IBM SG24-4817-00 manual ATM Connections, ATM Addressing

This soft copy for use by IBM employees only.

1.1.2 ATM Connections

ATM, being session-oriented, requires that a path through the network be determined and maintained for the duration of the session. This path is comprised of virtual channel links (switch-to-switch connections), which are linked together to form a virtual channel connection (VCC) (end-to-end connection), which are aggregated into virtual paths (VP). Just like a virtual channel (VC), a virtual path can be a virtual path link (switch-to-switch connection) or a virtual path connection (VPC) (end-to-end connection). More importantly, a virtual path can be switched to a new route (to avoid congestion or a failure) without affecting or individually processing the VCs it contains.

Connections through the network can be either fixed and pre-determined, or can be defined dynamically through a signalling protocol. A pre-determined path, defined by the network operator, is called a permanent virtual connection (PVC), while a dynamically determined temporary path is called a switched virtual connection (SVC). In either case, a connection will be implemented only if there is adequate capacity in the network to meet the requisite end-to-end bandwidth and Quality of Service (QoS) parameters, or if an existing connection can be preempted to make it possible to meet bandwidth and QoS requirements.

1.1.3 ATM Addressing

Figure 1. ATM Addressing Format Cell

An ATM address consists of two parts: a 13-byte network prefix and a 7-byte terminal identifier (consisting of a 6-byte end station identifier (ESI), and a 1-byte selector field). Further information on specific requirements for ATM addressing can be found in IBM 8285 Nways ATM Workgroup Switch: Installation and User′ s Guide and in ISO-8348 (CCITT X.213). Of specific relevance to us, are the following addressing restrictions:

2ATM Workgroup Solutions: Implementing the 8285 ATM Switch