Nice synopsis, Phil. I would add that the issue about bandwidth overlap in densly populated areas can be partially mitigated by making sure you select a vendor that has the ability to automatically decrease power to reduce overlap. Some do this, some don't.
-----Original Message----- From: Phil Raymond [mailto:[EMAIL PROTECTED] Sent: Wednesday, November 09, 2005 8:58 AM To: WIRELESS-LAN@LISTSERV.EDUCAUSE.EDU Subject: Re: [WIRELESS-LAN] Wireless-only Dorms? If someone forced me to assign a rule of thumb at this high level, I would assign a conservative data rate of 1 Mbps to each student as a requirement. For an 802.11g ONLY network running at the highest data rate (aka strongest signal) using enterprise class AP's (data thruput does vary between AP vendors, be careful here), you should expect to get 15-20 Mbps of upper layer thruput per AP. That would yield 15-20 students per AP. For 802.11a, this will probably hold. For 802.11g, due to the limit of 3 channels, you will get an overall reduction in capacity due to shared bandwidth between AP's in a densely deployed AP environment. Also, this assumes that you design the network for the highest signal strength - a very important point. In most instances this won't be possible due to the environment. Thus I would reduce the available bandwidth by 33% and say that 10Mbps is available. Hence I would go with the low end of 10Mbps available per AP. To take this to a lower level of analysis, I would want to know what applications the students would be running. Perhaps you use the analogy of a low end DSL connection that provides 768Kbps downlink and 128kbps uplink. Then you stick with the 1 Mbps/student and assume it supports most if not all applications they will use. You might also consider a swag at peak operating times (evenings) and assume ~50% of the available students are online (simple queuing theory assumption). Then you could say that a single AP would cover minimally 20 students. There is my rule of thumb at this high level. I would consider it conservative if you design the network properly. In a typical dorm with a lot of walls (and bookcases...), you will probably find that your coverage requirements and capacity requirements will be in alignment (and thus balanced). What I mean by that is that you will find that in order to provide a good signal in a dorm environment you will need to place a denser AP deployment (due to the thick walls, etc.). This means that as a consequence your capacity will also be increased due to the denser deployment. Other factors not considered here are the use of client cards. Performance between different manufacturers (you get what you pay for) will vary. Some cards will be noisy and interfere, others will have higher SNR requirements, etc. Hope this helps and not confuses - as I said, it is not a trivial subject. -----Original Message----- From: Larry Press [mailto:[EMAIL PROTECTED] Sent: Wednesday, November 09, 2005 9:51 AM To: WIRELESS-LAN@LISTSERV.EDUCAUSE.EDU Subject: Re: [WIRELESS-LAN] Wireless-only Dorms? Phil Raymond wrote: > The initial design needs to consider coverage AND capacity. Phil (and others), Have you got a rule of thumb for the number of students per G access point in a college dorm? Larry Press ********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/groups/. ********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/groups/. ********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/groups/.
