Explanation of WDS

[dbcook]

I have seen a few posts, notably bcastner, mentioning WDS but am still having trouble getting my head around this. The concept I'm looking for is.


<----- wireless roaming with no user intervention ----->

\ / \ /
+--+ +--+
+--+ ap1 ap2 +--+
| |
|-----+--------------------------------+-------|
ethernet

Is this what WDS is? bcastner says it is part of the standard but dissappointed in the results. I'd like some clarification on what's wrong with it and what a 2 radio setup will mean to the results when they come along.

Clarfication on these points would be very welcomed by this wireless newbie.

dbc.

 

[bcastner]

You see how in your diagram you have a cabled link to the ethernet backbone for all APs.

The notion of WDS is to remove this requirement. That wirelessly you can have each AP act as both AP and repeater for downstream devices. The fully blown notion of a wireless "Mesh" would impose a repeater role on nearly all devices.

Now the technical problems. Wi-fi is a half-duplex protocol (a device cannot listen and send at the same time, roughly). To make WDS "practical" you either:

. increase bandwidth
. add a second radio

Both of these steps are being developed. Likely the second, (two radios) will appear first (likely by the end of this year), although "SuperG" or "TurboG" products exist that reflect the first approach: increase bandwidth. But they pale in comparison to the standards up for industry agreement now (and FCC and Pentagon approval.

My opinion is that the combination of inexpensive two-radio chipsets, terrific work done on low form factor antennas, and evolving 802.11x bandwidth specifications will completely revolutionize existing cable plant considerations.

See for a good overview of WDS under existing IEEE standards:

http://www.oreillynet.com/pub/a/wireless/2003/08/28/wireless_bridging.html

 

[dbcook]

Ok, I get it.

As for my diagram though, using the backbone. Is this part of the standard and should I expect all AP's or router combos like the WRTG54 to be able to function this way?

dbc.

 

[bcastner]

The Sveasoft WRT54G and WAP54G firmware can implement WDS now.

http://www.sveasoft.com/modules/phpBB2/index.php

But you effectively halve your bandwidth by doing so. I believe d-link and Buffalo offer a repeater role for some of their APs.

Until the two-radio chipset becomes widely used I do not think much attention will be given to WDS.

 

[bcastner]

dbcook,

I reread what I wrote above, and believe a more affirmative answer is necessary.

WDS is possible now with same OEM manufacturer equipment, and often using third-party firmware. But mixed vendor equipment, legacy wi-fi devices, any 802.11b devices, makes it not really ready for introduction in a production setting.

Traditional wi-fi is facing challenges from Bluetooth and similar standards, by the likely industry concordance on powerline devices in the next three months (108 mbs!), and by evolution to higher bandwidth forms of wi-fi up for IEEE approval.

And pushed by the incredible acceptance of cell phones over the last ten years. "If I can make a voice call anywhere, why cannot my d-link router make a reliable connection to my laptop thirty feet away?".

I would not personally recommend a WDS solution at present. I would do, as your original diagram shows, cabled APs. But watch this product space, as this is an extremely hot issue, and there will be at end-year a blizzard of announcements.

Concomittant with the hardware side, there is on the client and server OS side a ton of stuff that has been done by Microsoft for one to accomodate mesh networks. You can see a vivid example in the Wireless Provisioning Service (WPS in Microspeak) as part of Service Pack 2 for XP. (SP2 RC1 Trial:

http://www.microsoft.com/technet/prodtechnol/winxppro/sp2preview.mspx

though wait about two weeks or so for RC2)

Whew.
I just wanted my thoughts to be clear on WDS.

Best,
Bill Castner

 

[bcastner]

dbcook,

I stumbled across this link, and I think while slightly overblown, suggests some possibilities now and in the near future, and recommend the read:

http://www.pbs.org/cringely/pulpit/pulpit20040527.html

 

[dbcook]

Thanks for the advice. Yes, actually I had seen the link ... that's what got me looking for these answers and joinging this forum.

I'll get a better handle on this end of the industry yet!

dbc.