|
Posted by on March 31, 2008, 11:26 am
If you were Registered and logged in, you could reply and use other advanced thread options
Anyone know what kind of "telegraph channels" are still supported
today? I thought they were all obsolete and removed some years ago.
(I recall seeing tariff announcements to that effect.)
In this month's Verizon phone bill, there is a notice of private line
rate increases. Most items seem to be contemporary digital services,
such as "DS1", "DDS", DSND, B-channel, D-packet, and VOI varieties.
There are also various "analog channels" and a separate group of
"voice grade channels" listed.
But there are some "Metallic Local Channel", "Metallic & Telegraph
Grade Local Channel", and "Telegraph Grade Local Channel" groups.
Would anyone know accurately what they are? There's a "Metallic
transmission function" at 77 cents in high density areas, and $13.37
in low density areas.
I thought in telephone usage the term "metallic" refers to when they
replaced single-wire--ground-return transmission with two-wire
transmission 100 years ago. Also, "telegraph" meant very low
bandwidth--50 to 100 baud--Baudot Teletype lines.
There's also a group called "Program Audio". Would this be high grade
lines for radio station usage?
Lastly, there's a group called "Secretarial". Is this answering
service?
Thanks. Public replies, please
***** Moderator's Note *****
"Metallic" means metal: in other words, it means a circuit using
direct current signalling on copper pairs instead of one that employs
tone-based or digital transmission of some sort. They were used for
central-station burglar alarms, such as those provided by ADT.
Burglar alarms used to be wired in series, since they used McCulloch
loops for signalling, just like municipal fire alarm boxes: each
station had a different code, and when the alarm was triggered, it
would break the loop in a prearranged pattern to tell the central
station which node was sending. At the central station, the signal was
recorded on paper tape by a register that either marked the tape with
a pen or punched holes in it for each pulse: this is exactly the same
way Morse designed the original telegraph system.
When I joined Ma Bell, we were taught to troubleshoot burglar alarm
circuits by using a Volt-Ohm-Milliammeter at the frame, checking from
one pair to the next to find an open circuit, because they were wired
with _SINGLE_ wires from the ring of the first pair to the tip of the
next, and so on until the last pair's ring lead would be connected
back to the first pair's tip.
I always loved working on BA's: it was a sure-fire four-hour overtime,
because the pairs were _never_ in the same order as the circuit card
called for, and there were often additional stations that had been
added or existing ones disconnected, without proper record
keeping. That meant that I and a cow-orker had to "pull" the leads
from each pair to the next, correct the record, test the (newly
documented) pair, and then pull to the next pair.
In the early 80's, the company switched to using "burlar alarm
multiples", which were just frame blocks that had been allocated for
connecting the pairs in a McCulloch loop together: the back of the
block was wired to provide the ring-tip, ring-tip connecitons, and
ordinary pair wire was run from each cable pair to the front
side. This simple innovation meant that I could find an open pair by
"running the block", i.e., by just moving the tips of my pliers across
the lugs so as to short each pair in turn, changing four hours of
overtime into (at most) four minutes of troubleshooting. When the open
pair was identified, it was only a moments time to wire a short across
it until the cable was fixed.
Metallic circuits are fairly rare these days: New England Telephone
dropped them years ago, ostensibly because of high maintenance costs:
however, I think it was really because too many companies were using
them for data circuits. A sophisticated telecom manager, faced with a
choice of paying thousands per month for a T-1 line or a few dollars
for a metallic "burglar alarm" circuit, would just buy some
line-drivers and make his own T-1. Of course, we testmen had a lot of
fun "repairing" such lines when we found them: my favorite trick was
to "Box change" them from a single pair onto two defective pairs that
had each had only one side open, thus providing a "metallic" circuit
that was utterly useless for data. Customers who complained of noise
would hear me recite a speech about the lack of a noise specification
in the metallic alarm tariff.
Yeah, I know, but I was young.
ADT and other central station providers changed over to computerized
alarms and modems as quickly as they could during the 80's: the new
equipment provided more data (building temperature, sprinkler
pressure, individual "door ajar" info, etc.), and was also _much_ more
difficult for burglars to bypass. The pairs assigned to metallic
McCulloch loops were converted to low-speed data, and moved from
BA-multiple blocks over to two-wire audio bridges. In the few cases
where metallic circuits were still provided, mostly because of
"grandfathered" circuits contracted to municipalities, we would wire
the local cable at each end to special T-Carrier channel units that
simulated McCulloch loop operation.
Program Audio lines are for radio stations, as you surmise. As a
senior testman, I did a stint on the "Radio Board": we thought nothing
of spending an entire day equalizing a pair so as to attain flat
frequency response from 300 to 15,000 Hz., even for a one-time remote
broadcast lasting only a few hours. The tariff called for it, we
delivered it, no questions asked.
I'm not familiar with Secretarial service, but I agree it's probably
for TAS.
Thanks for the trip down memory lane!
Bill Horne
Temporary Moderator
(Please put [Telecom] at the end of the subject line of your post, or
I may never see it. Thanks!)
|
 
| |
Posted by Sam Spade on March 31, 2008, 3:36 pm
If you were Registered and logged in, you could reply and use other advanced thread options
> ***** Moderator's Note *****
when we found them: my favorite trick was
> to "Box change" them from a single pair onto two defective pairs that
> had each had only one side open, thus providing a "metallic" circuit
> that was utterly useless for data. Customers who complained of noise
> would hear me recite a speech about the lack of a noise specification
> in the metallic alarm tariff.
>
> Yeah, I know, but I was young.
> Bill Horne
> Temporary Moderator
So that was you who Ernestine [called]! "Listen Buster, I'll send him
over there to rip your instrument out!" ;-)
***** Moderator's Note *****
Well, I *was* a high school graduate ... ;-)
I should explain, before the conspiracy theorists get here, that cable
pairs were in extremely short supply at the time, and because Boston
had a lot of wire centers, toll cables were sometimes needed for
circuits between adjacent buildings that straddled a boundary.
Sometimes we'd need a pair in a certain place, so I'd check for
defective pairs in that terminal or on the toll cable that were listed
as "one side open" , and if I could find two, I'd check for a burglar
alarm and move it onto the "bad" pairs. The burglar alarm companies
didn't care: they were _really_ using them for alarms, so continuity
was all that mattered to them. But, during a six-month period, I did
this twice to "burglar alarms" that were being used for high-speed
data, and I had to tell the subscribers that they were getting what
they had paid for, and that the pairs they used to use were now in
service for someone else who was paying more.
They didn't like it, but I didn't apologize, then or now: if the tariff
called for it, we provided it, no questions asked. The funny part was
that that kind of a workaround became impossible when COSMOS was
introduced: the computer-driven pair assignments couldn't be used if
they were marked as "defective", even though only one side was
open. COSMOS didn't have any code to show a pair as "Defective but
usable", so the things we could do when the records were kept by hand
just weren't possible when the computers took over.
I was always puzzled that the toll cables were never arranged to
create Phantom, Ghost, or Wraith pairs: we certainly had enough 120C
coils, but for some reason the company's policy forbade the practice
and the shortage of toll cables continued well into the eighties, when
T-carrier took over almost all inter-office circuits.
I used to set up "Hoot and Holler" lines between the offices by using
phantoms: during slow nights when I was on "swing" shift, we'd wire up
"ringdown" SF units so that the testboards could ring each other
without having the boss complain about our numbers being busied
out. Of course, the fact that we had a lot of vacant SF slots and
extra selcal equipment was due to the fact that T-carrier _was_ taking
over, so I can't protest too much.
Bill Horne
Temporary Moderator
(Please put [Telecom] at the end of the subject line of your post, or
I may never see it. Thanks!)
|
|
Posted by Scott Dorsey on March 31, 2008, 8:06 pm
If you were Registered and logged in, you could reply and use other advanced thread options >But there are some "Metallic Local Channel", "Metallic & Telegraph
>Grade Local Channel", and "Telegraph Grade Local Channel" groups.
>Would anyone know accurately what they are? There's a "Metallic
>transmission function" at 77 cents in high density areas, and $13.37
>in low density areas.
These are low bandwidth metallic lines. Just two or four wires from
point to point, with DC continuity.
They are graded for bandwidth... you can get a circuit guaranteed for
16KC operation, and you can get a circuit guaranteed for 10 baud contact
closure.
The radio guys get the 8KC and 16KC loops. The burglar alarm guys get
the 10 baud contact closure circuits.
SOMETIMES you can get good audio bandwidth across an alarm circuit, but
it's not guaranteed. It sure is cheap, though. Likewise I have run
T-1 circuits over 48F leased lines for five bucks a month... but it
is not guaranteed.
>I thought in telephone usage the term "metallic" refers to when they
>replaced single-wire--ground-return transmission with two-wire
>transmission 100 years ago.
Today it means there is physical copper from one end of the line to the
other. The circuit is balanced, but it's not being multiplexed over any
sort of trunk circuit.
>Also, "telegraph" meant very low
>bandwidth--50 to 100 baud--Baudot Teletype lines.
Yes, precisely. There are still plenty of remote sensing applications
where low bandwidth signals and DC circuits are needed.
>There's also a group called "Program Audio". Would this be high grade
>lines for radio station usage?
Yes, that is where the 16KC and 8KC radio loops would be. IF you can
get them today, which is rapidly becoming an issue.
>Lastly, there's a group called "Secretarial". Is this answering
service?
Dunno.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
***** Moderator's Note *****
IIRC, D-4 banks can be equipped with 5 KHz and 8 KHz program audio
cards: they work by using multiple timeslots. I don't think D-4 can be
used for 15 KHz, but it's been awhile.
Broadcast stations have other options now: remote pickup
transmitter/receiver setups, adapters that allow program audio on ISDN
or multiple POTS lines, and satellite.
Bill Horne
Temporary Moderator
(Please put [Telecom] at the end of the subject line of your post, or
I may never see it. Thanks!)
|
|
Posted by Bill on April 5, 2008, 11:55 am
If you were Registered and logged in, you could reply and use other advanced thread options
> ***** Moderator's Note *****
>
> IIRC, D-4 banks can be equipped with 5 KHz and 8 KHz program audio
> cards: they work by using multiple timeslots. I don't think D-4 can be
> used for 15 KHz, but it's been awhile.
WECo Channel units for D4 Channel Banks supported three types of PG
(Program Grade) audio services. 5Khz, 7.5/8Khz, and 15Khz. 3Khz lines
were provisioned using TO4 channel units that were wired based on the A
to Z circuit configuration. Coastcom also produced PG channel units for
D4.
As the market for D4 PG audio channel units began to dry up in the early
1990's, Pure Digital end to end systems replaced the hard to find D4 PG
channel units. The newer digital systems employed proprietary HDSL over
a single wire pair to a HDSL remote audio unit that is capable of
supporting up to 768Kb/s. Equal to twelve DS0 channels.
The 768Kb/s provided capacity for two 15Kh/z audio channels in a stereo
L-R configuration over a single wire pair. The PG system used by NYNEX,
latter Bell Atlantic-North, employed equipment from XEL Communications.
The XEL system was compatible with the WECo & Coastcom 15Khz units when
used at the far end D4 bank of the T1 system.
I was on the Transmission Engineering staff at NY Telephone who
evaluated the XEL equipment, as well as other D4 based FT1 equipment in
1995-6.
Boardcasters were not too fond of the XEL digital units, since one of
the main complaints was the lack of audio headroom on digital equipment,
along with quantizing noise/distortion. Radio ststions transmitting
classical music were the most critical of the XEL units.
In 2001 I specified funtional requirements, then performed test &
acceptance for deployment in Verizon East (fBA region) of a replacement
for the D4 XEL HDSL units. The replacement comprised an Adtran ISDN
channel unit (UBR1TE-V), and a station package manufactured by Pulsecom
known as the Program Channel Audio Unit (PCAU).
Using the PCAU, and a UBR1TE-V (With the D Channel turned off, DDS
mode), a 7.5 or 15Khz program audio channel can be transported across a
T1 line using one or two DS0 chanels. The PCAU employs a patented
compression scheme that permits up a 7.5Khz audio channel to be carried
over a single DS0 B channel, and two DS0 B channels to carry a 15Khz
line.
A PCAU is required at each end of a PG audio channel. WECo/Coastcom and
XEL PG equipment are not compatible with the PCAU/UBR1TE-V circuit
combination.
The ISDL/PCAU circuit design allows for the first time provisioning of
PG audio channels over digital loop carrier systems using native ISDN
channel unit equipment. A capability that was not possible, except on
SLC-96 systems.
I hold the US Patent, assigned to Vz, that permits a UBR1TE ISDN channel
unit to respond to in-band DDS loop codes (When the D channel is
disabled on the D4/SLC-5 channel unit), and when used in conjunction with
an Adtran OCU-R at the customer location. The IDSL design will deliver
traditional 4W DDS services over a 2W IDSL loop.
During the development of the Adtran channel unit, I required the
manufacturer incorporate additional features to support loopback
capabilities not typically used in the DDS-IDSL application. Such as
remapping in-band DDS latching CSU loopback (Along with DS0-DP
loopbacks), over the ISDN's embedded eoc channel as a NT1 loopback
message.
The idea was to permit a digital leased line service capable of up to
128Kb/s to be introduced using a U interface at the customer location
that terminated into either an ISDN/ISDL capable router interface (WIC),
or ISDL (non-switched ISDN) data communications equipment.
The PCAU was designed to respond to a NT1 loopback over the IDSL eoc,
similar to an end office switch performing NT1 BER test on an ISDN-BRI
loop. The PCAU also incorporates a V.54 in-band loopback to further help
maintenance personnel sectionalize circuit troubles over the metallic
or DLC loop(s).
Testing the T1 portion of the audio channel is performed by operating a
remote loopback at the UBR1TE-V via an in-band DDS DS0-DP latching
loopback. On tandem BR1TE cad connections, such as on back to back
channel bank designs, use of DS0-DP loop codes follows conventonal DDS
testing strategy.
For test center personnel, the learning curve involved with PG audio
testing is not as difficult to adopt when compared to previous methods.
The first application of a PCAU/UBR1TE-V circuit design was at a New
York classical radio station in 2002. Two circuits were ordered by the
station to evaluate the new equipment. One circuit was used on a remote
studio audio broadcast link used during newscasts, and the second
circuit as a talk-back audio feed for the broadcast news link. Both
circuits were provisioned for 15Khz.
Since the initial introduction of the 7.5/15Khz PCAU in 2002, Pulsecom
has introduced a HD PCAU capable of supporting 20Khz audio. Unfortunatly
I am not intimate with the newer HD PCAU since I am no longer with Vz,
however based on information from Pulsecom's web site, the HD version
appears compatible with the original IDSL transport equipment I
performed development work on.
Bill
***** Moderator's Note *****
Thanks for your post, Bill: that fills in a big gap in my
understanding. Since D-4 banks were "sorta" MD'd years ago, I'm
curious if any of our readers know whether the IBOC's are still
getting them from second-source suppliers, or if they've been
replaced.
Bill Horne
Temporary Moderator
(Please put [Telecom] at the end of the subject line of your post, or
I may never see it. Thanks!)
|
|
Posted by Garrett Wollman on April 6, 2008, 10:50 am
If you were Registered and logged in, you could reply and use other advanced thread options
>The first application of a PCAU/UBR1TE-V circuit design was at a New
>York classical radio station in 2002. Two circuits were ordered by the
>station to evaluate the new equipment. One circuit was used on a remote
>studio audio broadcast link used during newscasts, and the second
>circuit as a talk-back audio feed for the broadcast news link. Both
>circuits were provisioned for 15Khz.
That would (assuming "New York" refers to the city) presumably be
WQXR, during the period when their newsroom was located in the /Times/
newsroom, in the old /Times/ facility, but the air studios were
elsewhere.
Most NYC stations use microwave (to the extent frequencies are
available) and telco T1 circuits for studio-transmitter links.
Normally the stations will do their own multiplexing on the T1 using a
Harris Interplex or similar products; this allows them to run digital
end-to-end, and to provide private-network IP connectivity at their
transmitter sites, which is becoming a necessity these days.
I suspect a few of them still have old copper program lines which they
keep as a backup-backup. (The radio engineers I know seem to spend an
inordinate amount of time dealing with telco issues.)
-GAWollman
--
Garrett A. Wollman | The real tragedy of human existence is not that we are
wollman@csail.mit.edu| nasty by nature, but that a cruel structural asymmetry
Opinions not those | grants to rare events of meanness such power to shape
of MIT or CSAIL. | our history. - S.J. Gould, Ten Thousand Acts of Kindness
|
| Similar Threads | Posted | | Re: Off premise extension (Was: Telegraph channels today? [Telecom] | April 8, 2008, 11:43 pm |
| Telegraph Office Scene in the Movie "The Sting" | February 13, 2006, 4:10 pm |
| Re: Telegraph Office Scene in the Movie "The Sting" | February 14, 2006, 9:57 pm |
| What Happened to FM Channels 1-199? | March 21, 2005, 3:39 pm |
| Re: What Happened to FM Channels 1-199? | March 21, 2005, 11:21 pm |
| Why Can't I Have Just the Cable Channels I Want? | April 16, 2006, 4:02 pm |
| Re: Why Can't I Have Just the Cable Channels I Want? | April 16, 2006, 8:35 pm |
| AT&T to Offer 20 Channels of TV For Web Viewers | September 12, 2006, 2:24 pm |
| AT&T to Serve Up TV Channels on PCs, Mobile Phones | March 23, 2007, 1:37 pm |
| Verizon to Carry Starz Movie Channels | April 15, 2005, 1:13 pm |
|
|
NewsGroups 
Yahoo! 
Google 
Windows Live 
del.icio.us 
digg 
Netscape 
XML site map