Subject: RE: Deprecate loop detection, was: Re: [Sip] bis draft: Pre-existing Route headers

From: "Chiou, Mark" <[email-masked]>
Date: Tue, 8 Jan 2002 12:11:39 -0600

I would prefer to synchronize with legacy networks such that we won't
break any existing network when we do interworking.
Default value to 20 for Max-forwards is way too much. 
 
Mark Chiou
Santera 

-----Original Message-----
From: Lathan Lewis [mailto:[email-masked]]
Sent: Tuesday, January 08, 2002 11:40 AM
To: 'Jonathan Rosenberg'; Drage, Keith (Keith)
Cc: [email-masked]
Subject: RE: Deprecate loop detection, was: Re: [Sip] bis draft:
Pre-existing Route headers

I would agree with your proposal to deprecate loop detection based on 
the fact that it is becoming more complex and expensive to implement
than 
it's worth. Our implementation currently relies on the Max-Forwards
header 
as you propose and is using a default value of 20. 

Lathan Lewis 
Nortel Networks 

-----Original Message----- 
From: Jonathan Rosenberg [ mailto:[email-masked]] 
Sent: Tuesday, January 08, 2002 11:17 AM 
To: Drage, Keith (Keith) 
Cc: [email-masked] 
Subject: Deprecate loop detection, was: Re: [Sip] bis draft: 
Pre-existing Route headers 

Drage, Keith (Keith) wrote: 

> Section 8.1.1.7 of the bis draft (lines 948 through 952) appears to be
the 
> text that allows pre-existing Route headers to be used in the initial 
> transaction of a dialogue, or in a stand-alone transaction. 
> 
>       "8.1.1.7 Request-URI The initial Request-URI of the message
SHOULD 
> be set to the value of the URI in the To field. One notable exception
is the 
> REGISTER method; behavior for setting the Request-URI of register is
given 
> in Section 10. Another exception is the case of pre-existing Route
headers; 
> in that case, the procedures of Section 12.2.1.1 as they pertain to
the 
> Request- URI are followed, even though there is no dialog." 

Right. We'll add a bit more text to explain what a "pre-existing route"
is. 

> 
> A set of Route headers created using the Record-Route mechanism
carries the 
> mechanism to ensure that when the route traverses a spiral, all the
URLs in 
> the Record-Route headers are unique, and therefore that the set of
Route 
> headers is also unique. 

Actually, I am not sure thats really needed anymore for routed requests.

Here's why. Remember, the point of loop detection is to reject a request

when you know that its processing will cause you do to the same thing to

it you did last time. Proxy processing is not based just on the URI; in 
the case of Route headers, the overall processing is the same only if 
the Route set through the loop has not changed. 

One of the things we have now in bis is that a proxy computes, as part 
of the via branch ID, a hash of those things in the request that affect 
its processing. Effectively, if this includes a hash of the route set, 
there is no need to ensure that the URI in the route set are not 
identical. Realistically I expect they almost always would be anyway, 
though. 

I am beginning to wonder, however, whether or not this whole business of

loop detection is worth the trouble. The Max-Forwards mechanism provides

a sufficient way to ensure that they don't persist forever. The loop 
detection mecahnism is more efficient, but given the probability of 
occurence in a well-engineered network, I'm not sure its worth all the 
pain it causes, and it does cause pain. A proxy has to hash over a bunch

of headers that it otherwise might be able to ignore... 

Anyone for deprecating loop detection? A proxy that doesn't do it would 
have to insert max-forwards if not already present, that is the penalty.

  We also need a minimum value for Max-Forwards, something like 20 is 
more than sufficient, I think. 

This is has the nice side effect of making the branch ID just a pure 
transaction identifier, as it should be. 

Comments? 

-Jonathan R. 

-- 
Jonathan D. Rosenberg, Ph.D.            72 Eagle Rock Avenue 
Chief Scientist                         First Floor 
dynamicsoft                             East Hanover, NJ 07936 
[email-masked]                 FAX: (973) 952-5050 
http://www.jdrosen.net                  PH:  (973) 952-5000 
http://www.dynamicsoft.com 

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---

From: "Cullen Jennings" <[email-masked]>
Date: Tue, 8 Jan 2002 13:20:34 -0800

>  Default value to 20 for Max-forwards is way too much.

I don't think that 20 is too much. It is amazing how many proxies one goes
through in some deployed systems today. When you start considering ASP's and
service route ideas it is going to get even larger than it is today.

Cullen