05 - Mobile Networks Flashcards
Explain:
- 1G
- 2G
- 2.5G
- 3G / 4G
- 1G: NMT-AMPS-TACS Voice (Analogue)
- 2G: GSM-Voice, fax, SMS, WAP-limited browsing (Digital)
- 2.5G: GPRS - EDGE, improved data for web, email, MMS (Digital)
- 3G/4G: UMTS-, LTE+, video calls, high speed data, WiMAX, UMB
What does GSM stand for?
Global System for Mobile Communication
Cell Network Basics. Explain the following abbreviations?
- MCC
- MNC
- LAC
- LAI
- CI
- CGI
- Mobile Country Code (MCC): Three decimal digits. An MCC is used in combination with an MNC (a combination known as an “MCC/MNC tuple”) to uniquely identify a mobile network operator (carrier). E.g. 228 - Switzerland
- Mobile Network Code (MNC): Two decimal digits. An MCC is used in combination with an MNC (a combination known as an “MCC/MNC tuple”) to uniquely identify a mobile network operator (carrier). E.g. 01 - Swisscom
- Location Area Code (LAC): Is a 16 bit number with two special values, thereby allowing 65534 location areas within a MNC.
- Location Area Identity (LAI): MCC + MNC + LAC. Can consists of multiple BTSs. SIM cards store this information.
- Cell Identity (CI): Each cell has its own BTS. Each cell has its own frequency slot.
- Cell Global Identity (CGI): Globally unique identifier of a cell.
What are the frequencies of GSM900?
- 890-915 Mhz Uplink MS to BTS
- 935-960 Mhz Downlink BTS to MS
- Duplex spacing of 45 Mhz
What are the frequencies of Extended GSM900?
- 880 - 915 Mhz Uplink MS to BTS
- 925 - 960 Mhz Downlink BTS to MS
- Duplex spacing of 45 Mhz
What are the frequencies of GSM1800?
- 1710 - 1785 Mhz Uplink MS to BTS
- 1805 - 1880 Mhz Downlink BTS to MTS
- Duplex spacing of 95 Mhz
- Also known as Digital Cellular System (DCS)
What are the frequencies of GSM850?
- 824 - 849 Mhz Uplink MS to BTS
- 869 - 894 Mhz Downlink BTS to MTS
- Duplex spacing of 45 Mhz
What are the frequencies of GSM1900?
- 1850 - 1910 Mhz Uplink MS to BTS
- 1930 - 1990 Mhz Downlink BTS to MTS
- Duplex spacing of 80 Mhz
- Also known as Personal Communications System (PCS)
How are GSM Channels looks like?
GSM 900 has a 25 Mhz bandwidth. 25 Mhz bandwidth divided into 124 Channels using Frequency Division Multiple Access (FDMA). Each GSM Channel is 200Khz in bandwidth. Each GSM Channel contains a GSM Frame which has 8 time slots (TDMA).
Provides multiuser access by separating the used frequencies. This is used in GSM to separate cells, which then use TDMA to separate users within the cell.
What is TDMA?
GSM Frame defines structure of messaging and signalling. Each frame consists of eight time slots to carry individual pieces of information. Allows eight simultaneous pieces of information to be transmitted or received depending on whether it is a receive or transmit frame. This technique is known as Time Division Multiple Access (TDMA).
Each time slot lasts 0.577 milliseconds. Eight burst time slots combined is a GSM frame lasting 4.615 milliseconds. Slots for transmit and receive are offset by three.
Explain the following GSM / GPRS Network Component?
- MS
- Um
- BSS
- BTS
- BSC
- Abis
- PCU
- MSC
- GMSC / VLR
- HLR / AUC / EIR
- SGSN
- GGSN
- GPRS Core Network / NSS
- PSTN
- SS7
- Mobile Station (MS) = Mobile Equipment (ME) + Subscriber Identity Module (SIM) .ME: Is the HW which incorporates the radio communication mechanism via the air. SIM: Contains subscriber information including Authentication Key (Ki) and IMSI
- Air Interface between Mobile Station (MS) and Base Transceiver Station (BTS)
- Base Station Subsystem (BSS) is the section of a traditional cellular telephone network which is responsible for handling traffic and signaling between a mobile phone and the network switching subsystem.
- Base Transceiver Station (BTS) = Cell towers. Allows wireless communication between User Equipment (handset) and network. Typically contains several transceivers operating on different frequencies. GSM uses the Gaussian Minimum Shift Keying (GMSK) modulation technique. EDGE uses Eight Phase Shift Keying or 8PSK for greater data throughput.
- Base Station Controller (BSC) : Provides the “intelligence” behind the BTSs. Typically controls tens to hundreds of BTSs. Location Area Code (LAC). Responsible for: Speech processing / conversion; Allocation of radio channels and time slots to mobile phones; Paging of handsets
- Abis : The interface between the BTS and BSC.
- Packet control unit (PCU) is a late addition to the GSM standard. It performs some of the processing tasks of the BSC, but for packet data.
- Mobile Switching Center (MSC) : Acts as a switching node between the mobile & fixed line network. Provides mobile subscriber functionality such as authentication, registration, location updating, hand over and call routing. Maintains a database of all roaming subscribers connected to the MSC.
- Gateway Mobile Switching Centre (GMSC) : Depending on Network at least one MSC. Gateway Mobile Switching Centre GMSC. Carries out switching functions. Acts as a switching node between the mobile & fixed line network. Provides mobile subscriber functionality such as authentication, registration, location updating, hand over and call routing. Maintains a database of all roaming subscribers connected to the MSC.
- Visitor Location Register (VLR) : Temporary database of subscribers using a particular area. One VLR per base station: Subscriber X can only be in one VLR at any one time. A roaming subscriber is assigned a Mobile Station Roaming Number (MSRN) by the VLR. Assigns 32 bit TMSI. One VLR per MSC. Communicates with HLR regarding movements of subscribers. Receives administrative information for call control and provisioning of the services available to the mobile subscriber.
- Home Location Register (HLR) : Central database containing details of each mobile phone subscriber authorised to use the network. Provisioning & Supplementary Services.
- Authentication Centre (AUC) : Function to authenticate each SIM attempting to connect to network.
- Equipment Identity Register (EIR) : Blacklist of stolen or non- approved mobile devices. Whitelist of approved devices. Greylist of monitored devices.
- Serving GPRS support node (SGSN) is the node that is serving the MS/UE. The SGSN keeps track of the location of an individual MS/UE and performs security functions and access control.
- Gateway GPRS support node (GGSN) is a main component of the GPRS network. The GGSN is responsible for the internetworking between the GPRS network and external packet switched networks, such as the Internet or an X.25 network.
- Network Switching Subsystem (NSS) or GSM Core Network is the component of a GSM system that carries out call out and mobility management functions for mobile phones roaming on the network of base stations. It is owned and deployed by mobile phone operators and allows mobile devices to communicate with each other and telephones in the wider public switched telephone network (PSTN).
- Public Switched Telephone Network
- Signaling System No. 7 (SS7) is a set of telephony signaling protocols developed in 1975, which is used to set up and tear down telephone calls in most parts of the world-wide public switched telephone network (PSTN). The protocol also performs number translation, local number portability, prepaid billing, Short Message Service (SMS), and other services.
Name the four cell types?
- Macro - provides wide area coverage such as rural usually on a high site with a range up to 35 km.
- Micro - used in urban areas for higher density coverage.
- Pico - is used for extremely high network loading and in building coverage.
- Femto - is a personal or small business base station. Multiple frequencies in use at the same cell location.
What are MVNO?
Mobile Virtual Network Operators (MVNO) - Usually don’t own network infrastructure. Do not own licensed frequency spectrum. Resell wireless service of another provider: E.g, Virgin Mobile in the UK use T-Mobile’s network or Tesco Mobile Ireland use Three Ireland’s network.
How does the Device Identification/Authentication Process works?
- Mobile Station switches on
- Mobile Station tunes to strongest available base station
- Mobile Station identifies to network
- MSC generates random number (RAND) and sends to Mobile Station
- Mobile Station generates signed response (SRES) using Ki (authentication key) and RAND
- AuC (Authentication Center) also generates SRES and forwards to MSC
- AuC SRES compared with Mobile Station SRES
- If both SRES are the same then network access granted to Mobile Station
- Cipher Enable command sent to Mobile Station and Temporary Mobile Subscriber Identity (TMSI) assigned
What is UMTS?
Universal Mobile Telecommunications System. IMT 2000. Third Generation (3G) Network. Core Network remains similar to GSM networks. Different modulation techniques. Originally different frequencies. Increased data throughput 2Mbs down, 384 Kb up. Improved over time with HSPA and HSPA+ (3.5G).
