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Tuesday, November 25, 2003
My cat is recovering from its surgery. Thanks to everyone who has asked about him and especially to Dr. Ted Schultz who performed the operation.
Here's a page to bookmark at my site: http://www.privateline.com/news.html (internal link) This page supplies current wireless and IT news, documents, and stock quotes. It's fed by an information stream from ITToolbox.com and changes daily. When you click on a report or news article a new window pops up in your browser. You're not taken away from this site. A good way to keep up.
Monday, November 24, 2003
Wireless number portability begins today in the States
Wireless number portability begins today in the 100 most populated areas in the United States. Things to remember:
1) You can keep your number but probably not your phone. Different carriers use incompatible technologies which means you'll have to change phones when you go to a different wireless company. My cell phones and plans page has a link a group you can donate your old phone to. In The Future, consider a phone you can sync your PC to, so you don't loose your address book and contact information. Again.
2.) If you cancel your existing contract you may face early cancellation fees, sometimes a huge amount.
3.) The carriers won't make it easy for you to change. Don't start by asking your old carrier to switch your service and number to a new provider. No. If you bought your phone over the counter, take it to a store with the phone and plan you now want, along with a recent bill. That bill will have the account information they need to switch. I'd try the same approach with on-line cellular dealers. Start with the company you want to go with now, and let them do the work.
4.) You can now transfer your house telephone number to your wireless device if both have the same area code. I don't know how exactly how this will work. Seems to me your landline would have to die, you could not have both numbers ring when someone calls. I also don't understand how people get by without a hard wired phone. You'd have no fast internet connection and it's harder for emergency services to locate you.
5.) Starting out with wireless? Think about buying a cell phone on-line. You can't compare several companies at your local wireless store but you can on the web. I have more on this on my cell phones and plans page. Most web sites are easy: put in your zip code and back comes a list of carriers and phones and prices. One caution. Many of these sites overlook regional wireless companies which could offer good deals. Shop around.
Good luck on dealing with this historic change. It may provide you the incentive to upgrade your phone or to try a new wireless carrier. Now, if only service and coverage could be improved by simply setting a date.
Sunday, November 23, 2003
Site work and writing on tubes and trasnistors goes on but slowly. My cat goes into surgery Monday morning and I am finding it difficult to concentrate.
Saturday, November 22, 2003
Wireless fraud before cellular
I sent our radio-telephone expert Geoff Fors the following paragraphs. I think they are from a 1985 article in Personal Communications Technology Magazine. I asked for his comments which you can read below:
"The earliest form of mobile telephony, unsquelched manual Mobile Telephone Service (MTS), was vulnerable to interception and eavesdropping. To place a call, the user listened for a free channel. When he found one, he would key his microphone to for service: 'Operator, this is Mobile 1234; may I please have 555-7890.' The operator knew to submit a billing ticket for account number 1234 to pay for the call. So did anybody else listening to the channel--hence the potential for spoofing and fraud."
"Squelched channel MTS hid the problem only slightly because users ordinarily didn't overhear channels being used by other parties. Fraud was still easy for those who turned off the squelch long enough to overhear account numbers."
"Direct-dial mobile telephone services such as Improved Mobile Telephone Service (IMTS) obscured the problem a bit more because subscriber identification was made automatically rather than by spoken exchange between caller and operator. Each time a user originated a call, the mobile telephone transmitted its identification number to the serving base station using some form of Audio Frequency Shift Keying (AFSK), which was not so easy for eavesdroppers to understand."
"Committing fraud under IMTS required modification of the mobile--restrapping of jumpers in the radio unit, or operating magic keyboard combinations in later units--to reprogram the unit to transmit an unauthorized identification number. Some mobile control heads even had convenient thumb wheel switches installed on them to facilitate easy and frequent ANI (Automatic Number Identification) changes."
Geoff here. The term squelch is a little misleading here, actually what is meant is "busy channel lockout." The MTS system went through a number of phases, and it depended upon where you were and what equipment the Telco installed in your car as to what you could do with it. Busy channel lockout was primarily a GE feature which lit a yellow lamp ("Busy") and wouldn't let you listen in if there was traffic on the channel. Older MTS sets didn't have that. I can put together some photos of assorted MTS control heads for you for future reference.
I think there was a busy channel lockout over-ride switch on the back of the control head on some GE models, intended for emergency use. The Motorola "Pushbutton Dial" system (not MTS and not IMTS but a proprietary scheme that laid an egg) had an emergency over-ride switch which also gave out a tone to let the parties using the channel know that someone was listening (as on the logo painted on the face of Nazi wartime military radios - "Feind hort mit." )
IMTS fraud wasn't widespread, maybe for one reason. The phones were so expensive that the general public had no access to them. The IMTS ANI is sent by the mobile at the beginning of the off-hook transmission. However, listening to traffic on the channels would pretty quickly reveal people giving their mobile number to the operator for various reasons. Smaller cities had a "block" of mobile numbers, and once you knew one, it would be easy to hack the others. For example, Chualar California (Salinas - Pacific Bell) had the mobile block of 679-5000 to 679-5100 as IMTS numbers. A crook could just pick one and away he went. It was also possible to park a scanner on the car to station channel in bigger cities and record calls, then slow the tape down and count the pulses of the ANI to determine the number. Then it would be obvious that any adjacent numbers were also IMTS. Not that I did this, but that's how it worked.
I never saw any control heads modified with thumbwheel switches by hackers. I suspect, frankly, that virtually all of the fraud was performed either by industry insiders or a few people who bought the equipment from them. Even though the mobile would have been hard to trace, the land side would not, as each call appeared on your bill with the number called and the time duration. Telephone company security did devote some time to this issue, with the usual result that the particular mobile number would get changed. I don't think they made much of a publicity issue out of it because 1) it would give others the idea and 2) bad for the company's shareholders to give out negative publicity.
Friday, November 21, 2003
History isn't boring. But texts and teachers sometimes are . . .
Hi,
I am a High School senior attending school in Maryland, and I had to do a research project on the effects of one technological advance on society. Well, as you may have guessed, I picked the telephone. I read the extensive history that was on your web site and I just wanted to say that it really helped me out a lot.
I actually became interested in the topic, and instead of considering it as just another boring research project I actually learned new things. The information was very helpful, and I just wanted to thank you for making it so interesting:-) H.W.
Thursday, November 20, 2003
Wireless network architecture
Question: I'm interested in what a network engineer considers when purchasing or obtaining switching equipment. In the wireless/cellular network equipment world, what kind of common questions would likely need to be answered? I'm also confused about where the cellular switch is located with respect to the base stations.
Answer: Mark van der Hoek here. The switch sits at some telephone company central office, not necessarily even in the same state as the cell sites. The sites themselves have some intelligence. For digital technologies, there's an additional box called a BSC or base station controller that handles most of the low level call processing. It sits (logically, not geographically) between the sites and the switch. Typically there will be multiple BSCs on a switch, each BSC having up to a couple of hundred sites that talk to it. BSCs have pretty much the same power, AC, and maintenance requirements as a switch, so are often located in the same building. (Unlike everyone else, Lucent CDMA and AMPS switches incorporate the BSC function in the switch.)
(Network element description of above is here AND, with nice little pictures, here.)
Other than that, the switch dimensioning is pretty much the same with cellular. Number of cell sites and subscribers is the main factor. In other words, capacity. One big difference is that cellular switches are not necessarily interchangeable. It depends on the technology. GSM systems have excellent interoperability. Buy a site from Ericsson, a BSC from Siemens, and a switch from Nortel. No problem. Build a network with Siemens switches and add a couple of Nortel switches down the road a few years. No problem.
With other technologies, such as CDMA or AMPS, you buy a complete system. Buy a Lucent system, or buy a Nortel system, or buy a Motorola system. But you can't mix and match. It's all or nothing, from cell site to switch. The only part that can be interchanged is the HLR. That can be just about anything, as it interfaces via an industry standard protocol, IS-41.
Was that all wonderfully confusing?
Mark van der Hoek
Editor's note: I have diagrams and easy to follow text on these pages which outline different GSM architectures. Kind of pHun to puzzle over. See the example below and these different pages:
Generic GSM architecture by Scourias / Lucent GSM architecture / Ericsson GSM architecture / Nokia architecture / Siemen's GSM architecture
AXE: Automatic Exchange Electric: Ericsson's digital switch. They operate as either a landline or wireless switch. OSS: Operations support system EET: Ericsson engineering tool, network planning software. SOG: service order gateway BGW: billing gateway. MIN: Mobile intelligent network. SCP: service control point.
Wednesday, November 19, 2003
The triode does not amplify, it regulates
I'm working on explaining the triode. Aside from the transistor it was the greatest help for the telephone system in the 20th century. Amplifiers developed from triode research enabled nation-wide calling for the first time in the mid-teens. I am drowning in pages and pages of information. A reader named Dante, a real radio expert, is helping me. I know the few sentences below won't make sense to most people, but I did want to show you that I am indeed working on what I said I would. Check back in another day or two. You'll find these paragraphs added to and modified to make them less cryptic.
I've written that a triode amplifies but this is wrong. A triode based amplifier certainly does make an audio frequency signal louder. But it takes a collection of components, arranged on a carefully designed circuit board, and, yes, the triode, to make amplifying possible. Think of the triode, for now, as a volume control, not an amplifier. The triode's "arrangement of filaments," modifies or regulates a current, it does not amplify.
When heated to incandescence the cathode begins to emit electrons, which flow from the negatively charged cathode toward the positively charged plate. The grid, where the original signal is introduced or injected , controls the electron flow. The result is that a tiny voltage, carrying the original signal, varies a much higher voltage at the plate or anode.
In our circuit high voltage drives a speaker. The amplifying, or better put, the gain, occurs when the audio frequency signals, say our voice, impinges on the existing current at the anode. These current variations act on the loudspeaker which then replicates speech. To sum up, you have a small current that varies a larger current. The triode itself regulates or modifies current, it does not amplify.
I write too much here today, it's back to work on the original article.
The grid. In this diagram the metal spiral where the unamplified signal is introduced. Located between the cathode and plate, the grid controls electrons passing through it by means of a negative electrostatic field.
Heater: Produces electrons by thermionic emission. Current passed through a filament-like heater makes it glow, boiling electrons off its surface.
Cathode: cylindrical, metal element in close proximity to and enclosing the heater. Electrons penetrate it easily and emit from its surface.
Anode or Plate: solid, cylindrical, metal element with high, positive potential, surrounding grid and heater/cathode assemblies. It accelerates electrons toward it and collects them for the external circuit.
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