Write a note on ATM layer performance measurement?

Answer 1

ATM LAYER PERFORMANCE MEASUREMENT

ATM Layer Performance:- It is known as information transfer performance and refers to performance related to cell transport service provided by network. The two key issues of ATM layer are:-

NP (Network performance)

Quality of Service (QOS)

1. Network Performance:- It is used to manage the network and include parameters that are meaningful to network providers for system design configuration, operation and maintenance.

Network performance is measure by network at various points while QOS is measure at end point. During continuation of service, these parameters can be calculating without affected users traffic. This require the NP procedure to be activated and de-activated. The calling end-point (A) generate an activation or de-activation request towards another end point (B) with request for action on either A to B, B to A or both direction. The requirement is generated with help of ATM OAM cell.

I. ATM OAM Cell, Activation, de-activation function specific fields:-

II.

Message ID

000001 à Activation request

000010 à Activation confirmed

000011 à Activation request denied

000101 à Deactivation request

000110 à Deactivation confirmed

000111 à Deactivation request denied

If other point B respond to all of request then activation or deactivation confirmed message is returned otherwise activation deactivation confirmed message, request denied message is confirmed.

2 Direction of action:

It has two value that is from activator(10) or towards activator(01).

3 Correlation tag:

It has same value for all packets.

4 PM block size A-B:

It is identifier performance measurement block which can supported from A to B by a bit mask of 1024 bytes, 512, 256, 00 128 bytes. From most significant bit to least significant bit respectively.

5 PM block size B-A:

It identifies the performance measurement block which can be supported from B to A by a bit mask of 1024, 512, 256, 128 bytes from most significant bit to least significant bit respectively.

Quality of Service (QOS):- QOS is end users view about working of network and includes parameters that can be directly observe and measure by user and are described in network independent terms.

QOS is defined in terms of following cell transfer outcomes:-

Successful cell transfer outcome:- the cell is received corresponding to transmitted cell within a specified time. The binary content of received cell confirm exactly to corresponding cell payload and the cell is received with valid header field.

Errored cell outcome:- the cell is received within specified time but binary content of received cell payload differs from that of corresponding transmitted cell.

Cost cell outcome:- no cell is received corresponding to transmitted cell within specified time.

Misinserted cell outcome:- a received cell for which there is no transmitted cell.

Severely error cell block outcome:- when N or more cell outcome or errored cell outcome are reserved in a received cell block of N-cells transmitted consecutively on a given connection.

Parameters for measuring information transfer performance:-

Cell delay variation.

Cell error ratio.

Cell Loss Ratio

Cell Misinsertion Ratio

Cell transfer delay

Cell error ratio: is the ratio of PDU's received at an end point which contains an invalid CRC in relation to total no. of cells properly transmitted associated with given traffic load.

Signal metrics:

1. CAC rejection or denial time: The amount of time required fo0r CAC to determine that cell must be rejected, it is measured in seconds.

Connection establishment time:- The amount of time between first setup message from calling party and connect message to it. It is also measured in seconds.

Connection teardown time:- The amount of time between the release message being sent and release complete message being received. It is also measured in seconds.