Path: utzoo!attcan!uunet!lll-winken!lll-lcc!ames!xanth!nic.MR.NET!umn-d-ub!umn-cs!bungia!orbit!pnet51!shawn From: shawn@pnet51.cts.com (Shawn Stanley) Newsgroups: comp.sys.apple Subject: Re: Re:modems Message-ID: <464@orbit.UUCP> Date: 10 Jan 89 16:45:27 GMT Sender: root@orbit.UUCP Organization: People-Net [pnet51], Minneapolis, MN. Lines: 96 L77@TAUNOS.BITNET (Yoram Ney) writes: >BTW,could someone explain what MNP *LEVEL* means? Does a higher MNP >level mean fewer errors? MNP stands for Microcom Networking Protocol. Each MNP level is a bit different, and some are better for certain applications than others. Here's a summary of each one that I know of: Class 1 MNP Class 1 uses an asynchronous byte-oriented half-duplex method of exchanging data. 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 beome 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. 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. Class 3 MNP Class 3 uses synchronous bit-oriented full-duplex data 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 baud modem will realize 2600 bps throughput. 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 channel 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 (tm) provides a method for eliminating some of the administrative information. 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. 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 user will see compression performance vary between 1.3 to 1 and 2 to 1 (some files may be compressed at even higher ratios). 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. [Note that Class 5 works quite well with ASCII transmissions. Binary files yield lower compression ratios.] 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. [Basically, Universal Link Negotiation (tm) allows modems to agree on the best baud rate for the connection, while Statistical Duplexing (tm) allows modems to work faster with the end sending the blocks, since not much is going on with the end sending the acknowledgements.] Class 7 MNP Class 7 defines an enhanced data compression technique which, like Class 5 Data Compression, can be negotiated into use on a call-by-call basis. However, in Class 7, the coding technique not only dynamically adjusts to the type of user data being transmitted, but also predicts the probability of characters in the data stream. This predictive nature of the algorithm allows user data to be represented by the shortest possible Huffman codes and thus results in an enhanced compression affect. [This means that if you send a binary file, it will do its best to recognize that fact and alter its compression technique accordingly.] A realistic estimate of the overall compression factor for Class 7 is 2.4 to 1 or 42%. Thus, a device using MNP Class 7 Data Compression with a 2400 bps modem will realize 7200 bps throughput. [Microcom, MNP Data Compression, Adaptive Packet Assembly, Data Phase Optimization, Universal Link Negotiation, and Statistical Duplexing are trademarks of Microcom, Inc. MNP is a registered trademark of Microcom, Inc.] ----------------------------------------------------------------------------- There you have it. Right from the horse's mouth, actually. UUCP: {rosevax, crash}!orbit!pnet51!shawn INET: shawn@pnet51.cts.com