IBM 9077 manual 111, Components in the ATM OC-3c Interface Name

See Figure 38 for the naming conventions of an ATM interface.

g a 0 x yz

1st:	always "g" for GRF
2nd:	media type, a (ATM)
3rd:	chassis number, always "0" (zero)
4th:	slot number in hex
5th-6th:	logical interface number in hex

Figure 38. Components in the ATM OC-3c Interface Name

Virtual Circuits

Avirtual circuit (VC) exists between two ATM devices. It is the point-to-point connection between them and is of no significance to other ATM devices.

Each VC is identified by a pair of numbers, representing a virtual path identifier (VPI) and a virtual circuit identifier (VCI). A slash (/) is used to separate the two numbers, for example, 0/2645. The VPI/VCI must be unique on a link. Because it is acceptable to use the same VPI/VCI on different links, a GRF can have the same VPI/VCI active on each physical interface.

The ATM OC-3c media card supports up to 1024 active VCs as defined in the ATM Forum UNI3.0 specification. VCs can be divided between the two physical interfaces in any manner required by the site, with 512 VCs active at any one time on each interface. Each VC has an associated IP address. VPI/VCIs are assigned to logical interfaces in /etc/gratm.conf, and provide the bridge between ATM and IP.

Virtual Paths

A virtual path (VP) connects two end stations, which may be separated by one or more network devices such as a router or switch. A path consists of one or more virtual circuits, as you can see in Figure 39.

Virtual Path

Virtual Circuit

Virtual Circuit

Figure 39. Components Forming a Virtual Path

Configuration of IP-Forwarding Media Cards 111