Lect 7 Cellular Internet Access 2G,3G.pdf

University of Science & Technology Faculty of Computer Science & Information Technology Department of information for communication and technology Mobile communications & wireless technology_ it 709 4year/sem 7 Tawffeeg Mohammed Tawfeeg Cellular...

University of Science & Technology Faculty of Computer Science & Information Technology Department of information for communication and technology Mobile communications & wireless technology_ it 709 4year/sem 7 Tawffeeg Mohammed Tawfeeg Cellular Internet Access 2  Cellular Network generations The earliest generations were designed primarily for voice traffic. First generation (1G) systems were analog FDMA systems designed exclusively for voice- only communication. These 1G systems are almost extinct now, having been replaced by digital 2G systems. 3  2 & 3 Generations The original 2G systems were also designed for voice, but later extended (2.5G) to support data (i.e., Internet) as well as voice service. The 3G systems that currently are being deployed also support voice and data, but with an ever increasing emphasis on data capabilities and higher-speed radio access links. 4 2G: Voice Connections to the Telephone Network The term cellular refers to the fact that the region covered by a cellular network is partitioned into a number of geographic coverage areas, known as cells, shown as hexagons. Each cell contains a base transceiver station (BTS) that transmits signals to and receives signals from the mobile stations in its cell. 5 The Coverage Area of a Cell The coverage area of a cell depends on many factors, including the transmitting power of the BTS, the transmitting power of the user devices, obstructing buildings in the cell, and the height of base station antennas. The GSM(Global System for Mobile Communications ) standard for 2G cellular systems uses combined FDM/TDM (radio) for the air interface. 6  FDM & TDM With pure FDM, the channel is partitioned into a number of frequency bands with each band devoted to a call. With pure TDM, time is partitioned into frames with each frame further partitioned into slots and each call being assigned the use of a particular slot in the revolving frame. 7  FDM/TDM In combined FDM/TDM systems, the channel is partitioned into a number of frequencysub-bands; within each sub- band, time is partitioned into frames and slots. Thus, for a combined FDM/TDM system, if the channel is partitioned into F sub-bands and time is partitioned into T slots, then the channel will be able to support F.T simultaneous calls. 8 Components of cellular network architecture MSC  connects cells to wired tel. net.  manages call setup (more later!) cell  handles mobility (more later!)  covers region geographical  base station (BS) Mobile analogous to 802.11 Switching Center AP Public telephone  mobile users attach to network network through BS air-interface: physical Mobile Switching and link layer protocol Center between mobile and BS wired network 9 Cellular networks: the first hop Two techniques for sharing mobile-to-BS radio spectrum  combined FDMA/TDMA: divide spectrum in frequency channels, divide each channel time slots into time slots  CDMA: code division multiple acces frequency bands s 10 Base Station Controller (BSC) A GSM network’s base station controller (BSC) will typically service several tens of base transceiver stations. The role of the BSC is to allocate BTS radio channels to mobile subscribers, perform paging (finding the cell in which a mobile user is resident), and perform handoff of mobile. The base station controller and its controlled base transceiver stations collectively constitute a GSM base station system (BSS). 11 Mobile switching centre (MSC) Mobile switching centre (MSC) plays the central role in user authorization and accounting (e.g., determining whether a mobile device is allowed to connect to the cellular network), call establishment and tear-down, and handoff. A single MSC will typically contain up to five BSCs, resulting in approximately 200K subscribers per MSC. 12  Gateway MSCs A cellular provider’s network will have a number of MSCs, with special MSCs known as gateway MSCs connecting the provider’s cellular network to the larger public telephone network. 13 2G (voice) network architecture Base station system (BSS) MSC BTS BSC G Public telephone network Gateway MSC Legend Base transceiver station (BTS) Base station controller (BSC) Mobile Switching Center (MSC) Mobile subscribers 14 3G Cellular Data Networks: Extending the Internet to Cellular Subscribers The 3G core cellular data network connects radio access networks to the public Internet. The core network interoperates with components of the existing cellular voice network 15  3G system architecture Given the considerable amount of existing infrastructure (and profitable services!) in the existing cellular voice network, the approach taken by the designers of 3G data services is clear: leave the existing core GSM cellular voice network untouched, adding additional cellular data functionality in parallel to the existing cellular voice network. 16  3G nodes The alternative—integrating new data services directly into the core of the existing cellular voice network. There are two types of nodes in the 3G core network: Serving GPRS Support Nodes (SGSNs) and Gateway GPRS Support Nodes (GGSNs). (GPRS stands for Generalized Packet Radio Service, an early cellular data service in 2G networks) 17  SGSN An SGSN is responsible for delivering datagrams to/from the mobile nodes in the radio access network to which the SGSN is attached. The SGSN interacts with the cellular voice network’s MSC for that area, providing user authorization and handoff, maintaining location (cell) information about active mobile nodes, and performing datagram forwarding between mobile nodes in the radio access net-work and a GGSN. 18  GGSN The GGSN acts as a gateway, connecting multiple SGSNs into the larger Internet. A GGSN is thus the last piece of 3G infrastructure that a datagram originating at a mobile node encounters before entering the larger Internet. To the outside world, the GGSN looks like any other gateway router; the mobility of the 3G nodes within the GGSN’s network is hidden from the outside world behind the GGSN. 19 The Radio Network Controller (RNC) The Radio Network Controller (RNC) typically controls several cell base transceiver stations similar to the base stations that we encountered in 2G systems 20 3G (voice + data) network architecture MSC G Public telephone network radio network Gateway controller MSC Key insight: new cellular data network operates in parallel G Public (except at edge) with existing SGSN Internet cellular voice network  voice network unchanged in core GGSN  data network operates in parallel Serving GPRS Support Node (SGSN) Gateway GPRS Support Node (GGSN) 21 3G (voice + data) network architecture MSC G Public telephone network radio network Gateway controller MSC G Public SGSN Internet GGSN radio interface (WCDMA, HSPA) radio access network core network public Universal Terrestrial Radio General Packet Radio Service Internet Access Network (GPRS) Core Network (UTRAN) 22 Thanks for attentions These slides are adapted from Computer Networking: A Top Down Approach Jim Kurose, Keith Ross Addison- Wesley March 2012 23