asterisk users - Apr 2006 - Shielding of T1/E1 cables WAS RE: Pinouts for T1/E1 crossover cable WAS "RE: what cable to connect a legacy PBX to a TE410P ?"

I was once told by a lineman that the cables they use didn't have that
many twists in them because it wasn't needed, and that the extra twists
would effectively use more cable and thus cost and weigh more than
triple what they do now. He told me that with the number of twists in
the Cat 5 cable it would cancel out any interference, but he also stated
that the effective length was calculated using a cable with less twists
and subsequently 'less dense' and that if using a Cat5e cable you must
factor that in. so if you use cat5e cable your are fine but you can't go
as far.

Regarding the Smart Jack it is mostly used as a location at the CPE
where the Telco can loop and make sure that the problem is at your end.
So your assumption is correct that you can plug anything you want into
it, its one your side of the demark, so if it doesn't work it's YOUR
problem.



> > Totally agree with you, unshielded cables are only usable if the
> > distance is short. Just curious, how should one ground the shield?
Do
> > you ground it to the ground bar in the server room? Any special
> > requirements?
> 
> That would be one way to do it, at both ends.
> 
> Personally, I would not try to install an rj45 on each end of a
shielded
> T1 cable, but rather terminate the cable on a patch panel.
> 
> _______________________________________________
> --Bandwidth and Colocation provided by Easynews.com --
> 
> Asterisk-Users mailing list
> To UNSUBSCRIBE or update options visit:
>    http://lists.digium.com/mailman/listinfo/asterisk-users

Alexander Lopez wrote:
> I was once told by a lineman that the cables they use didn't have that
> many twists in them because it wasn't needed, and that the extra twists
> would effectively use more cable and thus cost and weigh more than
> triple what they do now. 
Good thing he doesn't work for a cable manufacturer as that's a total 
crock of crap that even an inexperienced person should be able to 
detect. (You can't twist two wires to make them weight three times as 
much, or cost three times as much.)
> He told me that with the number of twists in
> the Cat 5 cable it would cancel out any interference, but he also stated
> that the effective length was calculated using a cable with less twists
> and subsequently 'less dense' and that if using a Cat5e cable you
must
> factor that in. so if you use cat5e cable your are fine but you can't
go
> as far.
Essentially true, but the impedance of a T1 cable is different from Cat5 
cables, which is one of the primary factors in limiting distance. Has 
nothing to do with the twists.

Shielded vs non-shielded has to do with the environment, and how much 
electrical noise there is near the T1 cable. Nothing more, nothing less.
> Regarding the Smart Jack it is mostly used as a location at the CPE
> where the Telco can loop and make sure that the problem is at your end.
> So your assumption is correct that you can plug anything you want into
> it, its one your side of the demark, so if it doesn't work it's
YOUR
> problem.