Question about CCCH and GSM
Skip contentSubject: Question about CCCH and GSM
From: Viju
Date: February 26, 2005
To: info@mobile-phone-directory.org
Why are two channels used for data transmissions, i.e. the uplink and downlink channels? Also, why can’t a single channel be used for data transmission?
Reply:
Hi Viju,
In reply to your question, the reason there are uplink and downlink channels is because GSM is a duplex system, i.e. the Base Station is continuously sending information to the mobile phone (downlink), and at the same time the mobile phone is continuously sending information to the Base Station (uplink). The uplink and downlink channels are transmitted on different frequencies. It would just be too problematic trying to send and receive on the same channel, and GSM is not designed that way.
You refer to CCCH. Although this is a form of data, it is not data as sent or received by the user of the phone (e.g. when exchanging SMS messages). CCCH is a channel for sending control messages used by the GSM system, so that the phone and the Base Station talk to each other to set up the way that they will be connected during a call.
The technical explanation about how GSM works can be a very complicated subject, and I am not sure you want to discuss such details. There are plenty of books and Web pages devoted to explaining these matters. I will send you a PDF file that has some diagrams of the GSM system for you to look at.
Please let me know if I have answered your question.
Regards,
Mike S
Technical Consultant
