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Software Vault: The Gold Collection
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Software Vault - The Gold Collection (American Databankers) (1993).ISO
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cdr37
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c1modinf.zip
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1993-01-01
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251 lines
Modems and Connecting to Channel 1
or
"You keep hanging up on me, what gives?"
Very few communications problems reported to us have
anything to do with Channel 1. We will outline common
problems and their solutions in this bulletin, but first
a little general orientation.
STATIC HAPPENS
--------------
A common mis-perception among new (and not-so-new) computer
users is to imagine that the telephone company and long-
distance switching network is a "transparent cloud." High-
speed modems, which mask line-noise and push communications
tolerances to their limit, enhance this illusion.
"I was 300K into my transfer and you dropped carrier on me."
"I'm only getting xxx cps, what's the problem?
"I can't believe how slow the system is tonight."
"My typing isn't showing up on the screen until two words later."
Generally, all these problems can be attributed to local
or long-distance communications network issues, better known as
LINE NOISE
Problems in signal transmission and recognition can take many
forms, and arise at many points in the PATH of a signal.
Here's a typical analysis of a problem call:
-----------------------------------------------------------------------
Chars sent 11813 Chars Received 147
Chars lost 0
Octets sent 7946 Octets Received 146
Blocks sent 269 Blocks Received 53
Blocks resent --> 275 (errors corrected)
Retrains Requested 0 Retrains Granted 0
Line Reversals 0 Blers (line burst) --> 173
Link Timeouts --> 35 Link Naks --> 1
Data Compression V42BIS 2048/32
Equalization Long
Fallback Enabled
Protocol LAPM
Speed 14400/7200 (V.32bis speed downshift)
Disconnect Reason is DTR dropped
-----------------------------------------------------------------------
The caller complained of buffered typing, slow system response,
and slow transfers, and was sure it was Channel 1's problem.
The reason? What's known in the business as "a really crappy
connection."
Although V.32bis modems have become commodity items, they
aren't equally good at dealing with line problems. Read
PC-Magazine for details.
"I can call MEGAZONE just fine but your modems stink."
The above example was a long-distance connection. Local
callers may have identical problems that depend on the
particular exchanges through which their calls are routed.
If you call from download Boston, complain to NET about
the Harrison Avenue Switching Station.
HELPFUL HINTS:
1. Minimize other connections to your phone line (answering
machine, fax, extension phones).
2. Use a short (six feet or less) serial cable.
3. If calling long distance, use an alternative long-distance
connection (Bulletin 32) to diagnose problems.
4. Have your line checked by the phone company.
5. Don't confuse your terminal with reality.
THE HARDWARE -- MODEMS
----------------------
A MODEM is a MOdulator-DEModlator device. It changes
the digital signals (bits) sent by your computers serial
interface to analogue signals that can be transmitted over
telephone networks.
Most communications programs will let you talk to the modem
directly (though some make it difficult by presenting a menu-
interface). The magic command for speaking to modems is to type
AT from the terminal screen. AT tells the modem to treat
every that follows as command (see below).
If the computer is communicating to the modem, and the modem
is at least basically set up, it should answer back OK .
If it doesn't, see below, MODEM CABLES, and SOFTWARE.
At this point, it is highly recommended that a new modem user
spend a few minutes with the manufacturer's instruction manual,
to locate the "commands summary and explanation" pages.
The second command everyone should know is AT&V . This will
tell -most- modems to display their configuration settings.
See your manual if you have an unusual modem. Most modems
will display an "Active Profile" and one or two "Stored
Profiles."
Most modems come with "default" settings, which often
need to be modified to function with bulletin board
systems and high-speed communications. Compare your
modems settings with these:
ACTIVE PROFILE:
B1 E1 L2 M1 Q0 V1 X4 &C1 &D2 &K3 &Q0 (or &Q5)
&R0 &S0 &X0 &Y0
The &K and &Q settings may not be available on non-
error-correction modems. This (abbreviated) report says:
Basic set
---------
B1 (Bell-compatible)
E1 (echo my typing)
L2 (set speaker volume)
M1 (turn on speaker so you can hear if it's dialing)
Q0 (return result codes so your comm program can understandit)
V1 (do it in English)
X4 (report call progress) (may be X5,X6,X7)
Needed for calling BBS's
------------------------
* &C1 (Data Carrier Detect on)
* &D2 (switch to command state when DTR dropped)
Necessary for error-correcting/high speed modems
------------------------------------------------
* &K3 (enable bi-directional hardware (CTS/RTS) flow-control)
&Q0 or &Q5 (asynchonous reliable mode)
Basic command string to set up modem for BBS operation:
AT&E1&Q0&V1&M1&C1&D2 (add &K3Q5 for fast modems)
Modem command set vary from manufacturer to manufacturer.
Read your manual. Read your manual. Read your manual.
MODEM CABLES AND THE WHOLE UART STORY CONDENSED
High-speed modems require serial cables which
support hardware (CTS/RTS) flow-control. Old
printer cables won't necessarily work.
If your modem is internal, you don't have to worry
about why motherboard and serial card manufacturers
are still designing equipment that won't support
high-speed modems.
If you've recently purchased a fast (V.32/V.32bis/HST)
modem, and you are experiencing dropped characters, CRC
errors and aborted downloads, you may need to upgrade
your serial port to a buffered UART (16550). Look for
82x50B, 16x450 part numbers on the large 40-pin chips on
the serial card to find out if your UART is brain-dead.
Or download a buffered-UART-detector like IS16550.ZIP
or PF271.ZIP and test your equipment.
THE SOFTWARE -- YOUR COMMUNICATIONS PROGRAM
-------------------------------------------
It's a fact of of life of a sysop's life that programs designed
to shield beginners from their modems make diagnostics more
difficult.
Tech Support: "Type AT and tell me what happens."
Caller: "There's no place to type."
If you are using a program that came with your modem,
like MTEZ or QLII or an old version of Crosstalk or
Windows Terminal, go immediately to the FREE conference
and download one the the communications programs available
there. Can't download? Read on.
Your communications program communicates with your
modem and handles many tasks. It must be configured
appropriately for your particular modem, computing
environment and the system you are calling.
You may need to select:
comm port
IRQ if you have alot of stuff in your computer
Terminal Emulation (ANSI-BBS or VT100/102 or RIP)
Dialing parameters (8 DataBits N no Parity 1 stopbit)
Dialout Speed (set for highest recommended by manufacturer)
IF YOU HAVE A HIGH SPEED MODEM
----------------------------------------------------------
* Flow Control (CTS/RTS Hardware flow control ON)
(counterpart to modem's &K3)
* Baud-Rate-Detect/Adjust OFF
(counterpart to modem's port-locking command)
-----------------------------------------------------------
* Modem initialization string ATH0 . Edit out long
setup strings and especially ATZ commands. General
philosophy -- setup your modem with the appropriate
settings and write them to the modem's memory (most
have them, these days). Keep comm program setups/changes
as short as possible and don't let them reset your modem.
Finally, you may need to tell your comm program about
your hard disk:
THE "FEATURE" THAT TRIGGERED 100,000 SUPPORT CALLS!
Procomm, in its seminal, classic 2.4.x version that everybody
passed all over the universe, requires a Default Download
Directory to be specified in ALT-S setup, Files and Paths.
If the new user doesn't type one in, the lack of an error
message doesn't impede their call to tech support.
APPENDIX I
==========
WEATHER
-------
Believe it or not, days of rain or winter storms coating
everything with 2 feet of ice can affect telecommunications.
Little known fact.
PC-Pursuit Problems
-------------------
Apparently influenced by celestial patterns or ether-sprites,
the MABOS outdials can be flakey. See the PC-Pursuit bulletins
for tips on MNP enablement. Complaints to Sprint are sometimes
effective.