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Path: euryale.cc.adfa.oz.au!newshost.anu.edu.au!harbinger.cc.monash.edu.au!news.mel.connect.com.au!munnari.OZ.AU!ihnp4.ucsd.edu!agate!violet.berkeley.edu!jkh From: jkh@violet.berkeley.edu (Jordan K. Hubbard) Newsgroups: comp.unix.bsd.freebsd.misc,comp.dcom.isdn Subject: Re: Motorola Bitsurfer Pro + FreeBSD Date: 15 Dec 1995 09:14:09 GMT Organization: University of California, Berkeley Lines: 79 Message-ID: <4are91$h5a@agate.berkeley.edu> References: <4ab9fe$d14@murphy.servtech.com> <DJKC80.Aqu@rci.ripco.com> <DJL3r9.MCC@calcite.rhyolite.com> NNTP-Posting-Host: violet.berkeley.edu Xref: euryale.cc.adfa.oz.au comp.unix.bsd.freebsd.misc:10938 comp.dcom.isdn:23658 In article <DJL3r9.MCC@calcite.rhyolite.com>, Vernon Schryver <vjs@calcite.rhyolite.com> wrote: >>To FreeBSD it'll just look like a fast serial port, and sets up like any >>other PPP connection. > >The channel aggregation of devices like that BitSurfer is a function >of PPP, albeit PPP in the ISDN Terminal Adapter. Judging from what Eh? I don't know much about the BitSurfer but this is most certainly *not* the case with the TAs I'm currently using, namely the L1 Express model from ADTRAN. Sync PPP or Multi-Link PPP are certainly ways of using an ISDN line but, using a TA, are hardly your *only* options. I think people are a little confused about how this all works. Here's the story: Your average semi-modern TA will support differing types of external and "internal" communications. To list just those which are the most relevant to this conversation, the two external comms types are synchronous serial and asynchronous serial. The internal comms (that is, TA to TA and not externally visible) supported are "bonded" and single channel. The external comms are fairly standard: If you're running sync, the TA will provide you with a data rate of up to 128Kbps (this requires some sort of syncronous serial capability, either with a router or a special sync-serial PC card). If you're running async, as I am, the TA will provide you with a data rate of up to 115.2Kbps, and you can pretty much use any standard serial port with it. The 16550 (FIFO) UART based boards provide the best performance, though I'm using a 16450 (no FIFO) board in my little 486 gateway machine (running FreeBSD) and it takes 115.2K just fine with no serial overruns. I wouldn't really worry about it either way unless you'll be using your gateway for other serious activity. The other issue with sync vs async comms is *overhead* - sync communications use (surprise!) 8 bits per byte, whereas async is forced to use 10 - one start bit, the 8 bit data, and one stop bit. This naturally cuts down on the number of bits you have available for actual data, and therefore sync serial will give you the faster data rate. On the flip side, sync serial interfaces cost a lot more than async ones. Nothing comes for free! Now the TAs themselves can use one or more B channels to implement their internal comms, with the D channel used for dialing and other out-of-band signaling. Depending on which area you live in, and how many Central Offices (COs) your connection spans, you're either limited to 56Kbps per B channel or you can do a full 64Kbps. The TAs can be set up to use a single channel as your "data pipe", giving you 56K or 64K, or they can make two ISDN calls automatically and use both B channels as a single pipe - this is what is referred to as "bonding". Some TAs also only support bonding for *sync* communications, not async, and it was the ADTRAN TA's ability to do the latter that led me to select it (that and the recent price drop to $349 also had something to do with it. :-) The bonding schemes used internally by the various TAs ARE NOT GENERALLY COMPATIBLE and if you try to put a BitSurfer on one end of a connection and an ADTRAN on the other, it WILL NOT WORK! Use TAs from the same manufacturer on each end if you want to do this. And that's basically it! Also note that since you're making two ISDN phone calls for bonded connections, you're also *paying* for two connections! Some RBOCs (your local telco) have different tarrifs for this, with "residential ISDN" and "business ISDN" classes being frequently offered. The residential ISDN service would generally appear to be unmetered (e.g. no per-minute charges while connected) during non-business hours, that is on weekends and between 5PM and 8AM. Business ISDN is invariably metered. Therefore, if you're trying to create a dedicated ISDN pipe, then you'd better be sure that either: A) You're one of the few lucky ones who's RBOC doesn't charge per-minute for ISDN connections. B) You are located in the same CO as your ISP and can apply for "Centrex ISDN", which isn't metered (this is what I do). C) You're not the one paying for it. :) Hope this helps! Jordan