bitwali1 Wireless Communication Introduction to Mobile Communication and Cellular System Lecture 3-4

bitwali2 Why Hexagon?

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Interfaces BSC VLR MSC Um Abis A ISDN, TUP

bitwali5 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 ISDN – Integrated Services Digital Network

bitwali6 Mobile Station The Mobile Station (MS) consists of the physical equipment used by a 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).

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8 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. ( The International Mobile Subscriber Identity or IMSI /ˈɪmziː/ is used to identify the user of a cellular network )( MSISDN (Mobile Station International Subscriber Directory Number) )/ˈɪmziː/cellular network 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 ( The International Mobile Equipment Identity )may be used to block certain types of equipment from accessing the network if they are unsuitable and also to check for stolen equipment.

MS and SIM

bitwali10 The mobile station consists of : mobile equipment (ME) subscriber identity module (SIM) The mobile equipment has a unique International Mobile Equipment Identity (IMEI), which is used by the EIR( Equipment Identity Register ). 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

bitwali11 Base Station Subsystem (BSS)

bitwali12 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 cables

bitwali13 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

bitwali14 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.

bitwali15 Functions of the MSC( Mobile Switching Center ): Logging calls, controlling calls and Switching calls Interface with PSTN, ISDN, PSPDN Mobility management over the radio network and other networks Radio Resource management - handovers between BSCs Billing Information PSPDN -> Packed-Switched Public Data Network

bitwali16 Access Network

bitwali17 BSS Configuration Collocated BTS Remote BTS Daisy Chain BTS Star Configuration Loop Configuration

bitwali18 Collocated BTS: BTS is situated along with BSC or the MSC and no additional E1 link is required. BSC/MSC BTS

bitwali19 Remote BTS : BTS is situated in a stand alone position and additional E1 links are required to connect to BSC. BSC BTS

Daisy Chain MSC BSC BTS 1 BTS 2 BTS 3 BTS 4

Star Configuration MSC BSC BTS 1 BTS 2 BTS 3 BTS 4 BSC BTS 3

Loop Configuration MSC BSC BTS 1 BTS 2 BTS 3 BTS 4

bitwali23 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.

bitwali24 NSS Topology

bitwali25 Objective Terminology used in Network Sub System Protocols and Interfaces inside NSS Call routing and circuit groups Switching modules Stand alone and integrated HLR Authentication, Ciphering, OMC, Billing center Transit Switch

bitwali26 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.

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

bitwali28 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

bitwali29 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. A 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 (3 digit) MNC = Mobile Network Code (3 digit) MSIN = Mobile Station Identification Number (9 digit)

bitwali30 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.

bitwali31 MSISDN – Mobile Station ISDN Number The MSISDN represents the ‘true’ or ‘dialed’ 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

bitwali32 Mobile Switching Center (MSC) The Mobile 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 ( زمرے میں شمار کرنا )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

bitwali33 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 (Equipment Identity Register). While it is possible for an MSC to communicate to multiple EIRs, this is highly unlikely ( امکان نہیں )since the EIR provides a centralized and geographic independent function. Section 3 – NSS Topology

bitwali34 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