Xref: utzoo comp.dcom.modems:3688 comp.unix.questions:12778 comp.sys.ibm.pc:27256 Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!rutgers!mit-eddie!uw-beaver!cornell!rochester!pt.cs.cmu.edu!cadre!pitt!amanue!oglvee!jr From: jr@oglvee.UUCP (Jim Rosenberg) Newsgroups: comp.dcom.modems,comp.unix.questions,comp.sys.ibm.pc Subject: MNP Auto-Reliable + getty: happy accident or design? Message-ID: <475@oglvee.UUCP> Date: 10 Apr 89 22:00:44 GMT Organization: Oglevee Computer Systems, Connellsville, Pa Lines: 27 Lately I've discovered that if a UNIX machine is answering the phone at 1200 baud and the caller is calling at 2400 in MNP auto-reliable mode, the MNP handshake seems to toggle the receiver's getty to 2400 just like that, just about every time. The modems in both cases are similar: Multitech external and Multitech internal. Both have MNP, but only the caller is in auto- reliable mode; the receiver is running plain vanilla. The manual describes the MNP handshake as a "Link Request". MNP functions with no start & stop bits, so I assume this Link Request is sent with no start & stop bits also. My understanding is that getty will be toggled by anything that looks like a null (0x0) -- and that's the *only* way getty toggles. (A break should appear as a null with a framing error at any baud rate.) Is the Link Request *guaranteed* to toggle getty? Under what combinations of baud rates? Or does this simply happen as a lucky accident? Lucky accidents do happen. It appears that if the caller is calling at 1200 and the receiver is answering the phone at 2400, if the caller transmits a CR the receiver will hear two bytes, one of which is 0x80. If getty is stripping parity this will come out as 0x0 and woila, getty will toggle. (Good luck going back!) What exactly is the composition of the Link Request? What will it look like to a modem not set up for MNP? More to the point, where can I read up on MNP? -- Jim Rosenberg pitt Oglevee Computer Systems >--!amanue!oglvee!jr 151 Oglevee Lane cgh Connellsville, PA 15425 #include