[SR-Users] SIP and conntrackd experience?

Grant Bagdasarian gb at cm.nl
Thu Oct 1 09:35:06 CEST 2015

Alright, I understand. Thanks for explaining. 

How do big carriers handle these kinds of scenarios where a sudden outage in a key component would cause calls to be dropped?
Is this the achilles heel of voice? Is there special kind of software or hardware (or both) for handling these kinds of scenarios?

-----Original Message-----
From: sr-users [mailto:sr-users-bounces at lists.sip-router.org] On Behalf Of Daniel Tryba
Sent: Wednesday, September 30, 2015 4:19 PM
To: sr-users at lists.sip-router.org
Subject: Re: [SR-Users] SIP and conntrackd experience?

On Wednesday 30 September 2015 13:07:12 Grant Bagdasarian wrote:
> A is connected to C in say 10 seconds and they're exchanging RTP.
> Now, the firewalls at B are turned off, or crash or whatever, mid call.
> Would this cause the session to be disconnected? The media is 
> obviously gone, but will the session remain active? I'm looking for a 
> way to restore almost instantly in case of any failure, be it firewall related.
> My idea was to configure conntrackd on the firewalls which are setup 
> in HA mode and where a crash of the primary would result in a failover 
> to the backup with full connection restore.

As long as there is no additional signalling (DTMF over SIP INFO, session timers, onhold events....) or endpoints detect the lack of RTP (or RTCP) after a short timeout, the SIP session is still alive according to the endpoints.

So if RTP is only forwarded by the kernel (like the kernel forwarding capabilities of rtpengine) and you could replicate these forwards to a standby server, you could do a failover of both SIP and RTP. Theoretically... 

If you are running rtpproxy, which actively accepts and forwards the RTP traffic, you'd have to replicate the state of the proxy to a standby machine. 
Which is AFAIK not possible. 

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