JP2013046114A - Multicast secession control device and system and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent momentary concentration of load on a multicast device, significant delay in withdrawal processing, and refusal of new participation processing.SOLUTION: In the present invention, when a prior withdrawal request signal including a "scheduled withdrawal time" sent from a user terminal is received, information on the prior withdrawal request signal is stored in prior withdrawal information storage means, and the number of user terminals requiring withdrawal processing at the scheduled withdrawal time is calculated on the basis of the scheduled withdrawal time included in prior withdrawal request signals. And a scheduled execution time at which withdrawal processing will actually be executed on the basis of the number of the user terminals and the scheduled withdrawal time is determined, which is then stored in the prior withdrawal information storage means. At a given time, the prior withdrawal information storage means is referred to, and withdrawal processing corresponding to the scheduled execution time corresponding to the referenced time is executed.

Description

  The present invention relates to a multicast leave control apparatus, system, and method, and more particularly, to a multicast leave control apparatus, system, and method for a user terminal to leave a system that distributes a stream such as a video to many recipients by multicast.

  When distributing the same video or the like to a large number of user terminals, there is a multicast technique in which a copy is distributed to user terminals participating in a multicast group instead of being distributed to individual user terminals by unicast. This technique can reduce the number of streams transferred in the network.

  There are IGMP (Internet Group Management Protocol) (for example, refer to Non-Patent Document 1) and MLD (Multicast Listener Discovery) (for example, refer to Non-Patent Document 2) as procedures for managing participation and withdrawal from multicast. For example, MLDv2 (Multicast Listener Discovery Version 2) stipulates that a host (user terminal) sends a State Change Report to a multicast router (multicast device) when joining or leaving. This is defined as a process for each link.

  When there are a plurality of user terminals that want to receive the same multicast stream in the same link, the multicast device may flow one stream per link. In other words, there is no need to flow as many streams as the number of user terminals. On the other hand, when there are user terminals that want to receive the same multicast stream on different links, the multicast device needs to create a copy and flow the multicast stream on each link. Also, when a multicast device receives a withdrawal signal from a user terminal, transmission of the multicast stream to the link is stopped unless other user terminals of the user terminal receive the multicast stream on the same link. Can do. MLDv2 sends a query to the link every time the withdrawal State Change Report arrives at the multicast router in order to check whether there are any user terminals that have received the multicast stream on the same link. Yes.

  In a network of a large-scale communication carrier, many user terminals are accommodated in a multicast device, and the number of links to be processed in parallel is large. For this reason, in the environment of a large-scale telecommunications carrier, it is necessary to perform withdrawal processing on withdrawal request signals from a large number of user terminals.

  Hereinafter, video distribution such as a television program will be described as an example. However, the stream to be distributed is not limited to video, and any content such as audio, music distribution, data distribution, etc. may be used.

  The user can designate in advance which program is to be viewed on the user terminal based on a program guide EPG (Electronic Program Guide) distributed in advance to the user terminal. For example, it is possible to register in advance that the program A is viewed or recorded from 19:00 to 20:00. Furthermore, a plurality of programs can be registered in advance, such as viewing or recording program A from 19:00 to 20:00, and viewing or recording program B from 20:00 to 21:00.

  In the prior art, according to the reservation registration status on the user terminal, in the above example, the user terminal sends a participation signal for program A at 19:00, a withdrawal signal for program A at 20:00, a participation signal for program B, and a program at 21:00 A withdrawal signal for B was sent to the multicast device. Upon receiving these messages, the multicast device that receives the withdrawal signal performs processing immediately.

IETF RFC3376 Internet Group Management Protocol, Version 3. IETF RFC3810 Multicast Listener Discovery Version 2 (MLDv2) for IPv6.

  However, since TV programs and the like often start at the hour on the hour (0 minutes per hour, 30 minutes per hour) etc., withdrawal signals and participation signals are sent to the network all at the same time, A load may be instantaneously concentrated on a multicast device, resulting in a congestion state. In the conventional technique, when a large amount of withdrawal signals arrive at the multicast device and the multicast device is congested, there is a possibility that the actual processing is delayed or the participation processing for new participation cannot be performed.

  Further, when the withdrawal process for program A and the participation process for program A are continuously performed, for example, when the user terminal switches from one program A to another program B so as to switch the TV channel, the multicast device If the network is congested, in the network where the upper limit is set for the number of multicast streams, the order of withdrawal processing and participation processing is reversed, and new participation processing cannot be performed due to the upper limit on the number of streams, or the order must be observed. There is a possibility that the participation process is not performed until the withdrawal process is completed, and the implementation of the participation process is delayed and the program B can be viewed on the user terminal after the program starts.

  The present invention realizes sending a withdrawal signal in advance, performs withdrawal processing prior to the scheduled withdrawal time, and streamlines the query processing for the same link, so that the load is instantaneously concentrated on the multicast device. It is an object of the present invention to provide a multicast leaving control apparatus, system and method capable of preventing the withdrawal process from being greatly delayed and preventing the new joining process from being rejected.

In order to solve the above-described problem, the present invention (Claim 1) is a multicast leaving control device for performing leaving control of a user terminal in a system that distributes a stream such as a video to a number of recipients by multicast,
When receiving a prior withdrawal request signal transmitted from the user terminal and including withdrawal information and a desired withdrawal time (hereinafter referred to as “withdrawal time”), information on the prior withdrawal request signal is stored in advance withdrawal information. A prior withdrawal request signal requesting means stored in the means;
Based on the scheduled withdrawal time of the advance withdrawal request signal, the number of user terminals that require withdrawal processing at the scheduled withdrawal time is obtained, and the withdrawal processing is actually performed based on the number of user terminals and the scheduled withdrawal time A scheduled execution time determining means for determining a scheduled time and storing it in said advance withdrawal information storage means;
And a withdrawal execution means for performing withdrawal processing corresponding to the scheduled execution time corresponding to the time with reference to the advance withdrawal information storage means at an arbitrary time.

Moreover, the multicast leaving control apparatus of the present invention (Claim 2) is the execution scheduled time determination unit according to Claim 1,
When the advance withdrawal request signal specifies a withdrawal allowance time difference that is an acceptable time width for the scheduled withdrawal time, a time width that determines the scheduled execution time including the time width minus the scheduled execution time Including determination means,
The time width-scheduled execution time determining means is
When there are a plurality of advance withdrawal request signals including the time width,
Performing in advance from those of the withdrawal allowable time difference,
Decide the order at random,
The one with the earlier reception time of the prior withdrawal request signal is set to the scheduled execution time close to the scheduled withdrawal time, and the one with the later prior withdrawal request signal reception time is performed earlier in time.
To determine the scheduled execution time.

Further, in the multicast leaving control device of the present invention (Claim 3), in the execution scheduled time determination means of Claim 1 or 2,
The number P (P = M−L) obtained by subtracting the number L of advance withdrawal request signals for which the withdrawal allowance time difference is designated from the total number M of the advance withdrawal request signals exceeds a predetermined processable number N. A means for storing the time after the scheduled withdrawal time as the scheduled execution time in the advance withdrawal information storage means.

Moreover, the multicast leaving control device of the present invention (Claim 4) is the execution scheduled time determination means of Claim 3,
Means for determining the processable number N based on either or both of the number of signals that the multicast apparatus can process at a predetermined time, the number of withdrawal signals expected at the scheduled execution time, or both;

Moreover, the multicast leaving control apparatus of the present invention (Claim 5) is the above-mentioned scheduled item time determination means according to Claim 4,
Means for determining the scheduled execution time so as to preferentially execute the participation process from another user terminal;

In addition, the multicast leaving control apparatus of the present invention (Claim 6) is as follows.
Means for transmitting a query all at once in response to a prior withdrawal request signal from the same link.

The present invention (Claim 7) is a multicast system comprising a user terminal and a multicast leaving control device that performs leaving control of the user terminal, and distributes a stream such as a video to a number of recipients by multicast,
The user terminal is
Means for transmitting a prior withdrawal request signal including information on withdrawal and a time for which withdrawal is desired (hereinafter referred to as “scheduled withdrawal time”) to the multicast device;
The multicast leaving control device is:
Upon receipt of the advance withdrawal request signal from the user terminal, advance withdrawal request signal receiving means for storing information on the advance withdrawal request signal in advance withdrawal information storage means;
Based on the scheduled withdrawal time of the advance withdrawal request signal, the number of user terminals that require withdrawal processing at the scheduled withdrawal time is obtained, and the withdrawal processing is actually performed based on the number of user terminals and the scheduled withdrawal time A scheduled execution time determining means for determining a scheduled time and storing it in said advance withdrawal information storage means;
Withdrawing execution means for performing withdrawal processing corresponding to the scheduled execution time corresponding to the time with reference to the advance withdrawal information storage means at an arbitrary time;
Have

The present invention (Claim 8) comprises a multicast leaving control method in a multicast system comprising a user terminal and a multicast leaving control device for controlling the leaving of the user terminal, and delivering a stream such as video to a number of recipients by multicast. And
The user terminal is
Sending a previous withdrawal request signal including withdrawal information and a desired withdrawal time (hereinafter referred to as “withdrawal scheduled time”) to the multicast device,
The multicast leaving control device is:
When the advance withdrawal request signal receiving means receives the advance withdrawal request signal from the user terminal, the advance withdrawal request signal receiving step of storing information on the advance withdrawal request signal in the advance withdrawal information storage means;
The scheduled execution time determining means obtains the number of user terminals that require withdrawal processing of the scheduled withdrawal time based on the scheduled withdrawal time of the advance withdrawal request signal, and based on the number of user terminals and the scheduled withdrawal time A scheduled execution time determining step for determining a scheduled execution time for actually performing the withdrawal process, and storing it in the advance withdrawal information storage means;
A withdrawal execution step in which the withdrawal execution means refers to the preliminary withdrawal information storage means at an arbitrary time and performs a withdrawal process corresponding to the scheduled execution time corresponding to the time;
And
The scheduled execution time determination step includes:
When the advance withdrawal request signal specifies a withdrawal allowance time difference that is an acceptable time width for the scheduled withdrawal time, a time width that determines the scheduled execution time including the time width minus the scheduled execution time Including determination means,
The time width-scheduled execution time determining means is
When there are a plurality of advance withdrawal request signals including the time width,
Performing in advance from those of the withdrawal allowable time difference,
Decide the order at random,
The one with the earlier reception time of the prior withdrawal request signal is set to the scheduled execution time close to the scheduled withdrawal time, and the one with the later prior withdrawal request signal reception time is performed earlier in time.
To determine the scheduled execution time.

  As described above, according to the present invention, even when the withdrawal request signals are expected to be concentrated in time, congestion of the multicast device can be prevented by dispersing the withdrawal processing in the preceding and following times.

  Furthermore, due to congestion of the multicast device due to a large number of withdrawal request signals, the participation process is delayed for a new participation request from the user terminal, and the time during which the user terminal can actually receive the multicast stream distribution is delayed. This prevents the participation process from being executed.

It is a block diagram of the multicast apparatus in one embodiment of this invention. It is an example of holding information of the advance reservation information holding part in one embodiment of the present invention. It is a sequence chart of an outline operation in one embodiment of the present invention. It is a flowchart of the determination process of the scheduled execution time in one embodiment of this invention.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a configuration diagram of a multicast apparatus according to an embodiment of the present invention.

  Note that functions not directly related to the present invention are omitted. For example, a multicast device receives a stream distributed from a distribution source device and performs routing control related to the route, but these functions are not shown. Further, a state holding unit for storing the multicast state is also omitted, and there is multicasting.

  Participation / withdrawal is controlled between the user terminal 20 and the multicast terminal 10 shown in FIG.

  In the case of IP multicast technology, the multicast device 10 is a so-called last hop router. In the multicast device 10, there are a line correspondence unit 11, a copy unit 12, a control unit 13, and an advance reservation information holding unit 14.

  Similar to the conventional multicast technology, the user terminal 20 has a function of sending a withdrawal signal including a reservation time in addition to a function of sending a join / leave signal to the multicast device. This signal is called a prior withdrawal request signal.

  The line corresponding unit 11 is installed for each link, and has a function of monitoring a reception state from the link and a transmission state to the link and blocking those other than those permitted.

  The copy unit 12 performs copying in order to transmit the stream distributed from the upstream to the user terminal 20 through the designated line corresponding unit 11. Further, when all the user terminals 20 that have received the multicast stream on the link have withdrawn, copying can be stopped.

  FIG. 2 is an example of information held by the advance withdrawal information holding unit according to the embodiment of the present invention. The advance withdrawal information holding unit 14 holds information on the advance withdrawal request signal received from the user terminal 20 and information on the scheduled execution time determined by the control unit 13.

  The control unit 13 controls the copy unit 12 and the line corresponding unit 11 in accordance with the signal received from the user terminal 20, and the content of the advance withdrawal request signal is stored in the advance withdrawal information holding unit 14 when the advance withdrawal request signal is received. Write. Further, the control unit 13 determines the scheduled execution time and writes it in the advance withdrawal information holding unit 14. Further, the control unit 13 controls the copy unit 12 and the line corresponding unit 11 according to the information held in the advance withdrawal information holding unit 14.

  The user terminal 20 can send a prior withdrawal request signal to the multicast device 10 at a previous time depending on the time at which the user terminal actually wants to leave. For example, when there is a reservation in the program guide, the user terminal can send a prior withdrawal request signal carrying the program end time to the multicast device 10 before the program start time. Note that the user terminal 20 can send a withdrawal signal in addition to the prior withdrawal request signal, as in the prior art.

  In the advance withdrawal request signal, in addition to the same information elements as in the conventional technology such as which multicast group to join and from which source the multicast stream is received, the time at which withdrawal is desired (hereinafter referred to as “withdrawal scheduled time”) ). Furthermore, it may be specified how long the processing is allowed for the desired withdrawal time. Hereinafter, this time width is referred to as “withdrawal allowable time difference”.

  FIG. 3 is a flowchart of an outline operation in one embodiment of the present invention.

  Step 100) The user terminal 20 transmits a prior withdrawal request signal to the multicast device 10.

  Step 200) Upon receiving the advance withdrawal request signal, the control unit 13 of the multicast device 10 fills in the advance withdrawal information holding unit 14 with the user terminal ID, scheduled withdrawal time, allowable time difference, and multicast information. The multicast information includes a multicast group ID (equivalent to a multicast address in the IP multicast technology), a source ID (equivalent to a source address in the IP multicast technology), and the like.

  Step 300) Furthermore, the control unit 130 writes the advance withdrawal request signal reception time and the scheduled execution time determined by a method described later in the advance withdrawal information holding unit 14. In the description, for the sake of convenience, the advance withdrawal information holding unit 14 is represented as one table, but these pieces of information may be managed in a distributed manner.

  The control unit 13 searches the advance withdrawal information holding unit 14 for each scheduled withdrawal time, and grasps the number of user terminals that require withdrawal processing. This search operation may be performed periodically or by a timer corresponding to the scheduled withdrawal time. It is also possible to perform the search operation a plurality of times before the scheduled withdrawal time.

  Based on information on how many advance withdrawal request signals are received at each scheduled withdrawal time, the control unit 13 performs the withdrawal process for which advance withdrawal request signal at a time before and after the scheduled withdrawal time. To decide. This prevents the processing load on the multicast device 10 from peaking only at the scheduled withdrawal time. Furthermore, when determining the time for actually performing the withdrawal process in response to the prior withdrawal request signal, the predicted value of how many withdrawal signals will arrive at that time from the past data (the previous day, the previous week, etc.) up to that point You can also use it.

  The control unit 13 writes the determined time as the scheduled execution time for each preliminary withdrawal request signal for the scheduled withdrawal time held in the preliminary withdrawal information holding unit 14.

  Step 400) The control unit 13 searches the scheduled execution time of the advance reservation information holding unit 14, and performs the withdrawal process at that time. When a normal (not prior) withdrawal signal at that time is received, priority may be given to the withdrawal processing of the prior withdrawal request signal.

  Next, the execution time determination process in step 300 will be described.

  FIG. 4 is a flowchart of the process for determining the scheduled execution time according to the embodiment of the present invention.

  Step 301) The control unit 13 searches the advance reservation information holding unit 14 periodically at a predetermined time or by a timer.

  Step 302) The control unit 13 counts the number M of user terminals that desire the withdrawal process at a certain time from the data acquired from the advance reservation information holding unit 14.

  Step 303) If the number M of user terminals desiring withdrawal processing at a certain time exceeds a predetermined number N, the process proceeds to step 304; otherwise, the process proceeds to step 309.

  The predetermined number N may be determined with reference to, for example, the number K of signals that can be processed per second from the viewpoint of the processing capability of the multicast device 10. Furthermore, N may be determined with reference to information on the number of withdrawal signals predicted at that time.

Step 304) With respect to a request for which the withdrawal allowance time difference is designated, the withdrawal processing is started from the time before the designated time by the time width designated by the withdrawal allowance time difference. The control unit 13 determines the scheduled execution time and fills in the scheduled execution time of the advance reservation information holding unit 14. If you have more than one such request,
・ Prior to those with a large difference in withdrawal allowance time;
・ Randomly decide the order;
-For those with early withdrawal request signal reception time, the time close to the scheduled withdrawal time is set as the scheduled execution time, and those with late withdrawal request signal reception time are performed earlier in time;
Etc. can be adopted. Here, what is late in advance withdrawal request signal reception time is performed first in time, for example, about withdrawal at 20:00, user terminal A that received the advance withdrawal request signal at 19:30, If there is a user terminal B that has received a prior withdrawal request signal at 19:55, a time close to the original time (20:00) for the actual withdrawal processing of the user terminal A (for example, 19:59:55) ) As the scheduled execution time.

  Step 305) If it is difficult to perform advance withdrawal processing within the withdrawal allowance time difference for all requests for which the withdrawal allowance time difference is designated from the viewpoint of the processing capability of the multicast device 10, the multicast device 10 determines that the user terminal 20 However, it may be notified by a signal that it is impossible to carry out within the withdrawal allowable time difference. Alternatively, the multicast device 10 may notify the user terminal 20 by a signal of how much the withdrawal allowable time difference can be increased. Upon receiving such a signal, the user terminal 20 increases the withdrawal allowance time difference, selects whether to withdraw from the scheduled withdrawal time in advance or to withdraw after the scheduled withdrawal time, and again sends the advance withdrawal request signal to the multicast device. 10 can be sent. Thereafter, when the scheduled execution time is determined, the multicast apparatus 10 may notify the user terminal 20 of the scheduled time.

  (Step 306) Further, out of requests (the total number M) designating a certain time as a scheduled withdrawal time, a number P (P = ML) obtained by subtracting the number of requests L designating the withdrawal allowable time difference is a predetermined number N. If exceeded, the process proceeds to step 307, and if not exceeded, the process proceeds to step 308.

  Step 307) The time after the scheduled withdrawal time is entered in the scheduled execution time of the advance reservation information holding unit 14. When there are a plurality of such requests, it is possible to adopt a method such as determining the order at random or performing the participation process first in time from the one having the latest reservation signal reception time.

  Step 308) If P ≦ N in Step 306, enter the desired scheduled withdrawal time in the scheduled execution time for P pieces.

  Step 309) In step 303, if M ≦ N, the desired withdrawal scheduled time is entered in the scheduled execution time for M.

  In addition to the processing of the above-described embodiment, the control unit 13 performs the participation request processing for viewing a new multicast stream in preference to the withdrawal processing for the advance withdrawal request signal. It is possible to receive a stream and improve serviceability.

  Furthermore, when sending a query like MLDv2 to a withdrawal request signal from the same link, the control unit 13 sends a query to a plurality of withdrawal request signals for the same withdrawal scheduled time at a time. It is also possible to reduce the number of query transmissions.

  The operation of each component of the multicast device 10 in FIG. 1 described above can be constructed as a program and installed in a computer used as the multicast device, or distributed via a network.

  The present invention is not limited to the above-described embodiments, and various modifications and applications can be made within the scope of the claims.

10 Multicast Device 11 Line Corresponding Unit 12 Copying Unit 13 Control Unit 14 Advance Reservation Information Holding Unit 20 User Terminal

Claims (8)

In a system that distributes a stream such as a video to a large number of recipients by multicast, a multicast leave control device that performs user terminal release control,
When receiving a prior withdrawal request signal transmitted from the user terminal and including withdrawal information and a desired withdrawal time (hereinafter referred to as “withdrawal time”), information on the prior withdrawal request signal is stored in advance withdrawal information. A prior withdrawal request signal receiving means stored in the means;
Based on the scheduled withdrawal time of the advance withdrawal request signal, the number of user terminals that require withdrawal processing at the scheduled withdrawal time is obtained, and the withdrawal processing is actually performed based on the number of user terminals and the scheduled withdrawal time A scheduled execution time determining means for determining a scheduled time and storing it in said advance withdrawal information storage means;
Withdrawing execution means for performing withdrawal processing corresponding to the scheduled execution time corresponding to the time with reference to the advance withdrawal information storage means at an arbitrary time;
A multicast leaving control device comprising: The execution scheduled time determining means is
When the advance withdrawal request signal specifies a withdrawal allowance time difference that is an acceptable time width for the scheduled withdrawal time, a time width that determines the scheduled execution time including the time width minus the scheduled execution time Including determination means,
The time width-scheduled execution time determining means is
When there are a plurality of advance withdrawal request signals including the time width,
Performing in advance from those of the withdrawal allowable time difference,
Decide the order at random,
The one with the earlier reception time of the prior withdrawal request signal is set to the scheduled execution time close to the scheduled withdrawal time, and the one with the later prior withdrawal request signal reception time is performed earlier in time.
The multicast leaving control apparatus according to claim 1, wherein the scheduled execution time is determined by any one of the following. The execution scheduled time determining means is
The number P (P = M−L) obtained by subtracting the number L of advance withdrawal request signals for which the withdrawal allowance time difference is designated from the total number M of the advance withdrawal request signals exceeds a predetermined processable number N. 3. The multicast leaving control device according to claim 1, further comprising means for storing, in the preliminary withdrawal information storage means, a time after the scheduled withdrawal time as the scheduled execution time. The execution scheduled time determining means is
4. The means for determining the processable number N based on either or both of the number of signals that can be processed by the multicast device at a predetermined time, the number of withdrawal signals expected at the scheduled execution time, or both. The multicast leaving control device described. The execution scheduled time determining means is
The multicast leaving control apparatus according to claim 4, further comprising means for determining the scheduled execution time so as to preferentially execute the participation process from another user terminal. The multicast leaving control apparatus according to claim 1, further comprising means for sending a query in a batch in response to a prior withdrawal request signal from the same link. A multicast system comprising a user terminal and a multicast leaving control device for controlling the leaving of the user terminal, and delivering a stream such as a video to a number of recipients by multicast,
The user terminal is
Means for transmitting a prior withdrawal request signal including information on withdrawal and a time for which withdrawal is desired (hereinafter referred to as “scheduled withdrawal time”) to the multicast device;
The multicast leaving control device is:
Upon receipt of the advance withdrawal request signal from the user terminal, advance withdrawal request signal receiving means for storing information on the advance withdrawal request signal in advance withdrawal information storage means;
Based on the scheduled withdrawal time of the advance withdrawal request signal, the number of user terminals that require withdrawal processing at the scheduled withdrawal time is obtained, and the withdrawal processing is actually performed based on the number of user terminals and the scheduled withdrawal time A scheduled execution time determining means for determining a scheduled time and storing it in said advance withdrawal information storage means;
Withdrawing execution means for performing withdrawal processing corresponding to the scheduled execution time corresponding to the time with reference to the advance withdrawal information storage means at an arbitrary time;
A multicast leaving control system comprising: There is a multicast leaving control method in a multicast system comprising a user terminal and a multicast leaving control device that performs leaving control of the user terminal, and distributes a stream such as video to a large number of recipients by multicast,
The user terminal is
Sending a previous withdrawal request signal including withdrawal information and a desired withdrawal time (hereinafter referred to as “withdrawal scheduled time”) to the multicast device,
The multicast leaving control device is:
When the advance withdrawal request signal receiving means receives the advance withdrawal request signal from the user terminal, the advance withdrawal request signal receiving step of storing information on the advance withdrawal request signal in the advance withdrawal information storage means;
The scheduled execution time determining means obtains the number of user terminals that require withdrawal processing of the scheduled withdrawal time based on the scheduled withdrawal time of the advance withdrawal request signal, and based on the number of user terminals and the scheduled withdrawal time A scheduled execution time determining step for determining a scheduled execution time for actually performing the withdrawal process, and storing it in the advance withdrawal information storage means;
A withdrawal execution step in which the withdrawal execution means refers to the preliminary withdrawal information storage means at an arbitrary time and performs a withdrawal process corresponding to the scheduled execution time corresponding to the time;
And
The scheduled execution time determination step includes:
When the advance withdrawal request signal specifies a withdrawal allowance time difference that is an acceptable time width for the scheduled withdrawal time, a time width that determines the scheduled execution time including the time width minus the scheduled execution time Including determination means,
The time width-scheduled execution time determining means is
When there are a plurality of advance withdrawal request signals including the time width,
Performing in advance from those of the withdrawal allowable time difference,
Decide the order at random,
The one with the earlier reception time of the prior withdrawal request signal is set to the scheduled execution time close to the scheduled withdrawal time, and the one with the later prior withdrawal request signal reception time is performed earlier in time.
The multicast leaving control method, wherein the scheduled execution time is determined by any of the above.

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