Filter
Top Products
Virtual Circuits and DLCIs
Page 29-6
Virtual Circuits and DLCIs
The WSX supports Permanent Virtual Circuits (PVCs), but not Switched Virtual Circuits (SVCs).
Most service carriers do not currently offer SVCs. PVCs are either static (configured) or
dynamic (learned). Static PVCs are user-configured and consist of Management, or Control,
PVCs and any configured Data PVCs. Management VCs are used by the WSX to communicate
with the Frame Relay network. Dynamic PVCs are usually data circuits, which are controlled
by the Frame Relay network and not configured in advance. A logical Frame Relay DTE
device like the WSX does not create or control dynamic data VCs. It is only informed of their
status through periodic Status updates from the Frame Relay network.
Each virtual circuit is locally defined by a Data Link Connection Identifier (
DLCI). The Frame
Relay network assigns the DLCIs and informs the WSX about them.
DLCI numbers from 0 to 15 and 992 to 1023 are reserved for Control VCs. If you are using
Annex A or Annex D as your DLCMI, the management control VC will be assigned DLCI 0. If
you are using the LMI Revision 1.0 DLCMI, then the management control VC will be assigned
DLCI 1023.
DLCI numbers from 16 to 991 are reserved for Data VCs.
You may have up to 256 virtual circuits and up to 128 virtual ports on a
WSX.
A VC may or may not have the same
DLCI on each side of a WAN link. For example, if a WSX
physical port contains three Frame Relay VCs on its local network with DLCIs 16, 17, and 18,
these same VCs on the other side of the Frame Relay network might be 30, 31, and 32. The
two sets of DLCIs are technically part of the same virtual circuits, but their values may or may
not be different. DLCIs are only significant locally.
At any one time, a virtual circuit will be active, inactive or deleted. If a virtual circuit is Active
it can transmit and receive data. If it is Inactive, the Frame Relay network still sees the virtual
circuit, but there is a problem with it and it is discarding data. If the virtual circuit is Deleted,
then the virtual circuit is not transmitting or receiving data and no
DLCI exists for it.