First of all, DO NOT send any message to both the sip and sip-implementors
lists. As it says at the bottom of every message on the sip list.
sip-implementor's is for current sip issues, the sip list is for
new developments in sip. You NEVER send to both.
Now, to your questions:
> 1) What role does User Agent plays ? Is it necessary that
> only through User
> Agent we can contact the SIP Server ? if yes then how does
> the ordinary
> Telephone, which everyone at their residences use can get connected ?
The user agent represents the endpoints of the SIP calls. Just because they
are the endpoints of the SIP part doesn't mean they are the things with the
microphones and speakers that you use. They could be, in which case the
user agent is in a sipphone, of which there are several available in the
marketplace. Another possibility is that there is some kind of a gateway
that connects an older technology analog (or maybe digital) phone to a sip
system. In this case, the user agent is in the gateway. When carriers
start offering residential services with sip signalling, many residences
will need gateways that have POTS ports on one side, and network ports on
the other. Alternatively, and probably ultimately, all phones will be sip
phones :)
Yes, sip servers (of which there are several kinds) are only contacted by
user agents. It is not strictly necessary to even have a sip server; a use
agent can directly contact another user agent without any servers.
>
> 2) Can a ordinary Telephone, which everyone at their
> residences have can
> contact SIP Server ? and from there interact with other SIP USERS ?
See above. An "ordinary" phone (POTS phone) would connect to a gateway,
which would have the user agent in it. The user agent would contact another
user agent, or more likely, a sip server, to connect calls.
>
> 3) When I transmit Voice over SIP which use TCP/IP, what role
> does SIP play
> at that time ?
SIP Is the signalling protocol to establish the media session(s). SIP
requires a transport protocol to transport sip messages between sip
entities. That protocol may be IP/TCP, but is more commonly IP/UDP.
The media flow is commonly IP/UDP/RTP, but there are other possibilities
such as Frame Relay or ATM. Generally, there is a sip transaction to
create the session (INVITE/ACK) and another to tear down the connection
(BYE/ACK). When the session is up, there are often no SIP messages
exchanged, although there could be (INFO). The media streams flow directly
between the user agents, using RTP for example. The servers
are not in the path of the media, an important sip concept.
>
_______________________________________________
Sip-implementors mailing list
[EMAIL PROTECTED]
http://lists.cs.columbia.edu/mailman/listinfo/sip-implementors
