Specifications

Glossary
GL-13
Cisco ONS 15454 Installation and Operations Guide, R3.2
March 2002
UPSR
Unidirectional Path Switched Ring. Path-switched SONET rings that employ redundant, fiber- optic transmission facilities in
a pair configuration. One fiber transmits in one direction and the backup fiber transmits in the other. If the primary ring fails,
the backup takes over.
Upstream
Set of frequencies used to send data from a subscriber to the headend.
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.