Subject: RE: [SIP] Some idea on Stateful SIP Proxy for Card Service

From: Jonathan Rosenberg <[email-masked]>
Date: Wed, 31 Jan 2001 13:56:46 -0500

> -----Original Message-----
> From: William Marshall [mailto:[email-masked]]
> Sent: Wednesday, January 17, 2001 7:47 AM
> To: [email-masked]
> Subject: Re: [SIP] Some idea on Stateful SIP Proxy for Card Service
> 
> 
> P is clearly a back-to-back-UA, since it speaks SIP to
> both user B and terminal C.  However, its need to initiate
> a BYE doesn't fit the profile of a proxy.  Just a B2BUA.
> 
> In looking at various enhanced services, it is not clear
> to me that a "stateful proxy" will ever exist.  They will
> all be B2BUAs for some case or another.
> 

No.

You only want to be a B2BUA if that is the only way. The requirements for
fault tolerance and scale are much harder with a B2BUA (on part with a UA,
not a surprise). Stateful proxies can record-route and insert vias with
domain names, and the result is that these devices can still fail and the
calls can be recovered by routing the request/response to an alternate. Not
so for a B2BUA, which has state that now needs to be replicated in some way
(I realize State header is another possibility, its still just a form of
state replication).

Many services require only a stateful proxy. Many personal mobility services
fall into this category, as do all CPL types of services. This isn't
everything, but its a decent number.

-Jonathan R.
---
Jonathan D. Rosenberg                       72 Eagle Rock Ave.
Chief Scientist                             First Floor
dynamicsoft                                 East Hanover, NJ 07936
[email-masked]                     FAX:   (973) 952-5050
http://www.cs.columbia.edu/~jdrosen         PHONE: (973) 952-5000
http://www.dynamicsoft.com

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---

From: "Henning G. Schulzrinne" <[email-masked]>
Date: Wed, 31 Jan 2001 14:06:10 -0500

Jonathan Rosenberg wrote:

> everything, but its a decent number.

As do firewall-type proxies.

Also, B2BUAs have a much harder time with loop detection, so it's harder
to "stack" them.

One also needs to consider the impact on signatures and authentication
in general. This can get pretty messy, depending on what fields the
B2BUA modifies in its newly generated messages. (This works well if the
B2BUA also appears as the trust entity to the next hop, but is iffy if
the original requestor is the one being authenticated.)

-- 
Henning Schulzrinne   http://www.cs.columbia.edu/~hgs