My understanding is that the use of STP instead of UTP actually
*de*creases the maximum length over which copper ethernet can be guaranteed.
If you're really interested in longer distances, and/or worried about interference, pickup etc., then fibre would probably be a better choice, and has become reasonably affordable in comparison, whereas the price differential used to be considerable.
Argggghhh ! I thougth wrong things about shielded cables. For me "shield" was equivalent of "better quality".
Our purpose is to interconnect network equipments within several 19' rack-cabinet with copper gigaethernet links. Rack-Cabinets are close from each other but sometimes the link's length could be higher than 100 meters.
What type of copper ethernet cable I can use for short connections ? What type of copper ethernet cable I can use for long connections ?
Is yours above recommendations could support ethernet protocol evolution (like 10 Gb) ?
Finally, do you have links which could help me to choose my cables ?
I think you're confusing 802.3ak, which is a released standard for a short range interconnect over 15 meters of STP Infiniband cable, with the coming
802.3an standard for 10 gig Ethernet over 55-100 meters of some kind of UTP.
The cable vendors are going to tell you that you will need CAT6 or CAT7 cable for 10 gig, but they also said that about gigabit, even after the standard that was designed around CAT5 was released, until one of the PHY vendors got sick of hearing about CAT6 and demonstrated gigabit running on
8 strands of barbed wire--that pretty much put an end to the notion that CAT6 was _required_. The actual requirement for 10 gig will not be known until the committee makes an announcement, but odds are that it will be much less stringent in its cable requirements than the cable vendors want it to be.
The usual STP cable is not 100 ohm impedance, so that does tend to decrease the maximum length with 100 ohm termination, and likely with matching termination.
Well, more expensive, yes. UTP cable depends on the signal being balanced. That is, the current in one wire of a pair is exactly equal and in the opposite direction to the other. Transformers are used to make that happen. A shielded cable has metal around the outside of either individual pairs or the whole cable. In either case current in the (inside of) the shield can cancel unbalanced currents from wires inside.
At some point, though, it is possible to get current on the outside of the shield, in which case the shield does not help, and actually radiates the signal. At higher frequencies it gets harder to keep the signal from the outside, and connector design gets very important.
The shield might have to couple to the metal box, and then you have problems with ground loops.
As far as I know, fiber. The cable prices aren't so different, and very likely less than STP cable. Connectors are more expensive, but likely less than STP connectors. Connector installation is more expensive, but again likely less than proper installation of STP connectors.
STP is need in electrically noisy environments. One office I know of was originally cabled with UTP which didn't work, so had to replaced by STP. The office was near wires carring a few gigawatts of electricity.