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 Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=41192t=41192 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: How fast do bits travel ? [7:41192]
In article , [EMAIL PROTECTED] says... 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 It depends on the medium used. The rough calculation for the propagation of an electromagnetic signal in wire is 66% of the speed of light in a vacuum. Or 186000 x 2/3 = 124000 miles/sec. Measurement on Cat5 are very close to this number. Coax is different. More on the order of 55% of the speed of light in a vacuum. If you are very interested in this, check out xxx.lanl.gov/abs/physics/0201053 -- Wes Knight MCT, MCSE, CNE, CCNP, ASE, etc. Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=41197t=41192 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: How fast do bits travel ? [7:41192]
In theory, doesn't electricity travel at the speed of light? 186,000 feet per second, I think. I once read theory that electricity flows through copper more efficiently than light flows through fiber, so the electrical bits would arrive first in a race. I have both interfaces here in the lab... I'll time it this afternoon... (just kidding). Jeffrey Reed Classic Networking, Inc. -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Matthew Tayler Sent: Thursday, April 11, 2002 12:01 PM 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 Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=41198t=41192 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: How fast do bits travel ? [7:41192]
The speed the bits travel should be negligible in comparison with the time it takes the intermediate(routers, switch,...) and end nodes to receive/process the signal. So if you're curious for computational purposes it wouldn;t matter. Electricty in a vacuum travels at light speed. I'm not sure the effect a copper medium would have. It would probably be less due to interference and other electromagnetic influeneces. sam sneed Matthew Tayler wrote in message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... 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 Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=41203t=41192 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: How fast do bits travel ? [7:41192]
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) = .15625 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 Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=41210t=41192 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: How fast do bits travel ? [7:41192]
At 12:50 PM 4/11/02, Jeffrey Reed wrote: In theory, doesn't electricity travel at the speed of light? 186,000 feet per second, I think. Miles per seconds! ;-) As Wes said, The rough calculation for the propagation of an electromagnetic signal in wire is 66% of the speed of light in a vacuum. Or 186000 x 2/3 = 124000 miles/sec. Here's what we'll be saying in our new book. (It is copyrighted, so don't steal the exact wording please, although the concepts are certainly universal! ;-) A signal in a cable propagates at roughly 2/3 the speed of light in a vacuum. The value 0.59c is used for twisted-pair cabling, where c stands for the speed of light in a vacuum, which is 300,000 km/s, or 186,282 mi/s. To determine how far a signal can travel in 1 second, use the following equation: 300,000 km/sec * 0.59 = 177,000 km/sec In 1 second, a signal can propagate 177,000 km. In that same second, there can be 10 million bits on a 10-Mbps Ethernet network. Hence, the electrical energy associated with a single bit stretches out 0.0177 km or 17.7 meters. A single bit is a very long thing on a cable. The mental image that many of us have of bits looking like numerous little box cars in a railroad train, moving along a cable, is not very accurate. The 100-meter cable between a workstation and a wiring closet, for example, contains only about five discrete bits. (By the way, this has some real-world relevance in Ethernet CSMA/CD. You know how you always hear that a single collision domain must not exceed the round-trip propagation delay of a minimum sized-frame, 512 bits? The info above can help you figure out if your network exceeds that or not.) Priscilla I once read theory that electricity flows through copper more efficiently than light flows through fiber, so the electrical bits would arrive first in a race. I have both interfaces here in the lab... I'll time it this afternoon... (just kidding). Jeffrey Reed Classic Networking, Inc. -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Matthew Tayler Sent: Thursday, April 11, 2002 12:01 PM 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=7i=41216t=41192 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: How fast do bits travel ? [7:41192]
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) = .15625 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=7i=41218t=41192 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: How fast do bits travel ? [7:41192]
now if he recited that from memory, we should all just throw in the towel hehe :) I certainly suck at math anyway...reciting some crazy formula to calculate latency would send me over the edge! Priscilla Oppenheimer 04/11/02 02:44PM 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) = .15625 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 Confidentiality Disclaimer This email and any files transmitted with it may contain confidential and /or proprietary information in the possession of WellStar Health System, Inc. (WellStar) and is intended only for the individual or entity to whom addressed. This email may contain information that is held to be privileged, confidential and exempt from disclosure under applicable law. If the reader of this message is not the intended recipient, you are hereby notified that any unauthorized access, dissemination, distribution or copying of any information from this email is strictly prohibited, and may subject you to criminal and/or civil liability. If you have received this email in error, please notify the sender by reply email and then delete this email and its attachments from your computer. Thank you. Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=41219t=41192 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: How fast do bits travel ? [7:41192]
I'm going to chip in both with some simplifying rules and some additional information. I suggest you also read RFCs 2679 and 2544. I will have the first white paper of a performance series available free on Certzone on May 1. now if he recited that from memory, we should all just throw in the towel hehe :) I certainly suck at math anyway...reciting some crazy formula to calculate latency would send me over the edge! Priscilla Oppenheimer 04/11/02 02:44PM 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 Both actual forwarding by the intermediary device plus internal buffering delays. 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: It actually varies among copper cable types. Thick Ethernet is about .66c, while thinwire is about .5 c. A practical approximation for WANs is six microseconds per kilometer of airline distance. In cities, multiply that distance by 3. 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) = .15625 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. Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=41232t=41192 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: How fast do bits travel ? [7:41192]
Not totally true. I will have to look up the formula but there is one for computing delay on a line and it does come into play. I have a large voice network to latin america. You are right the each router adds a chunk - about 20 ms of delay if they are not overloaded, but a line down to Argentina adds almost as much and that is if it is fiber all the way. When you start looking at voice budgets you have to take line delay into account. From: sam sneed Reply-To: sam sneed To: [EMAIL PROTECTED] Subject: Re: How fast do bits travel ? [7:41192] Date: Thu, 11 Apr 2002 13:35:02 -0400 The speed the bits travel should be negligible in comparison with the time it takes the intermediate(routers, switch,...) and end nodes to receive/process the signal. So if you're curious for computational purposes it wouldn;t matter. Electricty in a vacuum travels at light speed. I'm not sure the effect a copper medium would have. It would probably be less due to interference and other electromagnetic influeneces. sam sneed Matthew Tayler wrote in message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... 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 _ Get your FREE download of MSN Explorer at http://explorer.msn.com/intl.asp. Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=41248t=41192 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
