Avaya M770 Routing and Signalling Concepts

Avaya M770 ATM Switch User’s Guide 301

Routing and Signalling Concepts

This chapter describes how the Avaya M770 ATM Switch switches ATM cells

through an ATM network, and provides background information about the

concepts of routing and signalling.

There are two types of connection that can be used to switch ATM cells through an

ATM network.

• Permanent Virtual Circuits (PVCs), which are created manually by the network

administrator. Every switch through which the connection will pass will need

to be configured separately. PVCs are used for communication between two

endpoints, through a pre-configured circuit, until the administrator disables the

PVC and frees the connection.

• Switched Virtual Circuits (SVCs), which are established on demand by UNI

(User-to-Network Interface)/NNI (Network-to-Network Interface) signalling

protocols. SVCs are used for communication between two endpoints until one

endpoint clears the connection. There are two types of SVCs:

— Point-to-point virtual circuits

— Point-to-multipoint virtual circuits.

In an ATM network, an end-station can establish a SVC to another end-station by

transmitting a signalling call setup request across the network. This request is

routed across the ATM network to the destination end-station. If the destination

agrees to accept the connection, a SVC is set up across the ATM network, between

the two end-stations.

In ATM networks data is multiplexed on physical links using virtual circuits and

virtual paths. A virtual circuit is a channel of communication that allows data

transfer between two ATM devices. A virtual path is used to group virtual circuits

within the same transmission medium so that they can be switched together. Virtual

circuits are identified by an unique Virtual Circuit Identifier (VCI). Virtual paths are

identified by an unique Virtual Path Identifier (VPI).

Figure C.1 shows how virtual circuits are bundled together within a virtual path.