WAN connections and VoIP issues

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When troubleshooting VoIP issues, please take in consideration the following:

1. Many gateway routers/brouters/all-in-one modems tend to cause VoIP issues because they come with a built in firewall that uses up quite a bit of memory on the device. This appears to be the case even when the firewall turned off and phones are placed in the DMZ. The issue is that VoIP is a memory hog for a layer 2 & 3 devices and the issue is exacerbated even more when you throw in all the other features that some of these devices have. Our suggestion is to keep things simple - use a simple modem bridged to a router that will be able to handle customer's phone & Internet traffic.
2. Before voice service is turned up, one must make an initial assessment on needs of the customer's network. How many phones will be deployed on the network? How many computers or other network devices will need to use the same network as the phones. The more phones and computers will be deployed, the more powerful their network devices will have to be. This isn't just bandwidth, but also the memory and type of firmware used on the router or gateway.
3. Tying all this together is overall WAN connection quality. Does the customer have enough bandwidth going to the outside world? Do they see a lot of jitter on their connection? If using DSL, what type quality is it (is there attenuation, high CRC error count, etc.)? Has the QoS been properly enabled and tested cusomter's network ? Many times partners will overlook the WAN connection in their troubleshooting. Remember, the WAN connection is the link to us. If it is poor, the service from us will be poor.

QoS for VoIP Networks