CS1: Wireless Communication and Mobile Programming Wireless Data Networks: Wireless LAN Dr. Khaled Mahmud Laurentian University International Global Experience Program Summer 2016

Agenda ISM Band IEEE 802.11 family WLAN devices Network structure Carrier Sensing (c) Khaled Mahmud

Reference Chapter 10 [TEL] Web references http://en.wikipedia.org/wiki/Wlan http://en.wikipedia.org/wiki/IEEE_802.11 (c) Khaled Mahmud

Unregulated Frequency Bands Unlicensed Frequency Frequency Range Total Bandwidth Common Use Industrial, Scientific and Medical (ISM) 902-928 MHz 2.4-2.4835 GHz 5.725-5,85 MHz 234.5 MHz Cordless Telephone, WLANs , Wireless Public Branch Exchanges Unlicensed Personal Communications Systems 1910-1930 MHz 2390-2400 MHz 30 MHz WLANs , Wireless Public Branch Exchanges Unlicensed National Information Infrastructure (U-NII) 5.15-5.25 GHz 5.25- 5.35 GHz 5.725-5.825 GHz 300 MHz WLANs , Wireless Public Branch Exchanges, Campus Applications, long outdoor links Millimtere Wave 59-64 GHz 5 GHz Home Networking Applications (c) Khaled Mahmud

Potential Interferers in ISM Band SN Band Uses 1 2.4 GHz IEEE 802.11 b/ g /n Microwave Oven Bluetooth, Zigbee Cordless Phone Remote Control Cars Car Alarms Wireless Keyboard, mouse AND anything you develop in this band 2 5.8 GHz HyperLAN (dead!) IEEE802.11a (c) Khaled Mahmud

IEEE 802.11 Standards ver Rel date Freq. BW Gross Data rate (per stream) Modulation rindoor routdoor Year (GHz) MHz (Mbps) (m) – 1997 2.4 20 2 DSSS ~20 ~100 a 1999 5 54 OFDM ~35 ~120 b 11 ~38 ~140 g 2003 DSSS, OFDM n 2009 2.4, 5 20, 40 72, 150 ~70 ~250 ac 2012 20, 40, 80, 160 87, 200, 433, 866 (c) Khaled Mahmud

Feature Summary: IEEE 802.11 Compatibility Value/Description Frequency 2.4 GHz (2.4 – 2.4835 GHz) Bandwidth 20 MHz No of channels 14 channels (some channels are not available in some countries) Carrier spacing 5 MHz Data rate 1, 2 Mbps; Dynamic Rate Shifting (DRS) Range Indoor: 20 m; Outdoor: 100 m Modulation DBPSK: 1 Mbps; DQPSK: 2 Mbps Coding/Spreading Barker code; DSSS, FHSS Power rating (EIRP) 100 mW (20 dBm) in Europe; 4 W (36 dBm) in US; 10mW/MHz in Japan Security Weak, WEP Compatibility Forward compatible with .11b/g Interference All 2.4 GHz devices (c) Khaled Mahmud

Feature Summary: IEEE 802.11b Value/Description Frequency 2.4 GHz (2.4 – 2.4835 GHz) Bandwidth 20 MHz No of channels 14 channels (some channels are not available in some countries) Carrier spacing 5 MHz Data rate 1, 2, 5.5, 11 Mbps (DRS) Range Indoor: 40 m; Outdoor: 150 m Modulation DBPSK: 1 Mbps; DQPSK: 2 Mbps; DQPSK (CCK): 5.5 and 11 Mbps Coding/Spreading Barker code/CCK; DSSS Power rating (EIRP) 100 mW (20 dBm) in Europe; 4 W (36 dBm) in US; 10mW/MHz in Japan Security WEP, WPA, WPA2 Compatibility compatible with .11 and .11g Interference All 2.4 GHz devices (c) Khaled Mahmud

Feature Summary: IEEE 802.11g Value/Description Frequency 2.4 GHz (2.4 – 2.4835 GHz) Bandwidth 20 MHz No of channels 14 channels (some channels are not available in some countries) Carrier spacing 5 MHz Data rate 1, 2, 5.5, 11, 6, 9, 12, 18, 24, 36, 48, and 54 Mbit/s, Range Indoor: 40 m; Outdoor: 140 m Modulation DBPSK: 1 Mbps; DQPSK: 2 Mbps; DQPSK (CCK): 5.5 and 11 Mbps; OFDM: 6, 9, 12, 18, 24, 36, 48, 54 Mbps Coding/Spreading Barker code/CCK; DSSS, OFDM Power rating (EIRP) 100 mW (20 dBm) in Europe; 4 W (36 dBm) in US; 10mW/MHz in Japan Security WEP, WPA, WPA2 Compatibility Backward compatible with .11b Interference All 2.4 GHz devices (c) Khaled Mahmud

Basic WLAN Components Minimal hardware needed for a WLAN WLAN Client (devices with WLAN interface card) Access point (AP) Wired LAN (switch/router) (c) Khaled Mahmud

WLAN Devices WLAN NIC Access Point PCMCIA/Compact Flash USB Single-radio (e.g. IEEE802.11b only) Multi-radio (e.g. IEEE 802.11a and b) (c) Khaled Mahmud

Advanced Devices Wireless Access Controllers Bridging Access Point Point to Point Bridge Multi-point Bridge Wireless Routers WLAN Antenna (c) Khaled Mahmud

Access point (AP) Provides wireless LAN devices with a point of access into a wired network AP parts Radio transceiver Antenna RJ-45 wired network interface port AP functions Wireless communications base station Bridge between the wireless and wired networks (c) Khaled Mahmud

Access Points (cont…) The range of an AP is approximately 100-150 meters An AP can generally support over 100 users Dynamic rate selection AP will automatically select the highest possible data rate for transmission Depending on the strength and quality of the signal (c) Khaled Mahmud

Basic WLAN Network Components Network Structure WLAN Modes Stations (STA): Wireless client devices and AP AP is a special type of STA Network Structure Basic Service Set (BSS): Simplest structure Extended Service Set (ESS): Multiple BSS combined Distribution System (DS): Wired network WLAN Modes Ad hoc mode (IBSS) Infrastructure mode (BSS or ESS) (c) Khaled Mahmud

Ad Hoc Mode (IBSS) Also known as peer-to-peer mode Formal name: Independent Basic Service Set (IBSS) mode No backbone network Wireless clients communicate directly among themselves without using an AP Quick and easy setup of a wireless network Drawback is that wireless clients can only communicate among themselves (c) Khaled Mahmud

STA D is not part of the ad hoc network Ad Hoc Mode STA A, B and C formed an ad hoc network STA C STA A STA D is not part of the ad hoc network STA D STA B (c) Khaled Mahmud

Infrastructure Mode Basic Service Set (BSS) Consists of wireless clients and an AP Clients communicates only through the AP AP is usually connected to the wired network Identified by SSID (c) Khaled Mahmud

Basic Service Set (BSS) (c) Khaled Mahmud

Anatomy of Wireless Router/Modem To phone line AP Switching Matrix Modem DHCP Server NAT Switch WAN Routing Engine LAN Firewall To LAN hosts Router To cable line (c) Khaled Mahmud

Extended Service Set (ESS) Two or more BSS wireless networks installed in same area Shares a common SSID Called ESSID Provides users with uninterrupted mobile access to the network All wireless clients and APs must be part of the same network For users to be able to roam freely (c) Khaled Mahmud

Extended Service Set (ESS) (c) Khaled Mahmud

Wireless LAN Standards and Operation Most WLANs are based on these same initial IEEE 802.11 standards (c) Khaled Mahmud

IEEE 802.11 Standards 802.11 standard Defines a local area network that provides cable-free data access for clients That are either mobile or in a fixed location At a rate of either 1 or 2 Mbps, using either diffused infrared (IR), or RF transmission Specifies that the features of a WLAN be transparent to the upper layers of the TCP/IP protocol stack Or the OSI protocol model (c) Khaled Mahmud

IEEE 802.11b Physical Layer Divided into two parts Physical Layer Convergence Procedure (PLCP) Physical Medium Dependent (PMD) (c) Khaled Mahmud

Physical Layer Convergence Procedure Based on direct sequence spread spectrum (DSSS) Must reformat the data received from the MAC layer into a frame that the PMD sublayer can transmit PLCP frame is made up of three parts: the preamble, the header, and the data Frame preamble and header are always transmitted at 1 Mbps Allows communication between slower and faster devices (c) Khaled Mahmud

IEEE 802.11b Channels 14 Channels defined 22 MHz each (30 dB below from the peak) Overlapping channels You cannot use neighbouring channel at the same locations (c) Khaled Mahmud

IEEE 802.11, b, g Channels (c) Khaled Mahmud

Media Access Control Layer 802.11b Data Link layer consists of two sublayers Logical Link Control (LLC) Media Access Control (MAC) Changes for 802.11b WLANs are confined to the MAC layer (c) Khaled Mahmud

MAC Access Modes Distributed Coordination Function (DCF) Contention-based services Basic functionality Point Coordination Function (PCF) Contention-free services possible Requires infrastructure mode Functionality provided by access point (point coordinator) (c) Khaled Mahmud

CSMA/CA for Wireless LAN Collision detection is not feasible due to WLAN radios are not full duplex Medium may be sensed clear near the transmitter, but the medium near the receiver may be busy Fading of the radio channel Loud transmitters To avoid collision, it employs InterFrame Spacing (IFS) Contention Window (CW), and Slotted random backoff counter Packet-by-packet acknowledge Automatic repeat request (ARQ) (c) Khaled Mahmud

Distributed Coordination Function Carrier sense multiple access with collision avoidance (CSMA/CA) Based on CSMA/CD CSMA/CD is designed to handle collisions CSMA/CA attempts to avoid collisions altogether CSMA/CA makes all devices wait a random amount of time CSMA/CA also reduces collisions by using explicit packet acknowledgment (ACK) (c) Khaled Mahmud

Additional Mechanisms to Reduce Collisions Virtual Carrier Sensing Request to Send/Clear to Send (RTS/CTS) protocol Network Allocation Vector (NAV) (c) Khaled Mahmud

Challenges of Carrier Sensing in Wireless Network Sensing the carrier by the transmitter is not very feasible because of Multipath Fading and Shadowing There is also the possibility of encountering the Hidden Node Problem (c) Khaled Mahmud

Transmission Mechanism A station willing to transmit senses the medium, if the medium is busy then it differs If the medium is free for a specified time (DIFS) then the station is allowed to transmit The receiving station will check the CRC of the received packet and send an acknowledgement packet (ACK) Receipt of ACK will indicate that no collision occurred If the sender does not receive ACK then it retransmit the packet until it gets the acknowledgement Or throws away the packet after a given number of retransmissions (c) Khaled Mahmud

CSMA/CA Procedure (c) Khaled Mahmud

Carrier Sensing Physical carrier sensing Virtual carrier sensing Depends on the modulation technique Listen before talk Virtual carrier sensing NAV (Network Allocation Vector) 802.11 frame carry a duration field Upon receipt of NAV station counts to zero before accessing the medium again (c) Khaled Mahmud

Contention Free Access Scheme: RTS/CTS A terminal ready to send data transmits a short request to send (RTS) packet identifying Source address Destination address Length of data to be transmitted The destination terminal responds with a clear to send (CTS) packet The source terminal can send the packet without contention After ACK from the destination, the channel is free for other users AP CTS MS RTS Packet Tx (c) Khaled Mahmud

InterFrame Spacing (IFS) Assign priorities to frames Types Short Interframe space (SIFS) Used to provide highest priority to transactions such as RTS/CTS frames PCF Interframe space (PIFS) Provision of contention-free services DCF Interframe space (DIFS) Minimum idle time for contention-based services Extended Interframe space (EIFS) Recover from transmission errors Interframe Space Duration microsec SIFS 10 PIFS 30 DIFS 50 (c) Khaled Mahmud

WLAN Applications Wireless networks are increasing in popularity Installing cabling is inconvenient and very expensive Wireless networks solve this problem With a wireless network Multiple users can share a single Internet connection Wireless residential gateway Device that combines a router, Ethernet switch, and wireless access point Also allows Internet and printer sharing (c) Khaled Mahmud

Cellular vs. WLAN WLAN Cellular Indoor Small area mobility Low mobility High bandwidth Low cost Good for hotspots of high-bandwidth activity Cellular Outdoor Wide area mobility Moderate to high mobility Moderate bandwidth High cost Good for everywhere except hotspots (c) Khaled Mahmud