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It is apparent that the MOS is very variable, and according to the middle graph above appears to be decreasing (getting worse) in time (see left hand and middle graphs). Some of this decrease is due to bringing on new hosts that have poorer MOS performance. If we fix on jusr aggregating the performance for hosts pairs that have been monitored for the whole period we get the graph on the right. This set of hosts consists of: PK.NEDUET.EDU.N1, PK.COMSATS.EDU.N2, PK.NCP.EDU.N3, PK.NIIT.EDU.N2, PK.NIIT.EDU.N7, PK.AUP.EDU.N2, PK.PERN.EDU.N1, PK.UET.EDU.N2 and PK.LSE.EDU.N3. In any case the MOS is well above the threshold of 3.5 mentioned above, so VoIP calls within Pakistan between these hosts should be successful.
Alpha
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The speed of light in fibre is roughly _0.66*c_ (where c is the speed of light in vacuum). Using 300,000km/s as c this yields Round Trip Distance = _RTD\[km\]=100\[km/msec\]*minimum_RTT\[msec\]_ as a way to derive the distance between the two hosts making the minimum RTT measurement. This assume the minimum RTT is only affected by the transmission of light in the fibre (i.e. no delays due to network devices such as routers) and that the fibre route is direct (a great circle route) between the two hosts. The use of minimum RTT is meant to eliminate most network device delays for reasonable fast circuits (at 100Mbits/s assuming no queing the router delays is ~ 0.12msec). To accomodate these extra delays one introduces a function alpha, so that _RTD\[km\]=alpha*100\[km/msec\]*minimum_RTT\[msec\]._ Large values of alpha close to one indicate a direct path, and small values usually indicate a very indirect path. This assumes no queuing and minimal network device delays. The chart below shows the alpha values between regions in Pakistan. It is based on the minimum RTTs seen between Dec 2009 and Nov 2010. |
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Average Alpha measured between regions of Pakistan with the standard deviations (as error bars) and the number of host pairs contributing to the measurement |
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It is seen that the links between Karachi and Lahore, Karachi and Islamabad, and Karachi and Peshawar are very direct (values of alpha close to one) and are also very consistent (low values of the standard deviations). Islamabad and Quetta apparently are connected very indirectly (low value of alpha). Looking at the map at the top this makes sense since the route goes via Karachi in the South and then back northwards to Quetta. The links between Islamabad and Lahore, Islamabad and Peshawar and Lahore and Peshawar all have lower vales of alpha and thus appear to be more indirect and have higher variability. A common element in the links between these three regions is that they all pass through Islamabad (see map at top).
Understanding the large variations Jan-Apr 2010
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