(Answers to Frequently Asked Questions)
Copyright 1995-1996 The Navas GroupSM,
All Rights Reserved.
Permission is granted to copy for private non-commercial use only.
Send mirror and commercial license inquiries to info@NavasGrp.Dublin.CA.US.
Posted as <http://www.aimnet.com/~jnavas/modem/faq.html>.
Updated Wednesday, January 22, 1997.
Breaking News
Copies of this document in either hypertext (HTML) or plain text
format may be obtained by email from an "agora" server
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or from web-mail.
For information on agora, send an email message to an agora server
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send a blank email message to web-mail@ebay.com.
Please note: The author has no present connection
with any modem company (other than as a customer), and does not
endorse the products of any company. This information was compiled
by the author and is provided as a public service. Neither the
author nor any organization mentioned herein are responsible for
any errors or omissions, or for any consequential problems that
might result. USE AT YOUR OWN RISK.
Please note: The author does
not have the time to give individual technical support, so please
do not email requests for assistance. Instead,
post them to Usenet. Thank you.
Email comments and suggestions to JNavas@NavasGrp.Dublin.CA.US
Contents
Section I:
[The Navas Group home page]
(If you see a connection speed of 38400, 57600, or 115200, don't
be fooled -- that is the serial port speed between your computer
and your modem, not the speed between your modem and the
remote modem. To report the modem-to-modem speed, your modem probably
needs a different initialization string. Consult your documentation.)
[new 7/27/96]
Note: Reported initial connect speeds won't necessarily
be dependable or even comparable from modem to modem or location
to location. The reason is that V.34 modems can (and often do)
speed shift up and down after the initial connection, and do so
in a manner that is dependent on the particular connection as
well as the particular equipment (including firmware versions)
at each end. (See "What are "fall-back" and "fall-forward"?")
Some modems connect at a more conservative speed and then quickly
upshift as conditions allow; other modems connect at a more aggressive
speed only to quickly downshift (or worse, lose performance due
to excessive errors). Another problem is that software may report
the receive speed for certain modems and the transmit speed for
other modems, which can be substantially different. (See "What are split/asymmetric speeds?")
Unfortunately, it is not possible to monitor the actual modem
speed during the connection for most modems. Regardless, the
only thing that really counts is net throughput, which can
be measured by many communications applications. [new
10/27/96]
If you consistently connect at 26400 or above, there may not be
much that you can do to go faster -- it's simply not possible
to achieve the highest V.34 speeds on many phone circuits. (This
is not false modem advertising -- 28800 modems are designed to
wring as much speed out of the actual real-world connection as
possible, and 28800 or higher speed is only possible on a near-perfect
connection.)
If you consistently connect at lower speeds (e.g., 24000
or even 21600), there may still not be much that you can do, but
you can at least try the following:
- Make sure that your serial port is locked at 38400 or higher
(57600 recommended). This is usually set within your comm application,
not the Windows Control Panel (see "How do I set a speed greater than 19200 bps in Windows?").
- Try connecting to known good 28800 numbers (e.g.,
Hayes at 800-"US-HAYES; Multi-Tech at 800/392-2432; USR at
847/982-5092). This will at least tell you whether the problem
is at your end or the other end of the connection. (The USR number
is particularly useful, because you can get an on-line reading
of connection quality from a USR BBS command.)
- Watch out for dialin numbers that are being forwarded to a
distant location. It's a "dirty little secret" that
many BBS (bulletin board systems) and ISP (Internet service providers)
use Call Forwarding to extend their local calling areas. (Where
location A to location C is a toll call, and an intermediate location
B is local to both A and C, Call Forwarding from B to C effectively
makes A to C a local call.) Although this can work fairly well
at lower speeds (e.g., 14400), the extra connection hop(s)
can degrade the signal enough to limit higher speeds (even as
compared to a direct long distance call).
- If possible, test for premises problems by disconnecting all
your premises wiring (and equipment) from the incoming telco terminating
block, and hooking your modem directly to it. If your connections
are better, you have a premises problem that you may be able to
isolate and fix. Premises problems (faulty wiring and/or
equipment like cheap phones and fax machines) are a frequent cause
of 28800 connection problems.
- If that doesn't help, listen carefully to the quality of your
voice connections. Note that you must dial a known quiet number,
since many otherwise good phone lines exhibit excessive noise
until you actually connect. (Dialing a single digit is not
enough.) After you connect, if you hear more than very faint hiss
and/or hum, then you probably have a line problem.
- While a quiet line is important, there are other line problems
that can reduce your speed: bandwidth (frequency response), distortion,
etc. It is difficult to test for these problems without
proper test equipment, but it's still a good idea to listen carefully
for audible problems, particularly if you can find a number that
will send you test tones.
- You may be able to get your phone company to improve the quality
of your line. Since phone companies are often reluctant or even
unwilling to work on data problems, it may help to report that
you are also having fax problems. Or you can try asking for a
data or fax "specialist." Ideally you want the service
technician to bring the right kind of test equipment, a sophisticated
line or transmission test set, not just the normal basic tester.
It may also help to ask for a BERT (bit error rate tester) or
"data test set."
- Sometimes switching to a different cable pair from the CO
(central office) will help. In extreme cases the author has resorted
to ordering a new line, making sure that it is good when installed,
and then canceling the old line.
- You may be told that you need a special "data" line,
more properly called a "conditioned" circuit, which
is considerably more expensive than a standard "voice-grade"
circuit. Don't waste your money. All you need
is a good quality "voice-grade" circuit.
A final note: Add-on noise filters will not help
-- they are the modem equivalent of snake oil. Your 28800 modem
already has all the filtering it can use. An add-on filter will
do nothing at best, and it may well make things worse.
[Return to top]
Here are some general, rough guidelines. Bear in mind that data
download speed is affected by many things other than modem-to-modem
connection speed, including: the load on the remote system; the
speed of any network links (e.g., Internet congestion);
the speed of the local computer-to-modem port (e.g., serial
port speed); the load on the local system; quality of the communications
software; and the transfer protocol (e.g., ZMODEM or FTP).
TYPICAL DOWNLOAD SPEEDS
MODEM CONNECTION
SPEED (BPS)
| UNCOMPRESSIBLE DATA
(e.g., .ZIP) SPEED (CPS)
| COMPRESSIBLE DATA
(e.g., text) SPEED (CPS)
|
14400
| 1600
| 3200
|
21600
| 2400
| 4800
|
24000
| 2670
| 5330
|
26400
| 2930
| 5870
|
28800
| 3200
| 6400
|
31200
| 3470
| 6930
|
33600
| 3730
| 7470
|
36000
| 4000
| 8000
|
40000
| 4440
| 8890
|
44000
| 4890
| 9780
|
48000
| 5330
| 10670
|
52000
| 5780
| 11560
|
56000
| 6220
| 12440
|
64000
| 7110
| 14220
|
Notes:
- Modem speeds over 33600 bps are only possible with 56K (see
"What are 56K modems?") or ISDN
(see "What is ISDN?").
- Modem speeds can and do vary over the course of a given connection.
(See Why don't I get 28800 bps (or more) on my connections?)
If your data speed seems a bit high or a bit low it may be because
the modems have shifted speed. (See "What are "fall-back" and "fall-forward"?")
- Speeds for compressible data can vary widely depending on
the potential for compression in that data.
- Speed limits:
- Speeds above about 5600 cps require a modem port speed of
115200 bps (or more).
- Speeds above about 12000 cps are not possible over a standard
PC serial port. (Faster ports are available, but they require
special software drivers.)
- FTP downloads over a PPP connection can run about 1-2% less
than these numbers (due to overhead).
- ZMODEM downloads over a standard modem connection to a bulletin
board system can run about 1-2% faster than these numbers.
[Return to top]
- V.FC
- A proprietary specification for speeds up to 28800 bps, based
on an early draft of the V.34 standard, that was rushed to market
by modem chipset leader Rockwell International.
It works reasonably well, but lacks the sophistication and robustness
of V.34; for example, V.FC does not support split speeds.
Many (but not all) V.FC modems are upgradable to V.34, but the
modem typically has to be returned to the manufacturer for a "datapump"
change. V.FC-only modems will not connect above 14400 bps to V.34
modems that lack V.FC support. With the advent of V.34, V.FC is
rapidly fading as modems are upgraded. In the opinion of the author
there is now little or no reason to get a modem that has V.FC
but not V.34, although until V.FC fades completely there will
still be a significant advantage to a modem that supports both
V.34 and V.FC.
- V.34
[updated 10/27/96]
- A true international standard for speeds up to 33600 bps (more
realistically 28800 bps) that is more sophisticated and robust
than V.FC. Some but not all V.34 implementations support optional
features like 31200 and 33600 speeds and/or split speeds
for transmit and receive. V.34 is rapidly replacing V.FC in the
marketplace. V.34-only modems will not connect above 14400 bps
to V.FC-only modems. In the opinion of the author V.34 is clearly
the modem standard of choice. It may well prove to be the last
widely-supported analog modem standard.
- 56 Kbps [updated 10/16/96]
- Rockwell Semiconductor Systems
(along with a number of its customers), USRobotics,
and Lucent Technologies have
announced plans to introduce modems that work over conventional
phone lines at speeds up to 56 Kbps. See "What are 56K modems?"
- 28800-33600 fax
- Fax is currently limited to 14400 bps over dialup analog phone
lines (Group III V.17). Efforts are underway to define a 28800-33600
bps fax specification, which would probably be widely adopted.
However, general availability is probably a few years away.
- Voice
- See "What are "voice" modems?"
- Plug and Play
- See "What is Plug and Play"
- ISDN
- See "What is ISDN?"
- "Cable modems"
- See What are "cable modems?"
- ADSL/SDSL/HDSL
- See "What are ADSL, SDSL, and HDSL?"
- Universal Serial Bus
- A better way to connect a modem to your computer than the
conventional UART or parallel port. (See "What is a UART?")
Expected to become a standard feature of many chipsets and motherboards
(e.g., those manufactured by Intel) and operating systems
(e.g., Windows 95), although USB is not yet available.
(See "Universal Serial Bus Home Page"
and Intel's "USB Interactive Tour")
See also "Modems: the make-it-happen machines for the ultimately wired of the 90's"
[Return to top]
Rockwell Semiconductor Systems
(along with a number of its OEM customers), USRobotics,
Lucent Technologies, and
Motorola Information Systems Group,
have announced plans to introduce modems that work over conventional
phone lines at speeds up to 56 Kbps. See:
- There are several catches however:
- Such products are vaporware and will stay that way
for some time to come. Even after introduction, it will take time
(and product updates) to achieve maturity and wide deployment.
- Such products are years away from standardization (if ever),
and there may well be serious interoperability problems,
particularly between Rockwell-based and USR-based products. (This
means that if you have a Rockwell-based 56K modem, you may only
get V.34 speed when connecting to USR equipment, and vice versa.
This could be another VHS versus Beta battle in which there will
be winners and losers.)
- The higher speed will only be for receiving -- sending
will be limited to V.34 speeds (although typical Internet access
is mostly receiving).
- The modem at the other end must be digital technology that
connects to the telephone network through a digital connection.
- If you are having trouble obtaining full V.34 speeds
now (see "Why don't I get 28800 bps (or more) on my connections?"),
then higher speeds may also be a problem.
- Standard PC serial ports will be a bottleneck for 56K
modems operating at higher speeds with compressible data. To take
full advantage of a 56K modem you'll need a serial connection
(port/modem) that goes significantly faster than 115.2 Kbps, a
parallel connection, or USB (see "Universal Serial Bus Home Page").
- This is probably bad news for smaller Internet Service
Providers, many of whom do not have upgradable digital equipment
installed and will have difficulty paying for hardware upgrades.
- Increasing overload of Internet connections often makes
it difficult to max out a V.34 link, much less a faster link.
- There could be a nasty patent battle. (Lucent Technologies
claims to have "already patented key elements of the new
56 kbps modem technology and has other required patents pending.")
As for the looming competitive battle between Rockwell and USRobotics,
the latter appears to be in the stronger position for two reasons:
- USR has a large market position among Internet Service Providers
(ISPs), with a substantial installed base that can be easily upgraded
to 56K ("x2") technology.
- USR claims that all of its modems currently in distribution
will be easily upgradable to 56K technology. (While choosing such
a modem would seem to be a good way to get ready for 56K deployment,
the higher speed may well only be possible when connecting to
an ISP that installs USR-brand digital "x2" technology.)
An interesting possible fallout is that the new 56K technology
may finally force down the price of ISDN. (See "What is ISDN?")
[Return to top]
In the past, most standard modems were only capable of transmitting
and receiving at the same speed. (The exceptions were proprietary
modems such as the USR HST that used greatly different transmit
and receive speeds.) Since most connections were made at the maximum
speed, there was little reason to support different transmit and
receive speeds.
With the advent of speeds up to 28800 bps that is no longer true.
It's now quite common to have a connection where at least one
(and often both) speeds must be limited to less than 28800 bps,
and it's not uncommon to find that a connection will support faster
speed in one direction than the other. (One reason is that send
and receive channels are separated for transmission between telephone
switching offices.)
Having been designed to optimize performance over a wide variety
of conditions, V.34 includes an optional specification
for asymmetric (differing or split) transmit and receive speeds.
For example, a connection might support a transmit speed of 28800
bps but a receive speed of only 26400 bps; without split speed,
the speed in both directions would have to be limited to 26400
bps. For this reason split speed capability is a worthwhile and
desirable feature.
Not all V.34-compliant modems support split speeds. For example,
at the time of this writing most "glue 'n go" Rockwell
V.34 clones, do not support split speeds. On the other hand, others,
including all USR V.34 modems (Sportster 28800/33600 as well as
the Courier V.34), Diamond/Supra, and Motorola, do support split
speeds.
[Return to top]
Selective Reject (SREJ) is an optional, advanced LAPM (V.42) error
correction capability that allows the receiving modem to request
retransmission of a given block while continuing to receive later
blocks; i.e., to receive the retransmission late (out
of order). Without it, the entire transmission has to start over
at the retransmitted block, which can result in later blocks being
resent unnecessarily. Hence, Selective Reject can improve throughput
where there is a significant error rate, particularly over links
with long delays (e.g., satellite links).
Not all modems support Selective Reject, which is typically found
only in high-end products.
[Return to top]
A UART (an acronym for Universal Asynchronous Receiver-Transmitter)
is simply an interface chip. Your computer needs one to "talk"
over a serial connection to serial devices such as serial printers
and modems. Each serial device needs a UART chip to "talk"
to your computer, even modems that are installed inside
your computer.
In computer terms the UART is very old technology. We continue
to use them because we own so much software that depends on there
being a specific kind of UART. Efforts to replace the UART and
its particular serial architecture are ongoing (e.g.,
Universal Serial Bus),
but it's doubtful that the UART will be replaced anytime soon.
There are many types of UART chips, but only two main types that
are used in IBM-compatible personal computers:
- 8250/16450. Major weaknesses of the 8250
and 16450 are a lack of built-in flow control, and buffers that
can only hold a single character. This means that the UART must
be promptly serviced by the system processor each time a character
is received, or that character will be wiped out by the following
character, a condition called "overrun." (See "Why am I getting CRC errors (overruns) when downloading?")
- 8250/8250A. The 8250 is the UART used in
the original IBM PC. "Urban legends" notwithstanding,
the 8250 and the improved 8250A are capable of speeds up to 115,200
bps.
- 16450. Slightly improved over the 8250, the
main advantage of the 16450 is that it works better on computers
with higher internal speeds. From a functional standpoint, however,
it is essentially indistinguishable from the 8250, and suffers
from the same weaknesses.
- 16550. A substantial advance over the 8250/16450,
the 16550 has both a fully 8250-compatible mode and a newer mode
that provides 16-character FIFO (an acronym for First In, First
Out) buffers. When the old mode is enabled, it works just like
an 8250; when the newer mode is enabled, the FIFO buffers greatly
extend the time available for responding to incoming characters.
The receive FIFO buffer has a variable threshold that can be set
to values of 1, 4, 8, or 14 characters, with higher numbers giving
less time to respond before the 16-character FIFO buffer is full;
on the other hand, higher numbers can give slightly better performance,
by allowing the system to process incoming characters in larger
"chunks." A good rule of thumb is a threshold
of 8 characters. (See "What about third-party comm drivers for Windows?")
Most (but not all) internal modems come with a 16550 UART.
- 16550. Certain versions of the original 16550
were buggy. It is best to avoid them.
- 16550A. Improved version of the 16550. Later
types, the 16550AF and 16550AFN, are essentially indistinguishable,
but even less likely to be buggy. These are the UARTs of choice.
Look for the National Semiconductor
brand.
- 16552. Two improved 16550 UARTs in a single
package.
- Clones. More recent designs typically package
UART functionality (often two of them) in a single "multi-I/O"
chip. Many of them work very well; however, some of them are buggy.
(See "Why does Windows lock up when I try to access my modem?")
Some internal modems emulate UARTs with on-board logic rather
than using actual UART chips; these products can provide more
effective buffering than a conventional UART. More advanced UARTs
(e.g., 32-character FIFO buffers, built-in flow control)
are becoming available, but they are generally not needed. Parallel
modem interfaces and the Hayes ESP card are alternatives to UARTs,
but they require special drivers and provide no significant advantage
over the 16550A in the opinion of the author.
In general, a single-task operating system like MS-DOS can get
by with an 8250/16450 UART with serial port speeds of 19200-57600
bps (depending on the speed of the system processor) and well-written
software. This is usually adequate for even a 28800 bps modem.
However, a multitasking operating system like Windows, OS/2, or
UNIX, will usually need a 16550 UART. (Nevertheless, if you are
stuck with an 8250/16450, you can probably still use a 28800 bps
modem if you are careful.)
You can tell what kind of UART chip you have by running Microsoft's
MSD
(which comes with Windows), being sure to run it outside of
Windows. (The reason is that Windows can hide the true state
of the UART from MSD.)
The Universal Serial Bus (USB) is a better way to connect a modem
to your computer than the conventional UART or parallel port.
USB is expected to become a standard feature of many chipsets
and motherboards (e.g., those manufactured by Intel)
and operating systems (e.g., Windows 95), although it
is not yet available. (See "Universal Serial Bus Home Page")
[Return to top]
- If your 8250 or 16450 UART is a single chip mounted in a socket,
it is easy to replace it with a 16550 UART chip. At the time of
this writing WH Networks was
selling real 16550 UART chips for US$10 each. (Replacement of
"multi-I/O" chips is usually not practical.)
- A source of I/O cards with 16550-type UARTs (not tested
by the author) is:
Byte Runner Technologies
406 Monitor Lane
Knoxville, TN 37922
voice: 800/274-7897 or 423/966-3667
fax: 423/675-3458
- TC-212 ($32): [new 4/24/96]
- Two 16550 serial ports (COM1-4) with "high" IRQ
support
- Enhanced parallel port supporting ECP & EPP modes (LPT1-LPT3)
- Winbond W83787F chip (not SMC!)
- TC-420 ($90): [new 4/24/96]
- Four 16550 serial ports (COM1-8) with "high"
IRQ support
- Two bi-directional (not enhanced) parallel ports (LPT1-LPT3)
- Startech ST16C552CJ chip (not SMC!)
- Supports sharable or independent interrupts
- Quickpath makes:
- A good, albeit pricey, "multi-I/O" card called the
"4 Serial 2 Parallel" that is available at retail (e.g.,
$100 at Central Computer in Santa Clara, CA, 408/248-5888), featuring:
- Four serial ports with "high" IRQ support
that use real 16552 chips.
- Two parallel ports
- A more complete, albeit pricey, "multi-I/O" card
called the "Port-Folio 550E" that is available at retail
(e.g., $120 at NCA Computer Products in Sunnyvale, CA,
408/739-9010)
- Pros:
- Four serial ports with "high" IRQ support
that use real 16552 chips
- Two parallel ports
- Four floppy support
- IDE and game port
- Con: Floppy support is only 1.44 Mb, not
2.88 Mb (inexcusable in a product at this price in the opinion
of the author)
- Another good high-end "multi-I/O" card is the GSI
Model 32, also available at retail (e.g., $120 at NCA
Computer Products in Sunnyvale, CA, 408/739-9010).
- Pros:
- Two serial ports with (limited) "high" IRQ support
that use a real 16552 chip
- One bi-directional parallel port
- Supports four floppies, up to 2.88 Mb (4 Mb unformatted),
with drive remapping
- Enhanced IDE support for two drives (including large
drives)
- On-board Flash BIOS
- Con: BIOS, IDE, and floppy support cannot
be disabled
- SIIG (Fremont, CA) makes I/O cards that are available at retail
(e.g., Fry's Electronics in Fremont, CA, 510/770-3797),
including the "IDE Professional" (Model 2404, about
$70 on the streeet).
- Pros:
- Two 16550-compatible serial ports (COM1-4) with "high"
IRQ support
- One EPP/ECP bi-directional parallel port (IRQ 7 or 5)
- Supports two floppies, up to 2.88 MB (4 Mb unformatted), which
can make your "floppy tape" (e.g., HP/Colorado
Jumbo 250/350) twice as fast as a 1.44 MB controller.
- IDE controller (hard disk or CD-ROM, primary or secondary
channel)
- Game port
- Con: Uses the SMC
FDC37C666GT "multi-I/O" chip, which can cause lockups
under Windows 3.1. (Warning: see "Why does Windows lock up when I try to access my modem?")
An extensive, excellent list of multiport serial cards
has been compiled by the amateur radio site ve7tcp.ampr.org.
[new 4/24/96]
[Return to top]
CRC errors (e.g., as reported by ZMODEM),
particularly when downloading, are usually a sign of overrun (incoming
data that is lost because the computer is unable to process it
in time). Overrun can result from a variety of causes. The following
are suggestions on how to avoid CRC/overrun errors (particularly
in Windows 3.1):
- Use a 16550A UART. (See "Do I need a 16550 UART? What is a UART?"
and "Why does Windows lock up when I access my modem?")
Note that most, but not all, internal modems have a 16550.
- Use hardware flow control, and make sure it is working properly.
This applies both to your modem and to your comm software. If
you experience overrun while uploading, then you almost certainly
have a flow control problem in your comm software and/or modem
configuration.
- If you are running anything other than the standard Windows
VGA driver, switch to the standard VGA driver and see if that
affects your problems -- certain video drivers are known to interfere
with communications. (See "Where can I get updated video drivers?")
- If you determine that your video driver is causing overruns:
- If your video card uses a recent S3
chipset (e.g., 864, 964, or 968), there may be an option
in the video driver to set "
Bus-throttle=On
"
(usually Off
by default) in the [display]
section of SYSTEM.INI, which may well solve the problem. ("Bus-throttle=On
"
may slightly reduce speed as measured by benchmarks, but the difference
will probably not be noticeable in the real world.) Contact the
manufacturer of your video card. (Note: Generic S3 video drivers
are available from S3. Unfortunately, they do not work on all
S3-based video cards.) [updated 3/29/96]
- If your video card is a PCI type and made by Matrox,
try adding
PCIChipSet=1
to the [MGA.DRV]
section of SYSTEM.INI, which may well solve the problem. (Add
the section header if it does not already exist.) If it does solve
the problem, check with Matrox for an updated video driver.
[new 6/13/96]
- If possible, use 32-bit disk access under standard Windows,
as well as 32-bit File Access under Windows for Workgroups. If
not, be sure you have a current version of a quality BIOS and/or
disk driver.
- Watch out for poorly-written firmware and/or device drivers
for local bus IDE interfaces, particularly in multi-sector mode.
Obtain the latest versions. (See "Where can I get updated disk/SCSI drivers?")
You may be able to alleviate an overrun problem by switching modes
and/or reducing the number of sectors per transfer.
- Are you using a SCSI drive? Certain SCSI drivers can cause
problems. Obtain the latest versions. (See "Where can I get updated disk/SCSI drivers?")
- Disable write caching on your download disk drive. (Read caching
should be OK.)
With the current
SMARTDRV (i.e., standard Windows, or Windows for Wordgroups
without 32-bit File Access), the /X parameter disables
all write caching. You can also disable write caching on individual
drives. (See "SMARTDrive Drive Letter Parameters Should Not Contain a Colon")
With 32-bit File
Access under Windows for Workgroups, put the following in the
[386Enh]
section of your SYSTEM.INI file:
ForceLazyOff=<drives>
where <drives>
is a drive letter string; e.g.,
ForceLazyOff=C
for drive C only, or ForceLazyOff=CD
for drives C and D. (See "How to Disable Write Caching for the 32-Bit File System")
- If you are using Procomm Plus for Windows
2.xx, set "
DropRTSAroundDiskWrites=1
" in
your PW2.INI file. (This won't help if you cache writes.)
- Beware of TSRs, especially network TSRs. Try booting your
system as clean as possible to see if that helps.
- Watch out for certain memory managers; e.g., the
use of QEMM "Stealth" may cause problems.
- Put your modem on COM2 if possible, rather than COM1, especially
if you are using a serial mouse, because COM2 has higher interrupt
priority than COM1. Even better is to use a "high" IRQ
(2/9, 10-12) which has higher interrupt priority than either COM1
or COM2. (See "Where can I get a 16550 UART?")
[updated 8/30/96]
- Under Windows, put the following in the
[386Enh]
section of your SYSTEM.INI file:
MinTimeslice=20
WinTimeslice=100,50
COMnFIFO=1
COMnBuffer=1024
where n is the number of your modem COM port (e.g., COM2FIFO=1
and COM2Buffer=1024
). The COMnFIFO
statement
won't help until you get a 16550A UART, but it won't hurt in the
meantime.
Note: The only legal values for COMnFIFO are 0 and 1.
(See "Windows Support of the 16550 UART")
- Do not use Microsoft's PC speaker sound driver!
Get a cheap sound card instead. (The Logitech Factory outlet in
Fremont, California, 800/231-7717, is a good place to get a cheap
sound card.)
- The Creative Labs Sound Blaster 16/AWE 32
driver bundled with the original release of Windows 95 can cause
CRC errors, and should be replaced with an updated version.
[new 9/7/96]
- Watch out for an IRQ conflict. (You normally cannot use both
COM1 and COM3, or COM2 and COM4, at the same time.)
- On a portable or "green" machine, you should also
try disabling the power management features, which can sometimes
"kick in" and interfere with data communications.
- Disable any screen savers, which can interfere with data communications.
- Don't run your serial port any faster than necessary. Marketing
hype notwithstanding, there's rarely any need to go faster
than 38.4 Kbps with a 14.4 Kbps modem, or 57.6 Kbps with a 28.8
Kbps modem. Caveat: With an acknowledgment protocol (e.g.,
XMODEM), as opposed to a streaming protocol (e.g., ZMODEM),
a higher serial port speed can improve the response time. (See
"Measurement of DTE Rate Latency")
- Try a third-party replacement for COMM.DRV. (See What about third-party comm drivers for Windows?)
- Switch to Windows for Workgroups or Windows 95, which have
a better serial architecture than standard Windows 3.x.
- With a 16550 UART (See "Do I need a 16550 UART? What is a UART?")
under regular Windows and a third-party comm driver (e.g.,
WFXCOMM.DRV)
or Windows for Workgroups or Windows 95, try dropping the receive
FIFO trigger level. For example, where n is the number of your
modem COM port:
WFXCOMM.DRV (default
14): ComnRXSize=8
(e.g., Com1RXSize=8
).
Recommended setting.
Windows for Workgroups
(default 8): COMnRxTRIGGER=4
(e.g., COM1RxTRIGGER=4
).
Legal receive FIFO trigger values are 14, 8, 4, and 1. The normal
recommended value is 8. You should not go down to 1 unless
you are really desperate.
[Return to top]
- The most obvious cause is that you've neglected to plug your
telephone line into your modem. Double check to make sure. Or
the telephone cable may be bad -- test it on a regular telephone.
- A common problem is plugging your telephone line into
the wrong jack on your modem. Many modems have two jacks,
one for the telephone line and one for a telephone handset. On
some of these modems (e.g., USRobotics), you won't be able
to get a dial tone or otherwise use the modem if you plug the
telephone line into the telephone handset jack. Double check to
make sure.
- Another common problem is that some other device on the same
telephone line (e.g., a telephone answering machine) is
off-hook. Double check to make sure that all other devices are
on-hook.
- There may be a problem on your telephone line. Make sure that
you can get a dial tone on a telephone handset connected to and
through your modem when the modem (or computer in the case of
an internal modem) is turned off.
- Many voicemail systems use a "stutter" dial tone
or beeping when you pick up the phone to indicate that you have
voicemail waiting. These unexpected sounds can make the modem
think there is no dial tone. If you must use the modem on a line
with these voicemail or similar sounds, you can try the following
workarounds: [new 10/7/96]
- Increase the amount of time that the modem waits for dial
tone by setting the number of seconds to wait in register
S6
(e.g., S6=5
).
- Lower the
Xn
setting to an odd number value to
make the modem ignore dial tone and dial blindly (e.g.,
X3
instead of X4
, or even X1
).
- Your modem may not be designed for the phone system in the
country in which you are trying to use it. As a workaround, try
lowering the
Xn
setting as described above.
[Return to top]
- Make absolutely sure that there is one and
only one WINSOCK.DLL on your system, and that it is the
right one.
- Make sure that the directory (e.g., C:\TRUMPET)
for your dialup SLIP/PPP package (e.g., Trumpet Winsock,
aka TCPMAN) is in your DOS PATH environment variable.
- Try the following settings in your dialup SLIP/PPP package:
- For true PPP or SLIP:
TCP MSS: 536
MTU: 576 [MSS + 40]
TCP RWIN: 2144 [MSS x 4]
(For reference see RFC 879)
Note: Increasing RWIN to larger multiples of MSS (e.g.,
2680, 3216, 3752, or 4288) may improve performance a bit on sluggish
links.
- For TIA Pseudo-SLIP (see comments on TIA
below):
TCP MSS: 1460
MTU: 1500 [MSS + 40]
TCP RWIN: 4096
(For reference see "Installation Instructions for Single-User TIA")
For more SLIP/PPP help see "Any Trumpet Winsock tips?"
and "Troubleshooting Reference."
Note: There is no significant performance difference between SLIP
and PPP. (See "SLIP vs PPP Performance Comparison"
and "Performance Issues")
The author recommends the following Winsock applications (all
of which are freeware or shareware):
- Dialup TCP/IP (SLIP/PPP) stack
- Windows 3.x: Trumpet Winsock (See Any Trumpet Winsock tips?)
(Usenet alt.winsock.trumpet):
- Version 2.0B
(no enforced limit on evaluation)
WARNING: A bug in 2.0B can cause a system crash
under certain rare conditions.
- Version 2.1F
(enforced 30-day limit on evaluation)
WARNING: Earlier 2.1 versions have serious bugs
and should not be used.
WARNING: The author has found problems with streaming
ZMODEM uploads in
a telnet session over a Trumpet TCP/IP link. A work-around is
to set a ZMODEM window size of 2 Kb.
- Windows 95: Microsoft Dial-Up Networking, but only if the
MaxMTU fix is installed. [updated
10/11/96]
- Mailer: Pegasus Mail for Windows
(Usenet bit.listserv.pmail)
- Web browser: Netscape;
helper applications:
- Usenet newsreader: Free Agent
- FTP (File Transfer Protocol): WS_FTP
- Telnet (login to remote host): EWAN
- Ping (is host alive): WS_PING
- Finger (find user) and WhoIs (find host): WSFINGER
- NSLookup (lookup DNS names): NSLookup
- Set clock from network timeserver: Tardis
- HTML editor: Microsoft Internet Assistant
(Word for Windows 6.0a or above required)
For more Winsock application information see:
You may be able to run dialup SLIP/PPP from a UNIX shell account
with The Internet Adapter
(TIA). Even when your Internet Service Provider offers a SLIP/PPP
option, it may be cheaper to run TIA from a shell account. TIA
is commercial but inexpensive. A freeware alternative is SLiRP.
For more information on TIA and SLiRP see "SLiRP/TIA and Trumpet Winsock Setup Reference."
(Usenet alt.dcom.slip-emulators)
Advanced/Professional Users
A good tool for debugging SLIP/PPP protocol problems is SerialView
from Klos Technologies. [new
10/27/96]
[Return to top]
- Where to get Trumpet Winsock:
- Version 2.0B
(no enforced limit on evaluation)
WARNING: A bug in 2.0B can cause a system crash
under certain rare conditions.
- Version 2.1F
(enforced 30-day limit on evaluation)
WARNING: Earlier 2.1 versions have serious bugs
and should not be used.
WARNING: The author has found problems with streaming
ZMODEM uploads in
a telnet session over a Trumpet TCP/IP link. A work-around is
to set a ZMODEM window size of 2 Kb.
- You can monitor Trumpet Winsock TCP/IP performance with TCPMeter.
(Execute once Trumpet Winsock is running. Click the left and right
mouse buttons to expand and contract the graph scale respectively,
and try a scale of 4K or 8K for a 28.8 connection. Incoming speed
graph bars point down; outgoing point up. Note that TCP/IP is
a full duplex link where data can flow at full speed in both directions
at the same time.)
- Here
for Trumpet Winsock 2.0
- Included with Trumpet Winsock 2.1 (do not
use the 2.0 version)
- Trumpet Winsock 2.0B locks an excessive amount of memory (107
Kb) below 1 Mb; 2.1F is improved, but still takes a substantial
amount (44 Kb) of low memory. (See "Any other Windows tips?")
The amount of low memory is not affected by the TCP/IP settings.
- The author recommends configuring your modem for Trumpet Winsock
with
&D1
rather than &D2
; that
way you can use DTR rather than the escape code to enter modem
commands when online.
- Trumpet Winsock is not recommended by the author for
Windows 95. Use the free Microsoft DUN (Dial-Up Networking) instead,
which if the MaxMTU fix is installed
is at least as good and arguably better. (See "Any Windows 95 tips?")
[new 10/11/96]
- Useful Trumpet Winsock scripts:
[Return to top]
Updated video drivers may help to correct CRC/overrun errors.
(See "Why am I getting CRC errors (overruns)?")
Updated drivers are available at:
Note: Only those companies that have drivers available for download
are listed.
[Return to top]
Updated disk and/or SCSI drivers may help to correct CRC/overrun
errors. (See "Why am I getting CRC errors (overruns)?")
Updated drivers are available at:
Note: Only those companies that have drivers available for download
are listed.
[Return to top]
The buffer size is mostly a flow control issue. When the buffer
fills up above the "high water mark" (e.g.,
75%), a Windows comm driver asserts receive flow control; then
when it drops below the "low water mark" (e.g.,
25%) a Windows comm driver releases receive flow control. (A Windows
comm application should have nothing to do with flow control.
DOS applications, on the other hand, do not use the Windows comm
driver and so must do their own flow control.)
For Windows applications then the only serious issue is that the
size of the buffer between the "high water mark" and
buffer-full must be big enough to give the local modem time to
respond to flow control being asserted -- there is inevitably
a certain amount of "dribble," but it's usually no more
than about 10-20 characters, for which even the default 128-byte
buffer should be adequate. For performance you want the buffer
large enough for the Windows application to be able to process
incoming data in reasonable sized chunks. (You also want the modem
to respond to flow control being released before the buffer is
drained by the application, although this is much less important
due to modem buffering.) Thus if multitasking is going on, a somewhat
larger buffer than the default (e.g., 256-1024) may improve
performance. The higher end of the range accommodates a typical
(YMODEM/ZMODEM)
block. Beyond that point diminishing returns set in rapidly.
For DOS applications the buffer size is more important, since
the DOS application is responsible for flow control and takes
much longer to respond than a Windows comm driver. That's why
it's a good idea to have a receive buffer as big as a typical
(YMODEM/ZMODEM) block (i.e., 1024 bytes). The alternative
is to turn the buffer off completely and give the DOS application
direct access to the COM port by setting a buffer size of 0.
On the transmit side (where there's no flow control concern) the
only consideration is performance -- you want the buffer to be
big enough so that it doesn't drain to empty when the application
is unable to respond fast enough to refill it. The default 128-byte
buffer will drain in only 22 ms at 5760 cps, which is less than
a single multitasking timeslice. A 1024-byte buffer takes 178
ms to drain, which is normally sufficient; above that point diminishing
returns set in rapidly. One reason is that modem buffering can
make up for (short) times that the transmit buffer drains to empty.
And if you make the transmit buffer too large, it can introduce
timing problems (due to the "long" buffer drain time)
with DOS applications and with poorly written Windows applications.
[Return to top]
It's very important to properly distinguish between (a) retraining
and (b) fall-back/forward. They are frequently confused but they
are not the same thing. If you turn on the modem
speaker with M2 you can easily hear the difference.
RETRAINING
Retraining is like the initial training -- several seconds where
the modems probe the line in order to configure themselves (equalization,
nonlinear coding, pre-emphasis, pre-coding, shaping, mapping,
etc.). Either modem can request a retrain, but the retrain
will only occur if the other modem grants it. You can hear the
distinctive training sounds if the modem speaker is on. During
the several seconds of retraining no data can flow. Because of
that we want the modems to only retrain when truly necessary,
as when line conditions have changed significantly and permanently,
something that is usually rare. Retraining may not necessarily
result in a higher speed. Excessive retrains can therefore be
a serious problem.
FALL-BACK/FORWARD
Fall-back/forward is simple speed shifting that is relatively
quick, so we would like the modems to fall back when needed to
keep the error rate low, and fall forward when possible to improve
throughput. With the modem speaker on you will hear only a small
beep or blip in the carrier hiss. If a noise burst causes a fall-back,
we want the modems to fall-forward as soon as the burst is gone.
What we don't want is for the modems to ping-pong back and forth
between two speeds, because that would result in lower throughput
than simply remaining at the lower speed. Again, fall-back/forward
can be requested by either modem, but will only occur if the other
modem permits it.
[Return to top]
You can set a speed faster than 19200 in the Windows Control Panel
by simply typing it in. However, there is almost never
a need to do so -- almost all Windows comm applications
set their own serial port speed. The settings in the Control Panel
are primarily for devices attached to the serial port; e.g.,
printers. (See "Control Panel Serial Port Settings Are for Printing Only")
[Return to top]
Despite "urban legends" to the contrary, the
standard Windows 3.1 COMM.DRV is capable of supporting high-speed
modems on a reasonably fast system, and does support the 16550
FIFO. (See "Windows Support of the 16550 UART")
However, it does have three limitations:
- It does not use the transmit FIFO. This rarely makes any difference
for data, but can be a problem for Class 1 fax timing above 9,600
bps.
- The receive FIFO threshold is fixed at 14 bytes, which leaves
only 2 bytes before overrun occurs. Dropping the receive threshold
to 8 bytes (or even lower) may help to reduce overruns. For that
you need a third-party comm driver.
- DOS comm programs running under Windows 386 Enhanced Mode
are fooled into thinking that the COM port only has a 16450 UART.
This can cause problems, particularly with poorly-written DOS
comm programs (i.e., those that do not drain the UART
buffer on each receive interrupt). The alternative is to give
the DOS application direct access to the COM port (see "Why 1024 bytes for the Windows COM buffer?")
or, better yet, upgrade to Windows for Workgroups 3.11 or Windows
95.
Also despite "urban legends" to the contrary, COMM.DRV
supports speeds up to 256,000 bps, hardware permitting, including
115,200 bps. (See "Setting Baud Rates in Windows 3.1")
How fast you can go will depend on your hardware. With only an
8250 or 16450 UART, you may not be able to go faster than 19,200
bps without overrun; with a 16550 UART and a reasonably fast system,
you should be able to go up to 57,600 bps, or even 115,200 bps.
57,600 bps is normally adequate for even a 28,800 bps
modem. Caveat: With an acknowledgment protocol (e.g.,
XMODEM), as opposed to a streaming protocol (e.g., ZMODEM),
a higher serial port speed can improve the response time. (See
"Measurement of DTE Rate Latency")
Third-party comm drivers include the freeware:
CYBERCOM.DRV
WFXCOMM.DRV
(from Symantec, particularly
recommended for use with WinFax)
Third-party drivers are not needed for and should
not be used with Windows for Workgroups 3.11 or
Windows 95, which have a better comm architecture than standard
Windows. An upgrade to Windows for Workgroups 3.11 or
Windows 95 is probably the best way to improve Windows communications.
(See "Any other Windows tips?")
Third-party Windows drivers should also not be
used with OS/2 (Warp).
[Return to top]
- Symantec WinComm PRO
can seamlessly share a modem with Symantec WinFax PRO. With WinFax
PRO set to automatically answer the telephone, WinComm PRO will
turn off WinFax PRO auto-answer to dial out, and turn WinFax PRO
auto-answer back on when it is through with the modem. The two
programs may be purchased together in a discounted bundle called
the Symantec Comm Suite.
- With other data comm programs you can use WfListen,
a program that will shut down Symantec WinFax when you start your
data comm program, and then restart WinFax when you shut down
your data comm program, all automatically. Shareware. (A companion
program, wfStatus,
modifies the WinFax icon to show whether it's ready to receive
faxes or not. Also shareware.)
- Another alternative is KingComm, a commercial virtual comm
port driver that allows multiple comm apps to share the same modem.
- Multi-Tech provides
a proprietary "Virtual Modem" comm driver for Windows
with certain modems that will reportedly route incoming data and
fax calls to appropriate applications. However, it does not support
the 16550 FIFO buffers, a serious drawback. (See "Do I need a 16550 UART? What is a UART?")
Note: Except for Multi-Tech, these alternatives do not
have the ability to automatically detect and properly route incoming
data and fax calls. For that you need a modem that supports incoming
Call Discrimination (also called "Adaptive Answer" or
"Call Select"), as well as data and fax comm software
which support that capability (e.g., WinFax PRO 7.0 for
Windows 95 [see "How can I use a single phone for fax/data/voice?"]
or Procomm Plus for Windows 2.xx).
[Return to top]
- Windows 3.x:
- ModemSta
displays an animated icon replica or larger indicator displays
of modem's front panel. Several 3D looks, with customizable colors.
For use with internal, external and PCMCIA modems. Modem initialization,
logging of incoming calls and connections, additional status info,
show communications settings, generation of sounds at comm events.
Can also monitor parallel ports. Unfortunately, ModemSta has
been withdrawn from shareware. [updated
1/3/97]
- Windows 95: [new 6/6/96]
- The System Monitor
accessory that comes with Windows 95 has a wealth of hidden capabilities,
among them the ability to measure Dial-Up Networking performance
in real time. See System Monitor
under "Any Windows 95 tips?"
Note: It is not possible to continuously display the modem-to-modem
speed of an internal modem. (Some drivers and applications display
data throughput, but that is not the same thing.) The reason is
that you have to have to escape the modem to command mode and
issue a special command, if available, which interrupts the flow
of data. (See "Any other USRobotics tips?")
[Return to top]
The most common cause of this problem is a 16550-compatible chip
that isn't fully compatible. Typically this is seen on
Pentium systems with serial ports integrated on the motherboard,
but it can also happen with add-on cards, particularly "multi-I/O"
cards based on popular SMC chips.
(See "PC Hangs While Running a Communications Application"
and "16550 UART FIFO Support under Windows NT")
- Updated drivers are available from SMC and Microsoft to work
around the problem. The SMC package
includes both SMC's updated COMM.DRV for regular Windows 3.1 and
Microsoft's updated SERIAL.386 for Windows for Workgroups 3.11;
the Microsoft package
includes only Microsoft's updated SERIAL.386 (10,620 bytes dated
2/17/94). But see warning below.
- Alternatively you should be able to completely solve (or simply
test) the problem by turning off the UART FIFO buffers. To do
that under regular Windows 3.1 or Windows for Workgroups 3.11,
put the following in the
[386Enh]
section of your
SYSTEM.INI file:
COMnFIFO=0
where n is the number of your modem COM port (e.g., COM2FIFO=0
).
Under Windows NT see "16550 UART FIFO Support under Windows NT."
The drawback is that you then won't get the benefit of the 16550
FIFO buffers. (See "Do I need a 16550 UART? What is a UART?")
Warning: Although Microsoft specifically identifies
the SMC '665 chip as the problem, the author has personally verified
that a problem also exists in the SMC '666 chip (FDC37C666GT).
Furthermore, although the original FIFO problem is reportedly
fixed in current chip production, the author has personally verified
that a problem (perhaps a different problem) still exists as of
August 1995. The author has also personally verified that:
- SMC's updated COMM.DRV does not correct this current problem;
and
- Microsoft's updated SERIAL.386 is not fully satisfactory:
lockups are very rare but not entirely eliminated, and Windows
multitasking is adversely affected during certain communications
operations (e.g., negotiating a dialup PPP link with
Trumpet Winsock 2.1F).
The only fully effective workaround is to disable the FIFO buffers
(as described above). For this reason the author does
not currently recommend products that use SMC "multi-I/O"
chips.
[Return to top]
While on-line you escape your modem to command mode with "+++",
and then try to get back into data mode with ATO
,
but the remote system no longer responds. You have to break the
connection to recover.
What's probably happening is that your "+++" escape
code is being echoed by the remote system back to the remote modem,
throwing it into command mode as well, a state from which you
cannot recover short of disconnecting. It really shouldn't be
happening, because any BBS SYSOP or Internet Provider worthy of
the name should either disable the escape sequence or at least
change it to an unusual value. But all too many don't.
The solution is to use modem register S2
to change
your modem escape character. The author uses S2=61
to change the escape character to "=", which is on the
same key as "+", making it easy to remember.
[Return to top]
There are several excellent programs, and what is best for one
won't necessarily be best for others.
For data comm, the personal favorites of the
author are HyperACCESS for Windows (commercial from Hilgraeve)
and the near-clone WinComm PRO (commercial from Symantec).
Both are extremely powerful while being very easy to use. For
those on a budget, there is a freeware version of WinComm called
WinComm Lite.
(There is also a freeware DOS comm program from Symantec called
FreeComm.
Neither WinComm Lite nor FreeComm has been reviewed by the author.)
Popular shareware alternatives include:
Softerm Plus
(X/Y/ZMODEM with SLIP and TCP/IP)
Telix for Windows
UniCom
WinQVT
(VT-220 emulator with X/Y/ZMODEM/Kermit)
WinRamp Lite
(w/RIP)
ZCOMM for Windows 95 (telnet
plus best ZMODEM) [new 4/11/96]
For fax comm, the personal favorite of the author
is WinFax PRO (commercial from Symantec).
It integrates well with WinComm PRO, and the two can be purchased
in a discounted bundle as the Symantec Comm Suite. (If you experience
fax problems with a USR modem, see "Any other USRobotics tips?")
Note: Delrina was acquired by Symantec.
The author does not recommend Version 2.xx of Procomm Plus for
Windows (commercial from Datastorm).
While version 1.xx evolved into a robust (albeit quirky) data
comm program, version 2.xx has suffered from "featuritis"
and has been plagued with many problems (e.g., greatly
excessive locking of memory below 1 Mb [See "PRB: Avoiding 'Insufficient Memory to Run' Errors"]).
[Return to top]
See below and also "Any other USR tips?".
- If you have Call Waiting, the incoming call "beep"
may sometimes (but not always) disconnect you. To avoid this problem,
you may be able to temporarily disable Call Waiting when you make
a data or fax call. (See "How do I shut off Call Waiting?")
[new 11/14/96]
- Disconnections may be caused by momentary drops of DTR by
certain comm applications. (By default most modems respond to
a drop of DTR by hanging up.)
- With most modems you can work around this problem by disabling
DTR (i.e.,
&D0
). Note that when DTR
is disabled you have to escape the modem to command mode and use
the "ATH" command to hang up.
- With USR modems you can also use register
S25
to work around the problem (e.g., S25=10
will ignore a DTR drop of less than 10/100 or 1/10 second, which
is twice the default of 5/100 second).
- For those experiencing disconnects (and/or erratic connection
speeds) when calling Rockwell-based V.FC modems from a USR 28800
(V.FC or V.34) modem, a firmware fix is now available for the
Sportster (dated 4/18/95 or later for USA modems) by calling USR
(847/982-5151); for the Courier, the fix (dated 7/5/95 or later
for USA modems) is available by FTP.
In the meantime, the author's workarounds (which may help in some
cases even if you have the updated firmware) are:
- Disable V.42 Detect Phase (i.e.,
S27=48
).
-- or --
- Disable V.42 completely (i.e.,
S27=32
).
If you then sometimes get non-error-correcting connections, force
error-correction mode (i.e., &M5
). You
may find that you have to redial several times to get connected;
if so, try the following.
-- and/or ---
- Disable the highest symbol rates (e.g.,
S54.5=1S54.4=1S54.3=1
).
This will limit your top speed (to 24000 in this example), depending
on how many symbol rates you disable (3429, 3200, and 3000 in
this example).
-- also --
- With V.FC-only firmware (as opposed to the newer V.34 firmware)
it may help to also disable the 32S-2D map (i.e.,
S55.2=1
).
-- finally --
- It may also help to set
S10=255
.
With a USR 28800 modem, you can determine the technical reason
for a disconnect by issuing the ATI6
command immediately
after the disconnection. Disconnect reasons are explained in the
Courier manual.
If possible, set these options on a phone number-specific basis.
With comm apps which lack that capability, you may be able to
embed them in the phone number; e.g., "^H^HS27=48DT555-1212
".
(The two "^H
" backspace characters erase
the "DT
" in an "ATDT
"
dial command so that the "S27=48
" will
be accepted, and then the following "DT
"
replaces the "DT
" that was erased; i.e.,
"ATDT
" + "^H^HS27=48DT555-1212
"
= "ATS27=48DT555-1212
".)
[Return to top]
The following is a discussion of the so-called "spiraling
death" problem that has been observed on the Sportster 28800
(and sometimes even the Courier V.34), where the modem will fall
back over time on certain connections to ever lower speeds.
What we are really concerned with here is fall-forward, not retraining.
(See "What is 'retraining'? and What are 'fall-back' and 'fall-forward'?")
Retraining is normally a rare event. So the problem is really
that the Sportster 28800 sometimes does not fall-forward when
it is able to do so. The symptom is that the Sportster 28800
is sometimes observed to fall back to progressively lower speeds
without ever being observed to fall forward back to higher speeds.
The implication is that line conditions would have permitted a
higher speed, which may or may not have been true. (It's impossible
to say for sure without elaborate test equipment.)
THE ATO1 CONNECT RESPONSE CONFUSION
Some of the evidence used to support the claim that the Sportster
28800 doesn't fall forward has been that ATO1
(forced
retraining) returned the modem to a higher speed. The problem
with at least some of these reports is that people have assumed
that the CONNECT response to ATO1
reports the new
speed after retraining. It doesn't, as should be obvious if you
notice that the response appears before the retraining
sound (heard with M2) is completed. The response sometimes shows
the previous connection speed, and sometimes shows the original
connection speed, but never the new speed. The only way
to correctly determine the connect speed after retraining is to
escape to command mode and use the ATI6
command!
(See "Any other USRobotics tips?",
"Any Trumpet Winsock tips?",
"Why can't I get back on-line after I escape to command mode?",
and "Any Windows 95 tips?")
Suppose that a phone connection is such that the Sportster 28800
CONNECTs at a high speed (e.g., 28800), but then falls
back to a lower speed (e.g., 24000) due to line conditions.
Escape to command-mode followed by ATO1
might well
make you think that retraining has returned the modem to the original
high speed (due to a CONNECT 28800 response) when it may well
not have. Disconnecting and reconnecting could
produce the same misleading indications. In other words, these
may just be plain old poor connections. The moral here is that
you must use ATI6
, and only ATI6
, to
check the current connection speed.
Another problem is that ATO1
may not change the current
speed, or may even reduce it, depending on changing line conditions.
And it's hard to keep ongoing auto fall-back/forward from confusing
the issue (unless you use M2 and listen carefully for the sound
of the speed shifts, a small beep or blip in the ongoing carrier
hiss). The only way to know for sure whether or not the
speed changed is to use ATI6
immediately before and
after ATO1
.
SPORTSTER PROBLEMS
Does the Sportster 28800 fall-forward automatically or not? From
extensive testing (literally hundreds of hours to both USR and
non-USR modems) the author concludes that the answer is: often
yes, but sometimes no. The author has run many tests where the
Sportster 28800 was forced back to (say) 16800, and then it rapidly
fall forward to a much higher speed. But the author has also run
some tests where it stayed at 16800. This seems to be a function
of both line conditions and the modem at the other end of the
connection.
Note that this problem is not absolute -- while some users do
encounter it on some connections, many users never encounter it.
Another possibly related problem that some have reported with
the external Sportster 28800 (not the internal Sportster, and
not either type of the Courier) is that adjusting the speaker
volume control while on-line causes the modem to fall back. Anecdotal
reports suggest that higher connection speeds may be possible
if the volume control is turned all the way down before the initial
negotiation (and left there). Turning off the speaker with M0
is apparently not effective.
WHAT TO DO [updated
10/11/96]
USR now has a fix for this problem in the form of updated modem
firmware. See "Sportster Supervisory Update Information".
(Note: the dates in the firmware table are not necessarily
the dates of the latest versions.)
While waiting for the fix, here are some workarounds to try:
- If possible try a different modem to see if the problems persist
or not.
- Try to improve your connection -- the Sportster 28800 may
be falling back in response to noise bursts on the line. (See
"Why don't I get 28800 bps speed on my connections?")
- If you have the external Sportster 28800, try turning the
volume control all the way down before the initial negotiation.
- You can disable fallback on the transmit side (the receive
side is not affected) by setting the undocumented option of
S15=2
.
The downside is that you may get disconnected if line conditions
deteriorate enough to warrant a fall-back and/or you may experience
more retraining. (This option is documented for the Courier V.34.)
- If you have 11/30/94 or later Sportster firmware (date for
USA modems), you can lock the transmit speed (but not the receive
speed) in a range with
&Nn&Un
(e.g.,
&N14&U12
locks the transmit speed between
28800 and 24000). With an appropriate range, this may be more
reliable than S15=2
. (However, it does not work on
the Courier.)
[Return to top]
You are on-line to a remote system, perhaps a distant system over
the Internet or a local bulletin board system (BBS), transferring
data or typing in commands, when suddenly communications stops.
Then after a few seconds, a few minutes, or possibly even longer,
things start flowing again. The question is, what happened? The
answer is, it depends. There are a great many things that can
cause this kind of pausing, and determining the real cause can
often be difficult, sometimes very difficult. Worse, the cause
may be out of your direct control. Here is a list of possible
causes, tips on how to identify them, and suggestions for ways
to deal with them:
Telephone connection problems
- Modem error recovery
- When a transmission error occurs, error correcting modems
will automatically retransmit the affected data. Under normal
conditions the retransmission will be brief, but when connections
are poor the retransmissions can result in "pauses"
that last for many seconds. Certain modems will help you diagnose
and/or detect this kind of problem (e.g., with a "link
diagnostics" screen, or flashing ARQ or SQ lights). The only
way to completely solve this problem is to get better connections
(see "Why don't I get 28800 bps (or more) on my connections?"),
but it may help to reduce the connection speed (so as to reduce
the frequency of errors).
- Modem retraining
- While modems are retraining due to a poor connection, no data
can flow. Although a single retrain lasts only a few seconds,
multiple retrains (and other related error recovery) can go on
for much longer, up to 30 seconds or more in the author's experience.
See "What is 'retraining'?"
Network (Internet) problems
- Lost TCP/IP packets
- When a TCP/IP network (e.g., the Internet) gets overloaded,
the network routers deal with the problem by dropping (discarding)
data packets. It then takes time for the sender to notice that
the receiver hasn't acknowledged packets that have been sent,
and to resend those packets (which may in turn get dropped). The
result is a general slowdown in data transmission speed, often
with long gaps or "pauses." In extreme cases packet
loss can go as high as 30% or more, bringing transmission down
to a fitful crawl with nothing flowing most of the time. This
problem can be diagnosed with "ping" and "traceroute"
tools (the use of which is beyond the scope of this document).
The only way to deal with this problem is by complaining to the
network administrator, but there may not be much that can be done
if the congestion problem is outside of the local network (e.g.,
elsewhere on the Internet)
- Remote server overload
- Remote servers can only handle so much load. When the load
gets excessive, there is a general slowdown to all those using
the server, often with long pauses when the server is busy serving
other users. As the Internet grows, this is becoming an ever-increasing
problem, particularly for popular sites. The only way to deal
with this problem is to access the server when the load is less
(e.g., in the wee hours of the morning).
- Routing and other problems
- Certain networks are adopting packet routing policies, particularly
during periods of peak load, that discriminate against certain
users, particularly smaller ISPs (Internet Service Providers).
At best the network may drop many packets or route them onto slower,
more congested links; at worst, the network may refuse to pass
them altogether. The only way to deal with this problem is to
be sure that your ISP has good connectivity (e.g., multiple
"peering" points, multiple "backbone" connections
and/or alternate transport providers). In the long run the smaller
ISPs may simply be squeezed out.
Computer problems
- Flaky serial port (UART)
- A flaky serial port (UART) can cause all sorts of communications
problems, including both long and short ("pausing")
lockups. See "Why does Windows lock up when I access my modem?"
- Improper flow control
- If flow control is not configured properly in both
the comm software and the modem, the result is overruns. These
overruns result in lost data, which can cause "pauses"
as well as delays due to data retransmission. See "Why am I getting CRC errors (overruns)?"
- Hardware conflict
- Hardware conflicts are a frequent cause of both long and short
("pausing") lockups, particularly when two COM ports
are set to the same I/O address or IRQ. For example, a mouse on
COM1 and a modem on COM3 will normally product such a conflict.
(Sometimes moving the mouse will cause modem data to flow, but
in other cases the modem may work fitfully or not at all.) See
"Why am I getting CRC errors (overruns)?"
Software problems
- TCP/IP configuration
- Improper TCP/IP configuration can lead to packet fragmentation
and other problems that may be manifested as "pausing."
See "What's wrong with my dialup SLIP/PPP connection?"
- Software configuration and interference
- Configuration problems in comm software applications can also
result in "pausing." The only solution is to ensure
that all comm applications are configured properly. It is also
possible for two software applications and/or device drivers (particularly
network drivers) to interfere with each other enough to cause
a "pausing" problem; the only solution is to eliminate
(one of) the offending application(s).
- Operating system swapping
- Sometime the operating system suddenly needs a lot more memory
for a given application, and has to swap megabytes of data between
memory and a disk drive. On less sophisticated operating systems
(e.g., Windows), this can result in a "pause"
in communications during the swapping. The symptom of this problem
is a large burst of disk activity.
Modem firmware problems
- USRobotics Sportster
- Certain USRobotics Sportster modems with firmware dated in
February and March of 1996 have a firmware timing problem that
can cause the modem to "pause" when the modem is being
used in an interactive mode on a normal dialup connection, typically
when typing commands while connected to a Bulletin Board System
(BBS) or asynchronous dialup UNIX shell. The "pause"
will clear itself if you wait long enough (up to about a minute).
To troubleshoot and correct this problem, see "Sportster Supervisory Update Information".
(Note: the dates in the USR firmware table are not necessarily
the dates of the latest versions.) For more SRO information see
"USRobotics on the Internet".
The author recommends that anyone with an affected modem exchange,
update, or return it.
- Modem interoperability
- Incompatibilities between certain modems car result in a variety
of problems, including "pausing." If disabling V.42
(and falling back to MNP) causes the problem(s) to go away, then
you probably have an interoperability problem. A firmware upgrade
that corrects the problem may be available for your modem. See
"Which modem companies have a full Internet presence?"
The simplest and most effective way to deal with a modem problem
is to return the modem to the dealer from whom you bought it for
refund, credit, or exchange. (Even when you are outside of
the normal return period, many dealers will still take back the
modem for credit or exchange, particularly if you are persistent.)
[Return to top]
The MaxMTU Fix [updated 10/18/96]
Have you found that your Internet file transfers (e.g.,
downloads) are very slow, in the range of 1,000-1,600 characters
per second, even on a 28800 modem connection? It may just be Internet
overload; on the other hand it may be a symptom of a Windows 95
MTU (Maximum Transmission Unit) problem. To find out which it
is, compare the display of "Bytes received/sec." in
System Monitor
(see "Any Windows 95 tips?"
to set that up) to the characters per second reported by your
downloading application (e.g., FTP client or Web browser).
These two values should be within about 10%; e.g.,
if your "Bytes received/sec." is 3,300 (typical of compressed
data on a good 28800 connection), your characters per second should
be about 3,000. If instead the characters per second is 1,000-1,600,
you are getting a lot of wasted retransmissions that are probably
due to the Windows 95 MTU problem.
The only reliable work-around that the author has found for this
problem is to add the "MaxMTU" parameter to your Registry
and set it to a value of 576. (MaxMTU and other networking parameters
are documented in the free Windows 95 Resource Kit Help File.)
There are two ways to accomplish this:
- Download and install TCPIPCFG,
a Control Panel "applet" that makes it easy to adjust
MaxMTU. (This applet will only run under Build 950 or 950a
of Windows 95, not "OEM Service Release 2" or later
versions. It will also not work on at least some non-English language
versions of Windows 95; e.g., Catalan.)
- Follow the manual procedure.
Note: There are (unconfirmed) reports that MaxMTU does not
work properly with SLIP, as opposed to PPP, connections. [new
10/18/96]
For those wishing to run tests, the author has found that (as
of 10/5/96) this problem is reliably reproduced when downloading
from <ftp://ftp.cygnus.com/pub/gnu-win32/>
(the official FTP site for GNU-WIN32,
the wonderful Win32 port of GNU
tools for UNIX).
The Default Receive Window Fix and Hack [updated
10/5/96]
The following was contributed by Eric Gisin:
"Occasionally one sees slow downloads over dial-up PPP connections.
I have never seen a plausible explanation for this in the comp.os.ms-windows.*
newsgroups, but did find an explanation in one of the UNIX newsgroups.
"Apparently Solaris 2.3/2.4/2.5 have a TCP/IP bug that causes
every packet to be sent twice when the network delay exceeds some
threshold. You will observe the modem receiving data most of the
time, but the transfer rate will be half of what it should be
(1.6KB/s for 14.4, 3.2KB/s for 28.8).
"You can work around this bug both on the server and in Windows
95. If your provider's Sun server has this problem, make them
fix it! [See 'Initialize the ReTransmit interval']
"In Windows the work-around is to reduce the Default Receive
Window from its default of 8192, thereby reducing the network
delay. I haven't verified this myself, as I rarely see the problem.
If you can verify this solution, let me know and I will get it
into an FAQ.
"If you aren't using TCP/IP on a LAN, you can set Receive
Window to 4096 with no drop in performance and an improvement
in interactive response (while downloading) of one or two seconds.
Reducing the size of the Default Receive Windows probably is probably
a general fix for many "mysterious" bugs, including
the Solaris bug.
"Here is a registry hack that makes
changing TCP/IP parameters easy. Maybe Microsoft could incorporate
these changes into nettrans.inf.
[Note: No benefit was observed from the Default Receive
Window Fix in extensive testing by the author of this FAQ, and
the Hack appears to produce results inconsistent with Microsoft
documentation on Default Receive Window. It is therefore presented
here only in the hope that it might help those for whom MaxMTU
might not work.]
[Return to top]
There are basically four methods of sharing an incoming
phone line (without resorting to custom programming):
- Install a "Call Router" device on your regular
phone line. (The cost is in the range of $50-300, depending on
features. Sources on the Internet include Black Box,
Hello Direct,
and Sparco Communications.)
You plug your modem, fax machine, answering machine, and/or voice
telephone into the device. The device answers incoming calls,
and directs them to the appropriate connected unit. Some devices
do this with a series of voice prompts that instruct the caller
to press different phone buttons for different services. Others
do it by listening to the incoming call, and making a selection
(guess) based on what they "hear." Drawbacks to this
method are that voice prompting can confuse calling modems, and
that your computer would need a second modem to receive both fax
and data calls.
- "Silent Answer."
This is a fax modem feature in certain Diamond/Supra
modems that allows a fax modem to share a voice line. The modem
answers, but does not use the normal fax answer tones. Instead
it listens for tones from a calling fax. If it hears such tones,
it automatically picks up the call and goes into fax mode, possibly
cutting off an answering machine. Otherwise, it does not disturb
the call. The drawback to this method is that it does not support
data calls.
- Obtain "Distinctive Ring" service, and use
a modem and software that support it. This service, offered by
some (but not all) local telephone companies, gives you more than
one phone number for a single phone line. Each number has a "distinctive"
ringing pattern that can be detected by attached equipment. An
attached fax/modem and software that support Distinctive Ring
can then tell whether a call is coming in on the fax, data, or
voice number, and handle the call in the appropriate manner. (Distinctive
Ring can also be used with certain kinds of Call Routers. See
above.) Distinctive Ring is usually not free, but less expensive
than multiple phone lines. The drawbacks to this method are the
monthly charge, and the possibility that the service may not be
available in your area.
- Use a modem and software that support incoming Call Discrimination
(also called "Adaptive Answer" or "Call Select").
Certain fax/data modems can discriminate between fax and data
calls; certain so-called "voice" modems
can discriminate between fax, data, and voice calls. The modem
answers the call, and uses a combination of listening and trying
(tones) to determine (guess) the type of incoming call. A voice
modem and appropriate software can also employ voice prompting
like certain Call Routers (see above). The modem then notifies
the software of the type of call. The software is expected to
take the appropriate action. Some modems do a better job of Call
Discrimination than others.
The personal preference of the author is Call Discrimination.
The problem is that good software that supports Call Discrimination
has been hard to find. Although Version 2.xx of Procomm Plus for
Windows has such support, it does not work well with all modems
(see "Does USR Adaptive Answer work with Procomm Plus for Windows?"),
and the author does not otherwise recommend the program (see "What are the best [data/fax] comm programs for Windows?").
Microsoft TAPI promised to address this
need, but TAPI has been slow in coming. (See "What is TAPI?")
Symantec WinFax PRO 7.0,
also available as part of the Symantec CommSuite 95, finally delivers
on that promise. Here's how to make Call Discrimination work on
the USR Sportster 28800 Vi in Windows 95 with fax and the Dial-Up
Networking Server (Microsoft Plus!):
- Make sure that you have current modem firmware.
- Install the latest INF file for the Vi
from the USR BBS/FTP server.
- Install the Unimodem V
driver from Microsoft.
- You must also have the latest WinFax 7.0 Maintenance Updates.
- Use Control Panel | Modems to first Remove your modem, and
then Add it back using the proper INF file entry.
- Configure your modem in WinFax Setup | Modem, and be sure
to select TAPI.
- Use WinFax Setup | Receive to enable Call Discrimination.
(You should not have to fool with the Registry settings.) Be
sure to click OK even if you made no changes.
- Open Dial-Up Networking and select Connections | Dial-Up server
to enable the Allow Caller Access option. Click Apply, and make
sure that Status shows or switches to "Monitoring."
- It's also important to be sure that you have NetBEUI installed
for your Dial-Up Adapter (under Control Panel | Networking) --
TCP/IP will not do the job.
- And don't forget to set the Sharing option (in My Computer
or Explorer) for drives and/or folders you want to be able to
access.
- For more tips on setting up the Dial-Up Networking Server,
see "Dial-Up Networking Server"
under "Any Windows 95 tips?".
[new 9/20/96]
Having done all this, the author's Windows 95 system, even with
just the Symantec CommBar running, will answer calls on a Sportster
28800 Vi (internal), and connect them to either WinFax or the
Windows 95 Dial-Up Networking Server as appropriate. It's also
possible for the author to retrieve faxes remotely. (When connected
to the Dial-Up Networking Server from a remote location, it's
even possible for the author to access UNIX hosts running Samba
that are connected to the Windows 95 PC over an Ethernet TCP/IP
network.) All in all, it's an impressive display of technology.
The one catch is that certain failure modes will cause WinFax
to go out of fax auto-answer mode, even though the option is still
checked; if and when this happens, open Setup | Receive and click
OK.
If for data you need "mini-BBS" capability instead of
networking, you can substitute the Host Mode in Symantec WinComm
PRO 7.0, also included in the Symantec CommSuite 95, although
this has not been tested by the author. The principal drawback
is that WinComm PRO 7.0 currently suffers from bugs and other
problems, including excessive CPU usage in Host Mode. Or you can
try some other TAPI-complaint application (e.g.,
remote access software), but be warned that this is still new
territory, and that you may have difficulty getting everything
to work together properly.
Symantec TalkWorks, also included in the Symantec CommSuite 95,
adds voice support, but has not been tested by the author.
[Return to top]
Caller ID is a technology that makes it possible for the called
party to see the telephone number of the caller on a special device
while the incoming call is ringing. It is also possible for a
modem with Caller ID capability to obtain the telephone number
data and report it to special software, which can use the data
for purposes like security validation, event logging, and/or data
access (e.g., of a caller's credit history). Caller ID
is an optional service that is being offered by more and more
local telephone companies now that the FCC
has mandated nationwide deployment. (See "Caller ID to be available nationwide")
Caller ID has obvious applications in telephone mail-order, emergency
services, dial-in communications, and for those that simply want
to screen their calls. However, it can also invade the privacy
of a caller, disclosing information that the caller would prefer
not to disclose. (Your telephone number is a key that could be
used to instantly access the vast amount of information about
you that has undoubtedly been compiled in public and private databases
without your knowledge or consent.) Caller ID can be blocked on
a per-call or a per-line basis. Check with your local telephone
company.
[Return to top]
Why won't Call Waiting interrupt my modem connection? [new
10/16/96]
Call Waiting is a phone service option that allows you to be interrupted
by an incoming call while you are using the phone line. If you
are using the phone line for data or fax, the "beep"
that signals the incoming call can cause an abrupt disconnection,
which can be a problem.
To temporarily disable Call Waiting for a single outgoing call,
there is often a special code that can be dialed before the phone
number. With tone dialing service, this special code is usually
"*70" (e.g., instead of dialing say "555-1212",
you would dial "*70,555-1212", with the comma being
used to signal your modem to insert a brief pause between the
special code and the phone number); with pulse dialing service,
this special code may be "1170". Check with your
local phone company to be sure. Better comm programs have
an option to insert the special code automatically.
On the other hand, you may actually want Call Waiting to
interrupt a data or fax call, so that you do not miss an important
incoming call. However, V.34 modems are designed to overcome "line
noise" like Call Waiting, and they may not be disconnected
by the "beep." Other than getting another phone line,
there may be no possible work-around.
[Return to top]
It goes like this. You have a single line with multiple extensions
that you use for both voice and fax/data. You are on-line in the
middle of a large file transfer. Someone else picks an extension
in another room, and bang, your connection is lost sending the
file transfer down the drain.
There is an easy way to prevent this problem. Obtain a "Line
Protector" for each extension phone. When your modem is on-line,
the Line Protector will automatically prevent the attached phone
from interrupting your connection. A Line Protector is inexpensive,
and readily available on the Internet (e.g., Black Box
or Hello Direct)
or from Radio Shack (which calls it a "TeleProtector").
Some "Call Routers" will also provide this kind of protection.
(See "How can I use a single phone for fax/data/voice?")
[Return to top]
There are three popular standards for fax modem commands (used
by fax software applications):
- Class 1
- A low-level standard, Class 1 puts the most burden on your
fax software and your host CPU, but also gives the most control.
Slower systems may have problems sending and receiving faxes in
the background with Class 1.
- Class 2
- A de facto standard promulgated by Rockwell, so-called Class
2 is widely supported by fax software, and takes much of the low-level
load off of your system, which can improve faxing in the background,
particularly if you have a slower system.
- Class 2.0
- A true standard for higher-level fax commands, Class 2.0 is
notably supported by USRobotics, but is not widely supported in
software as of this writing. It is not compatible with
Class 2, although it can provide similar benefits.
Consumer-grade fax modems have a number of weaknesses and deficiencies,
not all of which can be completely overcome. That noted, here
are some suggestions for making your fax work better:
- If you are having trouble getting fax to work at all, try
any software that came bundled with your fax modem. While that
software may not be fully satisfactory, it should at least tell
you whether your fax modem is working properly or not.
- Make sure that you have specified the correct fax Class
for your modem in your fax software.
- Make sure that you have the latest updates for your fax software.
- Make sure that you are using the recommended initialization
string for your modem.
- Slower systems may have problems faxing at 14.4 Kbps. If you
are having problems, try dropping the maximum fax speed down to
9600 bps, if possible.
- Slower systems in particular may not be able to do much in
the foreground without interfering with background faxing, particularly
with Class 1. 32-bit operating systems like OS/2 Warp, Windows
NT, and Windows 95 are better able to handle fax in the background
than 16-bit operating systems like Windows 3.x.
- For fax reliability on a budget consider a Rockwell-based
fax modem -- Rockwell makes most of the fax chipsets in fax machines,
so Rockwell-based fax modems tend to have an edge in fax interoperability.
- See other fax tips throughout this document.
High-end fax modem products have significantly better fax machine
coverage, reliability, and performance than consumer-grade fax
modems. Such products are made by:
[Return to top]
How to get Adaptive Answer to work on USR Sportster modems with
Procomm Plus for Windows 2.xx (PW2.xx):
Adaptive Answer (called Call Selection by USR) works in Class
1 as well as Class 2.0 mode with 28.8 versions of both the USR
Courier and Sportster. PW2.xx does not support Class 2.0 (only
Class 1 and so-called Class 2), so it must be configured for Class
1 fax with USR modems.
The USR Adaptive Answer problem is that Datastorm
apparently assumed that all modems are like Rockwell clones, which
can enable Adaptive Answer while still in data mode. That doesn't
work with USR modems, which require the modem to be in fax mode
to enable Adaptive Answer.
Hopefully this problem will be fixed in a maintenance release.
In the meantime the author's workaround to this problem is to
put the USR Sportster modem into fax mode before enabling Adaptive
Answer. (Apparently this method does not work on the Courier.)
On the Setup | Fax Connection screen you will need to set:
Fax class: Class 1
Maximum transmit rate: 9600 [for reliability]
Maximum receive rate: 9600 [for reliability]
Class 1 adaptive answer command: +FCLASS=1+FAA=1 [no AT or ^M]
Adaptive answer connect message: FAX
Now you should be able to Setup | Auto Answer | Data and Fax.
The command won't take when done online, but don't worry, just
wait for PW2.xx to time out, and then Online | Initialize Data
Modem to get everything working. Startup Host Mode, and you should
be in business. Note: If you leave Auto Answer set to Data and
Fax and put PW2.xx with HOST.WAX as an argument in your Startup
group, PW2.xx will launch and initialize correctly for Adaptive
Answer when you startup Windows.
Be sure to turn off Auto Answer before trying to make a data call
out, or the call will fail since the modem will be in fax mode.
Just Setup | Auto Answer | Off, and then Online | Initialize Data
Modem.
A little bit of a kludge, but it does work on the Sportster.
[Return to top]
Warning: USR has indiscriminately slapped the
"Sportster" name on so many different products that
the author no longer feels it is a reliable product guide. For
example, recent "Sportster 28800" and "Sportster
33600" modems have considerably different S-register settings
as compared to the original "Sportster 28800" product.
This invalidates a good deal of advice, including some of
the material in this FAQ.
- Certain 28800 Sportster models can be inexpensively upgraded to 33600
(including Selective Reject). See "Sportster Supervisory Update Information"
(Note: the dates in the firmware table are not necessarily
the dates of the latest versions.)
- Useful modem commands:
ATI6
, issued after a disconnect,
will tell you the reason for the disconnect. Disconnect reasons
are explained in the Courier manual.
ATI6
will tell you your current modem-to-modem
connection speed if you escape (e.g., with "+++")
to command mode while online. With split/asymmetric speeds (see
What are split/asymmetric speeds?),
ATI6
will report the two speeds as receive/transmit
.
(See also "Why can't I get back on-line after I escape to command mode?"
To display the current connection speed when using Trumpet Winsock
on a SLIP/PPP link, see "Any Trumpet Winsock tips?")
ATO
will return you to on-line mode after you
escape to command mode; ATO1
will also request a
retrain (which may help if line conditions
have changed substantially).
ATI7
will tell you what firmware version (date)
you have.
- For a good description of the output of the
ATI6
and ATI11
commands, see the FAQ by USR UK.
- Another good technical reference for modem Link Diagnostics
output is the documentation that accompanies USRST406.ZIP.
[new 10/27/96]
- If you are running Windows 95, the output of all the
ATIn
commands can be easily displayed with Modem Diagnostics. (See
"Any Windows 95 tips?") [new
10/11/96]
- If you experience problems connecting to certain V.34 modems:
- It may help to disable the 3429 symbol rate (
S54.5=1
),
which confuses certain modems (e.g., Hayes) that are
not fully V.34 compliant during negotiation.
- It may help to disable V.FC (
S56.7=1
).
- It may help to disable V.42 detect phase (
S27=48
).
- If you experience problems connecting to certain V.34/V.FC
modems, or you otherwise want to connect with V.FC when the remote
modem supports both V.34 and V.FC, disable V.8 (
S54.7=1
),
which effectively disables V.34.
- If you have a particular number where you sometimes connect
at a very slow speed but get a much higher speed when you immediately
redial, find out if there is a Hayes modem at the other end. If
so, it may be possible to correct the problem by updating the
Hayes firmware.
- If you experience problems connecting to certain older MNP
modems (esp. at 2400 bps), try
S15=64
. This option
is only documented for the Courier ("Unusual MNP-Incompatibility"),
but may work for the Sportster as well.
- If you hear a strange ringing sound after dialing and before
the remote answers, that's Call Indicate. It's a good idea to
disable it (
S54.6=1
), because it can cause connection
problems with certain modems.
- Some users have reported that resetting the modem before each
call improves the chances of a good connection. To do this, use
ATZn
instead of AT&Fn
. The options
for ATZn
are:
Z
- reset and load profile Yn
Z1
- reset and load profile 0
Z2
- reset and load profile 1
Z3
- reset and load &F0
defaults
Z4
- reset and load &F1
defaults
Z5
- reset and load &F2
defaults
In other words, ATZ4
is a good alternative to AT&F1
.
Generally the only problem is that you can't put more commands
on the same line with ATZn
as you can with AT&Fn
;
e.g., you can do AT&F1S11=55
but not
ATZ4S11=55
. If you have a comm program that can issue
more than one initialization string (e.g., HyperACCESS
for Windows or WinComm PRO), you can simply put additional commands
in a second command string; e.g., ATZ4 followed by ATS11=55
.
- If you experience faxing problems, in addition to the other
suggestions in this document (e.g., "What about third-party comm drivers for Windows?"
and "Any other Windows tips?")
you should make sure that you have firmware dated 4/18/95
or later. (For a firmware upgrade, call USR at 847/982-5151.)
Otherwise, it might help to initialize the modem with
S36=0
.
If you are using Symantec WinFax, you might also try limiting
your send and receive speeds to 9600 bps by adding the following
to the [General]
section of your WINFAX.INI file:
MaxTxSpeed=9600
MaxRxSpeed=9600
- With the Sportster (not the Courier), watch out for which
profile you have set. If Y1 is set (which selects profile 1 rather
than profile 0), and you do (say)
ATS11=55&W
,
and then later use ATZ
to initialize your modem,
you won't get the S11
setting you saved!
The reason is that &W always saves to the profile
0, while ATZ loads whatever profile Yn is set
to, in this case profile 1.
- Options that are controlled by dipswitches are not
saved in NVRAM (profiles 0 and 1). If you want them to be in a
known state without worrying about the dipswitches, you should
set them in your initialization string (e.g.,
E1Q0V1S0=0&C1&D2
for the default settings).
- An official table of Sportster models and firmware versions
is available at "Sportster Supervisory Update Information".
[new 10/11/96]
- To obtain an SRO (Service Request Order) number for
modem repair or upgrade, see "USRobotics on the Internet".
[new 10/11/96]
[Return to top]
- An upgrade to Windows for Workgroups 3.11 or Windows
95 is probably the best way to improve Windows communications.
- To improve transmit (upload) performance and/or fax reliability
under Windows for Workgroups 3.11, put the following in the
[386Enh]
section of your SYSTEM.INI file:
COMnTXFIFO=1
where n is the number of your modem COM port (e.g.,
COM2TXFIFO=1
). This enables use of the 16550 Transmit
FIFO. (See "Do I need a 16550 UART? What is a UART?")
- Be careful not to confuse Windows (standard) 3.11 with Windows
for Workgroups 3.11 -- version numbers notwithstanding, they are
not the same. Windows (standard) 3.11 is essentially
Windows 3.1 with a few bug fixes (that do not directly affect
modem communications), whereas Windows for Workgroups 3.11 has
a considerably different internal architecture.
- If you get "Insufficient Memory to Run" errors when
starting new applications when you still have sufficient Free
Memory and System Resources (as displayed by Program Manager Help
| About), one of your running applications is probably locking
an excessive amount of memory below 1 Mb. (See "PRB: Avoiding 'Insufficient Memory to Run' Errors")
Utilities are available to deal with this problem:
- If you experience lockups or strange behavior, try setting
MaxBPs=400
(or more) in the [386Enh]
section of your SYSTEM.INI file.
- Contrary to "urban legends" it is possible to have
a DOS application temporarily take over a COM port from a Windows
application; i.e., it is possible to use a DOS program
like DSZ to handle
ZMODEM file transfers
for a Windows comm app with a less efficient ZMODEM implementation.
The key to doing this is to set
ComxAutoAssign=0
,
where x is the number of your modem COM port (e.g., Com1AutoAssign=0
),
in the [386Enh]
section of your SYSTEM.INI file.
(Because the exact details will vary from comm app to comm app,
the rest of the exercise is left to the reader.)
- Updated Windows 3.x drivers
are available from Microsoft.
- Good general resources are Microsoft's:
- The Windows Resource Kit
is also good, particularly the SYSTEM.INI section, which is viewable
on the Web:
[Return to top]
So-called voice modems fall into one (or sometimes more) of three
categories:
- Modems that can function as an answering machine or voice-mail
system. Some can also function as a speakerphone.
- Modems that can transmit data or voice over
the same connection. (Radish "VoiceView")
- Modems that can transmit data and voice simultaneously
over the same connection. (DSVD) Note that when voice
is active, the speed of data transmission drops substantially.
Modems in the category 1 have been on the market for some time.
Modems in categories 2 and 3 are just coming onto the market --
expect a continuing stream of new product announcements.
Note: None of these (current) voice modems permit
you to:
- Receive a voice call while your modem is in use. (For that
you need a second phone line -- these modems cannot deal with
Call Waiting.)
- Talk over the Internet. (For that you need a soundcard, and
preferably one that is full-duplex, although this would be possible
with a properly designed combo modem-soundcard product.)
See "Modems: the make-it-happen machines for the ultimately wired of the 90's"
[Return to top]
Probably the most likely successor to V.34, ISDN (Integrated Services
Digital Network) provides up to 2-4 times the speed of V.34 over
a standard local telephone line by using digital, rather than
analog, signals. Years in the making, ISDN is finally being widely
deployed in the U.S. at the time of this writing. To use ISDN
you will need special, expensive equipment. A problem is that
ISDN transmissions are typically not compressed; as a result,
with compressible data the speed of a V.34 modem is often comparable
to a single ISDN channel. In the opinion of the author, V.34 will
probably be a cost-effective alternative to ISDN for years to
come.
Although ISDN is a digital transmission medium, there are some
ISDN products that will also allow you to connect to conventional
analog modems (e.g., USR Courier I-modem with ISDN/V.34,
ZyXEL Elite 2864I,
and ZyXEL Prestige 2864I).
Microsoft has released an updated "ISDN Accelerator Pack"
for Windows 95, which enables Windows 95 to make Dial-up Network
connections over ISDN lines. [updated
10/11/96]
ISDN information is available at:
See also:
[Return to top]
So-called "cable modems" are devices which provide computer
connectivity to and through a cable TV system. Despite a lot of
hype, the technology is still experimental and the prospects are
uncertain. One of several major problem is that many cable systems
are not able to handle large incoming, as opposed to the more
normal outgoing, bandwidth. Contact your local cable TV company
for more information. See also:
Other "cable modem" resources on the Internet. (Note:
This author cannot vouch for the accuracy of these resources.)
[Return to top]
ADSL (asymmetric-digital-subscriber-line), SDSL (symmetric-digital-subscriber-line),
and HDSL (high-bit-rate, digital subscriber line) are new telco
technologies that have the potential to blow ISDN
away. See:
Other ADSL, SDSL, and HDSL resources on the Internet. (Note:
This author cannot vouch for the accuracy of these resources.)
[Return to top]
- Connecting to the Internet [new
6/13/96]
- An excellent resource is Microsoft's "Connecting to the Internet with Windows 95 Dial-Up Networking."
- Connection Statistics [updated
10/11/96]
- If you have a USR modem and want to access your ATI6 Link
Diagnostics (see "Any other USRobotics tips?")
for a dialup TCP/IP session, do the following:
1. You first have to "hack" the Registry:
(a) Run "REGEDIT" to launch the Registry Editor.
(b) Find the entry for your modem, which should be something like:
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Class\Modem\0000
(If you have more than one modem, the number may be 0001
,
0002
, etc.)
(c) Change the "Reset" value, which will probably be
"ATZ<cr>
" or "ATZ4<cr>
",
to "AT&FE1Q0V1S0=0&C1&D2+FCLASS=0<cr>
"
or "AT&F1E1Q0V1S0=0&C1&D2+FCLASS=0<cr>
"
respectively.
(d) Restart Windows 95.
2. After disconnecting from a dialup TCP/IP session:
(a) Open Control Panel | Modems, and click on Diagnostics. You
should see the name of your modem next to the COM port that it
is on.
(b) Select the appropriate COM port and click on More Info. Windows
95 will run all of the common In
commands, and then
display the results.
Note: This is a temporary change for diagnostic purposes --
it is not recommended for regular use.
- Dial-Up Networking improvements
[updated 10/18/96]
- Microsoft has released Dial-Up Networking (DUN) improvements
as part of Version 1.1 of the ISDN Accelerator Pack.
(You can safely install the ISDN Accelerator Pack even if you
don't have or use ISDN, and then delete the ISDN support [under
Control Panel | Add/Remove Programs | Windows Setup | Communications]
leaving the improvements behind.) Improvements include DUN Server
(previously available only in Microsoft Plus!),
optional automatic connection without confirmation, integrated
scripting (and SLIP), and placement of the DUN icon on the Tray
rather than the Task Bar. Once installed, the new DUN capabilities
can be accessed through My Computer | Dial-Up Networking | Connections
| Settings. (Unfortunately, the improvements do not
include a fix for the serious DUN MTU problem. See "Why does my Internet connection run at half-speed?")
- Dial-Up Networking Freeware/Shareware
[new 4/11/96]
- Dunce:
Dial-Up Networking Connection Enhancement
Keep Going:
skips the dial-up Connect dialog box.
RoboDUN:
alternative to Microsoft scripting.
RASPlus: "Hands
free" Internet connection.
RTVReco: automatically
re-establish dropped connections.
- Dial-Up Networking Server [updated
10/18/96]
- Available either in Microsoft Plus!
or Version 1.1 of the ISDN Accelerator Pack
(see "Dial-Up Networking improvements" above).
Information on setting up a dial-up networking server and/or client
is available in:
"How to Enable Dial-Up Networking Server Capabilities"
"How to Connect to a Remote Server"
"Troubleshooting Browsing with Client for Microsoft Networks"
"Microsoft Plus! Readme.txt File Contents (2 of 2)"
"Technical Guide to Windows 95 Remote Connectivity"
Other Microsoft (Knowledge Base) resources
- Dial-Up SLIP and Scripting Support
[updated 10/11/96]
- Adds SLIP and scripting capabilities to the basic PPP support
in Windows 95 Dial-Up Networking. Part of the Windows 95 on CD-ROM Extras,
and also included (and better integrated, along with other Dial-Up
Networking improvements) in Version 1.1 of the ISDN Accelerator Pack.
(You can safely install the ISDN Accelerator Pack even if you
don't have or use ISDN, and then delete the ISDN support [under
Control Panel | Add/Remove Programs | Windows Setup | Communications]
leaving the improvements behind.)
- HyperTerminal PE
- HyperTerminal Personal Edition, an upgrade to Windows 95 HyperTerminal
that provides improvements (auto-redial on busy and ZMODEM
Crash Recovery) as well as bug fixes, is available from Hilgraeve
at no charge.
- Installing your modem "driver" [new
7/27/96]
- It is very important to use the correct
and latest INF file for your modem -- "Standard modem"
may well cause problems. To change or install a new INF file:
Obtain the correct
and latest INF file for your modem from the modem manufacturer
(see "Modem Companies on the Internet").
Copy it to your \WINDOWS\INF directory (which is hidden, but definitely
there).
Delete the files
DRVIDX.BIN and DRVDATA.BIN from your \WINDOWS\INF directory. (You
do not need to back them up, because they will be recreated automatically.)
Open Settings |
Control Panel | Modems.
Remove your modem.
Restart Windows
95. During the restart, it should detect your modem automatically
and install the driver. If it does, you're done; if not,
continue
Open Settings |
Control Panel | Modems.
Click Add, and run
through the automatic process. If it still does not find your
modem, select if from the list of modems manually. Be sure
that you know the manufacturer and correct, exact model of your
modem.
- Internet Explorer
[updated 4/11/96]
- Download the latest version of Microsoft's World Wide Web
browser. Note: Installing Internet Explorer will give you
auto-dial support for Windows 95 Dial-Up Networking with all 32-bit
(but not 16-bit) Winsock applications. You can then uninstall
Internet Explorer without losing auto-dial support if you prefer
another browser (which you should reinstall after uninstalling
Internet Explorer).
- ISDN Accelerator Pack
[updated 10/11/96]
- Enables Windows 95 to make Dial-up Network connections over
ISDN lines. The updated version also includes Dial-Up Networking
enhancements (see above).
- Kernel Update
[new 4/24/96]
- Solves WinSock memory leak problem. Not included in Service
Pack 1 (below). Highly recommended. There have been a few
reports of serious problems installing and/or running the kernel
update, so be sure to back up your system before installing
it (as you should with any system update).
- Logs [updated 10/5/96]
- Windows 95 can record log files that can be helpful in diagnosing
problems:
Modem Log:
Settings | Control Panel | Modems | [select modem] | Properties
| Connection | Advanced | Record a log file (look for the file
as \WINDOWS\MODEMLOG.TXT
). See "How to Create and Use the Modemlog.txt File."
Dial-Up Network
Log: Settings | Control Panel | Network | Dial-Up Adapter
| Properties | Advanced | Record a Log File | Yes (look for the
file as \WINDOWS\PPPLOG.TXT
). See "How to Create a Ppplog.txt File."
Note: The logs do not keep growing indefinitely.
- Microsoft AnswerStation
[new 6/13/96]
- Put your VoiceView modem (see "What are "voice" modems?")
to work!
- Modem Diagnostics
- The best way to verify that your modem is working is to open
Control Panel | Modems, and click on Diagnostics. You should see
the name of your modem next to the COM port that it is on. (If
not, you need to reinstall your modem, as described above.) Select
the appropriate COM port and click on More Info. Windows 95 will
try all of the common
In
commands, and then display
the results. The display will frequently include a description
of the modem and the version of firmware it is running.
- Modem Initialization [new
10/11/96]
- To modify your modem initialization, go to Control Panel |
Modems. Select your modem and then click Properties. Click Connection,
then Advanced. Enter any extra settings in Extra Settings (without
the "
AT
").
- MTU [new 10/5/96]
- Unless you explicitly set MaxMTU in the Registry, you
may experience abnormally low file transfer speeds (half-speed
or even less) with certain servers under Windows 95 Dial-Up Networking.
See "Why does my Internet connection run at half-speed?"
- Plug and Play
- Windows 95 supports "Plug and Play," a standard
that makes it possible for the operating system to automatically
detect and configure most peripheral devices. Plug and Play modems
are available from USRobotics,
Diamond/Supra,
and other manufacturers.
- Resource Kit
[new 10/5/96]
- The free Resource Kit Help File
is an invaluable source of Windows 95 technical information, particularly
on networking (including Dial-Up Networking).
- Service Pack 1
[new 4/11/96]
- Various fixes and improvements have been collected by Microsoft
into the first Service Pack. Highly recommended.
- Support
[new 6/13/96]
- Microsoft support on the Internet.
- Symantec
CommSuite 95
[new 3/1/96]
- While providing a rich feature set, this product, including
WinFax PRO 7.0 and WinComm PRO 7.0, suffered in its first release
from excessive memory requirements, poor performance (even on
fast systems), modem compatibility problems (particularly with
USRobotics modems), and bugs. The WinFax 7.0 Maintenance Updates
correct many (although not all) of those problems -- be sure to
get them.
- System Monitor
[updated 10/5/96]
- The System Monitor accessory that comes with Windows 95 has
a wealth of hidden features, among them the ability to display
modem throughput in real time. To get it working:
Open Control Panel
| Modems; select your modem; click Properties | Connection | Advanced;
check "Record a log file"; and then click OK to close
all the dialogs.
Make a connection
with your modem using 32-bit software (e.g., HyperTerminal,
which comes with Windows 95).
Start System Monitor;
choose Edit | Add Item. You should see your modem under Category.
Select your modem, then under Item select "Bytes received/sec."
and/or "Bytes sent/sec.", and click OK.
If you have problems, see "System Monitor Does Not Display Modem Statistics."
- TAPI
- TAPI (Telephony Application Programming Interface) is an architecture
being developed by Microsoft to bring order out of the past chaos
in comm software and modem interaction. "TAPI compliant"
applications rely on new standard Windows services (provided by
the Unimodem driver/provider) rather than controlling the modem
directly, which makes it possible for multiple comm applications
to share the same modem. With a proper modem INF file and a sufficiently
capable modem, separate data, fax, and voice applications could
be "registered" with TAPI (once Microsoft's implementation
is complete) such that an incoming call is automatically connected
to the right application. (See "How can I use a single phone for fax/data/voice?")
TAPI is being developed first for Windows 95, with Windows NT
to follow. TAPI resources for developers
are available on the Internet. [updated
4/24/96]
- Telephony Location Selector
[new 4/11/96]
- For mobile users, provides an easy way to change your location
for telephony applications (e.g., Windows 95 Dial-Up Networking).
Part of the Microsoft Power Toys.
- Unimodem V
- "Unimodem V is Microsoft's newest release of Unimodem,
the Windows universal modem driver/telephony service provider
for data/fax modems. Unimodem V provides the driver support that
sits between telephony applications and voice modems and allows
them to work together. This driver adds the most-requested features
to support data/fax/voice modems, including wave playback and
record to/from the phone line, wave playback and record to/from
the handset, and support for speakerphone, Caller ID, distinctive
ringing, and call forwarding." [Quote from Microsoft] Unimodem
is TAPI-complaint. At initial release, Unimodem V supports the
following modems:
Aztech Systems
Cirrus Logic
Compaq Presario
models 520, 720, 820, and 920
Compaq Presario
wave driver and wrapper
Creative Labs Phone Blaster
Diamond Multimedia TeleCommander 2500
Logicode 14.4 data/fax/voice PCMCIA
Rockwell
PCMCIA reference design
- Updated Drivers
[updated 4/9/96]
- Audio
CD-ROM
Display
IrDA (Infrared Driver)
ISDN Accelerator Pack
Modem (Microsoft)
Mouse
Network
Other
Pointer
Printers
Storage
Unimodem V
UPS
[Return to top]
[Return to top]
Newsgroups can be excellent resources. You can often find answers
to questions you didn't even know you had. If you don't find what
you are looking for, you can post your own questions, and usually
get answers within a day or two, sometimes within hours. Just
remember that a good deal of nonsense also gets posted to Usenet.
NOTE: It is very important to "learn the ropes" before
posting to newsgroups. Resources to help you do this include:
The modem-related newsgroup resources include:
Usenet
- comp.dcom.fax
- Unmoderated discussion of fax modem-related issues (not conventional
fax machines).
- comp.dcom.isdn
- Unmoderated discussion of ISDN. (See "What is ISDN?")
- comp.dcom.modems
- Unmoderated discussion of data modem-related issues.
- comp.os.ms-windows.apps.comm
- Unmoderated discussion of Microsoft Windows communications
applications
- comp.os.os2.comm
- Unmoderated discussion of IBM OS/2 communications-related
issues
- comp.sys.mac.comm
- Unmoderated discussion of Apple Macintosh communications-related
issues
- comp.sys.ibm.pc.hardware.comm
- Unmoderated discussion of communications hardware (e.g.,
serial ports) for PC-compatible computers
Microsoft
- microsoft.public.win95.commtelephony
- Unmoderated discussion of communications over telephone lines
(e.g., data/fax/voice modems, ISDN) under Windows 95
- microsoft.public.win95.dialupnetworking
- Unmoderated discussion of Dial-Up Networking (DUN) under Windows
95
[Return to top]
Your modem won't work on the kind of digital phone that you typically
find in businesses and hotel rooms, and it can be hard to find
a standard phone jack when you need one. There are a number of
devices on the market to solve the problem. Typically you have
to disconnect the handset from a digital phone, plug the handset
into the device, and then plug the device into the handset jack
on the phone. Then you connect your modem to the device with a
standard phone cord.
The author gives a qualified recommendation to the Konexx
Konnector Model 111.
The product can be powered by a 9v battery or from an AC power
adapter, both of which are included. The biggest weakness of the
Konnector Model 111 is that, like other similar products, you
have to experiment with a non-intuitive 4-position switch.
[Return to top]
- The best resource for modem initialization strings is the
documentation that came with your modem, or other information
provided by your modem manufacturer.
- Windows 95 comes with INFormation files that provide proper
initialization for many popular modems. (It is very
important to use the correct and latest INF file
for your modem -- "Standard modem" may well cause problems.
See "Installing your modem 'driver'" under "Any Windows 95 tips?")
[new 11/8/96]
- Many comm apps are another good resource, because they come
with recommended modem initialization strings.
- An online resource is Ask Mr. Modem.
Note: This author cannot vouch for the accuracy of Ask
Mr. Modem. [updated 11/8/96]
[Return to top]
The best source for information is of course the modem manufacturer.
Generic information is available from Rockwell International.
"RPI" (Rockwell Protocol Interface)
The author advises against the purchase of any RPI modem.
RPI uses your system processor, rather than a processor in the
modem, to implement protocols. This requires special software
support, which may well not be available for your favorite comm
app.
[Return to top]
Take magazine modem reviews with a grain of salt -- few
if any magazines perform the kind of thorough interoperability
and real-world tests that are needed to properly compare modems.
Note that the apparently diverse computer magazine publishing
field is actually dominated by a relatively small number of publishers,
particularly Ziff Davis.
Reviews from different magazines owned by the same publisher tend
to have a shared editorial bias, if for no other reason than that
testing is often done by a shared facility (e.g., ZD Labs).
The publisher is noted in parentheses.
Analog Modems:
ISDN: [new
8/30/96]
[Return to top]
In the opinion of the author, 28800 modems are still too immature
to shop on price alone because there are still performance and
interoperability problems. (To avoid interoperability problems
you may want to purchase the same brand as the modem you will
be most frequently calling.)
Take magazine modem reviews with a grain of salt -- few
if any magazines perform the kind of thorough interoperability
and real-world tests that are needed to properly compare modems.
(See "What about magazine reviews?")
Furthermore, like software, modem preferences are a highly personal
matter -- a terrific modem for one person may be a dog for another
person, and vice versa. That noted, the personal assessment of
the author is as follows:
- USRobotics Courier V.Everything
- In the opinion of the author, this is quite simply the best
reasonably-priced modem available. It's a particularly good choice
if you have poor phone lines, if you have to make difficult connections,
or if you have to connect to a wide range of modems. A strength
that the Courier shares with the Sportster is that its DSP code
is stored with its firmware (in Flash in the Courier, ROM in the
Sportster), so that it can be easily updated (unlike most modems,
which have fixed "datapumps"). A firmware update
(7/5/95 or later for USA modems) that supports Selective Reject
and draft V.34 speeds up to 33.6 Kbps is now available. The Courier
is a good choice for a small BBS, and USR has an attractive SYSOP
program. Otherwise the best way to get a good deal may be to find
a cheap used 9600 bps or above Courier and take advantage of the
USR upgrade program.
- Motorola [updated
6/13/96]
- An excellent company with ISO 9001
registration and a reputation for excellent products. Not evaluated
by the author:
326XFAST:
V.34 modems designed for networking.
V.3400:
A reputation as an excellent, if pricey, modem. Does not support
V.FC.
V.34R:
Similar to the V.3400, but without the LCD display.
Premier 33.6:
Positioned to compete with the USR Courier. Firmware in Flash.
Claimed maximum compression is 8:1. Does not support V.FC and
only supports Class 1 fax.
- Microcom
- A reputation for very good modems. Not evaluated by the author.
- Bay Networks/Penril
- A reputation for excellent, if pricey, modems. Not evaluated
by the author.
- Telebit
- A reputation for excellent, if pricey, modems. Not evaluated
by the author. Does not support V.FC.
- Zyxel
- The Elite 2864
is feature rich (although it does not support V.FC), Flash upgradable,
and has the added advantage of being user-upgradable to ISDN (Elite
2864I). However, in the author's tests it does not yet measure
up to other modems in connection speed and reliability.
- AT&T Paradyne
- A reputation for excellent, if pricey, modems. Not evaluated
by the author. Does not support V.FC. Supports a proprietary V.34
extension for speeds up to 33.6 Kbps. (Note: Paradyne is reportedly
up for sale, so its future is uncertain -- see "AT&T Seeks Buyer For Paradyne"
and "PC Magazine Newswatch for Thursday, October 19, 1995")
- Motorola [updated
6/13/96]
- An excellent company with ISO 9001
registration and a reputation for excellent products. Reports
on the PowerClass
and Lifestyle
modems (distinguished from each other only by features) are mostly
positive. However, there have been reports of a few problems (e.g.,
Motorola's Customer Note of July 27, 1995,
which Motorola is to be commended for publishing). Limitations
include a maximum speed of 28.8 Kbps, no V.FC, and no Class 2
or 2.0 fax.
Newer models include:
VoiceSURFR:
V.34 28.8 internal modem with data, fax (Classes 1 & 2), voice
and full-duplex speakerphone.
ModemSURFR:
V.34 28.8 internal/external modem with data and fax (Classes 1
& 2).
OnlineSURFR:
ModemSURFR with bundled Internet software.
- USRobotics Sportster 28800/33600
[updated 4/27/96]
- The popularly-priced Sportster 28800/33600 is a very good
modem. (See "SHOOTOUT: Sportster vs. Courier")
A strength of the Sportster is that it supports several optional
V.34 features (notably split speed)
that are not supported by some other popularly-priced modems.
Be sure to get firmware dated 4/18/95 or later for USA modems;
if necessary, call USR (847/982-5151) to get an upgrade. Certain
28800 Sportster models can be inexpensively upgraded to 33600
(including Selective Reject).
The "Vi"
model includes voicemail capabilities. It is otherwise the same
as the standard model.
The "Voice"
model includes voicemail and speakerphone capabilities. It is
otherwise the same as the standard model.
The "DSVD"
model includes Flash (like the Courier V.Everything) and DSVD
(simultaneous voice and data over the same connection) capabilities.
Warning:
The Sportster "WinModem"
is a proprietary design that requires special USR drivers that
work only under Microsoft Windows. Make sure that you are
willing to live with the attendant risks and inherent limitations
before purchasing any proprietary product. [new
3/29/96]
Warning:
The Sportster Si is essentially a Rockwell "Glue
'n Go" clone (see below); worse, it uses software (RPI)
rather than hardware protocols. The author advises against
the purchase of any RPI modem. (See Where can I get information on my Rockwell-based modem?)
Warning:
USR has indiscriminately slapped the "Sportster" name
on so many different products that the author no longer feels
it is a reliable product guide. For example, recent "Sportster
28800" modems have considerably different S-register settings
as compared to the original "Sportster 28800" product.
This invalidates a good deal of advice, including some of
the material in this FAQ.
- Diamond/Supra [updated
6/6/96]
- In the opinion of the author, Diamond/Supra is the probably
the best bet among the Rockwell chipset-based modems, particularly
now that it has released firmware that supports split speeds.
All 28800 Diamond/Supra modems can be upgraded to 33600.
- Multi-Tech
- Although high-end Multi-Tech modems have a good reputation,
the author cannot recommend the popularly-priced MT2834ZDX. In
the author's head-to-head real-world tests against the USR Sportster
28800, the MT2834ZDX was consistently one step slower, worse on
difficult connections; in addition, operational idiosyncrasies
caused problems with certain comm apps (e.g., HyperACCESS
for Windows).
- Hayes
- Although Hayes has made excellent modems in the past, of late
it has been slipping, and its 28800 products have exhibited interoperability
problems. Because Hayes (inc. PPI) has now emerged from Chapter
11 (Bankruptcy) protection, the author no longer recommends against
the purchase of Hayes products, but still advises caution for
at least the next few months.
- Practical Peripherals Inc.
(PPI)
- PPI is owned by and has been folded into Hayes. The same general
comments apply.
- Zyxel
- The Omni 288S
is the consumer grade version of the Elite 2864.
Not evaluated by the author.
- AT&T
- AT&T has bailed out of consumer modems.
Although good liquidation deals may be found, support could be
a problem. Also be warned that there were two completely different
AT&T consumer modem lines with similar names. The Dataport
was based on AT&T's own modem technology; the low-cost Dataport
Express was essentially a Rockwell "Glue 'n Go"
clone (see below).
- "Glue 'n Go" clones
- In the opinion of the author, companies that simply slap a
modem chipset on a board are currently a poor bet given the immaturity
of 28800 products. (The author puts Best Data,
Boca, GVC, and Zoom
in this category.) Some do not support optional V.34 features
such as split speeds.
Other modem companies on the Internet include:
Whatever modem you decide to purchase, the author strongly
recommends that you get a return privilege from the dealer (in
case you run into problems).
Note: No consumer grade modem should be used for a large
BBS or an Internet service provider. In the long run
the savings in maintenance and support costs with rack mount modems
more than offsets their higher initial purchase price. The author
recommends the USRobotics Total Control
system.
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In the opinion of the author, 28800 modems are still too immature
to shop on price alone. If you run into (all too common) performance
or interoperability problems, the best way to deal with them may
be to return the modem and try a different brand, which may not
be possible with a low price source.
The author recommends WH Networks Communications.
Other sources on the Internet include:
One of the best mail-order sources is Computability
(800/554-9950 or 414/357-8181).
Please note that the author has no connection to any of the sources
listed here.
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