Lucent Technologies PortMaster - Manual (Page 208)

Overview of Frame Relay
13-2 PortMaster Configuration Guide
PVCs and DLCIs
PortMaster products support permanent virtual circuits (PVCs). PVCs are used to form a
connection between any two devices attached to a Frame Relay cloud. Each PVC is
given a unique number on each physical circuit along the path between the two
devices. This unique number is called a data link connection identifier (DLCI). The DLCI
is automatically changed to the PVC number of the next physical circuit as it passes
through each switch along the path. A DLCI is different from a network address because
it identifies a circuit in both directions, not a particular endpoint. A frame contains only
one DLCI, not a source and destination.
In general, the only DLCI numbers you see are those numbers assigned to the physical
circuits on the perimeter of the Frame Relay cloud.
Line Speed
The physical circuit between point A and the network must be ordered with a certain
line speed. This speed is the physical maximum bandwidth for your connection to the
Frame Relay network. Expansion beyond this limit is not possible without a hardware
change and a new circuit installation.
Port Speed
The connection into the telecommunications provider’s Frame Relay network must be
ordered at a particular port speed, which is the maximum bandwidth rate that the
telecommunications provider accepts from your connection. This number must be less
than or equal to the line speed. This speed is the maximum rate at which you can
transmit data to any of your PVCs under any circumstances. The port speed differs from
line speed only in that it can be upgraded through software without a circuit installation
or hardware change.
CIR and Burst Speed
Each PVC has a property known as committed information rate (CIR), which represents
the guaranteed minimum bandwidth available to the particular PVC under all
conditions. In some implementations, an additional property can be assigned to a PVC,
known as “burst speed” or “maximum burst.” This speed represents the highest rate at
which data is allowed to flow over a given PVC, regardless of bandwidth availability.