Chapter 7 - Wireless Networks1 Chapter 7 Wireless Local Area Networks Some new material added!

Chapter 7 - Wireless Networks2 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 Networks3 I. Wireless Ethernet (802.11b/g) WLAN topology looks like wired star with access point at center as hub Can apply security settings: encryption b – up to 11 Mbps g – 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 Networks4 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 b/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 Networks6 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? g can “shift down” to b but all clients must be b in low-end APs

Chapter 7 - Wireless Networks7 Wireless Adapters 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 Connector for antenna

Chapter 7 - Wireless Networks8 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 Networks9 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 Networks10 Speed on b/g b=11 Mbps, g=54 Mbps (shorter range) Actual speed depends on … Signal strength effects of range up to 200+ feet without obstructions Practical is feet with obstructions: experiment! g is shorter range than b Trans. errors (distance, obstructions, quality of antennas) Traffic effects on speed b: low (4.8), moderate (1.9), or high (960K) g: low (17.2), moderate (6.9), high (3.4) Super G = version of g at 108 Mbps Aka Wireless-G Enhanced

Chapter 7 - Wireless Networks11 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 Networks12 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 Networks13 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 Networks14 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 Networks15 II. Wireless a (newer) Speedy: a – up to 54 Mbps! This is newer than b Operates in the 5.0 GHz range Frequency relatively free from interference (unlike b) 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 Networks16 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 Networks17 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 g – long distance (MAN) Joink Fixed wireless – 2-10 mile range at DSL like speeds

Chapter 7 - Wireless Networks18 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 Networks19 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 Networks20 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 – i Disable DHCP and preset IP addresses on certain machines – smart and easy. Adjust router location to reduce outside footprint

Chapter 7 - Wireless Networks i – 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)