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From: jbreeden@netcom.COM (John Breeden)
Newsgroups: comp.dcom.lans
Subject: Re: 10BaseT vs. Twisted Pair?
Message-ID: <1991Apr16.175210.5468@netcom.COM>
Date: 16 Apr 91 17:52:10 GMT
References: <1991Apr8.135731.2901@eng.umd.edu>
Organization: Netcom - Somewhere in the S.F. Bay Area
Lines: 46

In article <1991Apr8.135731.2901@eng.umd.edu> naiming@eng.umd.edu (Naiming Shen) writes:
>
>I was told by a salesman that Twisted Pair scheme is different than
>the 10BaseT. He said 10BaseT uses 2 pairs of wires, while Twisted Pair
>uses only one pair of wires and a converter can be added to this twisted
>pair so that thin net cable can be connected to the converter. It sounds
>great for the Twisted Pair scheme(only one pair of wires, thin wire can
>be added), I am wondoring if there is any shortcomings?
>

Your *salesman* needs to go back to school..... Twisted pair is WIRE and
10baseT runs on twisted pair (2 pairs rx and tx). BTW, the two pairs
defined in the standard (pair 1&2 and pair 3&6) are defined as data
pairs in the AT&T Premise Distribution Spec (what 10baseT's wiring is
based on and also where the RJ45 comes from). The remaining two pairs
are for phone or ISDN (both ISDN and PBXs use 4,5,7,8 as the two voice pairs).

What your *salesman* is referring to is a twisted pair balun (3Com makes
one called the PairTamer). The advantage? Real Cheep and only uses 1 pair.
Disadvantage? NOT a standard (10baseT specifically outlaws baluns (passive
device) and calls for repeaters - a 10baseT hub is a multiport repeater - 
an active device). Baluns are passive devices, prone to noise and jitter
(compaired to 10baseT) and are propriatory (ie: not defined by any standards
body).

The *standard* PDS twisted pair wire pulled to the desktop is 4 pair 
twisted. What your *salesman* SHOULD have said is there are a *number*
of ways to run ethernet over twisted pair, 10baseT (an IEEE standard),
baluns (ala PairTamers) and propriatary protocols used before the 10baseT
standards (ie: Synoptic's Lattisnet, Cabletron and David System's old
protocols etc).

10baseT is installed today more than any other medium in large nets because
it's a standard (ie: You can mix and match different vendors based on best
price/performance/features) is more reliable (10baseT hubs jam bad ports,
are active repeaters and compensate for jitter on the receive end) and 
is easier to manage (the many different vendor MAC level hub "management" 
"features" built into products).

-- 
 John Robert Breeden, 
    jbreeden@netcom.com, apple!netcom!jbreeden, ATTMAIL:!jbreeden
 -------------------------------------------------------------------
 "The nice thing about standards is that you have so many to choose 
  from. If you don't like any of them, you just wait for next year's 
  model."