Date: Fri, 21 Apr 95 11:14:47 EDT From: jeffa@sybase.com (Jeff Anuszczyk) To: mcw@hpato.aus.hp.com Cc: questions@FreeBSD.org, jeffa@sybase.com Subject: Re: Annex router Message-ID: <9504211514.AA13041@red_oak.sybgate.sybase.com>
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> From owner-freebsd-questions@freefall.cdrom.com Thu Apr 20 21:43:42 1995 > From: M C Wong <mcw@hpato.aus.hp.com> > Subject: Annex router > To: freebsd-questions@freefall.cdrom.com (freebsd-questions@freefall.cdrom.com) > The problem I have is the carrier keeps dropping once per day, and if lucky > it will stay up to 2 days, and that's about it. My questions are : Well, as much as I'd love to say you can do *MUCH* better, in the states I find that two days would be very good indeed. Mostly slight glitches in the telco line cause the modem to drop. Not exactly sure why. But I have setup a few perm. on-line systems and the modems pretty much always drop every day or two... sometimes even more often. Perhaps some with much more experience can give their experiences... but in my mind, unless it's a leased line, 24 hours of uptime is good, anymore is great. > 1) Is there a way for one to determine which side is actually the culprit ? Some modems have the ability to query them to determine why the modem dropped (actually why was the last disconnection made). I know that some AT&T modems have this as an AT&V7 type of query. > 2) Assume it's the ISP side that drops carrier, is there any setting on > the Annex which *may* cause such interruption, is there config parameters > on Annex that will, say, reset, intitialize the port etc etc that *may* > affect my connection ? What commands to view/configure them (since I > have no `hands-on' experience with an Annex) ? Can't answer this, although any of which you can *can* happen. Don't know if it *is* happening though. > 3) If it's my side which drops carrier, can anyone think of a likely cause > apart from bad line quality, unreliable modem (although this is what > I suspect the most as I can get them swapped for `real' Netcomm!) ? Bad line quality (i.e. intermittent line noise) usually is the #1 culprit. Please be aware that the faster the modem the more susseptible to noise it is. 28.8K modems (V.34) are pretty decent in their recovery capability but they can drop the link when the noise gets bad enough. I should point out that a "normal" voice grade line is not warranted against noise. As such periodic static bursts can and do happen. I believe it is these that cause the line drop. > 4) Also, with 2 identical brand and model of modems, I still fail to > get them connected at 38.4K when I kermit at 38.4K on FreeBSD box. I > rang their tech support and was told that I need to kermit at 57.6K > to get the 2 modems connected at 38.4K! > This kind of confuses me as I tried kermit at 38.4K with a Dynalink 14.4K > and it connected at 38.4K straight away! So my quesitions are : > 4.1) why ? > 4.2) Is there a way one can force both modems to talk at fixed 38.4K. > 4.3) Assumes two modes connect at speed XXX, does it mean the PC is talking > to the modem at speed XXX as well ? Also, with V.34 modem, does one > need to enable compression to get 38.4K ? Hmmm, first, you should try and set both ends of the link to at least 57.6K. Remember the max uncompressed speed of a V.34 modem is 28.8KB not 38.4KB. As such the "link" speed will never exceed 28.8. However, the connection speed to the modem should be much higher to allow the modem to compress. It is *possible* to get 4x or more compression from V.34 although it is totally data dependant and is usally more like 2x. In any case, connecting to the modem at 38.4KB will only allow the modem to do limited compression. So, to answer your questions: 1) Connecting to the MODEM at > 28.8KB is definately desireable. Pick the fastest speed your hardward can support (usually 57.6KB) Note this is not the modem to modem connect speed (that can't be higher than 28.8) but the modem to computer speed. 2) The remote side modem (the one you are dialing into) will probably need to be set to a fixed speed. Validate that this modem to annex connection speed is at least 57.6KB and that the modem won't auto reset to some other speed upon disconnection. This, by the way, is a very common problem and will subtely keep your total throughput down. 3) In reply to "Is there a way one can force both modems to talk at fixed 38.4K." I'm going to assume you mean computer to modem not modem to modem (see #1 above). The answer to this is yes but you need to look at your owners manual for a description of how to lock the serial port baud rate. 4) As for connect messages, remember there are two connect speeds involved. The computer to modem and the modem to modem speeds. These are independent of each other and should not normally be the same. The computer to modem speed should be very high (57.6KB or higher), the modem to modem connect speed cannot be higher than the V.34 standard of 28.8KB (and normally doesn't even get that high due to line noise... expect 26.4 or so as the normal "real" speed). Hope that answered some of your questions. - Jeff
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