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Navas 28800-56K Modem FAQTM
(Answers to Frequently Asked Questions)
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C. MODEM FEATURES
Copyright 1999-2017
The Navas
GroupSM, All Rights Reserved.
Permission is granted to copy for private non-commercial use only.
Send mirror and commercial license inquiries to John Navas.
Posted as <http://modemfaq.navasgroup.com/faq_c.htm>.
Important Notes:
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Privacy Policy: This site makes no use of personal information;
does not require registration; and does not use browser "cookies."
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Copies of this (or other Web) document may be obtained by email from a
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server in hypertext (HTML) or plain text format. For more information,
send an email message to the server with a body of "help". Another alternative
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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.
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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.
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Email comments and suggestions to John Navas
What's the difference between V.FC and V.34? What's
next?
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V.FC
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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.
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V.34
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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.
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56 Kbps
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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. These proprietary protocols are now being replaced by V.90,
a true international standard. See "What are 56K modems?"
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28800-33600 fax
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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.
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Voice
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See "What are 'voice' modems?"
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Plug and Play
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See "What is Plug and Play"
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ISDN
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See "What is ISDN?"
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"Cable modems"
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See What are "cable modems?"
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ADSL/SDSL/HDSL
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See "What are ADSL, SDSL, and HDSL?"
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Universal Serial Bus
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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 95/98), 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"
What are 56K modems?
Rockwell Semiconductor Systems
(along with a number of its OEM customers), USRobotics,
Lucent
Technologies, and
Motorola Information
Systems Group, are introducing modems that can work over conventional
phone lines at speeds up to 56 Kbps under certain conditions (as noted
below). The industry has aligned itself around two incompatible technologies:
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K56
(also known as K56Plus and K56flex)
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Supported by Rockwell, Lucent, Motorola, and others (including 3Com).
How to find a K56 POP (point of presence):
Ascend Directory
Epoch Internet
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x2
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Supported by USRobotics, Texas Instruments,
and others.
How to find an x2 POP (point of presence):
x2 Directory
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V.90
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The new international standard
For more information see:
Class
action nemesis to go after 56K modem claims
PCWorld
New Radio interviews John Navas on 56K modems [new
4/23/97] "ISPs
take sides" "USR
may join 56-kbps group" So-called "Open
56K Forum" [new 2/27/97]
[The name notwithstanding, this appears to
be a "K56flex" promotional organization.]
One of the members of the "Open 56K Forum,"
3Com,
is acquiring
USRobotics. It's unclear what impact the acquisition
will have on the competition with "x2" from USRobotics. Motorola
and Rockwell Announce Plans to Cooperate on K56 Modem Technology[new
2/14/97]
[It is unclear if Motorola will also interoperate with Lucent]Rockwell
And Lucent Announce Their Intention To Interoperate At 56KbpsRockwell
Semiconductor Systems:
Rockwell OEM customers:
USRobotics:
x2 licensees:
Lucent Technologies:
Motorola Information Systems Group:
Other material:
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"Behind
The 56Kbps Modem Hype"
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"Modem
Technology May Speed Net Access -- Rockwell To Show 56-Kbit/s System"
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There are several catches however:
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It will take time (and product updates) for these products to achieve maturity
and wide deployment.
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These products are a year or more away from standardization, and there
may well be serious interoperability problems. This could be another
VHS versus Beta battle in which there will be winners and losers.)
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The higher speed is only be for receiving -- sending is limited
to V.34 speeds (although typical Internet access is mostly receiving).
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The modem at the other end must be digital technology that connects to
the telephone network through a digital connection.
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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, particularly if your ISP uses Forwarding to connect
your local dial-in number to distant equipment. A local number does
not necessarily mean a local call. [updated
06/06/97]
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Standard PC serial ports can be a bottleneck for 56K modems operating
at higher speeds with compressible data. To take full advantage of a 56K
modem you need a serial connection (port/modem) that goes significantly
faster than 115.2 Kbps (see "Where can
I get a 16550 UART?"), a parallel connection, or USB (see "Universal
Serial Bus Home Page").
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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.
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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." Motorola has sued
USRobotics for alleged patent infringement.)
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Early Rockwell-based products may be rushed to market by using fixed-function
datapumps that may not be readily field-upgradable to fix bugs and
to conform to an eventual 56K modem standard. (This author advises
consumers to avoid any 56K product that is not fully field-upgradable.
Flash memory is not enough if the datapump is fixed-function.) [new
03/16/97]
As the competitive battle between Rockwell/Lucent and USRobotics heats
up, the latter appears to be in the stronger position for two reasons:
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USR has a substantial market position among major Internet Service Providers
(ISPs), with a substantial installed base that can be easily upgraded to
56K ("x2") technology.
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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?")
What are "voice" modems?
So-called voice modems fall into one (or sometimes more) of three categories:
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Modems that can function as an answering machine or voice-mail system.
Some can also function as a speakerphone.
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Modems that can transmit data or voice over the same connection.
(Radish "VoiceView")
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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:
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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.)
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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"
What are "PCI" modems?
PCI modems are internal modems that use a PCI slot rather than a legacy ISA
slot. Many (but not all) PCI modems are either host-based (see "What
are 'software' or 'soft' modems?") or controllerless (see "What are
'Windows' modems?")
Pros:
-
ISA is being phased out.
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ISA slots may be limited.
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Can share an IRQ with another PCI slot.
Cons:
-
May work only under Windows (e.g., not with legacy DOS software or with
other operating systems).
-
If either host-based or controllerless, see "cons" for
that modem type.
PCI modems based on standard controllers include:
What are "software" or "soft"
modems?
So-called "software" modems use the main system processor for both modem
control and modem datapump functions, thereby putting a heavy load on the
system processor (e.g.., about 22% of a Pentium 300). In
the opinion of this author, "software" modems are only suitable for higher-end
systems (Pentium 166 and above) with a lot of extra main processor power
to burn. This technology is sometimes known as "Host Signal Processing."
Pros:
-
Very low cost (ignoring the cost of the main system processor).
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Small size. (Can be integrated on the computer motherboard.)
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No comm port overruns. (See "Why am I getting
CRC errors (overruns)?")
-
Easy upgradability.
Cons:
-
A different, complex software driver is needed for each different operating
system (sometimes for different versions of the same operating system),
and not all operating systems may be supported.
-
Incompatibility with software designed for standard serial ports (e.g.,
DOS programs) , although Pacific CommWare
sells a Windows 95 driver
that overcomes that limitation.
-
Can interfere with multimedia applications (e.g., computer games
played over a modem connection).
-
Make sure that you are willing to live with the attendant risks and
inherent limitations before purchasing any proprietary product.
More information:
(See also "What are 'Windows' modems?" and
"What are 'RPI' or 'WinRPI' modems?")
What are "Windows" modems?
So-called "Windows" modems use the main system processor for modem control
(but not modem datapump) functions, thereby putting some load on the system
processor (e.g., about 4% of a Pentium 300).
Pros:
Cons:
-
A different software driver is needed for each different operating system
(sometimes for different versions of the same operating system), and not
all operating systems may be supported.
-
Internal version only.
-
Incompatibility with software designed for standard serial ports (e.g.,
DOS programs), although Pacific CommWare
sells a Windows 95 driver
that overcomes that limitation.
-
Can interfere with multimedia applications (e.g., computer games
played over a modem connection).
-
Make sure that you are willing to live with the attendant risks and
inherent limitations before purchasing any proprietary product.
More information:
(See also "What are 'software' or 'soft' modems?"
and "What are 'RPI' or 'WinRPI' modems?")
What are "RPI" or "WinRPI" modems?
So-called "RPI" (Rockwell Protocol Interface) modems use the main system
processor for modem control (but not modem datapump) functions, thereby
putting some load on the system processor.
Pros:
-
Lower cost (ignoring the cost of the main system processor).
-
Both internal and external versions.
-
Much less overhead than "software" modems. (See "What
are 'software' or 'soft' modems?")
Cons:
-
A different software driver is needed for each different operating system
(sometimes for different versions of the same operating system), and not
all operating systems may be supported.
-
Incompatibility with software designed for standard modems (e.g.,
DOS programs).
-
Can interfere with multimedia applications (e.g., computer games
played over a modem connection).
-
Make sure that you are willing to live with the attendant risks and
inherent limitations before purchasing any proprietary product.
More information:
(See also "What are 'software' or 'soft' modems?"
and "What are 'Windows' modems?")
What are "cellular" modems?
Standard modems have a difficult time transmitting data over cellular phone
connections. Certain modems (typically in PC
Card or PCMCIA form) have special protocols designed to enhance cellular
communications, and may also have various adapters that connect them to
different cellular phones. However, even with such special support, data
transmission over a cellular connection is problematic, typically in the
range of only 9600 bps, and disconnections are not uncommon.
What are split/asymmetric speeds?
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.
What is Selective Reject (SREJ)?
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.
Trademarks belong to their respective owners.
