Virtual Path - Channel Hierarchy; Switched Virtual Channels - 3Com CoreBuilder 9000 User Manual

352 C 13: E
HAPTER STABLISHING
Virtual Path —
Channel Hierarchy
Switched Virtual
Channels
ATM C
HANNELS
The values of VPI and VCI can be allocated independently of each other.
These two degrees of freedom allow you to construct a channel
hierarchy. If several virtual channels with different VCI values are given the
same VPI value, then you can group all these channels together by
relating only to the VPI value. A virtual channel defined by its VPI only is
called a virtual path.
For the purposes of switching, a virtual path with a certain VPI value is a
high-level "container" channel that carries all virtual channels with that
common VPI value; when the virtual path is switched, all the virtual
channels are also switched.
A virtual channel can be set up either automatically by signalling, which is
called a switched virtual channel (SVC), or you can set it up manually
through the LMA, which is called a permanent virtual channel (PVC).
Switched Virtual Channels (SVC) connections are defined dynamically
when they are needed and released when they are not needed, using
signalling as per ATM Forum UNI standards. By using SVC, ATM devices
can exchange connection characteristics when establishing connections.
These connections remain active for as long as the application demands.
Both point-to-point and point-to-multipoint connections can be
established. SVC eliminates the need for the external management
station to set up virtual channels.
The characteristics of the SVC connection include:


Connections initiated by the user or application


Connections established and released dynamically


Connections established via the signalling protocol


Varied connection duration
Table 44 presents a comparison between the two types of virtual
channels.