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

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

3. Reference Chapter 10 [TEL] Web references
(c) Khaled Mahmud

4. Unregulated Frequency Bands
Unlicensed Frequency
Frequency Range
Total Bandwidth
Common Use
Industrial, Scientific and Medical (ISM)
MHz
GHz
,85 MHz
234.5 MHz
Cordless Telephone, WLANs , Wireless Public Branch Exchanges
Unlicensed Personal Communications Systems
MHz
MHz
30 MHz
WLANs , Wireless Public Branch Exchanges
Unlicensed National Information Infrastructure (U-NII)
GHz
GHz
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

5. Potential Interferers in ISM BandSN
Band
Uses 1
2.4 GHz
IEEE 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

6. 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

7. Feature Summary: IEEE 802.11 Compatibility
Value/Description
Frequency
2.4 GHz (2.4 – 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

8. Feature Summary: IEEE 802.11b
Value/Description
Frequency
2.4 GHz (2.4 – 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

9. Feature Summary: IEEE 802.11g
Value/Description
Frequency
2.4 GHz (2.4 – 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

10. 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

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

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

13. 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

14. Access Points (cont…)
The range of an AP is approximately 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

15. 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

16. 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

17. 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

18. 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

19. Basic Service Set (BSS)
(c) Khaled Mahmud

20. 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

21. 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

22. Extended Service Set (ESS)
(c) Khaled Mahmud

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

24. 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

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

26. 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

27. 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

28. IEEE , b, g Channels
(c) Khaled Mahmud

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

30. 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

31. 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

32. 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

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

34. 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

35. 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

36. CSMA/CA Procedure
(c) Khaled Mahmud

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

38. 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

39. 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

40. 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

41. 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