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What Factors Determine the End Users' Qo... > Packet Loss Ratio - Pg. 17

What Factors Determine the End Users' QoS Perception? 17 talking over a satellite link, the delay is usually long (for example, 400 ms). However, if delay variation is small, the talker can estimate how long it will take the listener to hear him or her, and determine whether the listener wants to talk or listen. The talker can then decide whether to continue talking or switch to listening. Consequently, although the delay is long, the conversation can go on. In contrast, if the delay variation is large, then after talking, the talker would not know whether the ensuing silence is caused by an unusually long delay, or is an indi- cation that the listener wants to continue listening. The talker can only guess, and if the guess is wrong, the talker and listener will end up either interrupting each other or waiting for each other to talk. Either way, the communication will become difficult. Different applications have different requirements on delay variation. This will be further discussed later in this chapter. Generally speaking, end-to-end delay variation below 50 ms would ensure good service quality even for delay variation- sensitive applications. Some applications don't have significant delay variation requirements. Like delay, delay variation must be measured. [InterQoS] recommends the fol- lowing measurement method: