JP2006054695A - Method for determining number of multicast reception terminals, and multicast repeating apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for determining the number of multicast reception terminals for receiving multicast data without increasing a network load, and to provide a multicast repeating apparatus. <P>SOLUTION: A router 10 transmits a Membership Query including a timer upper-limit value. The receiving terminal 20 starts the timer with time that does not exceed the timer upper-limit value and is determined randomly according to uniform distribution as a timer value. The router 10 receives a Membership Report from the reception terminal 10 at first timer expiration. A response time calculator 13 of the router 10 calculates response time, and an average response time calculator 14 calculates the average value of the response time. A receiving terminal totallizer 15 for totallizing the number of receiving terminals totallizes the number of receiving terminals for receiving multicast data, based on the average value of response time and the timer upper-limit value. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a multicast reception terminal number determination method for determining the number of reception terminals that receive multicast data, and a multicast relay apparatus.

  Non-Patent Document 1 describes a multicast mechanism for distributing multicast data from a single data distribution device to a specific number of receiving terminals. In particular, regarding a communication mechanism between a receiving terminal (end host) and a router that relays data distribution to the receiving terminal, RFC3376 (IGMP (Internet Group Management Protocol)) or RFC2710 (MLD (Multicast Listener Discovery)) It is described in. IGMP is used in IP version 4 and MLD is used in IP version 6.

IGMP and MLD are communication protocols for examining whether or not there is a receiving terminal (member) that receives multicast data in a link to which a router is connected. Hereinafter, IGMP will be briefly described.
As shown in FIG. 3, in order to check whether or not a member exists in the link, the router multicasts a Membership Query to all receiving terminals in the link. At this time, the router sets information specifying the upper limit of the timer value (time until the timer expires) in the Membership Query.

  The receiving terminal is able to receive the multicast data by performing a predetermined procedure process for receiving the multicast data distributed via the multicast channel. Hereinafter, the fact that the receiving terminal is “in a state where it can receive multicast data” is referred to as “receiving a multicast channel”. A multicast channel is a one-to-many communication channel set between a router and a plurality of receiving terminals.

When each receiving terminal receives the Membership Query, as shown in FIG. 4, for each received multicast channel, a time randomly determined within the range from 0 (zero) to the timer upper limit value is used as a timer value. Start the timer held by the terminal itself.
When the time elapses, as shown in FIG. 5, the timer set with the minimum timer value among the timers associated with the specific multicast channel expires. The receiving terminal holding the timer multicast-transmits a Membership Report including identification information of the specific multicast channel to the router and the receiving terminal receiving the same specific multicast channel. Thus, the router knows that there is a receiving terminal that receives a specific multicast channel. On the other hand, other receiving terminals that have received the Membership Report stop the timer for the specific multicast channel. This prevents multiple Membership Reports from occurring for the same multicast channel.

The name of the message is the case of IGMP used in IP version 4. In the case of MLD used in IP version 6, Membership Query is read as Multicast Listener Query, and Membership Report is read as Multicast Listener Report.
Since the conventional multicast method uses the member existence confirmation method as described above, the router knows how many receiving terminals exist even if it knows that there are multicast receiving terminals. could not. For this reason, it was impossible to grasp how much demand there was for what information.
In order to solve such a problem, there is a technique for grasping the number of multicast receiving terminals. For example, Patent Document 1 describes the technical content of performing authentication processing each time a router receives a join request and a leave request from a receiving terminal and recording the number of receiving terminals.

Further, Patent Document 2 describes the technical content in which the information generation device measures the number of receiving terminals by transferring a special inquiry message to all routers and receiving a response of measurement results.
JP 2004-056584 A (paragraph 0055-, FIG. 4) JP 2004-165915 A (paragraphs 0042, 0043, FIG. 4, FIG. 9) By Thomas A. Maufer, translated by Hiroyuki Enomoto, “Introduction to IP Multicast”

However, in the techniques described in Patent Documents 1 and 2, each device needs to perform authentication processing and measurement processing, and processing load is applied. In addition, it is necessary to exchange a large number of messages between apparatuses accompanying the authentication process and the measurement process, which places a load on the communication line. As described above, when the techniques described in Patent Documents 1 and 2 are used, there is a problem that the network load increases.
The present invention has been made in view of the above points, and provides a multicast receiving terminal number determination method and a multicast relay apparatus that determine the number of receiving terminals that receive multicast data without increasing the network load. For the purpose.

In order to solve the above problem, the invention according to claim 1 is a multicast receiving terminal number determining method for determining the number of receiving terminals that receive multicast data transmitted from a multicast relay apparatus, wherein the multicast relay apparatus includes: A presence confirmation transmission step of transmitting a member presence confirmation message including a timer upper limit value, and a time during which the receiving terminal does not exceed the timer upper limit value included in the member presence confirmation message transmitted in the presence confirmation transmission step, In addition, a timer starting step of starting a timer held by the own terminal using a time determined at random according to a uniform distribution as a timer value, and before the other receiving terminal transmits a response message to the member presence confirmation message, When the timer held by the receiving terminal expires, A response message transmitting step in which a receiving terminal transmits a response message to the member presence confirmation message, a response time calculating step in which the multicast relay device calculates a response time of the receiving terminal, and the multicast relay device in the response time An average response time calculating step of calculating an average value of the response times calculated in the calculating step; and the multicast relay apparatus based on the average value of the response times calculated in the average response time calculating step and the timer upper limit value. And a receiving terminal number calculating step for calculating the number of receiving terminals that receive the multicast data.
According to this method, the number of receiving terminals can be calculated only by the multicast relay device performing computation without increasing data exchange between devices, and the number of receiving terminals can be determined without increasing the network load. can do.

According to a second aspect of the present invention, in the multicast receiving terminal number determining method according to the first aspect, in the response time calculating step, the multicast relay apparatus starts the time point when the receiving terminal receives the member existence confirmation message. The time until the time when the response message is transmitted is calculated as the response time.
According to this method, the multicast relay apparatus can accurately calculate the timer value set in the receiving terminal.

The invention according to claim 3 comprises message transmitting means for transmitting a member existence confirmation message including a timer upper limit value to the receiving terminal, and message receiving means for receiving a response message for the member existence confirmation message from the receiving terminal. In a multicast relay device, response time calculating means for calculating the response time of the receiving terminal, average response time calculating means for calculating an average value of the response times calculated by the response time calculating means, and the average response time calculating means Receiving terminal number calculating means for calculating the number of receiving terminals that receive the multicast data transmitted from the own apparatus based on the average value of the response times calculated by the above and the timer upper limit value. A multicast relay device is provided.
According to this configuration, the number of receiving terminals that receive the multicast data can be calculated simply by performing the operation of the multicast relay apparatus, while the mechanism for sending and receiving messages between the receiving terminal and the multicast relay apparatus remains the same. The number of receiving terminals can be determined without increasing the network load.

According to a fourth aspect of the present invention, in the multicast relay device according to the third aspect, the response time calculation means is from the time when the receiving terminal receives the member existence confirmation message to the time when the response message is transmitted. Time is calculated as response time.
According to this configuration, the multicast relay apparatus can accurately calculate the timer value set in the receiving terminal.

The invention according to claim 5 is the multicast relay device according to claim 3 or 4, wherein the average response time calculation means calculates the response time to the response time calculated by the response time calculation means. The average value is calculated after weighting according to time.
According to this configuration, since the multicast relay apparatus can calculate the average value after weighting the response time according to the time when the response time is calculated, the response that accurately reflects the current state An average value of time can be calculated.

  According to the present invention, since the multicast relay device can calculate the number of receiving terminals that receive multicast data based on the average value of the response time and the timer upper limit value, without increasing data exchange between the devices. The number of receiving terminals can be calculated only by the multicast relay device performing calculations, and the number of receiving terminals can be determined without increasing the network load.

Next, embodiments of the present invention will be described with reference to the drawings.
[1. Constitution]
FIG. 1 is a diagram showing an overall configuration of a multicast distribution system. As shown in the figure, the multicast distribution system includes a router 10 that relays multicast data distributed by multicast and a plurality of receiving terminals 20 that receive the multicast data.

  The receiving terminal 20 is a personal computer, for example, and includes a CPU (Central Processing Unit), a memory, a communication interface, and a timer. The receiving terminal 20 responds to a periodic member presence confirmation from the router 10 according to known IGMP. Specifically, when the receiving terminal 20 receives a member presence confirmation message (Membership Query) from the router 10, for the received multicast channel, a response message is transmitted to notify that the multicast channel is received. Starts a timer to count the timing. At this time, the timer has a time that does not exceed the timer upper limit value included in the member presence confirmation message (that is, a time in the range from 0 to the timer upper limit value), and is random according to a uniform distribution. A short time is set as the timer value.

When the timer held by the receiving terminal 20 has expired without receiving a response message (Membership Report) including identification information of a certain multicast channel from another receiving terminal 20, the receiving terminal 20 and a certain multicast A response message including identification information of a certain multicast channel is multicast transmitted to the other receiving terminals 20 receiving the channel.
With the above mechanism, among the plurality of receiving terminals 20 that receive a certain multicast channel, only the receiving terminal 20 that holds a timer having a minimum timer value is notified that a certain multicast channel is received. The response message is sent.

Next, the configuration of the router 10 will be described. The router 10 includes a CPU that controls the entire router 10, a storage unit including a volatile memory and a non-volatile memory, an internal clock that measures time, and a communication interface that controls transmission and reception of data via a communication network. ing.
Various software is stored in the storage unit of the router 10. The software includes a program for calculating the number of receiving terminals.
The functions of the router 10 shown in FIG. 1 are realized by these software and hardware. The message transmission unit 11 shown in the figure is a member presence confirmation message (Membership Query) for inquiring whether or not there is a receiving terminal 20 that receives multicast data transmitted from the router 20 in the communication link of the router 10. Is multicast transmitted at predetermined intervals. The member existence confirmation message to be transmitted includes a timer upper limit value designated by the router 10.

The message receiving unit 12 receives a response message (Membership Report) from the receiving terminal 20. The response message is transmitted only when any one of the timers activated by the receiving terminal 20 that receives the same multicast channel expires according to IGMP.
The response time calculation unit 13 calculates the time from when the receiving terminal 20 receives the member presence confirmation message to the time when the response message is transmitted as the response time.

A specific calculation method will be described. The response time calculation unit 13 measures the time when the member presence confirmation message is transmitted to the receiving terminal 20 and the time when the response message is received from the receiving terminal 20 using an internal clock. Then, the response time calculation unit 13 calculates a time from the time when the response message is received to the time when the member existence confirmation message is transmitted, and calculates a value obtained by subtracting the transmission delay time from the calculated time as the response time. Here, the transmission delay time is the time taken to exchange data between devices using a communication link for multicast distribution. For example, the transmission delay time obtained in advance by experiments or theory is stored in the storage unit. It is good to keep. Note that, when the transmission delay time is small or when it is not required to calculate a precise value, the transmission delay time may not be subtracted.
The response time calculated here is equal to the minimum timer value among the timer values set in the timers held by the plurality of receiving terminals 20.

  The average response time calculation unit 14 calculates an average value of the response times calculated by the response time calculation unit 13. As a calculation method of the average value of the response time, the sum of the response times measured a plurality of times may be simply divided by the number of measurements, or according to the time when the response time is calculated by the response time calculation unit 13. The response time may be calculated by weighting the response time exponentially. As a weighting method, for example, in order to accurately reflect the current state, the response time calculated at a time closer to the time at which the average response time calculation unit 14 calculates the average value increases the weighting. A way to do this is conceivable. Further, not only the average response time calculated by one router 10 but also the average response time calculated by a plurality of routers 10 can be considered.

  The receiving terminal number calculation unit 15 calculates the number of receiving terminals that receive the multicast data transmitted from the router 10 based on the average value of the response times calculated by the average response time calculation unit 14 and the timer upper limit value. . Specifically, the receiving terminal number calculation unit 15 calculates a value obtained by subtracting 1 from the value obtained by dividing the timer upper limit value by the average value of the response times as the receiving terminal number.

  Hereinafter, the calculation method of the number of receiving terminals will be described in detail. As described above, when receiving the member presence confirmation message from the router 10, the receiving terminal 20 existing in the link of the router 10 starts a timer in association with the received multicast channel. The timer value at this time is set to a time that does not exceed the timer upper limit value specified for the router 10 and is randomly determined according to a uniform distribution. Then, the router 10 receives a response message including identification information of a certain multicast channel only when one of a plurality of timers started in association with the certain multicast channel expires. At this time, the distribution of the response time from when the receiving terminal 10 receives the member presence confirmation message to when the response message is transmitted is, when the timer upper limit value is T and the number of receiving terminals is N, the average value D Indicates a distribution of T / (N + 1).

Hereinafter, it will be mathematically proved that the average value D of the response time is T / (N + 1).
Consider uniformly distributed random variables X ₁ , X ₂ ,..., X _n in the interval [0, T]. Each probability density function is 1 / T in the interval [0, T]. Random variables _{X1, X 2, ···, X} n shall be independent of each other. The maximum value _{Y = max (X1, X 2} , ···, X n) When, which is also a random variable.
The cumulative distribution function F (x), which is an integral value of the probability density function of the maximum value Y, is represented by the following equation. In the following equation, it is used that an event where the maximum value Y is smaller than x is equal to an event where X ₁ , X ₂ ,..., X _n are all smaller than x.

  Since the probability density function f (x) of the maximum value Y is obtained by differentiating the cumulative distribution function F (x), the following expression is obtained.

  The average value is represented by the following formula.

When Z = min (X ₁ , X ₂ ,..., X _n ) is considered, it can be considered that the probability density function is horizontally reversed in the interval [0, T]. Therefore, the average value D is as follows.

In the above formula, “·” represents multiplication.
With the above mathematical proof, the average value D = T / (N + 1) of the response time is satisfied, and N = (T / D) −1 obtained by modifying this equation is satisfied. Accordingly, the receiving terminal number calculation unit 15 can estimate the number of multicast receiving terminals by calculating the value obtained by subtracting 1 from the timer upper limit value divided by the average response time as the receiving terminal number. It becomes. When the calculated N is not a natural number, the receiving terminal number calculation unit 15 may further perform arithmetic processing such as rounding off, rounding down, rounding up, etc. with respect to the decimal point of N.
[2. Operation] Next, an operation example in the above configuration will be described with reference to FIG.

As a premise, in this operation example, the plurality of receiving terminals 20 receive a certain multicast channel, and the router 10 and the receiving terminal 20 communicate according to IGMP. The storage unit of the router 10 stores a predetermined transmission delay time d, a timer upper limit value T, and a predetermined time that is a time interval for transmitting the Membership Query.
First, the message transmission unit 11 of the router 10 multicast-transmits a Membership Query including the timer upper limit value T to all the receiving terminals 20 in the link in order to check whether or not the multicast receiving terminal 20 exists ( Step S1). The router 10 acquires the time Ta when the Membership Query is transmitted from the internal clock and records it in the storage unit.

  When receiving the Membership Query, the receiving terminal 20 performs a process according to a known IGMP. Specifically, the receiving terminal 20 acquires the timer upper limit value Tmax included in the Membership Query. The receiving terminal 20 sets a random value according to the uniform distribution as a timer value within a range from 0 to the timer upper limit value Tmax. Then, the receiving terminal 20 starts a timer associated with a certain multicast channel in order to measure the timing of membership report transmission for the certain multicast channel (step S2).

Among a plurality of receiving terminals 20 that have started a timer in association with a certain multicast channel, the receiving terminal 20 holding the timer whose timer value has elapsed first transmits a Membership Report including identification information of a certain multicast channel (step S3).
The message receiving unit 12 of the router 10 receives the Membership Report. The router 10 acquires the time Tb at which the Membership Report is received from the internal clock and records it in the storage unit.

The response time calculation unit 13 of the router 10 calculates the response time Td (step S4). Specifically, the response time calculation unit 13 reads the time Ta at which the Membership Query is transmitted, the time Tb at which the Membership Report is received, and the transmission delay time d from the storage unit, and calculates the response time Td by the following equation. calculate.
Td = Tb-Ta-d

The average response time calculation unit 14 calculates the average value Tave of the response times Td calculated in step S4 (step S5). Specifically, the average response time calculation unit 14 calculates the average value Tave by the following formula.
Average value Tave = previous average value Tave × (1−p) + response time Td × p
Here, p is a constant that determines the weighting for the response time Td.

Based on the average value Tave and the upper limit value Tmax calculated in step S5, the receiving terminal number calculation unit 15 calculates an estimated value of the number N of receiving terminals that receive a certain multicast channel by the following equation.
N = (Tmax / Tave) -1
The message transmission unit 11 transmits the Membership Query again when a predetermined time has elapsed from the time Ta at which the Membership Query is transmitted (Step S1). And the process from step S1 to step S6 is repeated for every predetermined period.

  In this way, the multicast receiving terminal 20 and the multicast communication protocol remain the same as the conventional method, and the router 10 can estimate the number of multicast receiving terminals using a simple calculation formula. Therefore, the router 10 can estimate the number of multicast receiving terminals without increasing the communication amount of the entire system and the processing load of the router 10.

  In the above-described operation example, the processing from step S1 to step S6 is repeated every predetermined cycle. However, the present invention is not limited to this. For example, the processing from step S1 to step S4 is repeated a plurality of times every predetermined cycle. After that, the average response time calculation unit 14 may calculate the average value using the plurality of response times calculated by the response time calculation unit 13 in step S4 (step S5).

As described above, since the number of receiving terminals 20 that receive multicast data can be calculated only by the operation of the router 10, the number of receiving terminals can be easily determined without increasing the network load. Thus, by making it possible to easily determine the number of receiving terminals, it is possible to easily estimate what information is in demand.
In the above-described embodiment, the multicast distribution system that performs communication according to IGMP has been described. However, the multicast distribution system that performs communication according to MLD also has the same embodiment except that the message name is different. Further, the present invention is not limited to IGMP or MLD, and the present invention can be applied to a multicast distribution system that uses a communication protocol for confirming only whether or not the receiving terminal 20 exists.

It is a figure which shows the structure of the multicast delivery system which concerns on embodiment of this invention. It is a figure explaining the procedure of the receiving terminal number determination which concerns on the same embodiment. It is a figure explaining a mode that the conventional router transmits a member presence confirmation message to a receiving terminal. It is a figure explaining a mode when the receiving terminal which received the conventional member presence confirmation message starts the timer in association with the received multicast channel. It is a figure explaining a mode when the conventional specific receiving terminal transmits the response message when the timer expires.

Explanation of symbols

10 router 11 message transmitting unit 12 message receiving unit 13 response time calculating unit 14 average response time calculating unit 15 receiving terminal number calculating unit 20 receiving terminal

Claims (5)

In the multicast receiving terminal number determination method for determining the number of receiving terminals that receive the multicast data transmitted from the multicast relay device,
The multicast relay device transmits a member presence confirmation message including a timer upper limit value;
The receiving terminal is a time that does not exceed the timer upper limit value included in the member presence confirmation message transmitted in the presence confirmation transmission step and is randomly determined according to a uniform distribution as a timer value. A timer start step for starting a timer held by the terminal;
A response message transmission step in which the receiving terminal transmits a response message for the member presence confirmation message when a timer held by the receiving terminal expires before another receiving terminal transmits a response message for the member presence confirmation message When,
A response time calculating step in which the multicast relay device calculates a response time of the receiving terminal;
An average response time calculating step in which the multicast relay device calculates an average value of the response times calculated in the response time calculating step;
A receiving terminal number calculating step in which the multicast relay device calculates the number of receiving terminals that receive the multicast data based on an average value of the response times calculated in the average response time calculating step and the timer upper limit value; A method for determining the number of multicast receiving terminals, comprising:   The response time calculating step, wherein the multicast relay device calculates a time from when the receiving terminal receives the member existence confirmation message to a time when the response message is transmitted as a response time. 2. The multicast receiving terminal number determining method according to 1. In a multicast relay apparatus comprising: a message transmission unit that transmits a member presence confirmation message including a timer upper limit value to a reception terminal; and a message reception unit that receives a response message to the member presence confirmation message from the reception terminal.
Response time calculating means for calculating the response time of the receiving terminal;
Average response time calculation means for calculating an average value of the response times calculated by the response time calculation means;
Receiving terminal number calculating means for calculating the number of receiving terminals that receive the multicast data transmitted from the own apparatus based on the average value of the response times calculated by the average response time calculating means and the timer upper limit value; A multicast relay device comprising: The response time calculation means includes
4. The multicast relay device according to claim 3, wherein a time from when the receiving terminal receives the member presence confirmation message to a time when the response message is transmitted is calculated as a response time. The average response time calculating means includes
5. The multicast according to claim 3, wherein the average value is calculated after weighting the response time calculated by the response time calculation means according to the time when the response time is calculated. Relay device.

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