Subject: [Simple] Alternate Connection Model Query

From: "Gaurav Nangla" <[email-masked]>
Date: Fri, 1 Apr 2011 08:21:43 +0530

Hello,

I've got an alternate connection model query.

Suppose there's a SBC/B2BUA lying in the signalling and media paths between two MSRP UAs.
The SBC manipulates the 'setup' attribute in a manner such that both parties can setup a MSRP session despite them both being behind NATs/firewalls.

i.e. 'a=setup:active' is received in OFFER from UA1, 'actpass' is sent in OFFER to UA2 by the SBC, 'active' is received from UA2 in ANSWER, 'passive' is sent in ANSWER to UA1 by the SBC.   

What this means is that the SBC will be receiving SYNs from both the UAs and handling them using the 'TCP splicing' technique.
It's basically making both the UAs think that they've each initiated and setup a MSRP TCP connection.

Scenario further described in greater detail at:  
http://lists.ag-projects.com/pipermail/blink/2011-March/001263.html

Q1> Does this mean that the alternate connection model is sufficient by itself for an end to end MSRP session?
Q2> Also on a related note, is a UA restricted (by the specs) from responding to a SEND request received while it's waiting for a response to its own unanswered SEND request?

Gaurav