By the way, I was in a hurry when I wrote my answer. I would just like to mention that testing latency with pings, as I mentioned below, is an over-simplification. You can get false results for many reasons, including rate-limiting of ICMP on routers, etc.
You should test with the application that you are concerned about. We had a similar discussion a couple months ago. I think it was nrf or maybe dre (I get them confused) who wrote a good reply about testing latency. Or was it Peter or Howard? Anyway, check the archives. This question comes up often. Priscilla Priscilla Oppenheimer wrote: > > Mirza, Timur wrote: > > > > does anyone have a good reference (e.g., white paper) on the > > nature of > > bandwidth vs latency & the distinction bet/ the two? > > Well, the distinction is easy. They don't mean the same thing > at all. A good site is Merriam Webster's online dictionary. The > 2nd definition for bandwidth is: > > Bandwidth: the capacity for data transfer of an electronic > communications system > > Latency, on the other hand, means delay. Websters isn't too > helpful in this case, but might help you understand the origin > of the word, which is related to dormancy. > > Cisco's Terms and Acronyms document has a couple definitions of > latency, which are somewhat helpful: > > 1. Delay between the time a device requests access to a network > and the time it is granted permission to transmit. > > 2. Delay between the time a device receives a frame and the > time that frame is forwarded out the destination port. > > Those definitions allude to the many contributors to delay > (latency) on a network: > > * media access time > * queuing time at internetworking devices > * processing time at internetworking devices and at the sender > and receiver > * serialization delay to send and receive bits at the rate > specified by the bandwidth of the sending and receiving > interfaces > * propagation delay which is distance dependent and to a > certain extent medium dependent, although most media support > about 2/3 the speed of light > > Testing latency is reasonably easy. Just do some pings. > Predicting, modeling, and simulating delay is advanced > engineering. A few books cover it at a very basic level, > including Top-Down Network Design by Oppenheimer, and Data > Network Design by Spohn. > > Howard Berkowitz has written some RFCs that discuss performance > measurement, if I recall. > > There are graduate level computer science classes that cover > performance measurement in computer networks at many > universities. > > And, finally, you can get some info from white papers written > by vendors who sell modelling software. For example, try > http://www.netpredict.com/ and http://www.opnet.com/. > > _______________________________ > > Priscilla Oppenheimer > www.troubleshootingnetworks.com > www.priscilla.com > > > > > > Timur Mirza > > Principal Network Engineer > > Network Planning & Engineering, West Region > > 15505-B Sand Canyon Avenue > > Irvine, California 92618 > > Verizon Wireless > > 949.286.6623 (o) > > 949.697.7964 (c) > > > > > > Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=57945&t=57899 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
