hello,
I'm just beginning to attempt a SIP implementation but I'm struggling to
understand some key concepts...
We're going to be deploying SIP in the following general system
configuration:-
EP11---EP12---EP13---Proxy1---+
+
+
EP21---EP22---EP23---Proxy2---+----Registrar/Proxy
+
+
EP31---EP32---EP33---Proxy3---+
Each "leaf segment" of the network is intended to have its own SIP proxy
which will act as an "Outbound Proxy" for each of that segment's
endpoints (usually SIP Phones)
Q1. Am I correct in thinking that (conventionally) each endpoint will be
configurable for BOTH 1) a Registrar, and 2) an Outbound Proxy ?
In the absence of DNS, it is intended to use the sip:IPv4 URI addressing
scheme in messages.
None of the leaf segments' endpoints will be aware of the specific IP
address of the Registrar in advance and it is intended to facilitate
their finding the Registrar through the Proxies, which will have the IP
address of the Registrar made known to them through a separate (non-SIP)
procedure.
Q2. How will the Request-URIs be constructed for outgoing REGISTER
requests from an endpoint?
That is, the RFC says the REGISTER Request-URI should simply be the
"domain of the location service", but in the absence of DNS, what?
Will it just be the IP address of the Outbound Proxy (if each endpoint
is configured with the IP address of its Proxy AS ITS REGISTRAR
ADDRESS)?
If so, can each Proxy then just substitute the REAL IP address of the
Registrar in forwarding the request?
e.g., from EP11 (192.168.1.2) to Proxy1 (192.168.1.1)
REGISTER sip:192.168.1.1 SIP/2.0
To: <sip:[EMAIL PROTECTED]>
From: <sip:[EMAIL PROTECTED]>
Contact: <sip:[EMAIL PROTECTED]>
Via: SIP/2.0/UDP 192.168.1.2:5060
---
then, from Proxy1 (192.168.1.1) to Registrar (192.168.100.1)
REGISTER sip:192.168.100.1 SIP/2.0
To: <sip:[EMAIL PROTECTED]>
From: <sip:[EMAIL PROTECTED]>
Contact: <sip:[EMAIL PROTECTED]>
Via: SIP/2.0/UDP 192.168.1.1:5060
Via: SIP/2.0/UDP 192.168.1.2:5060
Q3. Generally, will all Request-URIs originating from an endpoint
a) automatically go first to the Outbound Proxy?, and
b) by necessity contain the IP address of the Outbound Proxy?
Q4. If the registered AoRs for each of these endpoints will be in IPv4
notation, will any other endpoint that wants to call (INVITE) one have
to use the full IP address of the intended destination in order to
initiate the call? This would not be at all flexible!
If not, what would the SIP INVITE look like for, e.g. EP11 calling EP21?
Q5. (Depending on the answer to Q4) Can the Proxies somehow manipulate
the endpoints' registrations so that the "To:" AoRs all refer to the
Registrar's common IP address (for example) (but the Contact fields
would refer to their ACTUAL IP addrs)? - in this way, ANY OTHER endpoint
could simply attempt to call another because only the username would be
significant (all AoRs in the Location Service would be
[EMAIL PROTECTED]) and each proxy could normalize all INVITE requests
to refer to the Registrar's IP address
e.g., from EP11 (192.168.1.2) to Proxy1 (192.168.1.1)
REGISTER sip:192.168.1.1 SIP/2.0
To: <sip:[EMAIL PROTECTED]>
From: <sip:[EMAIL PROTECTED]>
Contact: <sip:[EMAIL PROTECTED]>
Via: SIP/2.0/UDP 192.168.1.2:5060
---
then, from Proxy1 (192.168.1.1) to Registrar (192.168.100.1)
REGISTER sip:192.168.100.1 SIP/2.0
To: <sip:[EMAIL PROTECTED]>
From: <sip:[EMAIL PROTECTED]>
Contact: <sip:[EMAIL PROTECTED]>
Via: SIP/2.0/UDP 192.168.1.1:5060
Via: SIP/2.0/UDP 192.168.1.2:5060
Q6. Perhaps it would help if I knew how a SIP phone would populate the
"To:" field of an outgoing INVITE request having just dialed a number -
can anybody enlighten me on this? Does it generate a
"sip:[EMAIL PROTECTED]" URI, or does it generate "tel:1234567" and pass
that along to the Outbound Proxy and expect that to resolve it to a
SIP-URI before forwarding? Is there a "standard" behaviour?
Thanks in advance to anybody who can (begin to) help clear up my
confusion on these issues.
Mark.
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