SIMPLE MODEM DIVERTER DESIGN A basic modem diverter is simple to make, and requires only a few common components. The design can be expanded in many ways, as well. The concept is not new, and I take no credit for anything other than the design specs given. DISCLAIMER Your work, your actions, your responsibility, your ass. FUNCTION A modem diverter is a piece of hardware that, when used, diverts an incoming signal on a phone line to another line. This particular design is for data only. In the most basic setup, it works like this: incoming line Your location ----> Diverter Line 1 (555-2222) (555-1111) | Diverter Line 2 (555-3333) ----> Target location outgoing line (555-4444) If you were to dial that target number (555-4444) from your home location (555-1111) a caller ID or trace would trace back to you at 555-1111. But after going through the diverter, a trace would only trace back to the Diverter line 2 at 555-3333! Here is a sample terminal session: ATZ OK ATDT555-2222 CONNECT 2400 _ (at this point, you just have a waiting cursor - the modem on line 2 (outgoing line) is waiting for your commands.) ATZ OK ATDT555-4444 CONNECT 2400 ====================================== Welcome to SomeSystem! Our caller-id says you are dialing in from 555-3333! ===================================== _ (Note that the hypothetical trace reads 555-3333, which is line 2 (outgoing line) of the diverter, and NOT your location of 555-1111! This is because 555-3333 is the one actually making the call.) USES The applications of such a unit are of obvious value. It can be useful to not have your true location appear on a caller ID or a trace. Note that should the diverter be discovered, the incoming line can be identified and calls made to it crosss-referenced with calls from the outgoing line. With enough work, it can still be traced. These issues (and safeguards) will be discussed later. Another possible use has nothing to do with subterfuge. Suppose you have a BBS or access number in a nearby city that is outside local calling range. If you can place the diverter in a location such that it is a local call to the diverter, and a local call from the diverter to the target, you can make the calls without long distance charges! COMPONENTS Components needed for a basic modem diverter are: 2 external modems 2 phone lines (1 for incoming, 1 for outgoing) 1 null-modem cable (male-male) Appropriate phone cables and connectors The null-modem cable must be of decent quality. Some null-modems (or null-modem adapters) do not connect all the pins. To make sure you have a decent cable, you can either: - Buy one and try it - if it doesn't work, try another - Plug it into a breakout box and make sure the connections are there - Don't use the cheapest cable - Check the packaging to see if it says whether or not all the pins are connected. Also, at least one of the modems themselves must be able to be set into DUMB MODE. Some newer modems do not have this ability, others do. There are two typical ways to put a modem into dumb mode: either there is a DIP switch (like the back of USR modems) for SMART MODE/DUMB MODE, or there is a jumper inside the modem to set it to SMART/DUMB. Most older modems have the jumper. The third way - putting the modem into DUMB mode via an AT command - is not desireable and should be avoided. Another term for DUMB mode is "turning off AT command recognition". Remember that your diverter will only be able to go as fast as the slower of the two modems. SETUP 1. Put one modem into DUMB mode, the other into SMART mode. 2. Configure the DUMB mode modem to auto-answer. A way to do this (not guaranteed to work on all modems) would be ATS0=1&W . Check your modem manual for details. If the modem has a DIP switch to enable auto-answer as well, make sure it is on. 3. Plug the null-modem cable into the butt of both modems. 4. Connect the incoming line to the DUMB mode modem. This is the modem you will be dialing INTO when you call the diverter with another modem. Many modems have 2 RJ-11 jacks on the back (phone jacks). The one you want to plug in to is probably labeled WALL, LINE, or TELCO. 5. Connect the outgoing line to the SMART mode modem. Again, the plug you want to plug into is labeled WALL, LINE, or TELCO. 6. Connect power to the modems. 7. Test the diverter by placing a call. USING THE DIVERTER To place a call: Set your terminal software to the baud rate of the slower of your two modems in the diverter. Dial the incoming line of the diverter with your modem. Since we configured it to auto-answer, it will answer your call. But, instead of being connected to a server of some kind, it is connected to the SMART modem. If you are using a terminal program, you would see something like: (comments in ()'s ) C:\1AM37337\SIMPLET>simplet.exe -------------------------- Welcome to SimpleTERMINAL! -------------------------- ATZ OK ATDT555-2222 (dial the incoming line of the diverter) (ring, ring) CONNECT 2400 (you are now connected to the outgoing modem - you can test that you are connected properly by typing AT and hitting ENTER. You should see OK.) AT OK (Now, you can dial out to your destination) ATDT555-4444 (The number you are trying to reach via the diverter) (ring, ring) CONNECT 2400 At this point, your connection is complete and the diverter should be transparent to the connection in every way. You should be able to type, download, etc normally. To End a Call: A way to force a disconnect on the outgoing modem is to type '+++' (three plus signs in rapid succession) to get back to the command mode of the outgoing (SMART) modem. You can then type ATH and ENTER to force the modem to hang up. You can then disconnect your own modem from the incoming (DUMB) modem to end the call. You should in theory be able to simply disconnect your own line from the incoming line of the diverter to hang up both sides of the diverter, but I would recommend testing this first before putting it into practice. LOCATION Is is important for the diverter to be in a secure location. Obviously, you don't want just anyone messing with it - not to mention walking off with it. If you are putting the diverter in the equivalent of "private property" (ie somewhere you don't belong) you should get permission where possible and practical. In any case, unless you are going to be near the unit all the time, it is adviseable to use a measure of safeguards. SAFEGUARDS & COUNTERMEASURES Normally, this means usually simple methods of preventing someone from opening, breaking, or walking off with your diverter. For the more paranoid, this can also include fingerprints, tamper alerts, and so on. For non-tamper safeguards, put the diverter in a sturdy box or container. You can even remove the modems from their cases and place those in the container to make it look more like a "product". Just be sure to insulate the modem PCBs. The case can be securely shut and/or bolted down. A purloined or counterfeit Telco company sticker or logo can also increase the illusion that it's something that is "supposed to be there". Do not ignore the more low-tech safeguards. If you have a need not to be traced to the diverter OR calls, do not call the diverter from your home line or from anywhere else you can be connected to. Do not use components that have your name stenciled into them, or your home number in the modem's NVRAM. For a truly paranoid safeguard, wipe all fingerprints from the modem and cables and case, then do all assembly while wearing latex gloves. Perhaps a false trail could be laid by social-engineering someone to hold/handle the box or components before you put it into use - therefore getting THEIR fingerprints on it. For those with electronics knowledge, a tamper-switch could be installed into the box that could trigger some kind of alert once the diverter is opened. This could be triggered to destroy the contents, or send some sort of remote alarm. IMPROVEMENTS A measure of security can be added with some work by programming a PIC or microcontroller to sit between the two modems in the diverter and not allow access unless a certain DTMF tone or password is used. This can be combined with the tamper-switch to, for example, change a welcome banner slightly upon someone messing with the diverter. This requires much more work and tools than the basic model, though. For more information about this design, or any other thoughts or suggestions, email me. digital/Digital digitaldigital@darkcore.com