Mikael Magnusson <[EMAIL PROTECTED]> wrote:
> On Mon, Nov 06, 2006 at 11:03:01AM +0100, Fredrik Thulin wrote:
>> What if you type in an address of "sip:[EMAIL PROTECTED];transport=udp"
>> in your user agent, but example.org has NAPTR/SRV records giving
>> precedence to TCP? When your user agent sends the request to your
>> YXA proxy (presumably using UDP), what transport should the YXA
>> server use after it resolves the NAPTR/SRV records of example.org
>> and sees that the UAC has requested one protocol, but example.org
>> prefers to be contacted using another?
>> I'll have to think about that at least over lunch.
>> /Fredrik
> I assume that the user agent is configured with a pre-set route set
> (AKA outbound proxy), otherwise the user agent should send the request
> directly to the example.org server.

Yes, this is more the normal case than not.

> Section 4.1 "Selecting Transport Protocol" in RFC 3263 is completed if
> the URI contains a transport parameter. There is no reason to select
> transport protocol using NAPTR. And you should only lookup SRV
> records for the selected transport protocol.

Let me illustrate the need to perform NAPTR/SRV resolving even if there 
is a transport parameter in the Request-URI using an example : the 
domain sip.su.se.

You HAVE to perform the NAPTR lookup to find out which ports at which 
hosts (and their order/preference) you should send your request to.

(SRV records present in every domain is explicitly for backwards 
compatibility witf RFC2543 clients, so I don't think their presence is 
relevant to this discussion)

> Btw, when using NAPTR you should select the most preferred transport
> protocol, and not use all.
> RFC 3263 4.1
>   The NAPTR processing as described in RFC 2915 will result in the
>   discovery of the most preferred transport protocol of the server
>   that is supported by the client, as well as an SRV record for the
> server.

Yes, I realized that a while ago after the question was brought up on 
the IETF SIP mailing list


I haven't had the time to look into it though.


Yxa-devel mailing list

Reply via email to