[Serdev] Concept for a SIP cluster implementation

[Andreas Granig]

Klaus Darilion wrote:
> Jan Janak wrote:
> 
>>   - A user agent does not have to send INVITE messages through the same
>>     proxy instance as REGISTER messages. The proxy server that received
>>     the INVITE request can make sure that the uac is reachable
>>     for the duration of the transaction by retransmitting the
>>     provisional response periodically (simulates NAT ping). All other
>>     transactions finish immediately and do not need this.
> 
> 
> What happens in the callee hangs up (send the BYE)? This will be 
> loose-routed via the same proxy, which may not have a pinhole to 
> traverse the NAT :-(

Not if the proxy which receives the first INVITE from the caller sets a 
record-route and NAT-pings the caller until the BYE is received. But 
this would require some sort of dialog-stateful mechanism.

I'd say it's much easier to handle if the outbound proxy equals the 
registrar from the UACs point of view. So the UAC always sends all 
requests to the same edge proxy, which then splits up REGISTERs from 
other requests and forwards them to the appropriate server.

Andy