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EN/LZT 108 6377 R4 - September 2003
97
- U -
UBR
Sort for Unspecified Bit Rate. A type of ATM service that does not
guarantee any throughput levels. This is used for applications, such as file
transfers, that can tolerate delays.
UDP
Short for User Datagram Protocol, which is a connectionless transport
service that dispenses with the reliability services provided by TCP. UDP
gives applications a direct interface with IP and the ability to address a
particular application process running on a host via a port number, without
setting up a connection session.
UPnP
Short for Universal Plug and Play, a networking architecture that provides
compatibility among networking equipment, software and peripherals of the
400+ vendors that are part of the Universal Plug and Play Forum. UPnP
works with wired or wireless networks and can be supported on any
operating system. UPnP boasts device-driver independence and zero-
configuration networking.
Upstream
The direction of an upstream signal is from the user's computer to the
ISP/service provider (uploading).
USB
Short for Universal Serial Bus, an external bus standard that supports data
transfer rates of 12 Mbps. A USB port can be used to connect peripheral
devices, such as mice, modems, and keyboards. USB also supports Plug-
and-Play installation and hot plugging.
- V -
VBR
Short for Variable Bit Rate. A type of ATM service that provides a specified
throughput capacity but is not sent evenly. This is a popular choice for
voice and videoconferencing data.
Virtual Server
A server, usually a Web server, that shares computer resources with other
virtual servers. In this context, the virtual part simply means that it is not a
dedicated server -- that is, the entire computer is not dedicated to running
the server software. Virtual Web servers are a very popular way of
providing low-cost web hosting services. Instead of requiring a separate
computer for each server, dozens of virtual servers can co-reside on the
same computer. In most cases, performance is not affected and each web
site behaves as if it is being served by a dedicated server. However, if too