John:
Thanks for responding. Two points: - Its not reasonable to ignore retransmits. One of Merus key technology strengths is its claim to pseudo-schedule client access. This reduces retransmits due to collisions. Meru argues (and the last Novarum study appeared to demonstrate) that in dense client situations Merus approach provides a higher aggregate throughput per AP. If you recall one of the first graphics on their web site many years ago was of a chart with the number of clients along the x axis and aggregate throughput along the y-axis. I dont want to ignore the fact that the other vendors involved in Novarums test didnt have an opportunity to optimize their product or want to participate, but not unlike ATM and Token Ring, it appears that Merus approach, in situations of high client density, should outperform the traditional approach. In other words, in the PowerPoint scenario you described, Meru would do better than their competitors. Their competitors would argue that the network should be designed differently .. - More (non-overlapping) channels is almost always better. The enterprise WLAN vendors could stack multiple APs on top of each other, each operating at one or more non-overlapping 5 GHz frequencies, but omni-directional antennas will make channel planning difficult. Xirrus does a nice job of packaging that up, and its directionality increases coverage and limits co-channel interference with neighboring arrays. My summary viewpoint: most enterprise WLAN vendors have been able to avoid the channel-stacking and co-channel interference challenges because actual usage levels have been low, they havent had to worry about it. Theyve been granted a reprieve with 802.11n. While one might be tempted to say that this will catch up on them, I believe that raw speed will continually increase, either through more efficient modulation schemes or smart antenna technologies. Its a little like enterprise-deployed Ethernet we generally dont deploy QoS in our network, it was cheaper to go from hubs to switches, 10 to 100, 100 to 1000 Mps, and later, it will be 10 Gbps. Its a lazy approach, but it deals with usage and service level issue problem 99.99% of the time. Frank From: The EDUCAUSE Wireless Issues Constituent Group Listserv [mailto:[EMAIL PROTECTED] On Behalf Of Jon Freeman Sent: Friday, April 11, 2008 12:52 PM To: WIRELESS-LAN@LISTSERV.EDUCAUSE.EDU Subject: Re: [WIRELESS-LAN] many clients, one room Some math offers insight on this question Assuming the following: · were looking at a single area (i.e. lecture hall), · No retransmits are allowed (not real world, but is a best case example) · were talking about an average sized PPT of 10MB (looking through my PPT folder this was just my average) · Student and teacher expectations of speed is drawn from their homes (i.e. cable and DSL), less than this will be noticed and likely complained about · the rooms average data rate is 54Mbs (10 people by 10 people = 50ftx50ft) · 100 people, all downloading at the same time · max radio density for Meru is 3 (i.e. 3 channels of coverage, this is the most non-overlapping channels you can light in this area without interference problems using their latest gear) · Actual throughput for TCP data is 20Mbs per channel (54Mbs less Wi-Fi management overheads this is a number referred to in the 802.11 spec and one Ive observed many times) · Max radio density available from other shipping solutions today is 15 channels Meru Solution: · 20Mbs x 3 = 60Mbs converting to Bytes /8 = 7.5MB/sec /100 people = .075MB/sec (using 1024KB to the MB, this is 76KB/sec/user of TCP!) · Time to download 10MB/.075MB = 133 sec/user to download a 10MB file (about 2 minutes), so a 40MB file would take ~8min/user . · Link throughput then is 76KBs TCP for each user .you decide if thats acceptable 14 channel solution: · 20Mbs x 15 = 300Mbs · 5 times the bandwidth = 5 times the throughput · 76KBs/user x 5 = 380KBs TCP for each user of link throughput (and this is a little bit better than most uplink speeds on home broadband, <http://www.speedtest.net> www.speedtest.net is what Ive used on many LANs) · Instead of 2 minutes waiting, the 10MB file downloads with this solution in 26 seconds, and about 1 ½ min for a 40MB file, versus 8 minutes. So, we can assume that Franks interviews from 2 years ago dont account for the latest technologies. Sorry Frank, I dont mean to poke holes in your study, but it is 2 years old and we are talking about technology. Didnt we stop trying to manage limited bandwidth when ATM failed? When did we go back to thinking thats ok? I like more power, more speed, better, faster . Jon 303-808-2666 Xirrus Array...the Air is the Network...visit us at www.xirrus.com From: The EDUCAUSE Wireless Issues Constituent Group Listserv [mailto:[EMAIL PROTECTED] On Behalf Of Frank Bulk Sent: Friday, April 11, 2008 10:07 AM To: WIRELESS-LAN@LISTSERV.EDUCAUSE.EDU Subject: Re: [WIRELESS-LAN] many clients, one room Based on research and interviews I performed two years ago, it appeared that for dense client usage in a confined space, Meru was the product most often implemented. These organizations chose Meru because it worked well or better than the competitor. Competitors argued that their product wasnt set up correctly or optimally. Ill let others with production networks pipe in with their experiences. Frank From: The EDUCAUSE Wireless Issues Constituent Group Listserv [mailto:[EMAIL PROTECTED] On Behalf Of Don Wright Sent: Friday, April 11, 2008 9:59 AM To: WIRELESS-LAN@LISTSERV.EDUCAUSE.EDU Subject: [WIRELESS-LAN] many clients, one room I know this has been talked about and debated on this list before, but what are people doing today when faced with a request like the need for 100 students simultaneously downloading a powerpoint presentation". Recently there was discussion on MCA vs. SCA vendors and how each handles this worst case scenario. Since we are an MCA (Aruba), Id be interested in hearing what others have done or are planning for large classrooms and auditoriums. -- Don Wright Network Technologies Group Brown University wire --- less, wi-fi ))) more ********** 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/. ********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/groups/.
