priate to ATM would require some very clever engineering, as knee- jerk responses to wide fluctuations might cause unnecessary, and wasteful, re-routes. The main techniques for ATM traffic management are: 1. resource management using virtual paths 2. connection admission control 3. usage parameter control 4. selective cell discard 5. traffic shaping. Discussion of points 3 and 4 will be omitted because they are technical and beyond the scope of this book. Since ATM is a well-established technology, the inter- ested reader will easily find an abundance of reading materials on these topics. 13.3.1 Resource Management Using Virtual Paths Network resource management is about separating traffic according to service characteristics. Virtual paths are used by the ATM Forum for traffic control based on network resource management. A Virtual Path Connection (VPC) groups similar Virtual Channel Connections (VCCs). Characteristics of the VPC are inherited and enjoyed by the VCCs. In a user- to-user application, the VPC extends between a pair of UNIs. The user must ensure that the total demand from the VCCs can be accommodated by the VPC. In a user-to-network application, the VPC extends between a UNI and a network node. The network is aware of and accommodates the QoS of the VCCs within the VPC. In a network-to-network application, the VPC extends between two network nodes, and the network is aware of and accommodates the QoS of the VCCs within the VPC. 13 Traffic Management The main QoS parameters are cell loss ratio, cell transfer delay and cell delay vari- ation. These are all affected by the resources allocated to the VPC. Where a VCC passes through multiple VPCs, the performance of the VCC depends on that of the consecutive VPCs and how the VCC is handled by nodes such as switches or con- centrators between and on VPCs. Handling by the nodes affects QoS through nodes' processing speed and cell prioritisation. An OSS should be aware of the capacity assigned to the VPCs and of the action and performance of the nodes. Ind