Jon,
Given that the clients make all the decisions, how can we
assure, given 14 channels, that the users will equally balance
themselves across all 14, rather than bunching up?
Wilson
Jon Freeman wrote:
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**™** 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:* [email protected]
*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:* [email protected]
*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
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