Modem Pool Hardware
 

Hi all.

I'm working on a modem server to answer incoming calls. The problem is the time is takes for the modem to recognize that a call is incoming and subsequently answer it. The modem has to actually hear a ring to recognize an incoming call.

After talking with U.S. Robotics' tech support, I've been told that their modems are not able to pick up any sooner, and that this sort of thing is usually handled by a modem bank/pool. As far as I can tell, a modem pool consists of a "Terminal Server" that hands incoming calls off to different modems on different lines.

First, how is the terminal server able to recognize an incoming call any faster than a modem? It seems it would have to have some type of modem thing to receive the call. How does it detect an incoming call without waiting for a ring? When my modem dials into an ISP, I don't hear a ring before the answer signal comes. How is this accomplished?

Any answer or links to further information are GREATLY appreciated.

Thanks,

Justin Manning

(This may be country-dependant; I'm talking about the UK here. Countries like Australia and South Africa seem to have a different ringer system) One reason for this could be that the two ends of a 'phone line ring at different times.

You know how there's a gap between each ring? Originally, this was done by switching a continuous tone back and forth between the caller and the callee; when your 'phone rings, the other end's 'phone doesn't, and so on. This is still done like this today, except now it tends to be software controlled.

The modem picks up the 'phone just as it hears it ring. If you listen to the connection from the dialing end, you'll hear one fewer ring (none if the modem picks up on the first ring).

I also have the niggling feeling that four-wire 'phone cables carry the ringer signal seperately from voice; this may be faster if so.

The modems used in modem banks/pools tend to be CNR riser modems, as far as I am aware.