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Modem protocol analyzers

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New Member
Hi, I recently completed my sophomore year in EE. I'm on summer
break right now and am not taking classes. I'm bored!

I'm looking to work on a non-academic EE project this summer.
I'm interested in learning more about modems.

There are companies that sell modem protocol analyzers which
seem to be pretty expensive. These devices can capture and
analyze data sent between two modems at low speed.


Are these devices difficult to build? I am thinking about spending
the summer trying to build one for myself.



New Member
Protocol analyser or spy software ?

Those links you show are interesting ...
I thought a protocol analyser just showed the comms format as per
I have got the DA100 with breakout box and LCD display but don't really trust it, it is better than nothing for 'cracking' an RS232 link but occasionally (maybe 20%) gets it wrong :cry:

Your links seem to show something closer to evesdropping software - not trying to find data rate, parity and number of stop bits as the actual data being sent ???
I appreciate these are connecting to the telephone line side of a modem but I'm still surprised by the name 'protocol analyser' - I guess you never stop learning :!:

As far as the modem comms is concerned - how much variation are you expecting in data rate, tone specification, data encryption ????
If this is little more than a third modem pre-configured to a known set-up feeding into a 'termonal' program then it would be easy to do.
If you need to automatically configure the modem to an unknown spec. then that could be a real challenge

I have had some success writing Visual Basic 'spy' software but this assumes the data format is already understood and just needs translation.
Can you give us more info on the application ? or is this purely a 'notional project' ?


New Member
Well, I am interested in just learning about modems in general.

I plan to use a PIC microcontroller for the device and so
I'm not expecting to be able to analyze stuff that is too fast.

I'd be happy with something that could handle traffic even as
slow as 300bps.

But also once I build the device, I would like to do a little
reverse engineering on the Ceiva picture frame.

One of my technophobic relatives has one of these things.
It is a digital picture frame, but it does not take a flash
memory card. THe product is designed for people who don't have
computers. You upload photos at Ceiva's website and the
picture frame has a phone jack in the back and everyday,
the product dials into the manufacturer and downloads new
photos and settings, etc.

Needless to say, the manufacturer does charge a monthly fee
for this service. I would like to use a modem protocol analyzer
to see exactly what data is being passed back and forth. The
bps rate is probably pretty high, but once I learn enough about
modems, I think I'll be able to force the connection to be slow
enough during the negotiation phase in order to be able to see
the data being passed.

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