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Appendix D
Glossary
V
Virtual fiber
A fiber that carries signals at different rates and uses the same fiber optic cable.
Virtual ring
Entity in a source-route bridging (SRB) network that logically connects two or more physical rings
together either locally or remotely. The concept of virtual rings can be expanded across router
boundaries.
Virtual wires
Virtual wires route external alarms to one or more alarm collection centers across the SONET transport
network.
VLAN
Virtual LAN. Group of devices located on a number of different LAN segments that are configured
(using management software) to communicate as if they were attached to the same wire. Because
VLANs are based on logical instead of physical connections, they are extremely flexible.
VPN
Virtual Private Network. Enables IP traffic to travel securely over a public TCP/IP network by
encrypting all traffic from one network to another. A VPN uses "tunneling" to encrypt all information
at the IP level. (See also Tunneling.)
VT
Virtual Tributary. A structure designed for the transport and switching of sub-DS3 payloads.
VT layer
The VT layer or electrical layer occurs when the SONET signal is broken down into an electrical signal.
Cisco ONS 15454 Installation and Operations Guide
D-14
November 2001
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