Thanks, Jim. As we type, EIA/TIA sanctioned Category 5, Cat5e (enhanced) and Cat6 (still to be ratified) all support Gb Ethernet to varying degrees of guarantee. About 90% of all installed Cat5 that meets the recent TIA Telecommunications Specifications Bulletin 95 (TSB95) will support GbE.
And, ostensibly, all Cat5e that tests okay for the same field test parameters will support GbE, too. Cat5e and Cat6 do not increase the reach, or distance, over which data can be sent. Rather, Cat5e guarantees improved crosstalk and de-coupling performance. A great deal of the problems encountered on unshielded twisted pairs (UTPs) are not found in the cable, itself, but rather in the coupling effects that occur between pins at the 8-pin modular termination gear (jacks and plugs).
This is why it's extremely important to ensure that when installing such category cabling systems one takes care not to skimp on jacks, plugs and patch cords... and why it's best to purchase all necessary parts and accessories from the same vendor.
Oftentimes, the ten and fifteen (sometimes even twenty) year warranties that are so characteristic these days of most vendors claims are void, if you don't use them end to end.
Cat6 adds to those gains by increasing the bandwidth of each of the four pairs to 250 MHz. Cat5 and Cat5e, in contrast, are rated only to 100 MHz per pair.
The one thing that remains constant for all levels of Cat x cabling, no matter which grade, is the distance. All TIA Category cables are designed for a maximum end-to-end "channel" distance of 100 meters. A further breakdown can be viewed as the sum of the actual floor link and the patch cords (both in the closet and at the desk).
The link distance limit, from the closet interconnect to the desk jack, is 90 meters. The total lengths of both closet and desk patch cords should not exceed 10 meters.
A typical worst case scenario, then, would resemble:
7 meters (closet patch)-->90 meters (floor link length)-->3 meters (desk patch) = 100 meters
I'm sure that some folks here may be wondering how four pairs, each rated at 100 MHz, could support a payload delivery rated at 1 Gb. Each pair of the four-pair cable supports a carrier signal that is modulated at some bit per Hertz factor to yield 250 Mb/s over each pair. Times four, equals 1 Gb. In each direction.
Which means that in the full duplex mode there is 1Gb going both ways, over the same metallic pairs, east-to-west and west-to-east, all made possible through the miracle of DSPs supporting echo cancellation. Sounds pretty fantastic, doesn't it? Over UTP.
I should also note here that there is very little "head room" for error in this scenario. Where Cat 5 installation practices were very forgiving in the past, when 100 Mb/s Fast Ethernet was the supported data rate, such leniency will be hard to find at 1,000 Mb/s. Which simply means that the level of craftsmanship and the adherence to standards and specifications must be all that much better, and tighter, respectively.
The conditions presented by FTTC are different than those that prevail for regular indoor Catx cables, though. TIA Category x cables are rated for indoor commercial building wiring conditions, whereas FTTC obviously would involve more hostile, outdoor conditions, hence at least a modified set of environmental and electrical rules would need to apply here if regular Cat x design advantages were to be leveraged for FTTC. Come to think of it, there is at least one manufacturer who I've come across who claims to support such Cat 5 "equivalent" cabling for outside plant, but their name escapes me at the moment. Anyone know who it is, or who "they" <plural> are?
In any event, I feel confident that with some work on the parts of TIA and the EIA the gains that were achieved in the design of ANSI/EIA/TIA Cat5e and Cat6 cables could be leveraged in the outside plant, as well. Something to keep an eye on.
Cat7, btw, has yet to be specified fully, and some say that it is unlikely that it ever will. Still others say that Cat 7 will be all glass ;-)
FAC |
