User Datagram Protocol. In TCP/IP, a connectionless transport layer protocol that exchanges datagrams without acknowledgments or guaranteed delivery, requiring that error processing and retransmission be handled by other protocols.

U interface

User reference point interface. A single-pair connection between the local ISDN provider and the customer premises equipment.


UNI management entity. The code residing in the ATM devices at each end of a UNI (user-to-network interface) circuit that functions as an SNMP agent, maintaining network and connection information specified in an ILMI MIB.


Universal mobile telecommunications system. Provides third-generation (3G), packet-based transmission of text, digitized voice, video, and multimedia, at data rates up to 2 Mbps.

UMTS Terrestrial Radio Access Network



User-to-network interface. ATM Forum specification that defines an interoperability standard for the interface between a router or an ATM switch located in a private network and the ATM switches located within the public carrier networks. Also used to describe similar connections in Frame Relay networks.


Operation of sending network traffic from one network node to another individual network node.

UNI management entity

See UME.

uninterruptible power supply

See UPS.


JUNOS software syntax that represents the logical properties of an interface.

universal mobile telecommunications system


Update message

BGP message that advertises path attributes and routing knowledge to an established neighbor.

update timer

Used in a distance-vector protocol to advertise routes to a neighbor on a regular basis.


Uninterruptible power supply. A device that sits between a power supply and a router (or other piece of equipment) and prevents power-source events, such as outages and surges, from affecting or damaging the device.


JUNOS software routing policy match type representing all routes that share the same most-significant bits and whose prefix length is smaller than the supplied subnet in the route filter.

User Datagram Protocol

See UDP.


The mean solar time at the Royal Greenwich Observatory in Greenwich near London, England. On January 1, 1972, GMT was replaced as the international time reference by Coordinated Universal Time (UTC), maintained by an ensemble of atomic clocks around the world.


UMTS Terrestrial Radio Access Network. The WCDMA radio network in UMTS.