Sunday, November 01, 2020
Words words words words words and more words
Ah, November—a few things come to mind:
- All Hallows Eve is over (did you remember to confiscate your kids' Reese's Peanut Butter Cups?) and it's now All Hallows Day;
- the end of the 2020 Presidential Election season (which means that the start of the 2024 Presidential Election season will start Any Day Now™);
- my favorite holiday of the year is this month—Gobble Gobble Day (woot! can't wait);
- it's the start of National Novel Writing Month, where you have to write a book of 50,000 fictional words (or is it a fictional book of 50,000 words?—I get confused);
- it's also the start of National Novel Generation Month, where you have a computer program write a book of 50,000 fictional words, or real words—it's up to you.
I stopped doing NaNoWriMo years ago, instead switching to doing NaNoGenMo as it's more my style to have a computer do the hard work for me. I was worried that I had no idea what to do for NaNoGenMo, but much to my surprise, I found I left notes to myself for this years NaNoGenMo during last year's NaNoGenMo. I don't think anyone has done this before, so I don't want to give too much away at this time since the idea is (at least to me) very obvious (and no, it's not a novel of 50,000 meows).
What ping times and the speed of light have in common
Back when I was wearing a network admin hat,
about ten to fifteen years ago,
one question I tried answering was how to determine the time it took a network packet to travel one way.
The ping command measures the round trip time:
[spc]lucy:~>ping -c 5 brevard.conman.org PING brevard.conman.org (66.252.224.242) 56(84) bytes of data. 64 bytes from brevard.conman.org (66.252.224.242): icmp_seq=0 ttl=49 time=26.7 ms 64 bytes from brevard.conman.org (66.252.224.242): icmp_seq=1 ttl=49 time=26.1 ms 64 bytes from brevard.conman.org (66.252.224.242): icmp_seq=2 ttl=49 time=26.9 ms 64 bytes from brevard.conman.org (66.252.224.242): icmp_seq=3 ttl=49 time=27.0 ms 64 bytes from brevard.conman.org (66.252.224.242): icmp_seq=4 ttl=49 time=27.1 ms --- brevard.conman.org ping statistics --- 5 packets transmitted, 5 received, 0% packet loss, time 4004ms rtt min/avg/max/mdev = 26.163/26.832/27.161/0.362 ms, pipe 2 [spc]lucy:~>
So,
can one assume that the one way time is a bit over 13ms?
Not really,
because asymetric routing—where the path to a remote destination does not match the path from said remote destination—does exist.
I've seen it happen several times while wearing my network admin hat.
Yes,
you can attempt to synchronize the clocks on the two systems—it's not easy,
but it is possible if you work hard to achieve it.
Over time,
I found it easier to just use the round trip time as reported by ping and assume the path is symetrical.
I was reminded of that when I watched “Why no one has measured the speed of light.” It never occured to me that scientists haven't actually measured the speed of light at 299,792,458 meters per second, but used the round trip time to calculate it and just assume the timing is symetrical because it's impossible to synchronize clocks between two sites (for the purpose of measuring the speed of light). Kind of mind blowing if you ask me.
