Eliminating Voice Tie Trunks

Unanswered Question
Oct 14th, 2008

Hi,

I just want to ask if this is possible. What we are using right now is Avaya and we want to eliminate or lessen the tie-trunks between sites. Is it possible to connect the Avaya switch to a Cisco router then Cisco will convert the voice traffic into IP, route it in the IP cloud then pass it to another Cisco router that will pass it again to Avaya switch?

So the phones are registered in Avaya then the one that will route the voice traffic is the Cisco switch.

Is this possible? Thanks.

John

I have this problem too.
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Rick Arps Tue, 10/14/2008 - 13:23

John,

This is possible. You'll need a router with whatever voice interfaces you need to connect to your Avaya, along with appropriate dsp resources, for each phone switch you want to hook into voip. If you have more than a few phone switches, I would setup a gatekeeper to keep things easier to manage.

Next, configure your voip gateways and gatekeeper to route calls with your existing dial plan. This will take some research and work.

Once you set this up, you need to set up your Avaya switches to point calls out the new interfaces to the routers.

Hope this helps,

Rick

CHRIS CHARLEBOIS Wed, 10/15/2008 - 07:58

You don't even need to modify the dial-plan. You can use Cisco routers to carry the voice traffic over the data WAN. However, you do need to take a hard look at your data WAN.

Realize that every call is going to use 80 kbps unless you use a compressed codec, which will a) require more DSP resources on the router and b) change how the voice sounds. G.729a is the best option for compression and that still uses 24 kbps per call. Also, you need to make sure that there is no more than 200 ms delay between sites (some say 150 ms is a better benchmark). And third, you need to configure QoS between the sites at each step. This could be a serious problem if you are connecting sites over the internet via VPN or across a provider's shared infrastructure that is outside of your control.

The QoS across the WAN is the make-or-break factor in this. If that is set-up correctly, then you can configure dial-peers in the routers to route traffic between them and you can unplug the Avaya PBXs from the wall and plug them into the Cisco VG's. No changes are needed in the Avaya; In fact, the Avaya won't even know the difference.

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