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Glossary
GL-9
Cisco 10000 Series Router Quality of Service Configuration Guide
OL-7433-09
U
UBR
See unspecified bit rate.
unspecified bit rate
A QoS class defined by the ATM Forum for ATM networks. UBR allows any amount of data up to a
specified maximum to be sent across the network, but there are not guarantees in terms of cell loss rate
and delay.
upstream rate
The line rate for message or data transfer from the source machine to a destination machine on the
network.
V
VAI
See virtual access interface.
VBR
See variable bit rate.
VBR-nrt
See variable bit rate-nonreal time.
VBR-rt
See variable bit rate-real time.
VC
See virtual circuit.
VCI
See virtual channel identifier.
VCL
See virtual channel link.
variable bit rate
A QoS class defined by the ATM Forum for ATM networks. Variable bit rate (VBR) is subdivided into
a real time (rt) class and nonreal time (nrt) class. See also variable bit rate-nonreal time and variable
bit rate-real time.
variable bit
rate-nonreal time
A QoS class defined by the ATM Forum for ATM networks. Variable bit rate-nonreal time (VBR-nrt)
is used for connections in which there is no fixed timing relationship between samples, but that still
need a guaranteed QoS.
variable bit rate-real
time
A QoS class defined by the ATM Forum for ATM networks. Variable bit rate-real time (VBR-rt) is used
for connections in which there is a fixed timing relationship between samples.
virtual access
interface
An instance of a unique virtual interface that is created dynamically and exists temporarily. Virtual
access interfaces can be created and configured differently by different applications, such as virtual
profiles and virtual private dialup networks (VPDNs).Virtual access interfaces are cloned from virtual
template interfaces.
virtual channel
identifier
A 16-bit field in the header of an ATM cell. The virtual channel identifier (VCI), together with the VPI,
is used to identify the next destination of a cell as it passes through a series of ATM switches on its way
to its destination. ATM switches use the VPI/VCI fields to identify the next network VCL that a cell
needs to transmit on its way to its final destination. The function of the VCI is similar to that of the
DLCI in Frame Relay.
virtual channel link
Connection between two ATM devices. A virtual channel connection is made up of one or more VCLs.