Subject: [Sip] Outbound-08: usage of keep-xxx parameter

From: "Christer Holmberg \(JO/LMF\)" <[email-masked]>
Date: Wed, 14 Mar 2007 14:25:36 +0100

Hi,

If all outbound compliant edge proxies MUST implement all keep-alive
mechanisms, why do we need to list the different keep-alive mechanisms
(keep-stun, keep-crlf etc) in the outbound-proxy-set URIs? Isn't it
enough to simply include the 'ob' URI parameter?

If all oubound compliant edge proxies MUST implement all keep-alive
mechanisms, do we need to keep-xxx parameters in the first place?

Regards,

Christer
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---

From: Cullen Jennings <[email-masked]>
Date: Thu, 15 Mar 2007 21:43:28 +0100

This is so that the  administrative domain that runs the server can  
pick what type of keep alive it wants to use (even though they are  
all supported). I think this is all too much complexity but it seemed  
that some people wanted this so that's what we wrote up.

Cullen <with my editor hat on>

On Mar 14, 2007, at 2:25 PM, Christer Holmberg ((JO/LMF)) wrote:

>
> Hi,
>
> If all outbound compliant edge proxies MUST implement all keep- 
> alive mechanisms, why do we need to list the different keep-alive  
> mechanisms (keep-stun, keep-crlf etc) in the outbound-proxy-set  
> URIs? Isn't it enough to simply include the 'ob' URI parameter?
>

---

From: "Christer Holmberg \(JO/LMF\)" <[email-masked]>
Date: Fri, 16 Mar 2007 15:35:19 +0100

Hi, 

>This is so that the  administrative domain that runs the 
>server can pick what type of keep alive it wants to use (even 
>though they are all supported). I think this is all too much 
>complexity but it seemed that some people wanted this so 
>that's what we wrote up.

I don't remember any recent discussion regarding this, but I may of
course have missed it.

But, if we can have multiple keep-alive mechanisms for a single
transport protocol I guess it's ok to have that possibility. BUT, I
still think that it should also be possible to only include the 'ob' URI
parameter, and let the UA choose whatever outbound keep-alive mechanism
he wants, and that we should describe that.

Also, when discussing outbound with Rohan in San Diego I believe we
agreed some text saying that the edge proxy can also insert the keep-xxx
parameters in the Path header. But, I don't find any text regarding
that.

Regards,

Christer

> > If all outbound compliant edge proxies MUST implement all 
> keep- alive

---

From: <[email-masked]>
Date: Mon, 19 Mar 2007 09:05:08 +0200

Hi,

>>complexity but it seemed that some people wanted this so 

I also think all that is too much complexity and can not even
see the value of it. Remember that Outbound has only one single
keepalive method (STUN) for UDP and two methods (CRLF and TCP
keepalive) for TCP. The reason for introducing the 'keepalive-stun'
flag was that multiplexing STUN to the SIP port was considered as
backwards incompatible change, so there was an extra reason for 
the UA to check that the proxy supports it. However sending 
double-CRLF or TCP keepalives is backwards compatible to SIP
servers compliant to RFC 3261, so no such reason exists here.

>I don't remember any recent discussion regarding this, but I may of

If you refer to the discussion related to STUN, the reasons for
the related flag are not as such applicable to the keepalive
methods currently proposed for TCP. For CRLF keepalives no
such discussion has been on the list (before this one).

>transport protocol I guess it's ok to have that possibility. BUT,
>I still think that it should also be possible to only include 
>the 'ob' URI parameter, and let the UA choose whatever outbound 
>keep-alive mechanism he wants, and that we should describe that.

I agree with Christer that it should go this way:

It should be possible for the UA to find out (in some way or 
another) that the configured or discovered outbound proxy 
supports SIP Outbound. UA should be able to find out the
transports supported by the proxy by DNS, unless the URI has an
explicit transport parameter. Finally the proxy has to support
all keepalive methods defined in SIP Outbound for the transports
it supports. As simple as that.

Defined like that, if the proxy would only support UDP, the
UA can only use STUN for keepalive. And if the proxy would
support TCP, the UA could use either CRLF or TCP keepalive.
For TCP case the choice would be done by the UA, exactly 
as the case was before replacing STUN with CRLF as one
keepalive method for TCP.

Regards,

Erkki

---

From: "Christer Holmberg \(JO/LMF\)" <[email-masked]>
Date: Mon, 19 Mar 2007 09:00:42 +0100

Hi, 

>>>pick what type of keep alive it wants to use (even though 
>>>they are all supported). I think this is all too much complexity but
it 
>>>seemed that some people wanted this so that's what we wrote up.
> 
>see the value of it. Remember that Outbound has only one 
>single keepalive method (STUN) for UDP and two methods (CRLF and TCP
>flag was that multiplexing STUN to the SIP port was 
>considered as backwards incompatible change, so there was an 
>extra reason for the UA to check that the proxy supports it. 
>However sending double-CRLF or TCP keepalives is backwards 
>compatible to SIP servers compliant to RFC 3261, so no such 
>reason exists here.
> 
>If you refer to the discussion related to STUN, the reasons 
>for the related flag are not as such applicable to the 
>keepalive methods currently proposed for TCP. For CRLF 
>keepalives no such discussion has been on the list (before this one).

I am refering to the decission to define mutliple keep-xxx parameters.

>>still think that it should also be possible to only include the 'ob' 
>>URI parameter, and let the UA choose whatever outbound keep-alive 
>>mechanism he wants, and that we should describe that.
> 
>transports supported by the proxy by DNS, unless the URI has 
>an explicit transport parameter.

Yes, and therefor I think it shall be described that the edge proxy can
insert the 'ob' and 'keep-xxx' parameters in the Path header. Currently
I beleive only inserting of 'ob' is described for the edge proxy, in
order for the home proxy to figure out that the edge proxy supports
outbound. I think we also need to say that the UA can use that
information.

>Finally the proxy has to support all keepalive methods defined in SIP
Outbound for the 
>transports it supports. As simple as that.

I agree, and that was the reason why I asked why we need to keep-xxx
parameters. 'ob' should be enough.
 
>support TCP, the UA could use either CRLF or TCP keepalive.

Yes.

>For TCP case the choice would be done by the UA, exactly as 
>the case was before replacing STUN with CRLF as one keepalive 
>method for TCP.

Yes.

Regards,

Christer

> >This list is for NEW development of the core SIP Protocol Use 
> >[email-masked] for questions on current sip Use 
> >[email-masked] for new developments on the application of sip
> >
>

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From: Cullen Jennings <[email-masked]>
Date: Mon, 26 Mar 2007 11:00:25 -0700

I did not read these emails until after the meeting but I see what  
you are getting at and I think we can simplify along these liens  
without any loss of functionality.  I will try and sort out some text  
with Rohan and see if it looks aceptable to people.