WO1997048213A2

WO1997048213A2 - Traffic measurement in an atm network

Info

Publication number: WO1997048213A2
Application number: PCT/FI1997/000363
Authority: WO
Inventors: Kalevi Kilkki
Original assignee: Telecom Finland Oy
Priority date: 1996-06-11
Filing date: 1997-06-10
Publication date: 1997-12-18
Also published as: FI962422A; WO1997048213A3; FI962422A0; AU3095797A

Abstract

The invention relates to a method and a system for traffic measurement in an ATM network. The bandwidth of a link (15) in the network is known. The traffic, i.e. bandwidth, is measured by letting the ATM cells enter and leave an imaginary buffer in a measuring device (30). In addition to the real cells, imaginary cells corresponding to an imaginary traffic stream are also entered into the imaginary buffer. If the bandwidth of the imaginary traffic is too large the imaginary buffer becomes full, cells are lost and an imaginary cell loss ratio is obtained. A predetermined imaginary cell loss ratio corresponds to utilising the total bandwidth of the link (15). The imaginary traffic corresponds to a known bandidth and by substracting the imaginary bandwidth from the bandwidth of the link (15) the bandwidth of the actual traffic is obtained.

Description

TRAFFIC MEASUREMENT IN AN ATM NETWORK

The object of the present invention is a method according to the preamble of the claim 1 and a system according to the preamble of the claim 6 for measuring traffic in ATM (Asyncronous Transfer Mode) network.

Various services utilising ATM-network are such, that traffic generated by them is difficult to estimate in advance. A typical example is services connecting local area networks. For this sake continuos traffic measurements are essential, so that on the other hand network's respective occupancy situation is known and on the other hand a network can be designed sensibly.

At this moment traffic measurements of ATM-network require either utilisation of very expensive equipment or then it is available only traffic information which is very difficult to handle, that nodes in nodal points of network produce very big amounts.

From point of view of network management and design the best measurement mode would be such, that with the aid of it network capacity utilised by connections in reality could be clarified directly. A capacity needed by one connection is called effective bandwidth (effective bandwidth). The effective bandwidth describes that band what a particular connection reserves on some bus of ATM-network, when a service level has been given. The most important variable describing a service level is a probability of loss of cells.

The effective bandwidth can be applied so, that a new connection is accepted for a certain bus in case a sum of the effective bandwidths do not exceed the bus capacity. Even though the band needed by the connection in reality depends also on other traffic (not merely traffic properties of the connection in question), it is very probable that the acceptance and design of ATM-network's connections will be based on the effective bandwidth. The traffic measurements of ATM-network are usually based on calculation of cell amount over a certain period. The period can be very short, when traffic measurement is in theory very accurate, but on the other hand an after-curing of information obtained this way is difficult, because it's amount is enormous, there do not exist simple methods, with which help the information could be converted into advantageous and visualised form. If again period is long, when continued handling is easier, a part of essential information concerning traffic can be lost.

The object of the invention is to realise traffic measurements by so simple principle, that it applies to continuos traffic monitoring use on all buses of ATM-network, by offering at the same time the essential information of traffic condition. This objective has been achieved by a method according to the invention, to which characterised features have been presented in the enclosed claims 1 -5, and by a system, to which characterised features have been presented in the enclosed claims 6-9.

With the aid of the invention an effective bandwidth of connections of a certain bus can be directly defined. The measurement is based on that it is defined the biggest allowed steady velocity traffic flow, which could have been added to the bus without that a share of lost cells would have exceeded the allowed value. The characterised features for the invention are presented in the enclosed claims.

The measurement principle is very simple, because it does not require else than a certain amount of accumulators, which are updated according to the simple principles. The result obtained by the presented system and method is applicable as such without complicated post processing of measurement information to describe an occupancy situation of a node of ATM-network.

The invention makes possible continuos monitoring of ATM -network's traffic situation in all busses of network, because the required equipment is very easy to realise.

The invention is described more particularly by referring to the enclosed drawings, in which figure 1 represents a concept of ATM^'s cell switching figure 2 represents ATM protocol architecture figure 3 represents general description of measurement system

In the figure 1 it has been presented a concept of ATM's cell switching. By ATM-cell it is meant 53 bytes long information element, of which bytes 48 is transferable data. Cell switching is taken care of by ATM-node 10. Different terminal devices have been connected to it such as for instance a computer workstation 1 1 , which carries the traffic by sending and receiving both constant- and variable bit speed data, a router located in local area network 12, which carries the traffic by sending and receiving variable bit speed data and a telephone switchboard 13, which carries the traffic by sending and receiving constant speed data. In order to connect terminal devices to ATM-node, they must have or they first have to connect to ATM-adapter 14, which changes data transfer packets used by these to ATM-cells and vice versa. Division to ATM-cells takes place so, that 48 data bytes of a cell include data from terminal device's data transfer packet and the 5 rest bytes information about, to which logical connection and data transfer packet data bytes belong to. From ATM-node exists connections 15 to the other ATM- nodes.

In the figure 2 it has been clarified ATM protocol architecture. ATM protocol architecture is formed of three layers. The lowest physical layer defines physical data transfer means, interfaces and, how ATM-cells are arranged for transfer. The next layer, ATM-layer takes care of routing cells through ATM-network. The function of these layers and definitions have been described in ITU-T's (International Telecommunication Union, Telecommunication Standardization Section) reference 1.31 1 . ATM -adaptation layer adapts various applications to cell transmission service provided by ATM-layer. Function and definitions of this layer has been described in ITU-T's reference 1.362. ATM protocol-architecture is further divided into user , control and management planes. ATM-terminal devices 20 communicate with ATM-nodes 21 through the agency of two lowest planes. Between ATM-terminal device and ATM-node is user-network interface UNI and between ATM-nodes is network-network-interface NNI. In the figure 3 is a general description of measurement system. In the figure a measurement device 30 is on the bus between two ATM-nodes, but it could also locate on the bus between terminal device and ATM-node. The node means data transmission connection, which has a certain capacity dependent on physical layer's transmission devices or maximum data transmission speed. The bus is divided on virtual paths (e.g. data transmission capacity reserved by one customer), which are further divided on virtual channels. In the following buffering of ATM-cells occurs on buffer 31 located at departure end of the bus. The buffer size can be from some thirty or forty to even thousands of cells.

In the basic form the invention concerns measurement of efficient bandwidth of the traffic of the whole bus. The measurement takes place so, that it is maintained N pieces accumulators towards the bus, which each form an imaginary puffer. A wanted N\s value is category of 10...20. The greatest allowable value of the accumulator (or wanted size) is same as the size of the right puffer as cells. Every accumulators are increased always when a measurement device detects ATM-cell's bus used in the measurement point. In addition to this to each imaginary buffer arrives constant capacity traffic on certain various velocities, or each accumulator is increased by one during regular various time intervals. These constant velocities are chosen as increasing series so, that at least in part of imaginary buffers the whole capacity of the bus will become utilised during the measurement sequence or at least some accumulators fill, when imaginary cell losses occur. A cell gets lost, if a buffer is full when cell is arriving to it. Cells leave from imaginary buffers or accumulator is diminished by velocity defined by capacity of the bus, as buffer as normally empties.

Each accumulator measures thus loss probability of cells on the condition that on the bus would be a certain constant speed source besides the real traffic. The effective bandwidth of constant speed sources is known, when with the aid of imaginary buffers can be defined an effective bandwidth of other traffic as a function of loss probability of cells. On a certain measurement sequence (e.g. one second) it is obtained from each accumulator one measurement value of the relative number of lost cells. These measurement values form an observation point sequence as a function of bandwidth of imaginary increased traffic. The effective bandwidth of the real traffic corresponding the allowable lost probability of cells (for instance 10e-9) is obtained by adapting the obtained value to a second degree curve by a logarithmic scale. The effective bandwidth of the real traffic is accordingly the effective bandwidth of the whole bus subtracted by the effective bandwidth of the imaginary increased traffic.

The measurement device is realised with the aid of accumulators, which keep book of the status of the imaginary buffers and arrived and lost cells. Besides the devise includes a part, which processes obtained number information and calculates the effective bandwidth.

Embodiments of the invention relate to further processing of the obtained measurement result. Calculation of a value of a loss probability of cells is based on a certain measurement sequence, which length can be for instance one second. After each measurement sequence it is read from accumulators the amount of arrived and lost cells, and these cell accumulators are cleared. The ratio of these is obtained as the loss probability of cells. Because amounts of cells are to add up, the loss probability of cells can be easily calculated, and thus also the effective bandwidth to various length time intervals, for instance one minute, 10 minutes and 1 hour. The calculations are fairly simple, so that carrying out them doesn't cause problems. With the aid of long time interval the effective bandwidth can be defined more accurately, when the allowable share of lost cells is very small. However if the time interval is very long, one can't be sure, that the traffic process has remained unchanged.

Another embodiment of the invention besides the above mentioned is to examine from each ATM-cells, to which virtual path or virtual channel it belongs to, and to calculate the effective bandwidth to all or wanted virtual paths or virtual channels of the bus. This requires the above mentioned amount of virtual accumulators per each virtual path or virtual channel. From other parts the calculation of the effective bandwidth of each virtual path or virtual channel takes place according to the invention by the same way as it has been previously presented when calculating the effective bandwidth of the whole bus. The invention can be realised relating to any ATM-bus, from which the information is obtained each time the utilised ATM-cell moves over a certain point. Besides the information of usable size of buffer is needed. The invention can be realised thus either as a part of ATM-node or ATM-measurement device.

The invention has been previously described by referring to one of it's preferable embodiment. By this it is not wanted by any means to restrict the invention to concern only this example but all modifications are possible in the spirit of the inventive idea presented by the following claims.

Claims

1. A method for measuring ATM (Asyncronous Transfer Mode) cell traffic including data in ATM-network with the aid of a terminal device, as e.g. computer work station (1 1 ), a local area network router (12) and a telephone exchange (13), which connects to ATM-network with the aid of ATM-adapter (14), which converts data transmission packets utilised by the terminal device to ATM-cells, which are measure of predetermined amount bytes information elements, and opposite, and ATM-node (10, 21), through which data transmission connection forms forward, or on a bus (15) between two ATM -nodes (10,21 ), which bus is a data transmission connection, in which method for measuring traffic it is defined the biggest allowable constant speed traffic flow, which is to add to the bus between two ATM -nodes (10,21) or the terminal device (1 1 ,12,13,20) and ATM-node so that a share of lost cells is under the predetermined allowable limiting value, and characterised in that, for measuring traffic of the bus ( 15) it is measured the effective bandwidth so, that on the bus (15) it is maintained a measurement device (30), by which it is formed an imaginary buffer, and by which it is measured loss probability of cells on the condition that on the bus (15) would be a certain constant speed source besides the real traffic.

2. A method according to the claim 1 , characterised in that towards the bus (15) it is maintained the measurement device (30) formed of several accumulators, which each accumulator establish an imaginary buffer, and by which each accumulator it is measured the loss probability of cells on the condition that on the bus (15) would be a certain constant capacity source besides the real traffic.

3. A method according to the claims 1 and/or 2, characterised in that, each accumulators are increased by one always when it is detected by the measurement device (30) ATM-cell being used in the measurement point of the bus (15), that to each imaginary buffer it is delivered constant speed traffic by certain various speeds, as which response each accumulator is increased by one between regular intervals, that the mentioned constant speeds are chosen as increasing sequence so, that at least in part of imaginary buffers the whole capacity of the bus (15) is utilised during the measurement cycle, as which implication the mentioned accumulators fill, when it is generated imaginary cell losses.

4. A method according to the claims 1 -3, characterised in that when the effective bandwidth of the constant capacity sources is known, with the aid of imaginary buffers it is defined the effective bandwidth of other traffic as a function of loss probability of cells, that on a certain measurement cycle it is obtained from each accumulator one measurement value from the relative amount of lost cells, from which measurement values it is formed an observation point sequence as a function of effective bandwidth of imaginary current added traffic, when the allowable loss probability of cells corresponding the effective bandwidth of the real traffic, which is the effective bandwidth of the whole bus (15) subtracted by the effective bandwidth of imaginary known increased traffic, it is obtained by adjusting the obtained measurement values to a second degree curve on a logarithmic scale.

5. A method according to the claims 1 -4, characterised in that it is examined from each ATM-cell, to which virtual path or virtual channel it belongs to, and the effective bandwidth is calculated to all or wanted virtual paths or virtual channels of the bus (15).

6. A system for measuring ATM (Asyncronous Transfer Mode) cell traffic including data in ATM-network with the aid of a terminal device, as e.g. a computer work station (1 1 ), a local area network router (12) and a telephone exchange (13), which connects to ATM-network with the aid of ATM-adapter (14). which converts data transmission packets utilised by the terminal device to ATM-cells, which are information elements of measure of predetermined amount bytes, and opposite, and ATM-node (10,21), through which data transmission connection forms forward, or on a bus (15) between two ATM-nodes (10,21 ), which is a data transmission connection, which system includes a measurement device (30), which is on the bus (15) between two ATM-network's nodes (10,21 ) intermediating traffic, or between the terminal equipment (1 1 ,12,13,20) and ATM-network's node ( 10,21), and for which it is defined the biggest allowable constant speed traffic flow, which is to add to the bus ( 15) so, that a portion of lost cells is under a predetermined allowable limiting value, characterised in that for measuring an effective bandwidth of traffic of the bus (15) the measurement equipment (30) forms to the bus (15) an imaginary buffer and measures lost probability of cells on the condition that on the bus ( 15) is a certain constant speed source besides the real traffic.

7. A system according to the claim 6, characterised in that for measuring the effective bandwidth of traffic of the bus (15) the measurement device (30) includes numbers of updating accumulators, of which each forms an imaginary buffer and measures lost probability of cells on the condition that on the bus (15) is a certain constant speed source besides the real traffic.

8. A System according to the claims 6 and/or 7, characterised in that each buffer of the measurement device (30) is increased by one, when the measurement device (30) detects ATM-cell being utilised in the measurement point of the bus (15), that to each imaginary buffer arrives constant speed traffic by certain various velocities, as which response each accumulator is increased by one between regular intervals, that the mentioned constant speeds has been chosen as an increasing sequence so, that at least in part of the imaginary buffers the whole capacity of the bus (15) will become utilised during the measurement cycle, as a consequence of which the accumulator of the measurement device (30) fills, when imaginary losses of cells occur.

9. A system according to the claim 3. characterised in that when the effective bandwidth of constant speed sources is known, the system defines with the aid of imaginary buffers the effective bandwidth of other traffic as a function of lost probability of cells so, that on a certain measurement cycle from each accumulator comes one measurement value from the relative amount of the lost cells, that these measurement values form an observation point sequence as a function of effective bandwidth of imaginary known increased traffic, when the effective bandwidth of the real traffic corresponding the allowable lost probability of cells, which the effective bandwidth of the whole bus (15) subtracted by the effective bandwidth of an imaginary known increased traffic, is determined with the aid of measurement values adjusted to a second degree's curve by a logarithmic scale.