Re: [Sip] Outbound-10 comments

[[e-mail]]

Hi,


  I composed the email below a month ago related to this thread and  
thought that I was missing something so I did not posted it, but it  
seems that there are some issues pending with the keepalive label and  
processing.

  Sorry to introduce more questions:

--

  My comments are about the keep-stun label.

  It is not very clear how the UA discovers that the Edge Proxy supports STUN.


In section 8 (keepalive processing). I read

"   When a URI is created that refers to a SIP node that supports STUN as
    described in this section, the 'keep-stun' URI parameter, as defined
    in Section 12 MUST be added to the URI.  This allows a UA to inspect
    the URI to decide if it should attempt to send STUN requests to this
    location.  For example, an edge proxy could insert this parameter
    into its Path URI so that the registering UA can discover the edge
    proxy supports STUN keepalives."


Q1. Why "an edge proxy COULD insert this parameter into its Path URI"  
and not MUST ? (considering that the UA supports STUN)


Q2. In what other header can I also add the keep-stun, so that it will  
be still present when I get back a response?


Note that in the example of section 9 the responses 200-OK haven't any  
keep-stun

(Also mentioned in  
http://www1.ietf.org/mail-archive/web/sip/current/msg20295.html)


Q3. For the case in this example, How will the Callee know that it is  
allowed to send STUN keepalives? (no keep-stun present)

For the case in the example, and considering:

       "Typically, a SIP node first sends a SIP request and waits to
       receive a final response (other than a 408 response) over a flow
       to a new target destination, before sending any STUN messages."

The callee will never send the keepalives...

--
Part II


  In my opinion, the edge proxy MUST add a list of the supported  
mechanisms for keepalive in the 200-OK response to REGISTER. The list  
MUST include ALL the supported mechanisms (so the UA can for example  
know that if some mechanism is not available for the transport it used  
to register there are other mechanisms for other protocols. In this  
case the UA will form a new flow by registering using another protocol.)

Example 1:

UA sends REGISTER over UDP.
It gets back a 200 OK with only keep-crlf.
UA recognizes that STUN is not available, so a UDP flow can not  
succeed. Then it sends a REGISTER over TCP.

Example 2:

UA sends REGISTER over UDP.
It gets back a 200 OK with keep-crlf and keep-stun.
UA recognizes that keep-crlf is present so (its logic) can judge that  
TCP is a better choice.
Then the UA forgets using UDP and switches to TCP: sends a REGISTER over TCP.

Q: Should not be handy to have something like keep-Scrlf so the UA can  
knows that TLS is also supported? The same for DTLS.




Sergio


Quoting [e-mail]:

> I agree with Jerry here, and believe this has come up before (?).  It is
> pointless for the originating UA to try to impose, or infer, the keepalive
> mechanism before it can know what is applicable.
>
> An additional comment along these lines.
>> a. UA sends REGISTER to the proxy with a "outbound" tag in the Supported
> header.
> ...
>> c. If the "outbound" tag is present in the 200 OK, and if the transport
> is UDP, using the STUN keep alive, other connection based transport using
> crlf keep alive.
>
> Step a) would really imply the originating UA MUST support both keepalive
> mechanisms, and c) implies it MUST begin using the appropriate one after
> 200 OK.  The usage is implied, not explicit, which I believe is sufficient
> in this case.  Alternatively, the usage could be made more explicit by
> listing the supported k-a mechanisms in Supported exchange, or some such.
> This should be spelled out either way.
>
> -- Peter Blatherwick
>
>
>
>
>
>
> Jerry Yin <[e-mail]>
> 19.09.07 16:40
>
>         To:     [e-mail], [e-mail], [e-mail]
>         cc:
>         Subject:        [Sip] Outbound-10 comments
>
>
> Hi Cullen and Rohan,
>
> In the draft, it requires the UA configure the next hop route header with
> "keep-stun", "keep-crlf", or "timed-keepalive" tags. This would cause some
> problems.
>
> 1. As an example, the route-set contains this route header as indicated in
> section 9 example:
> Route: <sip:pri.example.com;lr;keep-stun>
> If the DNS NAPTR resolution for pri.example.com is TCP, SCTP or TLS, the
> keep-stun will be useless. Vice versa, if the pri.example.com is resolved
> as UDP, and if "keep-crlf" was manually configured, it is not working
> either.
>
> 2. Before sending the REGISTER request, the admin/or user does not know
> what keep-alive mechanism the proxy (or edge proxy) supports. Blindly
> configure the keep-stun, or keep-crlf would cause the problem that the
> draft indicated itself in section 8: "the node could be blacklisted for
> UDP traffic".
> The better approach is to let the UA and the proxy to negotiate, not
> manually configure from UA side.
> a. UA sends REGISTER to the proxy with a "outbound" tag in the Supported
> header.
> b. Proxy insert the "outbound" tag in the 200 OK, if the UA indicated that
> it supports the outbound.
> c. If the "outbound" tag is present in the 200 OK, and if the transport is
> UDP, using the STUN keep alive, other connection based transport using
> crlf keep alive.
> There would be no way to mass up by configurations with this approach. Let
> me know if I missed something.
>
> Regards,
> Jerry Yin
>
>  Yahoo! oneSearch: Finally, mobile search that gives answers, not web
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