Glossary V

VC12, VC3 trail

The channel rates of the VC12 trail and VC3 trail are respectively 2.048Mbit/s and 34.368Mbit/s. The VC12 and VC3 trails are transparent channels (i. e. circuit group) provided for circuit-layer network nodes (e. g. a switch) in a path-layer network, and act as the basic unit of transport capacity among circuit-layer network node channels. Its server layer trail is VC4 server trail. The VC12 or VC3 trail is established on the basis of VC4 server trail, which can only be created after the VC4 server trail. If the VC12 and VC3 trails only pass one VC4 server trail, lower order cross-connect is performed over the NEs at the two ends during the creation, the VC4 pass-through is configured over the intermediate NE. If the VC12 and VC3 trails pass multiple VC4 server trails, in addition to that mentioned above, lower order cross-connect is configured over the NE at the crosspoint of two VC4 server trails during the creation, thus making the VC12 and VC3 trails pass through.

VC4 loopback

The fault of each VC4 path on the optical fiber can be located by setting loopback for each VC4 path of the line. There are three kinds of loopback modes. 1. No loopback: It is the normal status. No loopback is needed when the equipment runs efficiently; 2. Outloop: When arriving at the line board after passing the input port in the local NE, the input signal is directly looped back to the service output end; 3. Inloop: The output signal is directly returned after passing the line board.

VC4 Server Trail

The path rate of the VC4 server trail is 150. 336Mbit/s. The VC4 server trail provides transparent channels (i. e. circuit group) for circuit-layer network nodes (e. g. a switch) in a path-layer network, and acts as the basic unit of inter-office communication path. The VC4 server trail is the basis of the VC3 and VC12 trails. When the VC4 server trail is configured, only the higher order cross-connection of VC4 is generated in the intermediate NE, but no cross-connection is generated at the two ends, that is, no service is added/dropped. Therefore, the VC4 server trail is not a traditional service. It is only the basis for VC3 and VC12 trail creation. The created VC4 is a point-to-point service trail, only the source/sink NE can be specified instead of the source/sink port.

VCC

The VCC is short for Virtual Channel Connection.

VCI

The VCI, shorted for Virtual Channel Identifier, occupies 16 bits in both NNI cell or UNI cell. It indicates the virtual channel in the path. The VPI and VCI together indicate a virtual connection.

Virtual concatenation

It is the payload whose transmission bandwidth is bigger than VC4. It combines multiple VC4 payloads (successive or non-successive) to form a virtual large structure VC4-Xv in cascade mode for transmission. The transmission of the broadband cascaded payload is implemented via the virtual cascade, thus improving the SDH transmission payload bandwidth capability from VC4 to VC4-4C. In virtual cascade mode, it is only necessary to add the terminal equipment (SV4 board of the OptiX 2500+, for example) with virtual cascade function at both ends and the network is little affected. The SV4 board of the OptiX 2500+ supports the virtual cascade of four VC4 payloads (adjacent or non-adjacent) of the same optical port.

Virtual NE

Like a common NE, a virtual NE is also displayed with an icon on a view, but it is only an NE simulated according to the practical situation, which does not represents an actual NE. Therefore, the actual status of this NE cannot be queried and its alarm status cannot be displayed with colors. Usually, when the trail management function is used for the NEs or sub-networks the U2000 Web LCT cannot manage, or the equipment is interconnected with other vendors NEs for service configuration, the end-to-end service configuration method and the trail management capability are provided.

VLAN ID

Namely, it is the virtual LAN identifier. One Ethernet port can support 4K VLAN routes, and one NE can support up to 8K VLAN routes.

VPC

The VPC is shorted for Virtual Path Connection.

VPI

The VPI, shorted for Virtual Path Identifier, occupies 12 bits in the NNI cell, and 8 bits in the UNI cell.