Problem 2-3. GSM GSM has logical control and traffic channels. “Common Control C

Question

Problem 2-3. GSM

GSM has logical control and traffic channels. “Common Control Channels” (CCCH) are used for signaling between a Base Station (BTS) and a mobile station (MS). “Broadcast Control Channel” (BCCH) is used to broadcast, for instance, information about the cell configuration and identity

(a) Find “CCCH System Information” BCCH messages. What is the MCC, MNC, and LAC of the BSC? What carrier frequencies does the BTS support (hint: find the ARFCNs). Explain where you found this information.

(b) Within the CCCH are “paging request” messages. Explain the purpose of these messages, and provide a TMSI observed in a paging request.

(c) Examine the raw hex bytes of the GSM messages, especially the end of the messages. What is the most frequently observed byte, and what is its significance? Explain your answer.

Explanation / Answer

a.

MCC - Mobile Country Code.

MNC - Mobile Network Code. These MCC and MNC parameters are used to to uniquely identify a mobile network operator.

LAC - Location Area Codes - shared among several BSC is the case where the size of the LAC doesn't depend on the size of the BSC

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b. PURPOSE OF PAGING REQUEST MESSAGES.

The BSC is able to handle all cell identifier types within the PAGING message.
The BSC uses IMSI value received in the PAGING message to calculate the mobile's paging group and sends the PAGING COMMAND (b) message to the BTS.

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