Glossary
GL-28
Cisco 6260 Hardware Installation Guide
OL-2365-02
U
UBR
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 no guarantees
in terms of cell loss rate and delay. Compare with
ABR
,
CBR
, and
VBR
.
UDP
User Datagram Protocol. A connectionless transport protocol that runs on top of the TCP/IP. UDP, like
TCP, uses IP for delivery; however, unlike TCP, UDP provides for exchange of datagrams without
acknowledgments or guaranteed delivery. This protocol is the best suited for small, independent
requests, such as requesting a MIB value from an SNMP agent, in which setting up a connection would
take more time than sending the data.
UL
Underwriters Laboratories. A private organization that tests and certifies electrical components and
devices against rigorous safety standards. A UL Listing Mark on a product means that representative
samples of the product have been tested and evaluated against nationally recognized safety standards
with regard to fire, electric shock, and other related safety hazards, and have met the standards.
Underwriters
Laboratories
See
UL
.
UNI
User-Network Interface.
UNI signaling
User-Network Interface signaling for ATM communications.
unicast
Message sent to a single network destination. Compare with
broadcast
and
multicast
.
unshielded twisted
pair
Four-pair wire medium used in a variety of networks. Sometimes referred to as UTP. See also
shielded
twisted pair
and
twisted pair
.
unspecified bit rate
See
UBR
.
upstream
Data that is coming from the subscriber lines to the NI-2 card. See also downstream.
User-Network
Interface
See
UNI
.
User Datagram
Protocol
See
UDP
.
V
variable bit rate
See
VBR
.
VBR
variable bit rate. A QoS defined by the ATM Forum for ATM networks. VBR is subdivided into a real
time (rt) class and non-real time (nrt) class. VBR-rt is used for connections in which there is a fixed
timing relationship between samples. VBR-nrt is used for connections in which there is no fixed
timing relationship between samples but that still need a guaranteed QoS. Compare with
ABR
,
CBR
,
and
UBR
.
VCC
virtual channel connection. A logical circuit, made up of links, that carries data between two endpoints
in an ATM network. It is sometimes called a virtual circuit connection. See also
VCI
and
VPI
.