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by Jeff Hicks
There's a number of reasons why a company would move to VoIP. Generally there's been some component of cost-savings - it may be in regular long distance savings, it may be in hardware cost savings (versus a PBX system), it may be that you only have one network infrastructure to deploy and manage.
But it's interesting how in the past couple of years, costs have become less of a factor in the decision process. Long-distance rates have dropped, so the cost factor is not quite as pronounced as it used to be, especially considering short-term rollout costs.
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Another up-and-coming factor in VoIP decision making are new types of applications that can be integrated into the VoIP phone system for enhanced productivity. These apps may integrate with your office environment to help you do your job better. One example is looking up the caller's information from a database as the caller dials in versus having a receptionist have to look up the data by typing it in. Another is letting communicators know where a person is - allowing for people to choose the most productive mode of conversation (whether that's a quick phone call, an instant message chat, or an e-mail.) These apps are becoming a lot more prevalent today, and it creates new areas of productivity savings for businesses to take advantage of.
VoIP rollouts, however, are particularly tricky for most IT departments. The majority of traffic on a corporate network before VoIP is typically Web, e-mail, and ERP applications. What all of these applications have in common is that they typically use the TCP protocol to send and receive data. TCP retransmits lost packets and sorts out-of-order packets. TCP also operates in an elastic manner - meaning that it's going to consume as much bandwidth as is available to the application. These applications are typically transaction-oriented. They send a series of requests and receive a response back from a server. The amount of time it's going to take to perform these requests and responses will give you an indication of how "responsive" the application feels. In fact, the key indicator of TCP application performance is response time.
VoIP traffic has additional performance requirements and real-time characteristics. It uses the Real-time Transport Protocol (RTP) which rides on top of UDP. UDP is a connectionless protocol - there's no retransmission of data, there's no re-ordering of data. RTP applications typically send packets at a fixed rate. If a packet is lost, it's lost, and there's no chance to retransmit it. Voice conversations are interactive in nature, and thus not very tolerant of large delays. The network causes a certain level of delay and if this delay is large enough (usually more than 150 milliseconds), it's going to be very difficult to talk to someone.
Networks have been tuned for long periods of time to handle the TCP applications very well. Now when you add VoIP traffic, you need to be careful to look at the performance, not only of the VoIP traffic, but what impact the VoIP traffic has on your other enterprise applications. As cool new integrated VoIP applications roll-out, now you have to consider the network performance characteristics of these applications as well. You need to have good QoS policies in place to give priority to VoIP traffic on the network. An inappropriately configured network would cause VoIP phone calls to have poor quality - they could be delayed, dropped, or just plain sound bad. These call quality issues would affect the end-user experience, and you'd end up getting a lot of calls to the help desk to fix the problem - or at least you would, if the phones were working.
Jeff Hicks is a software archetect at NetQoS
Technorati Tags: IT+management UDP TCP RTP VoIP Networking Network+Engineering IT
