1-1CHAPTER 1 Configuring PVCsIn order to interoperate with other vendors’ equipment, it is often necessaryto create Permanent Virtual Circuits (PVCs) on a Cabletron switch. This canbe accomplished through the ATM Management Interface (AMI). This chap-ter will discuss the creation of PVCs through AMI on a Cabletron switch.1.1 General ConceptsEach ATM cell contains a virtual path identifier (VPI) and a virtual channelidentifier (VCI) as part of its five-byte ATM header. The VPI and VCI are usedto route the cell through the ATM network. When a switch fabric receives acell, it examines the ATM header to determine the correct output port, VPI,and VCI for the cell. For example, an ATM switch fabric can be configuredsuch that any cell received on port A1 with VPI|VCI = 0|32 is switched toport B2 with VPI|VCI = 0|35. The translation from input port, VPI, and VCIto output port, VPI, and VCI is achieved via a mapping table in the switchfabric’s memory.The VCI value of cells does not change as the cell is switched through theATM network via a virtual path. In a single switch environment, a cell’s VPIand VCI are translated only once, but in a multiple switch environment acell’s VPI and VCI are translated many times. It is important to remember thata cell’s VPI and VCI are of local significance only (i.e., link-by-link). It is alsoimportant to note that virtual connections are unidirectional; that is, they arevalid in one direction only. The VPI and VCI may change as the cell isswitched through the network.
