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Glossary
GL-10
Cisco IP Phone Models 7905G and 7912G Administrator Guide (SIP)
OL-4277-01
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TFTP
Trivial File Transfer Protocol. Simplified version of FTP that allows files to be
transferred from one computer to another over a network, usually without the
use of client authentication (for example, username and password).
ToS
Type of service. See CoS.
U
UAC
User agent client. A client application that initiates the SIP request.
UAS
User agent server (or user agent). A server application that contacts the user
when a SIP request is received, and then returns a response on behalf of the user.
The response accepts, rejects, or redirects the request.
UDP
User Datagram Protocol. Connectionless transport layer protocol in the TCP/IP
protocol stack. UDP is a simple protocol that exchanges datagrams without
acknowledgments or guaranteed delivery, requiring that error processing and
retransmission be handled by other protocols. UDP is defined in RFC 768.
u-law
See mu-law.
V
VAD
Voice activity detection. When enabled on a voice port or a dial peer, silence is
not transmitted over the network, only audible speech. When VAD is enabled,
the sound quality is slightly degraded but the connection monopolizes much less
bandwidth.
VoIP
Voice over IP. The capability to carry normal telephony-style voice over an
IP-based Internet with POTS-like functionality, reliability, and voice quality.
VoIP enables a router to carry voice traffic (for example, telephone calls and
faxes) over an IP network. In VoIP, the DSP segments the voice signal into
frames, which then are coupled in groups of two and stored in voice packets.
VoIP is a blanket term, which generally refers to Cisco’s standard-based
approach to IP voice traffic.