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Electronics Forum / Electronics / March 2009Why do we have cross-over cables.
Or maybe the question should be why do we have cables that are not crossover. My first encounter with this concept came when connecting serial ports together. Turned out there were two kinds - data set, and data terminal. Not content with that, when UTP cables came out, we had a similar situation. Maybe I've missed something, but it's always seemed to me that a logical approach would be to define some pins as input and some as output, and for cables to connect input pins to output pins, thus obviating the need for two different ways of wiring up connecting cables. Did I miss something? Is there a reason this situation persists? Sylvia. > Or maybe the question should be why do we have cables that are not > crossover. [quoted text clipped - 11 lines] > > Did I miss something? Is there a reason this situation persists? Consider the case when you want to connect two of the same type together. For example, a normal PC is considered a data terminal. If you want to connect two together, the transmit pins on one must connect to the receive pins on the other. Hence the crossover cable, often called a "null modem" for the serial cable case. The same reasoning applies to CAT5 cables, but in this case there are a total of four pairs, two transmit and two receive. Both sets are not always used, but the ones in use must be "crossed over" to connect two of the same type equipment. Many routers can sense the type of cable required and will automatically do the crossover internally if required. Hope all this is not too confusing. :-)  SignatureVirg Wall, PE >> Or maybe the question should be why do we have cables that are not >> crossover. [quoted text clipped - 17 lines] > to the receive pins on the other. Hence the crossover cable, often > called a "null modem" for the serial cable case. If the transmit and receive pins on a data set (typically a modem) were transposed in the original design, then the same cables could have been used in all cases. > The same reasoning applies to CAT5 cables, but in this case there are a > total of four pairs, two transmit and two receive. Both sets are not > always used, but the ones in use must be "crossed over" to connect two > of the same type equipment. Many routers can sense the type of cable > required and will automatically do the crossover internally if required. Ditto. Sylvia. > >> Or maybe the question should be why do we have cables that are not > >> crossover. [quoted text clipped - 21 lines] > transposed in the original design, then the same cables could have been > used in all cases. They were. >If the transmit and receive pins on a data set (typically a modem) were >transposed in the original design, then the same cables could have been >used in all cases. Serial cables are pin for pin. This makes creating one an easy process with low error rate during assembly, which was ALL by hand at that time. Switching the gear was far more reliable than switching cable conductors around, and counting on low paid assemblers to do so consistently. And that's a fact, Jack. >> The same reasoning applies to CAT5 cables, but in this case there are a >> total of four pairs, two transmit and two receive. Both sets are not [quoted text clipped - 3 lines] > >Ditto. Same reason. MAKING an RJ-11 cable is easier if the crimped on connector is wired the same way ALL the time. Especially during field service scenarios. The error rate in cables is much higher if specific cross-overs have to be made from end to end. Also, one would need to observe the one completed end to reference what would be needed on the other end. Doing them all the same practically guarantees success. Requiring cross-over practically guarantees a much higher prime pass yield in manufacturing circles, and a higher failure rate in field installations as well. And that's a fact, Jack. >>> The same reasoning applies to CAT5 cables, but in this case there are a >>> total of four pairs, two transmit and two receive. Both sets are not [quoted text clipped - 12 lines] > yield in manufacturing circles, and a higher failure rate in field > installations as well. OK, I can accept the field installation error issue, though the existence of two different standard ways of wiring the plugs seems at least partly to defeat the goal of reducing errors. I'd have thought that in a mass-production environment it would be as simple as having one person do one end and another person do the other end. Sylvia. >>>> The same reasoning applies to CAT5 cables, but in this case there are a >>>> total of four pairs, two transmit and two receive. Both sets are not [quoted text clipped - 21 lines] > >Sylvia. You still do not understand. When these standards were made, and when such production began "mass production" was individual hand assembly, and regardless of who does which end (passing it off to another wastes yet more time), other than pin for pin wiring can and does increase prime pass yield failure rates. If the wires change, the error rate goes up. If ALL assemblers wire ALL cables the same on ALL ends, the likelihood for error decreases exponentially, because they all learn, and inspect the same pin-out every time. Errors get made less often, and inspection error get made less often. With the advent of cable test fixtures, the only place left for the errors to occur is at the individual cable builder's bench. That builder's learned mindset, if hard wired to one spec, becomes less prone to error. >>>>> The same reasoning applies to CAT5 cables, but in this case there are a >>>>> total of four pairs, two transmit and two receive. Both sets are not [quoted text clipped - 26 lines] > more time), other than pin for pin wiring can and does increase prime > pass yield failure rates. Wire coloured x goes to pin y. You just need two groups of people, who've learned different schemes. Sylvia. >Wire coloured x goes to pin y. You just need two groups of people, >who've learned different schemes. > >Sylvia. You have no concept of hand assembly processes. One person wire both ends. That ONE person only needs to examine the wiring of that one cable, one cable at a time. Gathering up a bunch of cables to pass them off to yet another assembler has an attached cost that reduces profit, and cable fab shops pinch every penny. That's why they hire unskilled workers. Then there is the error rate thing, which invariably also goes up. When a single lost cable occurs, it costs the company more than twice the value of the lost labor. Usually about 5 times when the error is caught in-house. It can be 16 times the cost if caught in the field. Rework is a very costly aspect of lean electronics manufacture. If error rates are high, it quickly becomes the most costly expenditure. Yes, cables are simple. But that just means that the assemblers *think* they can be more casual. Otherwise there would be ZERO failures for a simple 9 pin interconnect. That is only 18 connections, after all, and that is if all pins were used. Yet still, we have much error. The cables that have historically shown to be the least error prone assemblies are, in fact, pin-for-pin matings. >>>> The same reasoning applies to CAT5 cables, but in this case there are a >>>> total of four pairs, two transmit and two receive. Both sets are not [quoted text clipped - 21 lines] > >Sylvia. Part of the issue was to make cable testing easier for low end techs, they are pin for pin. >> you want to connect two together, the transmit pins on one must connect >> to the receive pins on the other. Hence the crossover cable, often [quoted text clipped - 3 lines] > transposed in the original design, then the same cables could have been > used in all cases. this would presumably require the DTE to have outputs for carrier and ring although thise concepts apply only to DCE. the standard was developed before the invention of the smartmodem(tm) which could indicate those two conditions as serial data. Early modems ware loosely speaking analogue filters coupled to serial line drivers, if you were lucky you could pulse dial by toggling the DTR line with the correct cadence... >>> you want to connect two together, the transmit pins on one must connect >>> to the receive pins on the other. Hence the crossover cable, often [quoted text clipped - 5 lines] > this would presumably require the DTE to have outputs for carrier and > ring although thise concepts apply only to DCE. Just means those pins would be tied to ground. This would have required more than the 9 pins on modern serial ports, but would have been easily done with the original 25 pin standard. > the standard was developed before the invention of the smartmodem(tm) > which could indicate those two conditions as serial data. > > Early modems ware loosely speaking analogue filters coupled to serial > line drivers, if you were lucky you could pulse dial by toggling the > DTR line with the correct cadence... Did something similar with a telephone in my teens, by pulsing the handset rest. Shame no TV suspense movie ever used it - devious villain leaves a phone with its dial detached so that he can call his imprisoned victims - but one captive knows better and calls the police despite the absence of a dial. Sylvia. >>>> you want to connect two together, the transmit pins on one must connect >>>> to the receive pins on the other. Hence the crossover cable, often [quoted text clipped - 19 lines] > Did something similar with a telephone in my teens, by pulsing the > handset rest. IIRC it was used in "War Games" (1983) >>>>> you want to connect two together, the transmit pins on one must connect >>>>> to the receive pins on the other. Hence the crossover cable, often [quoted text clipped - 21 lines] > >IIRC it was used in "War Games" (1983) Want to play a game? > Did something similar with a telephone in my teens, by pulsing the > handset rest. [quoted text clipped - 3 lines] > one captive knows better and calls the police despite the absence of a > dial. Hannibal Lecter used that trick to make phone calls from prison in the movie _Manhunter_. I used to tap the handset cradle to make free calls as a teenager. SignatureW . | ,. w , "Some people are alive only because \|/ \|/ it is illegal to kill them." Perna condita delenda est ---^----^--------------------------------------------------------------- >> Did something similar with a telephone in my teens, by pulsing the >> handset rest. [quoted text clipped - 7 lines] > movie _Manhunter_. I used to tap the handset cradle to make free calls > as a teenager. I can't see why it would make the calls free. Sylvia. >>> Did something similar with a telephone in my teens, by pulsing the >>> handset rest. [quoted text clipped - 11 lines] > > Sylvia. Old type phone boxes in the UK had the dial linked to the coin mechanism. You had to pay to use the dial. Handset rest pulsing cut that out. >>>> Did something similar with a telephone in my teens, by pulsing the >>>> handset rest. [quoted text clipped - 13 lines] > Old type phone boxes in the UK had the dial linked to the coin mechanism. > You had to pay to use the dial. Handset rest pulsing cut that out. Must have been very old. I remember the push button A/push button B type, and then the later ones where you put the coins in when the other party answered (I hated them!). I don't remember any where there was a link between the dial and the coins. Sylvia. >>>>> Did something similar with a telephone in my teens, by pulsing the >>>>> handset rest. [quoted text clipped - 20 lines] > > Sylvia. They were the ones! >>>>>> Did something similar with a telephone in my teens, by pulsing the >>>>>> handset rest. [quoted text clipped - 20 lines] > > They were the ones! Which? It was always possible to call the operator, or the emergency services, without any coins, so I don't see how there can have been an interlock. Sylvia. >>>>>>> Did something similar with a telephone in my teens, by pulsing the >>>>>>> handset rest. [quoted text clipped - 28 lines] > > Sylvia. The 9 and the 0 were OK. It was not possible to get through to anyone else without pressing button A. See 'Atkinson's Telephony' for details. >>> Did something similar with a telephone in my teens, by pulsing the >>> handset rest. [quoted text clipped - 9 lines] > > I can't see why it would make the calls free. Public phone. The trick doesn't work anymore, because they now damp the hook switch. SignatureW . | ,. w , "Some people are alive only because \|/ \|/ it is illegal to kill them." Perna condita delenda est ---^----^--------------------------------------------------------------- >Early modems ware loosely speaking analogue filters coupled to serial >line drivers, if you were lucky you could pulse dial by toggling the >DTR line with the correct cadence... No luck about it. Make-and-break dialing STILL works. >>Early modems ware loosely speaking analogue filters coupled to serial >>line drivers, if you were lucky you could pulse dial by toggling the >>DTR line with the correct cadence... >> > No luck about it. Make-and-break dialing STILL works. Not all modems provided electronic control of the "hook switch" (i forget the correct term) if you were lucky you had one that did. >>>Early modems ware loosely speaking analogue filters coupled to serial >>>line drivers, if you were lucky you could pulse dial by toggling the [quoted text clipped - 4 lines] >Not all modems provided electronic control of the "hook switch" (i >forget the correct term) if you were lucky you had one that did. Most ALL do actually provide such control. It is referred to as "pulse dialing" and modems allow selection of pulse or tome dialing. Pulse dialing IS make-and-break dialing utilizing "the hook switch" as that is what pulse dialing is. > Most ALL do actually provide such control. It is referred to as "pulse > dialing" and modems allow selection of pulse or tome dialing. Pulse > dialing IS make-and-break dialing utilizing "the hook switch" as that is > what pulse dialing is. Is tome dialing where you throw a book at the phone? Signature"Electricity is of two kinds, positive and negative. The difference is, I presume, that one comes a little more expensive, but is more durable; the other is a cheaper thing, but the moths get into it." (Stephen Leacock) >> Most ALL do actually provide such control. It is referred to as "pulse >> dialing" and modems allow selection of pulse or tome dialing. Pulse >> dialing IS make-and-break dialing utilizing "the hook switch" as that is >> what pulse dialing is. > > Is tome dialing where you throw a book at the phone? Sure. After you've read the fat manual (RTFM), you throw that at it. Hence FM modulation. > >> Most ALL do actually provide such control. It is referred to as "pulse > >> dialing" and modems allow selection of pulse or tome dialing. Pulse [quoted text clipped - 5 lines] > Sure. After you've read the fat manual (RTFM), you > throw that at it. Hence FM modulation. FM modulation - is that like ATM machine? >Is tome dialing where you throw a book at the phone? One opens the i ching and picks a tome and speaks it. >>> Or maybe the question should be why do we have cables that are not >>> crossover. [quoted text clipped - 34 lines] > > Sylvia. My reference states From DTE: pin 2 transmit, pin 4, request to send, pin 20 data terminal ready (ie output); To DTE: pin 3 received data, pin 5 clear to send, pin 6 data set ready. I left out DCD and secondary / reverse channel info. For a non-cross, one would need to have pin 2 as transmit on one end and receive on the other, etc. Not so nice. >>>> Or maybe the question should be why do we have cables that are not >>>> crossover. [quoted text clipped - 41 lines] > and receive on the other, etc. > Not so nice. That's exactly the situation we do have. Pin 2 is transmit on the DTE and receive on the DCE. Sylvia. >>>>> Or maybe the question should be why do we have cables that are not >>>>> crossover. [quoted text clipped - 46 lines] > >Sylvia. EXACTLY! Which is why, when one needs to hook up a computer that expects to see a modem to another computer, a reversal is needed on those two lines so that the two devices *think* they are communicating with a modem device. Hence "null modem" cable. >The same reasoning applies to CAT5 cables, but in this case there are a >total of four pairs, two transmit and two receive. Both sets are not >always used, but the ones in use must be "crossed over" to connect two >of the same type equipment. Many routers can sense the type of cable >required and will automatically do the crossover internally if required. Many (most? all?) Intel GB NICs will also crossover automatically. >Or maybe the question should be why do we have cables that are not >crossover. [quoted text clipped - 8 lines] >for cables to connect input pins to output pins, thus obviating the need >for two different ways of wiring up connecting cables. I agree, it does make a great deal of sense to set up the interfaces in a symmetrical fashion whenever possible. I've grown fond of the Yost method of doing serial-port hookup... there's no differentiation between DTE (e.g. terminal or PC) and DCE (e.g. modem), and you can hook either to the other. 10BaseT could also have been designed with this sort of symmetry in mind, I suppose, if we'd started out using the sort of highly-intelligent auto-adaptive interfaces that we use today on e.g. 100BaseT. However... these sorts of symmetrical cabling systems don't tend to arise when there's a big functional asymmetry between the sorts of devices at either end. In the case of serial ports, there are some functions provided by the DCE (e.g. carrier detect, ring indicate, and master-clock timing in the case of synchronous ports) that the DTE is physically or philosophically unable to provide... the DTE is a consumer of these, not a provider. The Yost serial standard deals with this issue by simply avoiding it - it doesn't carry those signals at all and thus they aren't available to the DTE. In the case of Ethernet, a similar asymmetry existed when the technology was developed... hubs had functions that clients did not, and tended to incorporate more-expensive electronics. It's only more recently that the "interface intelligence" in a client (e.g. PC) and a switch have become more comparable and symmetric. Also (minor issue) it's a trifle easier to extend a straight-through cable with another... you just use a second straight-through cable and a one-to-one butt-heads splicer. You can't do this with two crossover cables, as you'll end up crossing everything over twice and creating the equivalent of a straight-through cable... your splicer needs to include a *third* crossover! SignatureDave Platt <dplatt@radagast.org> AE6EO Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! >I agree, it does make a great deal of sense to set up the interfaces >in a symmetrical fashion whenever possible. I've grown fond of the [quoted text clipped - 6 lines] >highly-intelligent auto-adaptive interfaces that we use today on e.g. >100BaseT. The problem is that when these systems of interface were designed, there was nearly no automated assembly. Hand assembly means failures, unless error conditions are reduced to a minimum. Wiring both ends identically means that less errors were made in manufacture of said interface devices and systems. Making the switch at the hardware itself was easy, and 100% repeatable. Prime pass yield was a huge consideration in labor intensive hand operation production procedures, and still is. That is why most interface cables are pin-for-pin. Particulalry those that have the same or very similar connectors on each end. >Also (minor issue) it's a trifle easier to extend a straight-through >cable with another... you just use a second straight-through cable and >a one-to-one butt-heads splicer. You can't do this with two crossover >cables, as you'll end up crossing everything over twice and creating >the equivalent of a straight-through cable... your splicer needs to >include a *third* crossover! Also a very good reason to refrain from the idea. It can easily be incorporated into a gender change DONGLE as well. Yes, folks, that term was in use LONG before software security keys used it. > Or maybe the question should be why do we have cables that are not > crossover. [quoted text clipped - 10 lines] > > Did I miss something? Is there a reason this situation persists? The reasn this situation persists is that it is written into the international standards, and a huge installed base of hardware out in the field conforms to those standards. I used to know about this when I worked for ITT-Creed in the U.K back in 1979-1982, in a group that used to send people to the CCIT standards committee meetings. The concept dates back to the Telex and Teleprinter networks. The ASR 33 Teletype printer was orginally a data set (IIRR - 1982 is the last time I was seriously involved) produced in huge numbers of the AT&T network, and its use as a computer terminal was never more than a minor spin-off. http://www.iso.org/iso/livelinkgetfile?llNodeId=21523&llVolId=-2000 -- Bill Sloman, Nijmegen >> Or maybe the question should be why do we have cables that are not >> crossover. [quoted text clipped - 26 lines] > >http://www.iso.org/iso/livelinkgetfile?llNodeId=21523&llVolId=-2000 Western Electric ALSO hand assembled practically everything back then, and they knew about error rates in cable assemblies, and they knew how best to reduce them by making remembering the wiring procedure an easy thing to do. > Or maybe the question should be why do we have cables that are not > crossover. [quoted text clipped - 13 lines] > > Sylvia. TROLLTROLLTROLL has to be ? no one could be that f.cking stupid >> Or maybe the question should be why do we have cables that are not >> crossover. [quoted text clipped - 16 lines] > has to be ? > no one could be that f.cking stupid Rod Speed of old? >>> Or maybe the question should be why do we have cables that are not >>> crossover. [quoted text clipped - 18 lines] > > Rod Speed of old? Maybe she is the result of a union between woddles and philthy ? of course the question is who was the bottom ? >>>> Or maybe the question should be why do we have cables that are not >>>> crossover. [quoted text clipped - 22 lines] > > of course the question is who was the bottom ? Have you seen her photo? The only sex that ugly ditz gets is from her fingers. She should do x rated. They'll shoot film of anybody doing anything. In article <49b78df5$0$4195$5a62ac22@per-qv1-newsreader- 01.iinet.net.au>, hgjhg@bjhgl.com says...> > >> Or maybe the question should be why do we have cables that are not > >> crossover. [quoted text clipped - 18 lines] > > Rod Speed of old? How is the "Rod Speed of old" [*] any different than the Rod Speed of new? He still infests many groups. [*] Ron Reaugh of old >>> Or maybe the question should be why do we have cables that are not >>> crossover. [quoted text clipped - 18 lines] > >Rod Speed of old? If so, he was a goddamned idiot with that moniker as well. >> Or maybe the question should be why do we have cables that are not >> crossover. [quoted text clipped - 16 lines] > has to be ? > no one could be that f.cking stupid She pops off with a stupid question every couple days. Considering the level of off topic posts here, it actually causes discussion of actual electronic issues. Still, it belongs over in the basic group, as does she... well... actually, she belongs in the kook group. >Or maybe the question should be why do we have cables that are not >crossover. [quoted text clipped - 12 lines] > >Sylvia. For modern ethernet, you don't need cross-over cables. The devices figure out the pair sorting. All the NICs, routers, and switches I've come across in the past 3 to 5 years have auto-sorting of the pairs. In article <kavfr41akr4d1a98s5cjv9f080u5qm269u@4ax.com>, SpamTrap@spam.net says...> > >Or maybe the question should be why do we have cables that are not > >crossover. [quoted text clipped - 16 lines] > figure out the pair sorting. All the NICs, routers, and switches I've > come across in the past 3 to 5 years have auto-sorting of the pairs. Don't count on it. We found a bunch of 'em that don't work as advertised. :-( >In article <kavfr41akr4d1a98s5cjv9f080u5qm269u@4ax.com>, >SpamTrap@spam.net says...> [quoted text clipped - 22 lines] >Don't count on it. We found a bunch of 'em that don't work as >advertised. :-( Best to actually use a known good, proper cable, and not rely on a nic or router to be your cable tester, or repair facility. Now tell me that one was wrong too. >>In article <kavfr41akr4d1a98s5cjv9f080u5qm269u@4ax.com>, >>SpamTrap@spam.net says...> [quoted text clipped - 27 lines] > > Now tell me that one was wrong too. You are. If you want to test cables, get a cable tester. If you just want to hook things up, try it. You might get lucky. You'll always get it wrong, in any case. >>>In article <kavfr41akr4d1a98s5cjv9f080u5qm269u@4ax.com>, >>>SpamTrap@spam.net says...> [quoted text clipped - 31 lines] >want to hook things up, try it. You might get lucky. You'll always >get it wrong, in any case. This krw idiot, folks... is a troll. In this case, however, you were baited into it. I was, in fact, correct. Note how it was me that stated that a nic is NOT a cable tester. You are just too retarded to have seen it in your glaring need to troll me and the group. f.ck off, KeithTard. >>>>In article <kavfr41akr4d1a98s5cjv9f080u5qm269u@4ax.com>, >>>>SpamTrap@spam.net says...> [quoted text clipped - 34 lines] > This krw idiot, folks... is a troll. In this case, however, you were >baited into it. AlwaysWrong is wrong again (surprise, surprise). BTW, how were "they" (whomever "they" is) baited, DimBulb? Seems you're the dead fish around here. > I was, in fact, correct. Wrong again, on many levels. >Note how it was me that stated that a nic is >NOT a cable tester. You are just too retarded to have seen it in your >glaring need to troll me and the group. f.ck off, KeithTard. No thanks. You're not my type, DimBulb. Be careful or you'll make Roy jealous. . > For modern ethernet, you don't need cross-over cables. The devices > figure out the pair sorting. All the NICs, routers, and switches I've > come across in the past 3 to 5 years have auto-sorting of the pairs. When you connect two computers to each other, you use the crossover cable and you don't need a router. Al >. >> [quoted text clipped - 6 lines] > >Al And due to your quick scan of the ONE post it appears you read, you completely missed the point of the entire thread, much less the one post you responded to. >>. >>> [quoted text clipped - 10 lines] > completely missed the point of the entire thread, much less the one post > you responded to. Ho hum! >> Or maybe the question should be why do we have cables that are not >> crossover. [quoted text clipped - 16 lines] > figure out the pair sorting. All the NICs, routers, and switches I've > come across in the past 3 to 5 years have auto-sorting of the pairs. Is there a standard specifying how this works? I'd have to wonder how two such interfaces manage when they are connected together. Sylvia. >>> Or maybe the question should be why do we have cables that are not >>> crossover. [quoted text clipped - 23 lines] > >Sylvia. If a handshake fails, a different connection schema is used (read switched in) until success is achieved. Pretty simple. >>>> Or maybe the question should be why do we have cables that are not >>>> crossover. [quoted text clipped - 25 lines] > If a handshake fails, a different connection schema is used (read > switched in) until success is achieved. Pretty simple. And the other end is doing the same. Might go on forever. Sylvia. >>>>> Or maybe the question should be why do we have cables that are not >>>>> crossover. [quoted text clipped - 29 lines] > >Sylvia. No. They are seldom happening at the same time, and their internal timeouts between tests and switch-outs differ from maker to maker. This means that one WILL eventually achieve a handshake, and then both will discontinue making switch-outs. >>>>>> Or maybe the question should be why do we have cables that are not >>>>>> crossover. [quoted text clipped - 31 lines] > No. They are seldom happening at the same time, and their internal > timeouts between tests and switch-outs differ from maker to maker. And if they're two identical NICs? Sylvia. >>>>>>> Or maybe the question should be why do we have cables that are not >>>>>>> crossover. [quoted text clipped - 35 lines] > >Sylvia. The time in which they perform the test differ as there is no communication between them in said regard. So one will always win, and then a success in the handshake will cause the other to stop trying. >>>>>>> Or maybe the question should be why do we have cables that are not >>>>>>> crossover. [quoted text clipped - 33 lines] > >And if they're two identical NICs? The Ethernet protocol assumes that packets will collide and become garbled. Each NIC will back off for a random amount of time. <http://en.wikipedia.org/wiki/Ethernet#CSMA.2FCD_shared_medium_Ethernet> >>>>> Is there a standard specifying how this works? >>>>> [quoted text clipped - 13 lines] > > And if they're two identical NICs? there's not such thing, derive the timimngs from the mac address >>>>>> Is there a standard specifying how this works? >>>>>> [quoted text clipped - 15 lines] > > derive the timimngs from the mac address Helps if there's a standard that says how, which was my original question. Sylvia. >>>>>>> Is there a standard specifying how this works? >>>>>>> [quoted text clipped - 17 lines] > >Helps if there's a standard that says how, which was my original question. --- No, it wasn't. Your original question was the subject of this thread, and when you were given the answer you quickly dodged and changed the subject in order to further your troll. With as much information as you've been presented with, by now it should be clear to you why things are done the way are and why your jibber-jabber is meaningless tripe. I suggest that if you're still as ignorant as you seem to be you start here: http://www.google.com/search?hl=en&q=rs-232c&aq=0&oq=RS-232 and work your way up to more modern telecommunications hardware and protocols. JF >>>>> Or maybe the question should be why do we have cables that are not >>>>> crossover. [quoted text clipped - 27 lines] > >And the other end is doing the same. Might go on forever. --- No. Have you never heard of taking turns? With a finite number of combinations possible and only one combination correct, a solution _must_ emerge. JF >>>>>> Or maybe the question should be why do we have cables that are not >>>>>> crossover. [quoted text clipped - 31 lines] > > Have you never heard of taking turns? Yep. All you have to do is establish communication first, so that you can decide whose turn it is. Sylvia. >>>>>>> Or maybe the question should be why do we have cables that are not >>>>>>> crossover. [quoted text clipped - 36 lines] > >Sylvia. Even when "communication"fails, as in no handshake acknowledged, the exchange will eventually match, with 'eventually' being a fairly quick process. In dumb systems handshake simply fails. In a smart system, it senses the presence of the comm cable, but the failed handshake sets off the pair swap retry. >>>>>>> Or maybe the question should be why do we have cables that are not >>>>>>> crossover. [quoted text clipped - 34 lines] >Yep. All you have to do is establish communication first, so that you >can decide whose turn it is. --- It's pretty much like calling someone on the phone. You're familiar with that procedure, aren't you? JF >>>>>>>> Or maybe the question should be why do we have cables that are not >>>>>>>> crossover. [quoted text clipped - 39 lines] > >You're familiar with that procedure, aren't you? She probably is. And with a small group of callers making a lot of calls to each other it is likely that none of them will ever get through. Everyone will get the engaged signal because the called party is dialing someone else. >JF >>>>>> Or maybe the question should be why do we have cables that are not >>>>>> crossover. [quoted text clipped - 35 lines] >With a finite number of combinations possible and only one combination >correct, a solution _must_ emerge. That is how Token Ring works but not Ethernet. Ethernet uses a "cocktail party" protocol where you wait for a pause in the conversation before speaking and, if after you start, someone else is speaking you back off until there is another pause. It's usually efficient but if the group is too large and a few speakers are too verbose there will be no communication. Token Ring works by passing the microphone around the group so that everyone who has something to say gets a chance to say it. It can't catastrophically fail but, for normal conversation, it can be extremely slow. >>>>>>> Or maybe the question should be why do we have cables that are not >>>>>>> crossover. [quoted text clipped - 45 lines] >say gets a chance to say it. It can't catastrophically fail but, for >normal conversation, it can be extremely slow. --- So you're supporting Sylvia's position? JF >>>>>>>> Or maybe the question should be why do we have cables that are not >>>>>>>> crossover. [quoted text clipped - 48 lines] >--- >So you're supporting Sylvia's position? Obviously, I think she is right in this sub-thread. I also tend to agree with her original post although others have explained why, historically, a crossover cable was not standard and why there was a distinction between terminal and communication equipment. The only point I might disagree with her on is the assumption that "this situation persists". Modern interfaces, like USB, use a single pair of wires for communication which avoids the problem. >Obviously, I think she is right in this sub-thread. I also tend to >agree with her original post although others have explained why, >historically, a crossover cable was not standard and why there was a >distinction between terminal and communication equipment. A cross-over cable most certainly WAS and IS the standard for attaching two like terminals through this interface (serial) When will you grasp the concept, dolt? >>Obviously, I think she is right in this sub-thread. I also tend to >>agree with her original post although others have explained why, [quoted text clipped - 3 lines] > A cross-over cable most certainly WAS and IS the standard for attaching >two like terminals through this interface (serial) You seem to have missed the point of the OP's question. You are excused because you are of an age when an RS232 or Centronics interface was normal. As other posters have pointed out it was cheaper to manufacture straight through cables and in those days there was a clear distinction the devices at each end of a cable. Pin n of one device could reasonably be defined as a receiver and Pin n of the "other" device could be defined as a transmitter. In the last thirty years that has changed and today it is preferable to treat all devices as peers. The OP wanted to know why the distinction between devices existed rather than _always_ connecting them with a crossover cable. It was a perfectly reasonable question and she has been provided with sensible answers by those who managed to understand it. > When will you grasp the concept, dolt? >The only point I might disagree with her on is the assumption that >"this situation persists". Modern interfaces, like USB, use a single >pair of wires for communication which avoids the problem. It is an entirely different schema altogether. Wake up. >>>>>>>> Or maybe the question should be why do we have cables that are not >>>>>>>> crossover. [quoted text clipped - 50 lines] > >JF Remember TCNS? I think it was token ring. It had hubs all over the place. Thomas Conrad Network Systems. I remember Tandy's 'Arcnet' at 150kb/s (small 'b'). :-) >>>>>>>> Or maybe the question should be why do we have cables that are not >>>>>>>> crossover. [quoted text clipped - 47 lines] > > JF It's not really relevant anyway. Neither a token ring, now Ethernet's backoff approach, can work before it's been established which wires are which. There may be a standard that describes the process of identifying the wires. Whether there is is what I asked. Sylvia. >> So you're supporting Sylvia's position? >> >> JF > >It's not really relevant anyway. --- It never was. --- >Neither a token ring, now Ethernet's >backoff approach, can work before it's been established which wires are >which. --- Neither a token ring nor what? --- >There may be a standard that describes the process of identifying the >wires. Whether there is is what I asked. --- Google is your friend. JF >>> So you're supporting Sylvia's position? >>> [quoted text clipped - 11 lines] > --- > Neither a token ring nor what? Typo. Should have been obvious. > --- > [quoted text clipped - 3 lines] > --- > Google is your friend. Sometimes. Sometimes not. If you know of a standard, then why not provide a reference? Sylvia. >>>> So you're supporting Sylvia's position? >>>> [quoted text clipped - 13 lines] > >Typo. Should have been obvious. --- As should have been the reason why we have crossover cables. --- >>> There may be a standard that describes the process of identifying the >>> wires. Whether there is is what I asked. [quoted text clipped - 3 lines] > >Sometimes. Sometimes not. --- If you're too ignorant to use Google properly that isn't Google's fault. --- >If you know of a standard, then why not provide a reference? --- Give a man a fish and you've fed him for a day. Teach a man to fish and you've fed him for life. Besides, you're not looking for a reference, you're interested in trolling. JF >Sometimes. Sometimes not. > >If you know of a standard, then why not provide a reference? If you know how to use Google, why be a lazy ditz? >>>> So you're supporting Sylvia's position? >>>> [quoted text clipped - 24 lines] > > If you know of a standard, then why not provide a reference? Here you go: <http://en.wikipedia.org/wiki/Ethernet_crossover_cable> And: <http://en.wikipedia.org/wiki/Auto-MDIX> for the auto detection standard. SignatureW . | ,. w , "Some people are alive only because \|/ \|/ it is illegal to kill them." Perna condita delenda est ---^----^--------------------------------------------------------------- >There may be a standard that describes the process of identifying the >wires. Whether there is is what I asked. I don't think it requires a "standard" to identify the wires. A NIC must be able to identify a valid packet so swapping two wires until it does so is not a demanding task now that a microprocessor is incorporated on every device. >> There may be a standard that describes the process of identifying the >> wires. Whether there is is what I asked. [quoted text clipped - 3 lines] > does so is not a demanding task now that a microprocessor is > incorporated on every device. I was thinking that a standard would be required that specified the delays, or the means of calculation of the delays, to be used between trying different combinations, so as to avoid the situation where two NICs undermine each other's attempts to find a working combination. Sylvia. >>> There may be a standard that describes the process of identifying the >>> wires. Whether there is is what I asked. [quoted text clipped - 8 lines] >trying different combinations, so as to avoid the situation where two >NICs undermine each other's attempts to find a working combination. I think you will find what you are looking for in "IEEE 802.3 LAN/MAN CSMA/CD Access Method" <http://standards.ieee.org/getieee802/802.3.html> but I have not read it. >>>> There may be a standard that describes the process of identifying the >>>> wires. Whether there is is what I asked. [quoted text clipped - 11 lines] > <http://standards.ieee.org/getieee802/802.3.html> but I have not read > it. Starting at paragraph 40.4.4. Thanks. Sylvia. >>> There may be a standard that describes the process of identifying the >>> wires. Whether there is is what I asked. [quoted text clipped - 10 lines] > >Sylvia. If thousands of iterations are tried at both ends, a matchup will occur within milliseconds. IF that were the way it happens. Still, it would be meaningless (read negligible)to the observer, and only needs to be done one time when the cable is attached. >>>>>>> Or maybe the question should be why do we have cables that are not >>>>>>> crossover. [quoted text clipped - 45 lines] >say gets a chance to say it. It can't catastrophically fail but, for >normal conversation, it can be extremely slow. Add some conditions. There is an orderly passing sequence. Each time you get the microphone you may speak a small permitted say or not. When done speaking or if you have nothing to say you immediately pass the microphone. . >>> Or maybe the question should be why do we have cables that are not >>> crossover. [quoted text clipped - 21 lines] >I'd have to wonder how two such interfaces manage when they are >connected together. --- Design, Sylvia, design... JF >>> Or maybe the question should be why do we have cables that are not >>> crossover. [quoted text clipped - 23 lines] > >Sylvia. Yes. It is part of the IEEE 802.3 series. See: http://standards.ieee.org/getieee802/802.3.html . >Or maybe the question should be why do we have cables that are not >crossover. > >My first encounter with this concept came when connecting serial ports >together. Turned out there were two kinds - data set, and data terminal. >Not content with that, when UTP cables came out, we had a similar situation. > [quoted text clipped - 6 lines] > >Sylvia. An even more logical approach is used by USB OTG ("On The Go"). A device can be either a host (power provider) or a peripheral (power consumer) depending on the status of a fifth pin. After power-up, both devices can negotiate to swap functions. The USB data interface is bidirectional. See http://en.wikipedia.org/wiki/USB_On-The-Go - Franc Zabkar SignaturePlease remove one 'i' from my address when replying by email. > Or maybe the question should be why do we have cables that are not > crossover. [quoted text clipped - 13 lines] > > Sylvia. Cabling was even more ambiguous when you consider hardware handshaking. In the earlier years, I have seen handshaking on various pins including 4, 5, 6, 8, 20, 21 and one printer used pin 19. The situation was not solely a serial problem either, one TI printer with a parallel interface used an inverted data available strobe. I presume this was to force the purchase of their over priced cables. It was easily possible to build a transistor inverter in the centronics head to resolve the issue. > Maybe I've missed something, but it's always seemed to me that a logical > approach would be to define some pins as input and some as output, and > for cables to connect input pins to output pins, That's how the Macintosh serial ports and printers/modems etc. were wired. It works. The old RS-232 days were different: it made sense to the original builders that a data communication device would attach onto a data terminal device, SO they were specified with mating connectors. The DCE (data communication equipment :== modem) had a female plug, the DTE (data terminal equipment :== terminal, computer) had a male plug. The connection was through simple extension cables, also convenient for insulation-displacement (ribbon cable) and for mass production. I think, historically, the decision to use male and female connectors (which allows docking modules without a cable) was the breakpoint. In the case of UTP wiring, the two wiring schemes are 568A and 568B (and everyone uses 568B, the "crossover cable" is 568A on one end). Computer-to-hub/router/switch uses straight-through cable, computer-to-computer uses crossover cable, hub/router/switch to hub/router/switch uses crossover cable (or a "special" crossover port). This is becoming irrelevant, though, with new chipsets: all the gigabit Ethernet I've seen has logic that corrects the signal for wire arrangement (the gigabit protocol requires bidirectional use of all the wire pairs anyhow, so send/receive is just a software setting). >> Maybe I've missed something, but it's always seemed to me that a logical >> approach would be to define some pins as input and some as output, and [quoted text clipped - 22 lines] >hub/router/switch uses crossover cable (or a "special" crossover >port). Wow, did you ever get that one wrong. See: http://en.wikipedia.org/wiki/TIA-568B >This is becoming irrelevant, though, with new chipsets: all the >gigabit Ethernet I've seen has logic that corrects the signal for >wire arrangement (the gigabit protocol requires bidirectional use >of all the wire pairs anyhow, so send/receive is just a software >setting). >Or maybe the question should be why do we have cables that are not >crossover. [quoted text clipped - 10 lines] > >Did I miss something? Is there a reason this situation persists? You missed something, and there's a good reason why this condition persists. In a minimalist DB25 connection between DTE and DCE we have this: DTE DCE DB25M CABLE DB25F +---------+ +---------+ | TXD 3>>3--------------------3>>3 RXD | | RXD 2>>2--------------------2>>2 TXD DCE | | SIG GND 7>>7--------------------7>>7 SIG GND | +---------+ \ / +---------+ DB25F DB25M Notice that the cable conductors do not cross and are wired 1:1 from end to end. But now assume someone wants two computers to talk to each other through their serial posts, and we wind up with this: DTE DTE DB25M DB25M +---------+ +---------+ | TXD 3> <3 TXD | | RXD 2> <2 RXD | | SIG GND 7> <7 SIG GND | +---------+ +---------+ How would you suggest wiring up the ports to accomplish that? JF >You missed something, and there's a good reason why this condition >persists. [quoted text clipped - 25 lines] > >How would you suggest wiring up the ports to accomplish that? The way the Yost wiring system works is one way around this. It uses an RJ-45 jack. Every device (DCE or DTE) is wired up to put the "data I am sending to you" on pin 6 (yellow wire), and to look for "data from you" on pin 3. In the case of DCE, "data I am sending" is RD and "data I am getting from you" is TD; in the case of DTE, the opposite is true. The 8-pin cable used for Yost is wired up with a "flip over", so it connects pin 3 at each end to pin 6 at the opposite end. There's a similar pairing-and-cable-flipping between "terminal ready" signals (DTR from the DTE and Carrier Detect from the DCE) and "flow control" signals (RTS from DTE, CTS from DCE). So, using the same cable, you can connect together a DCE and DTE, or two DCEs, or two DTEs. Every device has the same sort of connection port, and any two ports can be connected successfully using an RF-45 8-wire flipover cable (which is *not* the same as an Ethernet crossover cable). The magic here depends on two things: you're always using a flipover cable, and the devices at either end (DCE or DTE) are responsible for connecting the RJ-45 goezintas and goesoutas to their correct internal signal points. [In practice, the latter is usually done by wiring up DTE- and DCE-specific "DB-9/25-to-RJ-45 adapters"). I've used the Yost methodology at home for several years and quite like it. SignatureDave Platt <dplatt@radagast.org> AE6EO Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! >>Or maybe the question should be why do we have cables that are not >>crossover. [quoted text clipped - 42 lines] > >JF The port would have to have an expensive multi pin switch incorporated into the panel next to it. Very bad. >>>Or maybe the question should be why do we have cables that are not >>>crossover. [quoted text clipped - 45 lines] > The port would have to have an expensive multi pin switch incorporated >into the panel next to it. Very bad. --- Much simpler is a cable with pins 2 and 3 crossed, an that's what's done. JF >>>>Or maybe the question should be why do we have cables that are not >>>>crossover. [quoted text clipped - 51 lines] > >JF Exactly. Far cheaper as well. Computer talks to modems. When computer needs to talk to another computer via the same ties directly, it is obvious that a conflict will be present. The 'null modem cable' was part of the spec, even before one was ever used. >> Or maybe the question should be why do we have cables that are not >> crossover. [quoted text clipped - 27 lines] > Notice that the cable conductors do not cross and are wired 1:1 from end > to end. Yes, clearly with the endpoints wired as they are we need different cables depending on the kind of endpoints we're connecting. But that wasn't my quesion. My question related to why this situation was created in the first place, since it is not a logical necessity. Sylvia. >>> Or maybe the question should be why do we have cables that are not >>> crossover. [quoted text clipped - 36 lines] > >Sylvia. He already showed how it WAS and still IS a necessity. > My question related to why this situation was created in the first > place, since it is not a logical necessity. Because the modem is "Data Communications Equipment", or DCE, and the computer/teletype is "Data Terminal Equipment", or DTE. When you use a computer to simulate a modem (or a server on the other end of the line) you need to turn the sense of the connector around. This is why reversing cables used to be called "null modem" cables. Hope This Helps! Rich >> My question related to why this situation was created in the first >> place, since it is not a logical necessity. [quoted text clipped - 7 lines] > Hope This Helps! > Rich No it doesn't. It entirely misses the point, which is why there is a distinction betwen DCE and DTE. Sylvia. >>> My question related to why this situation was created in the first >>> place, since it is not a logical necessity. [quoted text clipped - 12 lines] > >Sylvia. Actually, it is YOU that is missing the entire point. >>> My question related to why this situation was created in the first >>> place, since it is not a logical necessity. [quoted text clipped - 10 lines] >No it doesn't. It entirely misses the point, which is why there is a >distinction betwen DCE and DTE. --- Are you a lesbian? JF >>>> My question related to why this situation was created in the first >>>> place, since it is not a logical necessity. [quoted text clipped - 15 lines] > >JF Is there a distinction between ugly and dyke? FunkShun Poignter >>>> My question related to why this situation was created in the first >>>> place, since it is not a logical necessity. [quoted text clipped - 15 lines] > >JF Probably. IIRC she refused to post a photograph. That would explain "her" difficulty in understanding gozinta/gozouta ;-) ...Jim Thompson | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine Sometimes I even put it in the food >>>> My question related to why this situation was created in the first >>>> place, since it is not a logical necessity. [quoted text clipped - 15 lines] > >JF Snide answers to Sylvia's History question do not redound well to your status. >>>>> My question related to why this situation was created in the first >>>>> place, since it is not a logical necessity. [quoted text clipped - 18 lines] >Snide answers to Sylvia's History question do not redound well to your >status. --- Why is the manner in which I address Sylvia or the status of my "status" any of your concern? JF >>>>>> My question related to why this situation was created in the first >>>>>> place, since it is not a logical necessity. [quoted text clipped - 24 lines] > >JF Not that you care, but i used to look up to you. Now you are just another prunt. . >>>>>>> My question related to why this situation was created in the first >>>>>>> place, since it is not a logical necessity. [quoted text clipped - 28 lines] >another prunt. > . You have been "something" for a long time. Not sure you want to hear what that is though. >>>>>>> My question related to why this situation was created in the first >>>>>>> place, since it is not a logical necessity. [quoted text clipped - 27 lines] >Not that you care, but i used to look up to you. Now you are just >another prunt. --- JF >>> My question related to why this situation was created in the first >>> place, since it is not a logical necessity. [quoted text clipped - 7 lines] > No it doesn't. It entirely misses the point, which is why there is a > distinction betwen DCE and DTE. BECAUSE THEY HAVE DIFFERENT FUNCTIONS!!!!!!!!!!!!!!!!!! How many different ways do we have to say the same thing before you get it into that pretty little head of yours? In the beginning, there were messengers. Then, some clever fellow invented the telegraph. There were the wires, and there were the transducers. Some other clever fellow figured out how to send voice signals through the wires - voila! The telephone. Again, wires, and telephone instruments. Then, along comes teletype. Once again, the wires, and the translation equipment. Somebody electronified teletype machines. Since they were getting a little bit more sophisticated than teletypes, they needed a more comples interface to the wires, thus the MODEM (modulator-demodulator), which connected your terminal to the wires. So there evolved two different types of equipment - the kind of equipment that talks to you, and they kind of equipment that talks to the wires. These were deemed "Data Terminal Equipment" for the one that talks to you, and "Data Communications Equipment" for the ones that talk to the wires. They had to be connected to one another. Yet another clever fellow (or gal; gender is irrelevant here, but I can feel your feminazidar going on orange alert) decided that, since most of the wires are consistent, and since most of the terminals would be consistent, that some consistent form of connecting one to the other should be THE STANDARD. Then, along comes some wiseacre who wants to connect two computers together, without the benefit of all of that communications equipment, wires, and so on, so they tried just plugging one into the other. DIDN'T WORK! Because BOTH computers expected to be plugged into a modem each, with the telephone network in between. So somebody really, really clever came up with the idea of replacing the whole phone network and the modems with the "crossover cable", which made the other computer LOOK JUST LIKE a modem with the whole phone network and another modem, and the target computer attached to it. NOW are you getting it? Thanks, Rich [snip] Maybe it would be easier to explain to Sylvia that the reason we have cross-over cables is because cross-under cables are too expensive to build. >Maybe it would be easier to explain to Sylvia that the >reason we have cross-over cables is because cross-under >cables are too expensive to build. Sno-o-o-o-ort ;-) ...Jim Thompson | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | It's what you learn, after you know it all, that counts. > [snip] > > Maybe it would be easier to explain to Sylvia that the > reason we have cross-over cables is because cross-under > cables are too expensive to build. MultiNym already covered that! -- Virg Wall, PE >[snip] > >Maybe it would be easier to explain to Sylvia that the >reason we have cross-over cables is because cross-under >cables are too expensive to build. Have not seen anything from her today. Perhaps *she* has crossed over. In article <pan.2009.03.12.17.46.50.297095@example.net>, rich@example.net says...> <snip> > Then, along comes some wiseacre who wants to connect two computers > together, without the benefit of all of that communications equipment, [quoted text clipped - 6 lines] > the other computer LOOK JUST LIKE a modem with the whole phone network > and another modem, and the target computer attached to it. No, that somebody invented the "null modem" (cable). It took them until the invention of the Ethernet to invent the "crossover cable". ;-) > NOW are you getting it? >Some other clever fellow figured out how to send voice signals through the >wires - voila! The telephone. That person was NOT A. G. Bell, however. >>Some other clever fellow figured out how to send voice signals through the >>wires - voila! The telephone. > That person was NOT A. G. Bell, however. Sure it was, he just wasn't the only one or necessarily the first. Exactly who invented the telephone first is largely a question of how you define "telephone" and whether or not you want to trust people who might have built such a device but didn't document it for posterity... >>>Some other clever fellow figured out how to send voice signals through the >>>wires - voila! The telephone. >> That person was NOT A. G. Bell, however. > >Sure it was, he just wasn't the only one or necessarily the first. Wrong. The INVENTOR was Meucci, and that was DECADES before Bell ripped him off. Bell was a thief that had huge research backing. >Exactly who invented the telephone first is largely a question of how you >define "telephone" You're an idiot. > and whether or not you want to trust people who might have >built such a device but didn't document it for posterity... You're a total retard that obviously has ZERO knowledge of the historical facts. >>Some other clever fellow figured out how to send voice signals through the >>wires - voila! The telephone. > > That person was NOT A. G. Bell, however. http://inventors.about.com/library/inventors/bl_Antonio_Meucci.htm >>>Some other clever fellow figured out how to send voice signals through the >>>wires - voila! The telephone. >> >> That person was NOT A. G. Bell, however. > >http://inventors.about.com/library/inventors/bl_Antonio_Meucci.htm You don't have to tell me. I have known about him for years. http://www.italianhistorical.org/MeucciStory.htm http://www.loc.gov/rr/scitech/mysteries/telephone.html >>>Some other clever fellow figured out how to send voice signals through the >>>wires - voila! The telephone. >> >> That person was NOT A. G. Bell, however. > >http://inventors.about.com/library/inventors/bl_Antonio_Meucci.htm He figured in Godfather III ;-) ...Jim Thompson | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine Sometimes I even put it in the food >>> My question related to why this situation was created in the first >>> place, since it is not a logical necessity. [quoted text clipped - 10 lines] > No it doesn't. It entirely misses the point, which is why there is a > distinction betwen DCE and DTE. You're either trolling, or extremely stupid. Either way, the solution is: *PLONK!* SignatureW . | ,. w , "Some people are alive only because \|/ \|/ it is illegal to kill them." Perna condita delenda est ---^----^--------------------------------------------------------------- >>>> My question related to why this situation was created in the first >>>> place, since it is not a logical necessity. [quoted text clipped - 13 lines] > You're either trolling, or extremely stupid. Either way, the solution is: > *PLONK!* She IS stupid . Sylvia Else wrote: > Rich Grise wrote: >> On Thu, 12 Mar 2009 10:54:59 +1100, Sylvia Else wrote: [quoted text clipped - 12 lines] > No it doesn't. It entirely misses the point, which is why there is a > distinction betwen DCE and DTE. It would surely be much nicer if equipment at both ends of the link used just a single pair to communicate in both directions, full duplex, too. If the plain old telephone system can do it, why not data communications equipment? No distinction between DCE or DTE, only one single pair of wire, only one type of cheap cable, cheap and simple connectors, no fuss, no confusion. Maybe it's this way because it was designed by a committee? Jeroen Belleman Jeroen Belleman wrote:. > It would surely be much nicer if equipment at both ends of the link used > just a single pair to communicate in both directions, full duplex, too. [quoted text clipped - 6 lines] > > Maybe it's this way because it was designed by a committee? No, because it was designed to work, and meet the requirements at the time. Signaturehttp://improve-usenet.org/index.html Goggle Groups, and Web TV users must request to be white listed, or I will not see your messages. If you have broadband, your ISP may have a NNTP news server included in your account: http://www.usenettools.net/ISP.htm > Jeroen Belleman wrote:. >> It would surely be much nicer if equipment at both ends of the link used [quoted text clipped - 10 lines] > No, because it was designed to work, and meet the requirements at the > time. Of course it works. That's not the point. The question was about why we don't come up with an interconnect that doesn't require cross-over cables. It's so nice, so simple. As for requirements; We all know that 'requirements' are really a mere description of the way the prototype behaved the day we got it to work. ;-) Jeroen Belleman (Standards are merely intended to cripple competition.) >> Jeroen Belleman wrote:. >>> It would surely be much nicer if equipment at both ends of the link used [quoted text clipped - 21 lines] >Jeroen Belleman >(Standards are merely intended to cripple competition.) I'll bet that it has to do with the speed of the wire limitations at the time. This is a question for Floyd Davidson. >The question was about >why we don't come up with an interconnect that doesn't require >cross-over cables. No. The original post asked why we don't have an interconnect that _only_ uses cross-over cables. The question has been answered on both the historical basis of a clear distinction between "transmitting" and "receiving" equipment and ease of manufacture of straight through cables. The modern trend has been to use a bidirectional interface such as USB but this is necessarily slower than a similar interface using three wires instead of two and a cross-over cable. Nobody has actually answered the question in the current context. >> The question was about >> why we don't come up with an interconnect that doesn't require >> cross-over cables. > > No. The original post asked why we don't have an interconnect that > _only_ uses cross-over cables. [...] Ah yes, that was indeed the question. > The modern trend has been to use a bidirectional interface such as USB > but this is necessarily slower than a similar interface using three > wires instead of two and a cross-over cable. [...] I suppose you are thinking of half-duplex traffic. It's quite possible to have full-duplex traffic on a single pair of wires. There would then be no speed penalty. Jeroen Belleman >There would then be no speed penalty. > >Jeroen Belleman Actually, there WOULD then be a speed issue. >> There would then be no speed penalty. >> >> Jeroen Belleman > > Actually, there WOULD then be a speed issue. Oh, that's very helpful. Would you mind motivating that statement just a little? Jeroen Belleman > Sylvia Else wrote: >> Rich Grise wrote: [quoted text clipped - 26 lines] > >Jeroen Belleman Consider the speed limitations of such a system. Even fiber optic transmission (transception<sic>)has two paths. >> Sylvia Else wrote: >>> Rich Grise wrote: [quoted text clipped - 30 lines] > > Even fiber optic transmission (transception<sic>)has two paths. Just because you have not seen bidirectional full duplex on a single fiber does not mean that it cannot exist. I have used such devices. They typically use wavelength division multiplexing. . >>> Sylvia Else wrote: >>>> Rich Grise wrote: [quoted text clipped - 34 lines] >fiber does not mean that it cannot exist. I have used such devices. >They typically use wavelength division multiplexing. --- Nothing new there, it's the same as frequency division multiplexing. The point is, though, for a medium of propagation with a finite bandwidth, two channels can only exploit up to half the bandwidth each if they're both active at the same time. Or 90/10 or 60/40 or whatever, as long as the bandwidth of the medium isn't exceeded. JF >>>> Sylvia Else wrote: >>>>> Rich Grise wrote: [quoted text clipped - 47 lines] > >JF A San Diego company just recently got 'near wire speed' (unheard of) on the new 10Gb/s standards being developed. They got 8.5Gb/s out of it. That is better than anything current. Most of the current stuff has far too much overhead. We are lucky if Gigabit Ethernet can push 600Mb/s on a good day. They did it with a Cell Broadband Engine CPU. There will be Cell processors in our future. Hell, if we make it past 12-20-2012 things will actually look good. Maybe we'll close off the borders and kick some illegal immigrant a.ses, and then clean up the gang problems too! Maybe the horses will ride after all! >>> Sylvia Else wrote: >>>> Rich Grise wrote: [quoted text clipped - 32 lines] > >Just because you have not seen EHHHH! Wrong ASSumption AGAIN, dumbfuckKK! >bidirectional full duplex on a single >fiber does not mean that it cannot exist. I NEVER once said that it didn't or couldn't, you RETARDED, PRESUMPTUOUS f.ck! > I have used such devices. Good for you, idiot. The remark was about what is in place and in use NOW! >They typically use wavelength division multiplexing. > . No sh.t. I knew what OC-96 was before you even knew what an optical fiber was. >> No it doesn't. It entirely misses the point, which is why there is a >> distinction betwen DCE and DTE. [quoted text clipped - 3 lines] > If the plain old telephone system can do it, why not data communications > equipment? RS485? > No distinction between DCE or DTE, only one single pair of wire, only > one type of cheap cable, cheap and simple connectors, no fuss, no > confusion. RS232 was the solution to a different problem (how to conect modems to terminals) >>> Or maybe the question should be why do we have cables that are not >>> crossover. [quoted text clipped - 34 lines] >My question related to why this situation was created in the first >place, since it is not a logical necessity. --- The answer to your question was posted in the question I posed, which you snipped. Why are you here? JF > Or maybe the question should be why do we have cables that are not > crossover. [quoted text clipped - 10 lines] > > Did I miss something? Is there a reason this situation persists? The world would be better with more hermaphroditic connectors. >> Or maybe the question should be why do we have cables that are not >> crossover. [quoted text clipped - 12 lines] > >The world would be better with more hermaphroditic connectors. Perhaps the term you were seeking is 'androgynous'. > Or maybe the question should be why do we have cables that are not > crossover. [quoted text clipped - 4 lines] > Not content with that, when UTP cables came out, we had a similar > situation. Well, the jargon might have changed, but there are still two of them, otherwise we would all die off. |
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