boomer@athena.princeton.edu (Don Alvarez) (01/31/90)
In article <3335@accuvax.nwu.edu> eli@pws.bull.com writes: >The speed of light in fiber is actually slower than the speed of light >in coax cable... (.72 to .76, or some such). Does anyone know the >propagation speed for light in copper phone wire, or whatever else is >used for long lines?? From the Reference Data for Radio Engineers, published by the Federal Telephone and Radio Corporation (an associate of the International Telephone and Telegraph Corporation) Copyright 1943. Telephone Transmission Line Data Characteristics of Standard Types of Aerial Wire Telephone Circuits At 1000 Cycles Per Second Type of Circuit Gauge Spacing Velocity (mils) (in.) (miles/s) Non-Pole Pair Physical 165 8 179,000 Non-Pole Pair Side 165 12 179,500 Pole Pair Side 165 18 178,000 Non-Pole Pair Phantom 165 12 177,500 Non-Pole Pair Physical 128 8 178,000 Non-Pole Pair Side 128 12 178,500 Pole Pair Side 128 18 177,000 Non-Pole Pair Phantom 128 12 177,000 Non-Pole Pair Physical 104 8 175,500 Non-Pole Pair Side 104 12 177,000 Pole Pair Side 104 18 175,500 Non-Pole Pair Phantom 104 12 176,000 Notes: (1) All values are for dry weather conditions and 20Degrees C (2) All capacity values assume a line carrying 40 wires (3) DP (double petticoat) Insulators assumed for all 12" and 18" spaced wires - CS (Special Glass with Steel Pin) Insulators assumed for all 8" spaced wires. Since the slowest speed listed here is about 94% C, and one can only assume wires have gotten better, not worse in the last 47 years, we clearly should all drop our fiber optic lines and go back to copper. (God, how I hate waiting for those 20ms delays!) -don
nomdenet@venera.isi.edu (02/01/90)
> ... Does anyone know the propagation speed for light in copper phone wire, > or whatever else is used for long lines?? Yep: 0 km/sec. Sorry; I couldn't resist. A. R. White nomdenet @ ISI.edu
stanley@uunet.uu.net> (02/02/90)
In article <3396@accuvax.nwu.edu> Don Alvarez <boomer@athena.princeton.edu> writes: X-Telecom-Digest: Volume 10, Issue 67, message 5 of 11 > [lots of numbers deleted] Plain copper wire has always had a good velocity factor. Unfortunatley, the coax variant can range anywhere from 95%c to 60%c. Even within the same type from the same manufacturer. This causes great havoc when trying to make resonant feedlines (Hmmm, is this the .6c RG-58 or the .78c RG-58?) nn m m RRR i John Stanley N8GFO n n m m m R R New Methods Research, Inc. n n m m m RRR i 6035 Corporate Drive n n m m m R R i East Syracuse, NY 13057 n n m m m R R i #include <disclaimer.h> stanley@nmri.com
wrf@mab.ecse.rpi.edu (Wm Randolph Franklin) (02/04/90)
In article <3396@accuvax.nwu.edu> Don Alvarez <boomer@athena.princeton.edu> writes: > Telephone Transmission Line Data >Characteristics of Standard Types of Aerial Wire Telephone Circuits > At 1000 Cycles Per Second >Type of Circuit Gauge Spacing Velocity > (mils) (in.) (miles/s) >Non-Pole Pair Physical 165 8 179,000 >Non-Pole Pair Side 165 12 179,500 == (etc) However, 8" or 12" spacing in the air is somewhat different from 0.05" spacing in a twisted pair. I thought that those signals traveled at about 2/3 c. Actually what we really want is the speed in a coax. Wm. Randolph Franklin Internet: wrf@ecse.rpi.edu (or @cs.rpi.edu) Bitnet: Wrfrankl@Rpitsmts Telephone: (518) 276-6077; Telex: 6716050 RPI TROU; Fax: (518) 276-6261 Paper: ECSE Dept., 6026 JEC, Rensselaer Polytechnic Inst, Troy NY, 12180
tjr@ihnet.att.com (Thomas J Roberts) (02/05/90)
From article <3396@accuvax.nwu.edu>, by boomer@athena.princeton.edu (Don Alvarez): > In article <3335@accuvax.nwu.edu> eli@pws.bull.com writes: >> [table of signal velocity characteristics in wire deleted] > Since the slowest speed listed here is about 94% C, and one can only > assume wires have gotten better, not worse in the last 47 years, we > clearly should all drop our fiber optic lines and go back to copper. > (God, how I hate waiting for those 20ms delays!) > -don Of course, the delay in the wire is only a small part of the total delay. Every modem (digital communication only) adds >1000 microseconds of delay. Every analog amplifier adds several to many microseconds of delay. Every analog Frequency Division Multiplexor adds several to many microseconds delay. Every digital regenerator adds up to a microsecond of delay. Every Analog->Digital or Digital->Analog conversion adds up to 125 microseconds of delay. Every time-slot-interchange within a digital switching system adds 125 microseconds of delay. Every satellite hop adds >100,000 microseconds of delay (but most of us don't have to worry about this). After you add all of these up, you then get to double the delay if you're concerned about the round-trip delay (and normally that's what is of interest). Fiber is very different, as the regenerators add only a few to many nanoseconds of delay, and they are spaced further apart. But the signal propagation in the fiber is slower than that of a wire or of a radio channel. The analysis of round-trip delay on a telecommunications channel is VERY complicated, and is extremely route dependent. If your path traverses a packet network, things can get downright bizarre. Note that signal delay is only a minor consideration when telcos engineer a transmission path (cost is the major factor, capacity, ease of maintenance, and reliability overwhelm delay considerations). Tom Roberts att!ihlpl!tjrob
lfd@lcuxlq.att.com (Leland F Derbenwick) (02/06/90)
In article <3396@accuvax.nwu.edu>, boomer@athena.princeton.edu (Don Alvarez) writes: > In article <3335@accuvax.nwu.edu> eli@pws.bull.com writes: > >The speed of light in fiber is actually slower than the speed of light > >in coax cable... (.72 to .76, or some such). Does anyone know the > >propagation speed for light in copper phone wire, or whatever else is > >used for long lines?? > [reference data for a bunch of open-wire lines, > showing velocity factors about .94 or better] > Since the slowest speed listed here is about 94% C, and one can only > assume wires have gotten better, not worse in the last 47 years, we > clearly should all drop our fiber optic lines and go back to copper. This is hardly news: open-wire lines always had much better velocity factors than coax or anything else with a non-air dielectric. (Basic EE, or physics if you prefer.) Of course, open-wire lines have noise problems and they tend to take up a little more space than you'd like. And since the time difference for a 3000 mile span is something less than 8 ms, who's going to notice? But the real question is, why does anyone think this is relevant to current long-distance service? Yes, once upon a time, when you asked the operator for a long distance connection, you got a pair of wires (two pairs?) just for your call. But it's 1990 now... Trunk lines have been _at least_ T1 running over twisted pair for years. A "long lines" connection involves a route via some or all of fiber, digital radio, satellite, or DS3 over coax. And most of the delay is in the conversions and regeneration, not in the transmission. [Except of course for satellite, which is just a tad more distant. :-) ] -- Speaking strictly for myself, -- Lee Derbenwick, AT&T Bell Laboratories, Warren, NJ -- lfd@cbnewsm.ATT.COM or <wherever>!att!cbnewsm!lfd -- (and no, I have nothing to do with "long lines", except to use them!)
m21198@mwvm.mitre.org (John McHarry) (02/07/90)
Tom Roberts wrote in V10 #77 that '...signal delay is only a minor consideration when telcos engineer a transmission path...'. While delay in the cable or fiber may, indeed, be overwhelmed by the other delay modes he mentioned, the total delay is not a minor consideration. It is at the heart of the 'via net loss plan', to which I am sure he can find a couple references in his company's library. Very roughly, the aggravation caused by echo is affected by the round trip delay. To partially circumvent this, more loss must be added on long paths than on short ones. Also, there are 'cross office delay' specs on switching equipment to ensure that it doesn't mess up the scheme. Sometimes echo suppressors or echo cancellers are required on very long delay paths. And that's the news from the bottom of the rain barrel, where no one has reviewed this but me and my echo...echo...echo... *************************************************************** * John McHarry (703)883-6100 McHarry@MITRE.ORG * ***************************************************************