The generateBranch() method can generate the same branch value

[jsbeltz]

From http://tools.ietf.org/html/rfc3261#page-39

The branch parameter value MUST be unique across space and time for
all requests sent by the UA. The exceptions to this rule are CANCEL
and ACK for non-2xx responses. As discussed below, a CANCEL request
will have the same value of the branch parameter as the request it
cancels. As discussed in Section 17.1.1.3, an ACK for a non-2xx
response will also have the same branch ID as the INVITE whose
response it acknowledges.

I locally have changed generateBranch to but you might have a better solution for this.

//transaction layer
var uuid = require('node-uuid');
function generateBranch() {
var buffer = new Buffer(16);
return ['z9hG4bK',uuid.v4({}, buffer).toString('hex')].join('');
// return ['z9hG4bK',Math.round(Math.random()*1000000)].join('');
}