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Chapter 14: Wireless Networks

Chapter 14: Wireless Networks. Principles of Computer Networks and Communications M. Barry Dumas and Morris Schwartz. Objectives. Describe the role of wireless transmission in computer communications and the physical phenomena that enable wireless communications

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Chapter 14: Wireless Networks

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  1. Chapter 14:Wireless Networks Principles of Computer Networks and Communications M. Barry Dumas and Morris Schwartz

  2. Objectives • Describe the role of wireless transmission in computer communications and the physical phenomena that enable wireless communications • Identify characteristics that are common in all wireless networks • Differentiate between contemporary wireless network configurations and provide practical examples of their application • Provide examples of alternative LAN protocol sets including their capabilities and drawbacks • Identify the essential elements of a wireless personal area network including various configurations, protocols, advantages, and disadvantages associated with Bluetooth • Describe the essential elements of the IEEE802.15.1 WPAN and IEEE 802.16 wireless standards • Explain various aspects of cellular telephony including current configurations • Provide characteristics of satellite communications including differentiating between orbital differences Principles of Computer Networks and Communications

  3. Overview “Wireless networks employ electromagnetic waves, primarily radio waves and microwaves, to carry transmissions over the air or through the vacuum of space using antennas to transmit and receive signals.” • For transmission • The electromagnetic carrier is modulated to represent the data signal • Multiplexing allows many transmissions to take place simultaneously without interfering with one another • Upon receipt • At the receiver, the signal is demodulated to extract the data Principles of Computer Networks and Communications

  4. Wireless Local Area Networks • Wireless local area networks (WLANs) • Use radio wave carriers to transmit signals among nodes • Typically share the networking burden with wired counterparts • Provide flexibility and mobility over wired LANs Most WLANs operate in 2.4 GHz and 5 GHz bands Principles of Computer Networks and Communications

  5. Wireless Local Area Networks • National information infrastructure (NII) • Collection of network types that includes • Radio and television • Public switched telecommunications network • Private communications networks • Includes the U-NII that defines the industrial, scientific, medical (ISM) bands that are unlicensed in the United States and most countries Principles of Computer Networks and Communications

  6. Wireless Local Area Networks • Wireless local area networks (WLANs) Advantages • Easy creation; no cables; can connect to wired LANs • Provide access in places where wiring is not feasible/too costly • Simple connection (usually automatic) for spontaneous participation • Mobility and unconstrained physical configuration (within range) Disadvantages • Possible interference from electromagnetic radiation in ISM bands • Potential for eavesdropping/security breaches • Limited data rates compared to wired networks • Incompatibilities due to proprietary schemes in the market Principles of Computer Networks and Communications

  7. Wireless Local Area Networks • WLANs—topology • Fundamental structure of a WLAN is a Basic service set (BSS) • Computers in a WLAN are called stations • Minimum BSS has two stations • Stations can be mobile or fixed computers • Can include an access point that connects • Wirelessly to the BSS • By wire (through LAN/backbone) to the organization’s wired network • Independent basic service set (IBSS) (aka “ad hoc network”) • An independent standalone LAN • LAN stations can communicate only within the LAN Mobile station vs. portable station Mobile stationoperates while moving Portable stationable to be moved within the LAN Principles of Computer Networks and Communications

  8. WLANs—Independent basic service set (IBSS) Devices within the IBSScan communicate with the serveror with one another Fig 14.1A WLAN IBSSwith server Principles of Computer Networks and Communications

  9. WLANs—Basic service set (BSS) wiredaccess Fig. 14.2A WLAN BSSwith access point Principles of Computer Networks and Communications

  10. Wireless Local Area Networks • WLANs—Basic service set (BSS) (cont.) • Basic building blocks of extended WLANs • When two or more BSSs are connected by their access points to the same wired LAN • Wired portion is called a distribution system (DS) DS + BSSs  extended service set (ESS) Principles of Computer Networks and Communications

  11. WLANsBSS and ESS Wired access Fig. 14.3 Principles of Computer Networks and Communications

  12. Wireless Local Area Networks • The distribution system (DS) (wired portion of an ESS) provides the following participation services • Association • Required for station participation • Stations can associate with only one access point at a time • Disassociation • When a station leaves a BSS or shuts down • Re-association • Within an ESS, a station can move to another BSS (different access point) • Distribution • Within an ESS, a station in one BSS needs to communicate with a station in a different BSS • Integration • The DS communicates between ESS stations and the other wired LANs in the corporate network • Inter-ESS movement • Stations can move from one ESS to another ESS Principles of Computer Networks and Communications

  13. Wireless Local Area Networks • The distribution system (DS) (wired portion of an ESS) provides the following station specific services • Authentication • A station must identify itself before it can associate with a BSS • Two versions of authentication • Open system authentication • Station access is never denied • Station simply identifies itself during association • Shared key • Controls station access • Station must possess a secret key to be authenticated • A secret key is distributed by Wired Equivalent Privacy (WEP) • De-authentication • A station’s authentication is terminated • Occurs when a station leaves a BSS oris disassociated Principles of Computer Networks and Communications

  14. Wireless Local Area Networks • WLAN protocols • Contained in the 802.11 specifications • Exist in lowest two architecture model layers • Physical—defines electrical/spectrum and bit transmission/receipt • Data link—responsible for • Frame assembly • Node-to-node error control • Physical addressing • Inter-node synchronization • Medium (channel) access • Two protocol sets • Client/server (LAN paradigm) • Employs 802.x protocols used by wired LANs • Ad hoc (wireless personal area networks paradigm) • Small coverage areas • Used in Bluetooth networks Principles of Computer Networks and Communications

  15. Wireless Local Area Networks • WLAN protocols—physical layer of 802.11 • Physical—defines electrical/spectrum and bit transmission/receipt • Defines four transmission methods (infrared or radio frequency) • (IR) Infrared (IR) • (RF) Frequency hopping spread spectrum (FHSS) • (RF) Direct sequence spread spectrum (including high rate) (HR/DSSS) • (RF) Orthogonal frequency division multiplexing (OFDM) For nodes to communicate, each must use the same transmission method. Principles of Computer Networks and Communications

  16. Wireless Local Area Networks • WLAN protocols—physical layer of 802.11 • Infrared (IR) • Signals are carried by infrared light • Very short useful range [5 to 6 meters; 15 to 20 feet] • Commonly found in TV remote controls and wireless computer peripherals (keyboard, mouse, etc.) • Standards developed by the infrared data association (IRDA) Advantages • Works in electrically noisy environments without interference • Signals can reflect (off walls, ceilings, etc.) to reach target • Inexpensive Disadvantages • Very limited span • Line-of-sight required • Unable to penetrate solid objects Except for Bluetoothrarely used in WLANs Could be an advantage if security is an issue(i.e., difficult to intercept) Principles of Computer Networks and Communications

  17. Wireless Local Area Networks • WLAN protocols—physical layer of 802.11 • Infrared (IR) irDA-defined physical layer protocols Principles of Computer Networks and Communications

  18. Wireless Local Area Networks • WLAN protocols—physical layer of 802.11 • (RF) Frequency hopping spread spectrum (FHSS) • Narrow bandwidth, only a small portion of 2.4 GHz spectrum • Entire spectrum is used by constantly shifting the signal (hopping) across the spectrum • A master station establishes the hopping sequence that is followed by participating stations • Transmissions appear to take place over a single (virtual) communications channel Particularly popular in Bluetooth and HomeRF networks Principles of Computer Networks and Communications

  19. Wireless Local Area Networks • WLAN protocols—physical layer of 802.11 • (RF) Direct sequence spread spectrum (high rate) (HR/DSSS) • Spreads the signal over the entire 2.4 GHz spectrum • Entire spectrum is used by substituting a redundant sequence of bits (chipping code) for each bit of the signal to be transmitted • Because the chipping code data rate is higher than the original signal rate, there is no delay in signal transmission • Most often used in WiFi802.11b (11 Mbps) or 802.11g(below 20 Mbps) DSSS and FHSS will interfere with each other!These are not usually found in business environments. Principles of Computer Networks and Communications

  20. Wireless Local Area Networks • WLAN protocols—physical layer of 802.11 • (RF) Orthogonal frequency division multiplexing (OFDM) • Similar to frequency division multiplexing (FDM), except • FDM transmits signals from multiple sources at the same time, with each source assigned a separate sub-band frequency • OFDM assigns all of the sub-bands to a single source for a specified time • Carrier frequencies are produced so that peak amplitudes of each frequency coincide with minimum amplitudes of adjacent frequencies • Modulators see frequencies in only a particular carrier sub-band Principles of Computer Networks and Communications

  21. Wireless Local Area Networks • WLAN protocols—802.11 variations • (2001) 802.11a (54 Mbps, 5 GHz) • (1999) 802.11b (11 Mbps, 2.4 GHz) • Original WiFi standard • (2003) 802.11g (54 Mbps, 2.4 GHz) • Backward compatible with 802.11b • Essentially eliminated need for 802.11a • (2006) 802.11n (100 to 600 Mbps, 5 GHz) • Uses multiple input/multiple output (MIMO) signaling with many data streams traveling over the same frequencies, and each data stream carrying different information Principles of Computer Networks and Communications

  22. Wireless Local Area Networks • WLAN protocols—802.11 variations summarized Susceptible to microwave/portable phone interference! Principles of Computer Networks and Communications

  23. Wireless Local Area Networks • WLAN protocols—data link layer of 802.11 • As with all 802 LANs, the data link layer is subdivided: • Logical link control (LLC) • Media access control (MAC) • When an ESS (collection of BSSs) is created, component BSSs appear to the LLC as a single IBSS • Stations can communicate with other stations on the ESS • Stations can move to any BSS on the ESS • A station’s physical address is one of the 48-bit MAC addresses of the (wireless) NIC Principles of Computer Networks and Communications

  24. Predominantly Bluetooth! Wireless Personal Area Networks • Wireless personal area network (WPAN) • Accommodates data sharing and connectivity • Small, often impromptu groups • Limited span (e.g., same room) • Originally designed to replace desktop cable connections Principles of Computer Networks and Communications

  25. Wireless Personal Area Networks 802.15.1 establishes Bluetoothas a de jure standard • WPAN—Bluetooth • Based on the 802.11 standard • However, does not use 802.x LAN protocols • Not designed for LAN communications, large-scale data • Operates in the 2.4 GHz band • Operates in a piconet (supporting 2 to 8 devices) • Uses FHSS to hop from channel to channel within the 79 (1 MHz)sub-bands (channels) of the 2.4 GHz band FHSS avoids interference from other 2.4 GHz devices(e.g., portable phones, baby monitors, microwaves, etc.) Principles of Computer Networks and Communications

  26. Wireless Personal Area Networks • WPAN—piconet • Supports 2 to 8 devices (needs at least two active members) • Is established automatically (on the fly) • Devices entering a piconet • [with less than 8 devices] are assigned an address • [with 8 or more devices] can be on standby • First member assumes the role of master; others act as slaves • Members can be mobile or stationary • Mobile members can move within a piconetas long as they stay within range of the master A collection of piconets is a scatternet Principles of Computer Networks and Communications

  27. WPAN—piconet 1 M 1 M 2 3 4 5 7 6 Fig 14.4A and B Principles of Computer Networks and Communications

  28. WPAN—piconet 1 M 2 M3 M1 1 M2 1 1 2 2 3 Fig 14.4C Principles of Computer Networks and Communications

  29. Wireless Metropolitan Area Networks • Wireless metropolitan area network (WMAN)[aka WiMAX] • 802.16 • Operates in 2 to 11 GHz band [as of 802.16a] • High data-data-rate broadband system (to 70 Mbps) • Can operate over substantial distances (> 30 miles) • Uses same logical link control (LLC) as other 802 networks, which means: WiMAX and WiFi networkscan interconnect! Principles of Computer Networks and Communications

  30. Wireless Metropolitan Area Networks • WMAN (WiMAX) • Provides four key wireless functionalities • High-speed connectivity • Alternative to contracting for wired services • Last-mile broadband • High speed without need for telco last-mile local loops • Hot spot (hot zone) coverage • Connects mobile devices to access points • Backhaul alternative • Provides wireless access from remote sites to the core network Principles of Computer Networks and Communications

  31. Wireless Metropolitan Area Networks • WMAN (WiMAX)—standards in other countries • European Telecommunications Standard Institute (ETSI) wireless standards • 802.11—WiFi HiperLAN—high performance radio LAN • 802.15—PAN HiperPAN—high performance radio PAN • 802.16—WiMAX HiperMAN—high performance radio MAN • Korean Telecommunications Technology Association (KTTA) • 802.16—WiMAX WiBro—wireless broadband Compatible! Principles of Computer Networks and Communications

  32. Cellular Telephony • Terms • Base stations • Stationary, ground-based sites linked to neighboring sites • Are connected to and controlled by MSCs • Cell • Logical way of thinking about a coverage region (usually hexagonal) • Base station coverage areas • Cell phone • Low-power transmitter/receiver for voice and data • Communicating wirelessly through a collection of base stations • Mobile switching centers (MSCs)(aka mobile telephone switching offices—MTSOs) • Establish call connections • Coordinate all base stations • Provide links to the wired telephone network and the Internet • Keep calling and billing records Principles of Computer Networks and Communications

  33. Cellular Telephony • Basic functionality (simple) • When a call is initiated, a connection is established between the caller’s cell phone and the base station of the cell the caller is in • As the caller begins to move out of range for that cell, the base station senses the drop in signal power and relays that information to the MSC • The MSC automatically “hands off” the call to the base station of the cell the caller is moving into Principles of Computer Networks and Communications

  34. Cellular Telephony • Where are cells located? Some viewpoints: Base station 1 coverage 1 Fig 14.5 Principles of Computer Networks and Communications

  35. Cellular Telephony • Generations and systems • First Generation (1G—early 1980s) • Analog based, multiplexed by FDMA • Advanced mobile phone system (AMPS) • Used 850 MHz band (824–894 MHz) • 824–849 MHz mobile unit to base station • 869–894 MHz base station to mobile unit Problems • Noise and poor quality • Coverage was limited • Cells had limited capacity • Easy to tap airborne signals (steal phone codes) Principles of Computer Networks and Communications

  36. Cellular Telephony European and U.S. GSMsare not compatible • Generations and systems • Second Generation (2G—late 1980s to 1990s) • Introduced digital service • Employ powerful authentication techniques • Three schemes • Digital AMPS [D-AMPS] • Digital version of AMPS, based on TDMA • Uses 850 MHz band [824–894 MHz; same as AMPS] • Phone voice coders (vocoders) converted analog voice to digital Principles of Computer Networks and Communications

  37. Cellular Telephony • Personal communication system (PCS) • Uses code division multiple access (CDMA) • Digital system combines DSSS with chipping codes • Uses 1,900 MHz band (1,850–1,910 MHz) • Global system for mobile communications (GSM)—developed in Europe • Uses combination of FDMA to divide bands into channelsand TDMA to create time slots within the channels • Uses 850 MHz and 1,900 MHz band in United States • Uses 900 MHz and 1,800 MHz band in Europe and Asia SprintVerizon AT&TCingularNextelT-Mobile Principles of Computer Networks and Communications

  38. Cellular Telephony • Generations and systems • Third Generation (3G) • Addressed speed shortcomings of 2G cell phones (144 Kbps to 2+ Mbps) • [With the speed] Enabled access to more services • Web browsing • Web-based applications • Multimedia • E-mail (with or without attachments) • Works with smart phones (i.e., cell phones, PDAs with cell phone features) Problems • Memory • Online costs Although 3G mobile devices can access broadband services,connection cost (at cell phone rates) is still a limiting factor. Principles of Computer Networks and Communications

  39. Cellular Telephony • Generations and systems • Evolving Third Generation (3G+) • Three schemes • Universal mobile telephone service (UMTS) (GSM-type, wide-band code division) • Designed to run over existing GSM networks • Will probably replace GSM • CDMA20000 (enhanced 2G code division multiple access) • TD-SCDMA (time division + synchronous code division) • Data rates as high as 14 Mbps Fourth generation (4G) technology holds the prospect of data rates between 100 Mbps–1 Gbps Principles of Computer Networks and Communications

  40. Satellites “…line of sight still is required from the earth transmitter to the satellite,from the satellite to the earth receiver, and indeed from one satellite to another.” • There cannot be successful communication • If the (transmit/receive) earth stations cannot “see” the satellite • If the satellites cannot “see” each other Echo I (994 mile altitude) orbited the earth every 90 minutes A spot on earth could “see” Echo I for only 10 minutes each orbit! Principles of Computer Networks and Communications

  41. Satellites • Transmission signals • Uplink—from earth location to satellite • Downlink—from satellite to an earthbound station • Orbits • Geosynchronous earth orbits (GEOs) • Medium earth orbits (MEOs) • Low earth orbits (LEOs) • Highly elliptical orbits (HEOs) None of these are synchronous Principles of Computer Networks and Communications

  42. If a GEO satellite is in line of sight, it will always be in line of sight. Satellites • Geosynchronous earth orbits (GEOs) • Appear stationary to an observer on earth • Match the rotation of the earth • 22,240 miles (35,786 km) above the earth • Typically centered around the equator • Can see 35 to 40% of the earth within latitude bands Principles of Computer Networks and Communications

  43. Satellites For non-synchronous orbits • Satellites do not appear to be stationary • Constellations (parades of satellites) are used for coverage • Transmissions from a “departing” satellite (moving out of line of sight)are handed off to an incoming satellite • Medium earth orbits (MEOs) • Range from 5,000–15,000 km(3,100–9,300 miles) • Low earth orbits (LEOs) • Range from 100–2,000 km(100–1,240 miles) • Highly elliptical orbits (HEOs) • Ranges in altitude from 500–50,000 km(less than 311–more than 31,000 miles) Only orbit used for polar regions Principles of Computer Networks and Communications

  44. Satellites • Communications satellites use microwave signals between 1.5 and30 GHz Table 14.1 Principles of Computer Networks and Communications

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