220 1768 article Newsgroups: comp.dcom.modems,comp.sys.ibm.pc.hardware.comm,netcom.modems Path: ix.netcom.com!netcomsv!decwrl!news.hal.COM!olivea!charnel.ecst.csuchico.edu!yeshua.marcam.com!news.kei.com!ddsw1!a2i!wolfgang.a2i!wolfgang From: wolfgang@whnet.com (Wolfgang Henke) Subject: Re: Modems FAQ Message-ID: Sender: news@rahul.net (Usenet News) Nntp-Posting-Host: bolero.rahul.net Organization: WH Networks X-Newsreader: TIN [version 1.2 PL2] References: <33kibp$pfc@status> Date: Sat, 27 Aug 1994 05:19:12 GMT Lines: 2056 Xref: ix.netcom.com comp.dcom.modems:65135 comp.sys.ibm.pc.hardware.comm:4712 netcom.modems:1768 This file was submitted by Karl Willdig. ftp.whnet.com /pub/wolfgang/ModemsFAQ.txt: What You Need to Know about Modems -------==================================------- May 31, 1992 Revised Aug, 1994 Version 1.1 Version 3.0 ======================================================================= I have updated this, I would say it is Public Domain, if the original author updated this then I never saw the update, and I'm sure that he wouldn't mind me changing it and redistributing it. This document may be redisbruted freely aslong as it is not used for profit, i.e. in a Magazine, without my and the original authors permission. Copyright (c) 1994-95 Karl Willdig & Patrik Chen. All Rights Reserved. If you have any problems with this then you may if you really have to contact me at karl@ak.planet.co.nz. I encourage manufacturers to do so and update me on information so I can continue updating this. ====================================================================== DISTRIBUTION NOTICE: This document may be distributed by electronic bulletin boards and commercial on-line services. This document may not be edited or changed in any way for redistribution. This article was Part One of a three-part book/report entitled "The Joy of Telecomputing." As a plain ASCII file, it cannot contain any of the illustrations and graphic elements provided in the printed version. This article should be useful to anyone interested in high-speed modems (or 2400-bps modems with MNP5 or V.42bis). Most modems mentioned in this article are external units. These modems can be used on any microcomputer system, be it a PC, a Macintosh or an Amiga. Although only certain communication programs are used as examples, the discussions about setting up software apply to packages not covered herein. It is assumed that the reader knows the basics about going online. For example, we would not discuss how to connect an external modem to your computer, nor would we explain what 8-N-1 means. Every effort has been made to supply current and accurate information. However, information contained herein is subject to change without notice and should not be construed as a commitment by the author who assumes no responsibilities for any errors that may appear. Trademarks: The author has attempted throughout this document to distinguish proprietary trademarks from descriptive terms by following the capitalization style used by the manufacturer. ======================================================================= CONTENTS I. Introduction II. Modulation Protocols 0. Overview of Protocoles 1. 2400-bps modems 2. High-speed modems a. V.32 (9600) b. V.32bis (14,400) c. v.FC (Fast Class) (28,800) d. Other proprietary protocols (v.32terbo) e. US Robotics HST f. Telebit PEP & Turbo PEP g. Hayes Express 96 h. CompuCom CSP 3. Things to come a. V.34 b. V.36 c. ISDN 4. Other Standards and Protocoles III. Error Control Protocols 1. V.42 and MNP4 2. V.42 and MNP4 can provide error-free connections 3. V.42 and MNP4 can improve throughput 4. Other Error Correction Protocoles 5. Are MNP 4 and V.42 useful? IV. Data Compression Protocols 1. MNP5 and V.42bis 2. Are MNP5 and V.42bis useful? 3. Compression by software vs. MNP5/V.42bis 4. Local flow control and data buffering 5. Macintosh and high-speed modems 6. PC and UART 7. Amiga Serial V. Cellular Protocoles 1. ETC - AT&T 2. HST - USRobotics 3. Zycellular - Zyxcel 4. MNP 10 VI. About Fax Modems 1. Protocols a. Group 3 b. V.27ter c. V.29 d. V.17 e. CAS f. Class 1 & Class 2 2. How useful is a fax modem? VII. Buying a High-speed Modem 1. Should you pay extra for a V.FC modem? 2. Should you buy a modem with a proprietary modulation protocol? 3. Should you buy a 2400-bps modem with V.42bis? 4. Standards You Can Count On In Modems 5. PCMCIA / Pocket or Normal Modems? 6. Internal or External Modems? VIII. Setting Up Software to Work with High-speed Modems 1. a. Speed setting b. File Transfer Protocoles a. ASCII b. Xmodem c. Xmodem-1K d. Ymodem e. Ymodem-g f. Zmodem g. Kermit h. Which FTP should you use? c. 8-N-1 or 7-E-1 (data bits/parity/stop bits) d. Data Lenght e. Parity f. Stop Bits g. Hardware flow control (RTC/CTS - Xon/Xoff) h. Comm Port i. Terminal Emulation j. Initialisation String k. Dial Type (Tone or Pulse) IX. Configuring Popular Communications Software to Work with High-speed Modems 1. Procomm 2.0 2. Telix 3. Qmodem 4. HyperAccess 5 5. Crosstalk for Windows 6. MicroPhone II (for Macintosh) 7. White Knight (for Macintosh) 8. ZTerm (for Macintosh) 9. NComm (Amiga) X. Conclusions X.1. Contact Info X.2. Thanks ======================================================================= I. Introduction ---------------------- Buying and using a modem used to be relatively easy. Not so long ago, almost all modems were 2400-bps units and they were all compatible with the Hayes Smartmodems (although some were more Hayes-compatible than others). How time have changed. Today, modems not only run faster, they are also loaded with features like error control and data compression. Suddenly, you are confronted with all the buzzwords: V.32, V.32bis, V.42, V.42bis, MNP5, LAP-M, etc. What do they mean? And what do they mean to you? To make the most of a high-speed modem, you need to understand three different kinds of protocols and the relationships among them. They are the modulation protocols, error control protocols and data compression protocols. II. Modulation Protocols --------------------------------- Modem stands for MOdulator/DEModulator. A modem converts digital signals generated by the computer into analog signals which can be transmitted over a telephone line and transforms incoming analog signals into their digital equivalents. The specific techniques used to encode the digital bits into analog signals are called modulation protocols. The various modulation protocols define the exact methods of encoding and the data transfer speed. In fact, you cannot have a modem without modulation protocols. A modem typically supports more than one modulation protocols. The raw speed (the speed without data compression) of a modem is determined by the modulation protocols. High-speed modems are modems that feature modulation protocols at 9600 bps or higher. A 2400-bps modem with data compression that can theoretically yield a 9600-bps throughput is not a high-speed modem. "CCITT" is a French acronym for the International Telegraph and Telephone Consultative Committee. CCITT, a United Nations agency, is an international telecommunications standards committee that makes recommendations on a broad range of subjects concerning data communications. CCITT recently changed its name to ITU-T so both terms are used in this. II.0. Overview of Protocoles DUPLEX MODEM TRANSMISSION STANDARDS ITU APPROVED Bell 103 300bps USA standard. V.21 300bps. Bell 212A 1200bps USA standard. V.22 1200bps with fall back to 600bps V.23 1200bps with 75bps back channel, fall back to 600bps/75bps Used by Brazilian and European Videotext service. V.22bis 2400bps with fall back to V.22 V.32 9600bps with fall back to 4800bps V.32bis 14400bps with fall back to 12000bps, 9600bps, 7200bps and 4800bps V.34 28800bps. Approved 6/9/94. Previously called V.FAST. Includes: o "line probing", to test reliability of a connection. o 28800bps half-duplex transmission for FAXes. o fallback to existing V-series modems. o 200bps channel for modem control data. o Trellis coding to correct for line noise. o Handshaking with telephone network equipment. * HALF-DUPLEX MODEM TRANSMISION STANDARDS (USED FOR FAX): V.27ter 4800bps with fall back to 2400bps V.29 9600bps with fall back to 7200bps and 4800bps V.17 14400bps with fall back to 12000bps, 9600bps and 7200bps V.34 28800bps. PROPRIETARY TRANSMISSION PROTOCOLS: V.32terbo 19200bps, with fall back to 16800bps. Designed by AT&T, and is public domain, so any manufacturer can use this standard and put it into their modems. V.FC "V.Fast Class" 28800bps defacto industry standard, by Rockwell and Hayes. Not an ITU-T recommendation, despite the "V." prefix. Incompatible with V.34, but many modem vendors may offer dual-standard modems. Currently all modems that are v.FC are upgradable to v.34. HST 9600bps/14.4kbps/16.8kbps/21kbps/24kbps "High Speed Technology", US Robotics' proprietary full duplex protocol. USR puts out modems that use HST, modems that use V.32bis, and modems that support both standards, called "dual-standard". the back channel is only 75 or 300 bps, depending on the version of HST being used. PEP "Packetized Ensemble Protocol", Telebit's proprietary 9600bps half duplex error-correcting protocol. Reported to sustain noisy connections better than V.32. TurboPEP is an improvement, and can achieve 24000bps or more. Express 96 "Ping Pong Protocol", Hayes' proprietary 9600bps protocol. CSP "CompuCom Speed Protocol", CompuCom's proprietary 9600bps protocol. In 1992, the SpeedModem Champ was unique in that it was cheaper than V.32, but CompCom went out of business. II.1. 2400-bps Modems A 2400-bps Hayes-compatible modem typically supports the following modulation protocols: Bell 103 (300 bps U.S. Standard) Bell 212A (1200 bps U.S. Standard) CCITT V.22 (1200 bps standard outside the U.S.) CCITT V.22bis (2400 bps International Standard) Some 2400-bps modems also support the following protocols: CCITT V.21 (300 bps standard outside the U.S.) CCITT V.23 (1200/75 and 75/1200 bps, used in Europe) In the past, most 2400-bps modems did not support any error correction or data compression protocols. Recently, however, many modem manufacturers have introduced 2400-bps modems with extra features like data compression, error correction and fax capability. Most 2400 Fax capable modems can only send or receive faxes, not both, or only at 4800 or 9600. II.2. High-speed Modems There are four standard modulation protocols for high-speed modems: V.32, V.32bis, v32terbo and v.FC. v.32 and v.32bis are standards established by the CCITT. v32terbo is a defacto standard for 19.2k and v.FC (Sometimes incorrectly called v.FAST) is a defacto standard for 28.8k. II.2.a. V.32 This is the standard for 9600 (and 4800) bps modems. CCITT V.32 is adopted by the CCITT in 1984. But the market has not taken off until 1990. V.32 modems used to cost more than modems using proprietary modulation protocols (Hayes introduced the Smartmodem 9600, a V.32 modem, in 1988 with a $1999 price tag). But it is no longer true. Companies that make modems with proprietary modulation protocols are making modems with "dual standard." U.S. Robotics, Telebit, Hayes and CompuCom all have modems that support V.32 and their own proprietary protocols. V.32 is now just a fallback protocole for most people, as it has been replaced with v.32bis or 14.4k modems. Not many modem manufacturers continue to make v.32 modems anymore. This is because v.32bis modems cost the same to make and the difference in speed does not constitute a need for v.32. II.2.b. V.32bis V.32bis, established in early 1991, is the CCITT standard for 14400-bps modems. A V.32bis modem also can fall back to 12000, 9600, 7200 and 4800 bps. V.32bis is downwardly compatible with V.32. Like 2400-bps modems where a single modulation protocol (V.22bis) is supported by all modem makers. The same applies for v.32bis, but there are several proprietary(non-standard) modulation protocols used by modems from different manufacturers. Three notable examples are the U.S.Robotics HST, Telebit PEP and Zyxcel. II.2.c. v.FC The current standard for 28.8k modems. This is a defacto standard released by Rockwell (The chip maker). On paper this is far inferioir to v.34 but 1,000,000 modems are expected to be using this protocole by the end of 1994. All of these modems will be upgradable to v.34 the ITU approved 28,800 standard and it will hopefully only be a matter of time that they all are upgraded. The main reason that people won't upgrade to v.34 from v.FC is those modems brought outside the US. As some manufacturers say they won't upgrade a non-US modem, and the cost of getting to and from the US may mean people opt not to upgrade the modem, but luckily it is expected that in the v.34 modems a fallback to v.FC will be part of the chipset. On the market are basically 3 different designs of v.FC modems which have their own upgrade path and features; 1. USR Courier 28.8k modem seems to be the best of the bunch, with a promise FREE upgrade via FlashROM to v.34. The Courier 28.8k Modem is being called the v.everything modem because it is the only modem that does ALL the v.xxxxxx protocoles including v.32terbo which no other manufacturers offer in a 28.8k modem. 2. ROCKWELL Complete Solution Chipset modems, these include Zoom, Microcom ES, Boca and other cheaper brands of modems on the market. These modems are basically designed by rockwell, and made by the respective companies, the only one of these modems that I would recommend is the Microcom ES, as both the Zoom and Boca modems seem to be less reliable at both the hardware and software level. 3. ROCKWELL Datapump Custom Controller Code modems, the Microcom FAST is the only modem I know that is in this catagory, but I also believe that the PPI modems are also in this catagory. The Microcom FAST is the first modem I know of with a Parallel and Serial port interface and seem to be the most reliable Rockwell based modem. PPI's 28.8k modems have only just been released but PPI have a good reputation for quality modems. The DSI v.FCi 28.8k modem may also come into this catagory, but again it is difficult to get information. II.2.d. Other proprietary modulation protocols There are modems using other proprietary modulation protocols. For example, Motorola Codex (a subsidiary of Motorola Inc.) just announced the 326XFast Series of modems. Although you may see those modems referred to as "V.fast", they use a proprietary protocol. Two modems can establish a connection only when they share a common modulation protocol. To connect at high speed, two modems have to support the same high- speed modulation protocol. Therefore, a modem with a proprietary modulation protocol can only establish a high-speed connection with another modem from the same manufacturer. A U.S. Robotics HST modem can only establish a high- speed connection (at 9600 or 14400 bps) with another HST or an USR Dual Standard modem. A Courier HST modem cannot establish a high-speed connection with a Courier V.32bis modem. They can only connect at 2400 bps. (All high- speed modems in the market support the CCITT V.22bis modulation protocol). On the other hand, two V.32 modems can talk to each other at 9600 bps. They do not have to be from the same manufacturer. Two V.32bis modems can talk to each other at 14400 bps. A V.32 modem can talk to a V.32bis modem at 9600 bps. The new (1994) protocoles which everyone is talking about are v32terbo the AT&T standard for 19.2k Data transmission (which BTW is Public Domain) and v.FC which is Rockwell's own 28.8k standard. v32terbo modems seem to be selling well, but now you can pick up a v.FC modem for a little extra cash so sales of v.32terbo modems have dropped because of this. V.32terbo will never take a hold of the market because it was released not long before v.FC modems. v.FC modems that you can buy on the market today will be upgraded to the ITU-T (International) standard of v.34, which will be the international standard for 28,800 baud transmissions. Before buying a v.FC modem check how much the upgrade to v.34 will be! II.2.e. U.S. Robotics HST Until the recent surge of V.32bis modems, the U.S. Robotics HST (High Speed Technology) was the de facto standard in the PC-based BBS community. U.S. Robotics introduced the Courier HST modem in 1986 and pioneered the market for high-speed modems in the IBM PC environment. The immense popularity of the HST modems was partly due to the generous discount program U.S. Robotics offered to the BBS Sysops (SYStem OPerators). Many modem manufacturers have implemented similar Sysop discount programs, but most BBS sysops remain loyal to the U.S. Robotics modems. The original Courier HST modem ran at 9600 bps. U.S. Robotics later (in 1989) improved the speed of the Courier HST to 14400 bps. In March 1992, U.S. Robotics further enhanced HST to 16800 bps (which yields an effective throughput around 2000 cps with compressed files). Now USR HST can yield a throughput 21.6k. Although U.S. Robotics remains committed to the HST modems, no other manufacturer support it, and it is slowly being phased out. NOTE : The following Protocoles are included more for history than currently used protocoles. II.2.f. Telebit PEP and Turbo PEP Telebit introduced the TrailBlazer in 1985 that employed a proprietary modulation protocol called PEP (Packetized Ensemble Protocol). While the Courier HST is popular among BBS, Telebit modems dominate the UNIX UUCP and Usenet communities. The TrailBlazer Plus owes its success partly to its builtin support for the UUCP g-protocol, thus allowing efficient and flawless UUCP session. PEP also performs well even with noisy telephone lines. The actual throughput is around 14400 bps. The TrailBlazer Plus has an installed base of more than 120,000 units. Not only won't it drop connections easily, it also doesn't degrade in huge steps like other protocols do. With V.32bis, for example, if you're running at 14.4 kbps and the modems have to step down, they'll step down to 12 kbps or lower, for a loss of at least 15% throughput and with a several-second delay for retraining. PEP and TurboPEP drop down in increments of only a few percent, and don't take very long to do it, either. Telebit also introduced a cheaper (and slower) PEP modem, the T1000, in 1988. Like U.S. Robotics, Telebit announced Turbo PEP which has an effective data tranfer throughput of 2300 cps (with compressed files). The Telebit WorldBlazer is a dual-mode modem which supports both V.32bis and Turbo PEP. Telebit is very rare to come across now, as modem manufacturers realise the need to be compatible properietary protocoles are being phased out, the only 3 will probably stick around for another year or 2 and they are HST, v32terbo and v.FC. II.2.g. Hayes Express 96 Hayes entered the high-speed modem arena in 1987 with the introduction of the V-series Smartmodem 9600. The modem used a proprietary modulation protocol called Express 96 (also known as Hayes "Ping Pong" protocol). The V-series modems have not been as successful as the U.S. Robotics or the Telebit modems. II.2.h. CompuCom CSP While every modem manufacturer was jumping on the V.32 bandwagon, CompuCom bucked the trend and came out with the SpeedModem Champ in early 1991. It's a 9600 bps modem with a proprietary modulation protocol called CSP (CompuCom Speed Protocol). The SpeedModem Champ was the only modem with a proprietary protocol that costs less than a generic V.32 modem. (The internal SpeedModem Champ was priced at $169. An external version was $199.) Hundreds of PC-based bulletin board systems installed the SpeedModem Champ. The Champ also works as a Hayes-compatible 2400-bps modem with MNP2-MNP4 error control and MNP5 data compression. (Unfortunately, CompuCom went out of business around 1992.) ====================================================================== II.3. Things to come ----------------------- II.3.a v.34 This is the next protocole to be given the ITU-T approval, in the mail voting stage now (JULY '94) it should be release and in modems by the end of '94. This protocole will slowly replace the expected 1,000,000 v.FC modem base out there with upgrades and backward compatibility. II.3.b v.36 V.36 is already being talked about, rumours say it will be 31,250 which is really only a minor upgrade on 28.8k. ISDN (See later) will probably be the next big step up in speed. II.3.c. ISDN In a couple of years we may not need modems at all. Integrated Services Digital Network (ISDN) has been coming for years. When will ISDN really become available for the rest of us? It depends on your local telephone company. It is estimated that by the end of 1997 about half the telephone connections in the U.S. will has access to it. With ISDN, you won't need a modem since no modulation or demodulation will be necessary. You will need an ISDN adapter instead. Germany seems to be leading the upgrade to ISDN New Zealand has test sites many, but about 200 business's have ISDN lines. Two levels of ISDN are availible, the more expensive version having a greater bandwidth will not be covered here, as it is for companies with money to burn (after ripping us off ;)), the cheaper version is discussed below. An ISDN line carries three digital channels: two "B" channels that carry various kinds of data at 64,000 bps and a "D" channel at 16,000 bps that can carry control signals or serve as a third data channel. A single ISDN channel can transfer uncompressed data bidirectionally at 64,000 bps. Combine that with a data compression scheme and you will be able to transfer data at hundreds of kilobits per second. Eventually, ISDN will provide widely available, low-cost digital communications for voice and data communication. Until ISDN is firmly in place, high-speed modems will be with us for a while. [Ralph Peters wrote] I don't use ISDN myself. The advantages are the higher transmission rate (64Kbit) (~7000 CPS), the high connection speed (time until connect is very short). The disadvantages are the higher fix-price (ca. DM 80/month). With ISDN you have 2 Lines. With the standard analog lines, you pay DM 40 for every 2 lines (DM 30 for the first, DM 10 for the second line). So, analog lines are cheaper. ISDN is only economic if you have much data to transmit, or if you really need the higher speed. A additive disadvantage of ISDN is that you can't use the old (analog) phones. To you them, you need an A/D adapter for each phone, that cost DM 800(!) each. II.4. OTHER STANDARDS AND PROTOCOLES ---------------------------------------- V.25bis A command language for modems. V.54 Modem diagnostics standard, frequently included by V.32 modems. V.18 Interoperability for communications devices for the deaf. -ISDN is ISDN is the Integrated Services Digital Network. Which can offer a large number of new services over the analogue phone lines most of us are still using. -ISDN Basic Rate Interface (BRI) ; The wires carry two "B channels", each capable of 64kbps. There is also a 16kbps "D channel" normally used only for signalling. V.24: List of definitions for interchange circuits between data terminal equipment (DTE) and data circuit-terminating equipment (DCE) V.110: Support of data terminal equipments (DTEs) with V-series type interfaces by an integrated services digital network (ISDN) V.58 is, as pointed out by others, a CMIP managed object template for V Series DCEs (e.g. modems). It adopts a building block approach, with templates for DTE interface, datapump, line interface etc. to allow vendors to construct representations of the range of devices in the field. The reason for using CMIP rather than SNMP is down to the ITU .. being a telecommunications oriented body it tends to be very OSI oriented and CMIP is the ISO management protocol. There are plans in process to convert V.58 into three formats: (i) SNMP The V.58 MOT will be translated into an SNMP MIB to permit the same essential management functionality to be obtained using SNMP. (ii) DMTF The Desktop Management Task Force are looking at the management of things in and attached to workstations. There is work in process to convert V.58 to "MIF" format (the DMTF equivalent to a MIB). This would allow, for example, an SNMP manager on a LAN to send a message to a LAN attached workstation requesting information on the state of a modem attached to the workstation .. this would be converted within the workstation from an SNMP operation on a MIB to an operation on a MIF. There is obvious benefit if the MIB and MIF are identical in function. (iii) Extended AT command set (V.25ter) There is a substantial draft of the extended AT command set standard, now known as V.25ter. This uses the AT+ prefix as a lead in to a set of AT commands for modem config. The TIA committee agreed that the function of each AT+ command should be based closely on the V.58 definitions, hence allowing easy translation of CMIP / SNMP / DMTF operations into the equivalent AT command. III. Error Control Protocols ---------------------------------- Besides high-speed modulation protocols, all current models of high-speed modems also support error control and data compression protocols. III.1. V.42 and MNP4 There are two standards for error control (error-correcting, error correction) protocols: MNP 4 and V.42. The Microcom Networking Protocol, MNP, is developed by Microcom. MNP2 to MNP4 are error correction protocols. MNP5 is a data compression protocol. V.42 is established by CCITT. V.42 actually incorporates two error control schemes. V.42 uses LAP-M (Link Access Procedure for Modems) as the primary scheme and includes MNP4 as the alternate scheme. Therefore, a V.42 modem will be able to establish an error-controlled connection with a modem that only supports MNP 4. A modem that uses a proprietary modulation protocol may also use a non- standard error control protocol. For example, Hayes V-series Smartmodem 9600 supports an error control protocol called LAP-B. CompuCom's SpeedModem Champ also uses a non-standard error control protocol. III.2. V.42 & MNP4 can provide errorfree connections Modems without error control protocols, such as most 2400-bps Hayes-compatible modems, cannot provide error-free data communications. The noise and other phone line anomalies are beyond the capabilities of any standard modem to deliver error- free data. V.42 (and MNP 2-4) copes with the phone line impairments by filtering out the line noise and automatically retransmitting corrupted data. If you have used a standard Hayes-compatible modem, you probably notice some garbled characters (like "@8d_\nw`[ce") show up on your screen from time to time. When two modems establish an error-controlled connection, they are said to have a reliable link and are capable of filtering out those garbled characters caused by the line noise. Notice that the line noise is still there, it just does not show up on your screen or the screen on the remote system. The filtering process used by V.42 (and MNP 2-4) is similar to the error correction scheme used by file transfer protocols (such as Xmodem). The two modems use a sophisticated algorithm to make sure that the data received match with the data sent. If there is a discrepancy, the data is resent. What is the difference between error control protocols (such as V.42) and file transfer protocols (such as Xmodem)? For one thing, file transfer protocols provide error detection and correction only during file transfers. File transfer protocols do not provide any error control when you are reading e-mail messages or chatting with other people online. In other words, an error control protocol is "on" all the time during your online session and file transfer protocols are "on" only some of the times, namely when you are sending or receiving files. Even though an error control protocol is "on" all the time, we still need file transfer protocols when two modems establish a reliable link. A modem works with bit streams, timing and tones. It does not understand what a file is. When you download or upload a file, your communications software needs to take care of the details related to the file: the filename, file size, etc. This is handled by the file transfer protocol which does more than error-checking. Some file transfer protocols, most notably Ymodem-g and Imodem, are developed to handle file transfer without performing any error-checking. The idea of using a protocol like Ymodem-g is to eliminate the redundancy - thus improve the transfer speed. Ymodem-g and Imodem should only be used with modems that provide built-in error control protocols. These file transfer protocols do not provide any error-detection or recovery capability. If a problem occurs during the file transfer, the transfer session will be aborted. Protocols like Ymodem-g or Imodem depend on the modems to provide assurance for the integrity of data being transferred. However, you should know that a reliable link between two modems does not provide absolute guarantee for the data integrity during file transfer. When you call a remote computer, there are really three links involved in the process. Besides the link between the two modems, there are still one link between your computer and your modem and another link between the remote modem and the remote computer. When two modems make a reliable connection using V.42 or MNP 4, only the data integrity between the two modems is ensured. It is still possible for errors to occur at either end between the serial port and the modem (in the cable) or in the computer itself. (Fortunately, such errors are rare.) For extra protection, you may still want to use a file transfer protocol such as Zmodem which also performs error checking even if you have a reliable link with the remote system. There is a common misconception that Ymodem-g is much faster than other file transfer protocols. Although Ymodem-g is significantly faster than Ymodem, it offers little over Zmodem. Zmodem has proven to be extremely efficient. (See benchmark below) Filename Ymodem Ymodem-g Zmodem -------------------------------------------------------- the-wave.txt 1527 cps 3261 cps 3296 cps dayrpt.arc 761 cps 1042 cps 1025 cps dayrpt.wks 1244 cps 2314 cps 2337 cps sunset.arc 745 cps 987 cps 965 cps sunset.pic 1297 cps 2594 cps 2588 cps text109k.arc 814 cps 1089 cps 1064 cps text109k.txt 1351 cps 2812 cps 2885 cps Unless noted otherwise, the results are obtained by using the following: Computer: Mac SE with Mobius Two Page Display with 68030 accelerator Modem: ATI 9600etc/e (the modem is set as V.32 with V.42bis enabled) Operating System: System 7.0 Communication Software: ZTerm (Comm port set to 38400 bps) File Transfer Protocol: Zmodem All results are reported by ZTerm. (I use several communication programs on both IBM PC and Mac. All of them show the average throughput while file transfer is in progress, but ZTerm actually produces a report after the transfer is completed). III.3. V.42 & MNP4 can improve throughput The other benefit of V.42 (or MNP4) is that it can improve throughput. Before sending the data to a remote system, a modem with V.42 (or MNP 4) assembles the data into packets and during that process it is able to reduce the size of the data by stripping out the start and stop bits. A character typically takes up 1 start bit, 8 data bits and 1 stop bit for a total of 10 bits. When two modems establish a reliable link using V.42 or MNP 4, the sending modem strips the start and stop bits (which subtracts 20% of the data) and sends the data to the other end. The receiving modem then reinserts the start and stop bits and pass the data to the remote computer. Therefore, even without compressing the data you can expect to see as much as 1150 characters per second on a 9600 bps connection. (Although the modem subtracts 20% of the data, the speed increase is less than 20% due to the overhead incurred by the error control protocol.) Here are the test results obtained by downlaoding the same file (1) without any error control protocol, (2) with MNP4, and (3) with V.42. No data compression protocol is used. Filename No EC MNP4 V.42 -------------------------------------------------------- the-wave.txt 935 cps 1151 cps 1128 cps dayrpt.arc 863 cps 1023 cps 1002 cps dayrpt.wks 898 cps 1071 cps 1052 cps sunset.arc 838 cps 971 cps 953 cps sunset.pic 903 cps 1080 cps 1065 cps text109k.arc 908 cps 1085 cps 1064 cps text109k.txt 937 cps 1150 cps 1127 cps III.4. Other Error Correction Protocoles Two other companies have there own error control, AT&T have OLI or Optical Line Interface, which works connected to any other modem to reduce the amount of echo and in general the effects of line noise. ZyXell also have a similar error correction which also monitors the line quality and shifts the speed of the modem up or down. III.5. Are MNP4 and V.42 useful? Absolutely. Anyone that has ever used a standard modem can appreciate the benefit of an error-free connection. And the increase in data throughput, though modest, is nothing to sneeze at. IV. Data Compression Protocols ------------------------------------- Besides error control protocols, all current high-speed modems also support data compression protocols. That means the sending modem will compress the data on-the-fly and the receiving modem will decompress the data to its original form. IV.0. ERROR CORRECTION & DATA COMPRESSION STANDARDS V.42 Error correction with asynchronous to synchronous conversion. Includes MNP-1 through MNP-4 and LAP M. V.42bis Data compression. The rhetoric claims you can get compression up to 4:1, but it is more typical to get 2:1 or maybe 5:2. V.42bis always uses V.42 error correction. You may get a greater data copression ratio, it all depends on how well the data can be compressed. MNP "Microcom Network Protocols" MNP1 Asynchronous, half duplex transfer. MNP2 Error correction, asynchronous, full duplex. MNP3 Error correction, synchronous. Not a big win over MNP2 about 20%. MNP4 Error correction, better throughput than MNP2-3. a modification which rides on top of MNP2 or 3 to improve throughput. MNP5 Simple data compression, about 2:1. MNP6 Statistical duplexing and Universal Link Negotiation. With V.29, modems can emulate full duplex operation. Also supports fall-forward operation between two MNP modems. MNP7 Data compression, about 3:1. MNP8 MNP7 for pseudo-duplex modems. MNP9 Data compression, about 3:1. Includes V.32 technology. (?) MNP10 Dynamic fall-back and fall-forward adjusts modulation speed with link quality. Intended for use for cellular, but doesn't work too well for cellular transmissions! LAPM "Link Access Protocol for Modems". BTLZ (British Telecom Lempel-Ziv) is a nickname for V.42bis. When buying a high speed modem, you should find that it does MNP 2-5, v.42 and v.42bis. Only when buying older modem may you find it doesn't support all the above standards. IV.1. MNP5 and V.42bis There are two major standards for data compression protocols, MNP5 and CCITT V.42bis. Some modems also use proprietary data compression protocols. A modem cannot support data compression without utilizing an error control protocol, although it is possible to have a modem that only supports an error control protocol but not any data compression protocol. A MNP5 modem requires MNP 4 error control protocol and a V.42bis modem requires V.42 error control protocol. Also note that although V.42 include MNP4, V.42bis does not include MNP5. However, virtually all high-speed modems that support CCITT V.42bis also incorporate MNP5. The standard compression ratio that a MNP5 modem can achieve is 2:1. That is to say, a 9600 bps MNP5 modem can transfer data up to 19200 bps. Some data however can be compressed 4:1 or higher with MNP 5, as with a V.42bis modem is 4:1 but if the data is easily compressed it may be as high as 10:1. That is why all those V.32 modem manufacturers claim that their modems provide throughput up to 38400 bps. **IMPORTANT** There are some modems advertised as having MNP5 and/or v.42bis but are not the real macoy, thats probably why they are so cheap. These modems do not have MNP5 implemented in the modems themselves, but rather depend on the communications software (e.g. Bitcom Deluxe) to do the tricks. Besides being slower than the real MNP5 modems, these modems will not provide an error-free connection unless you use the accompanying software. If you buy one of these modems and decide to use your own software (e.g. Procomm Plus), you have to treat the modem as a plain vanilla 2400-bps modem. IV.2. Are MNP5 and V.42bis useful? Don't be fooled by the claim. It is extremely rare, if ever, that you will be able to transfer files at 38400 bps. In fact, V.42bis and MNP5 are not very useful when you are downloading files from online services. Why? How well the modem compression works depends on what kind of files are being transferred. In general, you will be able to achieve twice the speed for transferring a standard text file (like the one you are reading right now). Decreasing by 50% means that you can double the throughput on the line so that a 9600 bps modem can effectively transmit 19200 bps. However, V.42bis and MNP5 modem cannot compress a file which is already compressed by software. In the case of MNP5, it will even try to compress a precompressed file and actually expand it, thus slow down the file transfer! Here are the test results obtained by downloading the three compressed files using (1) MNP4 without data compression, (2) MNP5, (3) V.42 without data compression, and (4) V.42bis. Filename MNP4 MNP5 V.42 V.42bis ---------------------------------------------------------------- dayrpt.arc 1023 cps 946 cps 1002 cps 1010 cps sunset.arc 971 cps 935 cps 953 cps 950 cps text109k.arc 1085 cps 988 cps 1064 cps 1053 cps If you have ever downloaded files from a BBS or online service, you know that almost all files are in a compressed format. Therefore, you should only expect to see an actual throughput between 950 to 1100 cps even if your V.32/V.42bis modem is supposed to offer throughput "up to" 38400 bps. Most PC files are in the ZIP format. Macintosh files are typically in the .SIT (Stuffit) or .CPT (Compact Pro) format. Amiga files are usually in the Lha and DMS format. Note that GIF files are also in a compressed format. IV.3. Compression Software vs. MNP5/V.42bis There are several reasons why compression software programs (such as PKZIP or Stuffit) are superior to MNP5 or V.42bis. 1. Compressed files save disk storage space. 2. Compression software programs are more versatile. Most of them allow you to group several files in a compressed file archive to ensure that all the related files get transferred at the same time. 3. Software compression is more efficient than on-the-fly modem compression. In the case of a small file, this may not make much difference. But the difference can be significant when you are transferring large files. Filename Size Time Throughput ---------------------------------------------------------- the-wave.txt 143579 bytes 43 seconds 3296 cps dayrpt.arc 8423 bytes 8 seconds 1010 cps dayrpt.wks 19712 bytes 8 seconds 2337 cps sunset.arc 5084 bytes 5 seconds 950 cps sunset.pic 16391 bytes 6 seconds 2643 cps text109k.arc 29775 bytes 28 seconds 1053 cps text109k.txt 111386 bytes 39 seconds 2822 cps As we can see from the test results, it is about 30% faster to transfer the compressed file text109k.arc than to download the text file with V.42bis. Hayes BBS does not provide a compressed version for the file the-wave.txt. Using PKZIP (for PC) and Stuffit (for Macintosh), we obtain the following results: the-wave.zip: 6812 bytes (PKZIP) the-wave.sit: 6081 bytes (Stuffit) Assuming a transfer speed of 1000 cps, the compressed file can be downloaded in 7 seconds. That's six times faster than downloading the text file with V.42bis! Here is another example. One of my local BBS has a Macintosh TIFF file (206,432 bytes) which can be downloaded in 56 seconds (with an effective throughput of 3745cps) with a V.32/V.42bis modem. The result may seem impressive at first. However, the file can be compressed to 6065 bytes (with Compact Pro) or 7385 bytes (with Stuffit). Assuming a transfer speed of 1000 cps, it would only take 6-8 seconds to transfer. Again, it is seven to nine times faster than downloading the file with V.42bis. On-the-fly modem compression does have one advantage. It is more convenient. You can send a file without compressing it first and the recipient does not need to decompress the file. IV.4. Local Flow Control and Data Buffering To get the most from a modem with data compression, you'll want to send data from your PC to the modem as quickly as possible. If the modem is idle and waiting for the computer to send data, you are not getting the maximum performance from the modem. For example, you have a V.32/V.42bis modem and you want to send a text file to a remote system which also has a V.32/V.42bis modem. Let's assume the modem is able to send the file at 20000 bps using V.42bis. If your computer is sending data to your modem at 9600 bps, your modem will have to stop and wait to receive data from your computer. To get the maximum performance, you want to set the computer to send data to the modem at 38400 bps (the maximum a V.32/V.42bis modem can achieve). Since the modem can only send the file to the other modem at 20000 bps, it will never have to wait. Here are the test results for downloading the text file thewave.txt by setting the communication port at different speeds (usually referred to as "DTE speed"): the-wave.txt: 946 cps (modem port speed 9600 bps) 1885 cps (modem port speed 19200 bps) 3296 cps (modem port speed 38400 bps) However, there is a new problem. Since your computer is sending data faster than the modem can handle, there needs to be some ways for the modem to ask the computer to stop sending data. Otherwise, data loss is sure to occur. This is where local flow control comes into play. A high-speed modem typically supports two kinds of local flow control: hardware handshaking (CTS/RTS) and software handshaking (XON/XOFF). Of the two, hardware flow control is the preferred method. We have mentioned earlier that there are three links involved when you are connected to a remote system: 1. The link between your computer and your modem 2. The link between the modems 3. The link between the remote modem and the remote computer Local flow control is used for the first and third links. Notice that the first link need not use the same kind of flow control as the third link. Hardware flow control (or hardware handshaking) works by altering voltage levels on the RTS (Request To Send) and CTS (Clear To Send) signal lines at the RS232 serial interface between the modem and the computer. **NOTE** : Both your computer software and your modem settings MUST be the same, either both RTS/CTS or Xon/Xoff. CTS is used by the modem on the sending end of a transmission. When the local modem is ready to receive data, it sends the CTS signal to the local computer and the computer starts transferring data. If the modem is unable to accept the data as fast as it is received from the computer, the modem will disable the CTS to inform the computer that the modem buffer is almost full (A high- speed modem typically contains a small amount of RAM which is used to provide data buffers). The computer will then suspend data transfer. Once the local modem has emptied its buffer by transmitting data to the remote modem, it will enable CTS again. RTS is used by the computer on the receiving end of a transmission. When the computer cannot accept data at the rate at which the modem is passing data, it will disable RTS. The computer enables RTS again when it is ready to resume receiving data from the modem. Software flow control (or software handshaking) is achieved by embedding control character in the data stream. XON and XOFF are the most commonly used control characters. XON is also known as ControlQ or DC3 (ASCII 19) while XOFF is known as ControlS or DC1 (ASCII 17). The use of XON and XOFF during data transfer can create problems when a binary file contain the ControlS (^S) character as a legitimate part of the data. Do not use this method if ^S and ^Q are part of the transmitted data. IV.5. Macintosh & High-speed Modems If you use a Macintosh with a high-speed modem, you will need a special modem cable that is wired correctly to support hardware handshaking. You can order the cable from most mailorder companies that sell high-speed modems. Unfortunately, the cable did not work with my SE. The cable is good since it worked fine on a Mac IIsi. It just refused to work on my SE. I was disappointed but not surprised. After all, my SE is equipped with a 25 Mhz 68030 accelerator. (Well, it is actually both an accelerator and a video adapter for a 19 inch dualpage monitor.) Since I will never want to run my SE without the accelerator, I have no choice but to use software handshaking. IV.6. PC & UART Your PC's serial port has a UART (Universal Asynchronous Receiver/Transmitter) chip to control the input/output. The XT usually has an 8250 UART, the AT usually has a 16450 UART. If you are running Windows, Desqview, OS/2 or any other multitasking environment, you should upgrade your UART with the 16550 (if your PC does not already have one). The 16550 is standard in most IBM PS/2 and many 386/486 or higher based computers. The 16550 UART has a 16 bytes FIFO (first in, first out) buffer that helps to prevent degradation when several programs are running at the same time. If you use an external modem, the UART is in your computer (either on the motherboard or on an I/O card that has the serial port). If you use an internal modem, the UART is on the modem. Most internal modems say they have 16650 UART Emulation, which is the same thing as the real UART but made by another company. When buying your computer, it would be a good idea to check which UART the computer has, as many manufacturers only put in the cheaper 8250 UART and not the 16550 UART. As most people reading this have a computer already you will find many diagnostic programs around which can tell you with reasonable accuracy which UART you have. IV.7. Amiga and High Speed Modems The Amiga computers serial port is locked to a maximum speed of 31,250 which allows for very little data compression. For the Amiga 2000,3000,4000 computers serial cards can be purchased which will allow upto 115,000baud rates. Most comms programmes support the higher speeds for this reason. 31250 is fine for speeds of 14.4k or less (Works fine for faster speeds but not at the optimum level), but for faster modems I would recommend a serial card to allow faster transfer rates. V. Cellular Protocoles ---------------------------- On the market currently are 4 contenders for the growing cellular transmissions Microcom's MNP 10, AT&T's ETC (Enhanced Throughput Cellular), USR's HST and ZyXell's Zycellular. I read recently in a post on internet that all four were put to lab tests to see howthey ranked. It quickly became apparent that MNP 10 was not suitable and pulled from the competition, the other 3 all worked fine. V.1 AT&T ETC Allows upto 14.4k data transmission. I do not have any further information on this. V.2 USR HST This protocole allows upto 16.8k data transmission I believe. V.3 ZyCellular ZyXEL's ZyCellular incorporates a proprietary technology that is used to strengthen the physical layer of the transmission, in order to handle the most common impairments encountered in cellular networks. It will automatically determine the best operating speed, given the adverse line conditions that exist in the cellular environment even after a connection is made. With V.42 error control and selective reject error control. Hand-off - Hand-off occurs when the communication frequency changes and the channel is interrutted ( when the cell station in communication is switching from one cell to another) for 0.2 to 1.2 seconds. A regular modem would respond with retrain or may even lose carrier. But ZyCellular modems perform fast synchronization with the remote modem immediately after the cell detects the hand-off. This results in smooth hand-off, without losing connection. Power Level Change - As you move towards or away from each cell site station the power level will fluctuate. The cellular unit's transmit power will be instructed to change by the cell site station. With each power level change, the channel is interrupted for about 0.2 seconds. ZyCellular modem responds to the interruption, with fast resynchronization as in the case of hand-off, allowing greater efficiencies in data transmission. V.4 MNP 10 Did not perform well enough to be compared to the others, cps rates reported to be around 240 if lucky. Changes in the cellular network occur very quickly. A protocol such as MNP10 is not as effective because it must receive several error blocks before any corrective action is taken. By the time a MNP10 modem reacts, the error condition may have already disappeared. VI. About Fax Modems ------------------------------ Since fax machines are essential business tools today, it has become a trend for modem vendors to add fax capability to their products. A fax machine is made up of a scanner, printer and fax modem. The sending fax machine scans a sheet of paper and convert its image into a code for transmission over the telephone line. The receiving machine reconverts the codes and prints a facsimile of the original. (However, some fax modems can send and receive fax, while others can only send but not receive fax.) VI.1. Protocols Here are some terms you'll need to know about fax modems: CAS IBM and DCA standard for computer-faxmodem interface. Class 1 Electronic Industries Association/Telecommunications Industry Association standard for minimal computer-faxmodem interface. EIA-578 Class 2 EIA/TIA standard for extended computer-faxmodem interface. EIA-592 specifies Class 2.0 "Class 2" is a non-standard based on an obsolete draft. Group 3 Fax protocol. 14400bps. 203x98dpi/203x196dpi. Compression. Group 4 ISDN Fax protocol. When buying, most Faxmodems are Group 3 Class 1 (IBM PC mdoems) or Class 2 (Amiga). It does not matter what class fax is sent, but you must have software that supports the class fax you are using. If software is packaged with a modem, then it will work with the modem. VI.1.a. Group 3 Group 3 is the international standard for communication between two fax devices (fax machines or fax boards). Fax machines have evolved over the past 20 years. Groups 1 and 2 fax machines transmit a single page at six and three minutes respectively and were used throughout the 1970s. Group 3 transmits one page in as little as 20 seconds (at 9600 bps). Group 3 resolution is 203x98 dpi in standard mode and 203x196 dpi in fine mode. Virtually all fax machines sold in the market today are Group 3 units. VI.1.b. V.27ter V.27ter is the modulation scheme used in Group 3 Facsimile for image transfer at 2400 and 4800 bps. VI.1.c. V.29 V.29 is the modulation scheme used in Group 3 Facsimile for image transfer over dial-up lines at 9600 and 7200 bps. VI.1.d. V.17 V.17 is a new CCITT standard. It's the modulation technique for use in extended Group 3 Facsimile that allows 12000- and 14400-bps fax transmission. VI.1.e. CAS CAS (Communications Application Specification) is a communications protocol developed by Intel and DCA (the software company know for Crosstalk) for a combination fax and modem board that allows personal computer users to exchange data more easily with fax machines. CAS was introduced in 1988. It has been supported in many applications software (e.g. WordPerfect). VI.1.f. Class 1 & Class 2 In the past, no standard existed for a microcomputer to deal with a fax board. As a result, the software for a particular fax board won't work with another fax board from a different manufacturer. (Although CAS has been moderately successfully, it hasn't become the industry standard.) The Electronic Industries Association/Telecommunications Industry Association (EIA/TIA) has been developing new standards (Class 1 & Class 2) for microcomputers to communicate with fax modems. As a result, you can buy a software program that will work with Class 1 (or Class 2) fax modems from different manufacturers. The Class 1 standard provides minimal hardware support for sending a fax from a microcomputer, while Class 2 adds over 40 AT-command set instructions and places more functionality into the modem. Most "Class 2" fax modems in the market today are based an obsolete draft. (It has become epidemic for computer vendors to announce products that are supposed to meet a standard while the standard doesn't even exist yet.) VI.2. How useful is a fax modem? A fax modem may not be as useful as you'd think. Fax modems are good for sending, but not receiving fax. You may still need (or want) a fax machine even if you have a fax modem. Fax machines are easy to use. Fax modems are a little more difficult. Anyone that knows how to use a phone can learn to use a fax machine within a few minutes. A fax machine will work no matter what kind of computer you have. It also doesn't matter what operating system or environment you are running on your computer. Fax software is now very good, recieving or sending faxs is a relatively simple process on most computers. The main problem is that the fax sometimes has to be printed out, which on a dop matrix is not a quick process. If you need to fax a printed document, you'll need to have a scanner to get it into your computer. To print out a fax received by your fax modem, you'd need a printer. Also, your computer needs to be on to receive fax. The other problem that may occur is a recieved fax can be sideways, not all software applications can cater for this, especially if you want to type in something on the fax and then resend it. Small business's may get away with a faxmodem by using a local paper sop to send some faxes but otherwise the fax option is more of a toy than anything. However, there are several advantages for using a fax modem (if you can live with its shortcomings): 1. You won't have a paper jam if you're faxing a multi-page document. 2. The software for fax boards are more flexible and versatile. A fax board can be a life-saver if you regularly fax the same document to several people. 3. You don't have to print out the document you want to fax if it's generated with your computer. And the quality is better. It's worth noting that many documents that are faxed should be sent by e-mail. (A high-tech employment agency recently asked me to fax my resume and then had it re-typed into the computer. I suggested that I sent the resume by e-mail, but they didn't use e-mail.) VII. Buying a High-speed Modem -------------------------------------- V.32bis and v.FC modems are clearly the standards of high-speed modems today. But with changing times and standards it is difficult to decide which to buy, especially as cheap 28.8k modems as not much more than expensive 14.4k modems. VII.1. Should you pay extra for a V.FC Modem? That really depends on what you need that extra speed for and whether you will be able to use it. As more and more BBS's upgrade to v.FC it becomes more and more a good move. Commercial BBS's are dragging there legs behind them waiting for the ITU-T to approve v.34. So if you mainly use these types of BBS's then it may be better to wait. But what will happen to modem prices when v.34 is released, some speculate that prices for v.34 modems will be higher, someone has to pay for ITU-T. But as upgrades for v.FC modems to v.34 range from $0 to $300 (US) one has to wonder which is the cheapest in the long run. Will you get you money's worth out of a 14.4k modem?? For mail and causal downloading these modems are great, but if your a major downloader then the extra expense may be justified, especially over long distance calls. It really is your decision, can you afford a decent 28.8k modem?, because as discussed in the conclusions, you pay for what you get. Or would you be better of with a decent 14.4k modem and saving the rest of the money for a faster modem next year or the year after? VII.2. Should you buy a modem with a proprietary protocol? It is generally not a good idea to purchase a modem which only supports a proprietary modulation protocol. You should consider getting a modem that supports dual modulation protocols (USR Courier Dual Standard, Telebit WorldBlazer, Hayes Ultra) if (i) you have to connect to a modem that uses a proprietary modulation protocol, or (ii) you need to have better throughput than a V.32bis modem can offer. The only proprietary modems that you should buy are those which are v.FC or if they have a cellular protocole that you wish to use. But remember if you buy a proprietary modem that you need the same type of modem on the other end to use the protocole. e.g. AT&T Dataport with ETC at the office and an AT&T PCMCIA Faxmodem in the Laptop somewhere on the planet. A lot of BBS's still use USR's HST standard, most of them however use Dual standard modems which mean a v.32bis/v.FC modem will still connect at 14.4k or higher. You should know already if you need a proprietary protocole, if you don't know, then chances are you don't need it. VII.3. Should you buy a 2400-bps modem? If you are thinking of purchasing a 2400 bps modem even with V.42bis or MNP 4 data compression, think again. We have mentioned earlier that V.42bis and MNP5 are nearly useless for downloading compressed files. There is one more reason why a 2400 bps with V.42bis is generally not useful when you are calling commercial online services or BBS. Online services and BBS usually have separate phone numbers for 2400-bps and high-speed modems. Most of them do not support V.42bis or MNP 5 on their 2400-bps lines. Also the biggest factor is, 2400 baud modems are very quickly becoming paper wieghts because they are very slow, especially if you look at the average size of a file to download now-a-days, 15meg files are not uncommon, at 2400 baud that = approx 17hours to download!! VII.4. Standards You Can Count On In Modems Current V.32bis modems support MNP 2-5 and V.42/V.42bis, and Group 3 Class 1 or 2 Fax. Also most v.32bis modems support 57600bps thoughput from the computer to the modem. At v.FC or 28.8k, the modem is basically the exact same as a v.32bis modem except it will be able to handle 115k bps thoughput and v.FC protocole. 2400 baud modems usually come with either send or Recieve Fax, some come with both, Don't buy a 2400 baud modem for fax capabilities. These modem are ok for mail, and small files, bt as BBS's start locking 2400 baud users off, you may find you'll have to buy another modem. A number of commercial BBS's charge more for 2400 users, especially if transfering files. VII.5. PCMCIA / Pocket or Normal Modems A number of different sizes of modems are on the market, and the price tends to get higher the smaller you get. Which modem is suitabe for you will depend on what you need the modem for, and what you WILL need the modem for in the future. PCMCIA card modems are for laptops, and shouldn't be use for any other sort of computer (unless you rich, and want the smallest and your computer can handle it). These modems are about the size of 4-6 credit cards stacked ontop of each other, which slot into most laptops, and some PDA's and various other small "desktop" diaries etc. The advantage of these are they use little power, and can be connected to a wall socket, or a cell phone (additional fittings may be needed depending on country and cell phone). POCKET modems aren't usually too much more expensive than the larger counterparts nowdays, but they use to be much more expensive. Pocket sized modems are just that, they should fit into the average sized pocket and be portable. But not only that, a true pocket modem will run off a battery as well as mains power, as these modems were made small for use with laptops. NORMAL modems, are your standard desktop modems. They basically come in two main types, like computers Tower or Desktop. The difference is preference, the tower takes up a less desk room, but more standing room. VII.6. Internal or External? This is a big question among a lot of people, why should I buy an external modem when the internal is cheaper. Talk to different people you will get different opinions based on THIER experience. I will briefy go over the advantages of both ; External Advantages ; 1. Easy to move to another computer 2. LED's and/or LCD's tell you what the modem is doing, so you do not have to relie on the software to tell you. 3. On/Off switch to drop carry quickly (Some BBS's may crash or freeze on you, and its quicker and easier than ATH) 4. Usually easier to set up than an internal 5. Compatible with almost all computers, some internals are only usable with IBM clones. Internal Advantages 1. Cheaper than externals 2. Includes a suitable UART VIII. Setting Up Software To Work With High Speed Modems -------------------------------------------------------------- Getting a high-speed modem is only half the battle. You will need to get it to work with your communications program. Most communications programs still come with settings configured for standard 2400-bps modems. All modems come with default settings preconfigured from the factory. Many V.32bis high-speed modems are preset to use V.42bis and hardware flow control when they are turned on. This optimal configuration enables the modem to automatically negotiate a connection with either another V.32 modem supporting V.42bis or MNP protocols (or even a standard modem). There is another change required. And it has to do with the parameters controlling how the modem deals with two of the RS232 signals: DTR (Data Terminal Ready) and CD (Carrier Detect). CD is a signal generated by the modem which is used to indicate its connection status. DTR is a signal generated by your computer. DTR is used to enable the modem to accept commands from your communications program, it is also used by most modems to determine when to disconnect a call. Most communications software programs expect the modem to follow DTR and expects CD to follow carrier. "&C1&D2" sets the parameters for the modem to handle the DTR and CD signals as expected by most communications programs. (However, if you use a Mac, you should use "&C1&D0".) VIII.1.a Speed Setting The main thing that you should have to change is the the baud rate depending on your modem speed. MODEM SPEED | Software Speed | ================================= 2400 | 2400 | 9600 | 19200 | 14400 | 19200/38400/57600 | * 19200 | As Above or 76000 | * 28800 | As Above or 115000| * ================================= * Set to the speed that you computer can handle ; Amiga 1000,500,600 19200 Amiga 1200,2000,3000,4000 38400 IBM's Pre-386 38400 or 19200 if you get errors etc IBM's Rest 38400 or Above Mac's VIII.1.b. File Protocole You will need to decide on a file transfer protocole, usually software comes with the most popular for use with general BBS's and commercial ones like Compuserve. Most BBS's support ZModem, which has the advantage of being able to resume the download/upload if you get disconnected and also has further error correction. Some software does not support this protocole and you may need to select YModem or XModem. VIII.1.b.a. -ASCII This is designed to work with ASCII text files only. Notice that you do not have to use this protocol when transferring text files. The ASCII protocol is useful for uploading a text file when you are composing e-mail online. VIII.1.b.b. -Xmodem Xmodem use to be one of the most widely used file transfer protocols. The original Xmodem protocol uses 128-byte packets and a simple "checksum" method of error detection. A later enhancement, XmodemCRC, uses a more secure Cyclic Redundancy Check (CRC) method for error detection. Xmodem protocol always attempts to use CRC first. If the sender does not acknowledge the requests for CRC, the receiver shifts to the checksum mode and continues its request for transmission. VIII.1.b.c. -Xmodem-1K Xmodem-1K is essentially Xmodem CRC with 1K (1024 byte) packets. On some systems and bulletin boards it may also be referred to as Ymodem. Some communication software programs, most notably Procomm Plus 1.x, also list Xmodem-1K as Ymodem. Procomm Plus 2.0 no longer refers to Xmodem-1K as Ymodem. VIII.1.b.d. -Ymodem Ymodem is essentially Xmodem-1K that allows multiple batch file transfer. On some systems it is listed as Ymodem Batch. VIII.1.b.e. -Ymodem-g Ymodem-g is a variant of Ymodem. It is designed to be used with modems that support error control. This protocol does not provide software error correction or recovery, but expects the modem to provide the service. It is a streaming protocol that sends and receives 1K packets in a continuous stream until instructed to stop. It does not wait for positive acknowledgement after each block is sent, but rather sends blocks in rapid succession. If any block is unsuccessfully transferred, the entire transfer is canceled. VIII.1.b.f. -Zmodem This is generally the best protocol to use if the electronic service you are calling supports it. Zmodem has two significant features: it is extremely efficient and it provides crash recovery. Like Ymodem-g, Zmodem does not wait for positive acknowledgement after each block is sent, but rather sends blocks in rapid succession. If a Zmodem transfer is canceled or interrupted for any reason, the transfer can be resurrected later and the previously transferred information need not be resent. VIII.1.b.g. -Kermit Kermit was developed at Columbia University. It was designed to facilitate the exchange of data among very different types of computers (mainly minicomputers and mainframes). You probably will not need to use Kermit unless you are calling a minicomputer or mainframe at an educational institution. VIII.1.b.h. Which file transfer protocol should you use? In general, I recommend Zmodem. If Zmodem is not supported by the system you are calling, use Ymodem-g. (If you are connecting to a UNIX system in a university, you may have to use Kermit or Xmodem to transfer files.) Compuserve prefers Compuserve-B. Here are the test results obtained by downloading the files using various file transfer protocols. The number before the parentheses is the transfer speed (in cps) and the number in the parentheses is the time elapsed (in seconds). Filename Xmodem Xmodem1K Ymodem Ymodem-g Zmodem ------------------------------------------------------------------------- the-wave.txt 429(334) 1508(95) 1527(94) 3261(44) 3296(43) dayrpt.arc 314(26) 758(11) 761(11) 1042(8) 1025(8) dayrpt.wks 415(47) 1252(15) 1244(15) 2314(8) 2337(8) sunset.arc 337(15) 771(6) 745(6) 987(5) 965(5) sunset.pic 399(41) 1337(12) 1297(12) 2594(6) 2588(6) text109k.arc 343(86) 817(36) 814(36) 1089(27) 1064(27) text109k.txt 410(271) 1379(80) 1351(82) 2812(39) 2885(38) ======================================================================= Duplex ------------ You will need to set the duplex option to Full Duplex for normal use with BBS's. If you are going to connect with a friend, Half Duplex is the norm. Data Lenght --------------- In general, set the parameters to 8-N-1. If you are calling a commercial online service (such as GEnie), you may need to set the parameters to 7-E-1. Set this to 8 bits, unless you are connecting to Compuserve, in which case 7 bits. You can usually tell that the Data Lenght is incorrectly set by garbage appearing on the screen usually going diagonally across the screen. Parity ------------ Set this to NONE for use with normal BSB's. Compuserve again is different and you need to set it to even. Stop Bits ----------- Set to 1 CTS/RTS or Xon/Xoff ------------------------ I recommend CTS/RTS for all modems, especially above 2400baud. Xon/Xoff is not as quick and reliable as CTS/RTS, and usually the modem configuration has to be changed especially at high speeds. Xon/ Xoff may interfer with binary file transfers, where-as CTS/RTS won't. Comm Port -------------- For your computer to talk to your modem, you need to tell the software where to find the modem. If you use a PC with an external modem, you need to specify which serial port the modem is connected to. If you have an internal modem, you need to configure the modem and tell the software which COM port the modem is configured for. Comm 2 or higher is usually used for modems, depending on other hardware connected like mice. If you use a Macintosh, specify whether your modem is connected to the modem port. Consult your manuals. Terminal Emulation -------------------- If you are using an IBM compatible, choose IBM PC or ANSI. Otherwise, try VT102, VT100, VT52, TTY. Unix sites and some BBS systems use VT100, ANSI is the emulation you want to use for "colourful" BBS's, most none commercial BBS's support ANSI, which allows animations and colour. Initialisation String ----------------------- This is possibly one of the most frustrating and difficult things to set up, most modems will work fine with the factory defaults so this should only be ATZ, which means load configuration in memory. If you have to make changes to the factory defaults then you need to save them to memory with a AT&W command, then when the modem is turned on, and the software says ATZ, those settings will be loaded. Some people need a couple of different settings for different computers etc, you can put in your commands in the Init String so the modem configuration is changed from the settings in its memory when that software is loaded. Consult your manuals for further information on settings as they vary from modem to modem. Your manual will tell you if more than 1 factory default is availible and what settings they are, for example the AT&T has 3 factory defaults, at&f1 (standard BBS's etc), at&f2 (slightly different), and at&f5 (cellular settings). Some things I change ; S11=50 Speeds up the dial rate S0=0 Stops the modem answering an imcoming call L3 Turns the modem volume up (L1 down) Dial Type ------------ Set this to your local dial type, tone or pulse, most countries in the Western world are Tone, which is dit diit dit dit, pulse dialing is when you can here the phone "tapping" the number out. If in doubt, try one then the other. Dial String: ATDT xxxx where xxxx is the number you want to dial, and ATDT means dial TONE. If you have to dial the digit 9 to obtain an outside line, Use ATDT9,<>. The comma (,) instructs the modem to pause two seconds. This allows enough time for the dial tone to occur before the modem dials. You can use as many commas as you like. If you have an option for "Locked Rate" use it, especially at when using a high speed modem. IX. Configuring Popular Communications Software ------------------------------------------------------- Below are brief instructions for configuring some popular communications programs to work with a high-speed modem. The particular initialization string is for the ATI 9600etc/e modem. It is assumed that the appropriate initialization string to use is "AT&F2&C1&D2S7=60" if you are using a PC. (Use "AT&F2&C1&D0S7=60" if you have a Macintosh.) Make sure you save the changes you make. IX.1. Procomm Plus 2.0 To change the modem initialization string: (Global, i.e. it works with every dialing entry) 1. Load Procomm, press Alt-S 2. Select Modem Options 3. Select Modem Commands 4. Press A 5. Change the initialization string to AT&F2&C1&D2S7=60^M To set the software to wait 60 seconds for connection: (Global) 1. Load Procomm, press Alt-S 2. Select Modem Options 3. Select General Options 4. Press A 5. Type 60 and press Return To enable hardware flow control: (Global) 1. Load Procomm, press Alt-S 2. Select Terminal Options 3. Press D (hardware flow control) 4. Press Space Bar to toggle, press Return to accept 5. Press C (software flow control) 6. Press Space Bar to toggle, press Return to accept IX.2. Telix To change the modem initialization string: (Global) 1. Press Alt-O 2. Select Modem and dialing 3. Select A (Init String) 4. Change the initialization string to ATZ^M~~~AT&F2&C1&D2S7=60^M To set the software to wait 60 seconds for connection: (Global) 1. Press Alt-O 2. Select Modem and dialing 3. Select K (Dial time) and enter 60 press Return To enable hardware flow control (Global) 1. Press Alt-O 2. Select Terminal options 3. Press J (XON/XOFF software flow control) 4. Select Off 5. Select K (CTS/RTS hardware flow control) 6. Select On 7. Press ESC to exit IX.3. Qmodem To change the modem initialization string: (Global) 1. Press Alt-N 2. Press M to select Modem menu 3. Select Modem Commands 4. Press Return 5. Change the initialization string to AT&F2&C1&D2S7=60^M To set the software to wait 60 seconds for connection: (Global) 1. Press Alt-N 2. Press M to select Modem menu and Press Return to select Communication Parameters 3. Press H to select Timeout delay 4. Type 60 and press Return 5. ESC to exit To enable hardware flow control: (Global) 1. Press Alt-N 2. Select Toggles 3. Press Return to toggle XON/XOFF flow 4. Select CTS/RTS flow 5. Press Return to toggle 6. ESC 7. ESC 8. Press E for Exit 9. Save Changes IX.4. HyperAccess 5 Note: HyperAccess 5 supports the ATI 9600etc/e. However, HyperAccess 5 does not let you edit the initialization string directly. You can add additional setup commands to change the modem settings for each individual dialing entry. To change the modem initialization string: (Individual, i.e. it works only with the particular dialing entry) 1. Select Define system settings from the Main menu 2. Select Modify 3. Use cursor to select the system to modify and press Enter 4. Select Hardware from the System settings menu 5. Select Modem 6. Select Additional modem setup commands 7. Type S7=60 8. Press ESC twice to go back the Main menu To set the software to wait 60 seconds for connection: N/A To enable hardware flow control: (Individual) 1. Select Define system settings from the Main menu 2. Select Modify 3. Use cursor to select the system to modify and press Enter 4. Select Hardware from the System settings menu 5. Make sure that Data terminal ready signal is output on DTR, delete RTS if it is listed 6. Select Communications port 7. Select Incoming hardware handshaking and type CTS 8. Select Outgoing hardware handshaking and type RTS IX.5. Crosstalk for Windows To change the modem initialization string: (Global) 1. Pull down Setup menu and select Modem... 2. Select Custom and click on Settings 3. Change the initialization string to ^M~AT&F2&C1&D2S7=60^M 4. Click OK To set the software to wait 60 seconds for connection: (Individual) 1. Pull down File menu and select Open a phone book entry 2. Open the phone book entry 3. Pull down Setup menu and select Session 4. Click on More 5. Change the value in Allow xx seconds for the host to answer To enable hardware flow control: (Individual) 1. Pull down File menu and select Open a phone book entry 2. Open the phone book entry 3. Pull down Setup menu and select Device 4. Click on RTS/CTS and click OK IX.6. MicroPhone II (Mac) To change the modem initialization string: (Individual) 1. Choose Settings Menu 2. Select Communications 3. Choose V.32 Standard from the Modem Driver list box 4. Click OK 5. Hold down the Command key and choose Scripts menu 6. Select Modify Script 7. Click the Modem Scripts button 8. Double-click on Modem_Init 9. Double-click on the first line that says Set Variable * mcmd from Expression "'AT....'" 10. Change the initialization string in the lower right box to 'AT&F2&C1&D2S7=60^M' 11. Double-click on the second line that says Set Variable * mcmd from Expression "'AT....'" 12. Change the initialization string in the lower right box to 'AT&F2&C1&D0S7=60^M' 13. Click OK 14. Press the Option key and choose the File menu 15. Select Save Modem Driver (If you want to save the driver under a new name, select Save Modem Driver As... in the File Menu. Name the new driver, and save it into the Modem Folder.) To set the software to wait 60 seconds for connection: N/A To enable hardware flow control: (Individual) 1. Pull down Settings Menu 2. Select Communications 3. Click on the Hardware Handshake box IX.7. White Knight (Mac) To change the modem initialization string: (Global) 1. Choose Local Menu and select Serial Port 2. Choose Modem Init Command to AT&F2&C1&D0S7=60 To set the software to wait 60 seconds for connection: (Global) 1. Choose Service Menu and select Dial or Redial Number 2. Change the value in Wait for Answer up to XX seconds to 60 To enable hardware flow control: (Global) 1. Choose Local Menu and select Serial Port 2. Check Use Hardware Handshake IX.8. ZTerm 0.85 (Mac) To change the modem initialization string: (Global) 1. Choose Settings Menu and select Modem 2. Change Init String to AT&F2&C1&D0S7=60^M To set the software to wait 60 seconds for connection: (Global) 1. Choose Settings Menu and select Modem 2. Edit Dial Timeout To enable hardware flow control: (Individual) 1. Choose Settings Menu and Select Flow Control 2. Uncheck Xon-Xoff Receive 3. Uncheck Xon-Xoff Send 4. Check HW Handshake IX.9. NComm (Amiga) To set up NComm for standard 14.4k or 28.8k Modems 1. Under the menu "TRANSFER" set the default paths where you want downloads and uploads to go to. 1.a. Set your sub menu "PROTOCOLE" option to ZModem, and select all the ZModem options under the "OPTIONS" sub menu. Buffer should be set between 16-64, change this if you have troubles uploading or downloading. 2. Under the "COM" menu set the baud rate to correct setting as suggested above under VIII. 2.a. Set all the other options as also recommended above in VIII. Select the Open Serial option. 3. Under the "EMULATION" menu set the sub menu "END OF LINE" to ; TX EOL = CR ticked RX EOL = CR ticked 3.a. Set character set to IBM under the "CHARACTER SET" sub menu. 4. Under the "MODEM" sub menu of the "PHONE" menu, set the following; Init String = ATZ Dial Command 1 = ATDT (Unless your Pulse in which case ATPT) Hang UP Command = \w\w+++\w\w\w\wATH\n (\w = wait \n = return) Use Locked Rate = YES Hard-DCD Checking = YES 5. Now save this config. The software is ready for some phone numbers, and you have many other options which you can play with, consult your maual or just play!! ===================================================================== X. CONCLUSIONS : I hope that the above file has helped you a little when it comes the the confusing world of high speed data commnuications. Overall you should only be looking at 4 things when buying a modem ; 1. Reliability of the modem (You pay for what you get) Go for the larger brands, like you do when buying a car or stero, you want a good modem, that won't break on you and can handle some line noise. DSP based modems tend to have the edge over other brands. SOME DSP MODEM MANUFACTURERS ; USR, Zyxcel, DSI, AT&T 2. Backup support and service, an EMail address for a company is a good indication, along with a 5 year warrenty, toll free tech support, FREE ROM upgrades. Some other things that you may want to check is will it cost YOU money to have a modem fixed in the way of shipping etc. Don't forget a lifetime warrenty is nice, but how long is a lifetime when it comes to modems? 3. Upgradability of a modem, either return/swap or daughter/FlashROM upgrades to to new protocoles etc. ROM's are getting old touch now, FlashROM's and reprogrammable ROM's are becoming the standard. 4. Check what else you will need to buy with the modem to get it working fully and properly, like serial cards, serial cables, sotware. When you buy the modem, buy it from a good dealer, not the cheapest. Good dealers have FULL refunds (7+ days, 30 is Excellent), and buy the modem from a dealer that is polite and nice to you, and doesn't treat your stupid questions with disgust, someone that doesn't mind helping you out, and who'll give you after sales support. Changes are after reading this file, you know more than most dealers!! ======================================================================== X.1. Contact Info This as my re-release of this old help file is in no way complete. Please if you would like to add and/or change this file EMail me at the below address, and I will amend this file, add your name in and post it a-fresh every month around the world...... EMail : karl@ak.planet.co.nz (Karl Willdig) : mycrocom@iconz.co.nz (Karl Willdig) Phone : 649 263 9666 Fax : 649 278 8221 Snail Mail : C/- MycroCom NZ : P.O. Box 23-608 : Hunters Corner : Auckland : New Zealand Yet to be added to this file, please post suggestions.... Internet Compuserve Prodigy (Author does not have access to) Common Problems with modems (Please send in your probs with solution) X.2. THANKS ------------- Bill Karwin - Protocole Definitions Stephen M. Dunn - stephen@bokonon.UUCP - Various nit pickings ;) Ralp Peters - peters@deculx.ba-loerrach.de - ISDN Germany ZyXell - Brent -- Wolfgang Henke ... http://www.whnet.com/wolfgang/ WH Networks ............................. ftp.whnet.com /pub/wolfgang 2672 Bayshore Parkway Suite 503 ....................... (415) 390-9316 Mountain View CA 94043 ............................ fax (415) 390-9317