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A VoIP System is
often associated with bandwidth savings and reduced cost. However, since
this is a relatively new technology, there are many quality related
issues to be dealt with. Many of these issues arise owing to the use of
packet switched networks.
A significant problem that is associated with a VoIP system is
the delay in packet transmission. This delay results in echo and talk
overlaps. An echo is usually caused if the round trip delay of the
signal from the destination back to the source is more than 50
milliseconds. In packet switched network, given the number of routers
and networks a voice packet has to traverse, the delay can be
considerable for long distance calls. Modern VoIP systems
therefore implement echo control and cancellations methods to deal with
the problem. Another problem caused with packet delays is talk overlaps.
This problem occurs if the packet delay in any direction exceeds 250
milliseconds.
Apart from delays, another problem associated with VoIP networks
is jitter. Jitter is caused by the inter-packet delay in the network.
This causes distortion in the talks. Jitters can be minimized by holding
the packets until the slowest packets arrive at the destination. This
can however increase the delay in playing the voice. Various approaches
are being tried at to compromise between delays and jitters.
Another severe problem affecting a packet network is packet losses. IP
networks usually have high incidences of packet loss as compared to ATM
networks. During peak traffics, the problem of packet losses can be
enormous. Data packets can be retransmitted, but in case of voice
packets a different approach is required. Some of the solutions proposed
for solving this problem include replaying the last packets until new
packets arrive, sending redundant information to compensate for the
loss, and a hybrid approach combining the previous two methods.
Article Information
This article is written
for AccessDirect, providers of Unified Messaging, Voice Mail, and
VoIP PBX Phone systems. Visit us at www.messagingservice.com
source: goarticles.com
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