Received: by buit1.bu.edu (3.2/4.7) id AA26397; Tue, 2 Jun 87 17:54:19 EDT Message-Id: <8706022154.AA26397@buit1.bu.edu> Date: Tue, 2 Jun 87 17:52:05 EDT From: The Moderator (JSol) Reply-To: TELECOM@BUIT1.BU.EDU Subject: TELECOM Digest V7 #10 To: TELECOM@BUIT1.BU.EDU Status: RO TELECOM Digest Tue, 2 Jun 87 17:52:05 EDT Volume 7 : Issue 10 Today's Topics: Steve Dyer's msg regarding LADS Circuits 9600 bps dialups Cellular Telephone System 890 prefix Re: Cellular Fraud A twist on modems calling people ---------------------------------------------------------------------- Date: Tue, 2 Jun 87 10:08:20 EDT From: dixon@bucsb.bu.edu (Jim Dixon) To: telecom@buit1.BU.EDU Subject: Steve Dyer's msg regarding LADS Circuits With a line of that length (like less then 4 km or so), it would be quite possible to run at a much higher speed. For example, the ISDN U-interface can be run at either 80kb or 160kb (full duplex over 1 pair, even) over distances like that with little or no problems. Sometime soon, I am going to be performing some experiments with this type of interface running at 160kb on a loop that is aprox 1.5 km long. I think that this type of setup could lend itself to be kind of a happy medium between a dial-up line (even at 9.6kb) and a VERY MEGA-EXPENSIVE dds line, which I dont think that any of us could personally afford. If anyone has any interest in these types of experiments, please contact me. P.S. My mail link was down today, so I dialed up into BU. I can normally be reached at DIXON@OZ.AI.MIT.EDU or more specifically JIM%EGGO%LAMBDA@OZ.AI.MIT.EDU Happy Networking... Jim Dixon.. ------------------------------ Date: Mon, 1 Jun 1987 21:32 MDT From: Keith Petersen To: Gene.Hastings@H.CS.CMU.EDU Cc: Info-Modems@SIMTEL20.ARPA, telecom@BUIT1.BU.EDU Subject: 9600 bps dialups The US Robotics HST 9600 modem is indeed full duplex. It uses a return channel of 300 baud, which is plenty fast enough for hand typing from a terminal. The modem runs at a fixed speed on the RS232 line so the switching between 300 and 9600 is transparent to your terminal. The end with the most data to send gets the 9600, the other 300. The negotiation between modems is fast and changes dynamicly. I recently installed an HST modem on my Remote CP/M bulletin board system. It is quite impressive in it's performance, handling both interactive terminal sessions and XMODEM file transfers (using the YMODEM 1k block size protocol). Those who predicted that the 300 baud return channel would be unusable for data, claiming it would be used only by the modem for MNP ack/nak's, were wrong! I am very impressed by the USR HST 9600 and would not hesitate to recommend it to anyone. I use one here at home to communicate with my RCP/M which is located in the computer club President's home about 5 miles away. We have received long distance calls from several other SysOps around the country who also have the HST. There have been no problems with any of the calls. It wouldn't surprise me if the HST becomes the defacto standard for 9600 bps. It beats those pseudo full duplex (really half duplex) modems. --Keith Petersen Arpa: W8SDZ@SIMTEL20.ARPA Uucp: {bellcore,decwrl,harvard,lll-crg,ucbvax,uw-beaver}!simtel20.arpa!w8sdz GEnie: W8SDZ RCP/M Royal Oak: 313-759-6569 - 300, 1200, 2400 (V.22bis) or 9600 (USR HST) ------------------------------ To: From: allegra!mikel@codas.att.com (Mikel Manitius) Subject: Cellular Telephone System Date: 2 Jun 87 16:59:56 GMT I have seen a lot of confusion here over cellular telephone technology latley. I will attempt to explain some of the basic principles of how cellular telephones work. Please keep in mind that beyond the basic technology, each Cellular Operatiing Company can change a lot of things. A cellular system consists of a geographical area, such as a city. I will use Orlando as an example here. The coverage in Orlando is well over a hundred miles from edge to edge, however there exist much larger systems such as the New York/New Jersey area. The size is limited only by the number of cells, and the system's capacity for number of cells. A system is divided into "cells". Each cell has it's own transmitter and receiver, which is connected via leased lines to the cellular central office (CO). Each cell has it's own "control" frequency on which it accepts and issues calls. Each mobile unit is identifed by two numbers that are encoded in it's memory. The first is a serrial number, which is guaranteed to be unique anywhere in the world (kind of like Ethernet), the second is the ten digit telephone number of the unit that it has been assigned. (ie: mine is 305-222-xxxx) Incomming calls: When an incomming call arrives at the cellular CO (305-222) the system announces the call to ALL CELLS on their control channel. A mobile unit is given a time threshold to respond on the control channel. If it does not respond, the caller is given some message such as "The Bell South Mobility customer you have dialed, has travelled beyond the service area, or has left the vehicle". If the mobile does respond, it sends it's two identification numbers, and is assigned a voice frequency by the CO from the nearest cell site (strongest signal). The mobile phone then begins ringing. And the call is left to complete (ie: either the person answers, or the phone keeps ringing). Outgoing calls: The customer enters the number he wishes to call, and pushes a "SEND" button on the phone. The mobile unit transmits it's two identification numbers, and the destination number over the control channel to the nearest cell, and the call is either validated, and a voice channel is assinged for the completion of the call, or the call is rejected, and the mobile issues a siren tone. Traveling within the service area: Once the call has been established, the cellular system constantly monitors the signal strength of each mobile in each cell that has an active call. As the signal drops below an acceptable level, the system automatically selectes a another cell and transmits the new frequency to the mobile. Then the call is switched in less than a second, and the change is usually inaudiable. Roaming: Roaming occurs when a cellular mobile from system A travels into the service area of system B (ie: Orlando to Miami). In most cases the unit is allowed to place credit card and local calls only. However if system B is operated by the same company (ie: Bell South) it's network may authorize billing and allow the mobile to place toll calls. The mobile may also receive calls. However the person who is calling you must know which city you are in, dial the access number for that city, wait for a second dial tone, and then key in your full ten digit telephone code (on a touch-tone telephone). Then the call proceeds as described above. >From my own personal experience, I have had a cellular phone in my car for almost a year. I drove from Orlando to Montreal with it over christmas, and was able to use my phone without any problems in the following cities: (I took I-95 to NY and then I-87 [thuway]) Jacksonville, Charleston, Norfolk, Richmond, Washington/Baltimore, Wilmington, New York/New Jersey, Albany, and Montreal. It most cities I was able to place toll calls directly, which later appeared on my regular Orlando bill as "Roamer" changes. I was also able to receive calls while driving from people who knew which city I was in (I had supplied them with time estimates and access numbers). What really surpried me was the size of the service area around Montreal. I was able to use my cellular telephone from within the Adirondak State Park on the New York Northway, my service was being provided by the "Bell Canada Northern Corridor Service", at that time I was over 35 miles away from the Canadian border! 70 miles away from Montreal! I did however later find out that this service was not part of the Montreal system. Cellular phone can get costly too. I pay $30/month for leasing the equipment, which I get to keep after 36 months. $20/month for service, and $0.35 peak/$0.22 off peak minus 6% AT&T corporate discount (even for personal use). A usual month's bill is $100. Roaming gets much more expensive. It's anywhere from $0.40 to $1 per minute while roaming, and some [but not many] cities also add a $1 to $5 /day charge for roamers. If I were a roamer in Orlando, I would be paying $0.55 per minute for airtime. These charges apply for inbound and outbound calls alike, and area *VERY* service area dependant. In Orlando, 911 and 811 (Customer Assitance) calls are free. The cellular companies also make out on mobile to mobile calls, since then they get two people paying for the call. -- Mikel Manitius @ AT&T-IS mikel@codas.att.com.uucp Copyright 1987. Redistribution via Stargate PROHIBITED ------------------------------ From: SPGDCM%UCBCMSA.Berkeley.EDU@berkeley.edu Date: Tue, 02 Jun 87 12:43:14 PDT To: telecom@buit1.bu.edu Subject: 890 prefix MSG:FROM: SPGDCM --UCBCMSA TO: NETWORK --NETWORK 06/02/87 12:43:13 To: NETWORK --NETWORK Network Address From: Doug Mosher Title: MVS/Tandem Systems Manager (415)642-5823 Office: Evans 257, Univ. of California, Berkeley, CA 94720 Subject: 890 prefix To: telecom@buit1.bu.edu Pacific Bell in California uses the prefix "811" to enable customers to call their business office from anywhere in the lata, toll-free; this sounds like the 890 prefix service mentioned here earlier. Different final 4 digits are used for different prefixes. It seems almost overkill to allow calls from anywhere in the lata, in that my most urgent calls when travelling are not usually to telco business offices. However, if they have chosen to route all calls to a central location for service, it makes more sense. Bank of America here routes all calls about statements and what checks have cleared to one central office in Cal. for all x hundred branches, and no longer can you go to your branch and review your checks. Thanks, Doug Z 890 prefix ------------------------------ To: comp-dcom-telecom@RUTGERS.EDU From: ron@topaz.rutgers.edu (Ron Natalie) Subject: Re: Cellular Fraud Date: 2 Jun 87 15:29:25 GMT > The Electronic Serial Number is an 8 digit Hexidecimal number. It is not > easily changed. Both the MIN, (Mobil Id Number, your phone number) and the > ESN are sent out when you press the send key. Your MIN is easily changed > by reprogramming your phone, but the ESN is not easily changed. To change Make that, it is not supposed to be easily changed. While the ESN is not in that NAM (the EPROM with the phone number) in it's nice ZIF socket, many manufacturers just put it in another ROM which anybody with a small amount of electronics background can change. I would expect the most common sort of Cellular fraud involves using phones from another system through automatic ROAM agreements. Presumably the ESN/Phone number checking isn't as rigourous or as up-to-date in remote systems as it is in your home system. -Ron ------------------------------ To: telecom@xx.lcs.mit.edu, risks@csl.sri.com Date: Tue, 2 Jun 87 13:10:25 EDT Subject: A twist on modems calling people From: smv@necis.NEC.COM The folks at our main facility just installed a new telephone switch, and made two changes which are not user-transparent. The two changes involve the method used to reach our remote switch, and the method used to dial an international call. If you haven't guessed yet, the old international prefix corresponds to the new method of ringing my extension from the main facility. This would be amusing if it weren't for all the auto-dial facsimile machines trying to phone home to Japan with the old dialing codes. They're not much fun to talk to, and they don't seem to report the fact that the calls aren't getting through. The moral of this story: Get your Fax straight, before you make changes. -- Steve Valentine, NEC Information Systems 289 Great Rd., Acton, MA 01720 smv@necis.nec.com Robots don't use software! Software uses Robots! ------------------------------ End of TELECOM Digest *********************