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Technology Stocks : The *NEW* Frank Coluccio Technology Forum -- Ignore unavailable to you. Want to Upgrade?

To: axial who wrote (421)	7/16/2000 2:05:39 AM
From: Jorj X Mckie	Read Replies (1) \| Respond to of 46821

Hi Jim, I've often wondered about this. I've said to myself, 'Surely the responsible bodies have had the foresight to deal with these contention issues.' I'm not so sure any more. It may be the case where unlicensed bands are scarce enough that the responsible bodies just had to go with the compromised contention situations. Of the three unlicensed bands within the ISM Frequencies - 900 MHz, 2.4 GHz, and 5.7 GHz, The 900 MHz band is obviously pretty crowded at this point with the cellular phone applications, and I understand that there are issues with the range for 5.7 GHz. It may simply have been a case of the lesser of all of the evils.

To: axial who wrote (421)	7/16/2000 2:11:20 AM
From: Frank A. Coluccio	Read Replies (1) \| Respond to of 46821

Hello Folks.. I blinked for a moment and when I opened my eyes I find that there's an excellent discussion going on concerning a topic that is going to have profound implications in a year or two, for better or worse, when the whiz kids get there way (and they are, indeed, asking for this) in the WLAN area. As well as IP on everything, follow me telephone over IP, instant messaging, presence, video wrist watches, etc. I've had my moments of trepidation concerning collisions, too, despite the promise of spread spectrum, purely from an intuitive sense that I have on the matter. Of course, I hope that I'm wrong about this. When I was a ham operator a thousand years ago it was okay to be on 40 meters with a million other people who had nothing better to do, because my ear could discern any one of a hundred different correspondents that I normally had contact with, purely from their "fist", i.e., the way they made Morse sound like musical instrumentation, each unique unto themselves. I don't know if any such idiosyncratic signaturization is possible here amongst spread spectrum frequencies that are overcrowded. I know for a fact that there are many discussions now underway among tenants in the same skyscrapers to use wireless LAN. This is an area that could turn out to be a godsend, or a disaster, depending on how reality unfolds.

To: axial who wrote (421)	7/16/2000 4:16:31 AM
From: ftth	Read Replies (2) \| Respond to of 46821

Hi Jim, just a little addendum on the CSMA/CD/CA stuff, to sort out the main differences at a high level: CD doesn't actually avoid collisions; it makes 'em stick out like a sore thumb by broadcasting a jam signal when they are detected so there can be no ambiguity to any station on the LAN that a collision happened. Collisions are a normal part of operation and (barring a massively overprovisioned collision domain or flakey hardware) normal operation continues immediately following the collision. CD can't really be used in the wireless case, in general, because not every station can "hear" every other station (unlike a LAN collision domain). For example, say station A is on the north side of a building and is transmitting to a base to the north. Say station B is located south and west of station A, sending to the same base. It's quite possible that neither A or B can hear each other. That's just a simple case. Any given station would have to be able to hear every other station in order to be able to unambiguously detect any collision (this is not completely true but I'm being general). This is why CA is used, rather than CD (CA essentially is a handshake for a station to claim the channel for a specified period, granted by the base, or receiving station). There's more to it, but this is the general idea.