| This paper is not about network simulation, but about empirical
measurements of network metrics (latency and bandwidth) using a
public domain tool called pathchar. It is TCP/IP specific.
As such it provides useful data for building a test network, and
as a comparison for simulation results.
The round trip time (rtt) of a packet from a to b is measured by sending
packets to b and decrementing the time to live (ttl) value until the
packet gets rejected by b, and a ICMP error message is returned. This is done
for packets of all sizes.
rtt = queue_1 + (lat + packet_size/bw) + queue_2 + forward_time + queue_3
+ (lat + error_size/bw) + queue_4
By sending enough packets, we assume that eventually some packets will
pass with negligible queue times. forward_time is assumed to be negligible.
error_size/bw is assumed to be negligible.
So:
rtt = (lat + packet_size/bw) + lat
This gives practical measurements of bandwidth and latency.
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