Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!iuvax!cica!tut.cis.ohio-state.edu!cs.utexas.edu!samsung!rex!wuarchive!texbell!attctc!vector!telecom-gateway From: goldstein@delni.enet.dec.com Newsgroups: comp.dcom.telecom Subject: Re: TCP/IP over ISDN Basic Rate Message-ID: Date: 17 Nov 89 17:30:20 GMT Sender: news@vector.Dallas.TX.US Organization: Digital Equipment Corporation, Littleton MA USA Lines: 33 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 519, message 4 of 8 In article , zweig@brutus.cs.uiuc. edu (Johnny Zweig) writes... >I can whip up a SLIP at 64000bps that will make me happy if I have a >line that takes 8000 bytes every second and hands them to whoever I >called. Routing and other considerations are research-problems and >belong in comp.protocols.tcp-ip. I just want as many bytes/second as >I can squeeze out of the wire. SLIP is a framing-protocol, so forget >HDLC. I promise to be the only one using the bits. If you are happy using SLIP then you have other problems to worry about! :-) SLIP is NOT a valid data link protocol. While it provides framing (as do HDLC, DDMCP, etc.), it provides NO error detection, let alone recovery. So you trust the weak checksums in TCP and IP to detect line noise. From a data integrity point of view that's seriously bad. (That's a general-purpose anti-SLIP diatribe, btw.) >I just don't get this business of taking a byte-stream protocol and >layering a bit-stream protocol on it (lowering the bandwidth available >to payload), and then putting a byte-stream on that (using, say, >bit-stuffing and further lowering available horsepower). Could >someone please explain? It seems dumb. You don't lose much with HDLC, about 1/63 to the bit-stuffing, and with only one flag at each end of the frame, it's probably comparably efficient to SLIP. You gain pretty good (not great) error detection (CRC_16), and optional hop-by-hop error recovery (I vs. UI frames). Since HDLC is used on the D channels already, it's built into ISDN chips, making it cheap. fred