Buying a V34 Modem? By Mycrocom V.34 and V.FC and V.FAST the 28.8k Protocols I get many calls everyday asking me have I got v.FAST modems in stock, or asking other questions because of the large amount of confusion out in the world about the 28.8k protocols. I hope in this article to help clear up your mind about these protocols so you can make a good buying decision. It starts of simple, and gets a little technical explaining the v.34 toolbox. V.FAST - This name appeared about 2-3 years ago as the "NEW" 28.8k (28,800bps) protocol. It was actually a working name for v.34 (more on that later) and was dropped just as the working name for Windows 95 was Chicago, which people still insist on calling it. People still refer today to v.FC or v.34 as v.FAST, which could led to some problems when you are talking to different people. V.FC - This is the 28.8k protocol invented, designed and (for the most part) manufactured by Rockwell, the giant modem chip manufacturer. Rockwell saw the need for a 28.8k protocol and the fact that an international standard was some time off designed their own. v.FC or v.FAST CLASS is Rockwells baby, and has been sold in modems since late 1993. It is a simple but effect 28.8k standard which a small porportion of the population purchased, but the majority of people have been waiting for the v.34 modems. Those people who purchased 28.8k modems from NZ suppliers which are upgradeable to v.34 should all be able to upgrade to v.34 within a couple of months. Modems that have been imported by yourself or purchased from unapproved resellers will either have great troubles upgrading or have a costly upgrade path. You will need to ring your dealer (or the importer) for information regarding upgrades. Modems which are able to be upgraded include MicroCom, USR Courier and Practical Peripherals. Modems which definatly aren't upgradable are Dynalinks, Ellcon and a variety of other cheaper modems. Modems that you may have troubles upgrading are Supra and Zoom and anything you or a friend imported, as many US companies won't support a product out USA unless they have sold the modems direct to a distrubutor in that country. V.34 - The much awaited and International ITU-T approved 28.8k protocol hit the scene in July last year. Production of v.34 modems started in August with the DSP (Digital Signal Processor or modems with a DSP co-processor for a datapump) modems being the first to sell v.34 modems. It wasn't until early this year that Rockwell based modems (Rockwell modems not having a DSP Datapump) started coming out with the v.34 protocol. ALL 19.2k and 28.8k modems are backward compatible with 14.4k and slower speeds, and all have Group 3 Class 1 or 2 14.4k fax capabilities. So when you buy a 28.8k modem you will still be able to connect to slower modems. Which modem is the best to buy? Well that is a question you should ask your dealer if they are knowledgeable about modems and have a range of modems they will be able to suggest the best modem for your needs. Some modems are more reliable than others for certain purposes, and some have features you may need, or will want in the future. In recent trials in the U.S. the Motorola v.34 modems came out No 1, with US Robotics Courier coming 2nd. The reason these modems are better at the v.34 protocol is they both use 100% of the v.34 code. Most know the saying "you pay for what you get". It is the same with modems, the cheaper brands on the market will only have the vital parts of the v.34 code (making the modem cheaper to produce) so these modems have proven not to be as reliable as a modem with all or most of the v.34 code. What about v.FC ? Well v.FC is out of date, and if you can still buy the modems which are v.FC only (not v.34) then I would seriously consider you don't buy from that dealer again! V.FC modems are being phased out, already our v.34 sales this year have surpassed all our v.FC sales for all of last year, and with a number of manufacturers making v.34 only modems (not v.FC compatible) at lot of people with v.FC modems will find they have a 14.4k modem by the years end. If you know you need to be able to connect to a v.FC modem, your best buy would be a "Dual Standard" modem, which is both v.FC and v.34 compatible. The USR Courier is the best in this field, but its price tag will put many home users off, ask your dealer, and check to find out how much of the v.34 code is in the v.34 modems before buying, and ensure you can return a modem if your not satisfied within at least 7 days. Again I would recommend you talk to a dealer with some good knowledge that can advise you on your best buy, as many brands on the market are of good to high quality, but also many are of low quality. Why is V.34 better than V.FC ?? V.34 has been under development for a number of years, and a large number of modem manufacturers help in designing this code including ; Motorola, US Robotics and Rockwell. V.34 has a number of features that make it superior to v.FC of which the most substantial advancement is the modems "adaptive intelligence capability. Unlike previous standards v.34 employs multiply modulation methods (MODEM = Modulator/Demodulator) and multiple impairments compensation techniques. This allows it to intelligently choose the optimum set of modulation tools to adapt to the telephone lines. The only other modem that is selling on the market in any sort of quantity is v.32bis (14,400 baud) modems. These modems as you can tell by the name are half the speed of a 28,800 baud modem and have the following differences ; V.32bis V.34 Modem Type Fixed Modulation Adaptive Intelligence Data Rates 14,400 - 7200 bps 28,800 - 2400 bps Bandwidth Fixed Variable Trellis Coding 2 Dimensional 4 Dimensional Adaptive Equalisation Linear Preceding Mapping 2D Shell Mapping 16 D Shell Mapping Aux Channel None 200 bps Operating Modes Full & Half Duplex (Fax) Full, Half (Fax) and Asymmetric Even if you don't understand the jargon above (Some even I don't know about) you can see that v.34 is a more flexible, higher quality transmission protocol. V.34 is also very flexible in the manufacturing stage. Modem manufacturers are able to select from a "toolbox" various features they want to include in their modems. This way they only pay for the features they use, meaning cheap modem can be built which although are 28.8k they are not using all the great features of v.34 making them less reliable etc than a modem with all the features. This has been proven by the fact that the two best v.34 modems on the market (Motorola and USR Courier) are fully v.34 compliant or have all the v.34 toolbox. 1. V.8 Negotiation handshake 2. Line Probing 3. Precoding 4. Adaptive Pre-Emphasis 5. Adaptive Power Control 6. Multi-dimensional Trellis Coding 7. Shell Mapping (aka shaping) 8. Warping 9. Fast Train & Training Recovery Procedures 10. High Speed DTE Interface V.8 MODEM NEGOTIATION HANDSHAKE - A new handshake start up procedure developed for v.34 products. V.8 is backwards compatible to all lower speed modems. v.8 is the first noise you will hear >from your modem between two v.34 modems. V.8 is an intelligent procedure allowing for a quick connection. V.8 has been built flexible, and can be easily upgraded in the future if the need arises. LINE PROBING - Line probing is the most significant tool in the toolbox. It allows the v.34 modem to intelligently choose the optimum operating parameters for any given telephone channel. Line Probing is a bi-directional exchange which is performed immediately after v.8 negotiation and involves the transmission of complex signals that allow the distant receiver to analyse the characteristics of the telephone channel before entering data transmission. This analysing sets a number of key parameters including ; - Carrier Frequency and Symbol Rate. Sets optimum bandwidth and placement from 11 combinations with 6 different symbol rates, each with 2 possible carrier frequencies - Pre Emphasis Selection. Modems choose the optimum transmit pre-emphasis filter from menu of 10 defined filters. - Power Control Selection. Modems choose the optimum transmitter output power level. The line probing features are performed on initial connecting and when ever line conditions change, which is very handy if your connection for periods of time, especially over leased lines or microwave links. PRECODING - Very techo, but basically for the best connection and to use all frequencies available on the line Precoding uses DFE or Decision Feedback Equalisers to compensate for ISI (Intersymbol Interference). ADAPTIVE PRE-EMPHASIS - This is an amazing feature which can compensate for known channel distortions learnt during Line probing. The modem has a selection of 10 different filters to choose from so that it can get the signal though as best as possible to the receiver. ADAPTIVE POWER CONTROL - Proper selection of transmitter power is critical in high speed modems to stop echo, and to maintain signal to noise ratio. Adaptive power control is an intelligent, adaptive scheme which automatically selects the optimum transmit level based on line probing results. MULTIDIMENSIONAL TRELLIS CODING - Trellis coding simply put is forward error correction coding scheme. The value of the coding is expressed as a "coding gain" which is a measure of the modems error rate improvement over an uncoded modem. The effective coding gain of the three new v.34 codes employed work to be the best trade-off between performance, delay and complexity. SHELL MAPPING - Shell mapping is a signal constellation mapping technique which attempts to distribute these signal points in the 2 dimensional space in such a way as to improve the resultant noise immunity by approximately 1 dB. WARPING (aka Non-linear Encoding) - Warping is another form of signal space coding specifically designed to combat the effects of signal dependent distortion also known as non-linear distortion or harmonic distortion. FAST TRAINING & TRAINING RECOVERY - Training is a general term used to describe the process by which the modems receiver synchronizes on the remote modems transmit signal at initial connection. It is also performed when extreme disruptions (line noise) occur. The v.34 training sequences are receiver timing based, therefore the time to complete a train can be minimised. Recovery is built into the v.34 code unlike v.32bis modems, allowing for quick detection and recovery from line noise. HIGH SPEED DTE INTERFACE - The v.34 specifications defines two interface connections, the preferred interface is a 25 or 26pin physical interface utilising a mix of v.10 and v.11 electrical standards. This is very similar to X.21 and will likely become the preferred interface for synchronous PC users. The alternative interface is backward compatible with the installed EIA232 based (Your standard 25 or 26 pin serial port on most computers including Amiga, IBM PC and the modified Macintosh interface. By Karl Willdig (c) Copyright as well! Maybe distrubuted electronically ONLY. Any commercial organization using this file please be polite and ask first. Karl Willdig P.O Box 23-608 Hunters Corner Auckland Ph 649 263 9666 Fx 649 278 6776 EMAIL : mycrocom@iconz.co.nz END ===