Virtual Circuit; Data Link Connection Identifier - H3C SR6600 Configuration Manual

As shown in Figure
devices Router A and Router D are attached. You can see that the DTE and DCE are identified on only
the UNI interface; a virtual circuit between two DTE devices can be assigned different DLCIs on
different segments.
Figure 8-1 An example frame relay network

Virtual Circuit

Virtual circuits are logical paths established between DTE devices. Depending on how they are set up,
virtual circuits fall into:
Permanent virtual circuits (PVCs), which are pre-configured by network administrators and
maintain until being manually removed.
Switched virtual circuits (SVCs), which are analogous to dialup connections, and are dynamically
set up or cleared on an as-needed basis through protocol negotiation.
At present, PVCs are used far more often than SVCs.

Data Link Connection Identifier

A data link connection identifier (DLCI) is a unique number assigned to a virtual circuit endpoint in a
frame relay network for the addressing purpose.
A DLCI uniquely identifies a particular virtual circuit on a physical link and has local significance only to
that link. This means that a DLCI can be used on different physical ports to address different virtual
circuits and a virtual circuit may be addressed with different DLCIs at the two ends, as shown in
8-1.
As the virtual circuits in a frame relay network are connection oriented, each DLCI on a physical port is
destined for a distinct remote router. DLCIs can thus be regarded the frame relay addresses of remote
routers.
Typically, DLCIs are assigned by the service provider, that is, by the DCE side to the DTE side.
The maximum number of PVCs that can be created on a frame relay interface is 1024. The user
configurable DLCIs for the PVCs are in the range 16 to 1007. Other DLCIs are reserved for special
purposes. For example, DLCI 0 and DLCI 1023 are reserved for the LMI protocol to transfer control
messages.
8-1, Router B and Router C form a simple frame relay network, to which DTE
8-112
Figure