Path: utzoo!telecom-request Date: 20 May 91 16:01:42 GMT From: oberman@ptavv.llnl.gov Newsgroups: comp.dcom.telecom Subject: Re: It Still Don't Network ... or? Message-ID: Organization: TELECOM Digest Sender: Telecom@eecs.nwu.edu Approved: Telecom@eecs.nwu.edu X-Submissions-To: telecom@eecs.nwu.edu X-Administrivia-To: telecom-request@eecs.nwu.edu X-Telecom-Digest: Volume 11, Issue 380, Message 4 of 10 Lines: 79 In article , hpa@casbah.acns.nwu.edu (H. Peter Anvin) writes: > A few questions about ISDN: > 1. Is is feasible/not feasible to use ISDN as a link in an IP or Ethernet > network? An ISDN B channel is simply a bit pipe. IP or anything else is perfectly feasible. It should be noted that Ethernet is a 10 Mhz system and ISDN is only 64Kb (B channel), so some sort of remote bridge would be required and protocols with tight timing requirements (IP is NOT one of these) might have problems. > 2. Is ISDN a worldwide standard, or another one of them "we decide > what we want" USA standards? Yes, ISDN is a worldwide standard. Yes, it is another one of them "we decide what we want US standards." It's "Two ... two ... two standards in one." Actually the problem is that the basic telephone link speed is different in the US and, as a result, the ISDN must be different to work. The US uses 1.5 Mhz T1 lines while much of the world uses 2 Mhz links. So there are two ISDNs, one carrying more B channels (30) than the other (23). But, since the B channels are the same, the phone company can handle conversion of the 2 Mhz version to the US 1.5. It does mean that the terminal equipment is totally incompatible. > 3. Does the 64 kbit/s B-channel rate over ISDN include error correction? It is just an HDLC bit pipe and has very little difference form LAPB, the link layer standard used for OSI networking. The error detection/correction is very limited because LAPD (the HDLC protocol used for ISDN) is very light weight. > 4. Does the D-channel protocol include service identification (say IP, > video, voice, modem)...? D-channel is a very different bird. It does include a "service identification, but the only defined protocols I am aware of are X.25 and native ISDN. I wouldn't be surprised to see others added. There are plenty of bits available. But you need to understand that D-channel is NOT a bit pipe and is a packet protocol. It run IP over a D channel (IMHO a silly idea) would have to be like running it over X.25. It would not be a protocol at this level. In fact, it probably would be over X.25 as would modem (by connection to an ISDN PAD). Voice and video on a shared 16 Kb channel? You're kidding, right? > 5. Is is possible to call a POTS line with a modem from an ISDN connection? Not directly. As mentioned above, you would not use a modem but an ISDN PAD. Our site has a pool of modems for outgoing calls from ISDN lines. You call a magic number to be assigned a modem and then enter the command sequence to dial the analog modem. You can't hook up any POTS equipment to an ISDN line. This includes modems, answering machines and any other analog component. > 6. What are typical rates for ISDN? Is it billed per minute or per block? ISDN is currently tariffed in California for Centrex service only. ISDN runs about $30 / mo. with all other services charged the same as POTS. I believe there is a new tariff on the docket, but I wouldn't swear to it. At this time there is no residential ISDN tariff in this state. But other states may vary. In the "For what it's worth department", Pac*Bell is hoping to have ISDN in my central office by late this year and SS7 for connection to other ISDN islands like Berkeley and Sunnyvale. Who knows. Some year I might even be able to get a connection to another state. R. Kevin Oberman Lawrence Livermore National Laboratory Internet: oberman@icdc.llnl.gov (415) 422-6955 Disclaimer: Don't take this too seriously. I just like to improve my typing and probably don't really know anything useful about anything.