Scientific Measure of Africa's Connectivity Page: 3 of 14
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High Energy Physics (HEP) experiments in the mid-90's. The technique involves sending out
a pulse, that is echoed back at the remote host, and timing the Round Trip Time (RTT). The
monitoring has low network impact and can be used for hosts with especially poor connec-
tivity. The resulting monitoring information is in the public domain. Today more than 750
remote sites are being monitored worldwide, more than 45 of them in Africa .
PingER (Ping End-to-end Reporting) is the name given to the IEPM project to monitor the
performance of Internet links. The main mechanism used is the Internet Control Message Pro-
tocol (ICMP) echo mechanism, also known as the Ping facility . ICMP packets are special
IP control messages that are used to send network information between two hosts. The Ping
facility allows sending an echo request packet of a user-selected length to a remote node and
having it echoed back. The response provides useful information such as the RTT it took to
get a reply, the variability of response time (jitter), the number of packets that were lost,
whether the packets were received in order, whether the remote site is reachable (no response
for a succession of pings) and so forth. Ping usually comes pre-installed on almost all plat-
forms. The server (i.e. the echo responder) runs at a high priority (e.g. in the kernel on Unix)
and so is more likely to provide a good measure of network performance than a user applica-
PingER has a very low network impact of less than 100 bits/second for each monitor-
ing-remote host, and can be set to less than 10 bits/second for hosts with especially poor con-
nectivity. It also provides end-to-end network information (as opposed to how well some part
of the network such as a backbone is working) and so should be closely related to end-user
There are over 750 remote sites in more than 123 countries being monitored by over 30
active monitoring Sites in 14 countries. These countries contain over 80% of the world's
population and over 99% of the online users of the Internet. Most of the hosts monitored are
at educational or research sites. PingER has historical data going back to January 1995, so a
wealth of trend information is available .
The Packet Loss is a good measure of the quality of the link for many applications. Loss
is typically caused by congestion which in turn causes queues (e.g. in routers) to fill and
packets to be dropped. Losses may also be caused by the network delivering an imperfect
copy of the packet. This is usually caused by bit errors in the links or in network devices.
When we get a zero packet loss sample (a sample refers to a set of n pings2), we refer to the
network as being quiescent or non-busy. We can then measure the percentage frequency of
how often the network was found to be quiescent. A high percentage is an indication of a
good network. This is particularly true for interactive applications, such as video conferencing
and audio chat, which require a low packet loss percentage, and is also true for bulk data
transport applications since losses cause long delays for timeouts etc. The loss levels that we
use to describe the link quality are the following: 0-1% of packet loss is good, 1%-2.5% is
The default value for n is 10.
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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/m1/3/: accessed October 16, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.