HP auroraTempo, Руководство пользователя

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aurora Tempo - User Guide
8-12 423972
PVC
A Permanent Virtual Circuit (PVC), as the name suggests,
is a fixed circuit in which the routes between two end points
are defined during network setup.
Most Frame Relay implementations use PVCs which are
usually full duplex i.e. they support the same traffic rates in
both directions. However some service providers also support
asymmetric or simplex PVCs which enable a network to be
configured in such a way that there is a higher transmission
rate in one direction than in the other.
Because PVCs represent a logical channel, multiple PVCs can
exist in a single physical circuit. A DLCI (Data Link
Connection Identifier) is used to identify the PVC at each
end and to denote which PVC ‘owns’ which frame of
information.
SVC
A Switched Virtual Circuit (SVC) is a temporary virtual
circuit which can be set up and cleared down on a call by
call basis. This type of circuit enables Frame Relay to be
used for purposes other than LAN interconnection, however
there is a greater network overhead with this method.
Messages relating to SVCs are transmitted across the UNI on
channel 0, the signalling channel. The format of the frame is
the same as that for the LMI frame (please refer to the
section on LMI in this Chapter for further details) but, for
SVC messages, the Call Reference field is utilized. This field
indicates whether the user or the network side of the
interface originated the call.