On the matter of the type of cabling to be used between the Telco Demarc and the
CPE, I have found this to be one of the most shrouded of all areas in telecom
standards. The jabber and deliberations that have taken place over this issue
border on folk lore and hijinx, and could fill a plant man's notebook in no time
flat.
Prior to metallic T1s being made available to end users by the incumbent carriers
(this is going back some tweny years or so), the carrier itself extended cabling
to the point of the customer's CPE/DTE. Reportedly (and in fact, most of the
time), they used individually shielded pairs, actually comprising two separate
cables - one for each direction.
The standard that was used in the latter case was the ancestor of today's ANSI
401.1 and it applied to the "telco's" EMI/RFI compliance responsibilities, not the
customer's.
Later on, the EIA/TIA drew up a set of commercial building wiring standards in the
way of TIA568, but neglected to include the T1 niche in its writings, relegating
it to an orphan state. Consequently, there has been much confusion amongst
enterprise IT staff and Telco guidelines, not to mention the list of different
recommendations that manufacturers of CSUs and DSUs place in their glossies.
I've seen where STP (shielded twisted-pair cabling) purists have succeeded in
having shielded cabling used, only to screw it up by mis-applying the necessary
grounding connections causing more problems than they solved.
And I've seen where wall fields of T1 demarcs in an MDF room have successfully
been deployed using nothing more than Cat3 UTP between spaces that were thirty
stories apart. Through all of this, the one area that is often overlooked is the
area where vendors of network hardware stipulate what type of cabling they will
support and will _not_ support, with pair shielding used as a determining factor.
About two years ago, after a client successfully deploying several shelves of T1s
for most normal enterprise purposes, they found that one certain VoIP gateway was
encountering excessive errors. After all self tests came up negative, as did an
end to end test on the T1, and after swapping out those T1s and their respective
patch cables, the problem persisted.
At one point the vendor's rep pointed to the fine print in the operator's manual.
It stipulated that the only cabling that would be supported between the gateway
and the telco demarc was individually shielded twisted pairs. When it was
discovered that the client had chosen to use UTP patch cords to extend their T1
demarcs some fifteen or so feet, the vendor would not even begin to diagnose the
problem further in depth until the client replaced those cables with shielded
ones.
Once replaced, the problem appeared to subside as evidenced by a lower incidence
of errored seconds initially (but still unacceptable from my view), only to
resurface at a later time to the same state of impairment that it was before.
But the salient point here isn't whether or not the problem was solved, as much as
it is the significance of abiding by vendor warranty conditions (if you've agreed
to them initially, even tacitly, in your contracts and SLAs) when selecting a T1
cabling solution.
If anyone on this list has a more authoritative source that stipulates the type of
cabling to be used for the section in question (between the demarc and the CPE),
perhaps something that has been written more recently than the experience I cited
above, it would be appreciated.