JP3386092B2 - ABR cell flow control method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ABR cell flow rate control method for maintaining communication quality in an ABR service without being affected by increase / decrease in the number of connections of other service classes (CBR, VBR) in an ATM network.

[0002]

2. Description of the Related Art ATM (Asynchronous Transfer Mode)
Divides the information to be transferred into blocks called cells,
This is a type of high-speed packet communication in which a header containing control information such as a destination is added to each cell for transfer. The AT
In the M network, it is expected that a plurality of types of calls (multi-source traffic) having different characteristics such as communication speed and quality of service will share the network equipment to realize economical design and efficient operation of the network. There is.

As described above, various types of traffic having different characteristics are transferred on the ATM network (traffic having severe conditions for transfer delay time, traffic having severe conditions for cell loss rate, etc.). CBR (Constant BitRate), VBR (Variable B
it Rate), ABR (Available Bit Rate), UBR (U
It is categorized into four categories, nspecified Bit Rate). Of these, CBR and VBR are traffic classes whose traffic patterns are known in advance.
BR handles fixed-rate transmission services, and VBR handles variable-rate transmission services.

On the other hand, ABR and UBR are traffic classes whose traffic patterns cannot be predicted in advance. Among them, in ABR communication (hereinafter, referred to as ABR service), by effectively utilizing the unused band of the priority class (CBR, VBR), the data traffic having a very strong burst characteristic like the conventional LAN service is used. Is expected as a service class for supporting the ATM on the ATM network.

Further, the ABR service is a service class in which the condition regarding the transfer delay time is loose and the condition regarding the cell loss rate is severe. Therefore, other priority classes (CBR,
By changing the cell transmission rate according to the usage status of the ATM network by VBR), it is possible to support very strong bursty traffic like a conventional LAN without affecting the communication quality of the priority class. I am aiming for.

By the way, the user of the ABR service declares an MCR (Minimum Cell Rate) at the time of connection, and the ABR service once connected to the network side.
Regarding services, no matter how busy the ATM network is,
Cell transmission on the MCR must be guaranteed. Therefore, at the time of accepting an ABR connection request, whether or not cell transmission at the declared MCR can be guaranteed is one of the important criteria for the acceptance judgment on the network side, and therefore, the available bandwidth available for the ABR service. Need to estimate.

A conventional flow control method for ABR cells in an ATM network will be described below with reference to the drawings. Figure 6
FIG. 4 is a block diagram showing a configuration example of a conventional ATM network.
In this figure, 1 is a terminal and 2 is a switch.

Although not shown in FIG. 6, the switch 2 has a cell buffer for ABR as shown in FIG.
(Referred to as BR buffer). Since the ABR cell is sent out on the transmission line 5 by the FIFO (first-in first-out) method through the ABR buffer, when the ATM network 6 becomes crowded and the available bandwidth becomes smaller, the A
BR cells are accumulated in the ABR buffer (in the example shown in FIG. 7, ABR cells waiting to be transmitted are accumulated from the right end of the ABR buffer toward the left). Waiting for delivery AB
When the amount of R cells exceeds the congestion detection threshold shown in FIG. 7, in order to prevent the overflow of the ABR buffer, the ABR
The cell delivery rate of the cell is reduced to MCR. In FIG. 7, l ₁ is the capacity portion that stores ABR cells in the period from the detection of congestion to the occurrence of overflow, and l 1
₂ is a capacity portion that stores ABR cells in the period from the release of congestion to the occurrence of underflow, and l ₃ is a capacity portion other than that.

Further, in FIG. 6, 3 is a call control unit. Reference numeral 104 denotes a free bandwidth estimation processing unit, which uses a procedure (see FIG. 8) described later to determine whether or not the ABR service that has requested the connection can be permitted to send cells in the declared MCR. I do. In addition, in FIG.
Reference numeral 5 is a transmission line, and 6 is an ATM network.

Next, the operation of the ATM network having the above configuration will be described. FIG. 8 is a flowchart showing an example of a processing procedure performed by the free band estimation processing unit 104. Hereinafter, the processing in each step will be described in order. 1. Step S1 In step S1, first, priority classes (CBR, VB
The identifier i (i = 1, ..., N) is given to the user R). When a user i requests a connection of a priority class service, PCR (Peak Cell Rate: maximum cell transfer rate, hereinafter, P _i is used as a variable indicating the value), SCR (Sustainable Cell Rate: average cell) in the service. Transfer rate, hereinafter S _i is used as a variable indicating the value thereof) and BT (Burst Tolerance: hereinafter B _i is used as a variable indicating the value thereof) are notified from the call control unit 3 to the free band estimation processing unit 104. (See FIG. 6). At this time, if the service class of the user i is CBR, SCR is equal to PCR (P _i = S _i ),
For BT, B _i = 0. Also, these quantities are
The one-cell transfer time L / C set to one slot is used as a unit of time. Here, C is the cell length, and L is the capacity (transmission path speed) of the entire band.

2. Step S2 In step S2, first, the free band estimation processing unit 104
Based on the declared P _i , S _i and B _i after confirming that the service class of the user i satisfies the GCRA (S _i , B _i ) defined by the UNI specifications of the ATM forum. , A traffic model as shown in FIG. 9 is determined. In this traffic model, burst-like cell transmission by PCR is

[Equation 1] Only the slots last and the cell rate of x _i (0 ≦ x _i ≦ S _i ) is

[Equation 2] The process of sustaining only slots is repeated cyclically. Here, x _i is a parameter that controls the interval at which bursty cell transmission occurs. Further, the repetition cycle is calculated based on the following equation (3).

[Equation 3]

Next, the average usage rate ρ of the band by the users of the priority classes (CBR, VBR) is calculated using the following equation (4).

[Equation 4]

Next, the measurement time interval T is calculated as follows. First, an identifier j (j
= 1 ,. ． ． , M), and the band usage rate ρ ^a by ABR users when all ABR users j perform cell transmission in MCR are calculated using the following equation (5).

[Equation 5] Here, M _j is the MCR of each user j.
Then, using the band usage rate ρ ^a , the measurement time interval T
Is calculated using the following equation (6). T = (l ₁ +1) / ρ ^a (6) where l ₁ is the period from the detection of congestion to the occurrence of overflow. It is a capacity portion that stores ABR cells (see FIG. 7).

Next, the variance (Allan variance) σ _i ² of the band usage rate by the user i of the priority class (CBR, VBR)
(T) is calculated using the following equation (7).

[Equation 6] Here, X _i (T) is the band usage rate by user i when measured over consecutive T slots.

The calculation of σ _i ² (T) is actually performed by the following method. First, when an arbitrary time is set to 0,
Let N _i (T _i ; x _i ) be the number of cells arriving from user i in the time interval [0, T). Also, a non-negative integer C _i
Define (x _i ) and D _i (x _i ). Where D _i (x
_i) The traffic model (period W _i (x _i see FIG. 9))
It is smaller (that is, D _i (x _i ) <W _i (x _i )) and has the relationship of the following expression (8) with respect to the measurement time interval T. T = C _i (x _i ) W _i (x _i ) + D _i (x _i ) ... (8)

[0016] Thus, N _i is expressed _{as;; (x i T i)} , said N _i ^min the minimum value of _{(T i x i) N i} min (T i; x i)
Is given by the following equation (9).

[Equation 7] The probability is given by the following equation (10).

[Equation 8]

[0017] Similarly, N _i; the maximum value of (T _i x _i) N _i
^When expressed as ^max (T _i ; x _i ), the N _i ^max (T _i ; x _i ) is
It is given by the following equation (11).

[Equation 9] The probability is given by the following equation (12).

[Equation 10]

As a result, when the parameter x _i of the traffic model (see FIG. 9) is given, the variance (Allan variance) σ _i ^{2 of} the band usage rate depending on the measurement time interval T.
(T; x _i ) is calculated using the following equation (13).

[Equation 11] Finally, a parameter x _i is given so as to maximize σ _i ² (T; x _i ) (see the following equation (14)), and σ _{i at} that time is given.
² (T; x _i ) is the variance σ of the bandwidth usage rate by user i
_i ² (T)

[Equation 12]

Next, the variance σ ² (T) of the band usage rate by all users i in the priority class (CBR, VBR) is calculated using the following equation (15).

[Equation 13]

3. Step S3 First, the probability P _loss from congestion detection to overflow in the ARB buffer is calculated using the following equation (16) in which the Chebyshev inequality is applied to the queue length of the ABR buffer (for details of the calculation method, See the IEICE Spring General Conference Reference B-848). P _loss = σ ² (T) / (1-ρ) ² ... (16) The probability P _loss is preset in the memory in the free band estimation processing unit 104. If it is smaller than the specified quality value P, the call control unit 3 is notified to connect the ABR service to the transmission line 5 (see FIG. 6).

By the processing in steps S1 to S3 described above, the declared value (PCR, SCR and BT) from the user
As a result, the available free band of the ABR service can be estimated, and the flow rate of the ABR cell using the available band can be controlled.

[0022]

As described above, in the conventional ABR cell flow rate control method by the ATM network, the transmission path use status by the priority class (CBR, VBR) is AB
The communication quality in the ABR service can be guaranteed only when the R service connection is maintained even after the reception of the R service connection. However, in general, the connection and release of the priority class is A
Since it is performed independently of the BR service connection, A
It is unlikely that the usage status of the transmission path at the time of receiving the BR service connection request will be maintained as it is even after the ABR service connection. Of course, in order to guarantee the communication quality of a specific ABR service, it is not allowed to forcibly disconnect the already-received connection of the ABR service or cancel the new connection of the priority class service. in this way,
The above-mentioned conventional ABR cell flow rate control method in the ATM network has a drawback that it is difficult to maintain the communication quality of the ABR service when the number of connections of the priority class service changes after the connection of the ABR service.

The present invention has been made under such a background, and even after the connection of the ABR service, even if the number of connections of the priority class service changes, the ABR cell which can maintain the communication quality of the ABR service. An object is to provide a flow rate control method.

[0024]

[0025]

[0026]

Means for Solving the Problems The invention according to claim 1,
If a buffer is provided in the ATM network and the amount of ABR cells in the transmission waiting state accumulated in the buffer exceeds a threshold value, the ABR cell that reduces the cell flow rate by the ABR service in the ATM network to MCR In the flow rate control method, each of the peak cell rate, sustainable cell rate, and burst tolerance declaration parameters declared by a user in a priority class having a higher priority than the ABR service when making a call setup request, and the user of the ABR service makes a call setup request. The minimum cell rate to be declared at that time is stored in advance, and the A
Each time the number of priority class services connected to the TM network changes, the peak cell rate, sustainable cell rate, and burst tolerance of the changed priority class services are acquired, and priority class users are acquired based on the sustainable cell rate. A bandwidth average usage rate is calculated, and a measurement time interval is determined from the bandwidth usage rate by the ABR user calculated from the minimum cell rate and the capacity of the cell buffer dedicated to the ABR service, and the measurement time interval and the priority class declaration. Based on the parameters, the variance of the bandwidth utilization by the priority class users is calculated, and the ABR buffer is calculated based on the sum of the average bandwidth utilization by the priority class users and the variance of the bandwidth utilization by the priority class users. By applying the Chebyshev inequality to the distribution of the number of waiting cells of It calculates the probability of reaching the overflow from the congestion detecting B buffer, so that said probability is equal to the predetermined quality specification value, and changes the threshold value of the ABR buffer.

According to the second aspect of the present invention, a buffer is provided in the ATM network, and A in the transmission waiting state accumulated in the buffer is stored.
When the amount of BR cells exceeds a threshold, in the ABR cell flow control method of reducing the cell flow by the ABR service in the ATM network to MCR, a user of a priority class having a higher priority than the ABR service. Each of the peak cell rate, sustainable cell rate, and burst tolerance declaration parameters declared by the user at the time of call setup request
The minimum cell rate declared by the user of the BR service at the time of call setup request is stored in advance, and each time the number of priority class services connected to the ATM network changes, the peak cell rate of the priority class service and the sustainable cell changed. Rate, burst tolerance, and based on the sustainable cell rate, the average bandwidth usage rate by the priority class user is calculated, and the bandwidth usage rate by the ABR user calculated from the minimum cell rate and the cell buffer dedicated to the ABR service. Determines the measurement time interval from the capacity of the, and based on the measurement time interval and the declaration parameters of the priority class, calculates the variance of the bandwidth usage rate by the priority class user, and the average bandwidth usage rate by the priority class user and the Based on the sum of the variances of bandwidth utilization by priority class users, AB Fokker of the number of wait cell of buffer
-By applying the diffusion approximation with the Planck equation ,
It is characterized in that the probability from the congestion detection of the ARB buffer to the overflow is calculated, and the threshold value of the ABR buffer is changed so that the probability becomes equal to a predetermined quality regulation value.

[0028]

DETAILED DESCRIPTION OF THE INVENTION

§1. Effect According to the present invention, in the ATM network that controls the flow rate of the ABR cell based on the threshold value of the buffer, each time the number of priority class services connected to the ATM network changes,
Since the usage status of the transmission path in the ATM network is obtained and the threshold value is changed according to the usage status of the transmission path, the ABR cell can be transmitted at the maximum cell flow rate at that time while avoiding the overflow of the buffer. it can.

§2. First Embodiment Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an A according to a first embodiment of the present invention.
It is a block diagram showing an example of composition of an ATM network to which a BR cell flow rate control method is applied. In this figure, parts corresponding to the parts in FIG. 6 are assigned the same reference numerals and explanations thereof are omitted. In the ATM network shown in this figure, a free band estimation processing unit 4 is newly provided in place of the free band estimation processing unit 104. The free band estimation processing unit 4 uses the procedure described later (see FIG. 2) to determine whether the ABR service that has requested the connection can be permitted to send cells in the declared MCR. To do. In addition, in FIG.
Reference numeral 2a is an ABR buffer, which is the same as that used in the conventional ATM network (see FIG. 7).

Next, the operation of the ATM network having the above configuration will be described. FIG. 2 is a flowchart showing an example of a processing procedure performed by the free band estimation processing unit 4. The processing in steps SA1 to SA3 shown in this figure is the same as the processing in steps S1 to S3 shown in FIG. That is, when the connection request for the ABR service is received, the free bandwidth estimation processing unit 4 performs the same processing as the free bandwidth estimation processing unit 104 (steps SA1 to SA3), and the probability P _loss from the congestion detection of the ARB service to the overflow P _loss. When the probability P _loss is smaller than the quality regulation value P preset in the memory in the free band estimation processing unit 4, the ABR service is connected to the transmission line 5,
Notify the call control unit 3 (see FIG. 1). As a result, the call controller 3 controls the switch 2 to connect the ABR service to the transmission line 5.

After the processing of steps SA1 to SA3 is completed, the process proceeds to step SA4. At step SA4, the ATM network 6
When the number of connections of the priority class (CBR, VBR) service in the above changes, the call control unit 3 determines whether the priority class PCR,
The SCR and BT are notified to the free band estimation processing unit 4 (see FIG. 1). The free band estimation processing unit 4 uses the same method as when the probability P _loss was previously calculated, and the PCR, S
Based on CR and BT, the probability P ″ _loss from congestion detection of the ARB service to overflow is newly calculated.

Next, the newly calculated probability P ″ _loss is
T ″ (> T) is selected so as to be equal to the quality regulation value P. That is, T ″ that satisfies the following expression (17) is selected.

[Equation 14] This is equivalent to selecting T ″ that satisfies the following Expression (18). Σ ² (T ″) = P (1−ρ) ² ... .. (18) At this time, σ ² (T) is obtained by using the property of decreasing with respect to T in the order of T ⁻² .

Here, selecting T ″ is equivalent to selecting l ₁ ″ (see FIG. 7) that satisfies the following expression (19).

[Equation 15] "After selecting, the l _1" l ₁ ABR buffer 2 on the basis of
It notifies the call control unit 3 to change the congestion detection threshold value of a (see FIG. 1).

The free band estimation processing unit 4 performs the above-described processing of step SA4 each time the number of priority class service connections in the ATM network 6 increases or decreases. By the above processing,
It is possible to guarantee the communication quality at the time of receiving the ABR service regardless of the increase or decrease in the number of connections of the priority class service after the connection of the ABR service.

§3. Second Embodiment Next, a second embodiment of the present invention will be described. The free band estimation method according to the present embodiment is realized by the process flow shown in FIG. 3 in the free band estimation processing unit 4 of FIG. Here, as shown in FIG. 4, the coordinate system is selected so that the coordinates at l ₁ ^# from the end of the ABR buffer are q = 0 and the ends of the ABR buffer are q = l ₁ ^# .

1. It is assumed that a prescribed value P that allows the probability that the ABR buffer overflows even if the ABR connection is lowered to MCR is given. The tail value q ^* of the standard normal distribution that gives this probability is

[Equation 16] Is determined in advance so that

2. An identifier i (i = 1, ..., N) is given to a user of a priority class such as CBR or VBR. As shown in FIG. 1, when the user i requests call setting, PCR P _i , SCR S _i , and BT B _i are notified from the call control unit 3 to the free band estimation processing unit 4 (step SB).
1). At this time, if the user i is CBR, SC
Let R be equal to PCR (P _i = S _i ), and zero for BT (B _i = 0).

3. The free band estimation processing unit 4 uses the CBR,
A user i in a priority class such as VBR is an ATM Forum.
PCR P _i , SCR declared as satisfying GCRA (S _i , B _i ) defined by the UNI specifications of
The following traffic model is determined from S _i and BT B _i . First, it is assumed that the cell length is C, the capacity (transmission path speed) of the entire band is L, and the time required to transfer one cell is one slot. Furthermore, let x _{i be} a parameter that governs the interval at which bursty cell transmission in PCR occurs. Also,
As shown in FIG. 9, the repetition period W _i (x _i ) is set to W _i
Let (x _i ) = W _i ^on + W _i ^off (x _i ).

Then, as shown in FIG. 9, CBR, VB
Traffic from a user i in a priority class such as R is sent to a PC
The burst-like cell transmission in R lasts for W _i ^on slots, and the cell rate of x _i (0 ≦ x _i ≦ S _i ) is W _i ^off (x _i ).
A process of periodically repeating a process of lasting only slots is adopted. Here, W _i ^on = (B _i S _i +1) / (P _i −S _i ), and W _i ^off (x _i ) = (B _i S _i +1) / (S _i −x _i ). .

4. The average usage rate ρ ^h of the band by the users of the priority classes such as CBR and VBR

[Equation 17] Calculate with. 5. The time interval T ₀ is calculated as follows. Now A
MC of user j (j = 1, ..., m) of BR service
When R is M _j , the band usage rate ρ by ABR users when all ABR users perform cell transmission in MCR.
^a is

[Equation 18] Given in.

Next, it is assumed that the cell buffer for ABR is prepared as shown in FIG. In the figure, l ₁ is the capacity from congestion detection to cell overflow, l ₂ is the capacity from congestion release to cell buffer underflow, and l ₃ is the capacity other than these. Also, considering the control delay required to reduce the rate of each ABR connection to MCR after detecting the congestion, the buffer capacity prepared for that is set to l ₁ ^c .

[0042] and the amount obtained by subtracting the l ₁ ^c from l ₁

[Formula 19] Focusing on the time interval T ₀

[Equation 20] And Therefore, the time interval T ₀ means the minimum number of slots until the ABR buffer overflows after the rate of each ABR connection becomes MCR.

6. The variance of the band usage rate by the user i of the priority class such as CBR and VBR is calculated as follows.
Let X be the bandwidth utilization by users i of these priority classes when measuring over consecutive t slots.
_{Let i} (t). At this time, the variance (Allan variance) σ _i ² (t) of the band usage rate depending on the measurement time interval t is σ _i ² (t) ≡E [(X _i (t) −S _i ) ² ] ( Step SB2).

In practice, this calculation is performed as follows. First, when an arbitrary time is set to 0, the number of cells arriving from the user i in the time interval [0, t) is N _i (t;
x _i ). In addition, the measurement time interval t is a non-negative integer C
By using (x _i ) and D (x _i ) <W _i (x _i ) to uniquely decompose as t = C _i (x _i ) W _i (x _i ) + D _i (x _i ), Define C (x _i ) and D (x _i ).

Further, the minimum value of N _i (t; x _i ) is set to N
_When expressed as _i ^min (t; x _i ), this means N _i ^min (t; x _i ) = C _i (x _i ) (P _i W _i ^on + x _i W _i ^off
(X _i )) + x _i min (D _i (x _i ), W _i ^off (x _i ))
+ P _i max (0, (D _i (x _i ) −W _i ^off (x _i ))). The probability is P _i ^min = Pr [N _i = N _i ^min ] = | D _i (x _i ) −W _i ^off
(X _i ) | / W _i (x _i )

[0046] Similarly, N _i; the maximum value of (t x _i) N _i ^max
Expressed as (t; x _i ), this is N _i ^max (t; x _i ) = C _i (x _i ) (P _i W _i ^on + x _i W _i ^off
(X _i )) + P _i min (D _i (x _i ), W _i ^on ) + x _i m
It is given by ax (0, (D _i (x _i ) −W _i ^on )). The probability is P _i ^max = Pr [N _i = N _i ^max ] = | D _i (x _i ) −W
_i ^on (x _i ) | / W _i (x _i ).

From the above, when the parameter xi of the traffic model is given, the variance (Allan variance) σ _i ² (t; x _i ) of the band usage rate depending on the measurement time interval t is σ _i ² (t; x _i ) = {P _i ^max (N _i ^max ) ² + P _i ^min (N _i
^min ) ² } / t ² + (1-P _i ^max −P _i ^min ) × {(N _i ^{max
_{-N i min) 2/3 +}} (N i min) 2 + N i min (N i max -N i
^min )} / t ² −S _i ² .

Then, the rate parameter x _i is σ
The variance σ _i ² (t) of the band usage rate by the user i is given so as to maximize _i ² (t; x _i ). That is,

[Equation 21] Is. 7. All users i in priority classes such as CBR, VBR, etc.
= 1 ,. ． ． , N the bandwidth usage variance σ ² (t) is calculated as follows.

[Equation 22]

8. Assuming that the queue length of the ABR buffer at the measurement time interval t = 0 is known, the variance of the queue length of the ABR buffer at the measurement time interval t = T is σ.
² (T) is given by T ^2, have been found to behave as in FIG. 5 with respect to the measurement time interval t. Based on this, the constant α

[Equation 23] And calculate.

9. σ ² (1) is

[Equation 24] Can be calculated without depending on the BT of GCRA or the rate parameter x _i of the periodic traffic model.
A method of setting σ ² (1) = ρ ^h (1-ρ ^h ) is also possible.

10. In FIG. 5, assuming that the intersection of σ ² (1) t ² and the constant α is t = T ₁ , T ₁ is

[Equation 25] Is calculated. 11. The distribution of the queue length of the ABR buffer is tε
For [0, T ₁ ) we have σ ² (1) t ² ··· (22) and for t ∈ [T ₁ , ∞) α ·・ ・ ・ ・ ・ ・ ・ ・ ・ (23) will be approximated. This approximation is excessive (safe side)
It is an evaluation.

12. At time t, the probability that the queue length of the ABR buffer is in the interval [q, q + dq) is P (q, t).
Let dq. As an initial state, P (q, 0) = δ
(Q). Here, δ is a Dirac delta function. Next, as an equation that P (q, t) should satisfy,
Fokker-Plan c k equation

[Equation 26] think of.

In this equation, the first term on the right-hand side describes a deterministic drift motion and the second term on the right-hand side describes a stochastic diffusion motion. Also, A (q, t) ≡−
(1-ρ ^a −ρ ^h ), and regarding B (q, t), the procedure 11. From Equations (22) and (23) showing approximation of queue length variance of ABR buffer based on Allan variance described in

[Equation 27] And

In order to simplify the handling, AB
Without setting the boundary condition corresponding to the R buffer capacity, the formula (2
Solving 4), if 0 ≦ t <T ₁ ,

[Equation 28] And when T ₁ ≤t

[Equation 29] Get the solution. Thus, in any case, P
(Q, t) has a normal distribution with respect to q.

13. The probability of falling into heavy congestion at time t = T

[Equation 30] As a general rule, the probability of reaching a heavy congestion state is P ^* _loss ≡ ma
It is approximated as x _t P _loss (t). If T ₁ <T ₀ ,
Clearly P ^* _loss = P _loss (T ₀ ). Also, T ₁ ≧
In the case of T ₀ , when the equation (25) is converted into the standard normal distribution, l ₁ ^# → {l ₁ ^# + (1-ρ ^a −ρ ^h ) t} / (σ
(1) t), which decreases as t increases, so P ^* _loss = P _loss (T ₁ ).

Therefore, in reality, T ^* = max (T ₀ ,
T ₁ ), P (q, T ^* ) obtained therefrom is transformed into a standard normal distribution, and the image l ₁ ^* of l ₁ ^# resulting from the transformation is converted.

[Equation 31] Ask as. 14. If l ₁ ^* ≧ q ^* , it is determined that the free band is sufficient, and if l ₁ ^* <q ^* , it is determined that it is insufficient (step SB3). Then, as shown in FIG. 1, the free band estimation processing unit 4 notifies the call control unit 3 of this result.

15. After ABR connection acceptance processing,
When the number of priority class connections is increased or decreased, PCR P _i , SCR S _i and BT B _i of the priority class connections are obtained (see FIG. 1), and l ₁ is newly calculated.

16. The newly calculated l ₁ is the value q ₀ according to the quality regulation value determined when the ABR connection is accepted.
T ₀ is reselected to be equal to, that is, q ₀ = l ₁ . This means l ₁ is max
If (T ₀ , T ₁ ) = T ₁ ,

[Equation 32] If max (T ₀ , T ₁ ) = T ₀ , then

[Expression 33] And reselecting, that is, changing the congestion determination threshold value.

17. The congestion determination threshold of the ABR buffer is changed based on the new l ₁ = l ₁ ^c + l ₁ ^# (see FIG. 1). 18. Every time the number of priority class connections increases or decreases, the above-mentioned procedure 4. The subsequent processing is repeated. With the above procedure, it is possible to guarantee the communication quality at the time of accepting an ABR connection regardless of the increase or decrease in the priority class connections thereafter.

The embodiment of the present invention has been described in detail above with reference to the drawings. However, the specific configuration is not limited to this embodiment, and the design change and the like without departing from the gist of the present invention. Even this is included in this invention.

[0061]

As described above, according to the present invention, in the ATM network in which the flow rate of the ABR cell is controlled based on the threshold value set in the buffer, the priority class service connected to the ATM network is provided. Each time the number of cells changes, the usage status of the transmission path in the ATM network is obtained, and the threshold value is changed according to the usage status of the transmission path. Therefore, while avoiding the overflow of the buffer, the maximum cell flow rate at that time is obtained. ABR cells can be sent at. As a result, the communication quality at the time of receiving the ABR service can be guaranteed regardless of the increase or decrease in the number of connections of the priority class service thereafter.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration example of an ATM network to which an ABR cell flow rate control method according to the present invention is applied.

FIG. 2 is a flowchart showing an example of a processing procedure of an ABR cell flow rate control method according to the first embodiment of the present invention.

FIG. 3 is a flowchart showing an example of a processing procedure of an ABR cell flow rate control method according to a second embodiment of the present invention.

FIG. 4 is an explanatory diagram showing a configuration of an ABR cell buffer and its coordinate system in the same embodiment.

FIG. 5 is a graph showing the behavior of the variance σ ² (t) t ² of the queue length of the ABR buffer in the same embodiment.

FIG. 6 is a block diagram showing a configuration example of a conventional ATM network.

FIG. 7 is an explanatory diagram showing a configuration example of an ABR buffer.

FIG. 8 is a flowchart showing an example of a processing procedure of a conventional ABR cell flow rate control method.

FIG. 9: G specified in the UNI specification of ATM Forum
It is explanatory drawing which shows an example of the traffic model according to CRA.

[Explanation of symbols]

1 ... Terminal, 2 ... Switch, 2a ... ABR buffer, 3 ... Call control unit, 4,104 ... Free band estimation processing unit, 5 ... Transmission line, 6 ... ATM network

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-7-154421 (JP, A) JP-A-6-244858 (JP, A) JP-A-9-102785 (JP, A) European Patent Application Publication 639014 (EP, A 1) 1995 IEICE Communication Conference, B-491 1995 IEICE General Conference, B-848 IEICE Technical Report, SSE95-71 IEICE Technical Report, SSE95-20 (58) Fields investigated (Int .Cl. ⁷ , DB name) H04L 12/56

Claims (2)

(57) [Claims] 1. A buffer is provided in an ATM network, and when the amount of ABR cells in the transmission waiting state accumulated in the buffer exceeds a threshold value, the flow rate of cells by the ABR service in the ATM network is changed. In an ABR cell flow rate control method for reducing to MCR, each of the peak cell rate, sustainable cell rate, and burst tolerance declaration parameters declared by a user in a priority class having a higher priority than the ABR service at the time of call setup request, and the ABR service The minimum cell rate that the user declares at the time of call setup request is stored in advance, and whenever the number of priority class services connected to the ATM network changes, the peak cell rate, sustainable cell rate, and burst of the changed priority class services are stored. Tolerance is obtained, and priority class user is based on the sustainable cell rate. The bandwidth average utilization rate by the A is calculated, the measurement time interval is determined from the bandwidth utilization rate by the ABR user calculated from the minimum cell rate and the capacity of the cell buffer dedicated to the ABR service, and the measurement time interval and the priority class Based on the declared parameters, the variance of the bandwidth usage rate by the priority class users is calculated, and based on the sum of the average bandwidth utilization rate by the priority class users and the variance of the bandwidth usage rates by the priority class users, the ABR Cheby in the distribution of the number of waiting cells in the buffer
By applying the Sev's inequality, the probability of ARB buffer congestion detection to overflow is calculated, and the ABR is adjusted so that the probability becomes equal to a predetermined quality regulation value.
ABR characterized by changing said threshold of buffer
Cell flow control method. 2. A buffer is provided in the ATM network, and when the amount of ABR cells in the transmission waiting state accumulated in the buffer exceeds a threshold value, the flow rate of cells by the ABR service in the ATM network is changed. In the ABR cell flow control method of reducing to MCR, each of the peak cell rate, sustainable cell rate, and burst tolerance declaration parameters declared by a user in a priority class having a higher priority than the ABR service at the time of call setup request, and the ABR service The minimum cell rate that the user declares at the time of call setup request is stored in advance, and whenever the number of priority class services connected to the ATM network changes, the peak cell rate, sustainable cell rate, and burst of the changed priority class services are stored. Tolerance is obtained, and priority class user is based on the sustainable cell rate. The bandwidth average utilization rate by the A is calculated, the measurement time interval is determined from the bandwidth utilization rate by the ABR user calculated from the minimum cell rate and the capacity of the cell buffer dedicated to the ABR service, and the measurement time interval and the priority class Based on the declared parameters, the variance of the bandwidth usage rate by the priority class users is calculated, and based on the sum of the average bandwidth utilization rate by the priority class users and the variance of the bandwidth usage rates by the priority class users, the ABR Fokker-Planck method for the number of waiting cells in the buffer
By applying the diffusion approximation according to the equation , the probability from the congestion detection of the ARB buffer to the overflow is calculated, and the ABR is adjusted so that the probability becomes equal to a predetermined quality regulation value.
ABR characterized by changing said threshold of buffer
Cell flow control method.