Re: [Sip] Outbound-10 comments

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 <jerry.yin@yahoo.com>
19.09.07 16:40

        To:     sip@ietf.org, fluffy@cisco.com, rohan@ekabal.com
        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

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