Works fine if you have PSTN trunks. Another option is to make sure you have one working SIP trunk internally to another device in your LAN. This could be another Asterisk server or something else that talks SIP... such as an SPA3000.
Hi
In commercial deployments I exclusively use IAX2 trunks, you get none of the nonsense with the PBX falling over when the ADSL goes down
I can do this because I run a hosted A2Billing server which is connected to the internet with a service level agreement.
Inbound DID are brought to the A2Billing server and then forwarded on to the Client PBX via IAX again, with a failover to drop onto landline / cellphone if the ADSL drops out.
On the PBX, if the IAX trunk to my A2Billing server has qualify=yes (or qualify=400) in it, then the IAX trunks will go offline the latency gets beyond acceptable, the outbound route selects the POTS as the outbound trunk.
For interest, Swisscom did a survey on VoIP a few years ago, and established that VoIP usage only drops off when the latency (not the ping times) exceeds about 350 ms, which is about the point when you start to interrupt each other, and it becomes useful to say "over" after each sentence;-) Under the 350ms, the human ear does not really detect any latency, or not to any degree to worry about, conversations are still comfortable.
This gives the following advantages:-
1. I only have to set up SIP trunks to various carriers once at the A2Billing server.
2. I know the settings to my A2Billing server, so that is a copy and paste to set up a trunk and if there if a problem, I can see both ends.
3. Using IAX gets rid of all NAT problems.
4. IAX does not suffer the same fate as SIP when ADSL goes down.
5. I charge the customer for the minutes, on a prepaid basis and make a small profit.
6. Because of the volume, I can get wholesale rates.
7. I can use multiple carriers for different destinations and least cost route between them.
8. It can also be useful in the case of disaster recovery, because you can point the inbound numbers anywhere.
Clearly this is only worthwhile if you have sufficient traffic to warrant the hosting costs.
Shameless Plug follows:
You should be able to work out from the minutes you are doing across all your PBX systems as to whether installing an A2Billing server is a worthwhile excercise for you, and whether it will be profitable to be your own Voice over IP service provider. The costs and consultancy prices are on the front page of the http://www.asterisk2billing.org website if you are nervous about setting up and configuring your own A2Billing server.
Drop me an email at [email protected] if you want more information.
This of course is not much help to you if you only have one PBX, so my advice would be to try and find a service provider who runs IAX2.
Joe Roper
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