on (CDV) Relevant Relevant Sustainable cell rate (SCR) Not relevant Relevant Burst tolerance Not relevant Relevant OSS for Telecom Networks 13.4 Congestion Control in ATM Networks ATM networks promise large bandwidth and guaranteed QoS wherever there are effective traffic management schemes. Nortel, for example, has developed a method of testing the robustness of flow control algorithms and studied network topologies in which two different congestion control schemes co-exist. Both pure ATM and IP-over-ATM networks have been studied. An Available Bit Rate (ABR) simulator is used to evaluate performance, which can overlay any set of Virtual Circuit (VC) routes on any topology. Nortel implemented five flow control algorithms, identified 10 performance metrics, studied key behav- iours, source-rate oscillations and interference in rate control by switch nodes which are not bottlenecked and established criteria for the ability of an algorithm to perform well regardless of changes in topology, feedback delays and traffic. After evaluating the interoperability of pairs of ABR flow control algorithms in diverse ATM networks, Nortel concluded that heterogeneous configurations with two different ABR flow control algorithms operating simultaneously cause users to receive disparate bandwidths if: 1. The algorithm at a bottlenecked switch is much more oscillatory than the algo- rithm at the non-bottlenecked switches. 2. At least one VC traverses only the more oscillatory algorithm and at least one VC traverses both algorithms. 13.5 Traffic Shaping Traffic shaping or traffic conditioning is the enforcement of the rules on network packets based on QoS policies. In networks which allow specification of QoS, it is necessary to specify the traffic profile for a "connection" to decide how to allocate various network resources. Traffic shaping ensures that traffic entering at an edge or a core node adheres to a specified profile, since the function is carried out at a node. In other words, traffic shaping is the forcing of traffic t