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Μια εισαγωγή στα Ασύρματα Δίκτυα και Επικοινωνίες Δρ. Χατζημίσιος Περικλής Types of Networks Coverage radius (P) (L) (M) (W) Area Networks Broadcast or Point-to-Point communication Circuit or packet networks Protocol (what is it?) Protocol stack / Layers (OSI and TCP-IP) Backbone and Access Networks Terminal Access Network Core Network Access Networks Wired PSTN, ISDN, xDSL, Ethernet (ΙΕΕΕ 802.3), CATV, Optics Wireless GSM/GPRS, UMTS, WLAN (IEEE 802.11), WMANs (IEEE 802.19), WPANs Access Network Backbone networks Optics Internet PDH/SONET/SDH Microwave Terminal The wireless revolution NO WIRES ! Goals One Wireless standard for Home - Office - on the Move Interoperability with wired networks Security, QoS, roaming users Usage: Entertainment (films, shows, gaming, music,..) Information (Internet, ..) E-commerce (secure home shopping,..) Social contacts (email, voice, interest groups,..) PC (documents, data, printing, scanner, server, ...) Wireless Timeline 1991 - Specification of DECT (cordless phone) Digital European Cordless Telephone (today: Digital Enhanced Cordless Telecommunications). 1880-1900MHz, ~100-500m range, 120 duplex channels, 1.2Mbit/s data transmission, voice encryption, authentication, up to several 10000 user/km2, used in more than 50 countries. 1992 - Start of GSM In Germany as D1 and D2, fully digital, 900MHz, 124 channels Automatic location, hand-over, cellular Roaming in Europe - now worldwide in more than 170 countries Services: data with 9.6kbit/s, FAX, voice, ... 1996 - HiperLAN (High Performance Radio Local Area Network) ETSI, standardization of type 1: 5.15 - 5.30GHz, 23.5Mbit/s Recommendations for type 2 and 3 (both 5GHz) and 4 (17GHz) as wireless ATM-networks (up to 155Mbit/s) …Wireless Timeline 1997 - Wireless LAN – IEEE 802.11: IEEE standard, 2.4 - 2.5GHz and infrared, 2Mbit/s Already many (proprietary) products available in the beginning 1998 - Specification of GSM successors: UMTS (Universal Mobile Telecommunication System) as European proposals for IMT-2000 Iridium: 66 satellites (+6 spare), 1.6GHz to the mobile phone 1999 - Standardization of additional wireless LANs: IEEE standard 802.11b, 2.4-2.5GHz, 11Mbit/s Bluetooth for piconets, 2.4Ghz, <1Mbit/s Decision about IMT-2000 Several “members” of a “family”: UMTS, cdma2000, DECT, … Start of WAP (Wireless Application Protocol) and i-mode Access to many (Internet) services via the mobile phone …Wireless Timeline 2000 - GSM with higher data rates: HSCSD offers up to 57,6kbit/s First GPRS trials with up to 50 kbit/s (packet oriented!) GSM Enhancements for data transmission pick up (EDGE, GPRS, HSCSD) UMTS auctions/beauty contests Hype followed by disillusionment (approx. 50 B$ payed in Germany for 6 UMTS licenses!) 2001 - Start of 3G systems: Cdma2000 in Korea, UMTS in Europe, Foma (almost UMTS) in Japan 2002 – Standardization of high-capacity wireless networks: IEEE 802.16 as Wireless MAN 2002 – today …… more wireless protocol standards are here! … Why Not Wireless? There are limitations and difficulties with using wireless communications: Wireless may be cheaper to deploy in some cases, but it may have usage fees (cellular service is still NOT cheap). Issues of security (for example, WEP). Incompatible standards that do not work well with each other. …Why Not Wireless? Some mobile or wireless devices have hardware or software limitations (small screen sizes, text only displays, support for WML but not HTML, etc.). Wireless networks do not support the same data rates as wired networks with the same reliability. Wireless Link Characteristics Differences from wired link …. Energy and computing-power limitations Decreased signal strength Obstacles and hidden-terminal problem Collision detection hard or impossible More noise Interference from other sources Multipath propagation different delays interferences between paths or (multipath) fading Lower signal/noise Higher bit error rate Wireless vs Mobile Two aspects of mobility: user mobility: users communicate (wireless) “anytime, anywhere, with anyone” device portability: devices can be connected anytime, anywhere to the network Wireless vs. mobile Examples stationary computer notebook in a hotel wireless LANs in historic buildings Personal Digital Assistant (PDA) Applications ? Everywhere! Vehicles Transmission of news, road condition, weather, music personal communication using GSM position via GPS local ad-hoc network with vehicles close-by to prevent accidents, guidance system, redundancy Emergencies Replacement of a fixed infrastructure in case of earthquakes, hurricanes (Katrina in USA), fire, etc Crisis, war, etc Entertainment, education, sensor … Bandwidth of access networks Dialup ~ 64 Kbps DSL/Cable Cable ADSL VDSL 1 ~ 40 Mbps 1~10 Mbps(shared) 1~10 Mbps(dedicated) 20~50 Mbps or more (dedicated) Ethernet 100 Mbps ~ 10 Gbps (dedicated) Bandwidth of access networks (2) Wireless LAN 802.11b 11 Mbps (shared) 802.11a 802.11g 802.16 54 Mbps (shared) 54 Mbps (shared) 50 Mbps (shared) Mobile Phone 2.5~3G 4G 0.1~2 Mbps (dedicated) 20~50 Mbps (dedicated) Access network evolution Development of fixed access technologies Developments in ADSL and VDSL technology Deployment of FTTx networks (FTTU - Fiber to the user) More user data rates than wireless technology Increase in per user data rates Ability to offer high data rate services NGN and triple play offers Access network evolution Developments in mobile access technologies Evolved HSPA/HSPA+ enhancement (MIMO and 64 QAM modulation 42 Mbps on single 5 MHz carrier) Evolved Packet System (EPS) – QoS concepts OFDM based technology - Long Term Evolution (LTE), mobile WiMAX Increase in per user data rates Mobile Broadband Increase consumption of multimedia services Issues in Wireless and Mobile Communications Wireless Environment Power consumption and energy efficiency Loss of data Restrictive regulations of frequencies Network and service convergence Cross-layer design Quality of Service (QoS) Cognitive radio networks / Software defined radios Economics Security The today (already old) of Wireless Communications Wireless Wide Area Network (WWAN) • Metro/Geographical area • “Always On” Services • Ubiquitous public connectivity with private virtual networks Mobility Outside Campus Walk Fixed/ Desktop DECT Bluetooth 0.1 1 HiperLAN2 802.11a Walk >3G 802.11b Within Campus Fixed CDMA2000 1X GSM/GPRS Vehicle Wireless Local Area Network (WLAN) • Public or Private Site or Campus • Enterprise / premises application voice & data network extension • Nomadic / “pull” services • Non-licensed spectrum 10 LAN 100 Mbps Mobile Wireless Technologies ● Mobile wireless (Cellular Phones) ● Fixed wireless (satellites, cordless phones) ● Local wireless networks WLAN 802.11 (WiFi) ● Personal wireless networks WPAN 802.15 (Bluetooth, ZigBee) ● More standards (e.g. WMAN 802.16 (WiMAX)) Wireless Technologies Overview Core technologies (IEEE 802.1x family) IEEE 802.16 (Wireless M(etropolitan) AN) – Under development IEEE 802.15 (Wireless PAN – Bluetooth) IEEE 802.11 (Wireless LAN) MAN Facilitating technologies RF-Id IrDA Home-RF LAN PAN Standardization What is a standard? Many standardization organizations exist: – – – – – – – – – – – IETF - Internet Engineering Task Force IEEE - Institute of Electrical and Electronics Engineers ANSI - American National Standards Institute ITU-T - International Telecommunication Union Telecommunication Section (previous CCITT) ISO - International Organization for Standardization TIA - Telecommunications Industry Association EIA - Electronics Industries Association ATMF – Asynchronous Tranfer Mode Forum OIF – Optical Inteρnetworking Forum W3C – World Wide Web Consortium TMF – Telecommunications Management Forum Generations in Mobile Wireless Service (Cellular Phones) First Generation (1G) Second Generation (2G) Higher data rates than 2G A bridge (for GSM) to 3G Third Generation (3G) Primarily voice, some low-speed data (circuit switched) Generation 2½ (2.5G) Mobile voice services Seamless integration of voice and data High data rates, full support for packet switched data Fourth Generation (4G) Evolution of Mobile Wireless (1) Advance Mobile Phone Service (AMPS) • FDMA • 824-849 MHz (UL), 869-894 MHz (DL) • U.S. (1983), So. America, Australia, China European Total Access Communication System (E-TACS) • FDMA • 872-905 MHz (UL), 917-950 MHz (DL) • Deployed throughout Europe Evolution of Mobile Wireless (2) Global System for Mobile communications (GSM) • TDMA • Different frequency bands for cellular and PCS • Developed in 1990, expected >1B subscriber by end of 2003 IS-95 • CDMA • 800/1900 MHz – Cellular/PCS • U.S., Europe, Asia Evolution of Mobile Wireless (3) General Packet Radio Services (GPRS) • Introduces packet switched data services for GSM • Transmission rate up to 170 kbps • Some support for QoS Enhanced Data rates for GSM Evolution (EDGE) • Circuit-switched voice (at up to 43.5 kbps/slot) • Packet-switched data (at up to 59.2 kbps/slot) • Can achieve on the order of 475 kbps on the downlink, by combining multiple slots Evolution of Mobile Wireless (4) Universal Mobile Telecommunication Systems (UMTS) • Wideband DS-CDMA • Bandwidth-on-demand, up to 2 Mbps • Supports handoff from GSM/GPRS IS2000 • CDMA2000: Multicarrier DS-CDMA • Bandwidth on demand (different flavors, up to a few Mbps) • Supports handoff from/to IS-95 Some more IEEE standards for mobile communications IEEE 802.16: Broadband Wireless Access: WMAN, WiMax IEEE 802.20: Mobile Broadband Wireless Access (MBWA) Licensed bands < 3.5 GHz, optimized for IP traffic Peak rate > 1 Mbit/s per user Different mobility classes up to 250 km/h and ranges up to 15 km IEEE 802.21: Media Independent Handover Interoperability Wireless distribution system for the last mile, alternative to DSL 75 Mbit/s up to 50 km LOS, up to 10 km NLOS; 2-66 GHz band Initial standards without roaming or mobility support 802.16e adds mobility support, allows for roaming at 150 km/h Standardize handover between different 802.x and/or non 802 networks IEEE 802.22: Wireless Regional Area Networks (WRAN) Radio-based PHY/MAC for use by license-exempt devices on a non-interfering basis in spectrum that is allocated to the TV Broadcast Service Elements of a wireless network network infrastructure wireless hosts laptop, PDA, IP phone run applications may be stationary (nonmobile) or mobile wireless does not always mean mobility Elements of a wireless network network infrastructure base station typically connected to wired network relay - responsible for sending packets between wired network and wireless host(s) in its “area” e.g., cell towers 802.11 access points Elements of a wireless network network infrastructure wireless link typically used to connect mobile(s) to base station also used as backbone link multiple access protocol coordinates link access various data rates, transmission distance Elements of a wireless network network infrastructure infrastructure mode base station connects mobiles into wired network handoff: mobile changes base station providing connection into wired network Elements of a wireless network Ad hoc mode no base stations nodes can only transmit to other nodes within link coverage nodes organize themselves into a network: route among themselves Mobility issues … Location dependent issues Location dependent carrier sensing Hidden nodes. A hidden node is one that is within the range of the intended destination but out of range of the sender Exposed nodes. An exposed node is one that is within the range of the sender but out of range of the destination Capture. This event occurs when a receiver can correctly receive a transmission from one of two (or more) simultaneous transmissions, all within its range, because the signal strength of the correctly received signal is much higher than strength of the other signals Hidden and Exposed Node Problems Hidden node • A is transmitting to B • C is out of range of A and is unaware of the transmission • If C transmits to B it will cause a collision at B • B is transmitting to A Exposed node • C wants to transmit to D • C senses transmission & declines even if its transmission will not cause any collision at A Capture Problem A dA B B dCB C D If A and C transmit simultaneously to B then the signal power of C, received at B, is higher than the one from A and there is a good probability that C’s signal can be correctly decoded in the presence of A’s transmission This capture of C’s signal can improve protocol performance, but it results in unfair sharing of the channel with preference given to nodes closer to the receiver. RTS-CTS Handshake* RTS-CTS handshake used to resolve hidden terminal problem RTS = Ready to send; transmitted by sender to inform receiver of available data CTS = Clear to send; broadcasted by receiver to inform all neighbors that channel will be occupied ACK = Acknowledgement; broadcasted by receiver to inform all neighbors that channel is free again. WLAN Standards Wireless LAN 2.4 GHz 5 GHz 802.11 802.11b 802.11g HiSWANa 802.11a HiperLAN2 (2 Mbps) (11 Mbps) (22-54 Mbps) (54 Mbps) (54 Mbps) (54 Mbps) HomeRF 2.0 Bluetooth HomeRF 1.0 (10 Mbps) (1 Mbps) (2 Mbps) 802.11e 802.11f 802.11h 802.11i (QoS) (IAPP) (TPC-DFS) (Security) Ευχαριστώ για την υπομονή σας! Ερωτήσεις ή σχόλια? Συζήτηση!