Cisco 10000 Series Configuration Manual page 828

Glossary
Logical circuit created to ensure reliable communication between two network devices. A virtual
virtual circuit
circuit is defined by a VPI/VCI pair, and can be either permanent (PVC) or switched (SVC). Virtual
circuits are used in Frame Relay and X.25. In ATM, a virtual circuit is called a virtual channel.
Sometimes abbreviated VC.
A group of devices on one or more local area networks (LANs) that are configured (using management
virtual LAN
software) so that they can communicate as if they were attached to the same wire, when in fact they are
located on a number of different LAN segments. Because virtual LANs (VLANs) are based on logical
instead of physical connections, they are extremely flexible.
One of two types of ATM circuits identified by a VPI. A virtual path is a bundle of virtual channels,
virtual path
all of which are switched transparently across an ATM network based on a common VPI.
An 8-bit field in the header of an ATM cell. The VPI, together with the VCI, is used to identify the next
virtual path
destination of a cell as it passes through a series of ATM switches on its way to its destination. ATM
identifier
switches use the VPI/VCI fields to identify the next VCL that a cell needs to transmit on its way to its
final destination. The function of the VPI is similar to that of the DLCI in Frame Relay.
A logical interface configured with generic configuration information for a specific purpose or
virtual template
interface configuration common to specific users, plus router-dependent information. The template takes the
form of a list of Cisco IOS interface commands that are applied to virtual access interfaces, as needed.
See virtual LAN.
VLAN
See virtual path identifier.
VPI
W
See wide area network.
WAN
Congestion management algorithm that identifies conversations (in the form of traffic streams),
weighted fair
separates packets that belong to each conversation, and ensures that capacity is shared fairly between
queuing
these individual conversations. WFQ is an automatic way of stabilizing network behavior during
congestion and results in increased performance and reduced retransmission.
A mechanism for avoiding congestion of Layer 3 queues. Weighted random early detection (WRED)
weighted random
combines the capabilities of the random early detection (RED) mechanism with IP precedence,
early detection
differential services code point (DSCP), and discard-class to provide preferential handling of higher
priority packets. WRED attempts to anticipate and avoid congestion. WRED implements a proactive
queuing strategy that manages congestion before a queue reaches its queue depth. By selectively
dropping packets, WRED prevents packets from enqueuing to the Layer 3 queue.
See weighted fair queuing.
WFQ
A data communications network that spans any distance and is usually provided by a public carrier
wide area network
(such as a telephone company or service provider).
See Weighted Random Early Detection.
WRED
X
Cisco 10000 Series Router Quality of Service Configuration Guide
GL-10
OL-7433-09