Subject: [Sipping] Questions on connect-reuse

From: Christer Holmberg <[email-masked]>
Date: Tue, 25 Mar 2003 12:14:56 +0200

Hi,

I have some intial questions on the connect-reuse stuff:

Q1.

Why is the reason the "alias" parameter is put in the Via header? Isn't
the Via used for response routing only? Wouldn't it fit better as a
header (or URI) parameter used in the Contact- and Record-Route headers
instead?

UA A                             PROXY
B                                 UA C

   4444 -------------> 5060          5555 --------------> 5060

Now, when UA A sends the INVITE, it will look like:

INVITE
Contact: sip:[email-masked]:5060;alias

Then, proxy B inserts a Record-Route, so the message will look like:

INVITE
Contact: sip:[email-masked]:5060;alias
Record-Route: sip:[email-masked]:5060;alias

Q2:

Assume I make a SRV lookup, and I get a list with different server
addresses.

Now, for one of the returned addresses I have an existing TCP connection
which I could use. But, I also receive another address, which has higher
priority. So, which has higher priority: an existing connection, or the
priority identifier in the SRV response? One may argue this is an
implementation/local policy/whatever issue, but I think it would be a
good idea to mention it in the textt.

Q3:

Assume I send an INVITE to an emphemeral port (the TCP connection was
established by the remote party), and I receive one or more provisional
responses, or a non-2xx responses. Then, the TCP connection goes down,
so I have to establish a new one, to send the CANCEL or ACK. Now, since
the remote party most likely isn't listening to the emphemeral port I
will have to send the CANCEL/ACK to the port I originally got in the SRV
lookup (or from configuration). I think it would be a good idea to also
mention this case, since RFC3261 says that CANCEL and non-2xx ACKs MUST
be sent to the same address, and port, as the INVITE.

Regards,

Christer Holmberg
Ericsson Finland

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