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PCBoard
9600/19200 BPS
Modem Operation
Chapter 17 17.1
PCBoard - 9600/19200 BPS Modem Operation
General Information
-------------------
In order to help you effectively use one of the new high speed
9600 bps and lower speed "compression" modems, please carefully
review the following information. First, some basics. When a
user calls a BBS system, there are generally 3 links between the
two machines which are speed related. The first is the speed or
bps rate at which the caller's CPU is connected to their modem,
the second is the link between the two modems themselves, and the
third is the link between the host modem and the host CPU. For
simplification, we will refer to these three speeds in the
remainder of this document as CLink (caller CPU to caller modem),
MLink (modem to modem), and Hlink (host CPU to host modem). A
simple diagram might help here:
-------- -------- ------- -------
Caller's Caller's Host Host
CPU Modem Modem CPU
-------- -------- ------- -------
|___ CLink ___| |___ MLink ___| |___ HLink ___|
RS-232 Cable Telephone Line RS-232 Cable
(DTE Link) (DCE Link) (DTE Link)
Understanding CPS Rates
-----------------------
Second, CPS or 'characters per second' is now used extensively by
various communications programs in order that a caller can judge
their throughput performance during a file transfer. For the
benefit of those who do not completely understand a CPS rate,
here is a very basic outline. Generally, a byte of data (one
character) is sent as a start bit, followed by the actual
character, followed by a stop bit. When running at 7,E,1, the
highest character which can be sent is a chr$(127). However,
that means you can not send any "binary" files which usually
contain many characters from chr$(128) to chr$(255). However,
when using 8,N,1 settings, any of these "high order" characters
can be transmitted - which not only allows for the transmission
of binary files - but also the use of "graphics" display files
which are comprised of many of these high order characters. If
you add the start bit, plus the 8 bit character length, plus the
stop bit, you end up with 10 bits needed to send one character
(or a single byte of data) to the other machine. At 1200 bps,
(1200 bits per second), if we divide the bps rate by 10 (the
number of bits per byte), we end up with a maximum throughput
rate of 120 characters per second (or 120 bytes per second if you
will). Similarly, at 2400 bps, the theoretical maximum
throughput rate is 240 characters per second. That is why when
doing an ASCII file transfer, CPS rates equal to bps rate/10 can
be achieved. However, when doing 'block' (ACK/NAK) protocol
transfers, the time delay between blocks, as well as block "error
17.2 Chapter 17
PCBoard - 9600/19200 BPS Modem Operation
checking" bytes which are added to chunks of data, end up cutting
down the actual throughput rate of the given file so that
something in the order of 85% effective rate is achieved. So,
how do some of the new modems do better than the bps rate/10
calculation? They do so by "compressing" the data to be sent
using algorithms similar to those used when 'ARC'ing a file - so
that they can send more bytes of the file at one time. Of
course, the modem on the opposite end must be able to "un-
compress" the data or the system will not work. Also, since the
modems are handling all error checking and not the software,
there is no need for the software to control the sending of
blocks and "waits" for an good acknowledgement. All it (the
software) needs to do is send the file out to the other end -
monitoring RTS/CTS flow control in the process. What all this
ends up doing is allowing some of the new high speed modems to
produce CPS throughput rates of 1100 to 1600 CPS or higher under
ideal conditions -including "clean" lines, maximum "horsepower"
CPU's and hard disks, and the transmission of files which have
not already been compressed using ARC type programs.
Additionally, some of the new 2400 bps modems also allow for
"compression" transfer of data when the HLink (or DTE link) is
locked into a fixed rate - such as 9600 bps.
Flow Control
------------
Next, we need to mention a little bit about flow control.
Generally speaking, there are two types of flow control -
XON/XOFF and CTS/RTS checking. XON/XOFF is the "standard" flow
control which has been used for years in async communications.
It is done by having one CPU send the other CPU's software a
signal to start or stop transmitting data. This works great at
baud rates up to about 4800 baud, as long as there is a
"communication buffer" of adequate size on both machines, and the
two softwares "look for" such signals quite frequently during all
of their processes. If they do not check for the appropriate
signal often enough, and their communication buffer is not large
enough, one machine can keep sending data to the other - even
though the other is not ready to receive it - causing a loss of
data. Most programs on the market today monitor XON/XOFF
checking very well, and have no problems with flow control at the
lower speeds. However, when operating at rates of 9600 bps and
above, data can be sent back and forth so quickly, a quicker and
more reliable method of controlling the flow of data must be
implemented. Here we use RTS/CTS (Ready to Send/Clear to Send)
flow control. What happens is that in effect, hardware bits are
toggled to immediately trigger the necessary start/stop sequences
to prevent data over-runs. Although the two software programs
must continually monitor the CTS/RTS bits, it can usually be done
much more quickly and effectively than having to check for the
XON/XOFF software signals.
Chapter 17 17.3
PCBoard - 9600/19200 BPS Modem Operation
Now, we know there are three links between the two machines, and
that there must be good flow control in order to prevent data
loss. What some callers don't realize is that each link can run
under its own type of flow control. In other words, the CLink
must have proper flow control, the MLink as well, and of course
the HLink. If you consider that the caller may only be using
XON/XOFF flow control for the CLink portion, while the host CPU
is trying to only use RTS/CTS flow control for the HLink, and the
two modems are using neither, you can imagine the problems that
may develop in trying to keep the data from being lost or
corrupted. So, how do we as sysops figure out how to set up our
"host" modems and HLinks, plus, how do we educate our callers to
do the same? Unfortunately, with the large variations in current
modem technology and configuration settings - that can be a very
difficult task.
When hooking up a 9600 bps or lower speed "compression" modem on
your host CPU, you need to determine your HLink speed of
operation and type of flow control. If you are running on a
"slow" machine, or under some sort of multi-tasking software
where the hardware may not be able to keep up with full 19200 bps
flow, you will have to limit yourself to a maximum rate of 9600
bps or lower in order to insure reliable operations. However, if
your hardware can support a full 19200 bps HLink, then you need
to change some of your modem settings versus a sysop who will be
using 9600 bps as their HLink speed. Why? Because of the way
PCBoard operates. If the opening speed of the modem is 9600 bps
or lower, PCBoard has been written to allow the HLink to AutoBaud
to match the speed of the MLink. However, if the opening speed
is 19200, or you have enabled the "Lock in Opening Baud Rate" in
the Modem Information screen of PCBSetup, PCBoard assumes that
you want to "lock-in" the maximum DTE throughput rate, and does
not AutoBaud the HLink to try and match the MLink (with the
exception of the Hayes 9600 V-Series modem. See note at end of
document). So, how do we adjust for that in the modem settings?
First, a word about AutoBauding and what happens.
17.4 Chapter 17
PCBoard - 9600/19200 BPS Modem Operation
AutoBauding
-----------
AutoBauding is simply a term to describe the ability of the host
software to change the speed of the HLink to match that of the
MLink. Here's how it works. A caller decides to call XYZ board
across town using an ACME 1200 bps modem. XYZ BBS across town is
using a GENERIC 2400 bps external modem - which the sysop has set
up with an initial port opening speed of 2400 bps. XYZ sysop
brings their board up on-line. PCBoard opens the com port at
2400 bps (the async card is now set to operate at 2400 bps).
Likewise, the modem at XYZ board also responds at 2400 to the
initial commands and is ready to answer the phone. The caller
dials XYZ board, and the board gets a ring detect. At that time,
PCBoard sends the modem an "ATA" command to answer the phone.
This is done of course at 2400 bps. The modem goes into auto-
answer mode and starts its initial handshaking with the caller's
modem. First, it tries to establish a good connection at 2400
bps. Since that fails, it drops down to 1200 bps and tries
again. Success! The modem-to-modem link (MLink) is now at 1200
bps. The modem now sends a "CONNECT xxxx" message to the host
CPU via the HLink at 2400 bps. The host software looks over the
response and is told that the connection was made at 1200 bps and
not 2400 bps. Since the connect message is the last command the
modem will send to the host via the HLink at 2400 bps, the host
CPU must automatically drop down to 1200 bps, or all future data
transfers on the HLink will be garbage. So, the host software
(PCBoard in this case), immediately adjusts the async card's bps
rate divisor "latches" on the fly - so that the HLink is now at
the same speed as the MLink -which is of course also the same
speed as the CLink. Now that all the links are "talking" at the
same speed, data starts to flow normally between the two
machines. All of this works fine if the host modem is able to
quickly change speeds to match the caller, and it properly
returns the correct "CONNECT xxxx" message to PCBoard. The older
300/1200/2400 bps modems usually have no problems with this.
However, enter the world of 9600 bps modems and some new low
speed "compression" modems - where there is yet no "standard"
among the various manufacturers on how the MLink should be
established. Plus, based on the firmware in the modem itself,
some may have a great deal of trouble in dropping down from the
higher speeds to the lower speeds in an attempt to establish a
good carrier (MLink) with the caller. And, since the sysop has
the option of either allowing the HLink to stay at a fixed rate
or to AutoBaud to match the MLink, things start to get a little
confusing.
Chapter 17 17.5
PCBoard - 9600/19200 BPS Modem Operation
Configuration
-------------
So, what do the sysops do to properly configure their system if
they want to run one of the new 9600 bps or low speed
"compression" modems? First, they must of course decide upon the
brand of modem they will use. Since most of the new modems use a
different technique for handling full duplex operation which
affects the 'turn-around' response time (the ability of the
callers to see on their screen the character they just typed),
sysops must be careful to purchase a modem which will meet their
needs in "interactive throughput". Since most 9600 bps modems
are not actually operating in full duplex mode (i.e. they are
simulating what normally happens at bps rates of 2400 and below
in the modem's ability to send and receive data at the same
time), there can be long delays between when the caller presses a
key on their keyboard and when they see the character on their
screen. This is very annoying and usually means file transfer
throughput rates may be affected in a similar manner. Second,
they must consider how well the modem will work in day-to-day
operations in handling the ability to establish a good carrier
with the caller - regardless of the speed of the HLink and the
quality of the line. Third, the sysop should consider how easy
it will be to configure the modem to operate reliably. If
configuration efforts requires a PhD in figuring out the modem
manual with the all the various combinations of settings, you may
want to check out a different brand of modem.
So, a modem is finally selected and is ready to be installed.
Now, we get back to the question of what speed are we going to
set the HLink - since that determines how the host modem should
be configured. If it is decided that the HLink is going to be
19200 bps (the host hardware can safely handle full 19200 bps
operations), the sysop needs to set up the modem so that the
HLink always stays at 19200 - since that is what PCBoard is going
to do. If 9600 bps is the highest speed which will specified,
then the modem must be configured to allow for AutoBauding to
occur unless you are running either a Hayes 9600 V-Series or
other low speed "compression" modem. (See Hayes 9600 V-Series
modem note at end of document). CAUTION: In either case however,
you must enable RTS/CTS flow control!!
At this point, you should check your modem manual for the
appropriate modem setting to accomplish the above. Note that the
manual will probably indicate not only a "send" flow control
parameter, but a "receive" one as well. In that case, all should
be set to allow for CTS/RTS flow control! CAUTION: If you are
going to be running at either 9600 or 19200 bps, and you disable
RTS/CTS flow control when configuring the host modem, any "full-
flow" protocol transfers (such as 1K-Xmodem Full-Flow) will not
work reliably - since data over-runs are sure to occur.
17.6 Chapter 17
PCBoard - 9600/19200 BPS Modem Operation
MNP 'CONNECT'
------------
Also, some modems which use MNP error checking, allow the modem
to either "look for" another MNP modem, or to ignore the fact
that there may be another MNP modem calling in. Since the time
to "look for" another MNP modem can take up to 6 seconds, the
sysop should be aware that their callers may get a delay between
the time the phone answers the caller and when the "CONNECT"
message is sent. Likewise, if the caller has "look for another
MNP modem" enabled on their end, while the host modem does not,
the host may send the "CONNECT" message to the caller -but since
the caller's modem is still trying to look for another MNP modem,
the initial data will be lost to the caller and may not appear on
their screen. This becomes very confusing for not only the
caller, but the sysop as well in trying to figure out why some
callers are loosing the initial logon message, while others
receive it fine. Unfortunately, the only answer to all of this
is education on the part of the callers as well as the sysops.
They both need to have an understanding of high speed
communications and the various modem's characteristics if they
want to enter the high speed arena. It is no longer simply a
matter of plugging in a modem, setting a few switches, giving the
modem a few simple commands, followed by totally reliable
unattended operation.
If all/any of the above makes sense, the next question usually
asked by the sysop is "Gee, where do I find out about all this
stuff and still - no one has told me how to set up my modem!"
Unfortunately, there are very few single sources of information
on how all of the various brands of new modems operate -
including the various commands needed to properly configure them
for both the caller as well as the sysop. For example, the US
Robotics Courier HST modem, when operating at 9600 bps, uses a
USR proprietary means of communication. However, at 1200/2400
bps, it can be configured to "talk" to other MNP based modems!
So, the sysop must be able to relate 1200/2400 bps MNP settings
to other MNP modems, while considering USR settings for 9600 bps
and above.
Chapter 17 17.7
PCBoard - 9600/19200 BPS Modem Operation
Proper Settings
---------------
What all this boils down to is that the PCBoard authors are
frequently asked if we can provide the necessary settings for the
various 9600 bps and other low speed "compression" modems which
will allow all of this to work properly. At present, we have
included many 'suggested' settings for various modems which have
been provided by our callers. These settings can be found in
Chapter 16. However, when configuring your modem (or selecting a
brand to purchase), please consider some of the following:
1. Do your callers want their CLink to be at a fixed rate?
2. Do your callers want their CLink to autobaud?
3. Do you want your HLink to remain at a fixed rate?
4. Do you want your HLink to autobaud?
5. Do you plan on 'locking-in' a low speed DTE
'compression' rate?
6. Does your machine have an 8250 UART (9600 bps max if
true)?
7. Are you running in a multitasking environment?
8. Are you using an EGA/VGA card which uses NMI's to
operate?
As can be seen, multiplying the above by the number of modems on
the market, and then compounding this effort with the fact that
there are currently a lot of ROM changes (hence modem setting
changes) going on in the industry - it is virtually impossible
for any one source to remain current on everything associated
with high speed or "compression" operation. Therefore the best
source of information, and obviously the most current, should be
obtained from the modem manufacturers themselves. Hopefully,
they will be fairly familiar with the software that is being used
at both ends of the connection to provide sufficient information
on the proper modem settings to use under those conditions.
However, we do provide a default modem setup program called
PCBModem which we use to configure modems tested on the Salt Air
BBS system for operation. We have found that when using the
settings in the PCBModem program, we are able to successfully
operate the Hayes 2400, Hayes 9600 V-Series, US Robotics Courier
HST, and Microcom AX9624C modems with PCBoard. Again, refer to
Chapter 16 for possible modem settings for your model.
17.8 Chapter 17
PCBoard - 9600/19200 BPS Modem Operation
Questions & Answers
-------------------
Here are some commonly asked questions and answers concerning
9600/19200 bps operation that may assist you in configuring your
system:
Question
--------
Why is it that on the local (host) screen, it appears that the
caller is using XON/XOFF flow control when operating the host at
19200 bps?
Answer
------
What is usually happening here is that the host modem may have an
internal buffer to store up to 8K of data it receives from the
host CPU via the HLink. It then funnels the data out to the
caller at the MLink speed. So, what the sysop usually sees on
the host side is a little blip of data going to the modem as
almost an entire screen of data is sent to the host modem and
buffered there. Then, the host modem dribbles out the data to
the caller at the MLink speed. No lights are usually present on
the host modem to indicate that the data is actually being sent
to the caller - since the TD or SD (transmit data or send data)
light only flashes when the host CPU sends data to the host modem
via the HLink - not when the host modem is sending data to the
caller's modem via the MLink. What this ends up looking like is
3/4 of a screen display appearing almost instantaneously on the
host, followed by a delay, followed by another quick screen
display, followed by a delay. This is normal, and you have to
remember that the caller is simply seeing what they always do at
the speed at which they are connected - rather than at 19200 bps.
The pauses are caused by having properly defined your CTS/RTS
flow control parms - since when the host modem's buffer is full
it signals (by toggling the RTS/CTS signals) the fact that the
host CPU should delay sending it (the host modem) any more data
until it has had a chance to empty out its internal buffer to the
caller.
Question
--------
My callers are complaining that since installing a 9600 bps modem
and running it at 19200 on the HLink, they are no longer able to
(Ctrl-K) abort a "non-stop" listing, or are unable to interrupt a
long message display. What's wrong with my settings or the
software?
Chapter 17 17.9
PCBoard - 9600/19200 BPS Modem Operation
Answer
------
Nothing is wrong with either of them! Your callers are simply
trying to perform functions against the internal buffer of the
host modem - over which you and/or the software may have no
control. When operating the host at 19200 as indicated above, a
whole screen of data can be sent to the modem in a fraction of a
second. There it will be buffered until it is sent to the caller
at the speed at which they can accept it. For example, a
complete message can be sent to the host modem - after which the
host pauses awaiting the caller's response to a "More" prompt.
In the meantime, the caller is just barely starting to have the
message displayed on their local screen. They decide they want
to (Ctrl-K) abort it. So, they press (Ctrl-K). Since the host
CPU has already sent all the data to the modem, and the modem
will not recognize the (Ctrl-K) as a signal to flush out what is
in its internal buffer, the caller continues to receive data from
the host modem until its buffer is empty. The slower the MLink
speed, the worse this situation will be. If your caller's
software supports the sending of a BREAK signal to your modem,
and your modem supports the "dumping" of its buffer upon receipt
of a BREAK signal, this delay can be defeated.
Question
--------
If this is the case above, why not let me define the host modem's
buffer size?
Answer
------
That is between you and the modem manufacturer and the various
settings they allow. However, decreasing the internal buffer
size of the host modem may degrade the modem's ability to operate
up to its advertised speed.
Question
--------
On my system, the best download cps rate that any of my callers
get when using my new GENERIC 9600 bps modem is 700 cps. But, on
my friend's system down the street, I see his caller's getting
over 1000 cps all the time! What am I doing wrong?
Answer
------
Possibly nothing! Some of the things that can cut cps figure
down VERY quickly are: 1)CPU speed, 2)multitasking the host CPU,
3)speed of the host hard disk, 4)line quality, 5)modem settings,
etc. Any of the above can make subtle differences in your
caller's CPS throughput. Remember, at 9600 bps, an increase of 1
17.10 Chapter 17
PCBoard - 9600/19200 BPS Modem Operation
second in the time it takes to send a given piece of information
can have dramatic effects on throughput rates - since ideally 1
second will cause a "loss in effectiveness" of approximately 1000
bytes! Additionally, some of our users have found conflicts
between their COM port and Networking card interrupts (IRQ's),
which effectively kills upload throughput. Also, some new high
speed CPUs have UARTS installed which to not allow for maximum
throughput.
Question
--------
Should I buy a 9600 bps modem, and which one should I buy?
Answer
------
Sorry, but that question can only be answered by you after
determining your needs, the needs of your callers, and what you
feel you can afford. Remember, at present there are very few if
any "standards" among the 9600 bps modem manufacturers - which
normally means only "like manufactured" modems can talk to each
other at 9600 bps. So, if you decide to buy one, only callers
who have the same brand of modem will be able to take advantage
of your "new technology". Second, your users will have a
tendency to look to you for leadership in what modem they should
buy so that they can talk to your system at the higher rates of
speed. If you recommend they go out and by an ACME 9600 bps
modem for $1,000, and 3 months from now the GENERIC 9600 modem at
$595 becomes the defacto "standard" which everyone else is buying
and running, your callers will be understandably a little upset
with you for influencing their buying decision in the wrong
direction. You are assuming a lot of responsibility as a PCBoard
sysop when you bring a system up on-line. Callers will expect
that you are a leader in the area because of your choice of
software. Be prepared to live up to their expectations.
Question
--------
Why is there a delay between what the caller types at their
keyboard and what they see on their screen?
Answer
------
At 2400 bps and below, the modem(s) can send and receive data at
the same time. Therefore, the "turnaround" time, (the time it
takes the caller to send the keystroke to the host, and for the
host to send it back to the caller for display on their screen)
is very short - measured in fractions of a second. However, at
9600 bps, most modems are not operating in full duplex mode with
instantaneous turnaround. Instead, they are "emulating" full
Chapter 17 17.11
PCBoard - 9600/19200 BPS Modem Operation
duplex operation since they are also providing full error
checking of the data that is being sent and received. In order
to do this, several schemes can be used. However, the end result
is that at 9600 bps and above (under current technology),
turnaround time may be longer at 9600 bps than it would be if the
caller were at 2400 bps. Some modems are better than others.
Some are very bad. You should check around to find one that will
meet your expectations. A $400 9600 bps modem which is prone to
errors and has terrible turnaround time is not a "bargain". Make
sure you are getting what you pay for. Remember also, that just
because you can buy a certain brand of modem cheaply does not
mean your callers can automatically do the same. If your callers
can't afford a modem which will talk to yours, your money has
also been wasted.
Question
--------
I am running under a network environment. What should I set my
upload buffer size to be inside PCBSetup to insure maximum
throughput during uploads to my system?
Answer
------
That depends on the speed of your network, the speed of your hard
disk, the type CPU's and UARTs you are using, and your over-all
network activity. For most networks, although it may sound
strange, you may get BETTER throughput during uploads if you set
your buffer size to 4 or 8 blocks! Only if you are running in a
true "standalone" environment with a fast hard disk and/or a very
fast network (10 meg throughput) will a large buffer size usually
benefit you or your callers. The reason being is that most
networks will more efficiently handle a small packet transfer
request on a more frequent basis than they will a large one -
based on other network activity. The ability to define an
"Upload Buffer" size in the PCBSetup program can provide
increased throughput to most standalone systems - especially
those running high speed modems. However, by defining a large
upload size buffer, you are going to be allocating additional low
memory for the buffer. This usually has minimal effect on a
system running in standalone mode, or in a true network
environment. However, if you are running under multitasking
software, you may have problems if you try and define too large
of an upload buffer. You may run out of memory and get all sorts
of strange error messages. The best recommendation we can
provide is to start with a buffer size of 8 blocks and work up
from there. If no strange errors occur, increase the number in 4
block increments.
17.12 Chapter 17
PCBoard - 9600/19200 BPS Modem Operation
Question
--------
My PC Pursuit callers are really griping about the new code and
my new 9600 bps modem! Seems none of them can download anymore!
What did you mess up in the new code?
Answer
------
Nothing! The routines used in the current code are the same as
those used in previous versions. The problem centers around PC
Pursuit and the communications program they are using. What
happens is if you are operating your HLink at 19200 and PC
Pursuit is a little busy, the caller's communication program may
abort - since PC Pursuit is not geared up to handle the high data
flow rate. To correct for the condition, have your callers
select a "relaxed" protocol transfer type in their communication
program, install a Zmodem DOOR application, or drop your HLink
down to 9600 bps. Additionally, some of the communications
program they (your callers) are using are very sensitive to
timing problems on their end. You can also suggest that they try
a different program.
Question
--------
My callers can perform downloads fine, but uploads slow way down
- achieving only about half the throughput rate of downloads.
Why is that?
Answer
------
There are a couple of possibilities, including: 1) an interrupt
conflict between your asnyc port and the network card you are
using - be sure the COM port IRQ interrupt is higher than the
network card's interrupt; 2) a slow UART chip in comparison to
the CPU speed - some older style XT async cards will not function
properly in the newer high speed AT class machines during an
upload.
Summary Notes
-------------
In summary, individuals purchasing one of the new 9600 bps error
correcting modems hope the new modem will really make their
system file transfers fly. Unfortunately, some will find that
19200 will not work on their system. The reasons are many, but
basically boil down to what type UART(s) and CPU the system is
using, what brand modem(s) the board is running, whether the
sysop is running any software which must control the COM port
buffer interrupts (this includes all multitasking software and
possible Networking card conflicts, etc.), and how the system
Chapter 17 17.13
PCBoard - 9600/19200 BPS Modem Operation
intends to support PC Pursuit callers. Unfortunately, some
multitasking software is unable to efficiently time slice
concurrent 19200 bps operations under one or more partitions,
causing device timeouts when the opposite partition attempts to
output anything to its respective COM port. PCBoard attempts to
trap for as many of these timeout conditions as possible.
However, in some cases, the multitasking software may never
"release" the opposite COM port, causing that node to effectively
loose its COM port. This has the effect of shutting down that
node. Additionally, even if 19200 does work under your
multitasker, you may find that file transfers are slower than at
a straight 9600 bps setting. The reason again is the way the
interrupts are handled and the amount of timeout errors which are
necessarily being trapped by the code. Basically, if you
experience a large number of errors while trying to run one or
more nodes at 19200 bps, you will have to set your modem open
speed to a max of 9600 bps. Additionally, if the CPS throughput
is less at 19200 that it was at 9600, you will likewise be best
to set back your modem speed to 9600 max. Please note that the
additional throughput gained by running the host modem in a
locked 19200 bps setting is minimal compared to straight 9600
bps. Plus, the chances of getting a device timeout on another
node is much less when running at 9600 rather than 19200. 19200
will work best for those individuals running either true
networking systems who have "tuned" their network for maximum
throughput, or for those running 19200 in a single node
standalone mode. We estimate 95% of all multitasker sysops will
find that 9600 bps is the maximum speed they will be able to
operate their nodes reliably.
17.14 Chapter 17
PCBoard - 9600/19200 BPS Modem Operation
Hayes 9600 V-Series Notes
-------------------------
PCBoard fully supports the new Hayes 9600 V-Series modem at all
speeds - including 19200, 9600 and lower bps rates. However,
since the Hayes 9600 V-Series operates entirely different than
the other current 9.6 modems on the market, it is essential you
properly indicate to PCBoard that you are using a Hayes 9600 and
that you understand the difference in its operation. To indicate
to the code that you are using a Hayes 9600, set the field "Using
Hayes V-Series 9600" to 'Y' in the Modem Information screen of
PCBSetup. Most of the new 9600 modems allow setting the HLink to
a fixed speed of operation - regardless of the speed of the
caller. However, the Hayes V-Series does not allow holding the
HLink at a fixed speed unless it detects an "error-corrected"
connection. This means that if and only if the caller is using
another error correcting V-Series modem and they establish an
error-correction link will the Hayes on the host stay at the
fixed DTE or HLink speed. Under all other conditions, the Hayes
9600 V-Series will AutoBaud down to match the speed of the caller
- even though the port was opened at 19200 on the host. DOOR
authors must consider this when writing their applications for
sysops with a Hayes 9600 V-Series on-line. In order to detect
this, a DOOR author should check the PCBOARD.DAT file to see if
the sysop has turned on the "Using Hayes V-Series 9600" modem
switch and adjust accordingly.
Pause/Abort Performance (Ctrl+K) (Ctrl+S)
-----------------------------------------
A sidenote when configuring your high speed modem to operate at a
maximum speed of 9600 bps. When you configure your modem's
opening speed to be 9600 instead of 19200, some of the problems
indicated above (such as failure to quickly detect a (Ctrl-K),
etc.) are no longer a problem - since the code will automatically
AutoBaud the modem to match the caller's connect speed. Since
under that condition, output from the code is much more closely
aligned to the speed at which the caller is able to receive the
data, normal (Ctrl-K) operations are restored. Additionally, the
Hayes 9600 V-Series modem automatically AutoBauds down unless an
error-corrected connection is established - which means it will
properly handle a caller's (Ctrl-K) requests as well. So, the
bottom line is, do you want to provide better support for your
low speed callers, or do you want to insure the maximum
throughput for your high speed ones? The question of how you
want to support the majority of your callers rests entirely with
you. You need to decide what course of action you wish to take
when configuring a 9600 bps modem.
Chapter 17 17.15
PCBoard - 9600/19200 BPS Modem Operation
NOTES
17.16 Chapter 17