Converged Networks Quality Issues

Telephone Call: "I cannot understand you; your voice is breaking up."

Telephone Call: "I cannot understand you; your voice is breaking up."

Teleconferencing: "The picture is very jerky. Voice not synchronized."

Brokerage House: "I needed that information two hours ago Where is it?"

Call Center: "Please hold while my screen refreshes."

With inadequate preparation of the network, voice transmission is choppy or unintelligible. Gaps in speech are particularly troublesome where pieces of speech are interspersed with silence. In voice-mail systems, this silence is a problem. For example, when 68614 is dialed and the gaps in speech are actually gaps in the tone, 68614 becomes 6688661144, because the gaps in speech are perceived as pauses in the touch tones.

Poor caller interactivity is the consequence of delay. Poor caller interactivity causes these problems:

■ Echo: Echo is caused by the signal reflecting the speaker voice from the far-end telephone equipment back into the speaker ear.

■ Talker overlap: Talker overlap is caused when one-way delay becomes greater than 250 ms. When this occurs, one talker steps in on the speech of the other talker, resulting in a "walkie-talkie" call mode.

Disconnected calls are the worst cases. If there are long gaps in speech, the parties will hang up. If there are signaling problems, calls are disconnected. Such events are completely unacceptable in voice communications, yet are quite common for an inadequately prepared data network that is attempting to carry voice.

Multimedia streams, such as those used in IP telephony or videoconferencing, may be extremely sensitive to delivery delays and may create unique QoS demands on the underlying networks that carry them. When packets are delivered using the Best-Effort delivery model, they may not arrive in order, in a timely manner, or at all. The result is unclear pictures, jerky and slow movement, and sound that is out of synchronization with the image.

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