08-01-2003, 11:00 AM
|
|
Editor Emeritus
Join Date: Sep 2006
Posts: 3,060
|
|
Slow Lane On The Information Superhighway?
In a paper presented at the Infocom 2003 conference, French researchers say they have identified a problem with standard WLANs that can severely slow down the overall speedof the network.
"Engineering experts at France's Centre Nationale de la Recherche Scientifique (CNRS) in Paris have demonstrated how a slow device connected to WLAN hotspot can cause an entire network to drop to a slower speed, citing a common channel access method as the cause...In other words, when a device with a low bit rate captures the channel, it penalizes other devices using a higher rate by degrading the speed of their connections."
Somebody needs to explain the technical details of their findings to me, but it sounds to me like they're saying that a slow or older wireless device on the network can have the same effect as getting stuck on the autobahn behind a 1956 DeSoto doing 25 mph. The important implication, of course, is that WLANs used by disparate devices, like public WiFi hotspots (or even corporate networks) can be subjected to troublesome slowdowns.
I sure hope that this isn't as bad as it sounds. If word spreads that connectivity can be hampered by a single slug on the system, this could make it even more difficult for WiFi hotspots to gain adoption and earn any real money.
|
| |
|
|
|
08-01-2003, 12:27 PM
|
|
Ponderer
Join Date: Jan 2003
Posts: 50
|
|
I believe (and I could be wrong) that the idea works like this: Connect an 802.11b device to a 'g' access point, and you're down to 'b' speeds across the board. It's the same with most ethernet hubs, where connecting a 10Mbs device to a 10/100 hub will slow the entire network down to the 10Mbs speed.
It makes sense, considering that you'd need to have two discrete wireless tranceivers to theoretically operate two protocalls at one time. I'm sure that someone will come out with a wireless device that acts more like an ethernet 'switch' or 'router', alternating protocalls on a per-data packet basis to deal with the issue... if it doesn't exist already.
However, for most internet purposes, 11Mbs is a pretty decent speed - considering it's faster than most xDSL lines... and, with multiple users connected, the available bandwidth decreases regardless. So you wouldn't get full speed on a crowded public access point anyway.
|
| |
|
|
|
08-01-2003, 12:33 PM
|
|
Contributing Editor Emeritus
Join Date: Aug 2006
Posts: 8,228
|
|
Oh great. That's all we need. Someone with a 66MHz Palm device and a SD WiFi card clogging up the system. :rotfl:
|
| |
|
|
|
08-01-2003, 01:32 PM
|
|
Intellectual
Join Date: Jul 2003
Posts: 221
|
|
Quote:
|
Originally Posted by phanprod
I believe (and I could be wrong) that the idea works like this: Connect an 802.11b device to a 'g' access point, and you're down to 'b' speeds across the board. It's the same with most ethernet hubs, where connecting a 10Mbs device to a 10/100 hub will slow the entire network down to the 10Mbs speed.
It makes sense, considering that you'd need to have two discrete wireless tranceivers to theoretically operate two protocalls at one time. I'm sure that someone will come out with a wireless device that acts more like an ethernet 'switch' or 'router', alternating protocalls on a per-data packet basis to deal with the issue... if it doesn't exist already.
However, for most internet purposes, 11Mbs is a pretty decent speed - considering it's faster than most xDSL lines... and, with multiple users connected, the available bandwidth decreases regardless. So you wouldn't get full speed on a crowded public access point anyway.
|
If this is the 802.11g/b issue (the link isn't working for me so I can't check) then this has been known for some time. - All devices connecting to the same point need to use the same version (a/b/g/whatever). At least one manufacturer is working on a way round this though and we'll probably see more flexible base stations next year. Also I think some devices allow you to force backwards compatibility off, too.
I've also heard of problems with bad/slow devices slowing the whole system down, but I must admit to not knowing the details there or if it's possible to fix.
|
| |
|
|
|
08-01-2003, 01:38 PM
|
|
Neophyte
Join Date: Jul 2003
Posts: 6
|
|
Slow lane
If you are driving a Skoda on the M25 you will be luck to reach 25 mph!
|
| |
|
|
|
08-01-2003, 01:39 PM
|
|
Swami
Join Date: May 2004
Posts: 4,396
|
|
It's Not About Processor Speed
Quote:
|
Originally Posted by Ed Hansberry
Oh great. That's all we need. Someone with a 66MHz Palm device and a SD WiFi card clogging up the system. :rotfl:
|
:lol: Unfortunately (or fortunately), I doubt processor speed has anything to do with it; it's the network speed only. If that 66 MHz Palm had an 802.11g SD card (if and when those exist), the 400 MHz Pocket PC with the 802.11b card would slow it down.
I wondered why a slow-down would occur, and it didn't make sense. Then I thought about it.
If my understanding of networking is correct, when a device sends a packet out, all devices on the network see it, but only the one that it's addressed to will actually process it. However, all devices need to be able to check the TCP/IP header to see if it's for them.
If all of the devices on the network work at the same speed, there aren't any problems. However, if a slower device connects, if the network kept sending data at its maximum speed, the slower device probably wouldn't be able to read its packets. So, in order to allow that device to see its packets, all traffic has to slow down.
Not being a networking guy, though, that's just a guess.
Steve
|
| |
|
|
|
08-01-2003, 02:03 PM
|
|
Contributing Editor Emeritus
Join Date: Aug 2006
Posts: 8,228
|
|
Re: It's Not About Processor Speed
Quote:
|
Originally Posted by Pony99CA
Quote:
|
Originally Posted by Ed Hansberry
Oh great. That's all we need. Someone with a 66MHz Palm device and a SD WiFi card clogging up the system. :rotfl:
|
:lol: Unfortunately (or fortunately), I doubt processor speed has anything to do with it; it's the network speed only. |
I remember reading that the Handspring Visor with an 802.11b springboard card was maxed out at around 700bps because the processor simply couldn't handle data coming in any faster.
|
| |
|
|
|
08-01-2003, 03:09 PM
|
|
Intellectual
Join Date: Feb 2006
Posts: 147
|
|
If the processor can handle the "bandwidth" of the wireless NIC, then the processor wouldn't slow it down. But yes, you could get an older Palm by way of an Ethernet sled that could slow things down.
And an 11MB (actually around 6MB of actual throughput - rest is communications overhead) will sow down a 802.11g access point. You need devices all running at the same level in order to get the maxium throughput (that includes the access point). This is one reason why hubs have all but disappeard from the wired Ethernet world. Everyone uses switches now for reasons like this. Unfortunately, your access point acts like a hub, not a switch, even if it has a switch built-in to it.
|
| |
|
|
|
08-01-2003, 05:33 PM
|
|
Pontificator
Join Date: Jul 2003
Posts: 1,213
|
|
Re: It's Not About Processor Speed
Quote:
|
Originally Posted by Pony99CA
... If my understanding of networking is correct, when a device sends a packet out, all devices on the network see it, but only the one that it's addressed to will actually process it. However, all devices need to be able to check the TCP/IP header to see if it's for them. ...
|
In a non-switched network, that is correct. This is why hubs suck and switches rock.  Switches have an internal buffer that does what's called "store and forward" that buffers the data intended for each port so that the attached device can be fed the data at whatever rate it can accept it. That's why you can have a 10/100 Mbps switch with both 10 Mbps and 100 Mbps devices attached with no decrease in performance. If the slower devices are especially slow, however, even with the data buffer in the switch, some data will likely need to be retransmitted since the buffer will eventually overflow.
As far as a know, all current wireless access points are essentially wireless hubs, not switches, which is why throughput drops when a slower device connects.
-- Dave
__________________
Parenthetical remarks (however relevant) are (usually) unnecessary.
|
| |
|
|
|
08-01-2003, 06:49 PM
|
|
|
|
|
Linear Mode
