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Glossary
U
unspecified bit rate. A QoS class defined by the ATM Forum for ATM networks. UBR allows any
UBR
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.
User Datagram Protocol. A connectionless transport protocol that runs on top of the TCP/IP. UDP, like
UDP
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.
Underwriters Laboratories. A private organization that tests and certifies electrical components and
UL
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.
See UL.
Underwriters
Laboratories
User-Network Interface.
UNI
User-Network Interface signaling for ATM communications.
UNI signaling
Message sent to a single network destination. Compare with broadcast and multicast.
unicast
Four-pair wire medium used in a variety of networks. Sometimes referred to as UTP. See also shielded
unshielded twisted
pair
twisted pair and twisted pair.
See UBR.
unspecified bit rate
Data that is coming from the subscriber lines to the NI-2 card. See also downstream.
upstream
See UNI.
User-Network
Interface
See UDP.
User Datagram
Protocol
V
See VBR.
variable bit rate
variable bit rate. A QoS defined by the ATM Forum for ATM networks. VBR is subdivided into a real
VBR
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.
virtual channel connection. A logical circuit, made up of links, that carries data between two endpoints
VCC
in an ATM network. It is sometimes called a virtual circuit connection. See also VCI and VPI.
Cisco 6260 Hardware Installation Guide
GL-28
OL-2365-02
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