IntroductionHere is a very common story. A customer has a data network based on TCP/IP that is working well. He can transfer files and run networked database applications among several locations with adequate speed and efficiency. He can also browse the Web and download files from the Internet.
He installs VOIP devices at each of his sites and connects them to the data network. The voice technology works very poorly. He has intermittent problems with sketchy voice quality, dropouts in conversation, even dropped or incomplete calls. His sturdy data network, which works fine for all kinds of data applications, barely works at all for voice applications.
The difficulty lies in the fact that voice applications require the network to provide some features that are not very important to data applications. File downloads and database programs require every byte to be delivered correctly, but they are flexible with regard to how long it takes to get the bytes from one location to another. Voice, on the other hand, requires the bytes to arrive in a very timely manner, although it is more flexible about losing a few bytes here and there.
In this document, we will address the issues that cause this situation and describe what is necessary to avoid it. These issues are network quality, available bandwidth, and packet competition. We will try to provide the reader with an understanding of what should be considered in planning a VOIP installation so that there will not be any unpleasant surprises.
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