TCP is a very polite protocol, slowing down when it sees congestion. It is singularly unsuited to voice, which has to be able to hog bandwidth and push its way through the crowd.
Out on the WAN, guaranteeing sufficient quality of service (QoS) for voice applications is still a problem in the public Internet, where service providers can't control the infrastructure from end to end. Some of the bigger players can constantly ping the network to check latency and choose routes paths accordingly, bumping some voice traffic over the public switched telephone network as needed. But we may never see ubiquitous toll-quality voice over the public Internet until the entire infrastructure has been upgraded to Ipv6.
The "private Internet" is a very different matter, because service providers can tune backbone networks and use various tricks of the trade, including peering relationships, to assure QoS levels.
On the LAN, enterprises have total end-to-end control and can just throw more bandwidth at the problem. However, voice over IP implementations to date have been too small to really test the infrastructure.
"Today's technology basically supports 100-line-or-less environments, so you don't get into QoS issues," says Larry Jones, vice president of enterprise integration services for Williams Communications Solutions in Houston. "In larger networks, you have less bandwidth per user, and you are dealing with more management and change.
"Typically, it's been the third generation when you get the QoS you need. That was the frame relay and ATM experience. And while new IP PBXes that are coming out are being positioned as second-generation technology, they are really first-generation products, so we're probably looking at another 12 to 18 months."
Meanwhile, it's important to remember that voice, while it has to be up all the time, isn't a strategic application.
"What does giving all this QoS priority to time-sensitive applications like voice do to your mission-critical data applications?" queries Steve Johnson, vice president of marketing for MIL 3, a Washington-based company that provides simulation and decision-support software to developers and implementers of IP telephony. "Are you starving them?"
The bottom line is that you can probably solve most of the QoS problems on the LAN and WAN today, as long as the latter doesn't include the public Internet.
"Customers we've worked with who have implemented voice over IP are very happy with the quality when it's done," sums up Eric Larson, director of networking products for Motorola's multiservice networks division in Mansfield, Mass. "But there is a lot of work to do before you get there. And, frankly, who has the time?"
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