CP/M/CPM_CDROM.iso/cpm/imp/imp245.lbr/IMP.IZF/IMP.INF

Text File | 1987-06-06 | 16KB | 337 lines

SUBJECT :  New IMP features

FROM    :  Irv Hoff

DATE    :  01 June 87



        IMP was the first program known to
        utilize the automatic stepdown feature
        offered by new 2400 bps modems.  It
        also It also was the first (and with
        TERM3, a commercial program) the only
        program that has automatic 1k protocol
        for faster file transfers at either
        1200 or 2400 bps.  All KMD pgms as well
        as XMODEM 112 and later support auto-
        matic 1k protocol.  Both KMD/YMODEM and
        MODEM7 types of batch mode are offered.


INTRODUCTION
------------
    This is a partial list of some of the features offered by IMP.
It was developed for the new 2400 bps modems, but also fully supports
older 300/1200 bps modems that use either the Racal-Vadic or the 'AT'
protocol developed by Hayes.  IMP also supports the extended Prometheus
protocol for the ProModem 1200.


AUTO STEPDOWN
-------------
    New modems offer automatic stepdown.  If not familiar with this
feature, they first attempt to connect at 2400 bps, then at 1200, then
at 300.  (The US Robotics Courier only steps from 2400 to 1200, this is
no limitation as few people using a 2400 bps modem would likely call a
300 bps system on a regular basis.)

    When a connection is made, the modem returns the result code
at the last speed originally selected (2400 at power up) and then
switches to match the speed of the other unit.    For instance if calling
a 1200 bps system, it will give a "5" result code for 1200 bps, but
at the last speed you used (normally 2400 by default) and then change
to 1200.

    IMP was the first and is currently one of the few free modem
programs that utilize this information to automatically set the I/O
baudrate on the computer to match the modem speed.

    Thus the user can dial any number in his phone library, or even
a hand-entered number, without knowing (or caring) in advance what speed
the other system can accomodate.  (He may have just added 2400 bps with
a new modem you do not even know about.)

    One of the biggest advantages to having automatic setting of the
computer involves linking several numbers for continuous dialing.  IMP
allows numbers to be dialed where some are known to use 2400, some 1200
and perhaps a few even at 300 only.


GENERAL IMP FEATURES
--------------------
    IMP shows the current modem baudrate quite often.  If for any
reason you leave the modem program while still online, to check on some
disk or otherwise use the editor or assembler, etc. quickly, IMP stores
the current baudrate.  When calling it up again, it resets to that same
baudrate.  This is not unusual, but other programs that do this require
the use of the "carrier detect" pin to see if still connected, and just
ignore any initialization in that case.  IMP never needs carrier detect
and that pin does not even need to be wired to the computer.

    You can clear the screen at any time, CTL-Z when in command mode
or ESC-z (or ESC-Z) when in the terminal mode, assuming you retain the
"ESC" character as the lead-in character for local command.

    Any CTL-character typed while in the terminal mode goes out the
modem.    (Which is why you need to use ESC-Z to clear the screen, as a
local command!)  This permits using remote editors such as WordStar.
(You need to also use ESC-p to control the printer, allowing a CTL-P
to go out the modem for remote control purposes.)

    In the termianl mode, typing 'ESC Q' will send a break.  This is
used to reset some mainframe computers and is handy on PC Pursuit for
use in disabling the '<ret> @ <ret>' disconnect combination that some-
times causes problems when sending file transfers.  (New for IMP245.)

    In the command mode, typing '? <ret>' shows all the current
parameters.  Typing an ESC <ret> shows the function key assignements
(unless the user has selected a different character than ESC for that
purpose.)  Typing a "M" shows the menu.  (Three pages, total.)

    In the command mode, while dialing a number, a CTL-X aborts
back to the command mode (as always), but a CTL-K aborts the current
attempt and starts the next one.  This saves time if you hear a phone
ring with no answer and don't want to wait until the modem tires of
trying for a "no answer" (usually takes 30 seconds or more).  At times,
an older switching office never does seem to place the call, and CTL-K
expedites another try.    Nice feature, try it 1-2 times to see how it
works.

    In the terminal mode, when sending a pretyped ASCII file will
automatically activate the X-off, X-on mode, which the user has to man-
ually select on many other modem programs.  The delays between characters
and/or between lines are only take effect after the I/O buffer is empty,
not after you send a character to the holding buffer in the I/O.  This
gives substantially more accurate timing delays than those provided by
most other modem programs.

    IMP has excellent progress reports while autodialing.  It num-
bers each attempt.  Many older 1200 bps modems (such as the Smartmodem
Hayes) do not give a result code for busy.  The newer 2400 bps modems
have such a result code.  IMP uses this to immediately start a redial.
The Racal-Vadic modems also return a "ring" report for each ring not
answered.  This is displayed.  Other reports such as "no dial tone",
"no answer", "failed", etc. are displayed by IMP for those modems with
extended result codes.

    (IMP has a special byte at 0C00H-2  (0BFEH) which can be easily
changed with DDT, etc.    This byte delays the time from receiving a busy
signal until a redial is attempted.  Obviously most people want a redial
as soon as is convenient.  Having this byte available allows the casual
user who needs a longer time (he might be going through the company's
switchboard, etc.) to adjust the delay suitably.  The telephone overlay
I2NM-2.ASM also includes this byte.)

    IMP also displays the modem speed when a connect is made.  With
the automatic stepdown units, that is normally the only way you would
find out, unless you started a file transfer where it could display the
time it would take at the current modem speed.

    You can select a new baudrate on the command line now.    If you
select an improper number it will display those availble and wait for a
correct response.  This opens the avenue for customization by asking for
"SET <ret>".

    Unless you do select a new speed manually via the SET command,
the modem thinks you want to accept the fastest speed it finds available.
You may prefer a slower speed.    Just use SET 300, for example and this
limits the modem to connecting at that speed.  Using SET 2400 resets to
fully automatic operation once more.  (You may want to call Compuserve,
for example, where you cannot type even 300 bps to answer messages and
1200 bps would be far more expensive.)

    None of the currently available or planned overlays require any
specific information buried in the main program.  Thus any subsequent
release should support any of those overlays.

    IMP turns off the auto-answer feature whenever a number has been
dialed, using DSC to disconnect or BYE to leave the program.  This in-
sures the modem will not try to answer the phone the next time it rings.
Some modems such as the Robotics Courier 2400 and Hayes 1200 Smartmodem
have manual switches that can be set for autoanswer.  Most users disable
those switches, so the phone can be used in a normal manner.


1k PROTOCOL
-----------
    At the faster baudrate, the efficiency drops rapidly with the
older XMODEM programs that can only send 128 characters per block.  They
wait for an answer of "ACK" or "NAK" from the receiving station.  By
sending 8 records (1k) per transmission, these waits are of course re-
duced to 1/8th normal frequency.  This increases the throughput at 1200
bps from 48 blocks per minute to the equivalent of 53 blocks per minute.
This is a gain of about 10% which means less $$$ in transferring files.
At 2400 bps 85 blocks per minute is normal.  This increases to 102 when
using the 1k protocol to the equivalent of 102 blocks per minute.  This
is an increase of 20% throughput.  At 9600, the effect is substantially
more pronounced.

    Chuck Forsberg has had 1k blocks available for several years
with his YAM (public domain) and PRO-YAM (commercial program for MS-DOS
users).  That is a manually operated system where the user has to type
"SK" at the sending end to initiate the 1k transmissions.  This system
has the disadvantage of requiring the operator to know why he should
type "SK", as well as remember he should.

    IMP uses a protocol that requires no operator intervention.  The
user does not even need to be aware he has such a feature.  He proceeds
normally and IMP automatically tells the sender it can accept 1k proto-
ol as well as the older 128 character blocks.  (IMP does support the
manual protocol used by MEX114, YAM and PRO-YAM if you prefer to type
"SK", or must - to use one of those modem programs.)

    This is transparent to older XMODEM programs.  Thus IMP works
normally on either type system - those that offer 1k automatic protocol
or those that do not.  KMD has offered both the automatic and manual
protocols since it was introduced in mid-July 1985.

    (If for any reason the operator wishes to disable the automatic
1k protocol, just type "RX" at the receiving end and it will not inform
the sending end that it has 1k protocol available.  This forces sending
128-character blocks.)

    There is little or no advantage to 1k blocks at 300 bps, so IMP
requires a speed of 1200 bps or greater to activate the 1k protocol.  A
1k block at 300 bps would take 34 seconds!  (Takes 9 seconds at 1200
bps and 4.7 seconds at 2400 bps.)

    CRC is required for the 1k protocol.  If the other system only
has checksum, IMP automatically sends 128 character blocks after setting
itself to checksum.  (Use 'TCC' when in the command mode to select the
checksum protocol.  It is automatically selected if sending to another
system that can only receive checksum.)


BATCH MODE WITH 1k
------------------
    IMP supports the KMD/YMODEM batch protocol in addition to the
older MODEM7 type.  They are both operated in the same manner but the
kMD type offers significant advantages in the way the file name is sent.
The MODEM7 method sends one character at a time, waiting for an echo
from the other system, then a checksum verification is made.  This is
slow and quite unsatisfactory for modern-day use with mainframe or net-
working systems.  (Both batch types incorporated into IMP use automatic
1k protocol.)

    The KMD method (compatible with the YMODEM protocol developed by
Chuck Forsberg use with IBM-PC computer running MS-DOS) has a special
128-character block for sending the file name.    Additional data can be
included, such as the file length and time/date stamp.    IMP uses the
file length feature.  (MODEM7 batch does not support this nice feature.)
This batch mode also sends and receives 1k automatic protocol, if the
file is longer than 8 records.

    Each file terminates in 128 character blocks if less than 1k re-
mains, but the 1k protocol is reinstated for the next file in the group.
The ratio checking is reset for each file so the accumulated errors are
more indicative of current conditions.

    Roy Robinson of the Osborne Corp. has used two Vixen computers
running at 19200 with IMP in the batch mode to transfer the contents of
entire disks from one machine to the other.  He says it is fascinating
to watch the results at that speed.  (A null cable was used between the
two machines which were in the same room.  Normally things like this are
done with computers of different brands, where it may be difficult to
make a disk that runs suitably on the other computer.)

    KMD and BYE5 support this KMD-batch mode for normal RCPM use.
The total time it will take to send all files is computed and displayed.
(If this exceeds the remaining time available, it aborts the request and
asking for a different file.)


RATIO CHECKING FOR 1k
---------------------
    If conditions are poor, any advantage to sending the longer 1k
blocks would be lost.  The program should check the ratio of good blocks
copied against the number of repeats that have been needed.  A point is
reached where staying in the 1k protocol would be detrimental.    This oc-
curs at 43 records/per hit at 2400 bps and at 71 records per hit at 1200
bps, where there is less to be gained by using 1k blocks to start with.

    (This is calculated for the time it would take to resend
    one 1k transmssion due to one hit, versus sending 128
    character transmissions with one hit, over a modest length
    connection.  The further the distance, the more delay you
    get waiting for the "ACK" and the more favorable the ratio
    becomes with regard to the ones chosen for normal operation.)

    IMP is the only program currently available that attemptes to
select an individual optimum ratio for the speed being used.  YAM stays
in 1k protocol, once requested, until the file transfer is finished.
XMODEM has a ratio check to switch back to 128 character blocks but uses
a single figure for all speeds.  This could cost extra time and money
under unfavorable conditions.  It would switch too soon for 2400 bps and
not soon enough for 1200, to be most economical.

    IMP also changes back to 128 character blocks if 4 or more con-
secutive hits are encountered.


IDEA OF 1k PROTOCOL
-------------------
    The name of the game is time spent on the telephone.  This not
only involves the actual long distance charges but the time the operator
has to spend in front of the machine.  The following needs little addi-
tional explanation:
                 100k file

            128 char blocks   1k blocks

         300 baud    61:32         n/a
        1200 bps    16:40        15:06
        2400 bps     9:18         7:51

    These figures based on modest length calls with direct
    lines.    The time gained when using satelite calls is
    far more dramatic.  Jon Saxton in Australia calls the
    USA via a satelite link and tests indicate an approxi-
    mate 30% decrease in file transfer time with 1k blocks.


    This indicates the entire concept should be fully automatic and
totally transparent to the user.  (Unless he is technically inclined and
likes to know about details of this sort.)  If it saves connect time and
money, the operator should not be required to manually make this choice
each transmission.  This is particularly beneficial if using PC Pursuit
where the following is typical:

            PC PURSUIT 1200 bps

        19.2  128 character blocks per minute
        44.3  1k blocks per minute

    IMP has become quite popular with PC Pursuit users since it auto-
matically selects 1k blocks for all files 1k or longer.


LAST BLOCK
----------
    When the file is finished, it is rare it quits on an even 1k.
IMP automatically switches back to 128 character blocks at this time.
This gives the same number of records the original program contained
and subsequent checks using CHEK.COM or will give identical results.
YAM never switches to 128 character blocks regardless of end of file
or excessive hits.


1k SUMMARY
----------
    The success with faster transmissions and less connect time in-
dicate other modem programs will likely soon follow suit with fully
transparent programs that can automatically select 1k blocks.  Remember
manual control of 1k blocks was developed by Chuck Forsberg and first
appeared with YAM.  The automatic selection and error ratio routines
were developed by the author and have been incorporated into both KMD
(the XMODEM replacement) and IMP.

    Currently no MS-DOS program supports automatic 1k protocol.
IMP and TERM3 (a commercial program) are the only ones known that do.


                    - Irv Hoff
                      Los Altos Hills, CA
                      [phone] PRACSA RCPM
                      [phone] voice