Sealing current on ISDN loops
Wynn Quon
Another question for ISDN gurus:
The Bellcore Layer 1 specs talk about
"sealing current." This is a low current (1-20mA) DC signal
applied to tip and ring. It serves two purposes as far as I
can tell: It is supposed to reduce oxidation at line splices
and it provides a troubleshooting aid in the field. Do you
know how widely this facility is used and how effective it is?
--
Wynn Quon | The greatest of all gifts is the power to
(not speaking for) Mitel Corp. | estimate things at their true worth...
| - La Rochefoucauld, "Reflexions"
David Lesher
qu...@software.mitel.com (Wynn Quon) writes:
>Another question for ISDN gurus:
> The Bellcore Layer 1 specs talk about
> "sealing current." This is a low current (1-20mA) DC signal
> applied to tip and ring. It serves two purposes as far as I
> can tell: It is supposed to reduce oxidation at line splices
> and it provides a troubleshooting aid in the field. Do you
> know how widely this facility is used and how effective it is?
I suspect it's universal. Sealing current is one of those lessons
that gets forgotten and relearned time and again.
I wonder, do we need 'sealing photons' in fiber?
--
A host is a host from coast to coast.................wb8foz@nrk.com
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433
Brad Bennett
Wynn Quon wrote:
>
> Another question for ISDN gurus:
>
> The Bellcore Layer 1 specs talk about
> "sealing current." This is a low current (1-20mA) DC signal
> applied to tip and ring. It serves two purposes as far as I
> can tell: It is supposed to reduce oxidation at line splices
> and it provides a troubleshooting aid in the field. Do you
> know how widely this facility is used and how effective it is?
>
Wynn:
Wow. It is great to see that someone actually noticed this! I was
personally the researcher that did the sealing current work while at
Bellcore. And you are right on target....sealing current does
effectively keep a copper loop intact (through a process called
electromigration). I could bore you with all the Material Science
theory behind it...but it does work on copper loops which have splices.
Now, how widely is it used? Well, for direct copper loops (CO to
customer sites) it is ALWAYS suppose to be applied (and is built into
the line cards). For other technologies (e.g. BRITE cards), which
synthesize ISDN from 3 DS0 circuits at a subscriber loop cabinet (SLC),
I am still not sure it is a requirement.
FYI....there were some other interesting upshots of all this work, which
I am not certain have ever made it to the public. For example there are
certain metal pairs which you definitely do NOT want to use sealing
current...or for that matter, even want to run any continuous DC current
(e.g. copper and precious metals). Such contacts (splices) are
materially designed to fail if current continually flows in the wrong
direction.
Anyway, on plain ol' copper wires, sealing current helps to maintain
good electrical connections. In both theory and practice!
Best Regards,
Brad
Quicomm
http://www.quicomm.com
Laurence V. Marks
In <32B1EB...@quicomm.com>, Brad Bennett <br...@quicomm.com> writes:
>Wynn Quon wrote:
>>
>
>Now, how widely is it used? Well, for direct copper loops (CO to
>customer sites) it is ALWAYS suppose to be applied (and is built into
>the line cards). For other technologies (e.g. BRITE cards), which
>synthesize ISDN from 3 DS0 circuits at a subscriber loop cabinet (SLC),
>I am still not sure it is a requirement.
>
The Adtran Mid-Span repeater does apply sealing current to the loop between it
and the customer premise--in fact if current can't flow, it's supply goes out
of regulation. There's a special free kit available for 7845 owners served by
one of these.
I would suspect that Adtran also uses sealing current in their BR1TE products.
Laurence V. Marks
IBM Corp. - Research Triangle Park, NC
Raymond Oschger
On 11 Dec 1996 15:33:46 GMT, qu...@software.mitel.com (Wynn Quon)
wrote:
>Another question for ISDN gurus:
>
> The Bellcore Layer 1 specs talk about
> "sealing current." This is a low current (1-20mA) DC signal
> applied to tip and ring. It serves two purposes as far as I
> can tell: It is supposed to reduce oxidation at line splices
> and it provides a troubleshooting aid in the field. Do you
> know how widely this facility is used and how effective it is?
>
>
>--
>Wynn Quon | The greatest of all gifts is the power to
>(not speaking for) Mitel Corp. | estimate things at their true worth...
> | - La Rochefoucauld, "Reflexions"
Sealing current is being used here in Illinois and I have found it to
be a handy trouble shooting tool with certain types of NT1. The early
AT&T NT1s had a LED pattern which would indicate "loss of signal with
sealing current present" or something like that. True line failures
were rare and the sealing current usually indicated that I had
continuity from the switch. (I knew that we were directly connected on
U-loops with no mid span repeaters.)
The only time I had massive failure without sealing current was when
Ameritech was down in the basement disconnecting all my lines. I
needed to run down to the demark and convince them that it was
possible to have a working telephone line without dial tone. It wasn't
easy by the way.
--
Regards, Ray Oschger
Raymond Oschger & Associates
ISDN Related Consulting Services
847-292-0192 (Chicago)