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Chapter 28. Voice Over Internet Protocol > The Special Requirements of Voice

The Special Requirements of Voice

Though voice is just another data application in an IP system, it nevertheless has some distinct requirements. Some unique characteristics set voice apart. These include all of the following:

  • Voice is a real-time application. This means data packets must be processed as they happen in the real world. They do not have the same tolerance for delay and packet loss as other data applications.

  • Data traffic sometimes happens at unpredictable intervals, or “bursts.” Voice, on the other hand, follows a consistent flow and is more predictable.

  • Data transmissions are generally “asymmetrical” because file transfers are typically much larger on the download side than they are on the upload side. Conversely, voice transmissions are typically “symmetrical” because the rate of transfer is almost the same in both directions.

  • An industry concern is the reliability in a migration from traditional PSTN-based voice to packetized voice. It is a critical application (and one people have come to expect rock-solid reliability from). Any voice network, traditional or digital, must provide nearly 100% reliability of uninterrupted service. Voice service must be accessible and predictable to provide the continuity human conversation depends on. In a digital voice network, this continuity requires that digital voice packets arrive in the same order in which they were transmitted and be assembled in proper order. Otherwise, it would not be an accurate representation of the source analog input.


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