JP7474078B2 - Distribution server and program - Google Patents

Description

The present invention relates to a distribution server and a program.

In distribution using Internet Protocol (IP) multicast (IP multicast distribution), the sender only needs to send the data once, and communication devices along the route replicate and send the data only to routes with receivers, so it is generally known to be efficient for large-scale one-to-many distribution. For example, Patent Document 1 discloses an efficient content distribution method using multicast.

Multicast delivery uses UDP (User Datagram Protocol) as the upper protocol, so there is no guarantee that packets will arrive or arrive in what order. To ensure reliable delivery, error correction and retransmission control must be implemented independently at the application layer. For this reason, research is being conducted on versatile, highly reliable multicast (see, for example, Non-Patent Document 1). Highly reliable multicast using retransmission control aims to achieve highly efficient delivery by devising flow control, but most of these do not take into account the load on the retransmission server.

International Publication No. 2012/011449

Shibata, et al., "Evaluation of Reliable Multicast Communication Using Protocol Selection Methods," Transactions of Information Processing Society of Japan, Vol. 42, No. 12, pp. 3102-3111.

When using multicast for distribution, FEC (Forward Error Correction) is generally used, but the need to distribute additional FEC packets to recover packets reduces distribution efficiency. On the other hand, reliable multicast using ARQ (Automatic repeat-request) resends only lost packets, so there is no wasteful distribution. However, there is an issue that the load on the distribution server increases depending on the number of terminals and the packet loss rate of the transmission path.

In view of the above, the objective of the present invention is to provide a distribution server and program that can reduce the load.

A distribution server according to one embodiment is a distribution server that, upon receiving a retransmission request for a lost packet from a plurality of receiving devices, transmits a response packet corresponding to the retransmission request to each receiving device, wherein the retransmission request includes a multicast ID for identifying a multicast group, a sequential number for identifying a packet, and a rate control identification ID for identifying a delivery rate of the packet, and the distribution server is equipped with a response packet generation unit that generates a packet corresponding to the multicast ID and the sequential number as a response packet , and a delivery rate determination unit that calculates a ratio of a retransmission rate to an allowable delivery rate determined for each multicast ID as a load factor for transmitting the response packet, and determines a delivery rate of a multicast stream for each multicast ID and rate control identification ID based on the load factor.

Furthermore, in one embodiment, the delivery rate determination unit may determine the delivery rate to be a smaller value as the load factor increases.

Furthermore, in one embodiment, the system includes a transmission buffer that temporarily stores the response packets, a transmission buffer management unit that monitors the free space of the transmission buffer, and a request information management unit that counts the number of retransmission request packets requested for retransmission from the multiple receiving devices for each of the rate control identification ID and the multicast ID during the first time until a preset timer times out and a second time until the free space of the transmission buffer falls below a threshold, whichever is earlier, and the delivery rate determination unit may calculate the retransmission rate for each of the rate control identification ID and the multicast ID using the number of retransmission request packets.

In addition, the program according to one embodiment causes a computer to function as the distribution server.

The present invention provides a distribution server and program that can reduce the load.

1 is a diagram illustrating an overview of a distribution system according to an embodiment. FIG. 2 is a block diagram illustrating an example of the configuration of a distribution server according to an embodiment. 11 is a flowchart illustrating an example of a process performed by a distribution server according to an embodiment when a retransmission request is received. 11 is a flowchart illustrating an example of a process for determining a distribution rate of a distribution server according to an embodiment.

One embodiment of the present invention will be described in detail below with reference to the drawings.

Figure 1 is a diagram showing an overview of a distribution system 1 according to one embodiment. The distribution system 1 shown in Figure 1 includes a distribution server 30 and multiple receiving devices 40, each of which is connected to a network that supports multicast routing (multicast-compatible network). The distribution server 30 includes a retransmission server 10 and a content distribution server 20. For ease of explanation, the retransmission server 10 and the content distribution server 20 are shown separately in the drawing, but some or all of these may be configured as an integrated server.

The distribution system 1 is a system that performs highly reliable multicast distribution (e.g., IP multicast distribution) using unicast retransmission control from the receiving device 40 to the retransmission server 10.

The content distribution server 20 is a server that performs multicast distribution of content, and divides multiple multicast streams (e.g., IP multicast streams) into multicast packets (hereinafter simply referred to as "packets") for distribution. The content distribution server 20 adds a multicast ID (MCID) for identifying the multicast group, a sequential number (s) for identifying the packet, and a rate control identification ID (d) for identifying the packet distribution rate to each packet, and distributes them to the receiving device 40.

The receiving device 40 is a terminal capable of multicast reception, and receives packets from the content distribution server 20. The receiving device 40 determines the packet order and packet loss based on the sequential number. When the receiving device 40 detects packet loss, it notifies the retransmission server 10 of a retransmission request that includes the multicast ID, sequential number, and rate control identification ID of the detected lost packet.

When the retransmission server 10 receives a retransmission request from the receiving device 40, it generates a response packet corresponding to the retransmission request and transmits it to the receiving device 40.

The retransmission server 10 also calculates the load rate (LR) of the retransmission server 10 for each multicast group from the retransmission rate (RSBR) that varies depending on the retransmission request from the receiving device 40. The retransmission server 10 then calculates the delivery rate (BR) of the content distribution server 20 for each multicast group based on the load rate, and notifies the content distribution server 20 of delivery rate information including the delivery rate, multicast ID, and rate control identification ID. The retransmission server 10 can know for which delivery rate packet loss occurred by the rate control identification ID, and can accurately calculate the load rate for each delivery rate. The retransmission server 10 also prevents the transmission buffer from collapsing by monitoring the free space in the transmission buffer. Details of the processing of the retransmission server 10 will be described later.

When the content distribution server 20 receives the distribution rate information from the retransmission server 10, it increments the rate control identification ID. Then, the content distribution server 20 dynamically switches the distribution rate of the specified multicast group to the specified distribution rate based on the distribution rate information.

(Configuration of retransmission server)
Next, a description will be given of the configuration of the retransmission server 10. Fig. 2 is a block diagram showing an example of the configuration of the retransmission server 10. The retransmission server 10 shown in Fig. 2 includes a retransmission request receiving unit 11, a request information managing unit 12, a response packet generating unit 13, a timer managing unit 14, a transmission buffer 15, a transmission buffer managing unit 16, a delivery rate determining unit 17, a response packet transmitting unit 18, and a delivery rate transmitting unit 19.

The retransmission request receiving unit 11 receives a retransmission request from the receiving device 40 and outputs it to the request information management unit 12.

The request information management unit 12 obtains the multicast ID, sequential number, and rate control identification ID from the retransmission request and outputs them to the response packet generation unit 13, and also outputs the rate control identification ID to the timer management unit 14.

When the rate control identification ID is updated, the request information management unit 12 resets the counter and counts the number of retransmission request packets (Rnum) requested from all receiving devices 40 until the rate control identification ID is next updated. The request information management unit 12 outputs the counted number of retransmission request packets to the delivery rate determination unit 17. As described below, when the earlier of the measured time t between the time T1 until the timer times out and the time T2 until the buffer amount of the transmission buffer 15 exceeds the threshold has elapsed, the delivery rate of the content delivery server 20 is determined and the content delivery server 20 updates the rate control identification ID.

The response packet generator 13 holds in advance a correspondence table showing data corresponding to a multicast ID and a sequential number, and identifies the data corresponding to the multicast ID and the sequential number included in the retransmission request from the receiving device 40 based on the correspondence table. The response packet generator 13 then obtains the corresponding data from a storage unit (not shown), adds the sequential number as a header, generates a response packet, and outputs it to the transmission buffer 15.

The transmission buffer 15 temporarily stores the response packets generated by the response packet generator 13.

The response packet transmission unit 18 retrieves the response packet from the transmission buffer 15 and transmits it to the receiving device 40 that has requested retransmission of the packet.

The transmission buffer management unit 16 monitors the free space in the transmission buffer 15, and when the free space falls below a threshold (the utilization rate is equal to or greater than the threshold), it notifies the delivery rate determination unit 17 of a buffer saturation event, which indicates that the utilization rate of the transmission buffer 15 is high.

When the rate control identification ID is changed, the timer management unit 14 sets the timer time T1 (e.g., 30 seconds). When the timer time T1 has elapsed, the timer management unit 14 outputs a timer firing event indicating that the timer time T1 has elapsed to the delivery rate determination unit 17. In addition, the timer management unit 14 notifies the delivery rate determination unit 17 of information indicating the elapsed time from the time the timer was set (the time the rate control identification ID was changed).

The delivery rate determination unit 17 determines the delivery rate of the multicast stream for each multicast ID and rate control identification ID based on the load rate related to the transmission of the response packets (the load rate calculated from the retransmission rate required to transmit the response packets). For example, the delivery rate determination unit 17 calculates the load rate (LR) of the retransmission server 10 for each multicast group from the retransmission rate (RSBR) required to transmit the response packets. Then, based on the load rate, the delivery rate determination unit 17 calculates the delivery rate (BR) of packets for each multicast ID transmitted by the content distribution server 20, and outputs it to the delivery rate transmission unit 19. A specific example of the calculation of the load rate and delivery rate is described below. The variables used here are shown in the table below.

The request information management unit 12 counts the number of retransmission request packets Rnum requested for retransmission from all receiving devices 40 for each rate control identification ID and multicast ID during the measurement time t until the rate control identification ID is updated (i.e., the earlier of the time T1 until the set timer times out or the time T2 from the time the timer is set until the free space in the transmission buffer 15 falls below the threshold).Then, the delivery rate determination unit 17 uses the number of retransmission request packets Rnum to calculate the retransmission rate RSBR required to transmit a response packet for each rate control identification ID and multicast ID using the following formula (1).

Next, the delivery rate determination unit 17 calculates the ratio of the retransmission rate RSBR to the allowable delivery rate MAX_RSBR defined for each multicast ID as the load rate LR of the retransmission server 10, as shown in the following formula (2).

Next, the delivery rate determination unit 17 sets the delivery rate BR based on the load rate LR. For example, as shown in the following formula (3), the delivery rate BR is set to a smaller value as the load rate LR increases. Formula (3) is an example of a formula for linearly lowering the delivery rate BR according to the load rate LR, but the delivery rate BR may be non-linearly lowered according to the load rate LR, or the delivery rate BR may be determined using other variables shown in Table 1. Note that the delivery rate BR does not exceed the maximum value MAX_BR of the delivery rate of the multicast stream. In this way, when the load rate LR of the retransmission server 10 is large, it is possible to reduce the number of lost packets per unit time of the receiving device 40 by lowering the delivery rate BR of the content distribution server 20.

The delivery rate transmission unit 19 notifies the content delivery server 20 of the delivery rate determined by the delivery rate determination unit 17 and the delivery rate information including the multicast ID.

When the content distribution server 20 receives the distribution rate information from the retransmission server 10, it increments the rate control identification ID. Then, the content distribution server 20 dynamically switches the distribution rate of the specified multicast group to the specified distribution rate based on the distribution rate information. This makes it possible to adjust the load on the retransmission server 10 for each multicast group.

The allowable delivery rate MAX_RSBR(MCID) of the retransmission server 10 can be set for each multicast group. For example, if there are two multicast groups with MCID=A and B, by setting MAX_RSBR(A) > MAX_RSBR(B), it becomes possible to preferentially allocate the resources of the retransmission server 10 to the multicast group with MCID=A. However, it is necessary to set it so that MAX_RSBR(A) + MAX_RSBR(B) does not exceed the delivery performance of the retransmission server 10.

(Processing when a resend request is received)
Next, the process performed by the retransmission server 10 when a retransmission request is received will be described with reference to Fig. 3. Fig. 3 is a flow chart showing an example of the process that occurs each time the retransmission server 10 receives request information.

In step S101, the retransmission request receiving unit 11 receives a retransmission request from the receiving device 40.

In step S102, the request information management unit 12 analyzes the retransmission request and detects the multicast ID (MCID), sequential number (s), and rate control identification ID (d).

In step S103, the response packet transmitting unit 18 transmits to the receiving device 40 a response packet corresponding to the packet requested for retransmission by the receiving device 40.

In step S104, the timer management unit 14 compares Lastd, which is the rate control identification ID currently being measured, with the rate control identification ID detected in step S102. The initial value of Lastd is set to -1. If the rate control identification ID is incremented so that d>Lastd, the process proceeds to step S107; otherwise, the process proceeds to step S105.

In step S105, the request information management unit 12 determines whether the rate control identification ID currently being measured, Lastd, matches the rate control identification ID detected in step S102. If d<Lastd, nothing is done, and if d=Lastd, the process proceeds to step S106.

In step S106, the request information management unit 12 increments the number of retransmission request packets Rnum.

In step S107, the timer management unit 14 sets the timer time T1 and starts measuring the elapsed time from the time the timer was set to the current time.

In step S108, the request information management unit 12 updates Lastd by substituting the latest rate control identification ID that will start measuring the number of retransmission request packets.

(Decision process of distribution rate)
Next, the process of determining the delivery rate by the retransmission server 10 will be described with reference to Fig. 4. Fig. 4 is a flow chart showing an example of the process of determining the delivery rate by the retransmission server 10.

In step S201, the delivery rate determination unit 17 detects a timer firing event indicating that the timer time set in step S107 in FIG. 3 has elapsed, or a buffer saturation event indicating that the utilization rate of the transmission buffer 15 is high. That is, when the timer time T1 has elapsed, or when the time T2 from the time the timer was set until the free space in the transmission buffer 15 becomes equal to or less than the threshold has elapsed, the delivery rate determination unit 17 advances the process to step S202.

In step S202, the delivery rate determination unit 17 calculates the load rate using the above formulas (1) and (2).

In step S203, the delivery rate determination unit 17 calculates the delivery rate using the above formula (3).

In step S204, the delivery rate transmission unit 19 notifies the content delivery server 20 of delivery rate information including the delivery rate and the multicast ID.

As described above, when the receiving device 40 receives a packet from the content distribution server 20 and detects a lost packet, it transmits a retransmission request including a multicast ID, a sequential number, and a rate control identification ID to the retransmission server 10. When the retransmission server 10 receives a retransmission request from the receiving device 40, it generates and transmits a response packet, and determines the delivery rate of the multicast stream for each multicast ID and rate control identification ID based on the load factor related to the transmission of the response packet (the load factor calculated from the retransmission rate required for the transmission of the response packet). With this configuration, according to the present invention, it is possible to realize multicast delivery while guaranteeing data arrival within limited resources for content that does not require real-time performance, such as operating system updates. Furthermore, since flow control is performed not only based on the network status but also on the performance of the content distribution server 20, it is possible to prevent failure due to concentrated access to the retransmission server 10 caused by an increase in the number of receiving devices 40.

Furthermore, by feedback of packet loss from the receiving device 40, it becomes possible to maximize the multicast delivery rate within a range in which the retransmission server 10 does not fail. Furthermore, by combining the delivery rate determined by the retransmission server 10 as the maximum value with other highly reliable multicast flow control, it becomes possible to increase delivery efficiency while preventing the retransmission server 10 from failing.

In addition, in the present invention, by introducing a multicast ID for identifying a multicast group, an allowable delivery rate can be set for each multicast stream, and the retransmission server 10 calculates the ratio of the retransmission rate to the allowable delivery rate set for each multicast ID as the load factor. Therefore, according to the present invention, the resources of the retransmission server 10 can be allocated for each multicast group, making it possible to increase the delivery rate of content that is to be preferentially transmitted, for example.

(program)
The distribution server 30 (retransmission server 10 and content distribution server 20) may be a computer that stores a program describing the processing contents for realizing each function in a storage unit and reads and executes the program using a processor such as a CPU (Central Processing Unit) or a DSP (Digital Signal Processor). At least a part of the processing contents may be realized by hardware. For example, a program for functioning as the distribution server 30 includes the steps described in Figures 3 and 4 above.

The program may also be recorded on a computer-readable recording medium. Using such a recording medium, the program can be installed on a computer. Here, the recording medium on which the program is recorded may be a non-transient recording medium. The non-transient recording medium is not particularly limited, and may be, for example, a CD-ROM, DVD-ROM, or other recording medium. The program may also be provided by downloading via a network.

The above-described embodiments have been described as representative examples, but it will be apparent to those skilled in the art that many modifications and substitutions can be made within the spirit and scope of the present invention. Therefore, the present invention should not be interpreted as being limited by the above-described embodiments, and various modifications and changes are possible without departing from the scope of the claims. For example, it is possible to combine multiple components or processing steps described in the embodiments into one, or to divide one into multiple components.

REFERENCE SIGNS LIST 1 distribution system 10 retransmission server 11 retransmission request receiving unit 12 request information management unit 13 response packet generating unit 14 timer management unit 15 transmission buffer 16 transmission buffer management unit 17 distribution rate determining unit 18 response packet transmitting unit 19 distribution rate transmitting unit 20 content distribution server 30 distribution server 40 receiving device

Claims (4)

A distribution server that, upon receiving a retransmission request for a lost packet from a plurality of receiving devices, transmits a response packet corresponding to the retransmission request to each of the receiving devices,
the retransmission request includes a multicast ID for identifying a multicast group, a sequential number for identifying a packet, and a rate control ID for identifying a delivery rate of the packet;
a response packet generating unit that generates a packet corresponding to the multicast ID and the sequential number as a response packet;
a delivery rate determination unit that calculates a ratio of a retransmission rate to an allowable delivery rate determined for each of the multicast IDs as a load factor related to the transmission of the response packets, and determines a delivery rate of a multicast stream for each of the multicast IDs and the rate control IDs based on the load factor;
A distribution server comprising: The delivery server according to claim 1, wherein the delivery rate determination unit determines the delivery rate to be a smaller value as the load factor increases. a transmission buffer for temporarily storing the response packet;
a transmission buffer management unit that monitors the free space of the transmission buffer;
a request information management unit that counts the number of retransmission request packets requested for retransmission from the plurality of receiving devices for each of the rate control identification ID and the multicast ID during an earlier period of a first period until a preset timer times out and a second period until an available capacity of a transmission buffer becomes equal to or less than a threshold,
3. The delivery server according to claim 1, wherein the delivery rate determination unit calculates the retransmission rate for each of the rate control identification IDs and the multicast IDs by using the number of retransmission request packets. A program for causing a computer to function as the distribution server according to any one of claims 1 to 3 .

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