Basic Wireless Network 1 Wireless ? A wireless LAN or WLAN is a wireless local area network that uses radio waves as its carrier. The last link with the users is wireless, to give a network connection to all users in a building or campus. The backbone network usually uses cables
Basic Wireless Network 1 Why Wireless LANs (WLANs) Mobility (portability) and Flexibility Places where there is no cabling infrastructure / Hard to wire areas Reduced cost of wireless systems Improved flexibility of wireless systems Cost – Relatively low cost of deployment – Continual drop in price for WLAN equipment
Basic Wireless Network 1 Common Topologies The wireless LAN connects to a wired LAN There is a need of an access point that bridges wireless LAN traffic into the wired LAN. The access point (AP) can also act as a repeater for wireless nodes, effectively doubling the maximum possible distance between nodes.
Basic Wireless Network 1 What is 802.11? A family of wireless LAN (WLAN) specifications developed by a working group at the Institute of Electrical and Electronic Engineers (IEEE) Defines standard for WLANs using the following four technologies Frequency Hopping Spread Spectrum (FHSS) Direct Sequence Spread Spectrum (DSSS) Infrared (IR) Orthogonal Frequency Division Multiplexing (OFDM) Versions: 802.11a, 802.11b, 802.11g, 802.11n, 802.11ac
Basic Wireless Network 1 ISM Frequency Bands ISM (Industrial, Scientific and Medical) frequency bands: 900 MHz band (902 … 928 MHz) 2.4 GHz band (2.4 … 2.4835 GHz) 5.8 GHz band (5.725 … 5.850 GHz) Anyone is allowed to use radio equipment for transmitting in these bands (provided specific transmission power limits are not exceeded) without obtaining a license.
Basic Wireless Network 1 WLAN Standards Several WLAN standards, e.g.: –IEEE 802.11b offering 11 Mbit/s at 2.4 GHz –The same radio spectrum is used by Bluetooth A short-range technology to set-up wireless personal area networks with gross data rates less than 1 Mbit/s –IEEE 802.11a, operating at 5 GHz and offering gross data rates of 54 Mbit/s –IEEE 802.11g offering up to 54 Mbit/s at 2.4 GHz. –IEEE 802.11n up and coming standard up to 300 Mbit/s (two spatial streams; 600 Mbit/s with 4 spatial streams) –…–…
Basic Wireless Network 1 IEEE 802 wireless network technology options Network definition Wireless personal area network (WPAN) Low-rate WPAN (LR-WPAN) Wireless local area network (WLAN) Wireless metroplitan area network (WMAN) IEEE standard IEEE 802.15.1 IEEE 802.15.4 IEEE 802.11 IEEE 802.16 Known as Bluetooth ZigBee WiFi WiMAX
Basic Wireless Network 1 WLAN : 802.11b -Expand The first 802.11 standard deployed. Supports 1, 2, 5.5 and 11 Mbps data rates in the 2.4 GHz ISM (Industrial-Scientific-Medical) band
Basic Wireless Network 1 WLAN : 802.11a -Expand Operates in the 5 GHz UNII (Unlicensed National Information Infrastructure) band Incompatible with devices operating in 2.4GHz (6,9,12,18,24,36,48,54 Mbps) Supports Data rates up to 54 Mbps (6,9,12,18,24,36,48,54 Mbps).
Basic Wireless Network 1 WLAN : 802.11g -Expand Supports data rates as high as 54 Mbps on the 2.4 GHz band Provides backward compatibility with 802.11b equipment (6,9,12,18,24,36,48,54 Mbps) Supports Data rates up to 54 Mbps (6,9,12,18,24,36,48,54 Mbps).
Basic Wireless Network 1 WLAN : 802.11n -Expand Supports data rates as high as 144 Mbps on the 2.4 GHz band (802.11g/n) and 300 Mbps on 5 GHz band (802.11a/n) for 2X2 stream The maximum bandwidth per spatial stream in 802.11a/n is 150 Mbps, which means that an 802.11a/n AP outfitted with three transmit and three receive antennas can deliver maximum theoretical throughput of 450 Mbps Supports up to 4 stream MIMO Provides backward compatibility with 802.11a/b/g equipment
Basic Wireless Network 1 WLAN : 802.11ac -Expand Supports data rates as high as 1.3 Gbps (also called gigabit wireless) Operates only in 5 GHz band Supports 80/160 MHz channel Supports up to 8 stream MIMO The maximum bandwidth in 802.11ac is 433 Mbps per spatial stream, and the maximum number of spatial streams supported are eight. So the theoretical maximum throughput on an 802.11ac network will eventually be several times that of Gigabit Ethernet. First-generation devices (wave 1), however, are limited to using either two or three transmit and receive antennas to deliver a theoretical throughput maximum of 866 Mbps or 1.3 Gbps
Basic Wireless Network 1 WLAN : MIMO 802.11 a/b/g: Supports 54 Mbps on single 20 MHz stream 802.11 n: Two stream 144 Mbps for 20MHz 2.4GHz band (802.11g/n) and 300 Mbps for 40 MHz 5GHz band (802.11a/n) or Three stream 450 Mbps for 40 MHz 5GHz band 802.11 ac: Three stream 1.3 Gbps for 80 MHz 5 Ghz band
Basic Wireless Network 1 Wireless Lan NIC hardware installed in computing device that enables it to communicate on a network.
Basic Wireless Network 1 Access Points (AP) Allows stations to associate with it Supports Distributed Coordination Function (DCF) and Point Coordination Function (PCF) Provides management features –Join/Associate with BSS –Time synchronisation (beaconing) –Power management all traffic flows through APs Supports roaming
Basic Wireless Network 1 WIFI Certification(1) Wi-Fi certification is provided by the Wi-Fi Alliance (http://www.wi-fi.org), a global, nonprofit, industry trade association devoted to promoting the growth and acceptance of WLANs. The Wi-Fi Alliance is an association of vendors whose objective is to improve the interoperability of products that are based on the 802.11 standard by certifying vendors for conformance to industry norms and adherence to standards.
Basic Wireless Network 1 WIFI Certification(2) Certification includes all three IEEE 802.11 RF technologies, as well as early adoption of pending IEEE drafts, such as 802.11n, and the WPA and WPA2 security standards based on IEEE 802.11i
Basic Wireless Network 1 WIFI Certification (3) The roles of these three organizations can be summarized as follows: ITU-R regulates allocation of RF bands. IEEE specifies how RF is modulated to carry information. Wi-Fi ensures that vendors make devices that are interoperable.
Basic Wireless Network 1 IEEE 802.11 terminology Basic Service Set (BSS) –group of stations using same radio frequency Access Point (AP) –station integrated into the wireless LAN and the distribution system Station (STA) –terminal with access mechanisms to wireless medium and radio contact to access point Distribution System (DS) –interconnection network to form one logical network Extended Service Set (EES) – based on several BSS System Architecture of an infrastructure network
Basic Wireless Network 1 IEEE 802.11 allows the building of ad hoc networks between stations, thus forming one or more BSSs. –In this case, a BSS comprises a group of stations using the same radio frequency. –Several BSSs can either be formed via the distance between the BSSs or by using different carrier frequencies. IEEE 802.11 BSS
Basic Wireless Network 1 IEEE 802.11 Extended Service Set
Basic Wireless Network 1 Divided into overlapping channels. For e.g. the 2.4000–2.4835 GHz band is divided into 13 channels each of width 22 MHz but spaced only 5 MHz apart, with channel 1 centred on 2.412 GHz and 13 on 2.472 GHz Availability of channels is regulated by country (e.g. Japan adds a 14th channel 12 MHz above channel 13). 3 channels are non overlapping Given the separation between channels 1, 6, and 11, the signal on any channel should be sufficiently attenuated to minimally interfere with a transmitter on any other channel.
Basic Wireless Network 1 802.11 MAC (Multiple Access Control) LLC MAC PHY : Multiple access control: Different nodes must gain access to the shared multiple (for instance a wireless channel) otherwise there will be collisions. FDMA TDMA CDMA CSMA Assigning channels in frequency domain Assigning time slots in time domain Assigning code sequences in code domain Assigning transmission opportunities in time domain on a statistical basis Access methods:
Basic Wireless Network 1 Station must be able to send and receive data at the same time. Collision may not be detected because of the hidden terminal problem. Distance between stations in wireless LANs can be great. Signal fading could prevent a station at one end from hearing a collision at other end. Wireless LAN cannot implement CSMA/CD for 3 reasons
Basic Wireless Network 1 Before sending a frame, source senses the medium by checking the energy level at the carrier frequency. Backoff until the channel is idle. After the channel is found idle, the station waits for a period of time called the Distributed interframe space (DIFS); then the station sends a control frame called request to send (RTS). After receiving RTS, the destination waits for a period called Short interframe space (SIFS), the destination station sends a control frame, called Clear to Send (CTS) to source. This control frame indicates that the destination station is ready to receive data. Source sends data after waiting for SIFS Destination sends ACK after waiting for SIFS. IEEE 802.11: CSMA/CA