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There are three factors that significantly impact call quality: latency, packet loss, and jitter. We calculate the jitter using the Inter Packet Delay Variability (IPDV) , see the http://www.slac.stanford.edu/comp/net/wan-mon/tutorial.html#mosTutorial. The jitter defined via IPDV is shown below. the Jitter is realtively distance independent, it measures congestion, has little impact on the Web and email. It decides the length of VoIP codec buffers and impacts streaming.
Most tool-based solutions calculate what is called an "R" value and then apply a formula to convert that to an MOS score. Then the R to MOS calculation is relatively standard. The R value score is from 0 to 100, where a higher number is better. To convert latency, loss, and jitter to MOS we follow Nessoft's method. The graph below shows the Exponetially Weighted Moving Average (using EWMI(i) \ = alpha * EWMI(i-1) + (1 - alpha) * Obs(i), where alpha = 0.7 and EWMI(1) = Obs(1)). EWMI~i~ EWMI i = alpha * EWMI~iEWMI i-1~ 1 + (1 - alpha) * Obs~i~Obs i
It can be seen from the above plot that VoIP ought to be successful between SLAC and the US, Europe, E. Asia, Russia and the Mid East (all above MOS = 3.5). S. E. Asia is marginal, S. Asia people will have to be very tolerant of one another, and C. Asia and Africa are pretty much out of the question in general. It is also seen that the Balkans, Russia and Latin America improved dramatically in 2000-2001. Much of latin America and Russia moved from satellite to land lines in this period.
Afghanistan Afghanistan
PingER has three three sites in Afghanistan that are monititored and they were quite hard to get. For example the Kabul University host is a firewall that does not have stable power and so is usually turned off at night. Also these sites have minimum RTTs greater than 700 ms which indicates that they are all on satellite. The Kabul host is connected via the Silk Roadsatellite that passes through DESY, Germany. The other two are connected via Telia a European ISP. On March 10, 2003, Afghanistan went live on the Web which was previous banned under the Taliban rule. The Internet infrastructure in Afghanistan is immature and the pricing for internet is quite high.
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