The third section of Figure E.3 shows that RAS data compression and decompression happen between computers (DTE-to-DTE link) without involving modem compression. The modem receives RAS-compressed data and just passes it along to the other modem. Thus, modem compression is not involved in this part of the Figure. With RAS data compression, MNP5 modem compression must be turned off in order to prevent redundancy, because data that are already highly compressed by RAS might grow larger before transmission if MNP5 modem compression is enabled simultaneously.
RAS data compression can be four times as efficient as MNP5, and about twice as efficient as V.42 bis modem data compression, unless a previously compressed file is transmitted. V.42 bis can detect whether it is about to expand data that it is supposed to compress. V.42 bis can also automatically suspend itself until the data is once again compressible. It is advised that you leave V.42 bis enabled at all times, but not use MNP5 with RAS data compression.
To avoid data loss due to data buffer overflow, you must enable hardware flow control in the RAS client whenever you are using modem compression or RAS data compression. You may turn hardware flow control on in the RAS user interface of the following RAS versions: Windows for Workgroups 3.11, Windows 95, Windows NT versions 3.1, 3.5, and 3.51. RAS versions 1.0 and 1.1 do not support hardware flow control. RAS version 1.1a requires that a hardware flow control command be set in the Modems.inf file on the command.init line containing the modem initialization string for your modem.
Note
RAS 1.1a ships with the Mcomp.inf file that issues hardware flow control and maximum baud rate commands for all modems supported by that file. To use hardware flow control with a supported modem, you must save the Modems.inf file (which contains modem commands that disable hardware flow control) and copy the Mcomp.inf file to the name Modems.inf.