Network Switching Subsystem (NSS)

NSSHLR

AUCAUCBTS

MSC/VLRBSC

BTS

Basic GSM Network Structure

2006-01-24 Lecture 1

Mobile Switching Center (MSC)

The primary node in a GSM network is the MSC. It is the node which controls calls establishment Thethe node which controls calls establishment. The primary functions of an MSC include the following: Switching and call routing to or from MS.

Ch i Charging. Service providinfng. Control of connected BSCs. Access to PSTN. Provides the gateway functionality to other

networks.networks. One MSC controls more than one BSC.

2006-01-24 Lecture 1

Mobile Switching Center (MSC)

2006-01-24 Lecture 1

Types of the MSC

There are three types of the MSC, the difference just in the function.

VMSC: Visited MSC

GMSC: Gateway MSC

TMSC: Transit MSCTMSC: Transit MSC

Visited Mobile Switching Center

Its function is to switch in the level of BSCs and it is combined with a VLR.

MSC/VLR

BSC BSC

Transit Mobile Switching Center

Its function is to switch between the different VMSC It is not combined with a VLRVMSC. It is not combined with a VLR.

TMSCTMSC

VMSC VMSC

Gateway Mobile Switching Center (GMSC)

Its function is to connect the PLMN to the PSTN or to the other PLMN existing in the country.g y

M bi il GMSC

PSTNVodafone

TMSC TMSC

Mobinil GMSC

TMSC TMSC

VMSC VMSC VMSC VMSC

Home Location Register (HLR)

The HLR is a centralized network database that stores and manages all mobile subscriptions belonging to a specific operatoroperator.

It acts as a permanent store for a persons subscription information until that subscription is cancelled.

The primary functions of the HLR include: Stores for each mobile subscriber:

Basic subscriber categories.Basic subscriber categories. Supplementary services. Current location.

All d/b d i Allowed/barred services. Authentication data.

Subscription database management

2006-01-24 Lecture 1

p g Controls the routing of mobile terminated calls and SMS

Home Location Register (HLR)

2006-01-24 Lecture 1

Visitor Location Register (VLR)

The role of a VLR in a GSM network is to act as a temporary storage location for subscription information for MSs, which are within a particular MSC service areaare within a particular MSC service area.

Thus, there is one VLR for each MSC service area. This means that the MSC does not have to contact the HLR (which may be located in another country) every time the subscriber uses a service or changes its status.

The VLR is always integrated with the MSC.

2006-01-24 Lecture 1

Visitor Location Register (VLR)

For the duration when the MS is within one MSC service area, then the VLR contains a complete copy of the necessary subscriptionthe VLR contains a complete copy of the necessary subscription details, including the following information: Identity numbers for the subscriber

S l t i i f ti ( D th b ib Supplementary service information (e.g. Does the subscriber has call waiting activated or not)

Activity of MS (e.g. idle or busy) Current Location Area of MS

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Visitor Location Register (VLR)

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Authentication Center (AUC)

To protect GSM systems, the following security functions have been defined:

S b ib th ti ti b f i th ti ti Subscriber authentication: by performing authentication, the network ensures that no unauthorized users can access the network, including those that are attempting to impersonate others.p

Radio information ciphering: the information sent between the network and an MS is ciphered. An MS can only decipher information intended for itdecipher information intended for it.

2006-01-24 Lecture 1

Equipment Identification Register(EIR)

In order to block the stolen mobiles equipments; the EIR equipment is used; also in case of the Mobile operator wants to block a certain type of Mobile phones.

Example, In Turkey all the mobile phones bought from outside Turkey are blocked and can not be used before paying fees.

The Mobile equipment is identified by a number called International Mobile Equipment Identity (IMEI) This number isInternational Mobile Equipment Identity (IMEI). This number is uniquely identifies the MS worldwide.

2006-01-24 Lecture 1

Equipment Identification Register (EIR)

Because the subscriber and equipment are separate in GSM, it is necessary to have a separate authentication process for the MS equipment.

The equipment identification procedure uses the identity of the equipment itself (IMEI) to ensure that the MS terminal equipment i lidis valid.

1. IMEI Request4. Access/ Barring Data

EIR2. IMEI 3. IMEI Check

MSC / VLR

2006-01-24 Lecture 1

Equipment Identification Register (EIR)

International Mobile Equipment Identity (IMEI)

6 Digits

TAC

2 Digits

FAC

6 Digits

SN

IMEI

TAC FAC SN

TAC: Type Approval Code,The first two digits are the code for the countrycode for the country approval

FAC: Final Assembly CodeSN: Serial Number

2006-01-24 Lecture 1

Equipment Identification Register (EIR)

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Interworking Function (IWF)

Interworking Function (IWF)The IWF provides the function to enable the GSM systemThe IWF provides the function to enable the GSM system to interface with the variousforms of public and private data networks currently

il blavailable.The basic features of the IWF are listed below.Data rate adaption.P t l iProtocol conversion.

2006-01-24 Lecture 1

Echo Canceller (EC)

An EC is used on the PSTN side of the MSC for all voice circuits. Echo control is required at the switch because the inherent GSM system delay can cause an unacceptable echoinherent GSM system delay can cause an unacceptable echo condition, even on short distance PSTN circuit connections.

2006-01-24 Lecture 1

Operation and Support Subsystem (OSS)

The operation and Maintenance center (OMC) is connected to all equipment (the GMSC, MSC, HLR, VLR, AUC, EIR and the BSC).

It can be viewed as a computerized monitoring center were staff can monitor and control the network remotely.

MSC

HLROMC LANHLR LAN

SMSCBSC

Operation and Support Subsystem (OSS)

2006-01-24 Lecture 1

Operation and Support Subsystem (OSS)

2006-01-24 Lecture 1

Operation and Support Subsystem (OSS)

Operations and maintenance center (OMC)

(OMC) is connected to all equipment in the switching system and to the BSC. The implementation of OMC is called the operation and support system (OSS). The OSS is theoperation and support system (OSS). The OSS is the functional entity from which the network operator monitors and controls the system. The purpose of OSS is to offer the customer cost-effective support for centralized, regional, and pp , g ,local operational and maintenance activities that are required for a GSM network. An important function of OSS is to provide a network overview and support the maintenance activities of pp

different operation and maintenance organizations.

2006-01-24 Lecture 1

Operation and Support Subsystem (OSS)

2006-01-24 Lecture 1