On 7/3/13 11:31 PM, SIP Learner wrote:
> Hi, guys!
>
>
> I have a question about the To header field of a SIP request, maybe there is
> some misunderstanding, I hope some of you will kindly make clear for me.
> Thanks in advance!
>
>
> When describing how to populate the To field of a SIP request, RFC 3261
> states in section 8.1.1.2 that:
>
>
> "...Frequently, *the user will not enter a complete URI*, but rather a string
> of digits or letters (for example, "bob"). It is at the discretion of the UA
> to choose how to interpret this input...."
>
>
> This implies that the user will not enter the domain to the right-hand-side
> of the at-sign in the SIP URI (Am I right?). But RFC3261 continues to state
> that:
>
>
> "Using the string to form the user part of a SIP URI implies that the UA
> wishes the name to be resolved in the domain to the right-hand side (RHS) of
> the at-sign in the SIP URI (for instance, sip:b...@example.com)."
>
>
> My question is: since *the user does NOT enter the complete URI*, how does
> the UA know what the domain to the RHS of the at-sign in the SIP URI is? How
> does the UA know in what domain is the name to be resolved?
Policy or configuration.
If what the user enters is a "phone number", the UA has a number of options:
- The UA may contain dial plan information to expand the number entered
to a full E.164 number. Then it can form a URI from the E.164.
- or the UA may take the dialstring as entered and form a URI from that,
leaving the transformation from dialstring to number to a downstream server.
- If the UA has formed an E.164 number, then it could just make that
into a TEL URI. (No domain.) But of course it still must decide where to
send the request, so it will have to pick a first hop domain. (Put that
in Route header.)
- Or the UA could form the E.164 number into a SIP URI, adding some
domain name or IP address. It most likely has no way to know what domain
is responsible for the particular number. So it will probably put in the
domain of some provider that will do the further routing.
- If the number is not an E.164, it will probably want to form into a
SIP URI using the domain of its own provider, that understands the dial
plan it uses.
Thanks,
Paul
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