Video chat requires high quality of service
(QoS) to meet user needs and expectations in
terms of packet loss rate, end-to-end delay, jitter,
and so on. Many standards bodies and industry
organizations have come up with various
classifications of services and associated QoS
parameters; for example, video chat over third
generation (3G), Universal Mobile Telecommunications
System (UMTS) falls under interactive
class with best effort service. Due to its interactive
nature, video chat has very strict timing constraints
and is intolerant of packet loss.
International Telecommunication Union (ITU)
Recommendation G.114 recommends a maximum
delay of 150 ms for video chat in order to
ensure lip synchronization. For “good” to “excellent”
performance, current uplink and downlink
data rate for video chat is in the range ª 130–330
kb/s, which is subject to change with more powerful
devices in the hands of end users.