Scientific Measure of Africa's Connectivity Page: 4 of 14
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acceptable, 2.5%-5% is poor, 5%-12% is very poor, and greater than 12% is regarded as bad.
Our observation is that above 4-6% packet loss video conferencing becomes irritating and
speakers of the non-native languages are unable to communicate. Above 10-12% packet loss
there is an unacceptable level of back-to-back loss of packets and long timeouts, TCP connec-
tions start to get broken, and video conferencing is unusable. These values are reinforced by
ITU studies of the impact of loss on voice conversations .
The RTT is another indicator of the quality of a link. However, unlike packet loss,
where it is possible to reduce losses to zero, it is impossible to reduce the RTT to less than the
time taken for information to travel the distance along a fiber or copper cable or wirelessly
(e.g. to a satellite and back). In addition to the cable or wireless delays, the measured RTT is
the time taken for the packet to be accepted by the router interface, the delay caused by the
queuing, and the time taken for the packet to be passed to the outbound interface. The mini-
mum RTT thus usually indicates the length of the route taken by the packets, the number of
hops, the line and router speeds. Increasingly as speeds of routers and links increase, the main
effect on minimum RTT is the aggregate distance of the links in the path. Changes in the
minimum RTT can be an indication of a route change. The major effect of poor response time
is felt on interactive applications such as telnet or 'packetized' video or voice, where even a
moderate delay (e.g. ITU studies show that RTTs of over 250-300ms result in interactive
voice participants having difficulty to know when the other person has finished speaking) can
cause severe disruption. Applications that do not require such a level of interactivity, such as
e-mail and web browsing, may appear to perform well even with high delay.
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Zennaro, M.; Canessa, E.; Sreenivasan, K. R.; Rehmatullah, A. A. & Cottrell, R. L. Scientific Measure of Africa's Connectivity, report, April 24, 2006; [Menlo Park, California]. (digital.library.unt.edu/ark:/67531/metadc885520/m1/4/: accessed October 17, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.