Primary objective of ATM is to provide QoS guarantees while transferring cells across the network. There are mainly three QoS parameters specified for ATM and they are indicators of the performance of the network
- Cell Transfer Delay (CTD):
The delay experienced by a cell between the first bit of the cell is transmitted by the source and the last bit of the cell is received by the destination. This includes propagation delay, processing delay and queuing delays at switches. Maximum Cell Transfer Delay (Max CTD) and Mean Cell Transfer Delay (Mean CTD) are used.
- Peak-to-peak Cell Delay Variation (CDV):
The difference of the maximum and minimum CTD experienced during the connection. Peak-to-peak CDV and Instantaneous CDV are used.
- Cell Loss Ratio (CLR):
The percentage of cells lost in the network due to error or congestion that are not received by the destination. CLR value is negotiated between user and network during call set up process and is usually in the range of 10-1 to 10-15.
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