Basic Wireless Network 1 Chapter 5

Basic Wireless Network 1 Wireless Networks Wireless Technology overview The IEEE WLAN Standards

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 ? 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: a, b, g, n, ac

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 … GHz) 5.8 GHz band (5.725 … 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 Wireless LAN 2.4 GHz5 GHz (2 Mbps) b (11 Mbps) g (22-54 Mbps) HiSWANa (54 Mbps) a (54 Mbps) HiperLAN2 (54 Mbps) HomeRF 2.0 (10 Mbps) Bluetooth (1 Mbps) HomeRF 1.0 (2 Mbps) e (QoS) i (Security) f (IAPP) h (TPC-DFS) Protocols under development

Basic Wireless Network 1 WLAN Standards Several WLAN standards, e.g.: –IEEE b 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 a, operating at 5 GHz and offering gross data rates of 54 Mbit/s –IEEE g offering up to 54 Mbit/s at 2.4 GHz. –IEEE n 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 IEEE IEEE IEEE Known as Bluetooth ZigBee WiFi WiMAX

Basic Wireless Network 1 Characteristics of selected wireless link standards Indoor 10-30m Outdoor m Mid-range outdoor 200m – 4 Km Long-range outdoor 5Km – 20 Km IS-95, CDMA, GSM 2G UMTS/WCDMA, CDMA2000 3G b a,g UMTS/WCDMA-HSPDA, CDMA2000-1xEVDO 3G cellular enhanced (WiMAX) a,g point-to-point n Data rate (Mbps) data

Basic Wireless Network 1 WLAN : b -Expand The first 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 : a -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 : g -Expand Supports data rates as high as 54 Mbps on the 2.4 GHz band Provides backward compatibility with b 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 : n -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 a/n is 150 Mbps, which means that an a/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 a/b/g equipment

Basic Wireless Network 1 WLAN : ac -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 ac is 433 Mbps per spatial stream, and the maximum number of spatial streams supported are eight. So the theoretical maximum throughput on an ac 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 a/b/g: Supports 54 Mbps on single 20 MHz stream 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 ac: Three stream 1.3 Gbps for 80 MHz 5 Ghz band

Basic Wireless Network 1 WLAN components

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 Access Points (AP)

Basic Wireless Network 1 Wireless Router

Basic Wireless Network 1 WIFI Certification(1) Wi-Fi certification is provided by the Wi-Fi Alliance ( 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 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 RF technologies, as well as early adoption of pending IEEE drafts, such as n, and the WPA and WPA2 security standards based on IEEE i

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 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 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 BSS

Basic Wireless Network 1 IEEE BSS

Basic Wireless Network 1 IEEE Extended Service Set

Basic Wireless Network 1 Divided into overlapping channels. For e.g. the – GHz band is divided into 13 channels each of width 22 MHz but spaced only 5 MHz apart, with channel 1 centred on GHz and 13 on 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 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 : CSMA/CA

Slot Time50 µsec SIFS28 µsec DIFSSIFS + (2 * Slot Time) Operating Frequency2.4 GHz Maximum Data Rate2 Mbps Basic Wireless Network 1 IEEE : CSMA/CA CSMA/CA Parameter

Basic Wireless Network 1 IEEE : CSMA/CA

Design Wireless Network 1