Exercise 3.5Z: GSM Network Components

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Base Station Subsystem of GSM

For the mobile phone standard  "Global System for Mobile Communications"  - abbreviated  $\rm GSM$ - the network infrastructure includes the following subsystems:

• "Base Station Subsystem"   $\rm (BSS)$,
• "Switching & Management Subsystem"   $\rm (SMSS)$,
• "Operation & Maintenance Subsystem"   $\rm (OMSS)$.

The  "Base Station Subsystem"  is mainly responsible for the GSM radio network (see diagram), while the  "Switching & Management Subsystem"  represents the switching network and the  "Operation & Maintenance Subsystem"  is responsible for operation and maintenance.

The following terms will continue to be used in the questions on these exercise:

• "Authentication Center"   $\rm (AUC)$,
• "Base Station Controller"   $\rm (BSC)$,
• "Base Transceiver Station"   $\rm (BTS)$,
• "Gateway Mobile Switching Center"   $\rm (GMSC)$,
• "Home Location Register"   $\rm (HLR)$,
• "Mobile Switching Center"   $\rm (MSC)$,
• "Operation and Maintenance Center"   $\rm (OMC)$,
• "Visitor Location Register"   $\rm (VLR)$.

Notes:     This exercise belongs to the chapter  Characteristics of GSM.

Fragebogen

1

With which of the three subsystems does the mobile station communicate?

	With the BSS,
	with the SMSS,
	with the OMSS.

2

Which statements apply to a base transceiver station  (BTS)?

	It includes the base station's transmitting and receiving devices.
	The task of the BTS is to switch calls.
	In most cases, several BTS are subordinate to a common base station controller  (BSC).

3

How many links can a BTS with multiple antennas support if each antenna covers a sector of  $120^\circ$ ?

$N_{\rm max}\ = \ $

4

Which of the following components are part of the OMSS?

	The GMSC.
	The MSC.
	The OMC.

5

Which of the following components are databases?

	The AUC.
	The GMSC.
	The HLR.
	The VLR.

Solution

Solution

(1)  Each mobile station (MS) is in communication with a base transceiver station (BTS). This is part of the Base Station Subsystem (BSS)   ⇒   solution 1.

(2)  Correct are the statements 1 and 3. In contrast, the base transceiver station is not responsible for switching tasks, but this is rather the task of a mobile switching center (MSC), which is part of the switching and management subsystem (SMSS).

(3) If, as is usually the case with GSM, the individual antennas cover $120^\circ$ sectors, a BTS can provide up to three connection paths   ⇒   $N_{\rm max} \hspace{0.15cm}\underline{= 3}$.

(4)  Only the Operation and Management Center (OMC) belongs to the OMSS   ⇒   Proposal 3 .

• In contrast, MSC and GMSC are components of the mobile switching network (SMSS).
• With regard to OMC, a distinction is made between OMC-B (for BSS monitoring) and OMC-S (for SMSS monitoring).

(5)  solutions 1, 3 und 4 are correct:

• The Gateway Mobile Switching Center (GMSC) is a hardware unit that is responsible for switching between the fixed network and the mobile network.
• The other three terms given actually describe databases of the Switching & Management Subsystem (SMSS).
• The Authentication Center (AUC) is responsible for the storage of confidential data and keys.
• The Home Location Register (HLR) is a central register for the entire Public Land Mobile Network (PLMN) for managing unencrypted subscriber data, subscribed services and routing for calls from a mobile operator's own subscribers.
• Contrary, the Visitors' Location Register (VLR) contains information about the current visitors of other operators who are located in the current PLMN.