JP2692212B2 - Bandwidth reservation method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for allocating bandwidth in order to easily and efficiently multiplex burst calls when accommodating burst calls in a packet network. .

(Prior Art) When accommodating a burst call in a packet network, if the load on the network increases, the buffer overflow and the delay increase. Therefore, it is necessary to regulate the input of the burst call in the network so that the required quality is satisfied. . Burst network input regulation,
Various flow control methods such as window control found in X25 etc. have been proposed.

However, in a high-speed packet network, which has been attracting attention in recent years, it is not suitable to regulate the network input by a complicated procedure such as window control because the in-network protocol is simplified.
Rather, it is preferable to predict the load of the incoming call at the time of call setup before inputting to the network and permit or reject the call setup.

A constant rate Continuous Bitstream Orie for incoming calls
There are two types of services, the nted service (CBO) and the variable-rate burst service. Regarding the prediction of the load of an input call, the former is uniquely determined, but the latter is not easy to predict. It is for the following reasons.

In general, a variable rate (variable band) burst call defines the band as an average band (long-term average) Ave. Maximum band Max. Burst length B _L fluctuation coefficient Var. At present, it is not clear how the parameters of such a burst call affect the delay characteristics and the buffer overflow rate characteristics in the network, but it is the current situation. Because there is. Reference 1 details these effects.

(1) Noguchi et al. “Traffic characteristics in multimedia switching networks” Technical Report of SE87-74,1987 Reference 2 defines burst calls with such complicated parameters in a virtual band called “virtual band”. We propose a method to reserve bandwidth for transit trunk lines.

(2) Watanabe et al. “Study on statistical multiplex control method in high-speed packet switching” IEICE Technical Report SE87-138, 1987, where the capacity of the trunk line is C and the virtual bandwidth is Rv It represents.

Rv = f (Ave, Max, Var, C), Are ≦ Rv ≦ Max. Especially Max / C, that is, the ratio of the maximum bandwidth to the line speed greatly affects the communication quality. Therefore, if Max / C is small, RvAve Max If / C is large, it is defined as RvMax.

At the time of call setup, first, the virtual band Rv as described above is defined, and the quality (delay, discard) of the relay line is predicted using this Rv. Only when the predicted quality meets the line quality standard, a new call is admitted.

(Problem to be Solved by the Invention) (I) The line buffer capacity is not considered as a parameter for determining the virtual bandwidth.

In the conventional technology, the characteristics of burst call (Max, Ave, Va
(eg r) and the line capacity C determines the virtual band. It is well known that the maximum number of multiplexes varies greatly depending on the ratio between the capacity of the network and the bandwidth of each burst call. In other words, if the capacity of the network is sufficiently larger than the burst call, the virtual band can be defined as a small average band.

Here, only the line speed is used as the capacity of the network, but in the packet network, the capacity of the line transmission waiting buffer is also the target. For example, if the buffer is large enough, the virtual band can be multiplexed without any problem in terms of the packet discard rate even if it is defined by the value of the average band of the call. Conversely, if the buffer capacity is small, it is necessary to define the virtual band with a value larger than the average band and reserve the band to suppress the actual load on the line even if the same burst call and the same line capacity (speed) are used. Becomes

In the conventional technology, the virtual bandwidth that does not depend on the buffer amount is defined, the virtual bandwidth of each call is summed, the virtual utilization rate of the line is calculated, and the buffer volume prepared when the line is loaded with the utilization rate It is judged whether the quality is satisfied. In the end, the buffer amount is taken into consideration, but no specific method has been shown as a method for determining the virtual bandwidth. This is because quality criteria are ignored in determining the virtual band. Specifying the amount of buffer inevitably defines how much the actual load needs to be suppressed in order to meet the discard rate, and then how much the reserved bandwidth of each call needs to be larger than the average bandwidth. Can be defined.

That is, the present invention explicitly provides a virtual band determination method for satisfying the discard rate condition by defining the buffer amount as compared with the prior art.

In the present invention, the discard rate is mentioned as the quality. This is because in high-speed packet networks, the intra-network delay can be minimized to satisfy the required quality in most cases by using high-speed links. In other words, the discard rate is the only main factor to consider in bandwidth reservation.

(II) The effect of ignoring fixed band calls passing through the transmission line is ignored.

When the line uses a fixed bandwidth call, for a variable bandwidth call, total multiplexing is performed in the residual bandwidth obtained by subtracting the total used bandwidth of the fixed bandwidth call from the line capacity.

However, ignoring this and defining the virtual band by the band ratio of the variable band call to the capacity of the transmission line means that multiplexing is actually carried out in a larger pipe. Therefore, since the virtual bandwidth is set to be smaller than it should be, the actual load cannot be kept low enough to satisfy the specified quality, and dangerous bandwidth reservation may be performed.

The present invention intends to ensure the bandwidth reservation and always satisfy the quality even when the fixed band call and the variable band call are simultaneously multiplexed.

(III) Bandwidth is not reserved because it reflects the usage status of the line.

When the line utilization rate is low and when the utilization rate is high, the influence of the addition of a call in the same band on the delay and buffer overflow rate is completely different. Therefore, the effect on the quality when there is an error between the predicted virtual band and the actual band becomes larger as the usage rate becomes higher.

However, in the prior art, the virtual band is uniformly defined by ignoring the use status of the line, and therefore it is expected that the quality degradation due to the prediction band error is large at the time of high load.

Therefore, in the present invention, when the line usage rate is large, a stronger input restriction is applied to more reliably perform band allocation and to endure the band prediction error.

(Means for Solving the Problems) In order to solve the above problems, the present invention provides a variable bandwidth in a bandwidth reservation system in the case of accommodating a plurality of fixed bandwidth calls and a plurality of variable bandwidth calls in a packet switching network. When setting up the call, the variable bandwidth is calculated by using the ratio of the maximum bandwidth of each call to the residual bandwidth obtained by subtracting the total used bandwidth of the fixed bandwidth call from the calls using the transmission link. A bandwidth reservation method characterized in that a virtual bandwidth having a value not less than an average bandwidth of a call and not more than a maximum bandwidth is calculated, and bandwidth of a transmission link is reserved by the calculated virtual bandwidth.

(Operation) The principle of band allocation according to the present invention will be described.

For each burst call, a virtual band is defined with a value between its maximum band and average band. The virtual band is determined in consideration of the capacity of the transmission line on which the burst call is to be multiplexed and the capacity of the link sending buffer. First, the maximum line utilization rate ρmax characteristic for making the buffer overflow rate below a certain quality with the given transmission buffer amount B is obtained. At that time, ρmax is generally represented by ρmax = f (Ave, Max, C, B) 0 ≦ ρmax ≦ 1 where the maximum bandwidth is Max and the line capacity is C. Using the average band Ave, the virtual band Rv can be expressed as follows.

That is, it means that the burst call is given from the virtual band by using the capacity buffer amount of the line in addition to the average maximum band.

However, this Ave.Max. May be the declared value of the terminal or the measured value.

Generally as a factor that determines ρmax It is known in Refs. 1) and 2) that this is the main cause. However, when the fixed band and the variable band are multiplexed here, the residual band Crest obtained by subtracting the total used band of the fixed band from the line capacity is the apparent capacity for the variable band call.
In particular, when the fixed band call is transmitted to the variable band call with high priority, the above correction is indispensable. After all, Rv = Ave / f (Ave, Max, C _rest , B) and if the main factor is Max / C _rest , then RvAve / f (Max / C _rest , B).

When the bandwidth is allocated as described above, the total bandwidth ρuse of the line is used to further increase the control stability. That is, the virtual band is defined so that Rv monotonically increases with respect to ρuse. When the ρuse is large, defining the virtual band to be larger and making the band reservation means that the reservation is made with a larger margin when the load is high, and the input restriction of new calls is further strengthened.

 Therefore, more stable control can be realized.

(Example) The Example of this invention is shown.

FIG. 2 shows an example of a packet switching network to which the present invention is applied. The calling terminals 201 to 203 and the called terminals 204 to 206 communicate with each other. Here, a virtual circuit is set between the departure and arrival terminals. The exchanges 211 and 212 set up each communication call. Attention is now directed to one transmission link 230. Each communication call is packet-multiplexed and transmitted through the transmission link 230.
At this time, since each packet arrives asynchronously, the transmission waiting buffer 220 on the link is required. Since the capacity of this transmission link and the buffer waiting to be sent is finite,
It is necessary to limit the load input.

The pattern will be described in detail in FIG. Reference numerals 101 to 103 are calls for each person, and reference numerals 111 to 113 are corresponding input rate patterns. The input pattern is changing with time. At this time, the call is called a burst call. The maximum bandwidth and average bandwidth of each burst call i are Maxi and Avei. Further, the value indicating the variability of the band includes variance, the duration of the Max value, and the like, which will be omitted here.

These are the capacity B is the capacity (line speed) via the buffer.
It is multiplexed on the C transmission link. At this time, it is necessary to perform control so that a load equal to or greater than the link capacity C is not constantly involved, and input restriction control that does not wait for the capacity B or more of the buffer even if a load is momentarily applied. .

Therefore, it is considered that a virtual band Rv is defined for each call and the link capacity is virtually reserved by Rv to allocate the capacity of each call. That is done by 140 bandwidth allocation reservation devices. The concept of the virtual band is shown in FIG.

300 in FIG. 3 reserves the bandwidth of each call in the virtual bandwidth Rv. Show the situation.

The bands of each 301, 302, 303 are Rv ₁ , Rv ₂ , and Rv ₃ . Here, each Rv is Ave ≤ Rv ≤ Max. In other words, the actual load of 311 to 313 is temporally fluctuated like a diagonal line. The reserved bandwidth can be represented by ΣRv _i .

At this time, it is the unreserved band C-ΣRv _i .

When a call setup request for a new call occurs, assuming that the virtual band of the call is Rv ', the call is accepted only when C-ΣRv _i <Rv' holds.

By doing so, the input can be limited when the actual load ΣAve is always ΣAve <C, and steady overload does not occur.

 However, ΣMax can be momentarily larger than C.

In that case, the packet is queued in the buffer. If the buffer capacity is exceeded, packets will be discarded. Each Rv to reduce such situations as much as possible
Needs to be set larger.

This effectively becomes ΣAve << C, which strengthens the input regulation. At this time, how to define Rv depends on the amount of buffer. The dependency is shown below.

Now, FIG. 4 shows how much the actual utilization rate ΣAve should be suppressed depending on the buffer amount.

Here, consider three cases where the buffer amount is B = 10,100,1000.

Of the burst characteristics, Max / C is known to have the greatest effect on quality, so the horizontal axis is taken. The vertical axis was set to satisfy the packet discard rate quality (here, 10 ^-6 ). The maximum utilization rate ΣAve = ρmax.

From this figure, it can be seen that ρmax that can be achieved differs depending on the buffer size B even with the same Max / C value.

From this, the virtual band Rv is obtained. Rv is as described in the section of action Given by This is shown in FIG.

In this way, it can be seen that the virtual bandwidth of each call is expressed according to the buffer size B and Max / C. However, Ave and Max described here may be the reported value of the terminal or the measured value. Further, Rv is a continuous function as shown in FIG. 5, but it may be simplified into a form of a step function which is easier to handle.

Now, an example of implementing the technique of the second invention will be further described.
Here, consider a case where a fixed band call and a variable band call are multiplexed on the same link. FIG. 6 schematically shows how the signals are multiplexed at this time. In Fig. 6, 601, 602 are bands This is a fixed band call.

On the other hand, 603 and 604 are variable band calls with virtual bands R _v1 and R _v2 . As shown in this figure, the ΣR _fix band of the link capacity is always in use. Therefore, the remaining C _rest is used for a plurality of variable band calls. As a matter of course, for a variable band call, overflow occurs when ΣMax> C _rest , so the apparent transmission link capacity becomes smaller than when the variable band is used. In other words, the link information for statistical multiplexing is shifted by the fixed bandwidth.

Therefore, the virtual band Rv is defined as one in which the remaining band C _rest obtained by subtracting the total usage amount ΣR _fix of the fixed band from the link capacity C is multiplexed.

For that purpose, _Cv may be used instead of C in FIG. 5, and Rv may be determined at M / C _rest .

By doing so, it is possible to obtain the Rv corrected by the use situation of the fixed band call even with the same burst and buffer amount.

Next, an application example of the third invention will be shown. This is the used bandwidth ρ
When the use is high, the input of a new call is strengthened to increase the tolerance against control error and to perform more stable control.

Here, for example, when the buffer capacity B in FIG.
Suppose a call request of /C=0.5 occurs. Then consider how to determine Rv. Rv 'is obtained from FIG. This value is changed as shown in FIG. 7 according to the used band.

Ρuse on the horizontal axis is the used band. The used band may be the sum of Rv or the measured average traffic volume. ρus
The larger e is, the larger Rv is set. Besides preparing the characteristics as shown in FIG. 7, the correction term α may be simply added to or subtracted from Rv ′ in FIG. 5 as follows.

When Rv = Rv′−α: ρuse is low Rv = Rv ′ + α: ρuse is high FIG. 7 is an example of correcting Rv.
It is within the scope of the present invention as long as is a monotonically increasing function.

FIG. 8 shows a block diagram of the bandwidth reservation / allocation apparatus 140 in the embodiment of the present invention. The registers 801, 802 hold the buffer capacity B and the transmission capacity C of each transmission link.

A variable bandwidth call declares an average Ave and maximum bandwidth. 80
Table 5 determines the virtual band Rv [from these parameters as follows. The line capacity C is deducted from the fixed bandwidth usage held in the fixed bandwidth usage counter C
It becomes _rest and is input to table 805.

The table of 805A holds the characteristics shown in Fig. 4, and B
And Max / C _rest , the maximum utilization ρmax can be obtained. The 805B table retains the characteristics shown in Fig. 5. Rv is required from. The Rv obtained in 805B is corrected by the usage rate ρuse of the link 130. Although 806 measures ρuse, ΣRv may be calculated to obtain ρuse. 807
Corrects the Rv output from the 805B by ρuse. An example of how to apply the correction is shown in FIG. 7 as described above. The Rv thus obtained is output.

Of the above, the Rv determination method by 801, 802, 805, the fixed band call correction by 803, 804, and the correction by ρuse by 806, 807 are independent of each other, and can be performed independently.

(Effect of the invention) By using the buffer capacity in the definition of the virtual band, the maximum line utilization ρmax characteristic can be easily obtained, and the virtual band is given by the following equation.

This is to easily define the virtual band Rv which has not been given explicitly.

As a result, it is possible to properly and easily regulate the input call when the burst call is multiplexed, and to use the packet network efficiently.

Further, according to the invention, even when a fixed band call and a variable band call are multiplexed, it becomes possible to define a virtual band in consideration of the occupied band of the fixed band call, and the band reservation can be made in accordance with the actual multiplexing operation. It will be possible. Therefore, reliable quality is always maintained.

Further, according to the third aspect of the present invention, even if a prediction error of the virtual band occurs under high load, quality deterioration does not occur, and high load input regulation can be reliably performed, so that stable control can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a bandwidth reservation method according to an embodiment of the present invention. FIG. 2 is an example of a packet switching network to which the bandwidth reservation method according to the present invention and the prior art is applied. FIG. 3 is a diagram illustrating reservation of a transmission link in a virtual band in the embodiment of the present invention. FIG. 4 shows the maximum bandwidth / link capacity-maximum line utilization rate characteristic with the buffer amount as a parameter in the embodiment of the present invention. FIG. 5 is a characteristic example of giving a virtual band by using the buffer amount in the embodiment of the present invention. FIG. 6 is a diagram showing that a fixed band call and a variable band call are multiplexed in the transmission link in the embodiment of the second aspect of the present invention. FIG. 7 is a diagram showing the characteristic of correcting the virtual band in accordance with the working band in the embodiment of the third aspect of the present invention. FIG. 8 is a block diagram of a bandwidth reservation allocation device in the embodiment of the present invention. In the figure, 140 ... Bandwidth allocation reservation device, 201 to 203, 204, to 206 ... Terminal, 2
11,212 ... Packet switch, 220 ... Buffer, 230 ... Transmission link, 801, 802 ... Register, 803 ... Counter, 804 ... Subtractor, 805A ... ρmax decision table, 805B ... Rv decision table.

Claims (1)

(57) [Claims] 1. A call using a transmission link when setting a call for each variable band in a band reservation method in the case where a plurality of fixed band calls and a plurality of variable band calls are accommodated in a packet switching network. Of the variable bandwidth, the virtual bandwidth of the value above the average bandwidth and below the maximum bandwidth of each call is calculated using the ratio of the maximum bandwidth of each call to the residual bandwidth obtained by subtracting the total used bandwidth of the fixed bandwidth call from the capacity of the transmission link. Then, the bandwidth reservation method is characterized in that the bandwidth of the transmission link is reserved by the calculated virtual bandwidth.