JP5592235B2 - Multicast pre-delivery method, system, and apparatus - Google Patents

Description

  The present invention relates to a multicast pre-distribution technique, and more particularly to a loss compensation technique for compensating for loss of pre-distribution content when the pre-distribution content distributed to a user is lost.

  Many Internet Service Providers (ISPs) have positioned Video On Demand as a killer service that differentiates their network services, such as movies and TV dramas. The company is focusing on popularizing VoD services that deliver high-quality video content (rich contents) produced by content production companies.

In general, viewing of moving image content tends to concentrate at night, and fluctuates greatly with a cycle of one day. In order for ISPs to improve profits and provide VoD services to users at low cost, reducing server load during peak hours is a major issue. In addition, since rich content has a large capacity, it is also important to suppress the influence of traffic generated by distribution on the network (NW).
Various methods for reducing the server load at the peak time have been studied and put into practical use, and can be classified mainly into multicast (MC) distribution and peer-to-peer (P2P) type distribution.

  MC distribution is to distribute to a plurality of users who requested the same content in a single distribution session using the MC distribution tree, and a reduction in server load can be expected in proportion to the improvement in user aggregation. . However, in order to increase the degree of user aggregation, it is necessary to wait for distribution without immediately starting distribution in response to a distribution request. For this reason, the immediacy of distribution is impaired, the waiting time from when the user requests distribution until the distribution is actually started increases, and the service quality deteriorates.

  On the other hand, a P2P type distribution system such as BitTorrent (registered trademark) that realizes content distribution by exchanging content held between users is widely spread. Conventionally, it has been used for the purpose of exchanging UGC (User Generated Contents), but in recent years, P2P distribution technology is also used as a means for distributing rich contents. However, there is a possibility that the user may leave the system in the middle of distribution, and it is necessary to use a measure for continuing distribution such as switching the connection destination to another peer. As for MC distribution, in order to support VCR (Video Cassette Recorder) operations such as playback and stop, complicated processing for dynamically switching distribution sessions is required.

  By the way, the increase in the downlink capacity of the access line is remarkable, and an environment in which a sufficiently large band can be used compared with the reproduction rate of rich content is becoming common. For this reason, in addition to the normal delivery that is delivered from the delivery server on demand to the user's delivery request, the unused transmission capacity is utilized, and the content is constantly delivered regardless of the user's delivery request, It is effective to store in an installed set top box (STB). Content distribution performed regardless of the user's distribution request is called pre-distribution.

  That is, when the requested content is already stored in the STB by the prior distribution when the user requests distribution, distribution from the distribution server can be avoided, and the load at the peak of the distribution server and NW can be reduced. Furthermore, when delivering to an STB regardless of the user's delivery request, the ISP can freely set the delivery content and delivery timing, so the same content is broadcast to all users (BC: Broadcast) delivery. By doing so, it is possible to suppress the load that pre-distribution gives to the distribution server and NW.

  Therefore, the inventors have proposed a BC pre-distribution method as a distribution method in the VoD service (see, for example, Non-Patent Document 1). In this BC pre-distribution method, unlike the P2P type distribution, since the content cached in the STB is viewed only by the user who owns each STB, there is no need to give the user an incentive to upload the content to other users. When viewing the pre-distributed content, no traffic is generated in the NW, so that it is possible to expect a reduction in the NW load in addition to the peak server load. Furthermore, it can easily cope with VCR operations.

  By the way, when distributing video content on the Internet, even if the transmission bandwidth is secured for each distribution session by session admission control, congestion occurs temporarily in the transit router due to burstiness of packet arrival, and transmission Packets can be lost. In general, the compression rate of large-capacity rich content is high, and viewing quality may be greatly degraded even when a small number of packet losses occur. Therefore, it is necessary to recover lost packets by some method. In the case of unicast (UC: Unicast) distribution that distributes to a single user from a single server, the receiving side includes the information of the lost packet in the NACK packet and sends it to the transmitting side, and the transmitting side only receives the lost packet. ARQ (Automatic Repeat Request) is widely used.

  It is conceivable to use ARQ in MC pre-distribution. When the STB (receiving host) detects a packet loss, it again requests the distribution server (transmitting host) to retransmit the packet using a NACK packet. The retransmission packet is MC-delivered to all STBs regardless of the STB in which the corresponding packet is actually lost. When a retransmission packet is lost, the same packet is repeatedly delivered to the MC until all STBs have been successfully received.

In addition, by dividing the transfer data into fixed-length blocks, a redundant packet is generated on the transmission side in advance for each block, and transmitted together with the data packet, so that it is retransmitted even when packet loss occurs Forward error correction (FEC) that makes it possible to recover lost packets on the receiving side without failure has been studied as a loss compensation method in MC distribution.
The method using FEC is further classified into Proactive FEC and Reactive FEC. The outline of each method will be described below (see, for example, Non-Patent Document 2).

[Proactive FEC]
Originally, in environments such as satellite links where the transmission path environment is poor, the bit error rate is high, and the increase in delay time caused by retransmission is long, the FEC redundant bits are added to the data on the transmission side. FEC has been studied as a technique for enabling error compensation without re-transmission even when a bit error occurs through transmission. However, in recent years, an application as a technique that enables recovery of a lost packet that is retransmitted even when a packet is lost during transmission by generating and transmitting an FEC redundant packet on the transmission side is seen. Here, it is considered that such Proactive FEC is applied to MC pre-distribution.

  Data is divided into blocks composed of k packets, and nk FEC redundant packets are generated using Reed-Solomon codes for each block. The distribution server MC distributes n packets obtained by adding FEC redundant packets to the original data to all STBs. If the STB can receive any k or more packets out of n packets in each block, the STB can restore the k data packets constituting the block. That is, when the number of lost packets in each block is nk or less, retransmission from the distribution server can be avoided. When the number of lost packets is n−k + 1 or more, the block cannot be restored even if FEC is used, so the block is retransmitted.

[Reactive FEC]
In the above-described Proactive FEC, MC packets are always delivered to all receiving hosts for each block, and therefore, especially when the number of lost packets is small, many FEC redundant packets are wasted. . In response to such a problem, a reactive FEC that delivers a necessary number of FEC redundant packets only when packet loss occurs has been proposed for MC delivery. Here, it is considered that Reactive FEC is applied to MC pre-distribution.

  Similar to Proactive FEC, the distribution server divides data into blocks composed of k packets and generates nk redundant packets for each block. However, unlike Proactive FEC, at the time of initial delivery, only k packets, which are original data, are delivered to each block by MC. Each STB examines the received packet and notifies the distribution server of the number of packets lost in each block by a NACK packet. The distribution server MC distributes the FEC redundant packets generated in advance to all STBs by the number corresponding to the maximum value of the number of lost packets notified from each STB to each block.

  As a result, the STB that still has a large number of lost packets and cannot restore the block even if the FEC redundant packet is used, also notifies the distribution server of the number of redundant packets necessary for the restoration using the NACK packet. Such a process is repeated until all STBs can restore the blocks. If there are STBs that cannot restore the blocks even after the distribution of nk redundant packets, k blocks are again obtained in units of blocks. Retransmit all data packets.

  In the block restoration using FEC, if the number of received packets is k or more, it is possible to restore the block regardless of which packet these packets are. Therefore, even when packets lost between STBs are different, all STBs can restore blocks by distributing the same FEC redundant packets with the maximum number of lost packets to all STBs. As described above, since the reactive FEC distributes the minimum number of redundant packets required for block restoration after the fact, it is possible to reduce the number of distribution packets as compared with the proactive FEC.

“Broadcast pre-distribution in VoD service”, IEICE Technical Report NS2009-1563. D. Li and D. Cheriton, “Evaluating the Utility of FECwith Reliable Multicast,” IEEE ICNP 99.

  However, such a conventional technique has a problem in that it is extremely inefficient when compensating for loss of pre-distributed content distributed to users in multicast pre-distribution.

In other words, when ARQ is used for MC distribution, a large number of NACKs may be transmitted from a large number of receiving hosts to the transmitting host. On the other hand, the same packet is retransmitted, which is very inefficient.
On the other hand, since FEC is being studied for cases where the bit error rate is high and packets are lost with a high probability, such as in a wireless environment, transfer of redundant packets when used on a wired network with a low packet loss rate. There is concern about the deterioration of transfer efficiency.

  In the MC pre-distribution method, a large amount of content is pre-distributed to the STB regardless of the user's viewing request, so the content actually viewed by the user is a small part of the pre-distributed content, and the STB is cached. The cache hit rate is as low as 0.2% to 0.5%. Accordingly, since the content that needs loss compensation is a very small part of the content that is actually viewed, it is extremely inefficient to perform loss compensation for all the pre-delivered content.

  The present invention has been made to solve such problems, and an object of the present invention is to provide a multicast pre-distribution technique capable of efficiently compensating for loss of pre-distributed contents distributed to users.

In order to achieve such an object, according to the multicast pre-distribution method of the present invention, a pre-distribution content selected by the pre-distribution unit of the multicast pre-distribution device from a plurality of stored contents is determined in advance. based on a pre-distribution step of distributing in multicast to a plurality of the user device via a communications network, pre delivery reception section of the user device, is distributed from the multicast pre distribution device via the communication network A pre-delivery reception step for receiving and storing the pre-delivery content, and a loss inspection for inspecting whether or not the pre-delivery content is lost when the loss inspection unit of each user device plays back the pre-delivery content stored. Step and the retransmission request unit of each user side device according to the loss detection of the pre-delivery content by the loss inspection unit A retransmission request step for notifying the multicast pre-distribution device of a retransmission request designating the missing data corresponding to the loss, and the missing data distribution unit of the multicast pre-distribution device is received from any user-side device among the user-side devices. In response to the retransmission request, the missing data distribution step of acquiring the missing data from the pre-delivery content specified in the retransmission request and distributing it to the retransmission requesting user side device via the communication network, and each user side device A loss compensation unit that receives the missing data distributed from the multicast pre-distribution device in response to the retransmission request and compensates for the loss of the stored pre-delivery content based on the missing data. comprising, in prepositioned step, when delivering pre-positioned content, loss complement based on Proactive FEC In this case, the total number of packets of the pre-delivery content is B, the number of original packets constituting each FEC coding block is k, the number of all packets constituting each FEC coding block is n, and the pre-delivery content Is U and the probability that the FEC encoded block cannot be recovered by the loss compensation control is E _BL , for loss compensation of each FEC encoded block obtained by the following equation (4). In this example , the minimum number of transfer packets F _pro (k) required for the above is used.

According to another multicast pre-distribution method of the present invention, a pre-distribution unit of a multicast pre-distribution device selects a pre-distribution content selected from a plurality of stored contents based on a predetermined distribution schedule. A pre-distribution step of multicast distribution to a plurality of user-side devices via a network, and a pre-distribution receiving unit of each user-side device receives and stores the pre-distributed content distributed from the multicast pre-distribution device via the communication network A pre-delivery reception step, a loss inspection unit of each user side device, when reproducing the stored pre-delivery content, a loss inspection step of inspecting the presence or absence of the pre-delivery content, When the retransmission request unit detects the loss of the pre-distributed content by the loss inspection unit, the retransmission request unit A retransmission request step for notifying a multicast pre-distribution device of a retransmission request designating data, and a missing data distribution unit of the multicast pre-distribution device in response to a retransmission request from any user-side device among user-side devices, The missing data distribution step of acquiring missing data from the pre-distributed content specified in the retransmission request and distributing it to the user side device of the retransmission request via the communication network by unicast, and the loss compensation unit of each user side device, A loss compensation step of receiving lost data distributed from the multicast pre-distribution device in response to the retransmission request and compensating for the loss of the stored pre-delivery content based on the missing data, , When distributing pre-distributed content, distribute with loss compensation control based on Reactive FEC, The total number of packets of pre-delivery content is B, the number of original packets constituting each FEC coding block is k, the number of all packets constituting each FEC coding block is n, and the number of user-side devices that deliver the pre-delivery content U, the probability that the FEC encoded block cannot be recovered by loss compensation control _BL When the probability that the maximum number of lost packets at the time of initial delivery is j is Q (j), the transfer required for loss compensation of each FEC encoded block, which is obtained by equation (7) described later Number of packets increased F _rea (K) is such that the minimum k is used.

At this time, in the retransmission request step, a plurality of different losses detected in the loss inspection step may be notified to the multicast pre-distribution device by one retransmission request.

Also, the multicast pre-distribution system according to the present invention distributes pre-delivery content selected from a plurality of stored contents to a plurality of user-side devices via a communication network based on a predetermined distribution schedule. Based on a re-transmission request from the pre-delivery unit and any one of the user-side devices, the missing data is acquired from the pre-delivery content and is transmitted to the user-side device that is the retransmission request source via the communication network. A multicast pre-distribution device including a missing data distribution unit for distribution by casting, a pre-distribution reception unit for receiving and storing pre-distribution content distributed from the multicast pre-distribution device via a communication network, and A loss inspection unit that inspects whether or not the pre-delivery content is lost when playing the pre-delivery content; In response to detection of loss of pre-distributed content by the loss checking unit, a retransmission request unit that notifies the multicast pre-distribution device of a retransmission request specifying missing data corresponding to the loss, and distribution from the multicast pre-distribution device in response to the retransmission request A plurality of user-side devices including a loss compensator that compensates for loss of stored pre-delivery content based on the missing data, and pre-delivery in the pre-delivery step When distributing content, it is distributed by loss compensation control based on Proactive FEC. At this time, the total number of packets of the pre-distributed content is B, the number of original packets constituting each FEC encoded block is k, and each FEC encoded block is N is the number of all the packets that make up, U is the number of user side devices that deliver pre-delivery content, and FE When the probability that the encoded block can not be recovered by the loss compensation control and E _BL, determined by Equation (4) described later, the transfer packet increase in the number F _pro (k required for the loss compensation of each FEC coding block ) Is the minimum k.

Another multicast pre-distribution system according to the present invention multicasts pre-distribution content selected from a plurality of stored contents to a plurality of user side devices via a communication network based on a predetermined distribution schedule. The user side device that obtains the missing data from the pre-delivery content based on the retransmission request from the user side device among the user side device and the pre-distribution unit that distributes in the user side device, via the communication network A multicast pre-distribution device comprising a missing data distribution unit for unicast distribution, a pre-distribution reception unit for receiving and storing pre-distribution content distributed from the multicast pre-distribution device via a communication network, Loss inspection unit that inspects the presence or absence of loss of pre-delivered content when playing pre-delivered content A retransmission request unit for notifying the multicast pre-distribution device of a retransmission request designating missing data corresponding to the loss in response to detection of loss of the pre-delivery content by the loss inspection unit, and a multicast pre-distribution device in response to the retransmission request A plurality of user-side devices including a loss compensation unit that receives the delivered missing data and compensates for the loss of the stored pre-delivered content based on the missing data. When distributing the distribution content, the distribution is performed by loss compensation control based on Reactive FEC. At this time, the total number of packets of the pre-distribution content is B, the number of original packets constituting each FEC encoded block is k, and each FEC encoded block N is the number of all packets that make up the content, U is the number of user side devices that deliver pre-delivery content, Block the loss compensation control E the probability that can not be recovered by _BL, when the maximum value of the number of lost packets during first run was probability and the Q (j) is a j, given by Equation (7) described below, each FEC The transfer packet increase number F _rea (k) required for the loss compensation of the coding block is used so that k is minimized.

At this time, the retransmission request unit may notify the multicast pre-distribution device of a plurality of different losses detected by the loss inspection unit by one retransmission request.

The multicast pre-distribution device according to the present invention distributes pre-distribution content selected from a plurality of accumulated contents to a plurality of user-side devices via a communication network based on a predetermined distribution schedule. Based on a re-transmission request from the pre-delivery unit and any one of the user-side devices, the missing data is acquired from the pre-delivery content and is transmitted to the user-side device that is the retransmission request source via the communication network. A loss data distribution unit that distributes by casting, and when distributing the pre-distributed content in the pre-distribution step, the distribution is performed by loss compensation control based on Proactive FEC. At this time, the total number of packets of the pre-distributed content is B, The number of original packets that make up the FEC coding block is k, and all of the FEC coding blocks When n is the number of packets, U is the number of user-side devices that distribute pre-distributed content, and E _BL is the probability that the FEC-encoded block cannot be recovered by loss compensation control, The transfer packet increase number F _pro (k) necessary for loss compensation of the FEC encoded block is used to minimize k.

Further, another multicast pre-distribution device according to the present invention multicasts pre-delivery content selected from a plurality of stored content to a plurality of user-side devices via a communication network based on a predetermined distribution schedule. The user side device that obtains the missing data from the pre-delivery content based on the retransmission request from the user side device among the user side device and the pre-distribution unit that distributes in the user side device, via the communication network A unicast-delivered data distribution unit. When the pre-distribution content is distributed by the pre-distribution unit, the pre-distribution content is distributed by loss compensation control based on Reactive FEC. , K is the number of original packets making up each FEC coding block, and all packets making up each FEC coding block. N is the number of packets, U is the number of user-side devices that deliver pre-delivery content, E _{BL is} the probability that the FEC-encoded block cannot be recovered by loss compensation control, and the maximum number of lost packets at the time of initial delivery is j When a certain probability is defined as Q (j), the transfer packet increase number F _rea (k) required for loss compensation of each FEC coding block, which is obtained by Expression (7) described later, is minimized. Is used.

According to the present invention, the missing data exchanged between the multicast pre-distribution device and the user-side device is limited to the pre-delivery content that has actually been requested to be reproduced. Data exchange can be omitted, and loss compensation for pre-delivered content can be performed very efficiently.
Moreover, since the missing data exchanged between the multicast pre-distribution device and the user-side device is limited to the user-side device that actually reproduces the pre-delivery content, Exchanges can be omitted, and loss compensation for pre-delivered contents can be performed very efficiently.

It is a block diagram which shows the structure of the multicast pre-distribution system concerning this Embodiment. It is a sequence diagram which shows operation | movement of a multicast pre-delivery system. It is a graph which shows the change of the transfer packet increase number with respect to the parameter k in Proactive FEC. It is a graph which shows the change of the transfer packet increase number with respect to the parameter k in Reactive FEC. It is explanatory drawing which shows the optimal value of the number of FEC redundant packets with respect to a packet loss rate. It is a graph which shows the change of the transfer total time ratio with respect to a packet loss rate. It is a graph which shows the change of the number of NACK packets with respect to a packet loss rate. It is a graph which shows the change of NW load with respect to a packet loss rate. It is a graph which shows the change of NW load with respect to a packet loss rate (NACK consideration).

Next, an embodiment of the present invention will be described with reference to the drawings.
[Multicast pre-distribution system]
First, a multicast pre-distribution system according to this embodiment of the present invention will be described with reference to FIG. FIG. 1 is a block diagram showing a configuration of a multicast pre-distribution system according to the present embodiment.

  This multicast pre-distribution system 1 sends pre-distribution contents such as popular contents selected from pre-stored contents to a plurality of user-side devices 20 connected via a communication network 30 such as the Internet. This is a system that distributes by multicast via the communication network 30 based on a predetermined distribution schedule.

  In the conventional multicast pre-distribution method, since a large amount of content is pre-distributed to the STB regardless of the user's viewing request, the content actually viewed by the user is a small part of the pre-distributed content, and the STB is cached. The cache hit rate is as low as 0.2% to 0.5%. On the other hand, the content that requires loss compensation is a very small part of the content that is actually viewed, and it is not necessary to perform loss compensation for all the pre-delivered content.

From this point of view, the present invention does not perform loss compensation control for missing data at the time of multicast pre-delivery, and at the timing when the user views the pre-delivered content, the lost packet of the corresponding content is unified to the requesting user. It is intended to be delivered by casting.
Since the retransmitted packet is distributed by unicast, the traffic flowing in the NW and the load on the multicast predistribution device 10 increase compared to the case of distributing the retransmitted packet and the FEC redundant packet by multicast, but the packet is actually viewed. By retransmitting a lost packet for only the content to be processed, a reduction in the amount of traffic required for loss compensation is expected.

  That is, according to the present embodiment, the multicast pre-distribution device 10 distributes the selected pre-distribution content to a plurality of user-side devices based on the distribution schedule without performing loss compensation control for missing data, When the pre-delivery content received from the multicast pre-distribution device 10 and stored in the side device 20 is reproduced, the pre-delivery content is checked for loss, and the loss data corresponding to the loss is detected according to the loss detection. Is transmitted to the multicast pre-distribution device 10, and the multicast pre-distribution device 10 acquires missing data from the specified pre-distribution content in response to the retransmission request from any user-side device 20. Unicast to the user side device 20 that is the retransmission request source. In the user device 20, based on the missing data received from the multicast prepositioning device in response to a retransmission request, it is obtained so as to compensate for the loss of pre-positioned content that has been saved.

[Multicast pre-distribution device]
Next, with reference to FIG. 1, the structure of the multicast pre-distribution apparatus 10 used with the multicast pre-distribution system 1 concerning this Embodiment is demonstrated.
The multicast pre-distribution device 10 includes an information processing device such as a server device as a whole, and a content storage unit 11, a pre-distribution unit 12, and a missing data distribution unit 13 are provided as main functional units.

The content storage unit 11 includes a storage device such as a hard disk, and has a function of storing a plurality of contents such as movies and TV dramas in advance.
The pre-distribution unit 12 transmits the pre-distribution content selected from each content stored in the content storage unit 11 to the plurality of user devices 20 via the communication network 30 based on a predetermined distribution schedule. It has a function to distribute by multicast without performing loss compensation control for. Note that the multicast distribution protocol without performing loss compensation control for missing data is the same as that used in the conventional content distribution system that distributes the above-mentioned content in real time.

  In response to a retransmission request from any one of the user side devices 20 received via the communication network 30, the missing data distribution unit 13 pre-loads the content storage unit 11 specified by the retransmission request. A function of acquiring the missing data specified in the retransmission request from the distribution content, and a function of distributing the acquired missing data to the user apparatus 20 as a retransmission request source via the communication network 30 by unicast. ing.

  The multicast pre-distribution apparatus 10 is provided with a data communication function and an arithmetic processing function that are provided in a general information processing apparatus. The pre-distribution unit 12 and the missing data distribution unit 13 may be realized by these data communication functions and arithmetic processing functions.

[User equipment]
Next, the configuration of the user side device 20 used in the multicast pre-distribution system 1 according to the present embodiment will be described with reference to FIG.
The user side device 20 is composed of a set top box (STB), a combination of STB and a content playback device such as a TV or a personal computer, or a content playback device including an ST _P function. As shown, a pre-delivery reception unit 21, a content storage unit 22, a content reproduction unit 23, a loss inspection unit 24, a retransmission request unit 25, and a loss compensation unit 26 are provided.

The pre-delivery reception unit 21 has a function of receiving pre-delivery content distributed by multicast from the multicast pre-distribution device 10 via the communication network 30 and storing it in the content storage unit 22.
The content storage unit 22 includes a storage device such as a hard disk or a semiconductor memory, and has a function of storing the pre-distributed content received by the pre-distribution receiving unit 21.
The content reproduction unit 23 has a function of reading and reproducing the pre-distributed content designated from the content storage unit 22 in the user's reproduction request operation.

  When reproducing the pre-distributed content stored in the content storage unit 22, the loss inspection unit 24 reads the pre-distributed content to be reproduced from the content storage unit 22 and determines whether or not the data constituting the pre-distributed content is lost. Has a function to inspect.

  When the loss inspection unit 24 detects a loss of data from the pre-delivery content, the retransmission request unit 25 sends a retransmission request designating missing data corresponding to the loss to the multicast pre-distribution device 10 via the communication network 30. It has a function to notify.

  The loss compensator 26 receives the missing data distributed from the multicast pre-distribution device 10 in response to the retransmission request notified from the retransmission request unit 25 via the communication network 30, and the content based on the missing data. Among the pre-distributed contents stored in the storage unit 22, it has a function of compensating for the loss of the pre-distributed contents to be reproduced.

  The user side device 20 is provided with a data communication function and an arithmetic processing function provided in a general STB or content reproduction device. The pre-distribution receiving unit 21, the content reproduction unit 23, the loss inspection unit 24, the retransmission request unit 25, and the loss compensation unit 26 may be realized by these data communication functions and arithmetic processing functions.

[Operation of this embodiment]
Next, the operation of the multicast pre-distribution system 1 according to the present embodiment will be described with reference to FIG. FIG. 2 is a sequence diagram showing the operation of the multicast pre-distribution system.

  The pre-distribution unit 12 of the multicast pre-distribution device 10 receives the pre-distribution content specified in the distribution schedule from each content stored in the content storage unit 11 when the distribution timing comes based on a predetermined distribution schedule. Select and distribute to the plurality of user devices 20 specified in the distribution schedule via the communication network 30 by multicast without performing loss compensation control on the missing data (step 100).

  In response to this, the pre-delivery reception unit 21 of the user-side device 20 receives the pre-delivery content distributed by multicast from the multicast pre-distribution device 10 via the communication network 30 and stores it in the content storage unit 22 ( Step 101). At this time, since loss compensation control is not performed on missing data, there is a possibility that the received pre-distributed content includes a loss.

Thereafter, in the user-side device 20, when the user requests the reproduction of the pre-distributed content, the loss detection unit 24 reads the pre-distributed content to be reproduced from the content storage unit 22 and configures the pre-distributed content. The presence or absence of loss is inspected (step 111).
If no data loss is found (step 112: NO), the content playback unit 23 reads the pre-delivery content to be played back from the content storage unit 22 and plays it back on the screen display device (step 117). .

  On the other hand, when a data loss is found (step 112: YES), the retransmission request unit 25 notifies the multicast pre-distribution apparatus 10 via the communication network 30 of a retransmission request specifying missing data corresponding to the found loss. (Step 113).

  The missing data distribution unit 13 of the multicast pre-distribution device 10 is designated by the retransmission request in response to the retransmission request from any of the user-side devices 20 received via the communication network 30. The missing data specified in the retransmission request is acquired from the pre-distributed content in the content storage unit 11 (step 114), and the acquired missing data is unicast to the user side device 20 that is the retransmission request source via the communication network 30. (Step 115).

The loss compensation unit 26 of the user-side device 20 receives the missing data distributed from the multicast pre-distribution device 10 in response to the retransmission request notified from the retransmission request unit 25 via the communication network 30, and based on this missing data. Thus, the loss of the pre-distributed content to be reproduced among the pre-distributed content stored in the content storage unit 22 is compensated (step 116).
Thereafter, the content playback unit 23 reads out the pre-delivery content to be played back that has been compensated for loss from the content storage unit 22 and plays it back on the screen display device (step 117).

[Effects of the present embodiment]
As described above, according to the present embodiment, the multicast pre-distribution device 10 distributes the selected pre-delivery content to the plurality of user-side devices based on the distribution schedule without performing loss compensation control for the missing data, Each user device 20 checks whether or not the pre-distributed content is lost when reproducing the pre-distributed content received and stored from the multicast pre-distributed device 10 and responds to the loss according to the loss detection. The multicast pre-distribution device 10 is notified of the retransmission request designating the missing data, and the multicast pre-distribution device 10 acquires the missing data from the designated pre-delivery content in response to the retransmission request from any of the user side devices 20 And unicast to the user side device 20 of the retransmission request source In the user device 20, based on the missing data received from the multicast prepositioning device in response to a retransmission request, it is obtained so as to compensate for the loss of pre-positioned content that has been saved.

As a result, the missing data exchanged between the multicast pre-distribution device 10 and the user-side device 20 is limited to the pre-delivery content that has actually been requested to be reproduced. Exchange can be omitted, and loss compensation for pre-delivered content can be performed very efficiently.
In addition, since the missing data exchanged between the multicast pre-distribution device 10 and the user-side device 20 is limited to the user-side device 20 that actually reproduces the pre-delivery content, Exchange of missing data can be omitted, and loss compensation for pre-delivered content can be performed very efficiently.

[Load on multicast pre-distribution device]
In the present embodiment, the total time T _RC during the log period required for the retransmission packet distributed from the multicast pre-distribution device 10 to the user side device 20 is the total distribution time T _P during the MC pre-distribution log period. The divided value is defined as φ _S. Φ _S is used as a measure for evaluating the load applied to multicast pre-distribution apparatus 10 in the present embodiment. When you define a η and utilization of pre-positioned content, η is the total Total viewer hours T _PV of pre-positioned content of all of the user during the log period, divided by the total total delivery time T _P of MC pre-positioned in the log period Is given as a value. Assuming that each user views content independently, when the number of users is U, T _RC = U _ηq T _P , so φ _S is obtained by the following equation (1).

[Load to NW]
In the present embodiment, the average value V _{RC of the} amount of retransmission packet traffic distributed from the multicast pre-distribution device 10 to the user-side device 20 flows through each link, and the traffic distributed by MC pre-distribution flows through each link The value divided by the average value V _P of the quantity is defined as φ _L. This embodiment is NW, i.e. using phi _L as a measure for evaluating the load applied to each link. When the total hop length via single packet if delivery to all users in MC and H _MC, the H _MC = N-1 from the N-1 pieces of link composing the MST. Also, assuming that the average hop length of the distribution flow at the time of UN distribution is H _UC , H _UC is the average hop length of the shortest hop route from the multicast pre-distribution device 10 to each other node, and is a unique value in each NW.

この際、Ｈ_UC＜Ｈ_MCであることから、φ_L＜φ_Sとなる。したがって、本実施の形態がＮＷに与える影響は、マルチキャスト事前配信装置１０に与える影響と比較して小さいことが分かる。 In addition, when a packet is transferred from the multicast pre-distribution apparatus 10 to any one node by UC, the average load applied to each link is H _UC / H _MC times the average load when it is distributed to all nodes by _MC. Therefore, V _RC = φ _S · H _UC / H _MC Therefore, φ _L is given by the following equation (2).

At this time, since H _UC <H _MC , φ _L <φ _S is satisfied. Therefore, it can be seen that the influence of the present embodiment on the NW is smaller than the influence on the multicast pre-distribution apparatus 10.

[Aggregation of lost packet information into NACK]
In the present embodiment, the retransmission request unit 25 of the user-side device 20 detects a plurality of different losses detected in the loss inspection unit 24 in the same pre-distributed content to the multicast pre-distribution device 10 by one retransmission request. You may make it notify.
In the conventional loss compensation method described above, loss compensation is performed for each packet or block when the packet or each block is delivered to the user side device 20, so that information on the lost packet is transmitted to the multicast pre-distribution device 10. In addition, a NACK is transmitted from each user side device 20 to the multicast pre-distribution device 10 for each packet or each block.

  On the other hand, in the present embodiment, in order to confirm the loss of data for the pre-distributed content in which the entire data has already been stored in the user-side device 20, and to notify the multicast pre-distributed device 10 of the loss, the pre-distributed content It is possible to aggregate information on packets lost for all the packets constituting the whole into a small number of NACK packets. Since header information is added to each NACK packet, a reduction in the amount of control traffic for loss compensation is expected by suppressing the number of NACK packets.

In the present embodiment, the amount of NACK packet data required for packet loss compensation of each content will be considered. When the number of packets constituting one content is Z, the position of each constituent packet can be expressed using a payload area of log ₂ Z bits. For example, in the commercial VoD service PowerInfo VoD system provided by China Telecom, the maximum content size is 2.5 Gbytes, and if the maximum packet size is 1,500 bytes, it corresponds to about 1.7 × 10 ⁶ packets. In this case, the position of each packet constituting each content can be expressed by 21 bits. Assuming that packet loss compensation is performed by the proposed method even for larger contents, it is assumed here that the position of each lost packet is expressed by a 4-byte payload area.

  Assuming that the size of the header area of the NACK packet is 28 bytes, when z packets are lost in the entire content, multicast is performed using c NACK packets obtained by a minimum integer (rounded up) that does not fall below z / 368. It is possible to transmit a lost packet to the pre-distribution apparatus 10, and the traffic amount caused by the NACK packet transfer for that purpose is 28c + 4z bytes.

[Performance evaluation]
Next, performance evaluation of the multicast pre-distribution system according to the present invention will be described.

[VoD access log data used for evaluation]
For the evaluation, access log data collected in a commercial VoD service PowerInfo VoD system provided by China Telecom was used. This log data includes all distribution requests for 20,921,657 that occurred in the seven months from June to December 2004. The total number of contents is 6,735 and the total number of users is 37,360. is there. The contents having a length of 45 minutes and 90 minutes each occupy about 40% of the total, and the average content length S is 3,510 seconds. The downlink capacity of the access line is set to A _d = 10 Mbps, and the content playback rate is set to R = 2 Mbps. γ = 4, MC pre-delivery rate is R _b = 8 Mbps, and the average number of MC pre-delivery contents per day is X = 98.46. A load equivalent to R _b / R = 4 UC distributions is always applied to the multicast pre-distribution apparatus 10 for MC pre-distribution.

[Design value in FEC]
In Proactive FEC, the problem is how to design FEC parameters, that is, n indicating the number of FEC encoded blocks and k indicating the number of original packets constituting each FEC encoded block. Regarding n, the greater the efficiency of FEC, the more the coding calculation amount for generating redundant packets increases. In this evaluation, n = 255 is set. For the design method of k, the following setting method is newly used.

Assume that each packet is independently lost with probability q. When n−k + 1 or more packets are lost in each block, the block cannot be recovered by FEC. Therefore, the probability E _BL that each block cannot be recovered by FEC is obtained by the following equation (3).

When the number of users is U, when there are one or more unrecoverable users among U users, the block is retransmitted. Therefore, if the probability of retransmitting each block is E, E = 1- (1-E _BL ) ^U If q is low, the probability that the same block will be repeatedly retransmitted more than once is small. Therefore, assuming that retransmission occurs at most once in each block, the increase in the number of transfer packets required for loss compensation of each block F _pro (k) is obtained by the following equation (4). However, in Formula (4), B is the total number of packets constituting the content. Here, a value that minimizes F _pro (k) is set as the value of k.

  On the other hand, the reactive FEC also has a problem of how to design the values of the FEC parameters n and k. For n, it is also set to n = 255. For k, the following setting method is used.

Similarly to the above, assuming that each packet is lost independently with probability q, the probability P (i) of losing i packets among k packets constituting each block at the time of initial delivery is Calculated in (5).

Further, when the number of users is U and the probability that the maximum number of lost packets at the time of initial delivery is j is Q (j), when j ≧ 1, the following equation (6) is obtained, and j In the case of = 0, Q (0) = {P (o)} ^U.

If q is low, the probability that the same block will be repeatedly retransmitted more than once is small. Therefore, assuming that retransmission occurs at most once in each block, the increase in the number of transfer packets required for loss compensation of each block F _rea (k) is expressed by the following equation (7). Here, a value that minimizes F _rea (k) is set as the value of k.

FIG. 3 is a graph showing a change in the number of transfer packets increased with respect to the parameter k in Proactive FEC. Here, the increase number F _pro (k) of transfer packets required for the loss compensation of each block calculated from the above-described equation (4) is plotted with respect to several values of k. FIG. 4 is a graph showing a change in the number of transfer packets increased with respect to the parameter k in Reactive FEC. Here, similarly to Reactive FEC, F _rea (k) calculated from the above-described equation (7) is plotted against k.

  In these FIGS. 3 and 4, n = 255 is set, and the number of users U is set to 37,360 users in the log data of PowerInfo VoD. Each of the four cases of packet loss rate q is plotted. As k increases and approaches n, the number of FEC redundant packets decreases and approaches zero.

As shown in FIG. 3, in the case of proactive FEC, in an area where the number of FEC redundant packets is large, the increase in the block retransmission probability due to the decrease in the number of redundant packets is small, so that F _pro (k ) Decreases, but in an area where the number of redundant packets is small, the block retransmission probability increases and the number of retransmission packets increases, so F _pro (k) increases rapidly. Therefore, F _pro (k) becomes a downwardly convex curve, and there exists an optimum value of k that minimizes F _pro (k).

  FIG. 5 is an explanatory diagram showing the optimum value of the number of FEC redundant packets with respect to the packet loss rate. Here, for Proactive FEC and Reactive FEC, the number of FEC redundant packets nk added to each block when k is set to an optimum value is shown. In the case of Proactive FEC, as the packet loss rate q decreases, the optimal value of k increases, and the optimal number of FEC redundant packets decreases.

On the other hand, as shown in FIG. 4, in the case of reactive FEC, FEC redundant packets are transferred only when packet loss actually occurs. Therefore, in an area where k is small and the number of redundant packets is large. F _rea (k) is almost independent of the value of k and is substantially constant. In an area where the number of redundant packets is small, the number of transferred redundant packets increases as k increases, and the probability that the entire block will be retransmitted without recovery by FEC increases, so F _rea (k) increases rapidly as k increases. To do. Therefore, when k is set to be equal to or less than the set value of k at which F _rea (k) is minimized, F _rea (k) is substantially constant regardless of the value of k. As shown in FIG. 5 described above, in the case of Reactive FEC as well, the optimal value of k increases and the optimal number of FEC redundant packets decreases as the packet loss rate q decreases. Note that the optimum value of the number of redundant packets in the same q is one value larger in the reactive FEC than in the reactive FEC.

[Simulation conditions]
In the CAIDA (Cooperative Association for Internet Data Analysis) web page, among the backbone NWs of commercial ISPs whose topologies and link capacities are disclosed, above. The net NW is used for evaluation. No regional bias in the demand for VoD service, distribution request ratio r _n generated from the node n is assumed to be consistent with the ratio p _n for population overall NW population node n accommodates accommodates.

In this simulation, the delivery destination node of each delivery session in the access log is randomly selected with a probability proportional to _pn . The delivery route in UC delivery is the shortest hop route, and when there are a plurality of shortest hop routes between the same nodes, one of them is selected at random. Also, a minimum tree (MST: Minimum Spanning Tree) rooted at the node where the distribution server is installed is configured using the Prime algorithm, and is used as a distribution path in MC pre-distribution.

また、全ての評価においてＭＣ事前配信されたコンテンツに対する損失補償のみを考えるものとし、非事前配信コンテンツに対するオンデマンドのＵＣ配信に対する損失補償は考えない。 The problem is in which node the distribution server is arranged. Here, the distribution server is arranged in a node where the average hop length of the distribution flow when the distribution server distributes by UC is minimum. That is, when h _ij is the shortest hop length from node i to node j, the average hop length H (i) weighted by the population ratio is given by the following equation (8), and this H (i The distribution server is installed at the node i where) is minimized.

Also, only loss compensation for MC pre-distributed content is considered in all evaluations, and loss compensation for on-demand UC distribution for non-pre-distributed content is not considered.

[Performance comparison]
Here, the load of the distribution server and NW that are increased for packet loss compensation control when the present invention is applied will be compared with the case where the above-described three methods are used. First, the load given to the distribution server (multicast pre-distribution device 10) by the packet loss compensation control is evaluated by φ _S. At this time, in the proposed method and ARQ, the ratio of the total time of the distribution server required to transfer the retransmission packet to the total time required for MC pre-distribution is φ _S. Further, in Proactive FEC and Reactive FEC, the ratio of the total time of the distribution server required for transferring the FEC redundant packet and the retransmission packet to the total time required for MC pre-distribution is φ _S.

FIG. 6 is a graph showing a change in the total transfer time ratio with respect to the packet loss rate. Here, φ _S in each of the four systems is plotted against the packet loss rate q. φ _S depends only on the access log data and is independent of the NW topology. In particular, when ARQ is used, retransmission occurs when packet loss occurs in at least one STB (user-side device 20). Therefore, when q is larger than about 10 ⁻⁴ , almost all packets are retransmitted. The efficiency is very bad.

  On the other hand, in the two FEC schemes, Reactive FEC that delivers only the necessary number of redundant packets shows better results than Proactive FEC. In an area where q is large, the effect of restoring lost packets using redundant packets is high, and the influence of the two FEC methods on the distribution server is small compared to the proposed method and ARQ. However, in a region where q is small, the proposed method that performs loss compensation only for content that is actually viewed has less influence on the distribution server than the two FEC methods.

  FIG. 7 is a graph showing changes in the number of NACK packets with respect to the packet loss rate. Here, the average number of NACK packets necessary for the STB to notify the distribution server of the packet loss is plotted against q per second. In Reactive FEC, the number of redundant packets to be transferred is suppressed, but at the time of initial distribution, the redundant packets are not sent and the block cannot be recovered by STB as in ARQ. Therefore, the number of transferred NACK packets is equal to ARQ. .

  On the other hand, Proactive FEC has a large number of redundant packets to be transferred, but can suppress the number of transferred NACK packets. According to the present invention, the number of NACKs can be reduced by two or more digits as compared with ARQ and Reactive FEC. Further, according to the present invention, since information on a plurality of lost packets can be aggregated into one NACK packet and transmitted to the distribution server, the number of generated NACKs is almost constant with respect to q.

Next, the load given to the NW by the packet loss compensation control is evaluated by φ _L. φ _L depends on the NW topology in addition to the access log data. FIG. 8 is a graph showing a change in NW load with respect to the packet loss rate. Here, φ _L when each method is applied to NW1 (above.net) is plotted against q. As is clear from comparison with FIG. 6 described above, φ _L when ARQ and two FECs are used is approximately equal to φ _S. This is because the data packet, redundant packet, and retransmission packet in the initial distribution in MC pre-distribution are all distributed on the same MC distribution tree.

On the other hand, φ _L when using the present invention is about an order of magnitude smaller than φ _S. In the proposed method, packets are distributed by MC at the time of initial distribution, whereas retransmission packets are retransmitted by UC only for the corresponding user, but UC distribution is the number of links used compared to MC distribution. This is because there are few. Therefore, from the viewpoint of link load, the superiority of the proposed method over other methods is greater.

Next, in addition to the FEC redundant packet and the retransmission packet, the NACK packet sent from the STB to the distribution server is also taken into consideration, thereby comparing all the traffic generated by the packet loss compensation control. Φ _L is defined as the ratio of the average value of the traffic volume generated in each link for these loss compensation controls over all links of each NW to the average value of the traffic volume generated in each link by MC pre-distribution. .
FIG. 9 is a graph showing a change in NW load (considering NACK) with respect to the packet loss rate. Here, Φ _L in consideration of the NACK packet when each method is used is plotted against q.

As shown in FIG. 7 described above, many NACK packets are generated when Reactive FEC is used, and Φ _L increases compared to φ _L. However, in the other three methods, the traffic amount of the NACK packet is increased. The influence is small compared to the traffic volume of redundant packets and retransmission packets, and Φ _L is almost equal to φ _L. Therefore, when q is large, the amount of traffic generated by loss compensation control in Reactive FEC is larger than that in Proactive FEC. The superiority of the proposed method over the other three methods is confirmed in the entire range of q evaluated.

[Extended embodiment]
The present invention has been described above with reference to the embodiments, but the present invention is not limited to the above embodiments. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.

  DESCRIPTION OF SYMBOLS 1 ... Multicast pre-delivery system, 10 ... Multicast pre-delivery apparatus, 11 ... Content storage part, 12 ... Pre-delivery part, 13 ... Missing data delivery part, 20 ... User side apparatus, 21 ... Pre-delivery reception part, 22 ... Content preservation | save , 23... Content reproduction unit, 24. Loss inspection unit, 25. Retransmission request unit, 26. Loss compensation unit, 30.

Claims (8)

The advance distribution unit of the multicast pre-distribution device distributes the pre-distribution content selected from the plurality of accumulated contents to the plurality of user-side devices via the communication network based on a predetermined distribution schedule in advance. A delivery step;
A pre-delivery reception step in which the pre-delivery reception unit of each user-side device receives and stores the pre-delivery content distributed from the multicast pre-distribution device via the communication network;
A loss inspection step of inspecting the presence or absence of loss of the pre-delivery content when the loss inspection unit of each user-side device reproduces the pre-delivery content stored,
The retransmission request unit of each user side device notifies the multicast pre-distribution device of a retransmission request specifying the missing data corresponding to the loss in response to the loss detection of the pre-distributed content by the loss inspection unit. A request step;
In response to the retransmission request from any of the user side devices, the missing data distribution unit of the multicast pre-distribution device receives the missing data from the pre-delivery content specified in the retransmission request. And the missing data distribution step of unicasting to the user side device of the retransmission request source via the communication network,
The loss compensation unit of each user side device receives the missing data delivered from the multicast pre-delivery device in response to the retransmission request, and based on the missing data, stores the pre-delivery content stored. A loss compensation step for compensating for the loss,
In the pre-distribution step, the pre-distribution content is distributed by loss compensation control based on Proactive FEC. At this time, the total number of packets of the pre-distribution content is set to B, and each FEC encoding block is configured. K is the number of original packets to be processed, n is the number of all packets constituting each FEC encoded block, U is the number of the user side devices that distribute the pre-distributed content, and the FEC encoded block is the loss compensation control. If the probability that cannot be recovered by EBL is E _BL ,

A multicast pre-distribution method characterized in that k is used that minimizes the number F _pro (k) of transfer packet increases required for loss compensation of each FEC encoded block obtained in step (1). The advance distribution unit of the multicast pre-distribution device distributes the pre-distribution content selected from the plurality of accumulated contents to the plurality of user-side devices via the communication network based on a predetermined distribution schedule in advance. A delivery step;
A pre-delivery reception step in which the pre-delivery reception unit of each user-side device receives and stores the pre-delivery content distributed from the multicast pre-distribution device via the communication network;
A loss inspection step of inspecting the presence or absence of loss of the pre-delivery content when the loss inspection unit of each user-side device reproduces the pre-delivery content stored,
The retransmission request unit of each user side device notifies the multicast pre-distribution device of a retransmission request specifying the missing data corresponding to the loss in response to the loss detection of the pre-distributed content by the loss inspection unit. A request step;
In response to the retransmission request from any of the user side devices, the missing data distribution unit of the multicast pre-distribution device receives the missing data from the pre-delivery content specified in the retransmission request. And the missing data distribution step of unicasting to the user side device of the retransmission request source via the communication network,
The loss compensation unit of each user side device receives the missing data delivered from the multicast pre-delivery device in response to the retransmission request, and based on the missing data, stores the pre-delivery content stored. A loss compensation step for compensating for the loss,
In the pre-distribution step, when distributing the pre-distribution content, the pre-distribution content is distributed by loss compensation control based on Reactive FEC. At this time, the total number of packets of the pre-distribution content is B, and each FEC coding block is configured. K is the number of original packets to be processed, n is the number of all packets constituting each FEC encoded block, U is the number of the user side devices that distribute the pre-distributed content, and the FEC encoded block is the loss compensation control. E _BL the probability that can not be recovered by, when the maximum value of the loss the number of packets at the time of the initial delivery was the probability that the j and Q (j), the following equation

A multicast pre-distribution method characterized in that k is used which minimizes the number of transfer packets increase F _rea (k) required for loss compensation of each FEC encoded block obtained in step (1). In the multicast pre-delivery method according to claim 1 or 2,
In the retransmission request step, the multicast pre-distribution method notifies the multicast pre-distribution device of a plurality of different losses detected in the loss check step by one retransmission request. A pre-distribution unit that multicasts pre-distribution content selected from a plurality of stored content to a plurality of user devices via a communication network based on a predetermined distribution schedule;
On the basis of the retransmission request from any of the user device of the user device, it acquires the pre-positioned content or al deficient data, the retransmission request source of the user device via the communication network A multicast pre-distribution device comprising a missing data distribution unit for unicast distribution;
A pre-delivery receiving unit that receives and stores pre-delivery content distributed from the multicast pre-distribution device via the communication network;
When playing back the pre-delivered content that has been stored, a loss inspection unit that inspects whether or not the pre-delivered content is lost;
In response to detection of loss of the pre-delivery content by the loss inspection unit, a retransmission request unit for notifying the multicast pre-distribution device of a retransmission request specifying missing data corresponding to the loss;
A plurality of loss compensation units that receive missing data delivered from the multicast pre-delivery device in response to the retransmission request and compensate for the loss of the pre-delivery content stored based on the missing data The user side device,
The pre-distribution unit distributes the pre-distribution content by loss compensation control based on Proactive FEC. At this time, the total number of packets of the pre-distribution content is B, and each FEC coding block is configured K is the number of original packets to be processed, n is the number of all packets constituting each FEC encoded block, U is the number of the user side devices that distribute the pre-distributed content, and the FEC encoded block is the loss compensation control. If the probability that cannot be recovered by EBL is E _BL ,

A multicast pre-distribution system, wherein k is used to minimize the number of transfer packet increases F _pro (k) required for loss compensation of each FEC encoded block obtained in step (1). A pre-distribution unit that multicasts pre-distribution content selected from a plurality of stored content to a plurality of user devices via a communication network based on a predetermined distribution schedule;
On the basis of the retransmission request from any of the user device of the user device, it acquires the pre-positioned content or al deficient data, the retransmission request source of the user device via the communication network A multicast pre-distribution device comprising a missing data distribution unit for unicast distribution;
A pre-delivery receiving unit that receives and stores pre-delivery content distributed from the multicast pre-distribution device via the communication network;
When playing back the pre-delivered content that has been stored, a loss inspection unit that inspects whether or not the pre-delivered content is lost;
In response to detection of loss of the pre-delivery content by the loss inspection unit, a retransmission request unit for notifying the multicast pre-distribution device of a retransmission request specifying missing data corresponding to the loss;
A plurality of loss compensation units that receive missing data delivered from the multicast pre-delivery device in response to the retransmission request and compensate for the loss of the pre-delivery content stored based on the missing data The user side device,
The pre-distribution unit distributes the pre-distribution content by loss compensation control based on Reactive FEC. At this time, the total number of packets of the pre-distribution content is B, and each FEC encoding block is configured. K is the number of original packets to be processed, n is the number of all packets constituting each FEC encoded block, U is the number of the user side devices that distribute the pre-distributed content, and the FEC encoded block is the loss compensation control. E _BL the probability that can not be recovered by, when the maximum value of the loss the number of packets at the time of the initial delivery was the probability that the j and Q (j), the following equation

A multicast pre-distribution system, wherein k is used to minimize the number of transfer packet increases F _rea (k) required for loss compensation of each FEC encoded block obtained in step (1). In the multicast pre-distribution system according to claim 4 or 5,
The retransmission request unit notifies the multicast pre-distribution device of a plurality of different losses detected by the loss inspection unit to the multicast pre-distribution device by one retransmission request. A pre-distribution unit that multicasts pre-distribution content selected from a plurality of stored content to a plurality of user devices via a communication network based on a predetermined distribution schedule;
On the basis of the retransmission request from any of the user device of the user device, it acquires the pre-positioned content or al deficient data, the retransmission request source of the user device via the communication network With a missing data delivery section that delivers by unicast,
The pre-distribution unit distributes the pre-distribution content by loss compensation control based on Proactive FEC. At this time, the total number of packets of the pre-distribution content is B, and each FEC coding block is configured K is the number of original packets to be processed, n is the number of all packets constituting each FEC encoded block, U is the number of the user side devices that distribute the pre-distributed content, and the FEC encoded block is the loss compensation control. If the probability that cannot be recovered by EBL is E _BL ,

A multicast pre-distribution apparatus, wherein k is used to minimize the transfer packet increase number F _pro (k) required for loss compensation of each FEC encoded block obtained in step (1). A pre-distribution unit that multicasts pre-distribution content selected from a plurality of stored content to a plurality of user devices via a communication network based on a predetermined distribution schedule;
On the basis of the retransmission request from any of the user device of the user device, it acquires the pre-positioned content or al deficient data, the retransmission request source of the user device via the communication network With a missing data delivery section that delivers by unicast,
The pre-distribution unit distributes the pre-distribution content by loss compensation control based on Reactive FEC. At this time, the total number of packets of the pre-distribution content is B, and each FEC encoding block is configured. K is the number of original packets to be processed, n is the number of all packets constituting each FEC encoded block, U is the number of the user side devices that distribute the pre-distributed content, and the FEC encoded block is the loss compensation control. E _BL the probability that can not be recovered by, when the maximum value of the loss the number of packets at the time of the initial delivery was the probability that the j and Q (j), the following equation

A multicast pre-distribution device characterized in that k is used to minimize the number of transfer packets increase F _rea (k) required to compensate for the loss of each FEC encoded block obtained in step (1).

Images