1. Wireless LAN Technology Chapter 13

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

3. 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 Buildings where installation and maintenance of wired LANs is not economical.

5. LAN extension There is a backbone wired LAN, such as Ethernet, that supports servers, workstations, and one or more bridges or routers to link with other networks. Control module (CM) that acts as an interface to a wireless LAN. Includes router functionality to link the wireless LAN to the backbone. Regulates the access from the end systems. user modules (UMs) are part of the wireless LAN configuration.

6. Multiple-cell Wireless LAN

7. LAN Extension The configuration of Figure 13.1 can be referred to as a single-cell wireless LAN; all of the wireless end systems are within range of a single control module. Another common configuration, suggested by Figure 13.2, is a multiple-cell wireless LAN. Multiple control modules interconnected by a wired LAN. Each control module supports a number of wireless end systems within its transmission range. For example, with an infrared LAN, transmission is limited to a single room; therefore, one cell is needed for each room in an office building that requires wireless support.

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. Nomadic Access Wireless link between LAN hub and mobile data terminal equipped with antenna Laptop computer or notepad computer Uses: Transfer data from portable computer to office server

10. 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

12. Wireless LAN Requirements Throughput: MAC protocol should make as efficient use as possible of the wireless medium to maximize capacity. Number of nodes Wireless LANs may need to support hundreds of nodes across multiple cells. Connection to backbone LAN In most cases, interconnection with stations on a wired backbone LAN is required. For infrastructure wireless LANs, this is easily accomplished through the use of control modules that connect to both types of LANs. Service area A typical coverage area for a wireless LAN has a diameter of 100 to 300 m.

13. Wireless LAN Requirements Battery power consumption Mobile workers use battery-powered workstations that need to have a long battery life when used with wireless adapters. This suggests that a MAC protocol that requires mobile nodes to monitor access points constantly or engage in frequent handshakes with a base station is inappropriate. Typical wireless LAN implementations have features to reduce power consumption while not using the network, such as a sleep mode. Transmission robustness and security Wireless LAN may be interference prone and easily eavesdropped. Design of a wireless LAN must permit reliable transmission even in a noisy environment and should provide some level of security from eavesdropping.

14. Wireless LAN Requirements Collocated network operation As wireless LANs become more popular, two or more wireless LANs can operate in the same area => interference between the LANs is possible. Such interference may thwart the normal operation of a MAC algorithm and may allow unauthorized access to a particular LAN. License-free operation Users would prefer to buy and operate wireless LAN products without having to secure a license for the frequency band used by the LAN.

15. Wireless LAN Requirements Handoff/roaming MAC protocol used in the wireless LAN should enable mobile stations to move from one cell to another. Dynamic configuration The MAC addressing and network management aspects of the LAN should permit dynamic and automated addition, deletion, and relocation of end systems without disruption to other users.

16. Wireless LAN Categories Infrared (IR) LANs Spread spectrum LANs Narrowband microwave

17. Strengths of Infrared Over Microwave Radio Spectrum for infrared virtually unlimited Possibility of high data rates Infrared spectrum unregulated Equipment inexpensive and simple Reflected by light-colored objects Ceiling reflection for entire room coverage Doesn’t penetrate walls More easily secured against eavesdropping Less interference between different rooms: a separate infrared installation can be operated in every room in the building

18. Drawbacks of Infrared Medium Indoor environments experience infrared background radiation Sunlight and indoor lighting Ambient radiation appears as noise in an infrared receiver Transmitters of higher power required Limited by concerns of eye safety and excessive power consumption

19. IR Data Transmission Techniques Directed Beam Infrared Focused and aimed (remote TV control) Ominidirectional Diffused Reflected from a light colored ceiling

20. Directed Beam Infrared Used to create point-to-point links Range depends on emitted power and degree of focusing Focused IR data link can have range of kilometers Cross-building interconnect between bridges or routers located in different buildings within line of sight of each others

22. Ominidirectional Single base station within line of sight of all other stations on LAN Station typically mounted on ceiling Ceiling transmitter broadcasts signal received by IR transceivers IR transceivers transmit with directional beam aimed at ceiling base unit

23. Diffused All IR transmitters focused and aimed at a point on diffusely reflecting ceiling IR radiation strikes ceiling Reradiated omnidirectionally Picked up by all receivers

24. Spread Spectrum LAN Configuration (most popular) Multiple-cell arrangement (Figure 13.2) Within a cell, either peer-to-peer or hub Peer-to-peer topology No hub Access controlled with MAC algorithm CSMA Appropriate for ad hoc LANs

25. Multiple-cell Wireless LAN

26. Spread Spectrum LAN Configuration Hub topology (Fig 13.2) Mounted on the ceiling and connected to backbone May control access May act as multiport repeater Automatic handoff of mobile stations Stations in cell either: Transmit to / receive from hub only Broadcast using omnidirectional antenna : logical bus configuration

27. Narrowband Microwave LANs Use of a microwave radio frequency band for signal transmission Relatively narrow bandwidth Licensed /Unlicensed licensed narrowband LAN guarantees interference-free communication. licensed spectrum gives the license holder a legal right to an interference-free data communications channel. Users of an unlicensed spectrum ISM-band LAN are at risk of interference disrupting their communications.

28. Licensed Narrowband RF Licensed within specific geographic areas to avoid potential interference Motorola - 600 licenses in 18-GHz range Covers all US metropolitan areas Can assure that independent LANs in nearby locations don’t interfere Encrypted transmissions prevent eavesdropping

29. Unlicensed Narrowband RF RadioLAN introduced narrowband wireless LAN in 1995 Uses unlicensed ISM spectrum Used at low power (0.5 watts or less) Operates at 10 Mbps in the 5.8-GHz band Range = 50 m to 100 m