Configuration for the WAN experiments
The traffic generator was run on the Video Clip Server (VCS) to generate traffic for the throughput measurements. It was configured to generate a load of 10 Mbps to measure the performance under saturated conditions. The sink program was run on the the Ultra 1 (the ERG test machine with 100 Mbps interface) to receive data and to take measurements.
A higher variation in throughput capacity was observed than that in the LAN. The throughput measurements varies between 6154.87 kbps and 8786.60 kbps with a mean value of 6871.45 kbps and a standard deviation of 670.60. This is consistent with a WAN built using links which are shared with other users (although the network was very lightly loaded during the test).
An application which aware of the limited network resources may generate a lesser load then maximum network capacity to optimise the performance for the application (e.g. a video application may use an encoder to generate a load at 2 Mbps).
The round trip delay between the VCS and ERG was measured as 2 ms using ICMP (ping). This values is probably accurate to ± 2 ms (the accuracy of the host course grain timer).
True delay measurements can only be made at a specified load less than the network capacity. (Increasing the load above the network capacity results in queue build-up or congestion). The aim of the next set of experiments is therefore to study the quality of a UDP data stream at 2 Mbps. One of the key parameters is not the absolute delay, but the relative delay from packet-to-packet or the medium-term delay variation.
Variation of packet interarrival time for a UDP source from VCS to ERG carried over the shared campus network (lightly loaded). The source was 2 Mbps of UDP data. The packet loss rate was 0.01% for 1500 B packets. Vertical and horizontal axes in Seconds.
Variation of delay for a UDP source from VCS to ERG carried over the shared campus network (lightly loaded). The source was 2 Mbps of UDP data. The round trip delay was independently measured as 2 ms using ICMP. Vertical and horizontal axes in Seconds.
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