"If I know that I'm going to have 10 concurrent calls then I should know that I'm going to need 1 meg of bandwidth just for my calls," he explains. "You'll need to do packet prioritization and shaping to makes sure that voice packets get higher priority."

Like Francis, Maloff also thinks that telecom workers can bring much-needed skills and perspective to the job of managing SIP-based voice networks that IT workers will need some time to acquire. However, he also thinks telecom workers should realize that preparing themselves to manage SIP will take a lot of time and effort since there are a lot more variables in a SIP system than a traditional TDM system.

"The hardest thing for people who have been in telephony is now there's so much more they need to think about," he says. "In the past if I'm a telecom manager I never had to pay for local outgoing calls. With SIP trunking it's more like a cellphone model where 'local' has no meaning because you're on the Internet."

Brian Graves, a network engineer at the University of Washington who has a background in managing telephony, says he has had to learn much more about implementing quality of service as his department started designing a SIP core that it plans on rolling out over the entire network over the next few years. The difficulty for many people on the telecom side, he says, is understanding that voice calls no longer get automatic preference for bandwidth or even the total amount of bandwidth they'll need to successfully complete calls on an IP network.

"TDM is a circuit-switched technology, so QoS is essentially built right in because you have a dedicated amount of bandwidth on your call," he says. "An IP network is packet-switched so you don't have natively the same bandwidth guarantee. You have to implement QoS to make sure it isn't delayed by other data."