Re: [Sip] Question on draft-ietf-sip-outbound-20 draft: multipleflowcreation

["Scott Lawrence" <scott.lawrence at nortel.com>]

On Mon, 2009-08-31 at 22:33 +0800, Vavilapalli Srikanth-A19563 wrote:
> True, UDP flow may not be required if TCP flow has been setup to route
> incoming traffic towards UA. But Won't it be an additional bonus if UA
> creates a UDP FLOW in addition to TCP FLOW, so that network can still
> reach the UA over the other transport FLOW when one FLOW is down
> (Unless if both FLOWs got created with same host and all the FLOWs
> connected to that host is down)? 
>  
> Also assume a UA has some local policy to prefer UDP transport over
> TCP to transmit the outgoing SIP messages of size less than MTU. In
> such scenarios, UA might want to establish both UDP and TCP FLOWs with
> the same edge proxy and keep alive both the connections and use the
> corresponding FLOW based on DNS lookup preferences and User's local
> policy preferences to transport outgoing messages.

That would not be a very sensible proxy if the phone is behind a NAT and
supports TCP.