Iphone

Hello there!!
I'm trying to understand the concept of GPRS. Searched the whole topic and couldnt' find something really clear.

Please understand on my questions below, that I refer "other side" as the remote point, away from where I'm origining my calls (or starting my communications) and suppose that the "other side" has sufficient technology to accept incoming calls. Normal modems are the kind of modems we used when dial-up internet still existed :-)

OK, I know that I have a GSM/ GPRS modem. As far as I know, from "normal" modems, I have one modem on one side and another on the other side, open up something like Hyperterminal, type ATDT1234567 and the modem on one side will dial to another modem that is on the other side that answers by the phone #1234567. Handshakes, etc, and I have a PPP connection between the two modems. Please correct me if I'm wrong.

When this connection is established - normal modem, the telephone line I'm using will be busy, even though there is no apparent data going thru. OK. Using this kind of connection, the telephone company would bill me by the time I spend with the two modem connected. Pretty smooth up to here, huh??


My question is regarding the same analogy, but using a GSM modem and GPRS.
First of all: am I right of imagining that a GSM modem works like a normal modem - connected all the time and billed all the time - and GPRS connected all the time but billed only by packets sent and received?
Going on, please explain what should I have on the other side of my communication - a normal modem plugged in a normal phone line or maybe another GPRS modem connected to a communication port of a PC. Will a normal modem on the other side accept the incoming GPRS packets or it will only be connected by the calling GSM modem like a "normal" modem. See what I'm trying here? I have one GSM/ GPRS modem on one side and trying to connect to the other side. I'm trying to understand what a GSM modem does and where the GPRS comes in. What kind of modem I should have on the other side?

Based on the question above, I have a connection and a PPP link. Like old modems, if I have two other modems sending in information to my PC, will this one also need to have two different modems to receive the incoming data? Or GPRS technology is intelligent enough to know that there are two modems sending different things and it opens up two different links with only one GPRS modem?

Using TCP/IP, which certain GSM/ GPRS modems have already built-in (remember, until now, I don't know what's the difference between those two kind of modems), does it connect directly to one PC connected to the internet? Obviously this PC would be prepared to receive incoming data throught a certain port. But how does it work and why on earth does it have this TCP/IP stack built-in?
How to work out with TCP/IP is another question that I will post for another 500 points.

Would appreciate that, like my question was asked if one was two years old, that answers could be given as if I was two years old :-)
Even though copy and paste are things for two year old chlidren, I would rather have something typed instead of only links. Links are good, but not enough to earn all points.

Plenty of examples illustrates well.

Not so difficult questions, but for it's extensiveness, 500 is even underpaid.

Thanks

Iphone

This document's a little old but still pretty current:

http://www.slipstreamsolutions.co.uk...s_overview.pdf

Basically:

1. GSM dials like an 'old modem'. It's a point-to-point connection, i.e. from your mobile device (PDA/laptop) to a modem using a specified phone number. You're billed per second of connectivity regardless of how much data is transferred.

2. GPRS works like broadband. It's connected all the time (kind of) and you're only billed for each Byte you use. As far as you're concerned it's not point-to-point because you would not connect to a modem that you own - instead you connect into the O2 / Voda (etc) cloud and then you go across the Internet to where your infrastructure is.

In my opinion GSM is much inferior to GPRS. Why have the risk of managing a bank of remote access modems when O2 / Voda etc will do it for you with GPRS? And why go to the cost of a lengthy phone call when you might only be transferring a couple of bytes?

And TCP/IP is just a protocol that sits on top of your GSM/GPRS connection.