23 feb 2010 kl. 01.47 skrev Kirill 'Big K' Katsnelson:

> On 100222 1313, JT wrote:
>> When a SIP device dials another SIP device...Asterisk connects the calls and
>> displays the channel information.
>> If one of those SIP devices hangs up, Asterisk receives the hangup notice
>> and disconnects the call/channel.
>> However - what does Asterisk do when the network cable is unplugged from one
>> of the SIP devices...?!
> 
> Jared already mentioned SIP session timers, which are supported starting with 
> 1.6. Here's my experience. While I am running 1.6, the software stack that is 
> used for agent softphone (PJSIP) does not support the session timers. If the 
> softphone crashes in a call, the call would get stuck exactly as you describe.
> 
> I am working around this problem by setting rtp timeouts in sip.conf:
> 
> [general]
> rtptimeout=10
> rtpholdtimeout=300
> 
> This means that if RTP flow stops while the agent is in the call, the call 
> will be disconnected in 10 seconds. If the call was put on hold by the agent, 
> it will be disconnected in 300 seconds. Your timeouts may vary.
> 
> The caveat here is that it is perfectly normal NOT to transmit any RTP data 
> in case of long silence.
Not in Asterisk - we do not really support silence suppression. The 
recommendation is to turn it off on the phones.

> This is why the SIP timers were introduced in the first place: there is no 
> correct way to detect when the client is going away, as no activity is a good 
> session state.
> 
> I am able to get away with the small timeout because I set the PJSIP client 
> to always transmit RTP, by turning off voice activity detection feature 
> (VAD). If you want to support that feature, set rtptimeout as high as for how 
> long you allow absolute silence on the line without disconnecting it.

Just to complete this discussion - we also have the absolute timeout that is a 
lifesaver in many cases. If you set this to a time that's larger than the 
normal calls, Asterisk will hang up the call. I very often set it to two hours, 
just to make sure that if anything strange happens, all calls will be cancelled 
out at some point.

/O
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