Convergence /

Prioritizing voice over data in VoIP

By Ron Nutter
Network World Fusion, 12/17/01

I run a company that takes reservations for vacation rental homes and I have the Altigen computer based phone system in my office. I also have browser based reservation software. I want my remote people to take the phone calls I forward over the internet from my office to them using the browser based reservation software on their computer. What choices do I have for prioritizing the voice packets over the data packets? I have a Cisco 1700 series router in my office.
-- Ted Mullikin

For prioritizing traffic, look at Cisco's QOS (Quality of Service). This will let you shape the traffic so that the VOP (Voice over IP) has a higher priority over the other traffic. To get the most up to date benefits of QOS, make sure that you are on the latest version of the Cisco IOS. This may require you to add flash and or dram to the router. I suggest you read Syngress's Administering Cisco QoS for IP Networks. Depending on your expertise with the Cisco router, you may need to hire someone who is more fluent with the IOS rather than do it yourself.

Look at the IP latency between locations that will be using Voice over IP. According to several carriers and equipment providers you should watch for a ping time between locations of 150ms or less. Going too far above that will create a drop in packets. This will appear to the callers as a choppy sounding conversation. While a point to point circuit will give you the best overall speed between locations, you might also look at setting up a Frame Relay cloud. A carrier will give you the IP latency between those remote locations and yours.

As to the voice over IP solutions, Cisco has an IP based phone that you could put at each location and point them back to a unit at your location. As I understand it, those remote phones would appear like extensions off of your phone system. The IP phones are more expensive that a standard single line phone. I have seen some available on some of the Internet auction sites if you can't find a reasonable price elsewhere. Nortel also has an option that doesn't require the same hardware at the remote location, but it would dictate having a NT based system at your office for remote office connection. Check both of these vendors web sites for more details.