The problem likes in enforcing a one-one association between a physical
entity and a logic role.
Proxy, Redirect, B2BUA are all logical roles - that means that it is very
possible that one "physical" entity
could behave like any of the logical roles at any point of time.
Here is an example: Lets suppose your company implements a "Feature server"
(for want of a better term)
which acts as a centralized node for routing, address resolution and
supplementary services for your network.
Now lets suppose you have two users who want to talk to make a call to each
other through this server.
He would then send an INVITE to this server, which would lookup the address
of the destination and send this request to the
other end. In this case, you are using your server to just "lookup and
route" a call. So for this transaction, your server takes
the role of a "Proxy Server".
Now lets suppose user joe wants to set up a web-chat with users moe and
boe. Your server has this facility as a "feature"
, but due to some policy, your server reserves the right to terminate this
session (maybe payment expiry). In this case, your server
needs to be able to originate sip messages and control both signalling
paths - so it will behave as a B2BUA for this call/transaction.
Or, maybe, depending on load, a server may choose to start redirecting
calls rather that stateful proxying it.
So basically, how your "server" behaves really depends on what you want to
do. If you want to implement a service which
needs centralised control, you select which logical role best suits it. How
your server selects one of these modes can vary depending on
1. type of message
2. Administration policies (eg stateless proxy for some subscribes,
stateful proxy for others)
3. Load confitions
4. others ?
I agree with a mail that I recently read where Bill wrote that in
commercial deployment it is very unlikely that only a pure proxy
will exist - it is very likely that the SIP server would be a combination
of one or more Proxy/Location/B2BUA/Registrar logical roles.
Regds
Arjun
--
Arjun Roychowdhury @ Hughes Software Systems
"Ford Cheng (Leela)" <[EMAIL PROTECTED]> on 01/31/2001 11:19:39 AM
To: [EMAIL PROTECTED]
cc:
Subject: [Sip-implementors] Discuss on the SIP Proxy and UA!!
Dear All:
I have one question to discuss, for example,
in practical network implementation, it is hard to
identify the role of UA and Proxy, for example,
when a SIP protocol stack receives a request message,
t this message is decided by upper layer that it
is used for interworking with PSTN, then the role
of this protocol stack is UA, otherwise, if this
mesage is to be forwarded , then this protocol stack's
role is Proxy.
According to the current RFC2543bis02, for example,
when stateful Proxy receives a BYE request, even if it knows
that this BYE request is invalid, it can not send final response,
then this will cause a problem, how can the implementator to
judge the role of protocol of protocol stack to be a UA or proxy?
Then if it is configured as UA, but this time, the role is proxy?
What should we do?
In implementation, SIP network has to work together with other
network, such as PSTN.
Could any one give me some suggestion and ideas? any suggestions
and ideas are welcome!
Best Regards!
Yours: Ford
Title: Discuss on the SIP Proxy and UA!!
Dear All:
I have one question to discuss, for example,
in practical network implementation, it is hard to
identify the role of UA and Proxy, for example,
when a SIP protocol stack receives a request message,
t this message is decided by upper layer that it
is used for interworking with PSTN, then the role
of this protocol stack is UA, otherwise, if this
mesage is to be forwarded , then this protocol stack's
role is Proxy.
According to the current RFC2543bis02, for example,
when stateful Proxy receives a BYE request, even if it knows
that this BYE request is invalid, it can not send final response,
then this will cause a problem, how can the implementator to
judge the role of protocol of protocol stack to be a UA or proxy?
Then if it is configured as UA, but this time, the role is proxy?
What should we do?
In implementation, SIP network has to work together with other
network, such as PSTN.
Could any one give me some suggestion and ideas? any suggestions
and ideas are welcome!
Best Regards!
Yours: Ford
