telecom@ucbvax.ARPA (06/01/85)
From: Jon Solomon (the Moderator) <Telecom-Request@BBNCCA>
TELECOM Digest Fri, 31 May 85 16:33:43 EDT Volume 4 : Issue 195
Today's Topics:
SBS, Sprint, MCI, Allnet
Call Waiting
Vadics and UUUUUU
Be the first on YOUR block...
call waiting on cordless phones
Re: TELECOM Digest V4 #194
Re: telephony signals
equal acces
212/224's Remote digital loopback mechanism
Re: TELECOM Digest V4 #194
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Date: Sat, 25-May-85 15:06:04 PDT
From: vortex!lauren@rand-unix (Lauren Weinstein)
Subject: SBS, Sprint, MCI, Allnet
To: TELECOM@MC.ARPA
I've been doing some more research into the alternate carriers, and
can add more points about SBS, Sprint, MCI, and Allnet:
SBS: All calls tend to sound like they're routing through Mars. Since
the SBS system is almost totally based on satellites, you end up
with fairly substantial amounts of circuit noise in almost all cases,
and the usual satellite delay problems. SBS is also less likely
to be around in five years than MCI or Sprint.
Sprint: New problems for data users. Lately, on many circuits, the
calls have an approximately 1.5 second dropout about 3-5 seconds
after the calling party answers. Just enough to break down many
connections. You can program around it with a smart enough modem,
but it hardly seems worth it given Sprint's other problems.
MCI: Nothing new. Same old stuff. Same billing irregularities due
to lack of called party supervision. In all fairness, Sprint is
just as bad in this area. Only with AT&T can you be SURE that
billing will be based on actual call durations, though SBS is
making strides in this direction, I'm told.
I guess I can add something about Allnet as well. I haven't had a
chance to hear too many connections, but they appear to be in the
same situation (if not worse) as SBS when it comes to probability
of longevity.
The same old maxim applies. If you find an alternate that gives
you consistently acceptable results, then you might as well use it.
But if you call many different points or make lots of data calls,
you're better off with AT&T. One thing I learned is that many times
when you call people on alternates they don't bother mentioning to
you that the call sounds terrible--they just suffer along and try
be polite. Especially with MCI and Sprint, the connection quality
often seems to vary tremendously between the two sides of the call.
Your side may sound great, but to the other person you're buried in
the noise. Sometimes this difference is EXTREMELY great, for reasons
that aren't immediately obvious.
--Lauren--
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Date: Sat 18 May 85 12:20:20-EDT
From: T.JOEL@MIT-EECS
Subject: Call Waiting
To: telecom@MIT-EECS
Call waiting does do some interesting things to phone lines that are hooked
up to a modem..At school, we have our own internal network (IBX) and it has
its own call waiting. If you are on the phone talking voice to someone, you
will here a little tone if someone is trying to call you. 1 tone for an inside
call (one from within the college) and 2 tones for an outside call. Then one
can simply put your party on hold and talk to the new caller..
But with a modem hooked up..I've found that these call waiting tones seem to
knock me off-line. They hang my modem up..It's because they interrupt the
carrier that you are connected to and the modem takes this as a hangup by the
other computer. This can be useful if you are hacking and still want to take
calls. We are able to forward our calls if what we are hacking is important.
You don't get any call waiting tones when you forward your calls..
Just as a sidenote..The computer system used at out school, RPI in Troy,ny is
and IBM running MTS software (Michigan Terminal Systems). I don't like it at
all but have to deal with it. Does anyone know anything about the MTSNET or
how one can send mail there???
Erb@oz
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Date: Mon 20 May 85 10:14:28-EDT
From: S.PAE@MIT-EECS
Subject: Vadics and UUUUUU
To: telecom@MIT-EECS
With the 1200 baud protocols, there needs to be a way of making sure
that the 2 modems are staying synchronized with each other. The modems
use signal transitions to get re-synchronized. (For qthe same reason
that the T1 lines discussed about 2 months ago need transitions.) To
maximize the number of transistions, the characters going across the line
are XORed(?) with the byte 01010101 (ASCII 'U'). This has the interesting
property that if your modem gets a bunch of U's in a row, it's getting
the minimum amount of synchronization information. On a Vadic protocol,
try sending yourself about 30 U's in a row at 1200 baud and see what happens.
I've heard that the 212 protocol (the other 1200-baud protocol) uses a
12-character sequence rather than just using the U. Can anyone describe
this system in more detail? Also, which system is used for the single
2400-baud protocol?
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Date: Thu 23 May 85 17:53:31-EDT
From: S.PAE@MIT-EECS
Subject: Be the first on YOUR block...
To: telecom@MIT-EECS
This is paraphrased from what I remember of an ad on a cable channel:
"The future is cellular phone technology. (Something about Billions and
Billions here...) Right now, people are getting in on the ground floor.
Unfortunately, getting a license to run the cellular technology takes
hundreds of pages of applications and reports. For a mere $5000, we will
do these reports for you...."
Has anyone else seen this? Is it for real or a scam? I thought each area
application would be unique and would certainly take more than $5000 of
research to generate.
-------
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Date: 28 May 1985 09:49-PDT
From: king@Kestrel.ARPA
Subject: call waiting on cordless phones
To: telecom@BBNCCA.ARPA
Anyone know of a cordless phone that can take a waiting call? Does
dialing "1" and thereby interrupting the line for 100 ms do it?
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Date: Tue, 28 May 85 10:30:06 pdt
From: dual!paul@Berkeley (Paul Wilcox-Baker)
To: telecom@Berkeley
Subject: Re: TELECOM Digest V4 #194
The standard for representing international dialling codes recommended
in England is to have a "+" followed by the country code and internal
"area codes". The "+" is replaced by the local international dialling
prefix, 011 in the U.S., 0101 in England & 001, I believe in Germany.
Most countries outside the U.S. have an initial digit for long distance
calls that has to be left off in the international case. Here are
three numbers in that representation:
Within country International
(0925) 34238 (England) +44 925 34238
(0221) 38 68 49 (Germany) +49 221 38 68 49
(415) 549 3854 (U.S.A.) +415 549 3854
------------------------------
Date: 28 May 1985 12:05-EST
From: ihnp4!mcb@Berkeley (Mark C Baker @ AT&T Network Systems)
Subject: Re: telephony signals
To: ihnp4!ucbvax!telecom@Berkeley
In response to Sesh Murthy's request (TELECOM Digest V4 #194)
here are the pre-divestiture Bell System standard signals taken
from "Basic Electronic Switching for Telephone Systems" by David
Talley.
Dial Tone 350 Hz and 440 Hz
Audible Ring 440 Hz and 480 Hz (2 seconds on,
4 seconds off)
Busy Tone 480 Hz and 620 Hz (0.5 seconds on, 0.5 off)
Fast Busy Tone 480 Hz and 620 Hz (0.25 seconds on, 0.25 off)
Ringing 105 VAC at 20 Hz (2 seconds on, 4 off)
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Date: 29 May 1985 11:03-PDT
From: king@Kestrel.ARPA
Subject: equal acces
To: telecom@mc
Does "equal access" eventually require that a company wishing to
establish an 800 number be able to use any carrier offering such
service? Does anyone know anything about this?
------------------------------
Date: Thu, 30 May 85 01:02:21 EST
From: Minh N. Hoang <MINH@MIT-MC.ARPA>
Subject: 212/224's Remote digital loopback mechanism
To: TELECOM@BBNCCA.ARPA
Recent messages indicated that quite a few modems are getting into remote
digital loops inadvertently so I poked around to find out how them modems
intentionally get into this. The following comes from CCITT V.22bis
recommendation which specifies the 2400/1200 bps modem. Except for the
answer back tone, the 1200 mode is 212-compatible, including the loop.
For reference, modem A is the instigator and modem B the one that loops
back data. (All the modems that see data echoed back are instigators.)
Here it goes:
*** Entering remote loopback ***
When modem A is instructed to instigate a remote loop, it shall transmit
an initiation signal of unscrambled binary one at the current operating
speed. (If you happen to listen to this, you'd hear a tone instead of
the usual hiss-like noise.)
Modem B shall detect 154 - 231 ms. of the initiation signal, and then
transmit to modem A scrambled alternating binary 1 and 0. (And your modem
faithfully passes this to your terminal - hence the UUUUs).
Modem A shall detect 231 - 308 ms. of scrambled reversals, cease transmission
of the initiation signal, and then transmit scrambled binary 1.
Modem B shall detect the loss of initiation signal and activate the loopback.
(Now, everything modem A transmits will be "echoed").
Modem A after receiving 231 - 308 ms. of scrambled binary 1 (which it sent),
shall indicate to the terminal that it may begin sending test messages.
(Modem A will now send terminal's data as usual so you can see all you type).
*** Exiting remote loopback ***
When modem A is instructed to terminate the remote loop, the line signal
shall be suppressed for 77 +- 10 ms, after which transmission shall be
restored. (A very short simulated carrier loss).
Modem B detects the loss of signal in 40 - 65 and its reappearance within
155 +- 50 ms, after which modem B returns to normal operation. (For most
modems, carrier loss of >300 ms may cause disconnect).
*** -+- ***
Thus, if you're inadvertently dumped into this loop and your modem doesn't
have a remote loop switch, it's kinda tough to get out without losing the
connection.
How does your modem initiate this loop? (It's usually not modem B's
fault.) A common cause is called scrambler lock-up. These modems use a
scrambler of the form D_tx[n] = D_in[n] .XOR. D_tx[n-14] .XOR. D_tx[n-17]
and transmit the scrambled output. If the scrambler's delay line happens
to be filled with 1's, then the modem effectively sends unscrambled 1's,
the initiation signal. The other modem responds with UUUUs. You type a
few characters in panic and end the lock-up. The other modem senses the
end of the initiation signal and voila... you're looping.
To prevent this, once the scrambler outputs 64 consecutive 1's, it
should invert the next input bit. Sometimes, the modem doesn't
incorporate this detector-inverter because the situation is relatively
rare, supposedly.
Cheers,
------------------------------
From: ihnp4!homxb!hrs@Berkeley (H.SILBIGER)
Subject: Re: TELECOM Digest V4 #194
Date: Tue, 28-May-85 20:27:13 EDT
In response to the question on how to display international
telephone numbers:
The CCITT standard method for displaying telephone
numbers is as follows.
First example a number in the Netherlands
National: (070) 75 11 11
--------------------------
Internat: +31 75 11 11
Second example a US number:
National: 1 (201) 555-1111
----------------------------
Internat: +1 201 555 1111
Note that above the line is the normal way a number is
displayed within the country, and is the dialing sequence you
would use when you were there.
Below the line is how you would dial if you were in another
country dialing abroad.
The sequence is: country code, area (or city) code, and local
number. It does not include the numbers you need for international
access, ie in the US 011 or 001.
I included the example from the Netherlands, because in the US
the country code is "1", and the access to the long distance network
also happens to be "1".
When displaying the international number, no dashes or parentheses
are used.
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End of TELECOM Digest
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