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The difficulty of the installations has varied host from site to hostsite. The technical installation of the software etc. has been simple and not resulted in delays. The delays between deciding to install a monitoring host and gathering measurements from the host have mostly been due to: machine availability; getting administrative approval within university;getting access to the concerned local people, and delays in making the DNS record entry. Note we still do not have a DNS entry for the Lahore School of Economics, and had to enhance our software tools to accommodate this. Problems once it starts taking data are poor power availability, lack of backup power and access to the site when there are problems that needs physical access. The table below shows the history of the installation and remarks concerning the difficulty of installation and the reliability of the host:
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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 (e.g. at 100Mbits/s assuming no queuing 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. Spreadsheet |
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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 PERN backbone map at top).
Conclusions
Acknowledge
We acknowledge the patient and persistent efforts by Kashif and Fahad Gilani of NUST to spearhead the installations of PingER at the various sites. The PingER map tool was developed by Faisal Zahid while at SLAC and turned out to be extremely effective in drilling down and understanding the connections. The Smokeping tool was developed by Fahad Satti while at SLAC. We also acknowledge the continued encouragement and support from Arshad Ali of NUST.