Pretend you are a teacher preparing a quiz for the text I will provide. 
            Each quiz question should follow the format below. 
            Ensure that you carefully recheck the questions and answers for accuracy. 
            The output should be a ready-to-use list of dictionaries for the Python eval function:

            [

                    "question": "WRITE THE QUESTION HERE",
                    "options": ["A) OPTION_1", "B) OPTION_2", "C) OPTION_3", "D) OPTION_4"],
                    "answer": INDEX_OF_CORRECT_ANSWER_IN_OPTIONS_LIST,
                    "explanation": "EXPLAIN WHY THE ANSWER IS CORRECT"

            ]

            Text:
            e function, the BTSs radio 
frequency power levels control, and channel setup.  
• Mobile Station (MS): is the technical name of the cellular or 
mobile phone. It consists of two prim elements, the mobile 
device, and the Subscriber Identity Module (SIM). The SIM is 
a smart card that contains the International Mobile Subscriber 
Identity (IMSI) number. More information is contained by The 
SIM such as Identifiers, Card Type, Serial number, List of 
subscribed services, Personal Identity Number (PIN), 
Authentication Key (K), and PIN unblocking key (PUK). 
 
 
 
 
 
 
 
 
 
Fig 3: GSM architecture. 
b) Network and Switching Subsystem (NSS): the central part of NSS 
is the MSC. It manages the switching functions of the system and 
allows MSCs to communicate with other networks. It consists of 
several parts. 
1) Mobile Switching Centre (MSC): The MSC does several 
functions such as: 
• 
It is the heart of the network. It manages communication 
between GSM and other networks. 
• Base Transceiver Station (BTS). 
•  Base Station Controller (BSC). 
•  Mobile Switch Centre (MSC). 
•  Home Location Register (HLR). 
•  Visitor Location Register (VLR). 
•  Authentication Centre (AuC). 
•  Equipment Identity Register (EIR). 
MS 
Radio air Interface 
Mobile Computing, Year Four, 2024/2025, Lecture 1                         Dr. Alyaa Al-Barrak 
6 
 
• 
It manages to call to set up function, routing and basic 
switching. 
• 
It performs mobility management including registration, 
location updating and inter BSS and inter MSC call handoff. 
• 
It provides billing information. 
• 
MSC does gateway function while its customers roam to 
another network by using HLR/VLR. 
2) Home Location Registers (HLR): it is a very important 
database used in GSM standard in the sense it consists of all 
user-related information. For example, ISDN number, K, ISIM, 
etc.  
3) Visitor Location Registers (VLR): It is a temporary database 
which updates whenever new MS enters its area by HLR 
database. - It controls mobiles roaming in its area. 
4) Authentication Centre (AUC): - It provides protection 
against intruders in the air interface. 
5) Equipment Identity Register (EIR): it is a database that 
contains information about the identity of mobile equipment 
that prevents calls from stolen, unauthorized, or defective 
mobile stations. 
c) Operation Subsystem (OSS): all functions related to networking 
maintenance and operation are done by OSS. Using the Signalling 
System 7 (SS7) the OSS can access other networks. 
d) Interfaces used for GSM network:  
• 
UM Interface: used to communicate between BTS with MS. 
• 
A-bis Interface: used to communicate BSC to BTS. 
• 
A Interface: used to communicate BSC and MSC. 
• 
Singling protocol (SS7): used to communicate MSC with other 
networks. 
3.2. GSM Services 
GSM services are classified as either teleservices or data services. 
Teleservices include standard mobile telephony and mobile-originated 
traffic. Data services include compu

            Quiz: