On Thursday 03 July 2003 06:23 am, John Tomany <[EMAIL PROTECTED]> wrote: > [...] > > Wouldn't that be the cat's meow? Physically they look ideal: rj45 > > jack on one end, bnc male coupling on the other. And they're small > > and not too expensive (in the $5 range). But the thing that > > confuses me is that there are other things advertised to convert > > 10 base2 to 10 baseT for 10 to 20 times the cost. Here's an > > example, snipped from the 'net:
The more expensive items probably WORK. A balun won't. Baluns can be used to provide MEDIA conversion -- usually to help with grounding issues on older technologies -- but doesn't "translate" 10Base-2 (coax) ethernet to 10Base-T (Unshielded Twisted Pair -- UTP) in any way. > [...] > I've never quite understood why the networking industry chose to > forego the huge bandwidth advantages of coax for the twisted-pair > varieties - except, of course, to boost profits from cheaper > materials. Coax MEDIA can carry more when used with BROADBAND technologies (i.e. RF, Cable TV). Ethernet does use coax (both "thick" and "thin"), but was still limited to 10Mbps. ARCnet used coax and capped at 2Mbps (though it belatedly got to 20 IIRC). Ethernet was ALWAYS meant as a "low cost" (relatively) technology. > The twisted-pair stuff uses "current-mode" amplifiers, which aren't > well suited to either simplex signaling (where signals travel both > directions in single coax or a pair) or the occasional "collision". Again, they were meant to be "cheap" and not much else. Another consideration is reliability though. Coax -- as used in 10Base-2/thin ethernet -- is a BUS, which runs through each intermediate node. At each node, there are THREE connections: One to each neighbor (or a terminator), and one to the PC itself. 10Base-5/thich was even more complex. With this many connections, cables were always an issue. I spent many an unhappy hour moving a terminator from station to station trying to find the faulty connector. One good twist in the cable could bring down the entire network. Along with a move to cheaper media, 10Base-T (UTP in general) also introduced a hub layout, which was (generally) easier to maintain. If a station wasn't working, the problem tended to be easily isolated. Not bulletproof of course, but definitely "easier". > Thus, most of the current windoze-style products use two pairs > - one for output, one for input: they use duplex transmission. There is nothing "Windoz" about UTP, or modern networking technology. It was developed quite independently of Windows, although MS has certainly dipped their paws into making PRODUCTS propriertary and closed. But the rise of 10Base-T predates Microsoft's market dominance on the corporate network. Still, there were perfectly good technological reasons why UTP was chosen, and the fact that they're now getting 1Gbps speeds over essentially the same media (when properly terminated etc. of course) has borne those decisions out. > The balun devices just combine them (via transformer) into the > single, simplex, coax connection. The network cards must then > either be able to detect/correct collisions, or to setup for > simplex (versus duplex) transmisions. They don't though! They COULD perhaps, but THEY DON'T. > In a windoze world, where the user isn't permitted to know anything > about what their hardware is doing, it is becoming increasingly > harder to change the hardware settings from the defaults which > either mickeysoft or the computer manufacturer desire. True, and that's one of the criteria one should use in selecting products. And particular care should be taken to ensure that the card will work with the OS of choice. The good news is that there are lots of quality products available cheaply that work with most. > (And I'm sure that in at least some cases, the cheap net cards or > motherboard-based networking CAN'T be changed!) It's one way for > the manufacturer to claim his equipment is "twice as fast" (duplex) > as other methods (simplex). The STANDARDS set the speed limits for ethernet. There's "half-duplex" and "full-duplex" for 10Mbps. Most switches and NICs these days work at full-duplex (which is a good thing). You are correct that the ability to alter settings varies among manufacturers, and getting full features sadly IS dependent on OS (Windows, natch) BUT there are also LOTS of alternatives for the informed consumer. > In reality, the coax often has a hundred times the possible bandwidth > compared to twisted pairs - but the chips on each end are the > limiting factor. And cost! Coax works well for cable broadband Internet offerings because the complexity stays in the provider's network. The user still only has to buy a cheap ethernet card in most cases. It's true that coax as media has more POTENTIAL bandwidth, better distance, etc. than UTP. The move to UTP and away from the old bus topology (layout) was a blessing for anyone doing networking. Things got cheaper, installs became more flexible, and troubleshooting became much more straightforward. Although I'm all for using old equipment (and I still have 10Base-2 gear around), I wouldn't necessarily RECOMMEND it unless other options weren't viable. - Bob To unsubscribe from SURVPC send a message to [EMAIL PROTECTED] with unsubscribe SURVPC in the body of the message. Also, trim this footer from any quoted replies. More info can be found at; http://www.softcon.com/archives/SURVPC.html
