Wireless LAN Technology

1. Wireless LAN Technology

2. Wireless LANs • A wireless LAN uses wireless transmission medium. • Used to have high prices, low data rates, occupational safety concerns, and licensing requirements. • Problems have been addressed. • Popularity of wireless LANs has grown rapidly.

3. Wireless LAN Applications • LAN Extension • Cross-building interconnect • Nomadic Access • Ad hoc networking

4. LAN Extension • Wireless LAN linked into a wired LAN on same premises • Wired LAN • Backbone • Support servers and stationary workstations • Wireless LAN • Stations in large open areas • Manufacturing plants, stock exchange trading floors, and warehouses

5. Saves installation of LAN cabling • Eases relocation and other modifications to network structure • However, increasing reliance on twisted pair cabling for LANs • Most older buildings already wired with Cat 3 cable • Newer buildings are prewired with Cat 5 • Wireless LAN to replace wired LANs is beginning to happen, but most popular as a team • In some environments, role for the wireless LAN • Buildings with large open areas • Manufacturing plants, stock exchange trading floors,warehouses • Historical buildings • Small offices where wired LANs not economical

6. Applications of Wireless LANs Single Cell Wireless LAN (typical)

7. Applications of Wireless LANs Multi-Cell Wireless LAN

8. Cross-Building Interconnect • Connect LANs in nearby buildings • Wired or wireless LANs • Point-to-point wireless link is used • Devices connected are typically bridges or routers

9. Ad Hoc Networking • Temporary peer-to-peer network set up to meet immediate need • Example: • Group of employees with laptops convene for a meeting; employees link computers in a temporary network for duration of meeting

10. Infrastructure Wireless LAN

11. Applications of Wireless LANs Ad Hoc Networking • Peer-to-peer network, • No centralised server, • No infrastructure, • Temporary nature.

12. Wireless LAN Requirements

13. IEEE 802.11 Wireless LANs • IEEE 802.11 (also known as Wi-Fi) defines a standard for the physical and the data link layers of wireless LANs. • The standard is defined for the license-free Industrial, Scientific, Medical (ISM) bands. ISM Bands

14. IEEE 802 Protocol Layers

15. Protocol Architecture • Functions of physical layer: • Encoding/decoding of signals • Preamble generation/removal (for synchronization) • Bit transmission/reception • Includes specification of the transmission medium

16. Protocol Architecture • Functions of medium access control (MAC) layer: • On transmission, assemble data into a frame with address and error detection fields • On reception, disassemble frame and perform address recognition and error detection • Govern access to the LAN transmission medium • Functions of logical link control (LLC) Layer: • Provide an interface to higher layers and perform flow and error control

17. IEEE 802.11 Protocol Stack

18. IEEE 802.11 Architecture

19. IEEE 802.11 Architecture • Distribution system (DS) • Access point (AP) • Basic service set (BSS) • Stations competing for access to shared wireless medium • Isolated or connected to backbone DS through AP • Extended service set (ESS) • Two or more basic service sets interconnected by DS

20. IEEE 802.11 – Architecture • Smallest building block is basic service set (BSS) • Number of stations • Same MAC protocol • Competing for access to same shared wireless medium • May be isolated or connected to backbone distribution system (DS) through access point (AP) • AP functions as bridge and a relay pt • MAC protocol may be distributed or controlled by central coordination function in AP • BSS generally corresponds to cell • DS can be switch, wired network, or wireless network

21. BSS Configuration • Simplest: each station belongs to single BSS • Within range only of other stations within BSS • Can have two BSS’s overlapping • Station could participate in more than one BSS • Association between station and BSS dynamic • Stations may turn off, come within range, and go out of range

22. Extended Service Set (ESS) • When two or more BSS are interconnected by DS • Typically, DS is wired backbone but can be any network • Appears as single logical LAN to LLC (logical Link Control) • In BSS, client stations do not communicate directly with each other, must pass through an AP • In IBSS stations all communicate directly, no AP is required

23. Access Point (AP) • Logic within station that provides access to DS • Provides DS services in addition to acting as station • To integrate IEEE 802.11 architecture with wired LAN, portal used • Portal logic implemented in devicethat is part of wired LAN and attached to DS • E.g. Bridge or router

24. IEEE 802.11 Protocol Stack

25. 802.11n • IEEE 802.11n has enhancements in three general areas: • multiple-input-multiple-output (MIMO) antenna architecture • most important enhancement • radio transmission scheme • increased capacity • MAC enhancements • most significant change is to aggregate multiple MAC frames into a single block for transmission

26. IEEE 802.11 MAC Sublayer CSMA/CD cannot be used in wireless LANs. Because not all stations are within the radio range of each other. It is also not possible to detect collision while transmitting because most stations are half-duplex. (a) The hidden station problem. (b) The exposed station problem

27. IEEE 802.11 MAC Sublayer • IEEE 802.11 MAC algorithm is called Distributed Foundation Wireless MAC (DFWMAC). • DFWMAC defines two sublayers. Distributed Coordination Function (DCF) and Point Coordination Function (PCF). • DCF is distributed with an optional centralised access control that works on top of that (i.e., PCF). • DCF is based on CSMA/CA (CSMA with Collision Avoidance) or MACAW. • All frame transmissions are acknowledged with ACK packets. This is the way collision is avoided.

28. IEEE 802.11 MAC Sublayer DCF/MACAW Virtual sensing A B C D

29. Summarise DCF • No Central Control • Stations Compete for Time, just as in Ethernet • 2 types • (a) When a station wants to transmit it senses the channel- if idle, sends frame, it does not sense while transmitting- data may be destroyed. If busy defers some time (t) using Ethernet binary exponential back-off. • (b) as discussed on previous slide- channel sensing

30. Distributed Coordination Function • DCF sublayer uses CSMA • no collision detection since on a wireless network • DCF includes delays that act as a priority scheme

31. IEEE 802.11 MAC Sublayer More on Distributed Coordination Function (DCF) IFS: InterFrame Space

32. IEEE 802.11 MAC Sublayer Point Coordination Function (PCF) • The access point periodically broadcasts beacon frames that contains system parameters and invites stations to request bandwidth. • The access point can provide guaranteed bandwidth to stations that are working in PCF mode. • PCF allows the transport of real-time traffic over the wireless LAN. • PCF is not very well defined in the standard, and not commonly implemented in most commercial access points. However, it exists in the standard specification.

33. Point Coordination Function (PCF)

34. 802.11 MAC Frame Format

35. WiFi’s future: faster, smarter, and fewer cables IEEE 802.11ac: Standard finalization is in late 2012, with final 802.11 Working Group approved in Feb 2014. Theoretically, this specification will enable multi-station WLAN throughput of at least 1 gigabit per second and a maximum single link throughput of at least 500 megabits per second (500 Mbit/s). This is accomplished by extending the air interface concepts embraced by 802.11n: wider RF bandwidth (up to 160 MHz), more MIMO spatial streams (up to 8), multi-user MIMO, and high-density modulation (up to 256 QAM). 802.11ac – revolution or evolution?

36. WiGig- Wireless Gigabit AllianceIEEE 802.11 ad • In June 2011, WiGig announced the release of its certification-ready version 1.1 specification. • The WiGig specification will allow devices to communicate without wires at multi-gigabit speeds. It enables high performance wireless data, display and audio applications that supplement the capabilities of today’s wireless LAN devices. WiGig tri-band enabled devices, which operate in the 2.4, 5 and 60 GHz bands, will deliver data transfer rates up to 7 Gbit/s, about as fast as an 8 antenna 802.11ac transmission, and nearly 50 times faster than the highest 802.11n rate, while maintaining compatibility with existing Wi-Fi devices.

37. IEEE 802.11ac And 802.11ad? IEEE 802.11ac and 802.11ad both provide much higher data throughputs than their predecessors. Yet they have much different potential uses. IEEE 802.11ac is an evolution of previous WLAN capability. It gives the “unwired office” the ability to compete directly with gigabit wired systems while offering much better layout and connection flexibility. In contrast, IEEE 802.11ad is a new solution that provides ad-hoc short-range connectivity in support of extremely high data rates.

38. WirelessHD • The specification was finalized in January 2008. • The WirelessHD specification is based on a 7 GHz channel in the 60 GHz Extremely High Frequency radio band. It allows either lightly-compressed (proprietary wireless link-aware codec) or uncompressed digital transmission of high-definition video and audio and data signals, essentially making it equivalent of a wireless HDMI. First-generation implementation achieves data rates from 4 Gbit/s, but the core technology allows theoretical data rates as high as 25 Gbit/s (compared to 10.2 Gbit/s for HDMI 1.3 and 21.6 Gbit/s for DisplayPort 1.2), permitting WirelessHD to scale to higher resolutions, color depth, and range. The 1.1 version of the specification increases the maximum data rate to 28 Gbit/s, supports common 3D formats, 4K resolution, WPAN data, low-power mode for portable devices, and HDCP 2.0 content protection.

39. William Stallings, “Data and Computer Communications”, chapter 13, 14. • A. S. Tanenbaum, “Computer Networks”, chapter 4. • http://iamwww.unibe.ch/~rvs/lectures/SS98/cn/applets/Ethernet/ethernet.htm (CSMA/CD applet) • http://www.wi-fiplanet.com/ • http://www.vicomsoft.com/knowledge/reference/wireless1.html