a. We saw in Chapter 3 that TRANSMISSION NETWORK OPTIMISATION propagation affects the performance of microwave links. Any degradation of the ESR and SESR will result in degradation in performance of the ATM layer as well. Traffic: ATM connections are designed for a given set of parameters. If the traffic load increases beyond what is expected, cell delays may result. In the light of this traffic increase, a higher QoS cannot be guaranteed. Architecture: Architecture of the network elements (e.g switches) can have a deep impact on the performance of the network. Factors such as buffer capacity, ATM cross-connection switching capacity and speed, etc., will affect the QoS. It was noted earlier that there are three negotiable traffic (QoS) parameters in ATM: CLR, CTD and CDV. Optimum performance of these three parameters will lead of optimum performance of the ATM layer. The performance objectives to be met by the ATM layer are described in recommendation ITU-TI.356, which gives the provisional QoS class definitions and network performance objectives for parameters such as CDV, CLR, CMR, SECBR and One important parameter that must be understood at this stage is CDVT. CDVT defines the upper bound in cell delay. This parameter is responsible for definition of the policing function in the network, that is, making sure that the traffic (or cells) reach their destinations within a required delay tolerance value. So basically, any cell that does not respect the service contract is discarded. For this purpose some algorithms are used. In general, CDVT can be calculated as the inverse of PCR. Transmission planning engineers should refer to recommendation ITU-T I.371 for more information on the appropriate values of CDVT. Functions like frame discard and partial packet discard are used to avoid congestion and improve throughput. Traffic shaping is one of the mechanisms that will affect the cell stream characteristics to ensure a more predictable incoming traffic with lower cell loss. Thus, both efficiency and quality of the c