WEEK 10

FACTOR EFFECT OF VOICE QUALITY

Delay is caused when packets of data / voice take more time than expected to reach their destination. This causes some disruption in the voice quality. However, if it is dealt with properly, its effects can be minimized . 
Delay mainly comes from three components :

1.  delay caused by voice codec algorithms 
2.  delay caused by queuing algorithms of communications equipment
3.  variable delay caused by various factors(i.e. network conditions, VoIP equipments, weathers etc).

It is very important to minimise the voice traffic delay. Thus, a codec algorithm and queuing algorithm needs to be carefully considered. High QoS should be assured by control delay so that one-way communication delay should be less than 150ms. (ITU states that one-way, end-to-end telephony applications should have less than 150ms delay in echo-free environments to ensure user satisfaction). Although traditionally think the end-to-end delay of 150 ms was considered as acceptable for most applications.
However, in reference [James, 2004], the authors state that a delay of up to 200ms is considered as acceptable. Moreover, a one way end-to-end delay between 150ms to 400ms is considered as acceptable for planning purposes. In this study, 200ms will be considered as the maximum acceptable one way end-to-end delay, high end-to-end delay can cause bad voice quality perceived by the end user.