Polycom MGC Administrator Administrator's Manual page 582

Appendix E: IP Network Components
E-8
although it is not required; support of SDP (Session Description Protocol) for
media description is. A SIP User Agent contains both a client application
(User Agent client, UAC) and a server application (User Agent server, UAS).
UACs originate requests and UASs originate responses to requests.
SIP Server
H.323
N/A
A SIP server is a server that provides routing functionality; it is an
intermediary that receives SIP messages and forwards them. Most SIP servers
support both TCP and UDP since they provide services to User Agents that
can use either type of protocol. The SIP server includes a registrar with a
proxy server or a registrar with a redirect server. Currently, the MGC MCU
supports only a registrar with a proxy server. These logical entities are usually
located on the same server.
SIP servers fulfills three main functions:
Proxy services—Deliver packets to their correct destinations. Each
•
network has a proxy(ies) that is an administration entity for the
incoming/outgoing traffic.
• Registration—List the aliases of SIP entities with their associated IP
addresses.
Presence—Some proxies provide presence tracking of registered aliases/
•
participants. Similar to 'Buddy lists' from instant messaging
applications, this feature allows checking of whether the invited aliases
are online and available, or not.
SIP Proxy
H.323
N/A
The SIP proxy server is a logical entity that is part of the SIP server. The SIP
proxy facilitates endpoints locating and contacting each other, but it can drop
out of the signaling path as soon as it no longer adds any value to the
exchange. It transfers only signaling messages while the media messages are
SIP
Optional
(Recommended)
SIP
Optional
(Recommended)