ethernet patch cables

[Lennart Sorensen]

On Tue, Jan 29, 2008 at 01:54:54PM -0500, D. Hugh Redelmeier wrote:
> Dollarama is selling Belkin 3.1m snagless CAT 5e patch cables for $1 each.  
> Perhaps not everywhere and all the time.
>   http://www.redflagdeals.com/forums/showthread.php?t=541877
> 
> I bought 15, thinking that I'd then feel free to discard some of my
> nastier cables.  But I am such a hoarder.  For example, I have "taken
> out of service" a patch cable with a broken hook (the first of
> several).  Will I throw it out?  Will I bring it to TLUG to give away?
> 
> 
> The packaging describes these Belkin patch cables as "FastCAT5E(tm)".
> "Each FastCAT5e cable has an increased frequency range of 250%,
> providing the bandwidth necessary to reliable deliver your voice,
> video, and data well beyond today's 100Mbps systems."  Isn't "well
> beyond" only 1000BASE-T and probably not the next thing beyond that
> (10Gig)?  Isn't CAT 5 OK for 1000BASE-T?  If CAT-5 is good enough, and
> CAT-5e is better, and FastCAT5e(tm) better still, why do we need
> CAT-6?
> 
> I don't really understand whether you want CAT 6 for 1G ethernet.
> Wikipedia says CAT 6 is a cable standard for Gigabit Ethernet.  But it
> also says 1000BASE-T was designed for CAT 5 and that CAT 5e is even
> better for it.

I have only ever seen 5e and 6 as valid for GBit ethernet.  Of course on
short cables you can probably get away with plain 5 at least if it is in
good condition, hasn't been bent too much and there isn't a lot of
interference around.

10GBase-T requires Cat6 for up to 55m cables and Cat6a for 100m.

So essentially the lower cable quality means shorter cables have to be
used.

> I see that 1000BASE-TX (apparently no longer important) required
> CAT-6.

Isn't that what most machines with gigabit use?  Well actually
1000Base-T (never heard of 1000Base-TX).  It can run on Cat5 but only
properly installed cat5 that hasn't been abused.

1000Base-T does put more demand on the cable than 100Base-TX since
100Base-TX runs 125MHz signal with a 5:4 encoding of the data to get
100Mbit, and hence has some error correcting and detecting ability and
runs traffic one way only on a single pair per direction.  1000Base-T
runs 125MHz signal with data on both high and low clock (so 250MBit on a
single pair) which looses the error correction and detection ability of
100Base-TX and it transmits and receives on all 4 pairs of wires at the
same time, so it has to deal with interference that may occour as well
as keeping the transmitted and received data seperate even though it
shares the wire and it has to deal with cross talk from 4 active pairs
rather than 2.  Since the actual frequency of the signal is still 125MHz
just like 100Base-TX the cable should be OK, but the reduced protection
against errors and the increased number of pairs carrying data puts
higher demand on a good quality cable.

> I also learned that "RJ45" is the wrong term for the connector.  It
> should be called "8P8C modular connector".

Yeah well what can you do.

> The warranty says that "For the life of the product, Belkin warrants
> that this cable shall be free of defects in design, assembly,
> material, and workmanship."  So if the cable dies, the warranty won't
> work.  I don't get it -- isn't that when you want the warranty to
> work?

Lawyers just don't know how to communicate.

--
Len Sorensen
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