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176 Glossary

Enterprise Edge Networking Operations Guide P0910464 Issue 01

UDP The User Datagram Protocol (UDP) is a protocol that offers a limited

amount of service when messages are exchanged between computers

in a network that uses IP. UDP is an alternative to the Transmission

Control Protocol (TCP) and, together with IP, is sometimes referred

to as UDP/IP.

Like the Transmission Control Protocol, UDP uses IP to actually

transfer a data unit (called a datagram) from one computer to another.

Unlike TCP, however, UDP does not provide the service of dividing a

message into packets (datagrams) and reassembling it at the other end.

Specifically, UDP doesn't provide sequencing of the packets that the

data arrives in. This means that the application program that uses

UDP must be able to make sure that the entire message has arrived

and is in the right order.

Network applications that want to save processing time because they

have very small data units to exchange (and therefore very little

message reassembling to do) may prefer UDP to TCP. The Trivial

File Transfer Protocol (TFTP) uses UDP instead of TCP.

VoIP Voice over IP (VoIP) is the capability to deliver voice using the

Internet Protocol. VoIP is a set of facilities for managing the delivery

of voice information using the IP. In general, this means sending

voice information in digital form in discrete packets rather than in the

traditional circuit-committed protocols of the public switched

telephone network (PSTN). A major advantage of VoIP and Internet

telephony is that it avoids the tolls charged by ordinary telephone

service.

In addition to IP, VoIP uses the real-time protocol (RTP) to help

ensure that packets get delivered in a timely way. Using public

networks, it is difficult to guarantee Quality of Service (QoS).

Using VoIP, an enterprise positions a VoIP device at a gateway. The

gateway receives packetized voice transmissions from users within

the company and then routes them to other parts of its intranet (local

area or wide area network) or, using a T-1 or E-1 interface, sends

them over the public switched telephone network.

WAN A wide area network (WAN) is a geographically dispersed

telecommunications network and the term distinguishes a broader

telecommunication structure from a local area network (LAN). A

wide area network may be privately owned or rented, but the term

usually connotes the inclusion of public (shared user) networks.

Web cache A web cache is a server or collection of servers that store copies of

Internet content. The web cache server can be either located on the

LAN where the clients it serves are also located, or it can be

embedded within the enterprise WAN or at the client’s Internet

Service Provider (ISP).

Web proxy (or HTTP

proxy)

A web proxy is a server that acts on behalf of the requester of pages

from an HTTP server and the Internet.

WFQ Weighted Fair Queuing (WFQ) is a queuing method that allows low

volume traffic such as Telnet to be given priority and interactive

traffic receives higher priority than batch transfers. Also, high

bandwidth usage traffic such as batch file transfer traffic gets equal

priority with other high bandwidth use traffic.

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