Network Sales and Services Handbook (Cisco Press Networking Technology)

Prior to data transmission, an end-to-end path needs to be established through the ATM WAN. Once this path has been provisioned, either on a Permanent (PVC) or Switched (SVC) basis, the following steps are performed:

1. At the sending side, the data is broken down into small, fixed-sized cell payloads (message data) for transmission. Each cell header provides the VPI/VCI (Virtual Path Identifier/Virtual Channel Identifier) values for the destination endpoint.

2. Each ATM switch along the path examines the cell header to determine the appropriate egress interface.

3. Cell payloads are extracted at the destination endpoint and transported data is passed on to upper-layer protocols or applications.

Figure 9-4 illustrates four ATM nodes using VPs and VCs to communicate across the ATM WAN. The ATM NSP is switching the VCs based on the VPI/VCI pairs in the ATM cell header.