Virtual Circuit; Dlci - HPE FlexNetwork MSR series Configuration Manual

Figure 69 Frame Relay network
Router A
Ser2/1/0
DTE

DLCI=100

Virtual circuit

Virtual circuits are logical connections established between two devices. Depending on how they are
established, virtual circuits include the following types:
•
Permanent virtual circuit (PVC)—A PVC is manually configured or dynamically learned
through the LMI negotiation. The availability of a PVC must be detected before the PVC can be
used.
•
Switched virtual circuit (SVC)—An SVC is dynamically established between two devices
through calls. The network provides data transmission services on established SVCs. The
terminal users can terminate an SVC through clearing the call.
Unlike SVCs, PVCs rarely break or disconnect. PVCs are used more than SVCs.
On a DTE device, the state of a PVC is determined by the DCE device. On a DCE device, the state of
a PVC depends on the way that the DCE device is connected to the DTE device.
•
When the DCE device is directly connected to the DTE device, they use LMI to negotiate the
state of a PVC.
•
When the DCE device is connected to the DTE device through a Frame Relay network, the
state of a PVC is determined by the LMI negotiation result and the virtual circuit state in the
Frame Relay network.
DLCI
A DLCI uniquely identifies a virtual circuit on a physical link and has local significance only for that
link. A DLCI can be used on different physical ports to address different virtual circuits. A virtual circuit
between two DTE devices can be addressed with different DLCIs at the two ends, as shown in
Figure 69.
Because the virtual circuits in a Frame Relay network are connection oriented, each DLCI on a
physical port is destined for a different peer device. DLCIs are the Frame Relay addresses of peer
devices.
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
example, DLCI 0 and DLCI 1023 are reserved for the LMI protocol to transfer control messages.
Router B
Ser2/1/0
Ser2/1/1
DCE NNI
UNI
Frame relay
network
Router C
Ser2/1/0 Ser2/1/1
NNI DCE
DLCI=200
NNI
222
Router D
Ser2/1/0
DTE
DLCI=300
UNI