That Buzz You Hear Is Voice over IP - Page 2

 By Paul Rubens
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Who's Got the Bandwidth for It?
One of the questions on the minds of network managers is what are bandwidth requirements of a VoIP system? After all, a small branch may have a fairly small IP data pipe connecting it to main office, and the last thing you want is for that pipe to be clogged with voice traffic.

"Clearly, the network has to be IP-based 100baseT Ethernet and you would also need to look at the firewall: Will it affect the quality of voice calls? Then you need to look at the network infrastructure: How many hops does a packet have to make, as this will delay the reception of a packet."

— Rogier Mol, IDC

It turns out that there are a number of ways of overcoming this potential problem. Branch offices need be linked only by a low capacity link (say 64kbps) to get telephony functions from the head office switch, while the voice traffic from the branch can actually be routed through the conventional phone system. Or the system can be programmed so that local calls go through the Public Switched Telephone Network (PSTN), while toll calls are routed through the IP link to head offices and out through the office's central telephone trunk — until a preset amount of the bandwidth between the branch and head office is used up. Any further toll calls are then routed locally through the PSTN.

If you have remote users who access the network from home using a broadband connection, there are a number of obvious advantages of being able to dial in to an IP telephony system: For example, using a software phone and headset connected to a laptop, teleworkers can make business calls through the company switch, while accessing data at the same time. The software phone becomes a company extension, so calls to the office number are seamlessly routed to the home, and all PBX functions such as voice messaging are available — just as if the teleworker were at his or her desk. (For remote call center workers, IP telephony is particularly valuable as calls can be routed from the actual call center to a worker's home automatically, and the caller's associated information — such as account details or past transactions — can also be pushed to the teleworker's computer.

IDC's Mol said the principal advantage of VoIP is a business one: providing workers with better communications features to enable them to do their jobs more efficiently. But for the network administrator, the major concern is whether or not the network is up to the job. "Clearly the network has to be IP-based 100baseT Ethernet, Mol said, "and you would also need to look at the firewall: Will it affect the quality of voice calls? Then you need to look at the network infrastructure: How many hops does a packet have to make, as this will delay the reception of a packet."

"The most important thing is that your network components support prioritization and quality of service forwarding features," Mol said. "Without this no system will work properly." The surprising thing is the small amount of data that IP telephony generates. Using compression, voice traffic may consume only 6-10kbps, with a further 6kbps overhead.

A VoIP Case in Point
One company that has already implemented VoIP successfully is Amicus, a customer contact outsourcing company based in the U.K. The company moved into new offices with no existing network infrastructure, and installed an Avaya system to provide IP telephony services to 102 staff members from day one.

"The networking hardware we needed was fairly similar in price to traditional equipment, but a major cost saving was that we had to wire up only one point per employee, for voice and data combined, instead of one for voice and one for data," Charles Burns, Amicus' commercial director, said. "This made it less expensive to install, and from a support point of view it is much cheaper as there is no longer a telephony piece and an IT piece. Our IT person supports phones and computers." The company used power over Ethernet to power its IP phones, sidestepping the issue of power supplies to each phone point.

Burns says the extra functionality that IP telephony offers is valuable. "Any employee can plug his or her phone in anywhere in the building without having to get calls rerouted first, and they can access the Web from the phones using a touch screen. There are also other handy features like the ability to access the call log on the phone's screen itself."

Moving in to a greenfield site, choosing IP telephony was a no brainer financially, concludes Burns. "From an ROI point of view, if you have an existing telephone switch it is difficult to justify replacing it with Voice over IP. But if you are considering changing switch or the business is starting up, then you would be mad not to move to Voice over IP."

» See All Articles by Columnist Paul Rubens

This article was originally published on Feb 17, 2004
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