marlon,

I have to disagree, and state the opposite.
I've always been a fan of TDD, especially when combined with DSSS to be able to survive the noise, with better SNRs. The problem occurs when DSSS is not enough to get above the noise. When the noise is other OFDM or Wifi contention gear, possibly louder than your own signal, using CSMA/CA actually performs much better in the severe interference environments. The reason is TDD is guaranteed to transmit during the noisy period, some percentage of time. With CSMA/CA the radio waits for FREE time, or at minimum retransmits until it gets FREE spectrum. This can increase latency significantly, but it does reduce packet loss, which is more important.

TDD w/ ARQ, can be even better, provided one has a high end radio, that can be engineered for both ARQ and optimal link quality. But not all ARQ radio can be optimized for best RSSI. I'd take 8 db of higher RSSI, than ARQ, because their is no need for ARQ, if you are adequately above the noise.

Alvarion's strength is it empowers an operator to engineer a more durable link, based on antenna quality and flexibility.



Tom DeReggi
RapidDSL & Wireless, Inc
IntAirNet- Fixed Wireless Broadband


----- Original Message ----- From: "Marlon K. Schafer (509) 982-2181" <[EMAIL PROTECTED]>
To: "WISPA General List" <wireless@wispa.org>
Sent: Tuesday, December 26, 2006 12:46 PM
Subject: Re: [WISPA] Alvarion Comnet Radios have arrived


Got it.  Thanks.

I guess my "beef" comes from being a wifi based wisp. I find it too difficult to reject interference with a csma based product. Anything with a "wait for clear air, then transmit" MAC is GREAT for collocation. But sucks when there are products around that don't follow that mechanism. That's (my personal belief) why Canopy went with it's GPS sync. It doesn't care who's already out there, when it's time to transmit it does. Trango does that to, just without sync'ing the AP's.

My REAL world experience so far is that csmak (or csma/ca, or whatever collision avoidance scheme you want to use) is GREAT where there aren't many other systems within ear shot of the radios. However, when there are other devices in the area, especially those that don't have a collision avoidance mechanism, the csma radio will pay a heavy price in performance.

Having used both csma and polling products, I'm not putting in any wifi type products at 5 gig. All of our next gen products will be polling as long as we can keep things that way.

These days, I'm learning to sacrifice raw performance for reliability and uptime. There's a balance, sure, but getting that last 10 to 20% out of a product is less important to me than having a product that can survive some of the games that my less scrupulous competitors play.

However, with EITHER technology choice, it's critical to design a network that can, and does, physically (antenna choice and ap locations) isolates your system as well as you possibly can. That seems to be the type of trick that just can't be taught. Your network designer either gets it or he doesn't. Heck, I've even done consulting gigs where I looked a guy right in the eye and gave them several choices for site locations. Only to have them pick something completely different, and sometimes unworkable.

80 to 90% of people's problems with wireless are self inflicted. Either outright or in a lack of forethought manner.

Here's an idea for you Patrick. Make this product work both ways. Give it the option to be either csma or some fancy new version of token ring. Then we could optimize performance for any environment that we find ourselves in.

Oh yeah, I remember the big hubbub about GPS in the BreezeACCESS II line. Why was it important for collocation then but not now?

Hope you guys all had a great Christmas!
Marlon
(509) 982-2181                                   Equipment sales
(408) 907-6910 (Vonage)                    Consulting services
42846865 (icq)                                    And I run my own wisp!
[EMAIL PROTECTED]
www.odessaoffice.com/wireless
www.odessaoffice.com/marlon/cam



----- Original Message ----- From: "Patrick Leary" <[EMAIL PROTECTED]>
To: "WISPA General List" <wireless@wispa.org>
Sent: Tuesday, December 26, 2006 9:26 AM
Subject: RE: [WISPA] Alvarion Comnet Radios have arrived


I'd never call you a neophyte, Marlon. A jolly elf maybe, neophyte
never...

CSMA/CA. But the MAC has been substantially altered, especially with 4.0
and the WLP (wireless link prioritization) feature where all stations
can be made to wait while those stations with spooled up voice can
release their packets regardless of where they are in the cell. Also, in
VL an operator can adjust numerous values of the CSMA/CA, such as
contention window duration, contention levels, etc. It is more
sophisticated than your basic polling and more efficient.

Patrick Leary
AVP WISP Markets
Alvarion, Inc.
o: 650.314.2628
c: 760.580.0080
Vonage: 650.641.1243
[EMAIL PROTECTED]

-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On
Behalf Of Marlon K. Schafer (509) 982-2181
Sent: Tuesday, December 26, 2006 9:13 AM
To: WISPA General List
Subject: Re: [WISPA] Alvarion Comnet Radios have arrived

Got that part.  I still didn't see in there anywhere, in plain English
that
a neophyte like me can understand, is this a polling or csmak product?
Marlon
(509) 982-2181                                   Equipment sales
(408) 907-6910 (Vonage)                    Consulting services
42846865 (icq)                                    And I run my own wisp!
[EMAIL PROTECTED]
www.odessaoffice.com/wireless
www.odessaoffice.com/marlon/cam



----- Original Message ----- From: "Patrick Leary" <[EMAIL PROTECTED]>
To: "WISPA General List" <wireless@wispa.org>
Sent: Friday, December 22, 2006 1:54 PM
Subject: RE: [WISPA] Alvarion Comnet Radios have arrived


Marlon, I'll answer this with a re-post of a September post that
explains, in part, why VL is not just regular CSMA:

<<trim>>

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