JP2000201158A - ATM switch - Google Patents

Abstract

(57) [Problem] To provide an ATM exchange capable of reducing a call loss rate and improving a line utilization rate in connection admission control in strict priority control. SOLUTION: At the time of a connection setting request from a terminal, an ATM exchange calculates a cell loss rate of each priority class in step 330. The cell loss rate is calculated by using the parameter related to the cell arrival rate and the cell overflow rate from the line calculated from the line capacity in step 310, and the parameter related to the burst length and the buffer length of each priority class in steps 322 and 323. It is approximately calculated as a synergistic effect of the cell loss rate reduction effect by the buffer calculated as above. When the cell loss rate is equal to or higher than the allowable cell loss rate, control is performed so as not to accept a connection setting request from the terminal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an ATM (Asynchronou).
s Transfer Mode), and more particularly to an ATM switch having a delay priority function that is indispensable for utilizing the multiplex effect.

[0002]

2. Description of the Related Art In multimedia communication, since information transfer requests are burst traffic that occurs intermittently,
If the maximum required transmission rate (band) is permanently assigned to each incoming line, the transmission rate (band)
The usage efficiency of the system becomes very poor. Therefore, in an ATM network, variable-length multimedia information is divided and transferred in units of 53 bytes called a cell, and a switch (and a multiplexer) transmits a cell from another input line to the idle time of one input line. And multiplex processing for reducing the transmission rate (band) required for the entire traffic is performed. In the ATM switch, which is a node of the network, when cells from a large number of incoming lines collide and cells overflow from the outgoing line, cell collision is buffered by a buffer provided in the ATM switch. Cell loss occurs only when cells overflow from the buffer, because the overflow from the outgoing line is too large to be buffered by the buffer.

[0003] In multimedia communication, delay-sensitive traffic such as images and sounds and loss-sensitive traffic from a LAN or the like are mixed. Therefore, in the ATM exchange, complete priority control is performed in order to satisfy both requirements of a delay amount for delay-sensitive traffic and a cell loss rate for loss-sensitive traffic. In this complete priority control, a buffer is separately provided for each priority class, and scheduling is performed so that cells in the buffer of the higher priority class are preferentially read out, so that there is no loss-sensitive space between the delay-sensitive traffic. It is intended to embed traffic and reduce the amount of delay in delay-sensitive traffic.

[0004] ATM with full priority control according to the prior art
In the exchange, for example, as described in JP-A-5-191436, delay-sensitive traffic such as voice is stored in a priority class buffer queue without performing any control on traffic characteristics and flow rate. In addition, loss-sensitive traffic from a LAN or the like is mechanically stored in a buffer queue of a non-priority class.

[0005] The cell loss rate in the ATM exchange changes depending on the traffic characteristics and the flow rate. The higher the flow rate, the more frequently large queue lengths occur in the buffer queue and the higher the cell loss rate. Also, if the flow rate is the same, the traffic with a longer burst length, or the traffic with a higher peak cell rate, will have a larger queue length in the buffer queue, and the cell loss rate will be larger. Become.

Further, when performing full priority control, the cell loss rate of the lower priority class is affected by the traffic characteristics of the upper class and the flow rate. If there is a cell of the higher priority class in the buffer queue, the traffic of the lower priority class is waited unnecessarily. Therefore, even if the traffic characteristics and flow rate of the lower priority class are the same, the flow rate of the higher priority class increases, or the traffic of the higher priority class has a long burst length, or the traffic has a large peak cell rate. In this case, a large queue length occurs in the buffer queue of the higher priority class, so that the frequency of the traffic of the lower priority class waiting in the buffer queue increases, and the cell loss rate of the lower priority class increases. .

[0007] For this purpose, international standard organizations such as ITU-T recommend that the ATM exchange perform connection admission control in order to suppress the cell loss rate to be equal to or less than the allowable cell loss rate. In this connection admission control, when a terminal makes a connection setting request, a traffic descriptor indicating characteristics of burst traffic that differs depending on the transfer speed and media characteristics of the terminal (hereinafter, the type of burst traffic having different characteristics is referred to as “call type”). A
Report to TM exchange. The ATM switch calculates the cell loss rate in the multiplex environment from the values of the traffic descriptors declared by the terminal that has made the connection request and the connected terminal, and when the cell loss rate falls below the allowable cell loss rate, A control for accepting the setting request and rejecting the connection setting request when the cell loss ratio becomes equal to or more than the allowable cell loss rate is performed. For example, Japanese Patent Application Laid-Open No. H10-65679 discloses a technique for performing connection acceptance determination so that the cell loss rates of both high-priority class and low-priority class connections are equal to or less than respective prescribed values.

[0008]

In the prior art, even if the amount of cell arrival exceeds the line capacity only excessively, the cell arrival rate is regarded as a loss, and the cell arrival rate is reduced. The probability that a cell overflows from the line is calculated from the parameters and the line capacity, and the network resource is effectively used by performing connection acceptance determination. However, since a buffer is present in a normal ATM switch, all the cells overflowing from the outgoing line are not lost, and the cell loss occurs because the overflow amount from the outgoing line is large and cannot be completely buffered. Only when cells overflow the buffer. Therefore,
In the prior art described above, the exchange often rejects connection acceptance even though it has a cell loss rate at which a connection can actually still accept a connection, and the call loss rate increases and the line utilization efficiency deteriorates. Problem.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an ATM switch which solves the above-mentioned problems and which can reduce a call loss rate and improve a line utilization rate in connection admission control.

[0010]

SUMMARY OF THE INVENTION The object of the present invention is to estimate a cell loss rate of each priority class in consideration of a cell loss rate reduction effect of a buffer, and to control whether connection can be accepted based on the cell loss rate. This is achieved by the fully prioritized control ATM switch described above.

More specifically, the ATM switch according to the present invention is configured such that, when a cell exists in a buffer of a higher priority class among a plurality of priority classes, a cell is read from the buffer of the higher priority class. When multiplexing burst traffic (call types) having different characteristics, when a connection setting request is issued, the traffic is calculated using the parameter related to the cell arrival rate and the line capacity used in the above-described conventional technology. Connection setting based on the probability of cells overflowing from the line, and the cell loss rate approximately obtained as a synergistic effect of the cell loss rate reduction effect of the buffer calculated using the parameter related to the burst length and the buffer length of each priority class. It is configured to control whether a request can be accepted. Here, the cell loss rate can be approximately calculated from an algorithm based on an approximate expression disclosed for the first time in this specification.

Further, the ATM switch according to the present invention calculates a cell loss rate of a priority class in strict priority control based on a traffic descriptor of the terminal, a line capacity of the switch, and a buffer length at the time of a connection setting request from the terminal, When the calculated cell loss rate is equal to or greater than the allowable cell loss rate, control is performed so as not to accept a connection setting request from a terminal. Where the traffic descriptors are average cell rate, peak cell rate, average burst length,
And the coefficient of variation of the burst length. With this configuration, it is possible to obtain an ATM exchange that can reduce the call loss rate and improve the line utilization rate in connection admission control.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Before describing the embodiments in detail, the principle of the present invention will be described first. For the first time disclosed in this specification, in addition to the parameter related to the cell arrival rate and the channel capacity, using the parameter related to the burst length and the buffer length of each priority class, the cell loss rate reduction effect of the buffer was taken into consideration. The approximate expression will be described. In the full priority control, as shown in FIG.
When there is a cell of a higher priority class in the cell, the cell is always read from the cell of the higher priority class via the output selector 9, so that each priority class is independent of the lower priority class. Therefore, in a switch that performs full delay priority, the cumulative sum of queue lengths from the highest priority class to the priority h or higher is from the highest priority class to the priority h + 1 or higher, which is the priority class one rank higher than the priority class. Is the sum of the cumulative sum of the queue lengths of the priority classes and the queue length of the priority class having the priority h. Therefore, the distribution of the accumulated queue lengths of the priority class or more that has made the connection request is a superposition of the distribution of the accumulated queue length of one or more higher priority classes and the distribution of the queue length of the priority class that has made the connection request. It is equivalent to the distribution.

[0014] Based on the above idea, priority control is not taken into account, but an approximation method taking into account the cell loss rate reduction effect of the buffer is described in the document "Atsuo Hatono,
Kawakita Kenji: AT of call type by linear filter approach
M-cell loss rate approximation model: Transactions of Information Processing Society of Japan Vol.39,
No. 1, pp111-122 (Jan. 1998)], the cell loss rate in the ATM switch of the strict priority control method is calculated as follows. , (Equation 1) to (Equation 5) below.

[0015]

(Equation 1)

[0016]

(Equation 2)

[0017]

(Equation 3)

[0018]

(Equation 4)

[0019]

(Equation 5)

Here, the meanings of the symbols in the above (Equation 1) to (Equation 5) will be described. x _h is the buffer length assigned to priority class h, <v _k > is the average cell rate for call type k, and v _k is the peak cell rate for call type k. <v _i > is the average cell rate of call type i, v _i is the peak cell rate of call type i, μ _i is the reciprocal of the average burst length of call type i, N _i is the multiplex number of call type i, C _i ² represents the square variation coefficient of the burst length of call type i. Furthermore, sigma _h priority represents the cumulative sum of the above call h. Further, ρ _{h represents} the cumulative outgoing line utilization rate for calls having a priority of h or higher, ρ _l represents the outgoing line utilization rate of each priority class, and V represents the outgoing line speed. It should be noted that the first expression in the expression (2)
The multiple sum of terms is the sum of combinations of two variables of s and r such that (rv _l > Vv _k -sv _h )> 0, and the sum of the second term is the sum of s for which sv _h > V It is the sum.

Next, the approximate feature of the cell loss rate will be described. In the above (Equation 1), the burst level outgoing line overflow rate L _k and the cell level outgoing line overflow rate L ₀ represent the “probability that a cell overflows from the line”, which is also calculated in the above prior art. ing. In (Equation 1), the exponential function part in {} represents the effect of reducing the cell loss rate by the buffer, and the argument of the exponential function is based on the parameter related to the burst length and the buffer length of each priority class (Equation 4). And (Equation 5). In the cell loss rate P _k disclosed in this specification, as shown by the hatched area A in FIG. 1B, for example, even when the cell arrival amount of the priority classes 1 to 3 transiently exceeds the line capacity, Since the effect of reducing the cell loss rate by temporarily retaining cells in the buffer is also taken into account, it is possible to reduce the call loss rate and improve the line utilization rate in connection admission control.

As described above, according to the present invention, in a multi-call environment in which a plurality of burst traffics having different characteristics are multiplexed,
The function to calculate the cell loss rate of each priority delay class when it is affected by the traffic characteristics and the flow rate of the upper class by the full priority control from the traffic descriptor and the output line capacity of the terminal has been realized. Thereby, when the cell loss rate exceeds the allowable cell loss rate, the connection request from the terminal is rejected, thereby suppressing the inflow of traffic and realizing the connection management function of guaranteeing the cell loss rate in all priority classes. be able to.

Based on the method described above, a connection management function comprising the following software processing is added to the ATM switch which performs the full priority control according to the above-mentioned conventional technology. (1) A process of identifying each priority class from a traffic descriptor indicating an allowable delay amount on a connection setting request cell. (2) From the traffic descriptors of the terminals up to the priority class for which the connection setting request was made, the outgoing line capacity, and the buffer length of the corresponding priority class, determine the worst call type cell loss rate in the priority class for which the connection request was made. Processing to calculate. (3) traffic descriptors and outgoing line capacities up to a priority class having a priority lower by k than the priority class for which connection was requested;
A process of calculating, from the buffer length of the corresponding priority class, the cell loss rate of the call type having the maximum peak cell rate in the corresponding priority class.

First, when the terminal makes a connection setting request,
As the traffic descriptor, the average cell rate, the peak cell rate, the average burst length, the square variation coefficient of the burst length, and the allowable delay amount are reported to the ATM exchange. The ATM exchange identifies the priority class of the terminal that has issued the connection request from the allowable delay amount declared from the terminal that has issued the connection setting request and the buffer length of each priority class provided in the exchange. When the priority class that has requested the connection is identified, the peak cell rate in the priority class is determined from the traffic descriptor and outgoing line capacity of the priority class higher than the priority class that has requested the connection, and the buffer length of the priority class that has requested the connection setting. An approximate value of the cell loss rate of the maximum call type is calculated. When the calculated approximate value of the cell loss rate is equal to or larger than the allowable cell loss rate, the connection setting request is not accepted, and the connection setting process is terminated.

When the calculated cell loss rate is equal to or less than the allowable cell loss rate, the traffic descriptor, the outgoing line capacity, and the priority of the call of the priority class whose priority is lower by one than the priority class having the connection request are one or more. From the buffer length of the next lower priority class, an approximate value of the worst call type cell loss rate in the lower priority class is calculated. When the calculated approximate value of the cell loss rate is equal to or larger than the allowable cell loss rate, the connection setting request is not accepted, and the connection setting process is terminated. When the approximate value of the calculated cell loss rate is equal to or less than the allowable cell loss rate, the above series of processing is repeated up to the lowest priority class, and when the cell loss rates of all the priority classes are equal to or less than the allowable cell loss rate. Receives a connection setting request.

Through a series of these processes, the cell loss rate of the call type that maximizes the peak cell rate in each priority class in a multi-call type environment in which a plurality of burst traffics having different characteristics are multiplexed is calculated, and the cells of all the priority classes are calculated. It is possible to realize an ATM switch having a complete delay priority function capable of suppressing the loss rate to be equal to or less than the allowable cell loss rate. Next, examples of the present invention will be described.

[Embodiment 1] In this embodiment, (Equation 1) to (Equation 5)
Using the approximation formula given by, the average cell rate, the peak cell rate, the average burst length, the traffic descriptor consisting of the square variation coefficient of the burst length, the outgoing line capacity, and each priority from the buffer length of each priority class By adding the process of calculating the cell loss rate of the call type having the maximum peak cell rate in the delay class to the ATM switch 100 shown in FIG. 3, the cell loss rates of all priority classes can be reduced to the allowable cell loss rate or less. ATM switch 100 that can perform a CAC (Connection Admission Control) that accepts a connection setting request when the cell loss rate of any one priority class is equal to or more than the allowable cell loss rate. Is realized.

[Configuration] (1) Overall Configuration (FIG. 5) FIG. 2 is a diagram showing an ATM network 6 composed of an ATM switch 100, ATM terminals 5-1 and 5-n, and a connection 7. In the ATM network 6, FIG.
Cells such as those shown in FIGS. In FIG.
(a) and (d) are call setup request cells, (b) is a response cell, (c)
Indicates the format of the release cell, and (e) indicates the format of the user cell.

FIG. 4 is a diagram showing an embodiment of the ATM exchange according to the present invention. As shown in the figure, the ATM exchange includes a switch circuit 110, an incoming line interface circuit 120, a buffer queue 130, an outgoing line interface circuit 135, a CP (Con
trol Processor) circuit 140. The point that the ATM switch 100 of this embodiment is different from the existing ATM switch is that the traffic characteristics are different from the traffic characteristics in order to make it possible to suppress the cell loss rates of all priority classes to the allowable cell loss ratio or less. When multiple burst traffic is multiplexed, the cell for evaluating the cell loss rate of the call type that maximizes the peak cell rate in each priority class, taking into account the influence from the higher priority class by strict priority control. That is, a loss rate evaluation circuit 150 is provided.

Of these, the incoming line interface circuit 120
Is composed of an optical / electrical conversion circuit 121 and a UPC circuit 122 for monitoring whether traffic does not violate the declared value. The incoming line interface circuit 120 performs optical / electrical conversion, observes the peak cell rate, average cell rate, and burst length from the terminal 5 and monitors whether the traffic of the terminal 5 does not violate the declared value. If a violation is detected, the cell is discarded. The switching circuit 110
In accordance with the VCI (Virtual Channel Identifier) of the TM cell 14, an exchange process of distributing to the buffer queue 130 provided for each output line and priority class is performed. The buffer queue 130 performs multiplexing and buffers cell collision caused by the switching process. Outgoing line interface circuit 135
Converts the cell 14 into an ATM network 6 after electrical / optical conversion.
Send to As shown in FIG. 5, the buffer queue 130 generally includes a buffer 131 for storing cells and a queue length counter for counting the number of cells in the buffer.
Consists of 132. When strict priority control is performed, in addition to those, when a cell of a higher priority class exists,
A cell read selector 133 for always performing control to read from a cell of a higher priority class is added.

The control (CP) circuit 140 performs processing by software such as CAC as shown in FIG. The CP circuit 140 is usually a CPU (Central Processing Unit) circuit.
141, CAC processing software memory 146, response processing software memory 147, release processing software memory 148,
It comprises a cell interface circuit 142 and a switch interface circuit 143, each of which is a bus control circuit 1
Combined with a bus controlled by 45. In the present embodiment, a cell loss rate evaluation circuit for evaluating the cell loss rate of the call type having the highest peak cell rate in each priority class, taking into account the influence of the higher priority class due to the full priority control. Because of adding 150, CP circuit 150
, An external interface circuit 144 is added.

(2) Configuration of Cell Loss Rate Evaluation Circuit 150 (FIG. 7) As shown in FIG.
gital signal processor) 151, a CP interface circuit 152, a traffic management table 160 for each priority class, a cell loss rate evaluation processing software memory 153, and a connection termination processing software memory 154, each of which is a bus control circuit 155. Are coupled by a bus controlled by As shown in FIG. 7, the traffic management table 160 includes a call type management table 161, a worst call type management table 162, an intra-class total management table 163, an effective traffic management table 164, and a cumulative total management table 165. FIG. 8 is a diagram showing the details. Call type management table
Reference numeral 161 includes columns for the peak cell rate, average cell rate, (determined) number of connected terminals, and (temporarily updated) number of connected terminals of connected terminals. The worst call type management table 162 includes (determined) peak cell rate, (temporary update) peak cell rate, and
It consists of columns of (determined) average cell speed and (temporary update) average cell speed. The intra-class sum management table 163 includes (determined) the sum of the peak cell speeds within the class, (temporarily updated) the sum of the peak cell speeds within the class, the (determined) variance within the class, the (temporarily updated) variance within the class, and the (decided) ) Number of multiplexes in class, (temporary update) The number of multiplexes in class is set.
The effective traffic management table 164 includes (determined) effective peak cell speed, (temporary update) effective peak cell speed, and
It consists of columns of (determined) effective multiplex number and (temporary update) effective multiplex number. The cumulative total management table 165 includes (determined) cumulative total of peak cell speeds, (temporarily updated) cumulative total of peak cell speeds, (determined) cumulative total of average cell speeds, (temporarily updated) cumulative total of average cell speeds, (Determined) cumulative sum of variance, (temporary update) cumulative sum of variance, (determined) cumulative sum of multiplexed number, (temporary updated) cumulative sum of multiplexed number, (determined) cumulative sum of effective average burst length, (temporary updated) The table includes columns for the effective average burst length, the (determined) cumulative multiplex number, the (temporary update) cumulative multiplex number, the (determined) cumulative total of the effective average cell length, and the (temporary update) cumulative total of the effective average cell length.

[Operation] A capable of suppressing the cell loss rate of the priority class according to the present embodiment to an allowable cell loss rate or less.
The operation of the TM exchange 100 is described as (1) operation outline, (2) CA
The C processing 170 (FIG. 9) and the (3) cell loss rate evaluation processing 300 (FIG. 12) will be described in this order. Among them, (1) the operation outline and (2) the CAC processing 170 are the ATM which is the premise of the present invention.
This describes the general operation of the exchange. (3)
The cell loss rate evaluation processing 300 (FIG. 12) describes the processing of evaluating the cell loss rate in each priority class, taking into account the influence of the higher priority class by the full priority control, which is a feature of the present invention. It is a thing.

(1) Outline of Operation When the cells 14 start flowing into the ATM switch 100, the switch circuit 110 performs a switching operation, sorts the cells for each output line and priority class, and stores the data in the buffer 131 provided in the buffer queue 130. To be stored. When a cell flows into the buffer 131, the queue length counter 132 counts up by +1 when the cell 14 is input. Cell read selector 133
Is the queue length counter 13 of the higher priority class
Access is made sequentially from 2 and the cell 14 is read from the first buffer in which the value of the queue length counter 132 is not 0. Also the cell
When 14 outputs from the buffer 131, the queue length counter 132 counts down by -1. The comparison circuit 133 compares the count value of the queue length counter 133 with the value of the buffer stored in the buffer threshold memory 134. When the count value exceeds the value of the buffer, the enable signal is turned off, and the switch circuit (SW) 110 is requested to discard the cell 14.

(2) CAC processing 600 The switch circuit 110 is connected to the ATM terminal 5 and other exchanges.
Call setup request cell 10, response cell 11, release cell 12 from 100
Is transferred to the CP circuit 140. The control cell transferred to the CP circuit 140 interrupts the CPU circuit 141. The interrupted CPU circuit 141 performs processing for each type of control cell.

(A) Processing for Call Setup Request Cell Reception As shown in FIG. 9, when the call setup request cell 10 is first received (step 170), the destination VCI is received.
Is determined (step 171). When the outgoing line is determined, the CP circuit 140 activates the cell loss rate evaluation circuit 150, and inputs the value of the traffic descriptor of the call setting request cell 10 to the cell loss rate evaluation circuit 150 (step 172).

The cell loss rate evaluation circuit 150 evaluates the cell loss rate when a connection request for a connection is received from the input traffic descriptor value, and determines that the cell loss rate of one of the priority classes is equal to the allowable cell loss. When the cell loss rate is equal to or more than the cell loss rate evaluation circuit 150, the cell loss rate evaluation circuit 150 determines that the connection request cannot be accepted. It is determined that the request can be accepted. The present invention takes into account the influence of higher priority classes due to strict priority control when multiplexing a plurality of burst traffics having different traffic characteristics in the process of evaluating the cell loss rate when judging whether a connection request is possible or not. The above is characterized in that the cell loss rate of the call type in which the peak cell rate is maximum in each priority class is evaluated.

When the cell loss rate evaluation circuit 150 determines that the connection request for the connection cannot be accepted (step 1).
73), the release cell 12 is transmitted (step 174), and the process returns to the call setting request waiting state (step 175). Cell loss rate evaluation circuit 150
Determines that a connection request can be accepted (step 1
73), extract VCIs that have not been assigned yet,
Is reserved (step 176). When the VCI is reserved, a call setup request cell 10 is created. This cell 10 is a switch circuit
The data is input to the unit 110 and transmitted to the upstream ATM exchange 100 using the control channel (step 177). Upon completion of the above processing, the flow shifts to a reception cell waiting state (step 17).
8) Wait for a response cell 11 from the upstream ATM exchange 100.

(B) Response Cell Reception Processing As shown in FIG. 10, when the CP circuit 140 receives the response cell 11 from the upstream ATM switch 100 (step 18).
5) The reserved VCI is determined (step 186).
Response cell 11 to downstream ATM switch 100 or ATM terminal 5
(Step 187), and returns to the call setting request waiting state (step 188).

(C) Processing for Receiving Release Cell 12 As shown in FIG. 11, when the CP circuit 140 receives the release cell 12 from the ATM switch 100 located upstream,
195), the CP circuit 140 activates the cell loss rate evaluation circuit 150,
The value of the traffic descriptor of the terminal that terminates the call connection is input to the cell loss rate evaluation circuit 150 (step 196). When the value of the traffic descriptor of the terminal that terminates the call connection is input, the cell loss rate evaluation circuit 150 performs a call termination process (FIG. 1).
2). When the call termination processing is completed, the VCI of the terminal terminating the call connection is released (step 197). When the VCI is released, the release cell 12 is transmitted to the ATM switch 100 or the ATM terminal 5 (step 198), and the process returns to a call setting request waiting state (step 199). (3) Cell Loss Rate Evaluation Processing In the present embodiment, the cell loss rate evaluation processing is performed by the burst level outgoing line overflow rate L _k represented by (Equation 2) and the cell represented by (Equation 3) Level overflow rate L ₀ , and
The processing consists of calculating β expressed by (Equation 4) and β ₀ expressed by (Equation 5). Incidentally, the outgoing line capacity V and buffer length x _h of each priority class is set at the time of start-up of the exchange.

(A) Processing for Cell Loss Rate Evaluation Request Processing using a cell loss rate evaluation request will be described with reference to FIG. When the cell loss rate evaluation processing is started by the cell loss rate evaluation request (step 172 in FIG. 9), the priority class for which connection has been requested from the CAC processing, the peak cell rate v _{i of the} terminal having requested connection, and the average cell rate <v _i >, average burst length μ _i ⁻¹ , and burst length square variation coefficient Ci ² are input (step 300). First, a current class representing a priority class currently being processed is set as a priority class for which a connection request has been issued (step 301). When the current class is set, the call type management table 161 in the traffic management table 160 provided for each priority class is used to set the peak cell rate value of the terminal that has made the connection request and the number of connected terminals corresponding to the average cell rate. +1
It counts up and temporarily updates (step 302).

Next, a call type having the worst cell loss rate in the current class is determined. Therefore, the value of the peak cell speed v _i of the terminal that has made the connection request is compared with the peak cell speed v _{k of the} worst traffic registered in the priority class that has made the connection request. When v _i > v _k , it is determined that the call type to which the terminal having made the connection request belongs is the call type having the worst cell loss rate in the current class, and the worst call type peak cell rate v _k and average cell rate <v _k> to be temporarily updated by the peak cell rate v _i and the average cell rates of made the connection request terminal <v _i> (step 303).

When the provisional update of the sum in the class is completed, the burst overflow rate is determined by the processing shown in FIG.
A cell-level outgoing line overflow rate L ₀ expressed by L _k (Equation 3) is calculated (step 310). In the outgoing line overflow rate evaluation process, if the priority class for which the connection request is made is not the highest priority class, the effective multiplexing number and the effective peak cell of the next higher priority class are obtained from the execution parameter 164 of the traffic management table 160. Load speed (Step 31
1). When the effective multiplex number and the effective peak cell speed are read, the total sum of the peak cell speeds, the total sum of the average cell speeds, and the cumulative sum of the variances are read from the cumulative total management table 165 (step 312). When the cumulative sum is read, the sum of the peak cell rate in the current class, the sum of the average cell rates in the class, and the sum of the variances of the cell rates in the class are added to the peak cell rate, the average cell rate, and the cell rate of the terminal that has made the connection request. Are added, and the sum of the multiplex numbers in the class is counted up by +1 to temporarily add the value of the sum in the class of the sum management table 163 in the traffic management table 160 in the current class. (Step 313). By temporarily adding the value of the intra-class sum of the intra-class sum management table 163, the effective multiplex number of the traffic of the next higher priority class, the sum of the peak cell rates in the priority class for which the connection request was made, and the average cell From the intra-class sum of the speed, the intra-class sum of the variance of the cell speed, the peak cell speed and the average cell speed of the worst traffic, and the outgoing line capacity,
Calculating a L _k for priority class for which the connection request (step 314).

After calculating L _k , the number of multiplexes in the class, the sum of the average cell rates in the class, and the cumulative number of multiplexes and the average cell rate up to the next higher class are calculated from the traffic management table 160. Read the sum. When reading from the traffic management table 160 is completed, the accumulated sum of the average cell rates of the next higher priority class, the sum of the average cell rates in the class, the sum of the multiplex numbers in the class, and the outgoing line capacity are represented by (Equation 3). ) To calculate L ₀ (step 31)
6).

[0045] L when calculating the _k and L _0, to temporarily update the value of the cumulative sum management table 165 in the traffic management table 160 in the priority class for which the connection request. Therefore, the cumulative sum of the peak cell rates, the cumulative sum of the average cell rates, and the cumulative sum of the variances of the cell rates include the peak cell rate v _i , the average cell rate <v _i >, the variance of the cell rate < v _i > {v _i − <v _i >} are provisionally added. Furthermore, in order to temporarily update the value of the cumulative total of the effective average burst length in the priority class that has received the connection request, the cumulative total of the effective average burst length is set to <v _i > {(1- <v _i > / v _i ) (1 + Ci ² )} /
The 2μ _i is temporarily added. Furthermore, in order to provisionally update the value of the cumulative sum of the effective average cell length in the priority class for which the connection request was made, the peak cell rate, the average cell rate,
Calculating the effective average cell length from the output line capacity, to temporarily adds the _{<v i> (1- <v} i> / V) (1-v i / V) / 2 to the cumulative sum of the effective average cell length. The cumulative multiplex number is also counted up by +1 and provisionally added (step 321).

When the provisional update of the cumulative total management table 165 in the traffic management table 160 is completed, β of the priority class is replaced by the cumulative total of the provisionally added cell rate, the cumulative total of the average cell rate, and the cumulative total of the effective average burst length. From the sum and the outgoing line capacity, β is calculated by (Equation 4) (step 322). Further, β ₀ is obtained by (Equation 5).
(Step 323).

When β and β ₀ are obtained, an approximate value of the cell loss rate of the call type that maximizes the peak cell rate of the priority class when the terminal that has made the connection is connected is obtained from (Equation 1). Step 330). When an approximate value of the cell loss rate of the call type in which the peak cell rate of the priority class is maximum is determined, it is determined whether or not it is determined that the cell loss rate of the call type in which the peak cell rate is maximum falls within the allowable cell loss rate. Check (step 331). When the sum does not fall below the allowable cell loss rate, the intra-class sum management table 163 in the traffic management table 160 and the cumulative sum management table 165 indicate that the temporarily updated intra-class sum, the cumulative sum, the peak cell rate and the average cell of the worst traffic are obtained. The speed is restored to the original value (step 332), and the reception flag is set to 1
(Step 323), and returns a rejection notice to the CAC process
(Step 334).

When the above condition is satisfied, the current class is decremented by one (step 335), and the above series of cell loss rate evaluation processing is repeated up to the lowest priority class (step 304). When the approximate value of the cell loss rate is equal to or less than the allowable cell loss rate for all priority classes, it is determined that the approximate value of the cell loss rate when the connection setting request is received falls within the allowable cell loss rate. The intra-class total management table 163 in the traffic management table 160 and the cumulative total management table 165
The temporarily updated value is determined (steps 341 and 342). When the value of the provisional update is determined, based on the provisionally updated cumulative total of the cell rates, the cumulative total of the average cell rates, and the cumulative total of the variances of the cell rates, the priority class for which the connection request has been made is obtained according to (Equation 5). And updates the effective multiplex number ml of the priority class equal to or lower than the priority class for which the connection request has been made by (Equation 4) (step 343). Effective peak cell speed v
_After updating _l and the effective multiplex number _ml , the reception flag is set to 0 (step 345), and a reception acceptability notification is returned to the CAC process (step 346).

[0049] (b) As shown in the process diagram 14 of a call termination processing request, the priority class was the CAC processing of connection termination request, the peak cell rate of the made the connection termination request terminal v _i, the average cell rate <v _i >, Average burst length μ _i ⁻¹ ,
The square length variation coefficient Ci ² of the burst length is input (step 350). First, the current class representing the priority class currently being processed is set as the priority class for which a connection request has been issued (step 351). When the current class is set, the traffic management table 16 provided for each priority class is set.
In the call type management table 161 at 0, the value of the peak cell rate and the number of connected terminals corresponding to the average cell rate of the terminal that has made the connection termination request are counted down by -1. Here, when the number of connected terminals of the worst traffic becomes 0,
From the worst call type management table 162 in the traffic management table 160 after the countdown, the peak cell rate and the average cell rate of the traffic having the maximum peak cell rate are searched, and the peak cell rate and the average cell rate of the worst traffic are searched to find the call type. Update with the peak cell rate and average cell rate (step 352).

When the update of the call type management table 161 is completed, the terminal sum is calculated from the sum of the peak cell rates in the priority class, the sum of the average cell rates within the class, and the sum of the dispersion of the cell arrival rate within the class of the priority class for which the connection termination request has been issued. Peak cell velocity
v _i , average cell rate <v _i >, variance of cell arrival rate <v _i > {v _i − <v
_i >}, and updates the value of the intra-class total management table 163 of the traffic management table 160 (step 35).
3).

When the processing of the values in the intra-class total management table 163 is completed, the cumulative sum of the peak cell speeds and the cumulative sum of the average cell speeds of the priority class and lower that have been requested to terminate the connection are calculated.
From the cumulative sum of the variance of the cell arrival rate and the cumulative sum of the effective average burst length, the peak cell rate v _i , the average cell rate <v _i >, and the variance of the cell rate <v _i > {v _i − <V _i
>}, The effective mean burst length _{<v i> (1- <v} i> / v i) (1 + Ci 2) / 2
mu _i, effective average cell length _{<v i> (1- <v} i> / V) (1-v i / V) / subtracting a value of 2, updates the value of the cumulative sum management table 165 of the traffic management table 160 (Step 361).

[0052] When the process of updating the cumulative total management table 165 is completed, the cumulative sum of the updated cell rate, cumulative sum of the average cell rate and the cumulative sum of the cell velocity dispersion, the connection request by v _h (Equation 2) there priority classes less effective peak cell rate of, by m _h (Equation 2), and updates the number of effective multiple (step 362). After updating the effective parameters,
Return to the CAC process (step 364). FIG. 15 is a source of the cell loss rate evaluation processing in the present embodiment (Equation 1).
9 is a graph comparing a cell loss rate obtained by an approximate expression of (Equation 5) with a cell loss rate obtained by simulation. In the figure, the horizontal axis represents the buffer length, and the vertical axis represents the cell loss rate. In the figure, call types 1 to 3 assume the traffic shown in the following (Table 1).

[0053]

[Table 1]

Here, the cell loss ratio was compared for the two cases. In the first case, 16 connections of call type 1, 2 connections of call type 2 and 10 connections of call type 3 were multiplexed on the same outgoing line. In the second case, 48 connections of the call type 1, 3 connections of the call type 2 and 30 connections of the call type 3 were multiplexed on the same outgoing line. From this comparison,
It can be seen that the approximate expressions (Equation 1) to (Equation 5) have sufficient accuracy for the connection management function.

[Effects of the First Embodiment] As described above, according to the present embodiment, when a plurality of burst traffics having different traffic characteristics are multiplexed in the ATM switch performing the strict priority control by the strict priority control, , The cell loss rate in the priority class can be guaranteed. Further, in an ATM switch that performs strict priority control by strict priority control, when a plurality of burst traffics having different average cell rates, peak cell rates, average burst lengths, and burst length square variation coefficients are multiplexed, the peak cell rate in each priority class is increased. Since the cell loss rate of the largest call type can be evaluated by binomial distribution, exponential function, and four arithmetic operations, the implementation of the connection management function becomes easy. Furthermore, according to this embodiment, since the cell loss rate of the call type in which the peak cell rate is the maximum in each priority class is evaluated,
The amount of calculation required for call admission control can be made clear only by evaluating the cell loss rates of at most the number of priority classes. Therefore, even if the number of call types to be connected increases, the amount of computation required for call admission control does not increase significantly.

[Embodiment 2] In Embodiment 2 described below, instead of the average burst length and the coefficient of variation of the square of the burst length declared in Embodiment 1, a maximum burst is used as a traffic descriptor to be declared at the time of a connection setting request. CA
By C, the ATM switch 100 capable of suppressing the cell loss rates of all priority classes to the allowable cell loss rate or less is realized. Other traffic descriptors use the average cell rate and the peak cell rate as in the first embodiment.

When the maximum burst length is declared instead of the average burst length and the square variation coefficient of the burst length, the asymptotic form of the burst length distribution function when multiplexing the burst traffic cannot be uniquely specified. . Therefore, using the asymptotic form of the burst length distribution function,
It is possible to calculate the upper limit value of the cell loss rate and control the cell loss rates of all priority classes to be equal to or less than the allowable cell loss rate.
The TM exchange 100 has been realized. If only the maximum burst length can be specified, the worst traffic is traffic whose burst lengths all match the maximum burst. Therefore, the average burst length of the worst traffic becomes the maximum burst length, and the square variation coefficient of the burst length becomes zero. Then, if (average burst length) = (maximum burst length) and (burst length square variation coefficient) = 0, the upper limit value of the cell loss rate is calculated by the approximation method shown in the first embodiment. be able to. Further, when the maximum burst length is reported, only the upper limit of the cell loss rate can be calculated. Therefore, even if the approximation formula shown in the first embodiment is faithfully executed, it is not technically meaningful. Absent. Then, the cell loss rate P _k is calculated as shown in the following (Equation 6).
Approximate with only one exponential function.

[0058]

(Equation 6)

Further, in the present embodiment, L _k = 1 is replaced with the upper limit value in order to omit the operation relating to the binomial distribution. Then, the upper limit of the cell loss rate is (Equation 7).

[0060]

(Equation 7)

Here, the logarithm of both sides is given by (Equation 8).

[0062]

(Equation 8)

-Ln (P _k /0.6) on the left side is a constant. Therefore, when a new connection is received, it is possible to determine whether or not the cell loss rate exceeds the allowable cell loss rate by using only the four arithmetic operations according to (Equation 8).

[Configuration] (1) Overall Configuration (FIG. 5) Since the configuration is the same as that of the first embodiment, the description is omitted. (2) Configuration of Cell Loss Rate Evaluation Circuit 250 As shown in FIG. 16, the configuration of the cell loss rate evaluation circuit 250 includes a DSP (Digital Signal Processor) 151, a CP interface circuit 152, and a cumulative sum management table 260 for each priority class. , And a cell loss rate evaluation processing software memory 251 and a termination processing software memory 251. These circuits are connected by a bus controlled by a bus control circuit 153. The cumulative total management table 260 is shown in FIG.
As shown in FIG. 7, (determined) cumulative sum of peak cell speeds, (temporary update) cumulative sum of peak cell speeds, and
(Fixed) Cumulative sum of average cell rate, (Temporary update) Cumulative sum of average cell rate, (Fixed) Cumulative sum of variance, (Temporary update)
Cumulative total of dispersion, (determined) cumulative sum of multiplexed number, (temporary update) cumulative sum of multiplexed number, (determined) cumulative total of effective average burst length, (temporary updated) effective average burst length, (determined) effective average cell Length cumulative sum, (temporary update) Cumulative sum of effective average cell length.

[Operation] (1) Outline of Operation Since the operation is the same as that of the first embodiment, the description is omitted. (2) CAC processing 600 Since this is the same as the second embodiment, the description is omitted. (3) Operation of Cell Loss Rate Evaluation Circuit 250 In the present embodiment, the cell loss rate evaluation processing is β
Only consists of calculating Also in this embodiment, the outgoing line capacity and the buffer length of each priority class are set when the exchange is started up.

(A) Connection Judgment Process (FIG. 18) When the connection judgment process is started by the cell loss rate evaluation request (step 172), the priority class of the connection request from the CAC process and the terminal of the connection request terminal Peak cell speed
The user is ^required to input v _i , the average cell rate <v _i >, and the maximum burst length μ _i ^-1 (step 400). First, the current class representing the priority class currently being processed is set as the priority class for which a connection request has been issued (step 401). When the current class is set, the peak cell rate of the terminal that has made the connection request is required to temporarily update the value of the cumulative total management table 260.
v _i , average cell rate <v _i >, effective maximum burst length <v _i > (1- <
_{v i> / v i) /} 2μ i the temporarily addition (step 411).

When the value of the cumulative sum management table 260 is provisionally updated, the provisionally added sum of the peak cell rate, the sum of the average cell rates, the sum of the effective maximum burst length, the outgoing line capacity, and (Equation 4) Β _h of the priority class is obtained by Expression 5) (step 412). When β _h is obtained, (Equation 8)
It is checked whether the condition (1) is satisfied (step 413). If not satisfied, it is determined that the upper limit of the cell loss rate when receiving the connection setting request is equal to or more than the allowable cell loss rate, the cumulative sum of the peak cell rate in the cumulative sum management table 260 of the priority class for which the connection request was made, The cumulative sum of the average cell rate and the cumulative sum of the effective maximum burst length are restored to their original values (step 414), the acceptance flag is set to 1 (step 415), and a rejection notice is returned to the CAC process (step 416).

When the above condition is satisfied, the current class is decremented by one (step 417), and the above series of cell loss rate evaluation processing is repeated up to the lowest priority class (step 410). When the above conditions are satisfied for all priority classes, it is determined that the upper limit value of the cell loss rate at the time of receiving the connection setting request is within the allowable cell loss rate, and the provisionally updated value is determined. (Step 4
20). When the determination of the provisional update value is completed, the reception flag is set to 0 (step 423), and a reception acceptability notification is returned to the CAC process (step 424).

[0069] (b) as shown in process 19 at the connection end processing request, the priority class was the CAC processing of connection termination request, peak cell rate v _i of made the connection request terminal, the average cell rate <v _i >, the maximum burst length mu _i ^- get type ¹ (step 430). First, the current class representing the priority class currently being processed is set as the priority class for which a connection request has been issued (step 431). When the current class is set, in order to update the value of the cumulative total management table 260, from the cumulative total of the peak cell rates, the cumulative total of the average cell rates, and the cumulative total of the effective maximum burst length, peak cell rate v _i of made the connection termination request terminal, the average cell rate <v _i>, the effective maximum burst length _{<v i> (1- <v} i> / v i) / subtracting the value of the 2.mu. _i (step 432 433, 434). When the cumulative sum subtraction process is completed, the process returns to the CAC process (step 435).

[Effects of Second Embodiment] As described above, according to the second embodiment, when a plurality of burst traffics having different traffic characteristics are multiplexed in an ATM switch performing strict priority control by strict priority control, , The cell loss rate in the priority class can be guaranteed. Also, in a case where a plurality of burst traffics having different average cell speeds, peak cell speeds, and maximum burst lengths are multiplexed in an ATM switch performing strict priority control by strict priority control, a cell of a call type in which the peak cell speed in each priority class is maximum. Since the upper limit value of the loss rate can be evaluated only by the four arithmetic operations, the exponential function and the function operation such as the binomial distribution are unnecessary, and the connection management function can be implemented only by the fixed-point operation. Further, according to the present embodiment, the amount of computation required for call admission control can be cleared only by evaluating the upper limit of the cell loss rate in each priority class. Therefore, even if the number of call types to be connected increases, the amount of computation required for call admission control does not increase significantly.

[0071]

According to the present invention, it is possible to obtain an ATM exchange which can reduce a call loss rate and improve a line utilization rate in control of acceptability of connection setting in strict priority control.

[Brief description of the drawings]

FIG. 1A is a diagram for explaining strict priority control;
(B) is a figure which shows a mode when the cell arrival rate exceeds the line capacity excessively.

FIG. 2 is a diagram illustrating a configuration example of an ATM network.

FIG. 3 shows a cell format used in an ATM network, wherein (a) is a call setup request cell, (b) is a response cell, (c) is a release cell, (d) is a call setup request cell, and (e). () Is a diagram showing the format of each user cell.

FIG. 4 is a diagram showing one embodiment of an ATM exchange according to the present invention.

FIG. 5 is a diagram illustrating a configuration example of a buffer queue.

FIG. 6 is a diagram showing a configuration of a control processing (CP) circuit.

FIG. 7 is a diagram illustrating a configuration example of a cell loss rate evaluation circuit.

FIG. 8 is a diagram illustrating a configuration example of a traffic management table.

FIG. 9 is a diagram showing a process of receiving a call setup request cell.

FIG. 10 is a diagram showing a process of receiving a response cell.

FIG. 11 is a diagram illustrating a process of receiving a released cell.

FIG. 12 is a diagram showing a cell loss rate evaluation process.

FIG. 13 is a diagram illustrating an outflow line overflow rate evaluation process.

FIG. 14 is a diagram illustrating connection termination processing.

FIG. 15 is a graph showing a cell loss rate obtained from an approximate expression and a simulation.

FIG. 16 is a diagram illustrating a configuration example of a cell loss rate evaluation processing circuit.

FIG. 17 is a diagram illustrating a configuration example of a cumulative total management table.

FIG. 18 is a diagram illustrating a connection determination process.

FIG. 19 is a diagram illustrating connection termination processing.

[Explanation of symbols]

 Reference Signs List 5 ATM terminal 6 ATM network 7 Connection 8 Buffer queue 9 Output selector 100 ATM switch, 150 Cell loss rate evaluation circuit

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Katsuhiko Taruya 216 Totsuka-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture F-term in Hitachi, Ltd. Information and Communication Division 5K030 GA00 HA10 HB14 HB29 KX11 KX29 LB02 LC06

Claims (4)

[Claims] An ATM switch for reading data from a cell of a higher priority class when a cell exists in a buffer of a higher priority class among a plurality of priority classes. When there is a setting request, the connection setting request acceptability is controlled based on an approximate value of the cell loss rate calculated using the parameter relating to the burst length of each connection and the buffer length of each priority class. ATM switch. 2. A cell loss rate of each priority class in strict priority control at the time of a connection setting request from a terminal is calculated based on a traffic descriptor of the terminal, an output line capacity of an exchange, and a buffer length of each priority class, When the calculated cell loss rate is equal to or greater than the allowable cell loss rate, control is performed so as not to accept a connection setting request from a terminal. 3. The ATM switch according to claim 2, wherein said traffic descriptor comprises an average cell rate, a peak cell rate, an average burst length, and a square variation coefficient of the burst length. 4. The ATM switch according to claim 2, wherein said traffic descriptor comprises an average cell rate, a peak cell rate, and a maximum burst length.