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Chapter 7

Chapter 7. Wireless Local Area Networks Some new material added!. Introduction. WLANs serve same purpose as LANs Connect a set of wireless computers into a wired network But can extend a LAN where it is not previously wired therefore making casual connections possible

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Chapter 7

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  1. Chapter 7 Wireless Local Area Networks Some new material added! Chapter 7 - Wireless Networks

  2. Introduction • WLANs serve same purpose as LANs • Connect a set of wireless computers into a wired network • But can extend a LAN where it is not previously wired therefore making casual connections possible • Aka WiFi – used by 90% of companies • This chapter looks at the data link layers and physical layers of several technologies Chapter 7 - Wireless Networks

  3. I. Wireless Ethernet (802.11b/g) • WLAN topology looks like wired star with access point at center as hub • Can apply security settings: encryption • 802.11b – up to 11 Mbps • 802.11g – up to 54 Mbps • Central access point is a radio transceiver that communicates like hub • It is a repeater to all clients connected • Can also be connected to wired network Chapter 7 - Wireless Networks

  4. Access Point • Home models are usually wireless routers. • Act as access point, wired switch, and firewall, NAT • WAN port; LAN ports; wireless ports • Business models are access points connected to a central management pt • ISU uses Cisco access points ~$600 Chapter 7 - Wireless Networks

  5. 802.11b/g technology • 3 radio frequencies used on 2.4 GHz • Same band as cordless phones and some microwave ovens • Can cause problems in apartment-type living • NIC listens (CSMA) to find strongest channel (may hear several APs) • As user roams through the network, NIC may reselect a different AP. • We can stay connected from COB to HMSU! Chapter 7 - Wireless Networks

  6. More Technology • Antennas – Fig 7.3 p. 225 • Directional – narrower, more focused • Omnidirectional – all directions • Size of antenna “cloud” affects • How well users are picked up • Security – does signal reach outside bldg? • 802.11g can “shift down” to 802.11b but all clients must be b in low-end APs Chapter 7 - Wireless Networks

  7. Wireless Adapters Connector for antenna • PC Card – Fig 7.2. Laptop slot • miniPCI card – fits inside laptop with antenna around the screen: better! • USB adapter – good for desktops or laptops Chapter 7 - Wireless Networks

  8. Wireless Connection Types • Infrastructure (access point) • Ad Hoc (computer to computer) • Any available network (AP preferred) • If you choose the wrong type, it will not work! Chapter 7 - Wireless Networks

  9. Media Access Control • Distributed Coordination – each computer listens to see if channel is open • Not good for wide networks where computers at edge may not be able to hear each other • Point Coordination – each computer sends a request to send (RTS) to the AP, then it allows one to talk. • Efficiency – capacity is shared by all active computers on the network (e.g., 11/2 = 5.5) Chapter 7 - Wireless Networks

  10. Speed on 802.11b/g • 802.11b=11 Mbps, 802.11g=54 Mbps (shorter range) • Actual speed depends on … • Signal strength effects of range • up to 200+ feet without obstructions • Practical is 15-50 feet with obstructions: experiment! • 802.11g is shorter range than 802.11b • Trans. errors (distance, obstructions, quality of antennas) • Traffic effects on speed • 802.11b: low (4.8), moderate (1.9), or high (960K) • 802.11g: low (17.2), moderate (6.9), high (3.4) • Super G = version of 802.11g at 108 Mbps • Aka Wireless-G Enhanced Chapter 7 - Wireless Networks

  11. Physical Design Concerns • Engineering is necessary! • Cathy’s older sorority house • ISU wireless project used engineering • Then did reengineering when the assumptions changed (to cover faculty offices) • Antenna design makes a big difference • Hand-off issues for mobile users Chapter 7 - Wireless Networks

  12. Configuration/Security • For a client to connect to an access point, must know the … • SSID of access point (Service Set ID) • Broadcast SSID (anyone can see it) • Silent SSID (client must already know it) • WEP key (wired equivalent privacy Encryption) • This seems like a good idea but it can be quickly broken ala Enigma Machine (periodic status reports allow working backward to get the WEP key) • Store up to 4 WEP keys Chapter 7 - Wireless Networks

  13. Pre-Windows XP Client • First install • Driver for wireless adapter • Client software for the wireless NIC • Next attach the wireless adapter • Configure the client SW for connection • for each access point set • SSID (network name) • WEP (key) if enabled • Can also configure for “choose any AP” Chapter 7 - Wireless Networks

  14. Windows XP Client • Install driver for wireless NIC and install adapter • Use Windows XP client software – built-in wireless client (it disables legacy client software) • Properties of the wireless NIC connection • Use the Wireless Networks tab • Can set up preferred networks in your order • You’ll get a message when an AP is in range • Advanced: enable 802.1x authentication (802.11i) • Look for connection status in the tray: signal strength color bar (red – yellow – green) • I have had to disable the wireless bridge (???) Chapter 7 - Wireless Networks

  15. II. Wireless 802.11a (newer) • Speedy: 802.11a – up to 54 Mbps! • This is newer than 802.11b • Operates in the 5.0 GHz range • Frequency relatively free from interference (unlike 802.11b) • http://www.networkcomputing.com/1201/1201ws1.html gives technical details about frequencies of .11a and .11b • A has more channels (4-12) than B (3) so could have more APs in a given location for more bandwidth • Each channel has 52 subchannels • Media access control and packet layout similar to B Chapter 7 - Wireless Networks

  16. III. Bluetooth (802.15) • Wireless Personal Area Network (WPAN) • Strikingly different purpose • Provide very small area wireless (<30 ft) • Connects two devices rather that to wired LAN • Replace short cable between computer and printer, PDA and cell phone, etc. • Speed is 1 Mbps – slow but OK • Up to 8 devices connected; mostly 2 • Not intended to do general networking • Named after Danish King Bluetooth (really!) Chapter 7 - Wireless Networks

  17. IV. Other Wireless • Infrared – requires direct line of sight • New version can bounce off walls, not direct line of sight, but only in same room • Infrared used for printers, Palm Pilot PDAs, others • 802.11g – long distance (MAN) • Joink Fixed wireless – 2-10 mile range at DSL like speeds Chapter 7 - Wireless Networks

  18. V. Best Practice WLAN Design • Tradeoff: data rate and cost • See Fig 7.12 p. 242 on data rate and users • See Tech Focus 7-1 p. 243 on distance and speed • Don’t forget the very high cost of installing wiring vs. wireless • Need for engineering approach • See Fig 7.13, 7.14 p. 246 for antenna layouts • We look like Fig 7.14 in COB • See Fig 7.15 p. 249 for coverage at IU • Reexamine usage levels for better placement Chapter 7 - Wireless Networks

  19. WLAN Security issues !! • Assume these networks are not secure • Ways to improve security • Don’t broadcast SSID • Use WEP • Change SSID and WEP keys frequently • Can use EAP – extensible authentication protocol where keys are produced dynamically for each session, then discarded Chapter 7 - Wireless Networks

  20. More WLAN Security Issues • Turn off remote management (like mine) so nobody can get in and change things • Change the admin password in the web server section • Consider VPN client only for access • Establish rules on who can connect when • Can use MAC addresses (but users can spoof an IP) • Use authentication – 802.11i • Disable DHCP and preset IP addresses on certain machines – smart and easy. • Adjust router location to reduce outside footprint Chapter 7 - Wireless Networks

  21. 802.11i – Future Standard • This adds client authentication to AP role along with changing keys • WPA – WiFi Protected Access (scaled down) • Temporal Key Integrity Protocol • WPA fixes WEP’s problems by rotating keys • RSN – Robust Security Network (.11i) • Dynamic negotiation of authentication and keys • Improves on WPA • Radius server does the authentication (AP talks to it) Chapter 7 - Wireless Networks

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