Date: Sat, 24 Feb 1996 17:47:30 +0100 From: petzi@zit.th-darmstadt.de (Michael Beckmann) To: Robert Shady <rls@server.id.net>, freebsd-hardware@freebsd.org Subject: Re: ISDN Questions Message-ID: <v02140b02ad54ed34f1d3@[130.83.177.1]>
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>The other advantage of a card vs. an external device is that with an internal >card, you are talking to it in Syncronous mode, which simply means you send >a byte, it sends 8 bits. An external device talks in Asynchronous mode, >which simply means you send a byte, it sends 10-11 bits. Right off the bat, >this means you will get an approximate 20% loss of throughput with an >Asyncronous device Vs. a Synchronous device... Now, you through in the fact >that most external Asynchronous devices have to do the Asynch->Sync conversion >"on-the-fly", it's possible you may loose a little more than that. Hmmm, but when you use 115.200 bps on the serial port, it can do 11.5 kbytes per second, even when the serial interface is asynchronous (10 Bits per byte). And ISDN can only do 8 kBytes per second, assuming you don't use channel bundling or V.42bis compression or the like. So you don't loose any throughput when you run an external ISDN adaptor over an async serial line. All you need is a serial line that is faster than ISDN, then you get the full troughput.
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