stu@tandem.com (Stuart G. Phillips) (06/04/91)
============================================================================== Weekly digest for WIRELESS mailing list Week ENDING June 1, 1991 This digest (or back issues) can be obtained by anonymous FTP to tandem.com from the wireless directory. The file wireless/wireless explains the purpose of the mailing list and describes how to subscribe and post. The WIRELESS mailing list is moderated by Stuart Phillips and Kevin Rowett. ============================================================================== From: Stuart G. Phillips <stu@tandem.com> Message-Id: <9105261841.AA26058@suntan.Tandem.COM> Subject: Effects of multi-path propagation There have been several recent papers (I can dig out the references if anyones interested) both as submissions to the IEEE 802.11 committee and the IEEE Trans. Comm on the amount of jitter caused by multi-path distortion. Some of the work has been done by the cellular folks, the rest by those working on Wireless LANs. Although the cellular folks were working over terrestial paths of a few kilometers and the WLAN folks over a few tens of meters, the results are remarkably similar. Multi-path distortion results in jitter between 100 and 200 nS. A good analysis of the effects of muli-path propagation on jitter can be found in IEEE 802.11/91-3 (Radio System multipath propagation analysis leading to possibilities for mitigation - Chandos Rypinski). To cut a long story short, multipath propagation results in two distinct problems - fading and intersymbol distortion. Some of the effects can be overcome by diversity reception (using two or more antennas) but there seems to be a fundamental issue. Given 100-200 nS of jitter it would seem to suggest that Wireless LANs are restricted in bandwidth to something between 256 Kbps and 1 Mbps (assuming a jitter to data period ratio of 10:1 or similar). The simplest way to reduce the effects of multi-path propagation is to use optical (line of sight) paths with narrow beamwidth antennas. I suspect this is partly how Motorola gets its claimed bandwidth (being at 18 GHz probably helps too :-) ! There are several products on the market that claim higher bandwidths than my postulated 256 K - 1 Mbps range. It would be interesting to see the results of some field trials and the types of BER that result. Does anyone have any results they would share or any comments (rebuttals are fine too !) on the limitations on bandwidth resulting from multi-path ? Stuart BTW, the WIRELESS mailing list is now some 80 folks strong as of today ! ----------------------------------------------------------------------------- From: "Jonathan M. Zweig" <zweig.PARC@xerox.com> Date: Tue, 28 May 1991 10:12:35 PDT Subject: Re: Effects of multi-path propagation What is the characterization of the 100-200 nS jitter? When I use the term jitter (I usually work in internetworking) I mean it as something like "the uncertainty in how long it will take a packet to reach its destination." That is, it may take 100 mS with a 20 mS jitter (whether this means 80/120 or 90/110 as the limits is another issue) to get through. But in radio, I think the term might mean something else.... Anyway, intuitively it seems like in a given setup without fast-moving reflectors and RFI sources and all, that the signal will settle down to a particular standing-wave interference pattern and what you get is what you get. I don't see how, say, a 4 MHz sine-wave (or 4 GHz for that matter) would arrive as anything other than a 4 MHz something-wave made up of all the different phase/attenuation values from the multiple paths. That is, I can't see my bit-stream getting overlaid with itself differently at different times, so once I get a signal that works, it works for a long (i.e. many bit-times) time. I can see how having the bit time be less than the difference between the signal propagation times for the major signal paths would make things unhappy -- but I would guesstimate that with 100-200nS difference (which sure as heck can't happen if the signal only goes 30-50 feet!) you could push it to 5 MHz without too much fuss. But then again, I'm no radio engineer.... -JohJonnhnyn MulMtultipaiptahth ----------------------------------------------------------------------------- From: bear@tcs.com (h.w. neff) Subject: Re: Effects of multi-path propagation # # >From zweig@parc.xerox.com Tue May 28 10:14:49 1991 # # -JohJonnhnyn MulMtultipaiptahth # effects ?- why, as with the quoted post, you see more than one copy of the information. effects ?- why, as with the quoted post, you see more than one copy of the information. 8^) 8^) levity quota now expired. ttfn, bear. ----------------------------------------------------------------------------- Date: Tue, 28 May 91 22:52:11 PDT From: Stuart G. Phillips <stu@tandem.com> Subject: Re: Effects on multi-path propagation Jonathan Zweig <zweig.PARC@xerox.com> writes... >What is the characterization of the 100-200 nS jitter? When I use the term >jitter (I usually work in internetworking) I mean it as something like "the >uncertainty in how long it will take a packet to reach its destination." That >is, it may take 100 mS with a 20 mS jitter (whether this means 80/120 or >90/110 as the limits is another issue) to get through. > >But in radio, I think the term might mean something else.... > Well now.... think of the time it takes a bit to propagate from transmitter to receiver; in actuality not much different from Ethernet. Signals (RF or otherwise) propagate at the speed of light (300 E6 m/s) in free space or at about 0.6 C (C= speed of light in a vacuum aka free space) on a cable (this modification ratio is called the velocity factor of the cable and is quoted by the manufacturer). Since we're talking wireless here, consider the physical length of a bit - at 10 Mbps, one bit period is 30 meters long (think of it as a wave train). Another way to think of it is that the bit takes 100 nS to travel 30 meters. Now think about the effects of multi-pathing; since we're dealing with RF from an antenna there will be several paths traversed by the wave train - the direct (sometimes called optical) path and reflections caused by the floor, ceiling, furniture, people ..... Rypinski's paper says that a path difference of 0.1 times the bit length (or 3 meters) begins to cause fading while more causes inter-symbol distortion. Think of the wave train over the optical path; the bit takes 100 nS to propagate from start to finish. A reflected component of the wave train shows up some delta time later (delayed by travelling a greater distance) and finishes correspondingly later. The late arrival causes the relected component to "smear" into the next bit period. If the time delay is greater than 0.1 times the bit period it begins to corrupt the next bit or symbols worth of data. The effect is similar to phase induced jitter since it creates an area of uncertainty at the beginning of the bit. Such jitter can occur over short paths (< 10 meters) and so creates problems running at high speeds (back to my assertion of jitter not exceeding 1/10 the bit period). Sorry for the long reply but this is an example of the problems facing the marriage of data comm and rf technology that gave rise to this list (BTW now over 120 strong !). Stu ------------------------------------------------------------------------------ From: Andrew Myles <andrewm@avalon.mqcs.mq.oz.au> Subject: References Date: Thu, 30 May 91 11:40:05 EST G'day all, Here are some references that I have already typed in to get things rolling: 1) John Craick, Telecom Australia, "The Paperless, Wireless, Peopleless Office: Human, Organisational and Social Issues", Telecommunications Journal of Australia Vol. 39, No. 3, 1989 2) Dr John Ellershaw, Telecom Australia, "The Paperless, Wireless, Peopleless Office: Technology Trends in the Office", Telecommunications Journal of Australia Vol. 39, No. 3, 1989 3) Malcolm H. Ross, Arthur D. Little International, "The Paperless, Wireless, Peopleless Office: The Future Prospects for the Wireless Office" Telecommunications Journal of Australia Vol. 39, No. 3, 1989 4) Alistair Fraser, Telecom Australia, Mike Buchanan, Communication Solutions, "The Paperless, Wireless, Peopleless Office: Telecom And the Value Added Services Evolution", Telecommunications Journal of Australia Vol. 39, No. 3, 1989 5) P. Bernhard, Telecom Australia, "The Paperless, Wireless, Peopleless Office: Laying the Foundations of The Office Of the '90s", Telecommunications Journal of Australia Vol. 39, No. 3, 1989. -- -------------------------------------------------------------------------------- E-Mail: andrewm@avalon.mqcs.mq.oz.au || andrewm@mpce.mq.edu.au In-Real-Life: Andrew Myles Organisation: High Speed Networks Group, Electronics Discipline, School of Mathematics, Physics, Computing and Electronics, Macquarie University, Sydney, Australia 2109. Telephone: +61 2 8058439 (W), +61 2 8058983 (Fax), +61 2 446315 (H). ------------------------------------------------------------------------------ Date: Wed, 29 May 1991 18:47 MST From: Aaron Leonard <LEONARD@Arizona.edu> Subject: NCR's spread-spectrum FCC request to be denied? Stu:: We do however have a distinct shortage of Stu:: contributions. Well, this new addition to the Wireless mailing list won't let his late arrival nor his lack of RF sophistication prevent him from contributing ... so here goes ... We've been looking at the NCR spread-spectrum PC transceiver cards as a potentially handy way to do some metro-area networking on the cheap. (Our interest would be particularly in using them in unidirectional mode ... getting a couple of yagi antennas, finding a line of sight, and then use PC-Bridge to extend our LANs via the spread-spectrum.) The pluses would be cheap (around $5K for all the hardware), quick to set up (supposedly no FCC approval a la microwave), fast (200Kbps??), and good distance (up to 5 miles?) However, I just heard a rumor that the FCC is "on the verge" of denying NCR's petition to use that range of spectrum for its spread-spectrum application. Supposedly the transceivers were only being allowed to operate in "experimental" mode, and supposedly the FCC is going to pull the plug on the experiment within the next couple of weeks. 1) Can anyone who knows more than I do (that is, anyone who knows anything at all) report on the FCC status of NCR's spread-spectrum products? 2) If the spread-spectrum stuff looks like a go FCC-wise, would anyone care to remark on the suitability of the NCR (or other) spread-spectrum transceivers for bridged or routed Ethernet? Thanks, Aaron Aaron Leonard (AL104), <Leonard@Arizona.EDU> University of Arizona Telecommunications, Tucson AZ 85721 ----------------------------------------------------------------------------- Date: Thu, 30 May 1991 08:41 EST From: "John D. Balogh, PSU OTC, 814.863.1252" <JDB@ecl.psu.edu> Subject: GUNNplexers for LAN use? To: wireless@tandem.com I just received a question from one of our student employees about the use of GUNNplexers (10.2GHz typically-HAM-Radio-only device) for extending an ethernet between two buildings that don't have fiber yet. Any experience with these beasts? I read articles about these devices in "QST" and "Ham Radio" more than 5 years ago. Seems that they would be great for short-distance (less than 500 meters) line-of-sight wide-bandwith (more than the usual audio 4KHz) applications. Just brew up an IF strip that has 20MHz bw and provide the appropriate signaling on an FM detector so that collision detect wasn't a problem, and away you go! As I recall, they are quite temperature sensitive, but that can be overcome with a styrofoam 6-pack cooler and a lightbulb/dimmer circuit. Any suggestions are (probably) appreciated. John Balogh, Data Engineer | Usual disclamers apply. ----- +--------------------------- Penn State, Office of Telecommunications | Your mileage may vary. Internet: JDB@ECL.PSU.EDU | Eat lots of fruit. Bitnet: JDB@PSUECL.BITNET | Be nice to your neighbors. AT&Tnet: +1 814 863-1252 (with voicemailgizmo) | Keep the time :-) Fax: +1 814 863-4092 | Use standards. SNAILmail: 205 Pine, Univ. Park, PA 16802 | Push for Interoperability. ------------------------------------------------------------------------------- From: scoggin@delmarva.delmarva.COM (John Scoggin) Subject: Motorola Altair System Date: Thu, 30 May 91 7:45:46 EDT Does anyone on this mailing list have the Motorola Altair wireless Ethernet installed? If so, how is it managed? SNMP, proprietary, or not-at-all? (don't laugh - we have a Motorola Computer-Aided Dispatch System which is one or the most poorly designed systems on the planet, from a network management standpoint!) Also, how has reliability been? Comparable to hard-wired. How about intereference from terrestrial 2GHz microwave? Thanks -- ---------------------------------------------------------------------- John K. Scoggin, Jr. Supervisor, Network Operations Phone: (302) 451-5200 Delmarva Power & Light Company Fax: (302) 451-5321 500 N. Wakefield Drive Email: scoggin@delmarva.com Newark, DE 19714-6066 ---------------------------------------------------------------------- From: Ron Gershon <gershon@vis.toronto.edu> Subject: A question about this newsgroup Date: Thu, 30 May 1991 09:43:04 -0400 Hi. Just wondering if this newsgroup applies to powerline communications as well. We, at Adaptive Networks, have developed yet another wireless communication solution using the AC powerline, and offer LANs using this module. Therefore I would be interested to know whether the membership of this newsgroup is interested in this medium. Thanks. Ron Gershon Adaptive Networks Ltd. ----------------------------------------------------------------------------- From: Ron Gershon <gershon@vis.toronto.edu> Subject: Info on Adaptive Networks' powerline communication products Date: Thu, 30 May 1991 12:07:32 -0400 I didn't know my message will be posted directly to the list, nor did I anticipate a lot of responses, so let me summarize what Adaptive Networks has to offer. Ron. ---------------------------------------------------------------------- Adaptive Networks' patented AN192 technology transmits data at an effective throughput of 19.2 Kbps over powerlines with the reliability of dedicated communications wiring. Designed into OEM products, it allows them to network over existing powerlines, thus eliminating the cost and hassle of installing wiring. An ISO standard for shipboard monitoring of refrigerated cargo containers was awarded to Adaptive Networks in January of this year over competing proposals from Westinghouse and NEC/Mitsubishi. We provide board-level products, as well as self-contained standalones units. In the 4th quarter of this year we will have a 2-chip set version of the product. Some of the current applications of the AN192: * School security system (time and attendance) in New York City * Shipboard monitoring of refrigerated containers * Materials handling through moving stacking cranes for storage and retrieval in an automated warehouse Prices vary with quantities. For the 3" x 5" module (board), prices vary from $650 per module for a quantity of 2, to $122 for quantities over 1000. The standalone product is slightly more expensive. The 2-chip set is expected to be in the double digit price range. Product specifications: Network Configurations: * Token Bus * Master/Slave centrally controlled bus Powerline Interface: AN Isolation module protects against powerline surges and spikes Network Size: Up to 65534 nodes User-effective throughput: 19.2 kbps Bit Error Rate: < 1 x 10^-9 Size (of module): 3.05" x 5.20" x 0.45" Power Requirements: Voltage: +5 VDC and +/- 12 to +/- 15 VDC Consumption: 5 Watts typical Head office (including Marketing): Toronto office (R&D): P.O.Box 1020 223 Tansley Rd. Kendall Square Branch Thornhill, Ontario Cambridge, MA 02142-0999 Canada, L4J 2Y8 (617) 497-5150 (416) 882-1922 (617) 787-8168 (fax) (416) 881-8429 (fax) ------------------------------------------------------------------------------- From: chk@alias.com (C. Harald Koch) Subject: Re: Powerline <wireless> Lans ? Date: Thu, 30 May 91 10:44:12 EDT > From: Ron Gershon <gershon@vis.toronto.edu> > > Just wondering if this newsgroup applies to powerline communications as > well. We, at Adaptive Networks, have developed yet another wireless > communication solution using the AC powerline, and offer LANs using this > module. Therefore I would be interested to know whether the membership > of this newsgroup is interested in this medium. How much noise does your network generate on the power lines? We already have several problems with noisy power here, from a braindead digital clock that runs at about 8 times realtime to random computer crashes. The experts claim that this is all caused by excessive noise on the power lines. Expensive power filters have solved the problem on our critical machines, but we aren't rich enough to put filters on all our electrical appliances. I'm quite skeptical about AC powerline networks (and control systems like BSR) because of the problems caused by power line noise. Here's your chance to change my mind... :-) -- C. Harald Koch VE3TLA Alias Research, Inc., Toronto ON Canada Internet: chk@alias.com chk@gpu.utcs.toronto.edu chk@chk.mef.org ------------------------------------------------------------------------------- Date: Thu, 30 May 91 14:02:33 -0400 (EDT) From: Anders.Klemets@cs.cmu.edu Subject: Re: NCR's spread-spectrum FCC request to be denied ? > Supposedly the transceivers > were only being allowed to operate in "experimental" mode, > and supposedly the FCC is going to pull the plug on the > experiment within the next couple of weeks. Sounds like complete baloney to me, unless you are talking about some NCR product other than the WaveLAN. The WaveLAN's have a sticker that says "FCC ID: IMR915RLAN-1." They operate at 2 Mbit/s on the 900 MHz band. I have a BSD UNIX style driver for them that I run on Mach 2.5. FTP gives a throughput of 120 kbyte/s at best. Just shipping UDP packets gives a throughput of 130-150 kbyte/s on average. Performance worsens if one tries to run more than two WaveLANs at the same time, as might be expected. I can make the driver source code available to anyone who has a MACH source license. And I would be interested in knowing whether someone has written an MSDOS packet driver for the WaveLAN. Anders ------------------------------------------------------------------------------ Date: Thu, 30 May 91 14:36:19 -0400 (EDT) From: Anders.Klemets@cs.cmu.edu Subject: Fwd: NCR Unveils WaveLan Network ---------- Forwarded message begins here ---------- Message-ID: <YcBxIx200UfAI0YvpN@andrew.cmu.edu> From: DowJones@andrew Subject: NCR Unveils WaveLan Network Date: Mon, 20 May 91 09:55:09 -0400 (EDT) ATLANTA -DJ- NCR Corp. said it unveiled a micro channel version of WaveLan high-speed wireless local area network. The company said in a press release that the network eliminates the need for wiring to connect personal computers in office settings. The company said that its WaveLan can be used with the vast majority of network operating systems currently being shipped. NCR WaveLan has a suggested retail price of $1,390 for the Network Interface Card including Novell NetWare v3, NetWare v2 and Microsoft Lan Manager drivers as well as the omnidirectional antenna. 9:54 AM From matthew@ucscb.UCSC.EDU Thu May 30 13:31:17 1991 ----------------------------------------------------------------------------- Date: Thu, 30 May 91 13:26:03 -0700 From: matthew@ucscb.UCSC.EDU (Matthew Kaufman) Subject: Re: GUNNplexers for LAN use ? I've been thinking about this very thing myself. One should note that amateur regulations on content are very restrictive, but it seems like a device operating under the new FCC Part 15 intentional radiator rules on 24 GHz should work pretty well. 24 GHz is more affected by atmospheric water vapor and the power limitation is 250 microvolts/meter measured at 3 meters, but it seems that a short hop wouldn't be too difficult. The trick is to build a receiver that can run at 10 MBps, of course, so the microwave tranceiver can be used with standard ethernet hardware instead of some sort of custom modem card or even T1, which are more expensive. Low power (1-2 mW) 24 GHz gunn tranceivers can be had for about $70 new and modulation is trivial, especially on those tranceivers with varactor diode modulators, so if the cost of the IF/demod hardware could be kept low, this might be one of the cheapest wireless network solutions available -matthew kaufman matthew@ucscb.ucsc.edu, or, kaufman@apple.com ---------------------------------------------------------------------------- From: scoggin@delmarva.delmarva.COM (John Scoggin) Subject: Re: Powerline <wireless> Lans ? Date: Thu, 30 May 91 17:32:27 EDT > >> From: Ron Gershon <gershon@vis.toronto.edu> >> >> Just wondering if this newsgroup applies to powerline communications as >> well. We, at Adaptive Networks, have developed yet another wireless >> communication solution using the AC powerline, and offer LANs using this >> module. Therefore I would be interested to know whether the membership >> of this newsgroup is interested in this medium. > >How much noise does your network generate on the power lines? We already >have several problems with noisy power here, from a braindead digital clock >that runs at about 8 times realtime to random computer crashes. The experts >claim that this is all caused by excessive noise on the power lines. >Expensive power filters have solved the problem on our critical machines, >but we aren't rich enough to put filters on all our electrical appliances. > >I'm quite skeptical about AC powerline networks (and control systems like >BSR) because of the problems caused by power line noise. Here's your chance >to change my mind... :-) > >-- >C. Harald Koch VE3TLA Alias Research, Inc., Toronto ON Canada >Internet: chk@alias.com chk@gpu.utcs.toronto.edu chk@chk.mef.org > > I suspect that MOST of these problems may be related to equipment-generated harmonic currents. There was a recent bulletin to sites with multiple IBM 3090 mainframes relating to harmonics generated by these machines with their MG sets causing MAJOR problems for UPS's. We have seen this cuasing problems with PC's and the like. John K. Scoggin, Jr.> Supervisor, Network Operations> Phone: (302) 451-5200 Delmarva Power & Light Company> Fax: (302) 451-5321 500 N. Wakefield Drive> Email: scoggin@delmarva.com Newark, DE 19714-6066> ---------------------------------------------------------------------------- Date: Thu, 30 May 91 17:29:12 -0700 From: woody@ucscb.UCSC.EDU (Bill Woodcock) Subject: NCR Wavelanproduct line extended... ...to NetWare 3, and OS/2 at Comdex last week. Also, they now support NDIS, which is some kind of Microsoft standard that Vines and 3Com comply with. They're shipping in December at $1,390 list. This was on p.5 of Network World v.8, n.21. -Bill Woodcock BMUG NetAdmin ________________________________________________________________________________ bill.woodcock.iv..woody@ucscb.ucsc.edu..2355.virginia.st..berkeley.ca.94709.1315 ------------------------------------------------------------------------------- Date: Thu, 30 May 91 17:23:43 -0700 From: woody@ucscb.UCSC.EDU (Bill Woodcock) Subject: Re: NCR's spread-spectrum FCC request to be denied ? Here's a little news item I wrote a couple of days ago for the ANMA Journal: Motorola Cuts Prices on Altair In the third week of May, Motorola announced that the prices of its Altair wireless Ethernet products were being cut by nearly three quarters. The suggested retail price for the Altair Control Module has been dropped from $3,995 to $995, while the User Module went from $3,495 to $995. -Bill Woodcock BMUG NetAdmin ________________________________________________________________________________ bill.woodcock.iv..woody@ucscb.ucsc.edu..2355.virginia.st..berkeley.ca.94709.1315 ------------------------------------------------------------------------------- Subject: CSMA/CA - a standard? Date: Thu, 30 May 91 08:25:33 PDT From: Paul Congdon <ptc@hprnd.rose.hp.com> Hello, Both NCR and Proxim boast the use of CSMA/CA. It sounds almost like a standard. Is there a description of the access protocol, or is it totally propriatry? Paul +---------------------------------+------------------------------------+ + Paul Congdon + Mail Stop: R3NF2 + + Network Architecture Lab + Email: ptc@hprnd.rose.hp.com + + 8000 Foothills Blvd + Phone: (916) 785-5753 + + Roseville, CA 95678 + Fax: (916) 786-9185 + +---------------------------------+------------------------------------+ ----------------------------------------------------------------------------- Date: Thu, 30 May 91 19:46:44 EDT From: Russ Nelson <nelson@sun.soe.clarkson.edu> Subject: NCR's spread-spectrum FCC request to be denied ? I can make the driver source code available to anyone who has a MACH source license. And I would be interested in knowing whether someone has written an MSDOS packet driver for the WaveLAN. Alas, no. NCR was supposed to send us a pair back in January, but we haven't seen hide nor hair of them. I've even called and bugged the product manager about his promise, but he's always out of the office. Maybe if more people call him and ask him for one. His name is Daryl Maddox, phone number is 513 445 1956. -russ ------------------------------------------------------------------------------ From: Ron Gershon <gershon@vis.toronto.edu> Subject: Re: noise introduced by powerline communication devices Date: >Fri, 31 May 1991 10:50:27 -0400 C. Harald Koch (chk@dino.alias.com) asks: > How much noise does your network generate on the power lines? We already > have several problems with noisy power here, from a braindead digital clock > that runs at about 8 times realtime to random computer crashes. The experts > claim that this is all caused by excessive noise on the power lines. > Expensive power filters have solved the problem on our critical machines, > but we aren't rich enough to put filters on all our electrical appliances. > > I'm quite skeptical about AC powerline networks (and control systems like > BSR) because of the problems caused by power line noise. Here's your chance > to change my mind... :-) Our technology employs advanced spread-spectrum techniques, incorporating an adaptive/wideband approach and noise-immune networking protocols specifically developed for handling worst-case powerline noise and attenuation. We use the 150-400 kHz bands for our purposes, and our transmission would seem like white noise to other systems. We put no more than 1 Watt of power on the line. Consequently, none of the users of the AN192s has ever complained of computers crashing as a result of the AN192 transmitting in their sites. As for BSR and other systems, they do not offer bit error rates < 10^-9 as we do, and we have systems in the field to prove it. In fact, we are currently developing a version which will be incorporated in a new commercial automated electric utility meter reading network. This will definitely allow for the use of the powerline as a communication medium, while recording how much electricity is being used by all your electrical appliances... Ron. ------------------------------------------------------------------------------ Date: Fri, 31 May 91 11:38:19 CDT From: zawada@ncsa.uiuc.edu (Paul Zawada) Subject: Re: Motorola Altair System Well, we don't have the Altair system installed, but I had a Motorola salesman here to demonstrate it. I was skeptical that it was going to work well, but I was really impressed! It did everything they said it would. It was pretty transparent, like the wire was there. It worked through doors and down hallways very well. (We did manage to push it to the limit by trying to bounce the signal around two corners, but you can only ask for so much...) First of all, the Altair system is not protocol dependent. Altair merely forwards ethernet frames. All it looks at is the ethernet addresses of the hosts involved. So if you have ethernet, Altair should work. i.e. Altair dosen't care if you're running TCP/IP, Appletalk, OSI, etc. One nice thing about the system is that the control module keeps track of the ethernet addresses connected to each user module. This allows it to pass only necessary traffic accross the radio link. i.e. it works almost like a smart bridge. Traffic between hosts on the user module does not get sent to the rest of the network. Similarly ALL traffic on the control module's ethernet does not get passed to the user modules. Each user module gets the traffic for the hosts attached to it. As for system management, currently there is an RS232 port on the control module. Don't ask me what functions are available, since I did not get a chance to play with that part of the system. The salesman said that SNMP was currently in the works. I really don't know how much of an issue this is, since the Altair system is pretty transparent. It would be nice to have SNMP, but since the devices are pretty much passive there isn't much you need to monitor other than if the link is up or down. (The user module has a green LED that blinks when it is searching for its control module and glows steadily when the link is up. So you can tell if the connection is there or not, you just can't do it via the network.) Is there such a thing like SNMP for ethernet cable? Remember, I only had this thing demonstrated for me. I don't have one installed. (yet) If it always works as well as it did for me those two hours, I would be more than satisfied! Hope this gives you some more info on the Altair system. --zawada __ Paul J. Zawada, KB9FMN |"This 'telephone' has too many shortcomings zawada@ncsa.uiuc.edu | to be seriously considered as a means of Network Administrator | communication. The device is inherently National Center for | of no value to us..." Supercomputing Applications | -Western Union memo, 1877 ------------------------------------------------------------------------------ Date: Fri, 31 May 91 12:41:59 BST From: "Pete Lucas, NCS-TLC, Holbrook House, Swindon" <PJML@ibma.nerc-wallingford.ac.uk> Subject: Power-line LANs. Much of the problem noise that affects these systems infact comes from switched-mode powersupplies (as used in almost every PC!). These rectify the AC line current, and due to the short conduction-time of the rectifiers, often result in a significant 3rd-harmonic current flowing down the supply mains. Also, being in effect a power-oscillator, harmonics etc. of the switching waveform get superimposed on the AC line. In an environment where many switching powersupplies are used, the 3rd harmonic current can approach (or exceed!) the total current drawn at the fundamental frequency; particularly in 3-phase systems the current in the nominally 'unused' neutral line can be greater than the sums of the currents on the three phases. This not only upsets the electric utility companies, but can seriously screw up systems that use the AC line cabling for data transmission. There is likely to be forthcoming European legislation limiting the allowed amount of waveform distortion caused by electrical equipment; makers of PCs etc. will have to fit better filtering. Pete Lucas PJML@UK.AC.NWL.IA PJML%IA.NWL.AC.UK@UKACRL Please use the following addresses for reply: + \/Natural + \/\Environment JANET : PJML@UK.AC.NERC-WALLINGFORD.IBMA + \/\/Research Internet : PJML%IA.NWL.AC.UK@NSFNET-RELAY.AC.UK + \/\/\Council EARN : PJML%UK.AC.NWL.IA@UKACRL + NERC Computer Services RADIO : G6WBJ@GB7SDN.GBR.EU {144.650MHz} + Holbrook House SPAN : STAR::\PJML%IA.NWL.AC.UK@NSFNET-RELAY.AC.UK + Station Road PHONE : +44 (0)793 411613 + SWINDON SN1 1DE FAX : +44 (0)793 411503 + GREAT BRITAIN Pete Lucas PJML@UK.AC.NWL.IA PJML%IA.NWL.AC.UK@UKACRL ------------------------------------------------------------------------------- Date: Fri, 31 May 91 18:01:45 EDT From: jdc@moscom.com (Jim Centanni) Subject: Low Power No-License RF Can someone please fill me in on the FCC requirements for low power transmitters that do not require special FCC licenses? At one time, no special licensing was required for transmitters with an output power below 100 milliwatts. If this is still valid, it might be possible to cover large facilities with several transmitters, where a direct connection would be made to each transmitter. Of course multi-path reception would become a much bigger problem now if a receiving antenna could hear more than one transmitter. However, it might still be worth looking at. Please advise restrictions, such as frequencies, ERP (effective radiated power), modes of operation (switched carrier, AM, FM, PSK, etc.), and other pertinent information, along with pros and cons associated with this approach. Jim Centanni Moscom Corp. (716) 385-6440 ------------------------------------------------------------------------------ From: "Jonathan M. Zweig" <zweig.parc@xerox.com> Subject: Re: CSMA/CD Date: >Fri, 31 May 1991 15:10:26 PDT I have been toying with the so-called hidden terminal problem, and have written a tiny simulation that agrees with an analytic solution to the following problem: >Assume I have magic radios that have a 0 dB capture range; that >is, a receiver is either in range of a transmitter or not. Further >assume that the range is a fixed, constant distance. If I have >two randomly located stations that wish to transmit at me (i.e. >they are both within range of me), what is the percentage likelihood >that they will be within range of each other? The question is of interest because whenever they are not within range of each other, it is inconceivable that they could determine (via their receivers) whether their transmissions to me are colliding -- they are hidden from each other. I won't bore the list with the math (the trick is to intersect the circle that is within range of me with the circle that is within range of the first station, then integrate the ratio of the intersection area to 2*pi for all the distances between 0 and 1), but the answer that both the calculus gives me (it's actually 3*sqrt(3)/4*pi) and the monte carlo simulation approximate is 0.586. That is, 41% of the time (assuming the spatial distribution is uniform across the circle that's within range of me) the two stations can't hear each other. I thought that was an interesting number, and a bit higher than I would have guessed. So if anyone else out there is thinking about collision avoidance algorithms, you can tattoo this on your arm. Carrier sense is a waste of time in this case. (Of course it _isn't_ a waste of time in some cases of interest, such as radios with nearly infinite range compared to the expected spatial distribution of stations....) -Johnny Hidden ------------------------------------------------------------------------------ Date: Sat, 1 Jun 91 00:29:05 -0700 From: woody@ucscb.UCSC.EDU (Bill Woodcock) Subject: Re: Low Power No-License RF jdc@moscom.com (Jim Centanni) writes: > Can someone please fill me in on the > FCC requirements for low power > transmitters that do not require > special FCC licenses? The following two tables should help you relate the products out there to the current FCC bandwidth allotments. They're from a recent column I wrote, primarily on the Apple PCS proposal. -Bill Woodcock BMUG NetAdmin ______________________________________________________________________ FCC-Approved Frequencies FCC Part 15.247: Unlicensed Spread Spectrum, 1.0W peak power. FCC Part 15.249: Unlicensed Low Power Radio, 0.75mW peak power. 902.0-928.0MHz 26MHz total 2,400.0-2,483.5MHz 83.5MHz total 5,725.0-5,850.0MHz 125MHz total 24.0-24.25GHz 250MHz total ______________________________________________________________________ Device Specifications Vendor Bandwidth Throughput Output Range Cal. Microwave 902.0-928MHz 250Kbps 26MHz@1W 800-2700 ft. NCR 902.0-928MHz 2Mbps 26MHz@250mW 100-800 ft. Apple 1850-1990MHz 10Mbps 40MHz@1W 150-450 ft. Motorola 18.82-19.21GHz 10Mbps 2x50MHz@25mW 40 ft. ________________________________________________________________________________ bill.woodcock.iv..woody@ucscb.ucsc.edu..2355.virginia.st..berkeley.ca.94709.1315 ------------------------------------------------------------------------------- Date: Sat, 1 Jun 91 15:31:29 -0700 From: woody@ucscb.UCSC.EDU (Bill Woodcock) Subject: Re: Low Power No-License RF Motorola's Altair boxes are real. NCR's WaveLan boxes are available now for NetWare, I believe, and will be available for MicroChannel late this year. California Microwave's boxes are done, and waiting for FCC certification. -Bill Woodcock BMUG NetAdmin ________________________________________________________________________________ bill.woodcock.iv..woody@ucscb.ucsc.edu..2355.virginia.st..berkeley.ca.94709.1315 -------------------------------------------------------------------------------