What would happen if I were to play a recording of the calling modem into a phone when calling a dial up server?

[38034580]

What would happen if I were to play a recording of the calling modem into a phone when calling a dial up server?

[da na]

That's how a lot of modems worked. Presumably nothing would happen if you don't have a dial up ISP though

[Eigenvektor]

If you did replay the sounds precisely the same way the modem would when connecting to the server, the other modem might accept it as a valid handshake and try to communicate with you. Unless you can keep up the correct signals after that, the session would most likely fail pretty quickly, with the other modem assuming the connection was faulty.

[An0maly_76]

Since OP specifically mentions calling a dial-up server (do these even exist anymore?), I would imagine it would depend, since there is a "handshake" sequence prior to actual connection. If the server does not get the correct handshake sequence when it does its own, connection will not be made, it will either wait for a time, repeating its handshake, or terminate the call, or both.

 

But Mel0nMan is right, in the early days of modems before RJ jacks were made more modular, acoustic couplers were used with phone handsets to isolate ambient noise.

[HanZie82]

Yes, as thats essentially how dial-up works.
You dial a number and communication hap[pens trough sound.
And a recording of said sound would be possible to trick the receiver into thinking its a real modem.
But then like @Eigenvektor said, it would stop pretty quick, since the communication has back and forth messages multiple times per second.

[Master Disaster]

 

[Master Disaster]

1 hour ago, An0maly_76 said:

Since OP specifically mentions calling a dial-up server (do these even exist anymore?), I would imagine it would depend, since there is a "handshake" sequence prior to actual connection. If the server does not get the correct handshake sequence when it does its own, connection will not be made, it will either wait for a time, repeating its handshake, or terminate the call, or both.

 

But Mel0nMan is right, in the early days of modems before RJ jacks were made more modular, acoustic couplers were used with phone handsets to isolate ambient noise.

AFAIK the handshake part would simply be establishing baud rate and verifying user account info (if required by the server). Assuming no account is needed you could easily trick the handshake but its still pointless, the call would simply time out after an rx command was issued by the server and no tx command was sent.

 

IIRC modems use pretty much bog standard serial commands.

[An0maly_76]

Hence why I asked if there were even any dial-up lines still in existence.

[Kilrah]

- Moved to Networking

 

2 hours ago, An0maly_76 said:

(do these even exist anymore?)

Not really but you can set up your own locally with a cheap ATA.

 

 

Did take mine out a couple of days ago again to answer "can you decode a wiretapped fax" CRD was sure there was no practical way to

[wseaton]

There are still dialups in service, typically running FAX. Hard to run malware against analog purple and white. 

 

Still used as back up credit card terminals. 

 

Rumour has it the dept of defense keeps some POTs lines available for redundancy in case digital telecom lines gets nuked with EMP, along with shortwave towers in reserve. Finding Operators for Shortwave? Good luck .

 

Playing a recording of a low baud carrier on a analog line works. Did it lots with my boot legged blue phone.