A few issues: - They don't factor the time the opto-electrical converstion takes at each hop. - They don't factor queueing and buffering in any devices - The

A few issues: - They don't factor the time the opto-electrical converstion takes at each hop. - They don't factor queueing and buffering in any devices - They assume the router was able to instantly generate the TTL exceeded message at each traceroute hop. - They don't seem to consider that the return path might be going via Japan with a hop through France, which won't show on the traceroute at all. - They assume each non-passive device on the path will show in the traceroute (this isn't true, L1/2 devices won't show, technologies like MPLS can obfuscate entire network cores). In terms of how fast light moves in single-mode fibre it's fairly constant, the variance here ins't to do with the fibre.