North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Re: Network Sizing Guidelines?
These guidelines will be badly misleading if you have serious streaming use, where K, T and P are basically undefined or irrelevant. BTW, I have asked numbers of people about the underprovisioning (or oversubscribing) they use, and have received responses ranging from a factor of 5 to a factor of 20 or more. Regards Marshall Eubanks Irwin Lazar wrote: > > I'd recommend taking a look at: Wide-Area Data Network Performance > Engineering By Cole, Robert G. / Ramaswamy, Ravi > ISBN: 0890065691 > > Here is a guideline based on Ravi's methodology that I wrote for our > customer newsletter some time ago: > > The bandwidth size that is required for any given connection is a function > of the following three factors, number of users, requirements of specific > applications, and how the application is used. For example, a site with five > users that all access a highly interactive application for twelve hours per > day may require more bandwidth than a site in which a dozen users > sporadically access a client-server application in which most of the > processing is performed by the remote server. > > In addition, another concern in the bandwidth selection process is delay. > Certain applications such as voice and video may require a low level of > delay (latency) as well as a low variability in delay (jitter). These > requirements may add significant complexity to the design process. > > The first step in sizing bandwidth is to determine the requirements for the > specific applications that will be deployed. During this step, a sniffer is > useful in tracing application sessions to determine the average packet size > and the average number of packets for a given transaction. Once you have > these values, the next step is to factor in the number of users, the > required latency, and the amount of time that typically exists between > transactions. > > Once you have obtained these values, you can use the following formula > (created by Ravi Ramaswamy of AT&T Solutions) to determine bandwidth > requirements: > > 8 x N x K x M / (K x P + T) Where: > > N = number of active users at a location (the number of users that will > simultaneously use an application) > > T = User think time (how much time typically exists between inquiries > > K = number of packets per transaction in any given direction > > M = number of bytes per packet in any one direction > > P = one-way network latency > > Note that this calculation must be performed for both directions of the > connection. The required bandwidth is then the maximum bandwidth estimated > by this formula (unless you are deploying a technology such as Frame Relay > which allows for different bandwidth allocations for each direction of the > connection). > > Note also that this formula only applies to client-server type applications > in which there is a substantial amount of two-way traffic. For additional > information on bandwidth sizing, please see "Optimizing Client-Server > Application Performance on the WAN" in the November issue of "Network > Magazine." > > ----- > Irwin Lazar - [email protected] <mailto:[email protected]> > Senior Consultant, The Burton Group > Office: 703-742-9659 > Cell: 703-402-4119 > http://www.tbg.com/ > "The Ultimate Resource For Network Architects" > > -----Original Message----- > From: Daniel R Glover [mailto:[email protected]] > Sent: Friday, March 02, 2001 5:00 PM > To: [email protected] > Subject: Network Sizing Guidelines? > > Can you point me to some current network sizing advice for Internet service > (WAN and LAN)? I am looking for rules-of-thumb, guidelines, equations, > books, or even anecdotal evidence that would help me in evaluating future > network design concepts. I have somewhat unconventional network > constraints, but I would like to start from current conventional > assumptions on, say, numbers of users (home or office) that can be > supported by various bandwidths. > > I've tried the related links off the NANOG pages, but some are old or > broken. I have found some advice like "a T1 will support 200 to 300 28K > modem users," but I hope there may be more current advice somewhere > especially with regard to QoS, future trends, and to larger networks. Any > relevant pointers or advice would be welcome. > > R/ > Dan Glover -- Multicast Technologies, Inc. 10301 Democracy Lane, Suite 410 Fairfax, Virginia 22030 Phone : 703-293-9624 Fax : 703-293-9609 e-mail : [email protected] http://www.on-the-i.com
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