Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!uwm.edu!gem.mps.ohio-state.edu!lavaca.uh.edu!uhnix1!texbell!vector!telecom-gateway From: goldstein@delni.enet.dec.com Newsgroups: comp.dcom.telecom Subject: Re: TCP/IP over ISDN Basic Rate Message-ID: Date: 23 Oct 89 16:12:49 GMT Sender: news@vector.Dallas.TX.US Organization: Digital Equipment Corporation, Littleton MA USA Lines: 43 Approved: telecom-request@vector.dallas.tx.us X-Submissions-To: telecom@eecs.nwu.edu X-Administrivia-To: telecom-request@vector.dallas.tx.us X-TELECOM-Digest: volume 9, issue 471, message 2 of 8 In article , gnu@toad.com (John Gilmore) writes... >I am interested in hooking up SPARCstations over ISDN. The machine >comes standard with an ISDN terminal interface chip (the "sound" chip, >really an ISDN speakerphone chip). The problem is data encoding; I >have seen no documentation of standard ways to encode data passing on >the 8000 byte/sec channel for IP. I have seen references to ways of >encoding e.g. 9600 baud async "RS232" traffic over ISDN, but I will be >talking ISDN-to-ISDN, so can use the full bandwidth. Rumor has it >that somebody had standardized bit-oriented protocols (HDLC) over ISDN >links, which is ridiculous since they are byte oriented links, sort of >like storing data in main memory with bit stuffing just in case you >ever need to do clock recovery on main memory. My preference would >just be something like "PPP". Okay, it's like this. ISDN provides "circuit mode" and "packet mode" data services. The "packet mode" is essentially X.25, with call setup either inband (after making a circuit call to the X.25 switch) or modified to use ISDN out of band signaling (i.e., Q.931). In any case, CCITT X.31 tells you all about packet mode. Circuit mode is just like modems, but faster. You get 64 kbps per second. It's "raw bits" (oat hulls, wheat chaff...) and no more. It's isochronous (sync) so you need to have some framing technique. It is NOT byte oriented at this point! So HDLC is quite natural, but byte-oriented protocols (i.e., DDCMP) are technically possible too. HDLC chips do all the work anyway, you don't ever put stuff-bits in main memory. To run async or lower speeds, you use rate adaptation. Two standards exist: V.120 is new and HDLC_based, while V.110 is older and more popular among Europeans than Americans. And you can of course create your own if you want, since it's end-to-end. (Northern Telecom has one called T-link that's widely used.) So to do framing, you can use essentially any L2 protocols. I wouldn't advise SLIP on my worst enemy (well, maybe if I really didn't like him and wanted his errors to go undetected) but ISDN isn't anything special in that regard; you just use whatever L2 that both ends agree to. fred