Networks are more frequently being prepared to allow specification of the quality of service needed by users.
For example: - a typical voice telephone call may give a QoS parameter for throughput of 64kbps and time delay less than 500msec. A user transmit video might need throughput of 2Mbps.
ATM QoS SPECIFICATIONS:
There are three kinds of QoS specifications, which are shown as follows:
CONSTANT BIT RATE (CBR):
It is defined for video and audio, since these have predefined maximum speed.
VARIABLE BIT RATE (VBR):
It is defined for compressed video and audio where the data rate relays on the level of compression that may be achieved.
AVAILABLE BIT RATE (ABR):
It is used for typical data functions and allows need of whatever bandwidth is available at a required time.