Some math offers insight on this question...

 

Assuming the following:

 

·         we're looking at a single area (i.e. lecture hall), 

·         No retransmits are allowed (not real world, but is a best case 
example)

·         we're 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 room's 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 
I've 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 
that's 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, 
www.speedtest.net <http://www.speedtest.net>  is what I've 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 Frank's interviews from 2 years ago don't account for 
the latest technologies.  Sorry Frank, I don't mean to poke holes in your 
study, but it is 2 years old and we are talking about technology.

 

Didn't we stop trying to manage limited bandwidth when ATM failed?  When did we 
go back to thinking that's ok?

 

I like more power, more speed, better, faster....

 

 Jon

303-808-2666

Xirrus(tm) Array...the Air  is the Network(tm)...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 wasn't set up correctly or optimally.  

 

I'll 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), I'd 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/.

Reply via email to