Cabletron Systems MMAC-Plus SFCS-1000, Configuration Manual

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CHAPTER 1
Configuring PVCs
In order to interoperate with other vendors’ equipment, it is often necessary
to create Permanent Virtual Circuits (PVCs) on a Cabletron switch. This can
be 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 Concepts
Each ATM cell contains a virtual path identifier (VPI) and a virtual channel
identifier (VCI) as part of its five-byte ATM header. The VPI and VCI are used
to route the cell through the ATM network. When a switch fabric receives a
cell, 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 configured
such that any cell received on port A1 with VPI|VCI = 0|32 is switched to
port B2 with VPI|VCI = 0|35. The translation from input port, VPI, and VCI
to output port, VPI, and VCI is achieved via a mapping table in the switch
fabric’s memory.
The VCI value of cells does not change as the cell is switched through the
ATM network via a virtual path. In a single switch environment, a cell’s VPI
and VCI are translated only once, but in a multiple switch environment a
cell’s VPI and VCI are translated many times. It is important to remember that
a cell’s VPI and VCI are of local significance only (i.e., link-by-link). It is also
important to note that virtual connections are unidirectional; that is, they are
valid in one direction only. The VPI and VCI
may change as the cell is
switched through the network.