Path: utzoo!mnetor!uunet!oddjob!hao!boulder!sunybcs!rutgers!cbmvax!grr From: grr@cbmvax.UUCP (George Robbins) Newsgroups: comp.dcom.modems Subject: Trailblazer Madness Message-ID: <3362@cbmvax.UUCP> Date: 24 Feb 88 10:49:05 GMT Reply-To: grr@cbmvax.UUCP (George Robbins) Distribution: comp Organization: Commodore Technology, West Chester, PA Lines: 72 Keywords: telebit trailblazer s50 carrier Summary: or what Telebit doesn't say about S50=1/2/3 Today, while trying to discover why my Trailblazer was absolutly refusing to connect to another site that I used to be able to contact but had been getting "NO CARRIER" for days, I found some intersting facts... Recently, I patched our uucp so that it would set S50=n, where n was appropriate to the kind of call I was making. This was needed so that I could contact sites in "fast" mode that had S92=1 or that I wanted to call at 1200 baud, despite there actually having a 1200/2400 baud modem. I've previously mentioned that Telebit needs an S50 mode that works somewhat like S50=0, but that gives priority to the transmission mode appropriate to the interface rate, so that connections can be made at the rate the user/dial program expects without having to modify S50 on a dynamic basis. Anyhow, after changing uucp to explicitly set S50, I noticed that I hadn't been able to get through to osu-cis for 3 days, and the success rate calling some other sites was pretty dismal. Well, maybe they were down? I called the number on the phone, and ring, ring, 2400 baud answer tone! Hmmm. I fire up kermit and pound in the ATDT stuff...RRING, RRING, CONNECT 2400. Can't get through for 3 days??? Wait a minute, something fishy. I set S50=3, and redial...NO CARRIER, try 5 times always NO CARRIER, change back to S50=0, works good every time! After some serious headscratching, manual contemplation and dicking around with random (S90/S91) S registers, I still get the same results. Taking a modem into the office so I can hear the speaker, I find that the remote modem does answer, you get the two-step answer tone, and the PSK static sounds, and the the modem says NO CARRIER. After some more headscratching, idea: S7=60... Magic! Now works every time, whether S50=0 or S50=3. Problem(s): The interpretation of S7 varies depending on what mode you select with S50. When you set S50 to 3 or 2 (and perhaps 1), you may need to set S7 to a longer carrier detect timeout to make connections than what you needed with S50=0. When S50 is set to 3 or 2 (and probably 1) you don't get the same call progress detection as with S50 set to 0 or 255, e.g. you don't get the RRING messages. The manual is silent about this. What Appears to Happen: In the S50=0 and S50=255 modes, the DSP chip is being used for call progress detection. This gives you the remote ring detection capability and the S7 time is being interpreted as the time from call initiation until the detection of an answer tone. When S50=1,2,3 the AMD "World Chip" is probably being used for carrier detection. This chip doesn't do much in the way of call progress interpretation, and only signals carrier detect at the end of the answer sequence, perhaps with some additional delay. This would pretty much explain why a longer time needs to be specified when you explicitly select one of the low speed modes. Solution: Users should increment their S7 settings. Telebit should either make the timeouts more consistent, or at least document the difference to prevent severe mental distress on the part of modem users who are under the illusion they understand what's going on. -- George Robbins - now working for, uucp: {uunet|ihnp4|rutgers}!cbmvax!grr but no way officially representing arpa: cbmvax!grr@uunet.uu.net Commodore, Engineering Department fone: 215-431-9255 (only by moonlite)