1 Wireless LAN --which standard to follow? Avirup Dasgupta IT Department, Jadavpur University. Guide: Utpal K. Ray 29 th June,2004

2 What is a Wireless LAN? A local-area network in which digital devices communicate through a wireless medium such as radio or infrared instead of copper or fiber-optic cable. once installed a wireless LAN(WLAN) is transparent to the user and performs exactly like a wired LAN IEEE standard is followed in WLAN What is a Hotspot? Area within which one can access the Internet on a wireless enabled laptop computer (using wlan). It can be an airport lounge(Kolkata), a coffee shop(Barista), a college campus(KIIT), a conference room, a hotel lobby or even a poolside area(Taj Bengal)!

3 Wireless LAN in Campus

4 Growth of Wireless Industry

5 Typical WLAN Device used to bridge the wireless-wired boundary, or to increase distance as a wireless packet repeater.

6 WLAN benefits over LAN Mobility: Access to information wherever you are Flexibility: Components can be easily removed Installation on difficult-to-wire areas Reduced installation time Cost: Long-term cost savings Regulation: : WLAN is not regulated,anyone can deploy APs

7 Connection Mode Adhoc Mode A temporary one made up of stations in mutual range. Infrastructure Mode One with one or more Access Points.

8 WLAN standards IEEE standards and rates b (1999) (2.4 GHz band) = Wi-Fi a (1999) (5 GHz band) g (2003) (2.4 GHz) backward compatible to b IEEE Ethernet (Carrier Sense) IEEE Token Bus IEEE Token Ring IEEE Wireless IEEE Logical Link Control (LLC) MAC PHY OSI Layer 2 (data link) OSI Layer 1 (physical)

vs Media Access Control (MAC) layer vary CSMA/CD vs CSMA/CA Medium is free for all A node senses the free medium and occupies it as long as data packet requires it CSMA/CD (Carrier Sense Multiple Access / Collision Detect) Collision detection possible because can send/receive simultaneously CSMA/CA (Carrier Sense Multiple Access / Collision Avoidance) Collision detection not possible because of near/far problem for radios. The stations have to assume that a collision always occurs Steps: sense the air, wait, send, wait for ACK, retransmit if needed Overhead of MAC layer reduces throughput by 40-50%

10 Where do they differ? a802.11b802.11g Average/Theoretic al throughput 27/54 Mbps5/11 Mbps20/54 Mbps Modulation Technique OFDMDSSS OFDM Range 75 feet 150 feet Interference No Bluetooth, Microwave oven Cordless Phone Bluetooth, Microwave oven Cordless Phone Security GoodInsecure WEP #Channels/Non- overlapping 12/811/3 Cost (AP+Wireless cards) Very high (20k+5k) Cheapest (10k+4k) Prices falling (12k+8k)

11 Where do they differ? a802.11b802.11g Compatibility No Widely adopted. Will work in g networks Backward compatible..Will work with b. But not a Obstruction Not muchVery much (Wall,door) Very much (Wall.Door) Simultaneous Users Increase Performance ok Performance degrades drastically Performance degrades Popularity User base still relatively small. Limited selection on a equipment Currently has the largest user base b is currently used in most hot spots including airports, hotels, campuses, and public areas. Wide selection of b equipment. With speeds up to 5 times faster than b, Expect this standard to overtake b as the standard of choice.

12 INTERFERNCE Microwave oven Use unaffected channels Keep certain distance Use RF absorber near microwave oven Use a Bluetooth (probability of frequency collision for one frame vary from 48% ~62%) Co-existing protocol IEEE (not ready) Limit the usage of BT in network 2.4 Ghz Cordless phones Use 5.8 Ghz phones

13 Conclusion No golden rule Laptops with built-in b cards In public places b g faster Natural replacement for b as backward compatible a more secure,fastest.least interference Commercially device not manufactured. Not work in PDA. SOHO segment ideal The wireless network engineer should choose a WLAN technology based on requirements of the network.

14 Future Research Scope Co-existence of Bluetooth & WLAN Modified Exponential Back-off Algorithm SecurityWPA algorithm?

15 Any Questions?