Great answer! Priscilla
At 02:01 PM 4/11/02, Kent Hundley wrote: >There are several factors: > >1) Clock rate of the line >2) Buffering delay by any intermediary devices such as ATM/FR switches >3) Speed of light > >If we take a simple case and say that there are no layer 2 devices in the >path and only digital cross-connects. I have read (somewhere) that the >speed of electron transference in copper is a little faster than the speed >of light in fiber over short distance, so use the speed of light in fiber >(roughly .7 X 186,000 miles per second) as the baseline. (note that the >reference given by another poster says the speed of electromagnetic signals >in copper is .66 of the speed of light, which would mean it is slightly >slower than speed of light in fiber, either way its pretty close to a wash) >Given these assumptions you get: > >speed of a single bit = speed of line insertion for 1 bit + speed of light >delay + speed of line removal for 1 bit > >speed of line insertion for 1 bit = speed of line removal for 1 bit = >1/clock rate > >speed of light delay = number of miles / (.7 * 186000 miles per second) > > > >As an example, for a clock rate of 128Kbps and a distance of 1000 miles: > >speed of line insertion and removal for 1 bit = 2 * (1/128000) = .000015625 >sec = .015625 ms > >speed of light delay = 1000 / (.7 * 186000) = .00768 sec = 7.68 ms > >7.68 ms + .015625 ms = 7.7 ms (roughly) > >Again, this assumes no delay in buffering in the path of any kind. It also >assumes that there is no congestion at either end of the link. Bottom line, >keep in mind these are rough numbers, but I think you get the idea. > >HTH, >Kent > > >-----Original Message----- >From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of >Matthew Tayler >Sent: Thursday, April 11, 2002 9:01 AM >To: [EMAIL PROTECTED] >Subject: How fast do bits travel ? [7:41192] > > >Ok I have spent ages trying to find an answer to this question, and probably >only added to my confusion. You know how it is you spend ages looking at >something and become snow blind or get tunnel vision or whatever, but I >cannot see the answer to the following: > >How far does a bit travel in say 1 second or put another way how long does a >bit take to travel a certain distance ? > >I understand, or think I do that if the line is say 128kbps then I can, in >theory at least, expect 128,000 (approx) bits start down that line every >second. > >But how long do they take to reach the other end, assuming a point to point >link and both ends being the same speed, obviously. > >There has to be a nice simple formula for this somewhere, you know the sort >of thing x= line speed, y = distance z = time etc > >Any ideas or poitners would be appreciated > >Thanks ________________________ Priscilla Oppenheimer http://www.priscilla.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=41218&t=41192 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
