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Unspecified Bit Rate is an ATM service category that does not appropriate fixed bandwidth or guarantee throughput and is best used for non-time-critical applications, such as e-mail.



UCD (Uplink Channel Description) is a WiMAX medium access control layer (MAC) message which describes the physical layer (PHY) characteristics of a uplink (UL) channel.



UDLD (UniDirectional Link Detection) is used to determine the link’s physical status and detect a unidirectional link.


UDP (User Datagram Protocol)

UDP is a connectionless transport service that dispenses with the reliability services provided by TCP. UDP gives applications a direct interface with the Internet Protocol (IP) and the ability to address a particular application process running on a host via a port number without setting up a connection session. A network protocol for transmitting data that does not require acknowledgement from the recipient of the data that is sent.



User IDentification is equivalent to your user name. Usually a password is associated with a UID or user name.



The UMTS (Universal Mobile Telecommunications System) is one of the third generation (3G) wireless standards, which is based on GSM. WCDMA (Wide Band Code Division Multiple Access) is the radio technology used in UMTS. Therefore, the terms “UMTS” and “WCDMA” are often used interchangeably. UMTS can allow data rates of up to 14 Mbps when using HSDPA (High Speed Downlink Packet Access), a mobile telephony protocol.



User Network Interface defines the connection between user equipment and the Frame Relay network, for instance, if your device is connected to a service provider.



A widely-used operating system in large networks. Usually used on workstations and servers.


Unknown packets

An unknown packet is a packet with a destination MAC address that the device has not yet learned (is not in its routing table).


Unlocked Volume

Unlock a locked encrypted volume to allow users to access its shares.


Untrusted ports

In IP source guard, there are two sets of untrusted ports, one for DHCP snooping and one for ARP inspection. For DHCP snooping, untrusted ports are connected to subscribers, so the system discards DHCP packets from untrusted ports. For ARP inspection, ARP packets from untrusted ports are discarded if the sender’s information in the ARP packet does not match any bindings.



In a network with varying telephone wiring lengths, the PSD (Power Spectral Density) on each line is different. This causes crosstalk between the lines. Enabling UPBO (Upstream Power Back Off) allows a device to adjust the transmit PSD of all lines based on a reference line length. This mitigates the upstream crosstalk between shorter loops and longer loops. It allows a CO device to provide better service in a network environment with telephone wiring of varying lengths. See also PSD.


UPBO/DPBO Electrical Length

In VDSL2, the electrical length is used for a reference of UPBO/DPBO calculation instead of the real physical distance according to G.997.1 format. Depending on the cable type the line used and physical line length, you can calculate the electrical length (in dB). For example, the distance is 1 kilometer and you use 24 AWG cable type, the electrical length 20.5 dB is suggested to be used.



To replace existing software or firmware with a newer version.


Uplink Port

This port connects to an external switching hub, router or server.



To transmit a file over a network.



Universal Plug and Play (UPnP) is a standard that allows devices to connect seamlessly to each other. A UPnP-enabled device can dynamically join a network, obtain an IP address, and learn about other devices on the network.



An UPS is a battery backup that maintains a continuous supply of electric power to connected equipment when the mains power system is not available.


Upstream Bandwidth Utilization

In load balancing, upstream (outgoing) bandwidth utilization is the measured upstream throughput as a ratio of the available upstream bandwidth.


Upstream Broadcast Control

A DSLAMs upstream broadcast control sets a bandwidth limit for upstream broadcast traffic allowed from a VDSL subscriber line. This helps reduce the incoming broadcast packets and the DSLAM!|s load.


URL (Uniform Resource Locator)

URL is an object on the Internet or an intranet that resides on a host system. Objects include directories and an assortment of file types, including text files, graphics, video and audio. A URL is the address of an object that is normally typed in the Address field of a Web browser. A URL is basically a pointer to the location of an object. The address of a file located on the Internet.


(Universal Serial Bus) A plug-and-play interface between a computer and peripheral devices (scanners, printers etc).



When creating an encrypted volume, the device can create a password and store it on a connected USB device. This is a USB key. If the volume later becomes locked, you must insert the USB key to unlock the volume.


User-aware access control

User-aware access control uses security policies that restrict access to shared resources based on the user who is trying to access it. Users must log in to use the shared resources. For example, you could allow only specific users to use MSN or the printers.



UTC is a standard time for use around the world (formerly known as Greenwich Mean Time or GMT). UTC is an international abbreviation that is neither French nor English. It means both “Temps Universel Coordonné” and “Coordinated Universal Time”.



A UTM (Unified Threat Management) appliance integrates firewall, content filtering, spam filtering, intrusion detection and anti virus functions into a single network appliance.