ProfitPress Mega CDROM2 Shareware Freeware (MSDOS)(1992)(Eng)

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Text File | 1990-10-12 | 13.1 KB | 323 lines

MNP Error Correcting Modems Overview The Microcom Networking Protocol, MNP, is a communications protocol that supports interactive and file-transfer applications. MNP is designed to conform to the International Organization for Standardization (ISO) Open System Interconnection (OSI) Network Reference Model, or simply the OSI model. The OSI model is a network protocol divided into standardized layers (or modules). The use of standardized layers assists in the interconnection of different vendors equipment. ZDDDDDDDDDDDDDDD? 3 3 3 Application 3 CDDDDDDDDDDDDDDD4 3 3 3 Presentation 3 CDDDDDDDDDDDDDDD4 3 3 3 Session 3 CDDDDDDDDDDDDDDD4 3 3 3 Transport 3 CDDDDDDDDDDDDDDD4 3 3 3 Network 3 CDDDDDDDDDDDDDDD4 ZD 3 3 D? Modem plus3 3 Data Link 3 3 File Transfer CDDDDDDDDDDDDDDD4 3 MNP Modem Connection Protocol 3 3 3 3 i.e.Xmodem@D 3 Physical 3 DY @DDDDDDDDDDDDDDDY The OSI model allows users to choose how their networking systems are partitioned and implemented. The Link Layer of the OSI Network Model is responsible for provide reliable date transfer. It uses the Physical Layer to transmit information through the data path. In dial-up data communications, the data transmission of the Physical Layer is performed by "traditional" modems using standards such as Bell 103, Bell 212A and V.22 bis. Traditional modems cannot provide guaranteed error-free data communications. The noise and distortion characteristics of voice-grade telephone circuits are beyond the capabilities of any signal processing to deliver error-free data. It is the task of the Link Layer to provide a means of error detection and error control. Error detection when accessing Bulletin Boards is provided for file transfers by an error-correcting protocol (Xmodem for example) but there is no error detection present when reading ASCII text. That's why garbled character can sneak thru but you can transfer a file successfully. Microcom's MNP error-correcting modems provide the integrity of data transmission over voice-grade circuits for both file and text transmission when connected to another MNP equipment modem. When connected to a "standard" modem there is no hardware error checking. The user demand for error-free data communications has made Microcom MNP error-correcting modems a "standard" in the modem industry implemented by many modem manufactures. (There is still a possibility of errors occurring in a MNP-to- MNP connection if they occur at either end between the serial port and the modem (in the cable) or in the computer itself. The probability for error is much, much less here than exists while the data is being transferred between modems. And, if you are transfering ARCed files, the CRC checking that occurs when the file is deARCed is enough to show you that the file transfer was successful. While some people run an MNP-to-MNP file transfer with no additional error checking protocol, there are low-overhead protocols which transfer large blocks of data between acknowledgments of successful receipt and these are particularly well suited to use with the MNP-to-MNP connections.) Performance Comparisons of MNP Classes MNP is designed for easy implementation on many hardware configurations. Different applications require different cost and performance mixes. MNP is deliberately structured to provide different levels of performance without sacrificing compatibility. Unlike other protocols, applications that require low-cost solutions can use simpler, less demanding implementations of MNP and MNP implementations at all performance levels are compatible with each other. A small application with a simple implementation of MNP can communicate with a more powerful system using a high performance implementation of MNP. The primary principle of MNP is each implementation communicates with all other implementations. When an MNP communications link is being established, the MNP implementations will negotiate to operate at the highest mutually supported class of MNP service. MNP assembles the user data into packets before retransmission. The use of data protocols by the overhead a protocol introduces to the communication channel. The protocol overhead reduces the effective data throughout of the communications channel. A description of each MNP performance level follows. The description shows how MNP offers the user greater throughput than the basic error-prone communication channel. Class 1 This is the first level of MNP performance. MNP Class 1 uses an asynchronous byte-oriented half-duplex method of exchanging data. MNP Class 1 implementations make minimum demands on processor speeds and memory storage MNP Class 1 makes it possible for devices with small hardware configurations to communicate error-free. The protocol efficiency of a Class 1 implementation is about 70%. A device using MNP Class 1 with a 2400 bps modem will realize 1690 bps throughput. Modern microprocessors have become so powerful that implementations of MNP Class 1 are uncommon in the U.S. Class 2 MNP Class 2 uses asynchronous byte-oriented full-duplex data exchange. Almost all microprocessor-based hardware is capable of supporting MNP Class 2 performance. Common microprocessor selected for MNP Class 2 implementations are Z80's and 6800's. The protocol efficiency of a Class 2 implementation is about 84%. A device using MNP Class 2 with a 2400 bps modem will realize 2000 bps throughput. Most microprocessor-based hardware can easily implement MNP Class 2. Class 3 MNP Class 3 uses synchronous bit-oriented full-duplex exchange. The synchronous bit-oriented data format is inherently more efficient than the asynchronous byte-oriented data format. It takes 10 bits to represent 8 data bits in the asynchronous data format because of the "start" and "stop" framing bits. The synchronous data format eliminates the need for start and stop bits. The user still sends data asynchronously to the Class 3 modem; meanwhile, the modems communicate with each other synchronously. The protocol efficiency of a Class 3 implementation is about 108%. A device using Class 3 with a 2400 bps modem will realize 2600 bps throughput. At Class 3 performance, the MNP protocol "rewards" the user for using an error-correcting modem by producing 8% extra throughput over an ordinary modem without MNP. The MultiTech 224E modem implements MNP Class 3. Class 4 MNP Class 4 introduces two new concepts, Adaptive Packet Assembly(tm) and Data Phase Optimization(tm), to further improve the performance of an MNP modem. During data transfer, MNP monitors the reliability of the transmission medium. If the data channel is relatively error-free, MNP assembles larger data packets to increase throughput. If the data is introducing many errors, then MNP assembles smaller data packets to transmit. while smaller data packets increase protocol overhead, they concurrently decrease the throughput penalty of data retransmissions. The result of smaller data packets is more data is successfully transmitted on the first try. MNP protocol recognizes that during the data transfer phase of a connection, most of the administrative information in the data packet never changes. Data Phase Optimization provides a method for eliminating some of the administrative information. This procedure further reduces protocol overhead. The protocol efficiency of a Class 4 implementation is about 120%. A device using MNP Class 4 with a 2400 bps modem will realize approximately 2900 bps throughput. With class 4 performance, the MNP protocol produces 20% more throughput than an ordinary modem without MNP. Microcom's AX/1200, AX/2400 and PC/2400 support class 4. Class 5 MNP Class 5 introduces Data Compression as a new feature to MNP Class 4 service. MNP Data Compression uses a real-time adaptive algorithm to compress data. The real-time aspects of the algorithm allow the data compression to operate on interactive terminal data as well as file-transfer data. Data compression delivers faster screen updates to the user. The adaptive nature of the algorithm means data compression is always optimized for the user's data. The compression algorithm continuously analyzes the user data and adjusts the compression parameters to maximize data throughput. Adaptive compression means users of file-transfers receive maximum data compression and data transfer. Data compression algorithms, like sort algorithms, are sensitive to the data pattern being processed. Most data being transmitted will benefit from data compression. The user will see compression performance vary between 1.3 to 1 and 2 to 1 (some files may be compressed at even higher ratios). The following types of common user files are listed in order of increasing compressibility: 1) COM or EXE files (ARCed files too) 2) Spreadsheet files 3) Word Processing files 4) Print Files A realistic estimate of the overall compression factor a user will experience is 1.6 to 1 or 63%. This is equivalent to having a net protocol efficiency of 200% for an MNP Class 5 implementation. A device using MNP Class 5 with a 2400 bps modem will realize 4800 bps throughput. At MNP Class 5 performance, the MNP protocol produces over 100% more throughput than an ordinary modem without MNP. Microcom's AX/1200c, AX/2400c and PC/2400c support class 5. CASE's 4696/VS supports Class 5. Class 6 MNP Class 6 introduces the new features Universal Link Negotiation(tm) and Statistical Duplexing(tm) to MNP Class 5 service. Universal Link Negotiation allows MNP to unify non- compatible modem modulation technology into the same MNP Error-Correcting Modem. Prior to Class 6, MNP was used to enhance current modem technology. MNP Class 6 allows Microcom to create new universal modems. Most 1200 bps and 2400 bps modems are designed to be compatible with lower speed modems. Bell 212A type modems operate at 1200 bps and incorporate the Bell 103 standard for 0-300 bps communications. Likewise, there are V.22 bis modems that operate as 300 bps 103 modems, 1200 bps 212A modems and 2400 bps modems. However, high speed V.29 and V.32 modems do not provide compatibility with each other or with the lower speed modulation techniques found in 212A and V.22 bis modems. Before the advent of MNP Class 6, it was impossible for a single modem to operate at a full range of speeds between 300 and 9600 bps. Universol Link Negotiation allows MNP modems to begin operations at a common slower speed and negotiate the use of an alternate high speed modulation technique. The Microcom AX/9624 is an example of a modem that uses Universal Link Negotiation. Universal Link Negotiation uses the 2400 bps V.22bis technology to negotiate a link. At the end of a successful link negotiation for Class 6 operation, the modem shifts to operation using 9600 bps V.29 technology. In the case where the high-speed carrier technology uses half- duplex modulation, MNP Class 6 provides Statistical Duplexing. The Statistical Duplexing algorithm monitors the user data traffic pattern to dynamically allocate utilization of the half- duplex modulation to deliver full-duplex service. An MNP Class 6 modem based on V.29 technology delivers maximum performance in file transfer applications; up to 19.2 kbps throughput is possible on dial-up circuits for most applications. In accordance with the principles of MNP, the Class 5 Data Compression is fully incorporated in MNP Class 6. The MNP Class 6 Modem will deliver optimum performance even on an interactive terminal using character echoplexing. Screen updates will occur at speeds between 9.6 kbps andf 19.2 kbps. Most screen updates will take less than a second. Microcom's AX/9612c, AX/9624c and PC/9624c support Class 6. Most of the above text was taken from a Microcom Features Description by Mike Focke 7/7/87 Class 7 MNP Class 7 Enhanced Data Compression, combined with Class 4, achieves improved throughput with efficiencies up to 300% via the latest data compression technology. Microcom's enhanced encoding technique not only ndynamically adjusts to the type of data being transmitted, but also predicts the probabality of characters in a data stream. This combined with run length encoding, which sends repeating characters as a single number code, results in the superior compression efficiencies supported in MNP Class 7. The Microcom QX/12K supports Class 7. Class 8 Nothing available. Class 9 MNP Class 9 utilizes Enhanced Data Compression combined with V.32 technology to deliver maximum throughput up to 300% greater than ordinary V.32 modems. Class 9 also features Enhanced Universal Link Negotiation which allows connection to both MNP and non-MNP modems at the highest performance level. The Microcom QX/.32c supports Class 9 The above was taken from product description buochures from Microcom by Mike Focke 8/1/88 Not quite what 2035@jimi.cs.unlv.edu wanted, but I've had a couple of folks ask for a re-post.