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Glossary
GL-5
Cisco ATA 187 Analog Telephone Adaptor Administration Guide for SIP (Version 1.0)
OL-21862-01
Proxy Server
An intermediary program that acts as both a server and a client for the purpose of making requests on
behalf of other clients. Requests are serviced internally or by passing them on, possibly after
translation, to other servers. A proxy interprets, and, if necessary, rewrites a request message before
forwarding it.
PSTN
Public switched phone network
Q
QoS
Quality of Service. The capability of a network to provide better service to selected network traffic
over various technologies, including Frame Relay, Asynchronous Transfer Mode (ATM), Ethernet and
802.1 networks, SONET, and IP-routed networks that may use any or all of these underlying
technologies. The primary goal of QoS is to provide priority including dedicated bandwidth,
controlled jitter and latency (required by some real-time and interactive traffic), and improved loss
characteristics.
R
Redirect Server
A redirect server is a server that accepts a SIP request, maps the address into zero or more new
addresses, and returns these addresses to the client. It does not initiate its own SIP request nor accept
calls.
Registrar Server
A registrar server is a server that accepts Register requests. A registrar is typically co-located with a
proxy or redirect server and may offer location services.
router
Network layer device that uses one or more metrics to determine the optimal path along which
network traffic should be forwarded. Routers forward packets from one network to another based on
network layer information. Occasionally called a gateway (although this definition of gateway is
becoming increasingly outdated). Compare with gateway.
RTP
Real-Time Transport Protocol. One of the IPv6 protocols. RTP is designed to provide end-to-end
network transport functions for applications transmitting real-time data, such as audio, video, or
simulation data, over multicast or unicast network services. RTP provides services such as payload
type identification, sequence numbering, timestamping, and delivery monitoring to real-time
applications.
S
SDP
Session Definition Protocol. An IETF protocol for the definition of Multimedia Services. SDP
messages can be part of SGCP and MGCP messages.
SIP
Session Initiation Protocol. Protocol developed by the IETF MMUSIC Working Group as an
alternative to H.323. SIP features are compliant with IETF RFC 2543, published in March 1999. SIP
equips platforms to signal the setup of voice and multimedia calls over IP networks.
SIP endpoint
A terminal or gateway that acts as a source or sink of Session Initiation Protocol (SIP) voice data. An
endpoint can call or be called, and it generates or terminates the information stream.