Introduction to Cellular Systems - GSM Services & Architecture Protocols Connection Establishment Frequency Allocation Routing Mobility Management Security GPRS- UMTS Architecture Handover - Security
- 1. UNIT - 3 GSM, GPRS & UMTS
- 2. GLOBAL SYSTEM FOR MOBILE ( GSM ) • The GSM is the standard for 2G pan. • It is the most successful digital mobile telecommunication system in the world today. • It is a special second generation (2G) system, replacing the first generation (1G) analog system. • It is initially deployed in Europe.
- 3. GSM - SERVICES • GSM permits the integration of different voice and data services. • GSM has defined 3 categories of services. • Telephone or tele services • Bearer or data services • Supplementary services
- 4. (i) Teleservices • GSM mainly focuses on voice oriented tele services. • The primary goal of the GSM is the high quality digital voice transmission. • Another service is emergency number. The same number is used through out the country. • Another useful service is the Short message service ( SMS ) – up to 160 characters.
- 5. (i) Teleservices • The successor of SMS, the Enhanced Message Service (EMS) offers a larger message service ( 760 characters ) , small images and ring tones. • It also offers Multimedia Message Service ( MMS ) which is used in transmission of large pictures ( GIF, JPG) and short video clips.
- 6. (ii) Bearer or Data services • GSM services provide capabilities to transmit information among user network – interfaces or access points (APs). • Bearer services permit transparent and non- transparent, synchronous or asynchronous data transmission. • Transparent bearer services ( GSM provides standard channel coding for the user data only ) use the functions of the physical layer to transmit data.
- 7. (ii) Bearer or Data services • Non transparent bearer services use protocols of layers ( two – data link layer and three – network layer) to implement error correction and flow control.
- 8. (iii) Supplementary services • These are not the stand alone services. But they are services that supplement a bearer or tele services. • This digital service includes call diversion or forwarding of ongoing calls, closed user groups and caller identification. • SMS may be used for safety and advisory application such as broadcast of highway or weather information to all GSM subscribers within reception with in reception range.
- 9. GSM Features • Subscriber Identity Module (SIM) - It is a memory device and stores the information such as the subscriber’s identification number, the networks and countries when the subscriber is entitled to service, privacy tags and other user specific information. • A subscriber uses the SIM with a 4 digit personal ID number to activate service from any GSM phone. • GSM equipment manufacturer must sign the MoU. • It is an International agreement which allows the sharing of cryptographic algorithm and other proprietary information between countries and carriers.
- 10. GSM System Architecture • It consists of 3 major inter connected subsystems. The subsystems are, 1. Radio sub system ( RSS) 2. Network and switching sub system (NSS) 3. Operation support sub system ( OSS )
- 11. GSM System Architecture BS C BS C MSC MS MS MS BT S BT S BT S GMSC PSTN ISDN PDN EIR AUC HLR VLR
- 12. 1. Radio sub systems • It comprises all media specific entities, ie the mobile stations (MS ) and Base Station Systems ( BSS ). • Base station sub systems ( BSS ) • BSS performs all functions necessary to maintain radio connection to a mobile station ( MS ), Coding / Decoding of voice. • It is controlled by Base Station Controller ( BSC ) and contains several Base Transceiver Station ( BTS )
- 13. • Base Transceiver station : – It comprises all radio equipment i.e. Antenna, signal processing, amplifiers necessary for radio transmission. Base Station Controller : ( BSC ) Basically manages BTSs. It reserves radio frequencies, handles hand over from one BTS to another with in BSS. Mobile Station ( MS ) It comprises all user equipment and software needed for communication with in a GSM network. MS contains a Subscriber Identity Module ( SIM ) which stores all user specific data that is relevant to GSM. It can also offer other types of interfaces to users with display, loud speaker, micro phone, computer modems. Blue tooth.
- 14. • Network and switching sub system ( NSS ) • The NSS manages the switching functions of the systems and allows the MSCs to communicate with other networks such as the PSTN ( Public Switched Telephone Network ) and ISDN ( Integrated Services Digital Network ). • Operation Support Subsystem ( OSS ) • The OSS supports the operation and maintenance of GSM and allows system engineers to monitor , diagnose and troubleshoot all aspects of the GSM system. • Here 3 different databases are used. I. Home location Register ( HLR ) II. Visitor Location Register ( VLR ) III. Authentication Center ( AuC)
- 15. I. Home location Register ( HLR ) • It is a register which contains subscriber information and location information for each user who resides in the same city. • Each subscriber has International Mobile subscriber identity ( ISMI ) • This number is identify each home user. ii. Visitor Location Register ( VLR ) • It is a database which temporarily stores the customer information for each roaming subscriber who is visiting the coverage area of a particular MSC.
- 16. III . Authentication Center ( AuC) • It is a strongly protected database handles the authentication and encryption keys for every single subscriber in the HLR and VLR. • The authentication center contains a register called the Equipment Identity Register ( EIR ) which identifies stolen or fraudulently altered phones that transmit identity data that does not match which information contained in either HLR and VLR.
- 17. Radio Interface Frame Structure of GSM
- 18. Radio Interface Frame structure of GSM – It provides various mechanisms for multiplexing and media access. – Mobile access combines TDMA and FDMA. – TDMA is used to seperate uplink ( 124 channels ) and down link ( 124 channels ) – Channel 1 and 124 are not used for transmission. – 32 channels are reserved for organizational data – Remaining 90 are used for customers. – A frame is sub divided into 8 GSM time slots. – Each time slot has 577 Micro sec duration.
- 19. Radio Interface Frame structure of GSM – Data is transmitted in bursts. – In diagram the burst is only 546.5 Micro seconds long and contains 148 bits. – The remaining 30.5 micro sec. Are used as guard space to avoid over lapping with other bursts.
- 20. Radio Interface Frame structure of GSM – The first and last 3 bits of a normal burst(tail ) are all set to 0 and can be used to enhance the receiver performance. – Data is transmitted as small portions called bursts. – A flag S indicates whether the data field contains user or network control data.
- 22. Incoming Call 1. Calling a GSM subscribers 2. Forwarding call to GSMC 3. Signal Setup to HLR 4. 5. Request MSRN from VLR 6. Forward responsible MSC to GMSC 7. Forward Call to current MSC 8. 9. Get current status of MS 10.11. Paging of MS 12.13. MS answers 14.15. Security checks 16.17. Set up connection
- 23. GENERAL PACKET RADIO SERVICE ( GPRS ) – It is an enhancement of GSM. – Allocation to GPRS is done dynamically according to capacity on demand. – GPRS is also allow for broadcast multicast and unicast services.
- 24. GPRS MS are of 3 types • Class – A : Terminals operate GPRS and other GSM services simultaneously. • Class – B : Terminals can monitor all services but operate either GPRS or GSM. • Class C : Terminals operate only GPRS service.
- 25. GPRS Architecture There are two types of GPRS support nodes, 1. Serving GPRS support Nodes ( SGSN ) 2. Gateway GPRS support node Before sending any data over GPRS network, a MS must attach a Temporary Logical Link Identity ( TLLI ) and a Ciphering key Sequence Number ( CKSN ) for data encryption.
- 26. GPRS Architecture For each MS a GPRS context is setup and stored in the MS and corresponding SGSN. This context comprises the status of MS . 1. Idle mode : MS is not reachable and all contexts are deleted. 2. Stand by : Movement across routing areas is updated to SGSN but not changes of the call. 3. Ready State : Every movement of MS is indicated to the SGSN.
- 27. GPRS Applications (a) Generic Application Internet access, E-mail, browsing, sports score, weather and flight information which are very useful while on move. (b) Chat : SMS and WAP ( Wireless Application Protocol ) (c) Multimedia Services : Photographs, Pictures, postcards, greeting cards, static web page can be sent and received.
- 28. GPRS Applications (d) Virtual Private Network ( VPN ) Many ATM machine uses VSAT to connect ATM system with bank server.
- 29. VSAT - Very Small Aperture Terminals. There are three main components • The Satellite • A Central Hub (With a Big Dish Antenna) • Number of smaller nodes (smaller dish antenna) kept at various remote locations Together form a Star topology (Even Mesh topologies are possible for small networks) using the satellite network.
- 30. GPRS Applications (e) Personal Information Management Personal diary, address book. Some of these are kept in phone and some in organizer and some in Internet. (f) Job sheet dispatch Assign and communicate job sheets from office based staff to mobile field staff. (g) Location based services : Ability to push and pull information services with user location. e.g. : - Hotel , Restaurant road side assistance.
- 31. GPRS - Advantages • Large amounts of data can be transferred to and from the mobile device over the Internet. • GPRS-enabled mobile phones also double up as portable Internet connections for laptops. • In some cases, where Internet access is not readily available but a mobile network is, GPRS can be a lifesaver. • Most phones can be used as a modem once connected to a laptop. • The Technological environment, is that it is a great backup option. • The portability factor has reduce somewhat, with the advent of much faster data cards, which plug directly into the laptop.
- 32. GPRS - Disadvantages • When a connection is active, calls and other network- related functions cannot be used. • The data session will go on standby. • This is a characteristic typical of the Class B GPRS device. • GPRS is usually billed per megabyte or kilobyte, depending on the individual service provider.
- 33. UMTS – 3G W-CDMA • Universal Mobile Tele Communication system. • It is a visionary Air Interface standard. • Evolved since late 1996 under the sponsorship of European Tele Communications Standards Institute ( ETSI ) • UMTS is third generation mobile cellular system based on the GSM standard networks. • It uses Wideband Code Division Multiple Access ( W-CDMA )
- 34. UMTS – ARCHITECTURE UE UTRAN CN Uu Iu
- 35. UMTS – Architecture It consists of 3 sub systems. (i) UTRAN ( UTRA Network ) (ii) UE ( User Equipment ) (iii) CN ( Core Network )
- 36. UMTS – Architecture • UTRA Network - Universal Terrestrial Radio Access Network . • It handles cell level mobility and comprises several Radio Network Sub system ( RNS ). • The functions of RNS include ciphering, deciphering hand over control, Radio resource management.
- 37. UMTS – Architecture • The UTRAN is connected to user equipment ( UE ) via a radio interface via Uu and via Iu interface the UTRAN communicates with core Network ( CN ). • It contains functions for inter system hand over, gate ways to other system networks etc.,
- 38. UMTS – Architecture • UMTS further subdivides the architecture into domains. • The user equipment domain is assigned to a single user and used to access UMTS services. • With in the equipment domain USIM domain and mobile equipment domain is available.
- 39. UMTS – Architecture • USIM contains SIM for UMTS which performs functions for encryption and authentication. • All functions for radio transmission as well as user interfaces are located inside mobile equipment domain. • The infrastructure domain is shared among all users and offers UMTS services to all accepted users.
- 40. UMTS – Architecture • This domain consists of access network domain which contains Radio Access Networks ( RAN ) and Core Network Domain. • The core network domain can be separated into three domains with specific tasks. • The serving network domain used to access UMTS services. • Home network domain used to maintain functions related to home network. • The transit network domain is necessary if serving network cannot directly contact the home network.
- 41. UTRA – FDD ( W – CDMA ) • The Frequency Division Duplex ( FDD ) mode for UTRA uses wide band CDMA. • The radio frame consists of 15 time slots. • One radio time consists 38,400 chips with a duration of 10ms. • There are three physical channels that are used for data transmission. • Two are used for uplink and one is used for downlink.
- 42. (i) Dedicated Physical Control CHannel ( DPCCH) • The channel conveys physical layer control data. • The pilot is used for channel estimation. • The transport Format Combination Identifier (TFCI) specifies the channels transported with in the DPDCHs. • Signaling for slot handover is supported by Feedback Information Field (FBI) • The Transmit Power Control ( TPC ) is used for controlling the transmission power of sender.
- 43. (ii) Dedicated Physical Data Channel ( DPDCH ) • The channel conveys user or signaling data • The spreading factor (SF) of this channel is vary from 4 to 256. • The data rates can offer this channel are : 960 kbits/s, 480,240,120,60,30 and 15 kbits / s. • Bandwidth used by the user equipment is wasted due to orthogonal variable spreading factor.
- 44. (ii) Dedicated Physical Channel ( DPCH ) • The downlink time of DPCH multiplexes both control and user data. • A Physical Random Access Channel (PRACH) is used for this purpose. • Spreading factors between 4 and 256 are used. • After power on the User Equipment ( UE ) has to perform the following steps during the search for a cell.
- 45. (ii) Dedicated Physical Channel ( DPCH ) (a) Primary synchronization : A UE has to synchronize with the time slot structure with the help of a 256 chip primary code. (b) Secondary synchronization : UE is now synchronized with the frame structure. (c) Identification of the scrambling code : To find the right code using a correlator.
- 46. UTRA – TDD ( TD -CDMA) • It is a second UTRA mode and separates uplink and downlink in time. • It has 5 time slots with 2560 chips. • A Guard Period ( GP ) is introduced at the end . • The frame can contain same number of uplink and downlink or several switching points.
- 47. UTRA Network( UTRAN) • It uses three major components. (1)Radio Network Controller (2)Node B (3)Code Network ( CN )
- 48. UTRA Network( UTRAN) • It contains several Radio Network Subsystem ( RNS ) • Each RNS is controlled by a Radio Network Controller ( RNC ) • Each RNC is connected with the Core Network ( CN )
- 49. (1) Radio Network Controller • An RNC in UMTS has a broad spectrum of tasks . (i)Call admission control (ii)Encryption / Decryption (iii)ATM switching and multiplexing , protocol conversion (iv)Radio Resource Control (v)Code Allocation (vi)Power control (vii)Hand over control (viii)Management
- 50. (2) Node - B • There are many components called as node – B and connects to one or more antennas creating one or more cells. • The cells either use FDD or TDD or both. • In comparison with 2G network the RNS is similar to BSS , RNC is similar to BSC, node – B is similar to BTS.
- 51. (3) Core Network ( CN ) • The Circuit Switched Domain ( CSD ) comprises the classical circuit switched services including signaling. • Resources are reserved at connection setup and GSM components MSC, GMSC ( Gate way Mobile Switching Network ) and VLR are used. • The Packet Switched Domain ( PSD ) uses GPRS components SGSN and CGSN and connects to the RNS interface.