Microsoft Point-to-Point Compression (MPPC; described in RFC 2118) is a

streaming data Streaming data is data that is continuously generated by different sources. Such data should be processed incrementally using stream processing techniques without having access to all of the data. In addition, it should be considered that concept d ...

compression Compression may refer to: Physical science *Compression (physics), size reduction due to forces *Compression member, a structural element such as a column *Compressibility, susceptibility to compression * Gas compression *Compression ratio, of a ...

algorithm based on an implementation of

Lempel–Ziv LZ77 and LZ78 are the two lossless data compression algorithms published in papers by Abraham Lempel and Jacob Ziv in 1977 and 1978. They are also known as LZ1 and LZ2 respectively. These two algorithms form the basis for many variations includin ...

using a

sliding window A sliding window protocol is a feature of packet-based data transmission protocols. Sliding window protocols are used where reliable in-order delivery of packets is required, such as in the data link layer ( OSI layer 2) as well as in the Tran ...

buffer. According to

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's IP statement, MPPC was

patent A patent is a type of intellectual property that gives its owner the legal right to exclude others from making, using, or selling an invention for a limited period of time in exchange for publishing an enabling disclosure of the invention."A ...

-encumbered (last US patent granted on 1996-07-02). Where

V.44 The ITU-T V-Series Recommendations on Data communication over the telephone network specify the protocols that govern approved modem communication standards and interfaces. ''Note:'' the '' bis'' and '' ter'' suffixes are ITU-T standard designat ...

or V.42bis operate at layer 1 on the

OSI model The Open Systems Interconnection model (OSI model) is a conceptual model that 'provides a common basis for the coordination of SOstandards development for the purpose of systems interconnection'. In the OSI reference model, the communications ...

, MPPC operates on layer 2, giving it a significant advantage in terms of computing resources available to it. The

dialup Dial-up Internet access is a form of Internet access that uses the facilities of the public switched telephone network (PSTN) to establish a connection to an Internet service provider (ISP) by dialing a telephone number on a conventional telep ...

modem A modulator-demodulator or modem is a computer hardware device that converts data from a digital format into a format suitable for an analog transmission medium such as telephone or radio. A modem transmits data by Modulation#Digital modulati ...

's in-built compression (V.44 or V.42bis) can only occur after the data has been serially transmitted to the modem, typically at a maximum rate of 115,200 bit/s. MPPC, as it is controlled by the

operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may also i ...

, can receive as much data as it wishes to compress, before forwarding it on to the modem. The modem's hardware must not delay data too much, while waiting for more to compress in one packet, otherwise an unacceptable latency level will result. It also cannot afford to, as this would require both sizable computing resources (on the scale of a modem) as well as significant buffer

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. Software compression such as MPPC is free to use the host computer's resources, exceeding the modem's by several orders of magnitude. This allows it to keep a much larger buffer to work on at any one time, and it processes through a given amount of data much faster. The end result is that where V.44 may achieve a maximum of 4:1 compression (230 kbit/s) but is usually limited to 115.2 kbit/s, MPPC is capable of a maximum of 8:1 compression (460 kbit/s). MPPC also, given the far greater computing power at its disposal, is more effective on data than V.44 and achieves higher compression ratios when 8:1 isn't achievable.

References

{{Compression Methods Modems Microsoft initiatives Lossless compression algorithms

See also

References