JP3051080B2 - Bandwidth variable communication network - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an ATM (Asynchronou).
s Transfer Mode: Used for communication.
INDUSTRIAL APPLICABILITY The present invention is suitable for use in a communication service that distributes the bandwidth of a plurality of virtual connections in the same network fairly.

[0002]

2. Description of the Related Art In an ATM, an ABR (Available Bit Rate) service is defined by the ATM Forum as a communication service for fairly distributing a band.

In the ABR service, a terminal device performs communication by fairly distributing a band. 5 and 6 show AB
It is a figure for explaining R service. For example, as shown in FIG. 5, when the terminal devices S1, S2, and S3 communicate with the terminal devices R1, R2, and R3, respectively, S _k (k = 1
3) and R _k between virtual connection VC
_k performs communication while occupying one-third of the bandwidth of the link on the way.

When a new virtual connection is set between the terminal device S4 and the terminal device R4 and communication is started, as shown in FIG. 6, the bandwidth distribution value of each virtual connection is reduced to 1/4. Become.

[0005] The communication of the communication start request and the bandwidth distribution value of the terminal device is performed by RM (Resource Manager) transmitted from the terminal device.
ment) is done using cells. The terminal device S _k transmits an RM cell every time a fixed number of cells are transmitted, and the RM cell is looped back by the terminal device R _k and received by the terminal device S _k again.

[0006] RM cell received terminal S _k is, describe the bandwidth allocation value allowed by the communication from the terminal device S _k to the terminal R _k. Each node in the network calculates the bandwidth distribution value of each virtual connection from the number of communicating virtual connections and the required bandwidth, and describes the value in the RM cell.

[0007] The method of calculating the bandwidth distribution value is described in, for example, “Data Network” by D. Bertsekas and R. Gallager.
s "Prentice Hall, 1992. There is a max-min rule. FIG. 7 is a conceptual diagram of a method of notifying a band distribution value using an RM cell. FIG. 8 is a flowchart showing an operation of a band management unit. 8, the band management unit 1 monitors the RM cell (ST1), and if the received RM cell includes a communication start request from the terminal device S4 (ST1).
2) Accept this (ST3). Subsequently, a bandwidth allocation of a new virtual connection for the terminal device S4 is set (ST4). Further, the new assigned bandwidth is notified to each of the terminal devices S1 to S3 (ST5).

[0008] When communication between the terminal device S4 and the terminal device R4 is started in this way, the terminal device S1 changes the band distribution value from 1/3 to 1/4 based on the received RM cell. I do. The terminal device S4 transmits an RM cell at the beginning of communication, and until the RM cell is returned from the network and the bandwidth distribution value is known, the initial cell rate (hereinafter, ICR)
(Initial Cell Rate)).

In consideration of such a virtual connection that starts a new communication, normally, a portion not allocated to a steady virtual connection is set as a safety margin. If such a safety margin is sufficient, congestion does not occur even if a newly started virtual connection performs communication for a while in ICR.

FIGS. 9 and 10 are diagrams for explaining a safety margin. For example, FIG. 9 shows a case where 10% of a link band is set as a safety margin. (100-10) ×× = 30% of the link bandwidth is allocated to each virtual connection VC _k .

Here, as shown in FIG. 10, when the terminal device S4 and the terminal device R4 newly start communication by the virtual connection VC4, each virtual connection VC _k (k
= 1 to 4), (100−10) × １ ／ = 22.5% of the link band is allocated.

Until the new bandwidth allocation value is determined, the virtual connection VC4 performs communication by ICR.
If R is less than the security margin (10% of the link bandwidth), the network will not be congested. As described above, the safety margin and the ICR are designed so that congestion does not occur between the time when a new virtual connection starts communication and the time when a new bandwidth allocation value is determined.

[0013]

In such an ABR service, the bandwidth allocation value is notified by using the RM cell. Therefore, the time from the start of communication of a new virtual connection to the steady state is the round-trip delay in the network. Time RTT (Round
It takes almost the same time as Trip Time).

When the RTT is large as in a public network,
The time required for the virtual connection to reach a steady state becomes longer, during which time the probability of the occurrence of a new virtual connection for starting communication increases.

FIG. 11 is a diagram showing the relationship between the safety margin and the backlog. The horizontal axis indicates time, and the vertical axis indicates the used bandwidth, and indicates the state of the change in the load applied to the link. In the example of FIG. 11, a case where the virtual connections VC5, VC6, and VC7 start communication at times t5, t6, and t7, respectively, during the time until the virtual connection VC4 that started communication at time t4 becomes steady. Is shown.

In this example, up to four virtual connections continue to communicate with the ICR. Hereinafter, the virtual connection that continues the ICR communication is referred to as a backlog.

The safety margin must be equal to or larger than the value obtained by multiplying the ICR by the maximum number of backlogs. Conversely, when the safety margin is given and the maximum number of backlogs increases, the ICR needs to be reduced. That is, ICR
Is given by ICR = γ · C / n (1) Where γ is the safety margin coefficient,
C is the link bandwidth, and n is the maximum number of backlogs. Theoretically, the maximum number of backlogs is infinite, but generally the tail value of the distribution is used. Here, the maximum value of the number of backlogs is set to the 99.9% point of the distribution.

Here, a quantitative relationship between the ICR and the RTT is considered, assuming that the time required for the virtual connection to reach a steady state is equal to the RTT. The maximum number of backlogs is determined by the time interval at which a new virtual connection for starting communication and the RTT. Time interval at which a new virtual connection for starting communication occurs is 1 / λ on average
If the RTT follows an exponential distribution with an average of 1 / μ according to the exponential distribution, the distribution of the number of backlogs follows the exponential distribution with an average of μ during the Poisson process in which the customer arrival rate is λ. / M / 1 queuing model. (Reference: "Communication Traffic Theory," PP.61-, Masaya Fujiki, Eiichi Kanbe, Maruzen Co., Ltd.) The maximum backlog number n is obtained by analyzing the M / M / 1 model, FIG. 12 shows a result obtained by substituting the relationship between ICR and RTT. FIG. 12 is a diagram showing the relationship between ICR and RTT, with the horizontal axis representing RTT and the vertical axis representing ICR. The RTT on the horizontal axis is normalized by the time interval at which a new virtual connection for starting communication is generated. The vertical axis is normalized by the safety margin.

FIG. 12 shows that when the RTT is 0.01, the ICR should be 0.5, but when the RTT is 0.5, the ICR needs to be 0.1. That is, when the link bandwidth is 150 Mb / s and the RTT is 50 milliseconds, and a virtual connection that newly starts communication at 0.1 second intervals occurs, the safety margin is increased by 10%.
This means that the ICR needs to be 150 kb / s or less. When the RTT exceeds "1", the ICR becomes zero and the ABR service itself cannot be established.

That is, when the RTT increases as in a public network, it is necessary to set the ICR to a remarkably small value. Further, when the ICR is reduced, the average throughput is reduced particularly in the case of transferring a short burst. In addition, even if the network has a sufficient free band, communication must be performed with a small ICR, so that the use efficiency of the network is reduced. Conversely, if the ICR is increased, congestion is likely to occur, which adversely affects a virtual connection that is already in a steady state, which is a problem.

The present invention has been made in such a background. A virtual connection which has newly started communication is distinguished from a connection which is already in a steady state, and congestion occurs while providing a high ICR. Another object of the present invention is to provide a variable bandwidth communication network that does not adversely affect a connection already in a steady state.

[0022]

SUMMARY OF THE INVENTION The present invention is a variable bandwidth communication network comprising a plurality of terminal devices and means for equally distributing the bands of a plurality of virtual connections used for communication between the terminal devices. The distributing means comprises a first step of receiving a communication start request coming from the terminal device, and setting a band to be distributed to the terminal device, and setting the band of the virtual connection already set to all Means for executing a second step of changing the bandwidth of the virtual connection so as to be equal, wherein the terminal device has an ICR set in advance between the first step and the second step. Therefore, it is a variable bandwidth communication network provided with means for transmitting cells.

Here, a feature of the present invention is that a means is provided for setting the priority of a cell transmitted from the terminal device in accordance with the ICR to be lower than the state after the end of the second step. There.

That is, the ICR is a predetermined band allocation irrespective of the traffic situation in the network. Therefore, sending a cell by ICR
It can adversely affect other virtual connections that are already in a steady state and are communicating. The bad effect here is that the bandwidth of another virtual connection is squeezed by the virtual connection transmitting a cell by ICR,
This is because the cell loss rate of another virtual connection in a steady state increases.

At this time, a lower priority is added to a cell transmitted by the ICR as compared with a cell transmitted by another virtual connection which is already in a steady state.
The priority information is written to the cell and transmitted.

Thus, when the cell of the virtual connection in another steady state and the cell transmitted by the ICR compete with each other, contention control is performed so that the cell of the virtual connection in another steady state wins. Therefore, the adverse effects can be eliminated.

It is preferable that a buffer for storing cells is provided, and this buffer is provided with means for storing cells with low priority when the number of cells stored with high priority is less than the threshold value.

As a result, it is possible to realize a variable bandwidth communication network in which the transfer of low priority cells does not prevent the transfer of high priority cells.

Alternatively, a buffer for accumulating cells for each priority is provided, and this buffer reads cells from the buffer for accumulating cells with low priority when the buffer for accumulating cells with high priority is empty. Means and means for moving, after the completion of the second step, cells stored in the buffer storing low priority cells to buffers storing high priority cells.

According to this, regardless of the priority level, cells are temporarily stored in one of the buffers. The cell reading from the buffer storing the high-priority cells is performed in preference to the cell reading from the buffer storing the low-priority cells. When transmission is completed and cells are transferred using the newly allocated band, cells that have been stored in the buffer where low-priority cells are stored are now replaced by buffers that store high-priority cells. Be moved. As a result, even if the cell has a low priority, the cell loss rate can be kept low, so that high communication quality can be maintained.

It is desirable that the buffer for storing the low priority cells is provided for each of a plurality of virtual connections.

As a result, the order of high priority cells and low priority cells in the same virtual connection can be guaranteed. Further, it is possible to quickly move cells from the buffer storing low priority cells to the buffer storing high priority cells.

[0033] The low setting means may be provided in the terminal device, or may be configured as a device accommodating a plurality of the terminal devices.

In particular, in the latter case, the conventional terminal device can be used as it is, so that the band variable communication network of the present invention can be used without forcing the user to install a terminal device having a new specification. Can be realized.

[0035]

BEST MODE FOR CARRYING OUT THE INVENTION

[0036]

【Example】

(First Embodiment) The configuration of the first embodiment of the present invention will be described with reference to FIG. FIG. 1 is an overall configuration diagram of the first embodiment of the present invention. The operation of the band management unit 1 is common to FIG. Although the terminal devices S1 to S4 and R1 to R4 can perform two-way communication with each other, here, for simplicity of explanation, the terminal devices S1 to S4 are assumed to be terminal devices on the transmitting side, and the terminal devices R1 to R4 are referred to as The description will be given as a terminal device on the receiving side.
Further, virtual connections VC1 to VC3 are already set between the terminal devices S1 to S3 and the terminal devices R1 to R3, and a new virtual connection VC4 is set between the terminal devices S4 and R4. The situation will be described.

The present invention is a bandwidth variable communication network, which is a means for equally distributing the bandwidths of terminal devices S1 to S4 and R1 to R4 and a plurality of virtual connections used for communication between the terminal devices. And a management unit 1.
The band management unit 1 performs a first step (S) of receiving a request to start communication with the terminal device R4 coming from the communication terminal S4.
T3), set a band to be distributed to the terminal devices S4 and R4, and change the band of the virtual connections VC1 to VC3 that have already been set to all the virtual connections V3.
A second step (ST4, ST5) of changing the bandwidth of C1 to VC4 to be equal, and the terminal device S4 sets in advance between the first step and the second step This is a variable bandwidth communication network that transmits cells according to the specified ICR.

The feature of the present invention is as follows.
The terminal device S4 is provided with means for setting the priority of the cell transmitted from the communication terminal S4 according to the CR lower than the state after the end of the second step.

The first embodiment of the present invention will be described in more detail. In the first embodiment of the present invention, the terminal device S4 sets a flag indicating that the priority is low in cells other than the RM cell at the start of communication. The node device 2 controls the cell discarding in the buffer B based on the flag given to the cell.

Considering that a CLP (Cell Loss Priority) bit of a cell header is used as a flag indicating that the priority is low, CLP = 1 is set to a low priority cell, and CLP = 0.
Represents a cell with a high priority.

The terminal device S4 performs communication by setting CLP = 1 in the cell while performing communication by ICR. When the first RM cell returns from the network and the bandwidth allocation value is known, in subsequent communication, the priority is raised by setting CLP of the cell to 0.

When a cell of CLP = 1 arrives, the node device 2 discards the cell if the number of cells in the buffer B, which is FIFO (First In First Out), is equal to or greater than a certain threshold, and discards the cell if it is less than the threshold. The cells are stored in buffer B.

In FIG. 1, the communication terminal S4 keeps the cell C while communicating with the ICR via the virtual connection VC4.
Transmit with LP = 1. The cells transmitted during that time are discarded according to the threshold value of buffer B. When the first RM cell returns and the bandwidth allocation value is determined, the cell is transmitted at CLP = 0 with that bandwidth allocation value. Also, if the threshold of buffer B is the product of ICR, RTT and the maximum number of backlogs,
A cell with CLP = 1 can be prevented from being discarded.

(Second Embodiment) A second embodiment of the present invention will be described with reference to FIGS. 2 and 3 are diagrams showing the buffer configuration of the node device 2 according to the second embodiment of the present invention. In the second embodiment of the present invention, as shown in FIG. 2, the buffer configuration of the node device 2 has a configuration in which buffers BH and BL are provided for each cell priority.

In the configuration shown in FIG. 2, when a cell of CLP = 1 arrives, the cell is stored in the buffer BL for CLP = 1, and when a cell of CLP = 0 arrives, CLP = 0.
The cells are stored in the buffer BH.

As long as there are cells in the buffer BH for CLP = 0, the cells in the buffer BH for CLP = 0 are read out.
Only when there is no cell in the buffer BH for CLP = 0, C
The cell of the buffer BL for LP = 1 is read.

If the capacity of the cell satisfying ICR × RTT × (maximum number of backlogs) is provided as the capacity of the buffer BL for CLP = 1, the cell with CLP = 1 can be eliminated. .

Further, when the communication terminal S _k transmitting a cell of CLP = 1 ends transmission by ICR and starts transmitting a cell of CLP = 0 by a newly allocated band, CLP stored in buffer BL =
By moving cell 1 to buffer BH, CL
Cell transfer can be performed without losing the cell of P = 1.

CLP = 1 accumulated in buffer BL
Is moved to the buffer BH as a specific method, so that the pointer at the end of the queue of the buffer BH points to the head of the queue of the buffer BL, and the pointer at the end of the queue of the buffer BL points to the end of the buffer BH. To do.

As a result, cells accumulate in the buffer BH instantaneously, but the safety margin is originally expected and the bandwidth is not used at 100%, so that the cells accumulated in the buffer BH will be read out soon. And the queue length is almost zero.

FIG. 3 shows an example in which the buffer BL for CLP = 1 shown in FIG. 2 is provided for each of a plurality of virtual connections, and the buffers BL _{1 to} BL ₃ are respectively provided. According to the configuration shown in FIG. 3, it is possible to guarantee the order of cells of CLP = 0 and CLP = 1 in the same virtual connection.

When the cell transmission by the ICR is completed and the terminal device starts transmitting the cell at CLP = 0 with the newly set bandwidth allocation value, the cell of CLP = 0 becomes the node device 2
At the time of arrival, the buffers BL ₁ -B for CLP = 1
If the cell is accumulated in the L _3, move it to the buffer BH for CLP = 0.

If the buffers BL _{1 to} BL ₃ for CLP = 1 are formed by forming FIFO queues for each virtual connection, cells can be instantaneously moved to the buffer BH for CLP = 0.

As a specific method of moving the cells stored in the buffers BL _{1 to} BL ₃ for CLP = 1 to the buffer BH for CLP = 0, a method of moving the cells stored at the end of the queue of the buffer BH for CLP = 0. pointer the to point to the beginning of the buffer BL ₁ to BL ₃ queues for virtual connections CLP = 1, buffers BL ₁ ~ for CLP = 1
Tail pointer of the queue of BL ₃ to point to the end of the buffer BH for CLP = 0.

By doing so, the order of the cells of CLP = 0 and CLP = 1 of the virtual connection does not reverse. Also, cells accumulate in the buffer BH momentarily.
Since the bandwidth is not used at 0%, buffer B
The cells stored in H are eventually read, and the queue length becomes almost zero.

(Third Embodiment) A third embodiment of the present invention will be described with reference to FIG. FIG. 4 is an overall configuration diagram of the third embodiment of the present invention. In the third embodiment of the present invention, the terminal devices S1 to S4
Transmits all cells with CLP = 0, and rewrites the value of CLP in virtual terminal device 3. Thereby, the terminal device S
There is no need to provide a new configuration for implementing the present invention in 1 to S4. For this reason, since it is not necessary to force a user who is a user of the terminal devices S1 to S4 to install a new device, the service quality for the user can be kept high, and a new method for realizing the present invention can be achieved. All equipment can be managed by the network management company.

The virtual terminal device 3 measures the cell transmission interval from the terminal devices S1 to S4, and if a cell does not arrive for a while, determines that the communication from the terminal devices S1 to S4 has once ended. Thereafter, when a new cell arrives again from the terminal devices S1 to S4, the virtual terminal device 3 determines that communication has started.

In this case, the virtual terminal device 3 transfers the RM cell to the band management unit 1 and, until the RM cell returns, sets the CLP to 1 by ICR and transfers the cell. During this time, the terminal device transmits the cell with CLP = 0.

When the RM cell returns and the allocation value of the band is determined, the virtual terminal device 3 transfers the cell with CLP = 0 according to the allocation value.

(Summary of Embodiment) In the variable bandwidth communication network shown in the first to third embodiments of the present invention, the ICR can be set high even when the RTT is large. High throughput can be maintained.

Even if the network is congested, the cells transmitted by the ICR do not adversely affect the cells transmitted in the steady state in the band variable communication network of the present invention. You do not need to be very careful about

Of course, if the network is crowded,
If R is set high, many cells are discarded. However, the throughput is different between the case where the ICR is set low from the beginning to reduce the number of cells discarded and the case where the data loss is compensated by retransmitting the cells discarded as a result of setting the ICR high. Absent.

Therefore, in the variable bandwidth communication network of the present invention, it is preferable to set the ICR higher.

In an actual network, except for the busiest time zone, there are few situations in which the bandwidth is always fully operated. Therefore, it is considered that the newly started virtual connection rarely encounters congestion. The effect is great.

[0065]

As described above, according to the present invention,
A variable-bandwidth communication network that distinguishes a newly started virtual connection from a connection that is already in a steady state and provides high ICR without adversely affecting a connection that is already in a steady state even if congestion occurs. Can be realized.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a buffer configuration of a node device according to a second embodiment of the present invention.

FIG. 3 is a diagram illustrating a buffer configuration of a node device according to a second embodiment of the present invention.

FIG. 4 is an overall configuration diagram of a third embodiment of the present invention.

FIG. 5 is a diagram for explaining an ABR service.

FIG. 6 is a diagram for explaining an ABR service.

FIG. 7 is a conceptual diagram of a method of notifying a band distribution value using an RM cell.

FIG. 8 is a flowchart showing the operation of the band management unit.

FIG. 9 is a diagram for explaining a safety margin.

FIG. 10 is a diagram for explaining a safety margin.

FIG. 11 is a diagram showing a relationship between a safety margin and a backlog.

FIG. 12 is a diagram showing a relationship between ICR and RTT.

[Explanation of symbols]

1 band management section 2 node device 3 terminal agent S1 to S4, R1 to R4 terminals _{B, BH, BL, BL 1} ~BL 3 buffer VC ₁ to Vc ₄ virtual connection

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-9-64877 (JP, A) JP-A-9-46344 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04L 12/28

Claims (6)

(57) [Claims] 1. A communication system comprising: a plurality of terminal devices; and means for equally distributing bands of a plurality of virtual connections used for communication between the terminal devices, wherein the distributing means includes communication coming from the terminal devices. A first step of receiving a start request, and a second step of setting a band to be distributed to the terminal device, and changing the already set virtual connection band so that all virtual connection bands are equal. And a means for executing a step, wherein the terminal device is a band variable communication network including means for transmitting cells according to an initial cell rate set in advance between the first step and the second step. The priority of cells transmitted from the terminal device according to the initial cell rate is determined by the state after the end of the second step. A variable bandwidth communication network comprising means for setting the bandwidth to a lower value. 2. The band according to claim 1, further comprising a buffer for storing cells, wherein said buffer includes means for storing cells with low priority when the number of cells stored with high priority is less than a threshold value. Variable communication network. 3. A buffer for accumulating cells for each priority, wherein the buffer reads cells from the buffer for accumulating low priority cells when the buffer for accumulating high priority cells is empty. 2. The band according to claim 1, further comprising: means for moving cells stored in a buffer storing low-priority cells to a buffer storing high-priority cells after completion of the second step. Variable communication network. 4. The buffer for accumulating the low-priority cells is provided for each of a plurality of virtual connections.
The variable bandwidth communication network according to claim 1. 5. The variable bandwidth communication network according to claim 1, wherein said low setting unit is provided in said terminal device. 6. The variable bandwidth communication network according to claim 1, wherein said low setting unit is configured as a device accommodating a plurality of said terminal devices.