1. Wifi: 802.11g Protocol By Truc Truong CS158B Prof. Mark Stamp

2. Introduction  The wireless market has been enjoying a steady growth.  Not connected to wires, people are able to access data and information anywhere they go.  The increase in mobility has changed the way of networking.  Also, open up new markets for the technology industry.

3. How companies benefits from wireless?  Doctors and Nurses traditionally access patients records from charts next to the patient’s bed. Imagine if patients’ charts are now accessible from a palm-pilot or tablet PC. With wireless access to network data, hospitals now are beginning to change their network architecture.

4. How companies benefits from wireless? Cont.  Imagine a business meeting taking place in 10mins for 20 people that need access to network resources. Not so easy laying out the wiring needed, if the room isn’t pre-wired for such an event. Not to mention, network troubleshooting if there’s problems with connectivity. With wireless, a network administrator simply put up an Access Point (AP) configure it and everyone at the meeting will be able to gain access.

5. History of Wireless  Network has always been predominately wired networks (ethernet 802.3). The diversity created a cheap and competitive market for 802.3 vendors.  These companies strived very hard to provide consumers with latest networking technology; this included wireless technology.  Early wireless network operated around 900Mhz band and had a bandwidth of 1-2Mbps. These early products where expensive.  Wireless became popular in retail, warehouse companies, and home users.

6. History of Wireless  In 1991, companies like Aironet and other wireless companies pushed for standards to wireless technologies.  Around 1992, companies began producing 2.4Ghz (unlicensed) frequence band wireless products. This created cheaper wireless products for consumers.  In 1997, IEEE released the 802.11 standards for wireless.

7. Wireless Market

8. The 802.11 Protocol – Physical Layer  802.11 protocol places parameters on both the physical (PHY) and access control (MAC) layers of the network. The physical layer handles the transmission of data between all nodes by using either direct sequence spread spectrum (DSSS), frequency-hopping spread spectrum (FHSS), or infrared (IR).

9. The 802.11 Protocol – Operation range  802.11 protocol operates in the 2.4Ghz – 5Ghz frequency band, which are unlicensed for industrial, scientific and medical field.  Infrared Red protocol operates in the 300- 428,000 Ghz range.  IR provides better security to eavesdropping, but is a line-of-sight service. While, 2Ghz and 5Ghz 802.11 uses radio wave which can penetrate solid objects such as: trees, and buildings.

10. The 802.11 Protocol – Protocol Output

11. The 802.11 Protocol – Mac layer  The access control (MAC) layer is responsible for maintaining order in the use of a shared medium. The MAC layer uses CSMA/CA protocol to specify a carrier for sense multiple access with collision avoidance.  CSMA/CA protocol works when a node receives a packet for transmission, it listens to the network to check no other nodes are transmitting. If the network is clear, it then transmits the packets. If the network is busy, the protocol then chooses a random “backoff factor” which is the amount of time the node must wait until it can transmit the packets. During the time the network is clear the node decrements the “backoff counter”. If the network is busy it does not decrement the “backoff counter”. Once the “backoff counter” reaches zero the node then transmit the packets. The probability that two nodes will choose the same “backoff counter” is very small, so the collisions between packets are rare.  The reason that IEEE had to create a new protocol (CSMA/CA) to listen to the network, because the transmitting wireless nodes can’t hear other nodes on the network when it’s transmitting, since its signal will drown out any other arriving at the node.

12. The 802.11 Protocol – sending data  When a packet is ready for transmission, the node sends out a short ready-to-send (RTS) packet containing information on the length of the transmitting packet.  The receiving node gets the RTS, then responds with a short clear-to-send (CTS) packet. After the connection has been established the two nodes then begin the communication.  Once the transmission is finished successfully the transmitting node then send a cyclic redundancy check (CRC), and the receiving node transmits an acknowledgement (ACK) packet.

13. The 802.11g Protocol  In July 1999, IEEE pushed for another protocol of 802.11 to extend the 2.4Ghz frequency to increase data rate beyond 20Mbps.  802.11g was approved in June 2003 and was backward compatible with 802.11b

14. The 802.11 comparison

15. The 802.11g Protocol  To achieve the desired data rate, 802.11g uses Orthogonal Frequency Division Multiplexing (OFDM) and Complementary Code Keying (CCK) modulation.  However, 802.11g was conceived by using physic of wave form properties.  There is an inverse relationship between wavelength and range. A signal transmitted at a lower frequency range of spectrum will carry further than a signal transmitted in a higher frequency range.  802.11b operating at 5Ghz provide high data rate, but had low range.  So, it is important that 802.11g should operate in 2.4Ghz frequency band.

17. The 802.11g Protocol  The new protocol focused on transmit power and receiver sensitivity.  High power coming from the radio’s transmitter leads to desensitization, a phenomenon known as Error Vector Magnitude (EVM). This phenomenon leads to a counterproductive stage, whereby increasing transmit power means the range of the device decreases.  802.11g achieved the 802.11b data rates by using lower transmit power under OFDM standard. By the performance of 802.11g one can see that it is a superset of 802.11b. So, it’s vital that 802.11g devices be able to operate with 802.11g devices. In order, to do this each 802.11 client performs a procedure to select the best transmission rate.

18. 802.11 Data Rate and Range

19. Conclusion  802.11g is an exciting technology that offers the performance of 802.11a, and the range of 802.11b.  It also provides investment solution to companies already using 802.11b AP devices, whose looking to upgrade to 802.11g devices in the future.  802.11g technology will be the standard for next generation of wireless networking.  The benefits of 802.11g are so great that is compelling to for customers to upgrade. Some of these benefits are: providing an increase in LAN speed, backward compatible with 802.11b products, and offer higher range and coverage for networks.

20. Reference  Broadcom, The New Mainstream Wireless LAN standard, Irvine, CA, 2003.  Cisco Systems, Capacity, Coverage, and Deployment Considerations, San Jose, CA, 2003.  Lough, Daniel L. and et al, A Short Tutorial on Wireless LANs and IEEE 802.11, Virginia Polytechnic, Blacksburg, Virginia, 1997.  http://net- services.ufl.edu/provided_services/wireless/back ground.html