Cisco ONS 15327 User Documentation page 539

Glossary
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 15327 User Documentation, R3.3
GL-15
June 2002