The ATM supports a guaranteed Quality of Service (Qos) which includes, .

1) Traffic Contract

2) Traffic Shaping

3) Traffic Policing

1) Traffic Contract:

A traffic contract specifies an envelope which describes the intended data flow.

It also specifies the values of peak and sustained bandwidth, burst size etc.

When one ATM system gets connected to an ATM network, it automatically enters into a contract based on QoS parameters.

2) Traffic Shaping and Traffic Policing:

Traffic shaping is done in order to fit the traffic within the promised envelope.

It uses the queues to constrain the data bursts, limit the peak data rate and reduce jitters.

The ATM switches can be used to measure the actual traffic flow, and compare it with the agreed upon traffic to enforce the contract.

If the actual traffic is higher than the agreed upon traffic, then the switch will set the Cell-Loss Priority (CLP) bit.

When this bit is set, the cell discard becomes eligible and any switch handling the cell is allowed to discard that cell in the event of congestion.