Chapter 10: Wireless LAN & VLANs Abdullah Konak School of Information Sciences and Technology Penn State Berks Wireless Transmission for LAN Radio Frequency Transmission (RF) Infrared Transmission 2 1
Wireless LAN Physical Layer: Radio Frequency Transmission: ISM Bands Individuals are free to use the ISM (Industrial -Scientific-Medical) bands for devices under 1 watt of power without any permission from FCC. 3 Frequency Hopping Spread Spectrum 4 2
Direct Sequence Spread Spectrum 5 Application Areas Manufacturing Warehousing Construction / Emergency Medical and health care facilities Education 6 3
Current Wireless LAN Technology Wireless LAN Technology IEEE 802.11 IEEE 802.15 Bluetooth LAN or PAN IEEE 802.11 Infared LAN IEEE 802.11 Radio Frequency LAN IEEE 802.11a IEEE 802.11b IEEE 802.11g 7 IEEE 802.11 Architecture Basic Service Set (BSS) Ad Hoc Network Extended Service Set (ESS) 8 4
IEEE 802.11b Frequency: 2.4 GHz band 14 channels (Channels 1, 6, 11 and 14 do not overlap ) Channels 10 and 11 are universally accepted. Data rate: raw throughput of 11 Mbit/s On the average 4~5 Mbps Will scale back to 5.5, then 2, then 1, if signal strength becomes an issue. Range: Officially up to 100 meters range, thick walls absorb signals and decrease the range drastically With high-gain external antennas, the protocol can also be used in fixed point-to-point arrangements (typically 8- kilometers). 9 IEEE 802.11a Frequency: 5-GHz band 12 non-overlapping channels. Data rate: raw throughput of 54 Mbit/s On the average mid-20 Mbps The speed is reduced to 48, 36, 34, 18, 12, 9 then 6 Mbps if required. Range: cannot reach as far as 802.11b thick walls absorb signals and decrease the range drastically Important Notes: Not compatible with 802.11b devices (or g) Not widely implemented and globally accepted. 10 5
IEEE 802.11g Frequency: Same with IEEE 802.11b. Data rate: raw throughput of 54 Mbps about 24.7 Mbps on the average Range: Same with IEEE 802.11b. Important Notes: Fully backward compatible with 802.11b devices 11 IEEE 802.11: Infrared Infrared point-to-point LAN Infrared diffused LAN 12 6
IEEE 802.15 Bluetooth It is a wireless radio standard primarily designed for low power consumption, with a short range (in a room or house) and a low-cost transceiver microchip in each device. Runs at ISM band at 2.45 GHz. Possibility of Interference with 802.11b Data rates 1-20 Mbps (mostly max of 1Mbps) A small network (8-16 stations) It can be used to wirelessly connect peripherals like printers or keyboards to computers, or to have PDAs communicate with other nearby PDAs or computers. Wireless Personal Area Networks (PANs) 13 Common Wireless LAN Devices Access Points (AP): Access points connect multiple users on a wireless LAN to each other and to a wired network. better wireless security better control Wireless Bridges: connect two or more AP to each other or a wired network. Used to extend the range of a wireless network. 14 7
Ad hoc mode Structured with an AP Structured with an AP Connecting AP with Bridges 15 Wireless Security Wired Equivalent Privacy (WEP) : uses WEP keys to encrypt the data stream. Not ON by default Every device use the same key (not a good idea!) Keys can be figured out by freely-available software in a few hours. Wi-Fi Protected Access (WPA) created to patch the security of WEP by increasing the size of the keys, the number of keys in use Not supported by every device. 16 8
Collision/Broadcast Domain The term collision domain defines the set of devices for which their frames could collide. A broadcast domain is a set of NICs for which a broadcast frame sent by one NIC will be received by all other NICs in the broadcast domain. Hub? Bridge? Switches? Routers? 17 Identify collision and broadcast domains for each case? 18 9
Virtual LANs (VLAN) VLAN technology is to divide a LAN into logical segments. VLAN is a software implementation at programmable switches. VLANs create broadcast domains, increasing security and performance. Membership to a VLAN can base on Switch Port Numbers, MAC Addresses, or IP addresses 19 10