Link Access Procedure for Modems: Difference between revisions

Revision as of 13:32, 3 July 2007

Revision as of 13:34, 3 July 2007

Line 1:

'''LAPM''', or Link Access Procedure for Modems,''' ('''LAPM''') is part of the [[V.42]] [[error correction]] [[Communications protocol|protocol]] for [[modems]].

<blockquote>

:LAPM is an error control protocol defined in ITU-T recommendations V.42. Like the MNP protocols, LAPM uses cyclic redundancy checking (CRC) and retransmission of corrupted data (ARQ) to ensure data reliability.

Line 14 ⟶ 12:

:V.42bis uses a string encoding algorithm called BTLZ, in which frequently occurring strings of characters are replaced by code words. The "dictionary" of strings is dynamically maintained during transmission and keeps track of changes in the data; new strings are added and old strings are deleted. As the data may not always be compressible (for example encrypted or pre-compressed data) the modem has the ability to switch between compressed and uncompressed modes of operation. Compression performance is continually monitored and, if no compression is obtained, the modem transmits the data in uncompressed form. Even while in uncompressed mode, the modem monitors the characteristics of the data and switches compression back on as soon as some benefit can be achieved.

</blockquote>

[[Category:modems]]

[[Category:Link access protocols]]

{{com-stub}}