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GSM ARCHITECTURE

The document provides an overview of the GSM network architecture, including its three main subsystems: the Mobile Station subsystem, the Base Station Subsystem, and the Network Switching Subsystem. It describes the key elements and interfaces within each subsystem, such as the Mobile Station, Base Transceiver Station, Base Station Controller, Mobile Switching Center, Home Location Register, and Visitor Location Register. The interfaces that connect these elements, such as the A, Abis, and Um interfaces, are also introduced.

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Section 1 – GSM Architecture Overview GSM Architecture Overview
Section 1 – GSM Architecture Overview Introduction It provides an overview of the GSM network architecture. This includes a brief explanation of the different network subsystems and a description of the functionality of the elements within each of the subsystems. Topics include: • General architecture overview • The Mobile Station (MS) Subsystem and Elements • The Base Station Subsystem (BSS) and Elements • The Network Subsystem (NSS) and Elements • Introduction to network interfaces
Section 1 – GSM Architecture Overview
Section 1 – GSM Architecture Overview A GSM network is made up of three subsystems: • The Mobile Station (MS) • The Base Station Sub-system (BSS) – comprising a BSC and several BTSs • The Network and Switching Sub-system (NSS) – comprising an MSC and associated registers The interfaces defined between each of these sub systems include: • 'A' interface between NSS and BSS • 'Abis' interface between BSC and BTS (within the BSS) • 'Um' air interface between the BSS and the MS
Section 1 – GSM Architecture Overview Abbreviations: MSC – Mobile Switching Center BSS – Base Station Sub-system BSC – Base Station Controller HLR – Home Location Register BTS – Base Transceiver Station VLR – Visitor Location Register TRX – Transceiver AuC – Authentication Center MS – Mobile Station EIR – Equipment Identity Register OMC – Operations and Maintenance Center PSTN – Public Switched Telephone Network
Section 1 – GSM Architecture Overview Mobile Station The Mobile Station (MS) consists of the physical equipment used by a PLMN subscriber to connect to the network. It comprises the Mobile Equipment (ME) and the Subscriber Identity Module (SIM). The ME forms part of the Mobile Termination (MT) which, depending on the application and services, may also include various types of Terminal Equipment (TE) and associated Terminal Adapter (TA).
Section 1 – GSM Architecture Overview
Section 1 – GSM Architecture Overview • The IMSI identifies the subscriber within the GSM network while the MS ISDN is the actual telephone number a caller (possibly in another network) uses to reach that person. • Security is provided by the use of an authentication key and by the transmission of a temporary subscriber identity (TMSI) across the radio interface where possible to avoid using the permanent IMSI identity. • The IMEI may be used to block certain types of equipment from accessing the network if they are unsuitable and also to check for stolen equipment.
Section 1 – GSM Architecture Overview MS and SIM
Section 1 – GSM Architecture Overview The mobile station consists of : • mobile equipment (ME) • subscriber identity module (SIM) The SIM stores permanent and temporary data about the mobile, the subscriber and the network, including : • The International Mobile Subscribers Identity (IMSI) • MS ISDN number of subscriber • Authentication key (Ki) and algorithms for authentication check The mobile equipment has a unique International Mobile Equipment Identity (IMEI), which is used by the EIR
Section 1 – GSM Architecture Overview Base Station Subsystem (BSS)
Section 1 – GSM Architecture Overview The BSS comprises: • Base Station Controller (BSC) • One or more Base Transceiver Stations (BTSs) The purpose of the BTS is to: • provide radio access to the mobile stations • manage the radio access aspects of the system BTS contains: • Radio Transmitter/Receiver (TRX) • Signal processing and control equipment • Antennas and feeder cables
Section 1 – GSM Architecture Overview The BSC: • allocates a channel for the duration of a call • maintains the call: monitors quality controls the power transmitted by the BTS or MS generates a handover to another cell when required
Section 1 – GSM Architecture Overview Network Switching System (NSS) The NSS combines the call routing switches (MSCs and GMSC) with database registers required to keep track of subscribers’ movements and use of the system. Call routing between MSCs is taken via existing PSTN or ISDN networks. Signaling between the registers uses Signaling System No. 7 protocol.
Section 1 – GSM Architecture Overview Functions of the MSC: • Switching calls, controlling calls and logging calls • Interface with PSTN, ISDN, PSPDN • Mobility management over the radio network and other networks • Radio Resource management - handovers between BSCs • Billing Information
Section 1 – GSM Architecture Overview Interfaces Um VLR Abis A BSC MSC ISDN, TUP
Section 1 – GSM Architecture Overview Exercise Q1. Name the interfaces used between Mobile and BTS BTS and BSC BSC and MSC
Section 2 – Access Network Access Network
Section 2 – Access Network Objective The Trainee will be able to understand: • Different BTS configuration commonly used in the network • Advantages of the configuration and optimal use of the trunks • Abis mapping
Section 2 – Access Network Introduction Access network is a connection between MS and NSS, comprise of BTSs & BSCs. It is responsible for radio management. BSC looks towards MSC through single A-interface as being the entity responsible for communicating with Mobile Stations in a certain area. The radio equipment of a BSS may support one or more cells. A BSS may consist of one or more base stations, where an A-bis- interface is implemented.
Section 2 – Access Network BSS Configuration • Collocated BTS • Remote BTS • Daisy Chain BTS • Star Configuration • Loop Configuration
Section 2 – Access Network Collocated BTS: BTS is situated along with BSC or the MSC and no additional E1 link is required. BTS BSC
Section 2 – Access Network Remote BTS : BTS is situated in a stand alone position and additional E1 links are required to connect to BSC. BSC BTS
Section 2 – Access Network Daisy Chain BTS 3 BTS 1 BTS 4 BSC BTS 2 MSC
Section 2 – Access Network Star Configuration BTS 3 BTS 1 BSC BTS 4 BTS 2 MSC
Section 2 – Access Network Loop Configuration BTS 3 BTS 1 BTS 4 BSC BTS 2 MSC
Section 2 – Access Network Comparison of Different Configurations • Daisy Chain: Easy to implement, effective utilization of transmission links but if one of the link fails, all the BTSs connected in the chain will went off. • Star Configuration: Easy to implement but poor utilization of links. Each BTS require one E1 to connect to BSC. But if link goes down only individual BTS will be affected. • Loop Configuration: Slightly difficult to implement but effective utilization of E1 links. Even if one link goes off BTS will continue to communicate with the network from the other side.
Section 2 – Access Network BSS Interfaces • Air Interface: Radio Interface between the BTS and Mobile the supports frequency hopping and diversity. • A Interface: Interface carried by a 2-Mb link between NSS and BSS. At this interface level, transcoding takes place. • OMC Interface: X25 Link.
Section 2 – Access Network
Section 2 – Access Network Abis Interface (BTS - BSC) If the BTS and BSC are not combined, A-bis interface will be used. Otherwise, BS interface will be used. Several frame unit channels are multiplexed on the same PCM support and BSC and BTS can be remote from each other. Its main functions are: • Conversion of 260 – bit encoded blocks (corresponding to 160x8 – bit samples for 20ms) • Encoded block synchronization • Vocal activity detection • Alarm dispatch to BSC via PCM • Test loop back operation
Section 2 – Access Network TRX 1 TRX 2
Section 2 – Access Network Exercise Q1. In How many ways BTSs can be connected and which configuration gives the optimal solution? Q2. What is a difference between BS interface and Abis interface? Q3. How many time slots are occupied by 1TRX on a PCM frame?
Section 3 – NSS Topology NSS Topology
Section 3 – NSS Topology Objective The Trainee will be able to understand: • Terminology used in Network Sub System • Protocols and Interfaces inside NSS • Call routing and circuit groups • Switching modules • Stand alone and integrated HLR • Echo canceller and TRAU location • Authentication, Ciphering, OMC, Billing center • Transit Switch
Section 3 – NSS Topology Introduction Network Sub System can be considered as a heart of the GSM Network. All the major activities like switching of calls, routing, security functions, call handling, charging, operation & maintenance, handover decisions, takes place within the entities of NSS. Various kinds of interfaces are used to communicate between the different entities. Different methods are used to optimize and provide the quality network with the minimum operating cost.
Section 3 – NSS Topology Network Switching System (NSS) Key elements of the NSS: • Mobile Switching Center (MSC) • Visitor Location Register (VLR) • Home Location Register (HLR) • Authentication Center (AuC) • Equipment Identity Register (EIR) • Gateway MSC (GMSC) These elements are interconnected by means of an SS7 network
Section 3 – NSS Topology NSS Identifier IMEI – International Mobile Equipment Identifier. The IMEI is an internationally-unique serial number allocated to the MS hardware at the time of manufacture. It is registered by the network operator and (optionally) stored in the AuC for validation purposes. IMEI = TAC + FAC + SNR +sp TAC = Type Approval Code by central GSM body FAC = Final Assembly Code, identifies the manufacturer SNR = Serial Number, unique six digit number sp = spare for future use
Section 3 – NSS Topology IMSI – International Mobile Subscriber Identifier When a subscriber registers with a network operator, a unique subscriber IMSI identifier is issued and stored in the SIM of the MS as well as in the HLR . An MS can only function fully if it is operated with a valid SIM inserted into an MS with a valid IMEI. IMSI consist of three parts: IMSI = MCC + MNC + MSIN MCC = Mobile Country Code MNC = Mobile Network Code MSIN = Mobile Station Identification Number
Section 3 – NSS Topology TMSI –Temporary Mobile Subscriber Identity A TMSI is used to protect the true identity (IMSI) of a subscriber. It is issued by and stored within a VLR (not in the HLR) when an IMSI attach takes place or a Location Area (LA) update takes place. At the MS it is stored in the MS’s SIM. The issued TMSI only has validity within a specific LA. Since TMSI has local significance, the structure may be chosen by the administration. It should not be more than four octets.
Section 3 – NSS Topology MSISDN – Mobile Station ISDN Number The MSISDN represents the ‘true’ or ‘dialled’ number associated with the subscriber. It is assigned to the subscriber by the network operator at registration and is stored in the SIM. According to the CCITT recommendations, it is composed in the following way: MSISDN = CC + NDC + SN CC = Country Code NDC = National Destination Code SN = Subscriber Number
Section 3 – NSS Topology MSRN – Mobile Station Roaming Number The MSRN is a temporary, location-dependant ISDN number issued by the parent VLR to all MSs within its area of responsibility. It is stored in the VLR and associated HLR but not in the MS. The MSRN is used by the VLR associated MSC for call routing within the MSC/VLR service area.
Section 3 – NSS Topology LAI – Location Area Identity Each Location Area within the PLMN has an associated internationally unique identifier (LAI). The LAI is broadcast regularly by BTSs on the Broadcast Control channel (BCCH), thus uniquely identifying each cell with an associated LA. LAI = MCC + MNC + LAC MCC = Mobile Country Code, same as in IMSI MNC = Mobile Network Code, same as in IMSI LAC = Location Area Code, identifies a location area within a GSM PLMN network. Maximum length of LAC is 16 bits.
Section 3 – NSS Topology Mobile Switching Center (MSC) The Mobile services Switching Center (MSC) performs the telephony switching functions of the system. It also controls calls to and from other telephony and data systems, such as the Public Switched Telephone Network (PSTN) and Public Land Mobile Network (PLMN). Difference between a MSC and an exchange in a fixed network is - MSC has to take into account the impact of the allocation of radio resources and the mobile nature of the subscribers and has to perform in addition, at least the following procedures:
Section 3 – NSS Topology • required for location registration • procedures required for handover An MSC can be connected to only one VLR. Therefore, all mobile stations that move around under base stations connected to the MSC are always managed by the same VLR. An MSC would communicate typically with one EIR. While it is possible for an MSC to communicate to multiple EIRs, this is highly unlikely since the EIR provides a centralized and geographic independent function.
Section 3 – NSS Topology The MSC consults an HLR to determine how a call should be routed to a given mobile station: • For incoming calls to a mobile station, the MSC would typically consult one HLR. • For mobile-to-mobile calls in larger networks, a MSC could consult HLRs of other systems to help minimize the trunk paths to the other mobile station. A given MSC can be interconnected to other MSCs to support inter-MSC handovers
Section 3 – NSS Topology The following are typical MSC functions in a cellular system: • Provide switched connections with PSTN • Provide switched connections between mobile subscribers • Provide coordination over signaling with mobiles • Coordinate the location and handover process • Provide custom services to mobile users • Collect billing data
Section 3 – NSS Topology Protocols MSC/BSC MSC/HLR OMC/MSC MSC/Fixed Network MSC/VLR OMC/HLR MSC/EIR OMC/VLR MSC/Voice messaging MSC/GMSC OMC/BSS VLR/VLR VLR/HLR MSC/MSC BSSMAP TCAP+MAP X.225 R2, ISUP other Signaling SCCP SCCP X.224 MTP MTP X.25 MTP SS7 SS7
Section 3 – NSS Topology Switching In MSC Signaling network is separated from the speech network and consists of • signaling Links (SL) • signaling Point (SP) • signaling Transfer Part (STP).
Section 3 – NSS Topology Telephony system contains: • Group Switch to switch the calls, • ST to perform signaling in accordance with SS7 • Trunk interfaces for interfacing the PCM. Group switch provides a semi permanent connection between time slot (PCM) and ST.
Section 3 – NSS Topology Signaling Point (SP) SP provides the functions of signaling and transmit and receive messages to and from different nodes. Each SP in the network will have an identification code termed as signaling Point Code (SPC).
Section 3 – NSS Topology Signaling Transfer Point (STP) Signaling Transfer Part is signaling point that only transfers messages from one signaling point (SP) to another. STP SP SP (SPC) STP (SPC)
Section 3 – NSS Topology Signaling Link (SL) Signaling Link is the 64kbps link interconnecting two signaling Points and provides the functions of message error control and message sequencing. Each signaling Link has an SLC (signaling Link Code), which identifies the signaling Link with in the signaling Link Set.
Section 3 – NSS Topology Service Switching Point (SSP) The MSC contains: • The Service Switching Point • One or more radio control point SSP handles the usual switching function and can be connected via 2Mbps PCM link with: • Other exchanges of fixed PSTN or mobile PLMN, • Points on the SS7 signaling network, • X.25 network Continued…..
Section 3 – NSS Topology • The OA&M network, • The Intelligent network, • PSTN via user data channels and signaling channels using ISUP and R2 protocols, • Other elements of the GSM
Section 3 – NSS Topology Switching Function of SSP: • Main control, • Switching matrix, • PCM multiplex connection, • Service circuits • Operation and maintenance • Establishing and releasing section of the links from and to mobiles, • Finding circuits to the BSS; special circuit groups are created. SSP selects an incoming and outgoing circuit.
Section 3 – NSS Topology Call Routing • If a number received is a national or international number, the address information is passed to the SSP. • If the number received is an HPLMN (Home PLMN), the RCP asks the HLR for a roaming number (MSRN). This MSRN is passed to the SSP for routing. • If the number received is an emergency service number, the originating geographic area is attached to it and the combined information passed to the SSP. Continued…..
Section 3 – NSS Topology In the SSP the number received from RCP follow the standard translation process: • Preliminary analysis: Selection of a translator (national, international), • Translation: Determination of a routing depend on the first digits dialled, • Routing: Determination of an outing circuit group.
Section 3 – NSS Topology Circuit Groups Call routes from the MSC through circuit groups. Different circuit groups are created inside it: • Group for the PSTN (according to the exchange) • Group for the BSCs • Group for the Supplementary services • Group for the IWF
Section 3 – NSS Topology CG1 BSC1 CG2 BSC2 CGn BSCn MSC CGa PSTN1 CGx PSTNx CG Supplementary Services CG IWF
Section 3 – NSS Topology Interfaces
Section 3 – NSS Topology A-Interface (MSC – BSC) The interface between the MSC and its BSS is specified in the 08-series of GSM Technical Specifications. The BSS-MSC interface is used to carry information concerning: • BSS management; • call handling; • mobility management.
Section 3 – NSS Topology B-Interface (MSC – VLR) The VLR is the location and management data base for the mobile subscribers roaming in the area controlled by the associated MSC(s). Whenever the MSC needs data related to a given mobile station currently located in its area, it interrogates the VLR. When a mobile station initiates a location updating procedure with an MSC, the MSC informs its VLR which stores the relevant information. This procedure occurs whenever an MS roams to another location area. Also, when a subscriber activates a specific supplementary service or modifies some data attached to a service, the MSC informs (via the VLR) the HLR which stores these modifications and updates the VLR if required.
Section 3 – NSS Topology C-Interface (HLR - MSC) The Gateway MSC must interrogate the HLR of the required subscriber to obtain routing information for a call or a short message directed to that subscriber.
Section 3 – NSS Topology D-Interface (HLR - VLR) This interface is used to exchange the data related to the location of the mobile station and to the management of the subscriber. The main service provided to the mobile subscriber is the capability to set up or to receive calls within the whole service area. To support this, the location registers have to exchange data. The VLR informs the HLR of the location of a mobile station managed by the latter and provides it (either at location updating or at call set-up) with the roaming number of that station. The HLR sends to the VLR all the data needed to support the service to the mobile subscriber. The HLR then instructs the previous VLR to cancel the location registration of this subscriber. Exchanges of data may occur when the mobile subscriber requires a particular service, when he wants to change some data attached to his subscription or when some parameters of the subscription are modified by administrative means
Section 3 – NSS Topology E-Interface (MSC - MSC) When a mobile station moves from one MSC area to another during a call, a handover procedure has to be performed in order to continue the communication. For that purpose the MSCs have to exchange data to initiate and then to realize the operation. After the handover operation has been completed, the MSCs will exchange information to transfer A-interface signaling as necessary. When a short message is to be transferred between a Mobile Station and Short Message Service Centre (SC), in either direction, this interface is used to transfer the message between the MSC serving the Mobile Station and the MSC which acts as the interface to the SC.
Section 3 – NSS Topology F-Interface (MSC - EIR) This interface is used between MSC and EIR to exchange data, in order that the EIR can verify the status of the IMEI retrieved from the Mobile Station.
Section 3 – NSS Topology G-Interface (VLR - VLR) When a mobile subscriber moves from a VLR area to another Location Registration procedure will happen. This procedure may include the retrieval of the IMSI and authentication parameters from the old VLR.
Section 3 – NSS Topology H-Interface (HLR - AUC) When an HLR receives a request for authentication and ciphering data for a Mobile Subscriber and it does not hold the requested data, the HLR requests the data from the AuC. The protocol used to transfer the data over this interface is not standardized.
Section 3 – NSS Topology Switch Modules Switch has three major types of equipment modules: • Switching module (SM) • Communication module (CM) • Administrative module (AM)
Section 3 – NSS Topology Switching Module (SM): All external lines, trunks, and special services circuits are terminated at the switching module. The analog and digital signals are converted to the digital format used inside the switch. The SM performs almost 95% of the call processing and maintenance functions including: • Line and trunk scanning • Tone generation • Announcements • Call progress supervision • Routine maintenance and self-maintenance.
Section 3 – NSS Topology The SM also provides subscriber calling features including: — call waiting — abbreviated dialing — call diversion — conference calls. SM further has two components: 9. Control units - Control all activities within the SM, such as call processing and maintenance functions. 2. Peripheral units - Perform testing functions and provide customers and other exchanges access to the switch.
Section 3 – NSS Topology Communication Module (CM): The CM serves as the hub (focal point) for all inter module communication in a switch. The CM has four main functions: 4. Call switching - The CM interconnects the paths between modules to complete telephone calls and to relay data. 2. Message switching - The CM provides paths to send information between processors to process calls, maintain records, and perform system tasks. Continued…..
Section 3 – NSS Topology 3. Network timing - The CM provides accurate timing and synchronization for the switch. 4. Fast pump - The CM provides resources to quickly download (pump) an SM’s software if needed.
Section 3 – NSS Topology Administrative Module (AM): The AM controls the CM and communicates with all the SMs (through the CM). The AM monitors itself and the CM for malfunctions. If there are any problems, they are reported to maintenance personnel. The AM performs resource allocation and processing functions that are done more efficiently on a centralized basis such as: • Call routing for inter module and intra module calls • Administrative data processing/billing data Continued…..
Section 3 – NSS Topology • Traffic measurement reports/system performance reports • Memory management • System maintenance • Maintaining file records of changes to the system Software Release. • Personnel interface/system monitoring • Allocating trunks for call processing.
Section 3 – NSS Topology Switch SM AM CM Control Peripheral MSGS TMS Unit Unit Control I/O Disk Tape MCC Unit Processor Unit Unit
Section 3 – NSS Topology Home Location Register HLR is a database that stores subscription and set of functions needed to manage subscriber data in one PLMN area. Any administrative action by the service provider or changes made by subscriber is first carried out on the HLR and then update the VLR. Following are the subscriber data which frequently changes: - Identification number MSISDN & IMSI - Service restriction - Teleservices - Bearer services - Supplementary services
Section 3 – NSS Topology Beside the permanent data it also include dynamic data of home subscriber including VLR address, call forward number and call barring numbers. Triplets are also stored in the HLR for the authentication purpose. The HLR communicates with other nodes: VLR, AUC, GMSC & SMS – SC via MAP (Mobile Access Protocol). To support this communication HLR needs MTP and SCCP
Section 3 – NSS Topology
Section 3 – NSS Topology MAP (Mobile Application Protocol) The only way via which HLR communicates with other GSM nodes is Mobile Access Protocol. Number of functional blocks exist to support different MAP operations eg HLCAP is used for location cancellation or HLUAP is required for location updating. Other functions defined on the MAP are: - Inter MSC Handover and subsequent handover - Update HLR and VLR - Fault Recovery - Management and handling of supplementary services. Continued…..
Section 3 – NSS Topology - Support of Short Message Services. - Call establishment / delivery - Security related data. - Retrieval of subscriber data during call setup. HLR also needs to communicate with GMSC, VLR, AUC and SMS-SC, for which MTP and SCCP is essential.
Section 3 – NSS Topology SCCP (Signaling Connection Control Point) All MAP messaging use SCCP to analyze the GT (Global Title) of incoming information. If GT belongs to anther node, then SCCP will use the services of MTP (Message Transfer Part) to reroute the message. SCCP must have the GT analysis to terminate and route MAP messages from all nodes it communicates with. To find out the DPC, SCCP looks in a routing case translation table. The information about the DPC is then sent to MTP which sends the message to the appropriate SP.
Section 3 – NSS Topology MTP (Message Transfer Part) MTP must be defined to allow the nodes to communicate with each other. The MTP provides the means for reliable transport and delivery of UP (User Part) information across the No. 7 network eg ISDN User part (ISUP), the Telephone User Part (TUP), Signaling Connection Control Part (SCCP), Interworking function User Part (IWUP) and Data User Part (DUP) Continued…..
Section 3 – NSS Topology MTP has the ability to react to system and network failure that affect the user information. MTP further has three functional levels: 4. MTP Level 1 – Signaling data link 5. MTP Level 2 – Signaling link 6. MTP Level 3 – Signaling network
Section 3 – NSS Topology HLR connects with MSC via C interface, VLR via D interface
Section 3 – NSS Topology HLR can be configured in two ways: 2. Integrated with MSC
Section 3 – NSS Topology • Hs • Stand Alone HLR (External Database)
Section 3 – NSS Topology Integrated Vs Stand Alone HLR The Integrated HLR is accessed by other MSC’s/ VLR’s via MAP, and the switch can use MAP to query other off switch HLRs. The main advantages with an integrated HLR solution at this early stage are: • Efficient use of HW and lower HW investments • Fewer physical connections required due to fewer physical nodes • Less capacity required in No. 7 network as major part of HLR signaling is internal within MSC/VLR/HLR
Section 3 – NSS Topology • A single fault will affect a smaller number of subscribers than if standalone HLR is used Major drawbacks are: • Less processing capacity available for MSC/VLR. Additional Switching capacity will be required earlier • Migration to standalone HLR (which is to be preferred in a mature larger network) will induce major changes in the network • Administration of subscriptions • Operation and maintenance for HLR geographically distributed
Section 3 – NSS Topology In Stand Alone HLR, call processing activities are not performed by the switch. Only HLR queries are handled via the GSM standard MAP messages coming over signaling links from other Mobile Switching Centers (MSCs) in the wireless network.
Section 3 – NSS Topology Benefits: • All HLR data is centralized, thus simplifying its ongoing maintenance and operation • High HLR Capacity • High processing capacity • On going enhancement There are some drawbacks with standalone HLR • A fault in a HLR will affect many subscribers • A fault in a HLR will increase the signaling substantially in the whole signaling network
Section 3 – NSS Topology HLR is responsible for: • Connection of mobile subscribers and definition of corresponding subscriber data. • Subscription to basic services. • Registration/deletion of supplementary services. • Activation/deactivation of supplementary services. • Interrogation of supplementary services status. Continued…..
Section 3 – NSS Topology • Functions for analysis of mobile subscriber numbers (MSISDN, IMSI, additional MSISDN) and other types of addresses. • Statistical functions for collecting data regarding the performance of the system. • Functions for communication with GMSC and VLR using the No. 7 signaling system and MAP • Handling of authentication and ciphering data for mobile subscribers including communication with an authentication center. Continue…..
Section 3 – NSS Topology • Get Password/Register Password • Alert Service Center • Provide Roaming Number • Send Routing Information for SMS • Send Routing Information for GMSC • Set Message Waiting Data
Section 3 – NSS Topology Visitor Location Register It is a subscriber database containing the information about all the MS currently located in the MSC service area. VLR can be considered as a distributed HLR in the case of a roaming subscriber. If MS moves into a new service area (MSC), VLR requests the HLR to provide the relevant data and store it, for making the calls for that MS. VLR is always integrated with MSC to avoid the signaling load on the system. It can also be viewed as a subset of a HLR.
Section 3 – NSS Topology VLR connects with MSC via B interface, HLR via D interface and with another VLR via G interface. G
Section 3 – NSS Topology VLR is responsible for • Setting up and controlling calls along with supplementary services. • Continuity of speech (Handover) • Location updating and registration • Updating the mobile subscriber data. • Maintain the security of the subscriber by allocating TMSI Continued…..
Section 3 – NSS Topology • Receiving and delivering short messages • Handling signaling to and from - BSC and MSs using BSSMAP - other networks eg PSTN, ISDN using TUP • IMEI check • Retrieve data from HLR like authentication data, IMSI, ciphering key Continued…..
Section 3 – NSS Topology • Retrieve information for incoming calls. • Retrieve information for outgoing calls. •Attach/Detach IMSI • Search for mobile subscriber, paging and complete the call.
Section 3 – NSS Topology Security Feature Both the users and the network operator must be protected against undesirable intrusion of third party. As a consequence, a security feature is implemented in the telecommunication services. The following parts of the system have been reinforced and provide the various security features: 2. Access to the network authentication 3. Radio part ciphering 4. Mobile equipment equipment identification 5. IMSI temporary identity