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 - ilazar@tbg.com <mailto:ilazar@tbg.com> 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:Daniel.R.Glover@grc.nasa.gov] Sent: Friday, March 02, 2001 5:00 PM To: nanog@merit.org 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