Newsgroups: comp.dcom.lans.ethernet

In comp.dcom.lans.ethernet, medici@dorm.rutgers.edu (Mark Medici) writes:

    You have conflicting specs here.  10Base-T and ISDN run over
    UNshielded, twisted pair (UTP) cabling.  Shielded, twisted-pair (STP)
    is used be Token-Ring and LatticeNet (LatticeNet is a pre-10Base-T
    single-vendor solution for running Ethernet over twisted pair
    cabling).

This is often a point of confusion.  No where in 10BASE-T (IEEE 802.3i,
which was recently approved to be added to ISO/IEC 8802-3 by the way)
does it require that the cable be unshielded.  10BASE-T will of course
run fine on UTP.  It will also run fine with a shield, provided the
cable characteristics such as impedance and delay are correct.  There
is 100 ohm shielded cable available.  This cable looks much like the
normal UTP cable except that it has an overall shield.  Some people
call this screened cable since STP is often understood to mean 150
ohm IBM type 1 or 2 cable.

Some German vendors are pushing shielded cable for 10BASE-T claiming that
EMI requirements cannot be met with UTP.  There are plenty of products
which have passed licensing tests running on UTP, so I disagree strongly
with their claim.  However, 10BASE-T will run over correctly chosen
shielded cable if that is what you wish to use.

There is one little problem with using shielded cable.  An RJ45 jack 
does not provide any way to terminate the shield.  I believe a shielded
version of the RJ45 is under development in Europe but I'm not sure 
how far along it is. 

    Level IV UTP is the recommended minimum cabling for 10Base-T.  I'm
    unfamiliar with ISDN, but there's a good chance it uses the same.
    Level V UTP has better electrical characteristics, and there's a
    better chance that higher-speed protocols will run over Level V than
    over Level IV.  In spite of the cost differences, I now use only
    Level V UTP in all new networks.

10BASE-T was designed to run fine over Category 3 wire (normal modern
telephony wire, 0.5 mm, twisted with one or two twists per foot).  Category
4 and 5 wire only became available towards the end of the development.
To run Token Ring over UTP (at least to a full 100 m), Category 4 wire
is likely to be necessary.  Current work on a Twisted-Pair PMD (TP PMD)
for FDDI is based on Category 5 UTP and 150 Ohm STP.  The specs can be
found in EIA/TIA Technical Standards Bulletin 36 (TSB-36) or in the draft
Generic Building Wiring spec under development in ISO/IEC JTC-1 SC 25.

    > Is this kind of cable at all available in Germany?

    I would be very surprised if both Level IV and Level V UTP wasn't
    available there.  Same for STP, if this is really what you need (which
    it seems is not the case).

It is available in Germany.  Some of the companies sell star-quad cable
rather than twisted-pair (a cable in which four conductors are twisted
together) which they claim also meets 10BASE-T specs.  I have not personally
tested the star-quad.  More importantly, some of the companies sell 120
ohm cable rather than 100 ohm.  In some cases, this impedance mismatch
can cause bit errors, particularly if you have runs which mix 100 ohm
and 120 ohm cables.

Pat Thaler