Network Sales and Services Handbook (Cisco Press Networking Technology)

QoS is the ability to define a level of performance in a data communications system. For example, ATM networks specify modes of service ensuring optimum performance for traffic such as real-time voice and video.

The QoS parameters selected to correspond to a network performance objective can be negotiated between the end-systems and the network for example, through signaling procedures or can be taken as default. These QoS parameters are often enabled on a per-connection basis and are listed here:

• CDV Measured in microseconds. CDV is the distortion caused by change in arrival times between cells, also known as jitter.

• Max CTD Sum of the fixed-delay component across the link or node and the CDV. Max CTD, or MCTD, is a required metric for CBR and VBRrt service categories; it is an optional metric for VBRnrt.

• CLR The ratio of lost cells to total cells transmitted on a link or node:

  CLR= Lost Cells/Total Cells

Two CLR attributes are calculated: CLR0 and CLR0+1. The cell loss priority portion of CLR0 considers only CLP=0 traffic; for CLR0+1, both CLP=0 (No discard) and CLP=1 (Discard Eligible) traffic are considered in the calculation.