nanog mailing list archives
Re: NANOG
From: Wolfgang Henke <wolfgang () whnet com>
Date: Wed, 3 Apr 1996 10:09:10 -0800 (PST)
bob_metcalfe () infoworld com (Bob Metcalfe) wrote: Perhaps I am confusing terms here. How can it be a fact that "store-and-forward delays are a mere fraction of wire propagation delays?" I don't think so. Check me on this: Packets travel over wires at large fractions of the speed of light, but then sadly at each hop they must be received, checked, routed, and then queued for forwarding. Do I have that right? Forget checking, routing, and queueing (ha!), and you get, I think, that store and forward delay is roughly proportional to the number of hops times packet length divided by circuit speed (N*P/C). For 10 hops of a thousand bit packet at Ethernet speed, that would be 1 ms, or a couple hundred miles of prop delay. Check me on this, one of us might be off by several orders of magnitude. Hmm... Using a real in use backbone of one of the mayor service providers, I find that a DS3 between silicon valley to Chicago has a 44 msec latency going through 4 hops. That's about the speed of light in fiber for the 5000 mile roundtrip ICMP ping packets. Using ATM will reduce the router latency. I estimate that with TCP/IP over ATM over SONET OC-3c the latency will be reduced from 44 msec to 40 msec, only a rather small improvement. The bandwidth used on the fiber wont matter much. With OC-12c I would still expect 40 msec or so since the speed of light in fiber is the limiting factor. Wolfgang
Current thread:
- RE: NANOG Bob Metcalfe (Apr 02)
- RE: NANOG Michael Dillon (Apr 02)
- Re: NANOG Paul Frommeyer (Apr 02)
- Re: NANOG Jeremy Porter (Apr 03)
- Re: NANOG Craig A. Huegen (Apr 04)
- <Possible follow-ups>
- RE: NANOG Stan Barber (Apr 02)
- RE: NANOG David C. Kovar (Apr 02)
- RE: NANOG Vadim Antonov (Apr 02)
- RE: NANOG Bob Metcalfe (Apr 03)
- Re: NANOG Bilal Chinoy (Apr 03)
- Re: NANOG Wolfgang Henke (Apr 03)
- RE: NANOG Jeff Ogden (Apr 03)
- RE: NANOG Michael Dillon (Apr 03)
- RE: NANOG Vadim Antonov (Apr 03)
- Re: NANOG Bob Metcalfe (Apr 04)
- Re: NANOG Hank Nussbacher (Apr 06)
- Re: Bob Metcalfe Edward Henigin (Apr 06)
(Thread continues...)
- RE: NANOG Michael Dillon (Apr 02)