Subject: RE: [Sip] The Problem with PRACK

From: "Samir Srivastava" <[email-masked]>
Date: Fri, 10 Mar 2006 02:58:30 -0600

ext Samir Srivastava wrote:
> It has been around 4 years. UA MUST have TCP. We need to draw a line 
> worrying about backward compatibility with 2543. UA is not 3261 
> compliant and should be fixed. If still it has only UDP, they will be 
> few and we get gain for optimizing most of the UA supporting TCP.

Implementing and using are two completely different things. 

SS>> Agreed. Do you mean to say we are going to have *increasing* number
of UAs which will be 
     ONLY supporting UDP in future, which have lot security holes
because TLS is not used.

Even if the proxy wanted to use TCP for the last hop towards the UA, it
won't be able to connect to a host behind a NAT. This is what
sip-outbound is trying to fix.

SS>> How UDP is going to help here, if UA is not keeping the bindings
alive. UA needs to keep 
     binding alive for every flow. Pl explain. 

Cheers,
Aki

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---

From: Aki Niemi <[email-masked]>
Date: Fri, 10 Mar 2006 14:23:38 +0200

Inline.

>      ONLY supporting UDP in future, which have lot security holes

I think (and hope) there will be an increasing number of UAs both
supporting *and* using TCP and TLS in the future.

>      binding alive for every flow. Pl explain. 

But if there is no contact registered for that UA that supports TCP,
then the proxy is out of luck and can only downgrade to UDP.

There's actually a wide range of associated problems with UAs I've used.
For example, some might allow you to switch over to using TCP, but after
that, the UA will only ever use TCP -- for registrations and invites
alike -- leaving domains that only accept UDP unreachable.

So again, implementing and using (let alone using wisely) are two
entirely different things.

Cheers,
Aki

Cheers,
Aki