[fa.telecom] TELECOM Digest V4 #173

telecom@ucbvax.ARPA (03/31/85)

From: Jon Solomon (the Moderator) <Telecom-Request@BBNCCA>


TELECOM Digest     Sun, 31 Mar 85 11:25:50 EST    Volume 4 : Issue 173

Today's Topics:
             Blocking Incoming Calls and other SL-1 hacks
                         Collect Wrong Number
news from the SW:   MCC's Bobby Inman named to SWB's board of directors
                        2400 baud modem review
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Date: Thu 28 Mar 85 02:31:14-CST
From: Clive Dawson <CC.Clive@UTEXAS-20.ARPA>
Subject: Blocking Incoming Calls and other SL-1 hacks
To: telecom@BBNCCA.ARPA

Does anybody know enough about the guts of the Northern Telecom
SL-1 PBX to tell me if there is a way to set up an extension which
cannot receive any incoming calls under any circumstances?

The situation is that we are setting up a call-back system for
extra dial-in security.  One of the vulnerable points of such
systems has to do with people dialing in on the lines used to
place the outgoing call-backs.  It is theoretically possible
that if an incoming call arrived at the same instant the call-back
system initiated a call, a break-in could occur.

In order to make efficient use of the outgoing trunk lines, we want the
outgoing lines connected to the call-back system to go through the PBX.
Unfortunately, there doesn't seem to be a fool-proof way to set up a line
which cannot be dialed into.  In particular, there seems to be no way to
set up permanent call-forwarding.  Another idea was to give these lines
4-digit extension numbers starting with something like 8, so that any
attempt to dial them would produce a WATS dial tone.  Apparently the
software doesn't let you do this sort of thing.  We are told that the only
way to properly do this would be to use the customer partition feature
(which is designed to let several customers share the same switch) and
declare all the call-back extensions to be a different "customer".  The
problem here is that they would either have to be given their own set of
outgoing trunk lines or else special hardware would be required to tie them
in to Customer 0's trunk lines.  In either case we are talking big bucks.
I'm still hoping that some sneaky trick exists to accomplish this.

And talking about sneaky tricks, somebody discovered a feature (bug?) in
the SL-1 which allows extensions to be call-forwarded to outgoing trunk
lines.  For example, if dialing 8 gives you access to a WATS line, then
call-forwarding an extension to "8" will give callers to that extension a
second dial tone and allow them to place long distance calls.  If the
extension can be dialed directly from outside the premises, this is
obviously a big security problem.  Furthermore, the audit-trail printout
produced by the SL-1, which normally logs all long-distance calls dialed
and identifies the extension, shows no record of such calls.  I'd be
interested to learn whether this is an inherent flaw, or whether our
switch was simply not configured correctly.

CLive
-------

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Date:    28 March 85 23:30-EST
From:      Michael Grant  <GRANT%UMDB.Bitnet@WISCVM.ARPA>
To: Telecom Digest <TELECOM@BBNCCA.ARPA>
Subject: Collect Wrong Number

I'm mad, I mean really mad. (not crazy mind you, but just plain pissed off)
About an hour ago I got this call, the conversation went as follows:

RING
Me: Hello
Operator: I have a collect call from Terry, will you pay for the call?
Me: No.
a few seconds of silence
Terry: Is Joe there?
Me: Ummm...I think you have a wrong number
Terry: Is this 202-439-6339
Me: Nope, that wasn't very nice of that operator
Terry: What do you mean? Why did you accept the call if you didn't know me?
       Maybe you know...
Me: I DIDN'T ACCEPT IT!
I got her number, and said goodbye.

I flashed the hook, and got an operator back on line,
Operator: Are you done?
Me: Yes, but I didn't accept the call, why did you put it through?
Operator: I'm not the same operator, I didn't put it through, it's not my
          problem.
she hung up on me.  That was the rudest encounter I have ever had with an
operator in my life.

I dialed O operator, and explained my problem, he told me I would have to
call my bussiness office and get it taken off my bill.  I'm going to also
lodge a formal complaint.  What's happening to phone service in this
country?  Don't anyone say it...Divestiture. Damn.
-Mike

------------------------------

Date: Sat 30 Mar 85 15:19:07-CST
From: Werner Uhrig  <CMP.WERNER@UTEXAS-20.ARPA>
Subject: news from the SW:   MCC's Bobby Inman named to SWB's board of directors
To: telecom@UTEXAS-20.ARPA

[ from the Austin American Statesman - March 30, 1985 ]

Bob Inman, chairman and chief executive officer of MCC has been elected to the
board of directors of Southwestern Bell Corp.
-------

------------------------------

Date: 31 Mar 1985  08:39 MST (Sun)
From: Keith Petersen <W8SDZ@SIMTEL20.ARPA>
To:   Telecom@BBNCCA
Subject: 2400 baud modem review

The following review was not written by me.  It was downloaded from a
Remote CP/M system.  Unfortunately there is no way to reach the author
because it is unsigned.  It is presented here for its possible
informational value.  Please address discussions/comments to the
mailing list, not me.  I don't own a 2400 baud modem.
--Keith

10 Mar 85

*** DISCLAIMER ***

The products described here were repeatedly tested for a specific
application only.  No value was placed on advanced features not
directly related to their intended use.  The opinion expressed herein
is that of the reviewer and may, in fact WILL differ considerably from
other reviewers' opinions.

This is an unsolicited review.  Anyone able to disprove the reviewes
claims is welcome to do so.  This review is about as unobjective as it
can get.

	In a data processing environment, chances are the employee
with a terminal and a modem (or computer) and access to the business
computer via dialup will be more productive and is more likely to put
in a few hours' worth of unsolicited overtime per week than the
employee who has access to the same computer only during working
hours.  Therefore, it was decided that the office computer be set up
with at least one high-speed dialup line and the most economical
choice was that of a 1200/2400 baud modem.

	The modems were going to be used for two purposes:
   1. unattended autoanswer
   2. occasional use for dialout

	Testing was started as soon as modems became available through
a local distributor.  Due to this factor only two brands were
evaluated. Here is the story on both of them:


1. PENRIL 2024

	The Penril 2024 seems to be the first widely available
1200/2400 baud modem, with the exception of the prohibitively priced
VADIC 4400 series.  The 2024's list price is somewhere around $900.

	The 2024 offers two baud rates, 1200 and 2400.  The 1200 baud
protocol can be switched from 212A to V.22 at configuration time.  By
today's standards, the 2024 cannot be considered a "smart" modem in
that its smartness is limited to the ability to dial a phone number.
Placing the modem in autoanswer mode is accomplished by simply
configuring the internal and external switches according to the
manual, releasing all front panel switches and plugging it in.  The
2024 does not have a power switch (a definite plus in this
application).

	Originating a phone call with the 2024 is a cumbersome
procedure, especially in an application where the modem may be 100
feet away from the terminal.  First, the modem must be taken out of
autoanswer mode by pressing a front panel switch.  Next, the originate
baud rate must be selected by locking the HI/LO switch IN or OUT.
Note that if you set up the modem for 2400 baud, you can call a 1200
baud number because of the "fallback" feature.  You just have to
adjust your terminal baud rate after connect.  The 2024 has no abort
provisions.  While dialing, the TALK/DATA switch can be used to abort.
When connected, you must either cause the remote computer to drop
carrier or you again have to hit the switch.  An alternative is
dropping the DTR line low, but in some instances that's a bit hard to
do.  Dialing a phone number is very awkward. The sequence is
"CRNnnnnnnn<CR><LF>" so to dial 555-1212, you type CRN5551212^M^J.
Fine if the ENTER key on your keyboard generates a CR-LF sequence;
with most terminals you have to hit two keys.  Sorry, no redial
capability.

	The Penril worked fine calling the local TYMNET 2400 baud
access number, but no connection was established to any long distance
modem at 2400 baud.

	The modem is superbly suited for unattended autoanswer mode.
the 2024 can be turned on and left alone and if something goes wrong
it's the software but not the modem.  The continuous high-pitched
noise coming out of the built-in speaker may be objectionable to
some -- it picks up the strongest local AM radio station.  the
speaker can be turned low or off via an internal jumper block.

	One 2024 modem was tested initially in early November 1984,
and two were again tested in late February 1985.  No difference was
found between the three modems, even though the early onemay have been
a preproduction unit.


2. USR COURIER 2400

	The USR Courier seems to be the first smart low-priced modem
to be released, probably due to the fact that, unlike many
manufacturers, it does not use the Rockwell chip set.  It features
Hayes 2400 compatibility.  I will briefly summarize the positive
aspects of the modem:

	- externally accessible, well-labeled configuration switches
	- external switch to reverse pins 2 & 3, thus eliminating the
	  need for a null modem
	- result codes can be completely turned off via switch
	- volume control for internal speaker

	After setting the configuration switches (an easy task for
anyone who has ever set up a modem) the Courier is ready for
operation.  With the appropriate switch setting, it can be used both
in originate and answer mode without any hardware changes.

	Originating a call can be accomplished with the now-famous
ATDT sequence, except that command letters no longer have to be in
caps. As with other smart modems, any character typed while dialing or
waiting for carrier aborts the action and hangs up the line.  The
"escape" character can be used to either return the modem to command
mode (like the Hayes) or to hang up (like other USR modems) depending
on a configuration switch setting.

	The Courier was used to successfully connect to the local
TYMNET number.  A later model also was able to talk to a VADIC 2400
baud unit over long distance (Wayne Masters' RCPM).  The Courier was
also able to call and be called by a Penril 2024 and another Courier.

	As to autoanswer mode, the modem was a complete washout to put
it mildly.  Surely, hard- and software are partly to blame but the
fact that other modems (including USR Password and AD212A) work with
the same setup indicates a serious flaw in the Courier.

	The hardware used, for whatever reason, drops DTR while
changing baud rates.  The duration is so short that all other modems
tested on the hardware, EXCEPT the Courier, are totally unaffected.
The Courier will, upon carrier lock and receipt of the first character
typed, drop the carrier 3 out of 4 times at 1200 and 2400 baud.  While
no considerations were given to 300 baud performance, it was noted
that those problems only exist at 1200 and 2400 baud.  Placing a 5MFD
capacitor from the DTR line to ground totally fixed this problem.

	In autoanswer mode, the modems were used as follows:
   - all result codes are inhibited
   - on carrier loss, computer reboots, cycles DTR, then waits for a
     character typed by constantly polling the data input port
   - on receipt of character, baud rate is tested and, if necessary,
      changed

	I must again stress that this method works with all modems
tested.  The USR Courier, however, would simply refuse to answer any
more phone calls after answering a few.  No set pattern was
discovered.  Sometimes, the modem would work properly for 5-10 calls
then refuse to answer, at other times it would only allow 1 or 2
calls.  When it refused to answer, no outside indication was given
as to the problem.  The appropriate LEDs on the front panel were lit
yet the modem did not respond to the ring.  Surely, this is a most
serious deficiency and I have decided that the Courier is unfit for
use in this particular application.  I am convinced the problem lies
solely with the Courier, particularyly sonce both the Auto Dial 212A
and the Password 1200 work in the exact same environment (except for
the much-needed 2400 capa- bility, of course).

	In closing I must again stress that the USR certainly is a
superb modem and very well suited to originate applications.
Considering that 99 out of 100 modems sold will never be used for pure
autoanswer purposes, the Courier is not at all a failure.

	One modem was tested in late November, two in late February
(both were preproduction units) and thre PRODUCTION units were tested
in March.  All five units exhibited the same problems.

	...may those who have the power to change things do so, may
those whose toes I stepped on test for themselves before stepping on
mine, may those who want to buy a Courier not be discouraged.

	If YOU intend to use a USR Courier in an autoanswer-only
environment, please by all means give it a try, it may sure work for
you.  If it doesn't, you have been warned, and if it does, either
"they" fixed it or the problem is installation-dependent...

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End of TELECOM Digest
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