Presentation on theme: "1 Wireless LAN --which standard to follow? Avirup Dasgupta IT Department, Jadavpur University. Guide: Utpal K. Ray 29 th June,2004 www.geocities.com/asoke_dasgupta/termpaper2.doc."— Presentation transcript:
1 Wireless LAN --which standard to follow? Avirup Dasgupta IT Department, Jadavpur University. Guide: Utpal K. Ray 29 th June,2004 www.geocities.com/asoke_dasgupta/termpaper2.doc
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 802.11 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)!
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 802.11 standards and rates 802.11b (1999) (2.4 GHz band) = Wi-Fi 802.11a (1999) (5 GHz band) 802.11g (2003) (2.4 GHz) backward compatible to 802.11b IEEE 802.3 Ethernet (Carrier Sense) IEEE 802.4 Token Bus IEEE 802.5 Token Ring IEEE 802.11 Wireless IEEE 802.2 Logical Link Control (LLC) MAC PHY OSI Layer 2 (data link) OSI Layer 1 (physical)
9 802.3 vs 802.11 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? 802.11a802.11b802.11g 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? 802.11a802.11b802.11g Compatibility No Widely adopted. Will work in 802.11g networks Backward compatible..Will work with 802.11b. But not 802.11a 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 802.11a equipment Currently has the largest user base. 802.11b is currently used in most hot spots including airports, hotels, campuses, and public areas. Wide selection of 802.11b equipment. With speeds up to 5 times faster than 802.11b, Expect this standard to overtake 802.11b as the standard of choice.
12 INTERFERNCE Microwave oven Use unaffected channels Keep certain distance Use RF absorber near microwave oven Use 802.11a Bluetooth (probability of frequency collision for one 802.11 frame vary from 48% ~62%) Co-existing protocol IEEE 802.15 (not ready) Limit the usage of BT in 802.11 network 2.4 Ghz Cordless phones Use 5.8 Ghz phones
13 Conclusion No golden rule Laptops with built-in 802.11b cards In public places 802.11b 802.11g faster Natural replacement for 802.11b as backward compatible 802.11a 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?