sjl@amdahl.amdahl.com (Steve Langdon) (11/10/87)
In article <16064@topaz.rutgers.edu> ron@topaz.rutgers.edu (Ron Natalie) writes: >Foo. Note that twisted pair Ethernet is a kludge. This high-speed >(Radio Frequency) unshielded twisted pair stuff is going to be put >to an end as this stuff is not going to comply with FCC regulations >on emissions. Ron is usually sensible but this time he shot from the hip and missed. Careful attention to impedance matching makes it possible to avoid the RF emission you would expect. The stunt boxes that real twisted pair Ethernet products use are there to do dynamic impedance matching. -- Steve Langdon sjl@amdahl.amdahl.com +1 408 746 6970 ...!{decwrl,sun,seismo,ihnp4,cbosgd}!amdahl!sjl [I speak for myself not others.]
ron@topaz.rutgers.edu (Ron Natalie) (11/11/87)
It wasn't a shot from the hip, it's plain good engineering sense. If I had a nice twisted pair wire, I'd probably also have a nice piece of COAX as well. However, what I usually have is phone wire, which does not have constant electrical characturistics at all. People who cheap out and run RF over phone wire, are eventually going to lose. -Ron
artm@phred.UUCP (Curmudgeon) (11/18/87)
In article <16411@topaz.rutgers.edu> ron@topaz.rutgers.edu (Ron Natalie) writes: > >People who cheap out and run RF over phone wire, are eventually going >to lose. Gee, that's funny...The telcos have been doing it for decades. ////////////////////////////////////////////////////////////////////////////// My employers only take responsibility for those of my opinions they pay me for. ////////////////////////////////////////////////////////////////////////////// Art Marriott ...tikal!phred!artm
farren@gethen.UUCP (11/19/87)
In article <1841@phred.UUCP> artm@phred.UUCP (Curmudgeon) writes: >ron@topaz.rutgers.edu (Ron Natalie) writes: >> >>People who cheap out and run RF over phone wire, are eventually going >>to lose. > >Gee, that's funny...The telcos have been doing it for decades. I think this will be big news to everyone who's ever worked at the phone company. The statement is absurd - TPC has NEVER run megahertz plus signals through standard phone wire. -- ---------------- Michael J. Farren "... if the church put in half the time on covetousness unisoft!gethen!farren that it does on lust, this would be a better world ..." gethen!farren@lll-winken.arpa Garrison Keillor, "Lake Wobegon Days"
larry@kitty.UUCP (11/19/87)
In article <361@gethen.UUCP>, farren@gethen.UUCP (Michael J. Farren) writes: > >>People who cheap out and run RF over phone wire, are eventually going > >>to lose. > > > >Gee, that's funny...The telcos have been doing it for decades. > > I think this will be big news to everyone who's ever worked at the phone > company. The statement is absurd - TPC has NEVER run megahertz plus > signals through standard phone wire. Really? What do you call T1 carrier circuits which run over pairs in regular telephone cable (adjacent to other circuits) at 1.544 Mbits/sec? Bring an AM radio into an equipment room with a T1 span line and tell me what you hear at the high end of the dial. Incidently, within telephone company central offices T1 circuits are run separate from all other circuits using either individually-shielded pairs, or in dedicated multi-pair cables (usually of a type called ABAM) having a common shield. <> Larry Lippman @ Recognition Research Corp., Clarence, New York <> UUCP: {allegra|ames|boulder|decvax|rutgers|watmath}!sunybcs!kitty!larry <> VOICE: 716/688-1231 {hplabs|ihnp4|mtune|utzoo|uunet}!/ <> FAX: 716/741-9635 {G1,G2,G3 modes} "Have you hugged your cat today?"
SNELSON@STL-HOST1.ARPA.UUCP (11/20/87)
LETS NOT MIX UP BITS AND HERTZ. ON IN HOUSE T-1 WE MAKE SURE THAT THE SEND AND RECEIVE ARE IN SEPARATE CABLE BUNDLES. THEY DON'T CROSS TALK TO EACH OTHER THAT WAY. STEVE
larry@kitty.UUCP (11/21/87)
In article <[STL-HOST1.ARPA]Fri,.20.Nov.87.07:29:01.CST.SNELSON>, SNELSON@STL-HOST1.ARPA writes: > LETS NOT MIX UP BITS AND HERTZ. ON IN HOUSE T-1 WE MAKE SURE THAT > THE SEND AND RECEIVE ARE IN SEPARATE CABLE BUNDLES. THEY DON'T > CROSS TALK TO EACH OTHER THAT WAY. There is special outside telephone cable available for T1 use which divides cable pairs into two major bundles, using a Z-shaped shield which makes contact with the outer alpeth shield. Such an arrangement allows separation of transmit and receive directions. However, much of the existing T1 carrier goes through conventional telephone cables comprising only one overall alpeth shield. Some attempt is made to keep transmit and receive pairs in different 25-pair binder groups, though. Crosstalk is not that much of a problem with T1 systems as long as: (1) the outside cable is in decent shape and moisture-free; and (2) the outside regenerators are installed at recommended locations. <> Larry Lippman @ Recognition Research Corp., Clarence, New York <> UUCP: {allegra|ames|boulder|decvax|rutgers|watmath}!sunybcs!kitty!larry <> VOICE: 716/688-1231 {hplabs|ihnp4|mtune|utzoo|uunet}!/ <> FAX: 716/741-9635 {G1,G2,G3 modes} "Have you hugged your cat today?"
farren@gethen.UUCP (Michael J. Farren) (11/21/87)
First, a retraction and apology - the telephone company does run T1 lines through their standard cables, so my argument that they do not was bogus. I should not have made the statement that they did not without a little further checking. However: if I have learned anything in a fairly long career in digital electronics, including a significant amount of work on high-speed signal transmission, it is that you have to treat any signals above 1MHz with significant respect, if you are to get the results you want. My initial assumption was that what was being discussed here was running Ethernet signals through standard 4-wire phone interconnect wire, as opposed to twisted-pair cable. If this assumption is correct, then I have to agree with one of the previous posters - you are courting disaster if you do so, especially if you are running the wire over any significant distance, say, as an off the cuff judgement, over 20 feet or so. (I'd probably limit it to three feet, and be paranoid even then, but then, I'm like that) If you are using twisted-pair, and someone has paid close attention to the characteristics required of the drivers and receivers for those signals, then you can get acceptable results. Personally, I'd rather pay the extra bucks and get a system I'd have confidence in. -- ---------------- Michael J. Farren "... if the church put in half the time on covetousness unisoft!gethen!farren that it does on lust, this would be a better world ..." gethen!farren@lll-winken.arpa Garrison Keillor, "Lake Wobegon Days"
martyl@bucket.UUCP (Marty Lee) (11/26/87)
In article <2250@kitty.UUCP>, larry@kitty.UUCP (Larry Lippman) writes: > In article <[STL-HOST1.ARPA]Fri,.20.Nov.87.07:29:01.CST.SNELSON>, SNELSON@STL-HOST1.ARPA writes: > > LETS NOT MIX UP BITS AND HERTZ. ON IN HOUSE T-1 WE MAKE SURE THAT > > THE SEND AND RECEIVE ARE IN SEPARATE CABLE BUNDLES. THEY DON'T > > CROSS TALK TO EACH OTHER THAT WAY. > > There is special outside telephone cable available for T1 use > which divides cable pairs into two major bundles, using a Z-shaped > shield which makes contact with the outer alpeth shield. Such an > arrangement allows separation of transmit and receive directions. > However, much of the existing T1 carrier goes through conventional > telephone cables comprising only one overall alpeth shield. Some attempt > is made to keep transmit and receive pairs in different 25-pair binder > groups, though. > Crosstalk is not that much of a problem with T1 systems as long as: > (1) the outside cable is in decent shape and moisture-free; and (2) the > outside regenerators are installed at recommended locations. > As far as the transmit and receive pairs are concerned there are only three types of separations, same binder group, adjacent binder groups and non-adjacentbinder groups. If the transmit and receive binder groups are separated by atleast one spare binder group then it is the same as T-screened cable or two cables. The density of carrier systems is not as good as a T-screened cable but cheaper most of the time and an existing cable may be converted. The binder(s) used between the tx and rx may then be used for low speed data and VF, so all is not lost. Now if you go to T1C (48 channels) then the whole ball game changes and all bets are off. T1C is much more sensitive to crosstalk and induced noise. Disclaimer: Good T1 designs are a must for any network. Take your time and don't rush into it, mistakes can be costly and will shape your network for the coming years. I work for a RBOC but they don't have to do all the work. (The Dept. of Justice may have something to say about this subject.) -- tektronix!reed!omen!bucket!martyl (Marty Lee)