Magnum One

home *** CD-ROM | disk | FTP | other *** search

/ Magnum One / Magnum One (Mid-American Digital) (Disc Manufacturing).iso / d7 / comproto.arc / PAPER-03.TXT < prev

Wrap

Text File | 1991-04-29 | 15.2 KB | 346 lines

9600 White Paper THE MIGRATION TO 9600 BPS COMMUNICATIONS FOR PERSONAL COMPUTERS Hayes Microcomputer Products, Inc. 705 Westech Drive Norcross, Georgia 30092 INTRODUCTION Whether you look at man's transportation of himself or the "transportation" of his information, the trend has always been toward a faster and more efficient means. Our trend in communications has enabled us to evolve from carrier pigeons and the Pony Express to the telegraph and telephone and into microwave and fiber optic data transmission. Our quest for faster communications continues. MODEMS AND THE MIGRATION TOWARD INCREASED SPEED AND FUNCTIONALITY Early modems were not intelligent devices, but simply translators which had to be opened prior to each hookup in order to rather laboriously set a series of switches that controlled the options that configured the modems' operation for the particular system they were connected to. Acoustic couplers, suction cup-like receptacles used with telephone handsets, while not as difficult to set up, were prone to error because of external noise or vibration. They also involved manual operation of dialing the phone, listening for a special tone from the receiving modem, and placing the headset in the coupler. This hands-on requirement, of course, eliminated the possibility of automated operation and bogged down the communications process. This unsophisticated environment of the late 1970s was ripe for an automated product that could streamline establishing and conducting data transmission activities in the Public Switched Telephone Network (PSTN). HAYES MODEMS AND THE HAYES STANDARD AT COMMAND SET Hayes Microcomputer Products, Inc. introduced its innovative modem series to fill this void that existed in the communications environment. By providing modems that were both easy to use and simple to connect directly to the PSTN, the problems the error-prone acoustic connection had been solved. Using these new modems meant the terminal or personal computer operator could control modem functions (such as dialing numbers or switching from command to on-line modes) from a keyboard or through communications software. This meant that communications had taken a great step forward since operation was now automated and repetitive activities (calling an on-line service and automatically logging on) could be stored and repeated quickly and more efficiently. What made the automation possible? By this time, microprocessors had progressed to a significant functional level and could provide a means for the modem to execute instructions coming from the terminal or personal computer. Since the modem now had the ability to interpret character strings sent to it and could respond with result codes, it was easier to control. The microprocessor enabled the modem to become a system element that was easier to integrate into the computer environment. The solution to modem control was the Hayes Standard AT Command Set. By taking all of the available standards for the data and physical aspects of communications (Bell 103C modulation, RS-232C physical interface, ASCII data format, and RJ-11 phone connector) and innovating on top of them, Hayes developed a new industry standard. The results were the first intelligent modem products to enjoy widespread distribution and use. INCREASED TECHNOLOGICAL ADVANCES Introduced in 1981, the Hayes Smartmodem 300 implemented the Bell 103 telephone signalling standard which uses Frequency Shift Keying (FSK). FSK is limited to lower speeds as a result of band width limitations of the voice telephone channel. True to history, personal computer modem users wanted more. Specifically, they wanted more speed with high data transfer accuracy. Modulation techniques were developed to permit increased data rates. Phase Shift Keying (PSK) allowed modems to quadruple their speed to 1200 bits per second (bps) communications. This method of transmission is considerably more complex than and increased the modulation/demodulation capabilities required of the modem. Both the Hayes Smartmodem 1200, introduced in 1982, and the Smartmodem 1200B, introduced in 1983, adhere to the PSK standard known as Bell 212A and can communicate with other modems which also use this signalling standard. Users once again demanded more speed and functionality, and 2400 bps communication implementing Quadrature Amplitude Modulation (QAM) was developed. Higher speeds meant the modems needed more sophisticated signal processing circuitry to enable reliable higher speed data transfer over the PSTN. In addition to 2400 bps communication speed, both the Hayes Smartmodem 2400, introduced in 1984, and Smartmodem 2400B, introduced in 1985, included call progress monitoring, adaptive equalization, self testing, and the ability to communicate both asynchronously and synchronously. EMPHASIS ON INTERNATIONAL STANDARDS Our evolution into a more global society presents new challenges and opportunities for personal computer communications. The rise in importance of standards setting bodies such as the International Telegraph and Telephone Consultative Committee (CCITT) is a reflection of the need for the establishment of global standards for interconnection of communications equipment. The work of the CCITT has resulted in the establishment of the V.22 and V.22bis recommendations for 1200 bps and 2400 bps communications. Users can confidently purchase modems adhering to these standards and be assured that communications with other modems (even in foreign countries) applying these standards will be compatible. All Hayes 1200 bps and 2400 bps modems are CCITT V.22 and V.22bis compatible and country-specific models have been approved for distribution in North America, Europe, Central America, the Middle-East, and the Pacific Basin. 9600 BPS COMMUNICATION When data transmission speed for personal computer modems accelerated from 300 bps to 1200 bps, the technological hurdles were rather lofty. By comparison, the migration from 1200 bps and 2400 bps to 9600 bps for dial-up modems was far more complex than the earlier advances. The CCITT V.29 recommendation originally addressed 9600 bps communications over four wire leased lines. At the time of the recommendation's drafting, the opinion was that dial-up lines would not support 9600 bps communications. As the quality of transmission lines on the PSTN improved, manufacturers began to re-orient the CCITT standard by introducing dial-up 9600 bps half-duplex V.29 modems using QAM techniques for transmitting data. This approach for modulation is similar to the method used for handling 2400 bps transmission. Communications equipment manufacturers perceived the need for full-duplex 9600 bps dial-up modems and the CCITT responded with its V.32 recommendation. V.32 modems are very expensive due to the echo cancellation technology the modems require. Echo cancellation allows the modem to ignore its own transmission and "focus" itself on the incoming data signal from the remote modem during full-duplex transmission. This increases the complexity of the modem and the technology to accomplish it is costly. Additionally, a characteristic associated with personal computer data communications applications is one-way communication. For example, in downloading a large data file from a mainframe to a personal computer, the data flow is essentially in direction. So, V.32 full-duplex capability is not only expensive, but for most personal computer data communications applications it is also unnecessary. What, then, are the options for affordable 9600 V.32 communications? HAYES V-SERIES 9600 BPS MODEMS Hayes has developed the V-series Smartmodem 9600 and the V-series Smartmodem 9600B, 9600 bps half-duplex, fast-turnaround modems providing simulated full-duplex V.32 dial-up communications at a considerably lower price compared to V.32 modems. Both modems implement Hayes-exclusive fast turn-around technology. By providing such rapid turn-around of the communications link, users receive the benefit of fast data transfer through simulated full-duplex at a reasonable cost. This fast turn-around allows data alternately to flow at 9600 bps in either direction. When high capacity is needed in one direction, that direction gets use of the channel for longer periods. These periods, however, are always short enough that reverse data is not delayed appreciably. TRELLIS CODE MODULATION Both Hayes 9600 bps modems implement the Trellis Code Modulation (TCM) scheme as described in the CCITT V.32 specification to add forward error correction to the basic signal. TCM is especially important as the telephone companies continue to implement Adaptive Differential Pulse Code Modulation (ADPCM). ADPCM is a voice signal encoding scheme that allows the phone companies to double the channel capacity of digital trunk lines. Unfortunately, V.29 and V.32 modems that use Quadrature Amplitude Modulation (QAM) without Trellis Coding will not be able to communicate successfully at 9600 bps when an ADPCM link is encountered. Modems without TCM will have their speed limited to only 4800 bps on ADPCM lines. The Hayes 9600 bps modems' TCM feature makes them more readily adaptable to the present and future demands and constraints of the PSTN. TCM can provide up to a four decibel improvement of signal-to-noise ratio when compared to a non-TCM scheme such as V.29. That improvement may appear small, but it provides huge dividends. Improving the signal to noise ratio allows a TCM modem to provide high quality, reliable communications over dial-up lines that can eliminate the need for using costly, conditioned, leased lines for 9600 bps communications. This enables the Hayes 9600 bps modems to achieve dial-up line performance with that of the Smartmodem 2400 or other V.22bis modems. ERROR-CONTROL Both Hayes 9600 bps modems implement the LAPB link level portion of the X.25 protocol for error-control at 2400 bps and 1200 bps. CCITT X.25 is a versatile and widely used synchronous protocol standard that enjoys popularity as a worldwide standard. At 4800 bps and 9600 bps both modems implement an error-control ping pong protocol which is an extension of LAPB. Use of this protocol paves the way for future Hayes products to continue the migration toward the standardized, synchronous communications environment that lies in the future. ADAPTIVE COMPRESSION Adaptive Data Compression in Hayes 9600 bps modems typically increases the data throughput to speeds of 19,200 bps. Using a Hayes-developed algorithm, data is compressed in real time, dynamically adapting to changes in the data being transmitted. This operation is transparent to the user and the amount of compression that occurs within the modem depends upon the type of data being transferred. Spreadsheet, data, and text files will typically flow in and out of the modem at 19,200 bps using the standard asynchronous data port. Other files will also experience improved throughput due to data compression between the modems. AUTOMATIC NEGOTIATION Automatic Feature Negotiation capabilities in both the V-series Smartmodem 9600 and V-series Smartmodem 9600B provide users with automatic setup of the error-control link. During the initial modem "handshake" the local and remote modems will connect at the data rate set in the answering modem. If the answering modem is set to a lower speed, the originating modem can fall back from 9600 bps to 4800 bps, 2400 bps, 1200 bps, or 300 bps for maximum flexibility in establishing a connection. Once the "handshake" is completed, detection of a non-V-series protocol device or synchronous-only device at the remote end occurs. Then, the negotiation of link parameters such as synchronous or asynchronous transmission, asynchronous transparency mode, or link address is conducted. The devices can also coordinate the use of X.25 LAPB or Asynchronous Framing Technique (AFT). AFT is an asynchronous augmentation for any bit-synchronous protocol such as LAPB, LAPD, or SDLC. It the lowest part of the link level of the synchronous protocol and brings error-control operation to asynchronous transmission links. Again, an existing standard has been built upon to continue the evolution of the communications environment. PRACTICAL APPLICATIONS FOR 9600 BPS COMMUNICATIONS The requirement for more speed is universal and the applications for the V-series Smartmodem 9600 and V-series Smartmodem 9600B permeate virtually every area of business. By combining high speed and data compression to improve throughput over an error-control link, the Hayes 9600 bps V-series system modems continue the company's tradition for providing fast, reliable data communications equipment. By using high speed communications when connecting personal computers to corporate mainframes, users can save both money and time. Faster transfer of data means shorter long distance connect time and translates quickly into significant dollar amounts. Additionally, faster data transfer means better utilization of time and shortening the length of time a personal computer is tied to the mainframe frees both systems to undertake additional, more useful activities. So, whether the data transferred is a quarterly sales report, monthly training schedule, or a credit application for processing, 9600 bps error-control communications offers significant opportunities to improve efficiency. Additionally, terminal to mainframe communications can expedite functions essential to maximize customer service and maintain a competitive edge. Integrating order entry equipment and cash registers into an inventory management system through 9600 bps modems can improve an organization's ability to manage inventory and ensure proper coordination throughout the distribution channel. THE HAYES COMMITMENT As the leader in communications hardware and software products for personal computers, Hayes has developed its products to adhere to the established standards of the industry. It is our intention to do so in the future and to innovate where no standards exist to augment the implementation of high speed, advanced technology products. Our commitment to quality, service, and value will allow users of Hayes products to benefit from that commitment in the future as they have in the past.