reased efficient performance of the network due to a lower number of entities to manage in totality. Reduced connection setup time and hence less processing involved as much of the work is done when the virtual path is being set up. Once the virtual paths have been set up, the new virtual channel connections can be established by simple signalling. The processing is required at the end nodes only and not at every node. This not only reduces the processing delay but also the total connection setup time. A better organised and simple network architecture is a result of the combination of many virtual channels into single virtual paths. Table 3.6 Table at node A Link in VC in Link out VC out Transmission Network Planning and Optimisation Delay Overhead Payload (Bytes) Figure 3.28 A graph indicating the importance of small sized cells Now that there is familiarity with the virtual connections, it is possible to take a look at how a call becomes established in an ATM system using the virtual paths and channels. Two important things should be kept in mind: The virtual path connection setup includes calculating routes, allocating the total capacity that the virtual channels might use, etc. For the virtual channel connection setup, control mechanisms are needed that check a few things before a channel is set up. These functions involve checking that there is a virtual path connection to the required destination node with sufficient available capacity to support the virtual channel, with the appropriate quality of service, etc. Consider a request for VCC establishment. This originates a call, which further checks whether a VPC exists. If a VPC does not exist then a new VPC is established and the capacity along with the quality of service is checked. If the capacity or the QoS is not guaranteed then the request of the VCC is blocked and more capacity is requested. If the capacity is not granted then the VCC request is rejected. However, if the QoS is guaranteed in the first stage or capacity is granted in the second stage,