ATM Connections

ATM is a connection-oriented technology that supports point-to-point (unicast) and point-to-multipoint (multicast) application connections. Regardless of the application, ATM cells are received in the same order in which they are sent.

ATM does not guarantee delivery of data across the WAN because data might encounter congestion in a backbone switch. ATM determines the handling of such congestion issues based on the class of service to which it is subscribed. (ATM classes of service will be discussed later in this chapter).

Virtual Paths

ATM virtual path connections comprise a bundle of virtual channel connections. The bundling of virtual channels having the same endpoints into a single virtual path simplifies the provisioning and implementation of a large number of virtual channels (VCs) having common endpoints. This provisioning and implementation is simplified as the VCs are multiplexed onto a single virtual path (VP). Virtual paths also simplify the task of switching data from source to destination because all the virtual channels are switched as a single virtual path.

Figure 18-7 illustrates an end-to-end ATM virtual path, with two virtual channels.

Figure 18-7. ATM end-to-end virtual path

Figure 18-7. ATM end-to-end virtual path

ATM Virtual Channels

ATM point-to-point connections are actually a pair of simplex connections—a simplex connection from end node A ""^end node B, and a simplex connection from end node B ""^end node A. Each connection pair comprises a virtual channel connection (VCC).

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