telecom@ucbvax.ARPA (01/31/85)
From: Jon Solomon (the Moderator) <Telecom-Request@BBNCCA> TELECOM Digest Wed, 30 Jan 85 16:37:29 EST Volume 4 : Issue 151 Today's Topics: T1 is wonderful Seperate AT&T and Local billing Re: TELECOM Digest V4 #150 What's Gerard K O'Neil doing these days? ---------------------------------------------------------------------- Date: 29 Jan 85 06:58:40 PST From: Murray.pa@XEROX.ARPA Subject: T1 is wonderful To: TELECOM@BBNCCA.ARPA Cc: Murray.pa@XEROX.ARPA We have a T1 link to a building a block away. It costs about $1500/month as compared to roughly $1100/month for a 56KB line. (Straight PacTel prices.) The error rate is so low that I can't even see it. How about 0 for 10^7 packets. Are we just lucky? Anybody got any more data? We built our own controller because I didn't find one that would connect to a Multibus. Anybody know of one? I don't want it to do me any favors (like talk TCP), just send and receive raw packets like a dumb ethernet controller. I don't know what a DMR-11 is like, but it probably won't be trivial to interface it to a T1 line. The first problem is that the receive side doesn't provide the clock on another pair of wires like RS232 modems do. You have to watch the line, and derive the clock with a PLL. Another problem is that you have to send ones occasionally. (15 zeros in a row max and you must have at least 3 ones in every 24 bits.) SDLC packet format meets this if you invert the data! The last problem I know about is that the actual interfacing to the wires is more complicated that just plugging in the 1488/1489 chips that everybody uses to talk to RS232 lines. I got an analog wizard down the hall to design that part: 4 chips, 2 transformers, 2 transistors and a few resistors. There must be a better way, but it works, it fits, and I didn't have any troubles with it. If you do decide to design something, check out the RPT-81 from Precision Monolithics and/or look at page 305, Electronic Design, 7-Jan-82. If you are thinking of generic T1 links, like a microwave gizmo rather than an official T1 line from your phone company, you may have some more options. The one by GE (GemLink) is availiable with RS422 interfacing. I don't know any more than it's an option on their data sheet. You should also look into closed circuit TV versions if you are willing to do the analog interfacing work. (I don't know much about it.) Then you can pick the data rate. That might be helpful if something like your DMR-11 really tops out at 1Mb rather than the 1.5 that a T1 expects. T1 is clearly a wonderful thing. The bypass market is going to support a lot of companys making whizbang microwave and fiber boxes, and they are all going to be talking T1. Interconnecting LANs that are scattered around a campus is going to get dragged along for the ride. The prices and flexibility can only get better.... Support your local T1 vendor. ------------------------------ Date: 29 January 85 22:20-EST From: Michael Grant <GRANT%UMDB.Bitnet@WISCVM.ARPA> To: Telecom Digest <TELECOM@BBNCCA.ARPA> Subject: Seperate AT&T and Local billing As I see it, AT&T might ask there local company to withdraw local service if a customer stopes paying there phone rental bill. After all, that phone IS connected to the local suplier's line. And, anyway, AT&T still has some ties to that local company, they can probebly drop little threats like 'Well, if you don't cut Mr. Shmo's phone for us because he's stopped paying for his phone, we're not going to renew that service contract on all that nice switching equipment we sold you.' On the other hand....they may just ignore you until the bill got 'big enough' to worry about. -Mike Grant ------------------------------ Date: Wed, 30 Jan 85 08:37:13 pst From: hplabs!sdcrdcf!darrelj@Berkeley (Darrel VanBuer) To: telecom@Berkeley Subject: Re: TELECOM Digest V4 #150 Cc: You can't generally use just a plain high-speed syncronous interface to a T1 facility because of coding restrictions (e.g. every 193rd bit must be a timing slot, and often every 8th bit must be reserved for control signaling). I.e. you have to follow the guidelines for the 24 telephone conversations which might be there instead, leaving you a slightly stuttery 1.344 Mbps. Darrel J. Van Buer, PhD System Development Corp. 2500 Colorado Ave Santa Monica, CA 90406 (213)820-4111 x5449 ...{allegra,burdvax,cbosgd,hplabs,ihnp4,orstcs,sdcsvax,ucla-cs,akgua} !sdcrdcf!darrelj VANBUER@USC-ECL.ARPA ------------------------------ Date: Wed 30 Jan 85 16:12:21-EST From: Ralph W. Hyre Jr. <RALPHW@MIT-XX.ARPA> Subject: What's Gerard K O'Neil doing these days? To: telecom@BBNCCA.ARPA I heard he was working on some kind of worldwide communications system, but I don't know anything else? If anyone has an address of more information I'd appreciate hearing about it. (Gerard K. O' Neil wrote 'The High Frontier', which advocates building space colonies.) - Ralph Hyre ------- ------------------------------ End of TELECOM Digest ******************************