divided bit strings CB already held in the receiving device 3, and immediately the divided bit string The CB is erased (S304).
Further, the content data CD is reconstructed from the content bit string CF of the FEC block (S305), and the content is reproduced (S306).

  By providing one or a plurality of relay nodes 1 in the network 0, each datagram loss rate between the distribution server 2 and the relay node 1, between the relay nodes 1, and between the relay node 1 and the receiving device 3 is determined as End-to- Generally smaller than end datagram loss rate, never larger. For this reason, the number of parity bits required for restoring the content data is reduced, and as a result, the number of parity datagrams in each section can be reduced.

  FIG. 2 is an example of a functional block configuration of the relay node according to the embodiment of the data transfer system. The relay node 1 includes input interface units 10a to 10n, a processing unit 30, a control unit 40, a switch unit 20, output interface units 11a to 11n, and a control unit input / output interface unit 50. The processing unit 30 includes, for example, a programmable processing circuit such as a CPU (Central Processing Unit), an FPGA (Field Programmable Gate Array), or a PLD (Programmable Logic Device) and a memory. The control unit 40 includes, for example, a CPU (Central Processing Unit) and a memory.

  In FIG. 2, between the relay node 1A and the relay node 1B, the relay node 1A functions as an upstream node and the relay node 1B functions as a downstream node, but the relay node 1 functions as both a downstream node and an upstream node. Therefore, it has both an upstream node function and a downstream node function. The processing unit 30 also includes a part of the upstream node function and a part of the downstream node function.

  FIG. 9 is an example of a functional block configuration in the processing unit 30. In the processing unit 30, a datagram sorting unit 31 for performing a datagram sorting procedure, a content datagram storing / checking unit 32 for performing a content datagram storing / checking procedure, and a parity datagram transmission requesting procedure are described. A parity datagram transmission request unit 33, a parity datagram storage / check unit 34 for performing a parity datagram check procedure, a lost content datagram reconstruction unit 35 for performing a lost content datagram reconstruction procedure, and a content bit string of an FEC block FEC block content bit string reconstruction unit 36 that performs a reconstruction procedure, parity datagram creation unit 37 that performs a parity datagram creation procedure, and “parity datagram transmission request” that performs a “parity datagram transmission request” reception procedure Request "a receiving portion 38.

  The relay node 1 may be realized by causing a CPU, FPGA, PLD, or the like and a memory to function as each functional unit in the processing unit 30. In this case, the function of each functional unit may be realized by the CPU in the relay node 1 executing a computer program stored in a storage unit (not shown).

  The relay node 1 has the following switch function. The input interface units 10 a to 10 n are connected to the distribution server 2, the relay device 1, other routers, network switches, and the like, and receive sent datagrams. The input interface units 10a to 10n transfer datagrams other than the specific datagram described later to the switch unit 20. The switch unit 20 transfers the datagram to the output interface units 11a to 11n corresponding to the destination. The output interface units 11a to 11n transmit the datagram to the relay node 1, the receiving device 3, other routers, network switches, or the like.

  The relay node 1 is connected to the operation device 4 via the control unit input / output interface unit 50. The operation device 4 can set each relay node 1 and obtain operation information of each relay node 1 from each relay node 1. Using these functions, the operation device 4 sends a specific datagram to the detector 100 provided in the input interface units 10a to 10n and the datagram distribution unit (reference numeral 31 shown in FIG. 9) in the processing unit 30. Register the features. The specific datagram is a content datagram, a parity datagram, or a “parity datagram transmission request” datagram that is a target of data transfer according to the present invention. The registered features include, for example, a destination address, a port number (in the case of an IP packet), an FEC block number, and the like.

  The data transfer method according to the present embodiment includes a datagram distribution procedure, a content datagram storage / check procedure, a parity datagram transmission request procedure, a parity datagram check procedure, a lost content datagram reconstruction procedure, A content datagram transmission procedure, a content bit string reconfiguration procedure of the FEC block, a parity datagram creation procedure, and a “parity datagram transmission request” reception procedure.

  When the relay node 1A in FIG. 2 receives a predetermined specific datagram, it first performs a datagram distribution procedure.

  In the datagram distribution procedure, the input interface units 10 a to 10 n transfer the corresponding specific datagram to the processing unit 30 without transferring to the switch unit 20. The transferred datagram is further sorted by the datagram sorting unit 31 in the processing unit 30 into functional blocks serving as respective destinations.

  If the relay node 1A receives a content datagram GC which is one of the specific datagrams from a further upstream node (relay node 1 or distribution server 2), the datagram sorting unit 31 selects the corresponding datagram. The data is transferred to the content datagram storage / check unit 32 (S101 in FIG. 7).

  The content datagram storage / check unit 32 performs a content datagram storage / check procedure on the transferred content datagram GC. That is, the transferred content datagram GC is stored for each FEC block number described in the datagram. Further, for each FEC block number, for example, the presence or absence of a content datagram GC that could not be received is checked after a preset time has elapsed since the arrival of the first content datagram GC (S102).

  If there is (Yes in S102), a parity datagram transmission request procedure is performed. That is, it notifies the parity datagram transmission request unit 33 of the FEC block number and the number of content datagrams GC that could not be received. The same information is also notified to the parity datagram storage / check unit 34. The parity datagram transmission request unit 33 notified of the information outputs a “parity datagram transmission request” datagram directed to the nearest upstream relay node 1. The datagram is switched by the switch unit 20 and output from the output interface unit 11 to the network (S201).

  The immediately upstream upstream relay node 1 that has received the “parity datagram transmission request” datagram transmits the corresponding parity datagram GP (details will be described later). Receiving this, the relay node 1 transfers the parity datagram GP to the parity datagram storage / check unit 34 by the above-described datagram distribution procedure (S202).

  If the parity datagram storage / check unit 34 has not received the required number of parity datagrams GP after a predetermined time has elapsed (No in S203), the parity datagram transmission request procedure is performed again. I do. That is, the parity datagram storage / check unit 34 notifies the parity datagram transmission request unit 33 of the FEC block number of the content datagram GC that could not be received, the number of received data, and the like. The parity datagram transmission request unit 33 notified of the information outputs a “parity datagram transmission request” datagram directed to the nearest upstream relay node 1. The datagram is switched by the switch unit 20 and output from the output interface unit 11 to the network (S201). Thus, the parity datagram GP sent from the nearest upstream relay node 1 is transferred to the parity datagram storage / check unit 34 by the above-mentioned datagram distribution procedure, and again, the necessary number of parity datagrams GP Is received (S203).

  If the parity datagram storage / check unit 34 has received the required number of parity datagrams GP (Yes in S203), the parity datagram storage / check unit 34 indicates that with the corresponding FEC block number. The lost content datagram reconstruction unit 35 is notified, and all parity datagrams GP of the corresponding FEC block number are transferred to the lost content datagram reconstruction unit 35.

The lost content datagram reconstruction unit 35 that has received this notification and the parity datagram GP performs a lost content datagram reconstruction procedure. That is, the lost content datagram reconstruction unit 35 extracts the parity bit string PB from the parity datagram GP of the corresponding FEC block number, and erases the parity datagram GP (S204).
At the same time, the lost content datagram reconstructing unit 35 notifies the corresponding FEC block number to the content datagram storage / check unit 32, and all the corresponding FEC block numbers in the content datagram storage / check unit 32 are notified. The content datagram GC is transferred, and the divided bit string CB is extracted from the received content datagram GC (S205). Thereafter, in order to reduce the amount of memory used, the content datagram GC in the lost content datagram reconstruction unit 35 is immediately deleted.

Next, the lost content datagram reconstruction unit 35 restores the “lost divided bit string CB” by the parity calculation from the divided bit string CB and the parity bit string PB, and erases the parity bit string PB (S206).
Next, the lost content datagram reconstruction unit 35 reconstructs the content datagram GC from the restored divided bit string CB (S207).

  If there is no content datagram GC that could not be received by the content datagram storage / check unit 32 (No in S102), as a continuation of the content datagram storage / check procedure, the content datagram storage / check unit 32 The entire content datagram of the corresponding FEC block number is transferred to the lost content datagram reconstructing unit 35, and the lost content datagram reconstructing unit 35 performs the same process as S205 from the divided content bitgram CB from all the content datagrams GC. Is taken out (S103).

  The procedure up to S103 and S207 in FIG. 7 has been described above. In either case, next, the entire content datagram transmission procedure of S104 is performed. In this procedure, all content datagrams GC corresponding to the corresponding FEC block number are transferred to the switch unit 20 and transmitted to the nearest downstream relay node. All content datagrams GC in the processing unit 30 are immediately deleted after being transferred to the switch unit 20 in order to reduce the amount of memory used (S104).

  Next, the content bit string reconstruction procedure of the FEC block is performed. That is, the divided bit string CB of the corresponding FEC block held in the lost content datagram reconstruction unit 35 is transferred to the content bit string reconstruction unit 36 of the FEC block and reconfigured into the content bit string CF. After the transfer, the divided bit string CB of the corresponding FEC block held in the lost content datagram reconstruction unit 35 is immediately deleted in order to reduce the amount of memory used (S105).

  The content bit string CF reconstructed by the content bit string reconstruction unit 36 of the FEC block is transferred to the parity datagram creation unit 37, and the parity datagram creation unit 37 performs a parity datagram creation procedure. In other words, the parity datagram creation unit 37 creates a parity bit string PB, erases the original content bit string CF (S106), and creates a parity datagram GP from the parity bit string PB. The parity bit string PB is erased (S107). The created parity datagram GP is held for a preset time.

  If a datagram of “parity datagram transmission request” is sent from the nearest downstream relay node 1 or receiving device 3, the relay node 1 performs a “parity datagram transmission request” reception procedure. That is, the data is received by the input interface unit 10, transferred to the processing unit 30 so as to match the characteristics designated in advance by the detector 100, and input to the datagram distribution unit 31. The datagram is transferred to the “parity datagram transmission request” receiving unit 38 because it matches the characteristics specified in advance in the datagram distributing unit 31. As a result, the “parity datagram transmission request” receiving unit 38 has received the “parity datagram transmission request” datagram (Yes in S108), and notifies the parity datagram creating unit 37 of the corresponding FEC block number. The parity datagram GP is transmitted from the parity datagram creation unit 37 toward the nearest relay node 1 or receiving device 3 downstream (S109).

  If the "parity datagram transmission request" receiving unit 38 does not receive the "parity datagram transmission request" datagram (No in S108), a parity datagram is created if a preset holding time has elapsed. The parity datagram GP held in the unit 37 is deleted (S111).

  In FIG. 2, the parity datagram transmitted from the relay node 1A to the relay node 1B may correspond to all the lost datagrams created by the relay node 1A by the prior setting, or the relay node 1B. It may be a number corresponding to the number of lost datagrams received. By setting the number according to the number of lost datagrams, it is possible to transmit as many parity datagrams as necessary for restoration in the section between the relay node 1A and the relay node 1B.

  The relay node 1B functions as a downstream node while also functioning as an upstream node. That is, the relay node 1B creates a predetermined number of parity datagrams from the bit string of the received datagram, and prepares for a parity datagram transmission request from the nearest downstream relay node 1 (not shown). . In this case, since the transmitted parity datagram can be used as it is, if it is larger than the number of parity datagrams set in advance in the relay node 1, it is erased except for the necessary number. Can be created in preparation for a parity datagram transmission request from the nearest downstream relay node 1.

  As described above, when one or a plurality of relay nodes 1 provided in the network 0 receive a datagram of content designated in advance, the FEC parity bits are calculated and held in the relay node 1A. When a datagram loss is detected at the nearest downstream relay node 1B, the relay node 1A that is the nearest upstream relay node of the relay node 1B is requested to transmit a parity bit, and the relay node that has received the request 1A transmits the datagram of the held parity bit to the relay node 1B, and the relay node 1B receiving the datagram restores the lost datagram using the parity bit, and performs a series of operations of the distribution server 2 Between each relay node 1 and the receiving device 3. As a result, if the datagram loss is within a recoverable range, the receiving device 3 can receive content without loss.

  From the above, a large amount of parity datagram does not flow in an unnecessary place in the network 0. This not only improves the utilization efficiency of the network, but also improves that further datagram loss is caused by a large amount of parity datagrams. Further, since the parity bit is retransmitted instead of retransmitting the datagram, it is possible to distribute with a small memory capacity of the relay node.

[Second Embodiment]
A second embodiment will be described with reference to FIGS. 1, 2, and 9. This embodiment is the same as the first embodiment except for the following operations in the parity datagram creation procedure.

  The content datagram storage / check unit 32 in the processing unit 30 of the relay node 1B that detects the loss of the content datagram GC notifies the parity datagram transmission request unit 33. The parity datagram transmission request unit 33 embeds the degree of datagram loss when transmitting a parity datagram transmission request to the nearest relay node 1A upstream of the relay node 1B. The degree of datagram loss is a numerical value indicating the degree of datagram loss such as the number of datagram losses and the datagram loss rate.

  The “parity datagram transmission request” reception unit 38 in the processing unit 30 of the relay node 1A that has received the “parity datagram transmission request” notifies the parity datagram creation unit 37 of it. At this time, the “parity datagram transmission request” receiving unit 38 adjusts and notifies the number of parity datagrams to be transmitted or the amount of parity bits according to the degree of datagram loss represented by the numerical value. For example, the number of parity datagrams to be transmitted is determined and notified in accordance with a preset calculation rule or correspondence table.

  As described above, when the relay node 1B detecting the datagram loss requests the transmission of the parity datagram from the relay node 1A immediately upstream of the relay node, the relay node 1B embeds the degree of the datagram loss as some numerical value. The relay node 1A requested to transmit the parity datagram adjusts the number of parity datagrams to be transmitted or the amount of parity bits according to the degree of datagram loss represented by the numerical value.

  As a result, it is not necessary to send a large amount of FEC parity datagrams required when FEC is performed end-to-end, and the number of parity datagrams corresponding to the datagram loss can be sent in a necessary interval. Therefore, the load on the network can be greatly reduced. Also, since the number of parity datagrams held in the relay node 1A is usually smaller than the number of content datagrams, the amount of memory prepared in the relay node 1A can be reduced.

[Third Embodiment]
The third embodiment is the same as the first and second embodiments except that a Reed-Solomon code is used as an error correction code for calculating parity bits.

  The content datagram storage / check unit 32 in the processing unit 30 of the relay node 1B that detects the loss of the content datagram GC notifies the parity datagram transmission request unit 33. When the parity datagram transmission request unit 33 transmits a parity datagram transmission request to the nearest relay node 1A upstream of the relay node 1B, as described in the second embodiment, the degree of datagram loss Is embedded as, for example, the number N of datagram losses.

  Upon receiving this, the “parity datagram transmission request” receiving unit 38 in the processing unit 30 of the relay node 1A reads the datagram loss number N from the datagram of the parity datagram transmission request, and generates a parity datagram creating unit 37. Notify The parity datagram creation unit 37 extracts N data from the held Reed-Solomon code parity datagram GP and transfers them to the switch unit 20. These are switched by the switch unit 20 and transmitted from the output interface unit 11 toward the relay node 1B.

  When the Reed-Solomon code is used as the parity bit of FEC, the lost content datagram reconstructing unit 35 in the processing unit 30 of the relay node 1B can obtain the original data if the number of lost parity datagrams can be obtained. Can be restored.

  As described above, only the minimum number of parity datagrams necessary for restoration are transmitted between the relay nodes 1, and excessive parity datagrams as in the conventional FEC scheme are not transferred.

  For example, when transferring content using a long-distance high-speed transmission path in which datagram loss between all relay nodes is 8 or less for 248 content datagrams, content data in 248 datagrams On the other hand, if eight FEC parity datagrams using Reed-Solomon codes are created, the datagram loss between relay nodes is less than eight for 248 content datagrams. 100% content data restoration can always be performed using the parity bit of the FEC in the parity datagram.

  Thus, in preparation for a datagram transmission request from the relay node 1B that has detected a datagram loss between the relay nodes 1, in this application, parity data held in a memory (not shown) in the processing unit 30 of the relay node 1A. There are 8 grams. Comparison with the case of using TCP is difficult because of the influence of window size, etc., but considering the corresponding points, it is unclear which content datagram is lost, so all content datagrams, that is, 248 data The gram needs to be held in a memory (not shown) in the processing unit 30 of the relay node 1A. When a large number of contents are distributed in the network, this difference becomes even greater if the method of the present application is used instead of TCP.

[Fourth Embodiment]
In the fourth embodiment, a Low Density Parity Check code (hereinafter referred to as an LDPC code) or a kind of Low Density Generator Matrix code (hereinafter referred to as an LDGM code) is used as an error correction code for calculating a parity bit. Except for, it is the same as the first and second embodiments.

  The content datagram storage / check unit 32 in the processing unit 30 of the relay node 1B that detects the loss of the content datagram GC notifies the parity datagram transmission request unit 33. When the parity datagram transmission request unit 33 transmits a parity datagram transmission request to the nearest relay node 1A upstream of the relay node 1B, as described in the second embodiment, the degree of datagram loss Is embedded as a datagram loss rate R, for example.

  Upon receiving this, the “parity datagram transmission request” receiving unit 38 in the processing unit 30 of the relay node 1A reads the datagram loss number N from the datagram of the parity datagram transmission request, and generates a parity datagram creating unit 37. Notify The parity datagram creation unit 37 extracts M data corresponding to the datagram loss rate R from the parity datagram GP of the LDPC code or LDGM code that has been started and held simultaneously with the arrival of the datagram. Transfer to the switch unit 20. These are switched by the switch unit 20 and transmitted from the output interface unit 11 to the relay node 1B.

  When an LDGM code is used as an FEC parity bit, it cannot be uniquely stated because it varies depending on various conditions. For example, when the datagram loss rate R is 7%, the number is equivalent to 10% of the number of transmitted datagrams. Thus, the lost content datagram reconstruction unit 35 in the processing unit 30 of the relay node 1B can restore the original data with a probability close to 100%.

  In this way, only the minimum number of parity datagrams necessary for restoration are transmitted between the relay nodes 1, and excessive parity datagrams as in the conventional FEC scheme are not transferred.

  Further, each relay node 1 does not hold the transmitted content datagram GC for a certain period of time, but holds only a preset number of parity datagrams in the memory in the processing unit 30. Compared to the above, the amount of memory used can be reduced.

  In all the embodiments, in each relay node 1, the received content datagram GC of one FEC block is deleted as soon as it becomes unnecessary. Therefore, each content datagram GC of one FEC block is stored in the memory in the processing unit 30. It is held for a short time by shifting the time little by little. For this reason, the amount of memory actually used can be made smaller than “the amount of memory that holds the content datagram GC of one FEC block” × “the number of content datagrams GC of one FEC block”. The memory can be effectively used.

  The present invention relates to an end-to-end between a distribution server and a receiving apparatus that is currently being performed in real-time distribution or near real-time distribution of a large-capacity content that is considered to be performed more and more to a remote place such as the back side of the earth. It is possible to solve the problem that an unnecessary load is imposed on the network as a route by transferring a large amount of unnecessary FEC packets, which is unavoidable by the transfer of FEC, and is often criticized.

0: Network 1: Relay node 2: Distribution server 3: Reception device 4: Operation device 10: Input interface unit 11: Output interface unit 20: Switch unit 30: Processing unit 31: Datagram distribution unit 32: Content datagram storage Check unit 33: Parity datagram transmission request unit 34: Parity datagram storage / check unit 35: Lost content datagram reconstruction unit 36: Content bit string reconstruction unit 37 of FEC block: Parity datagram creation unit 38: “Parity data Gram transmission request "receiving unit 40: control unit 50: control unit input / output interface unit 100: detector

Claims (6)

A data transfer system in which a distribution server or an upstream node is connected to an upstream side of a network, and a downstream node or a receiving device is connected to a downstream side of the network,
The distribution server or upstream node is
A parity datagram transmission request receiving unit for receiving a parity datagram transmission request for requesting transmission of a parity datagram from the downstream node or the receiving device;
When a predetermined content datagram is received, a parity datagram for performing forward error correction of the content datagram is created and held using the content datagram, and notified from the parity datagram transmission request receiving unit A parity datagram creating unit that outputs a parity datagram corresponding to the parity datagram transmission request to be sent to the downstream node or a switch that transmits to the receiving device;
With
The downstream node or receiving device is:
A parity datagram transmission requesting unit for transmitting the parity datagram transmission request to the distribution server or the upstream node when a loss is detected in a predetermined content datagram from the distribution server or the upstream node;
When a parity datagram is received from the distribution server or upstream node, a lost content datagram reconstructing unit that reconstructs a lost content datagram using the received parity datagram;
Comprising
Data transfer system. The parity datagram transmission request unit transmits a numerical value indicating the degree of content datagram loss to the distribution server or upstream node in addition to the parity datagram transmission request,
The parity datagram transmission request receiving unit adjusts the amount of parity bits to be transmitted according to the degree of content datagram loss represented by the numerical value and notifies the parity datagram creation unit,
The data transfer system according to claim 1. The distribution server or upstream node is a distribution server that distributes content datagrams or a relay node that transfers the content datagrams to a receiving device,
The downstream node or receiving device is a relay node that transfers the content datagram toward the receiving device or a receiving device that receives the content datagram.
The data transfer system according to claim 1 or 2. A relay node that forwards a datagram from a delivery server or upstream node connected upstream to a downstream node or receiving device connected downstream;
A parity datagram transmission request receiving unit for receiving a parity datagram transmission request for requesting transmission of a parity datagram from the downstream node or the receiving device;
When a predetermined content datagram is received, a parity datagram for performing forward error correction of the content datagram is created and held using the content datagram, and notified from the parity datagram transmission request receiving unit A parity datagram creating unit that outputs a parity datagram corresponding to the parity datagram transmission request to be sent to the downstream node or a switch that transmits to the receiving device;
A relay node comprising: A relay node that forwards a datagram from a delivery server or upstream node connected upstream to a downstream node or receiving device connected downstream;
When a loss is detected in a predetermined content datagram from the distribution server or upstream node, a parity datagram transmission request for requesting transmission of a parity datagram for performing error correction of the content datagram is sent to the upstream node Or a parity datagram transmission request part to be transmitted to the receiving device;
When receiving a parity datagram from the distribution server or upstream node, a lost content datagram reconstructing unit for reconstructing a lost content datagram using the received parity datagram;
A relay node comprising: A data transfer method in a data transfer system in which a distribution server or an upstream node is connected to an upstream side of a network and a downstream node or a receiving device is connected to a downstream side of the network,
When the distribution server or upstream node receives a predetermined content datagram, a parity datagram that creates and holds a parity datagram for performing forward error correction of the content datagram using the content datagram Creation procedure and
Parity data to request transmission of a parity datagram held by the distribution server or upstream node when the downstream node or receiving device detects a loss in a predetermined content datagram from the distribution server or upstream node A parity datagram transmission request procedure for transmitting a grams transmission request to the distribution server or upstream node;
When the downstream node or the receiving device receives a parity datagram from the distribution server or the upstream node, a lost content datagram reconfiguration procedure for reconstructing a lost content datagram using the received parity datagram;
A data transfer method comprising:

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