DOCUMENT:Q97879 30-JUL-2001 [lanman] TITLE :RAS and US Robotics HST PRODUCT :Microsoft LAN Manager PROD/VER: OPER/SYS: KEYWORDS: ====================================================================== SUMMARY ======= Do not use US Robotics HST (High Speed Technology) mode on USR Dual Standard or USR HST modems with Microsoft Remote Access Service (RAS). It will actually slow down data communication rates. MORE INFORMATION ================ HST is a proprietary high speed modulation scheme owned by US Robotics. With HST, data flow is asymmetrical - 14,400 bps high band width in one direction and 450 bps low band width in the return direction. This seems like a reasonable thing to do for most typical terminal type applications where most work is done in one direction only. HST modems will automatically switch the high\low speed lines based on which direction has the heaviest traffic. However, RAS extends a fully bi-directional network across the asynchronous connection. For a 14.4 kbps connection, AsyBeui [or NBF] adjusts its timing parameters [T1, T2, TI, and so on] based on the assumption that data frame acknowledgments [ACKs] will be returning faster on a high speed connection. LAN Manager may pause until it receives this ACK. If the returning line is very slow compared to the send line, this will cause unnecessary delays. If LAN Manager does not get an ACK with a given period of time it will automatically timeout and possibly retransmit. These return delays and retransmissions on a 14.4 kbps RAS "connection" with the HST modem will actually get closer to 2400 bps throughput. In fact, a standard v.22bis 2400 bps connection is faster than HST with RAS. USR even recommends in their manuals that you use v.32bis for interactive applications, which is essentially what RAS is. To explicitly specify V.32bis mode [14.4 kbps in both directions] on USR HST Dual Standard modems, add "B0" to COMMAND= the in the Init string in the MODEMS.INF file. See the "RAS Administrator's Guide" for more information on editing the MODEMS.INF file. Additional query words: 2.20 compression correction tuning baud ====================================================================== Keywords : ============================================================================= THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY. Copyright Microsoft Corporation 2001.