Discuss WIFI topology, MAC, and types of WIFI (IEEE 802.11B, IEEE 802.11A, IEEE 802.11G)
Wifi is the commercial name for a set of standards, developed by the IEEE standards group. A group of vendors selling 802.11 equipment trademarked the name WiFi to refer to 802.11.
Topology - The logical and physical topologies of WiFi are the same as those of shared ethernet. They are a physical star and logical bus. There is a central AP to which all computers direct their transmissions (star), but the radio frequencies are shared (bus) so that all computers must take turns transmitting.
MAC - Media access control in WiFi is Carrier Sense Multiple Access with Collison Avoidance (CSMA/CA), which is similar to contention based CSMA/CD approached used by traditional ethernet. With CSMA/CA, computers listen before they transmit and if no one else is transmitting, they proceed with transmission. Detecting collisions is more difficult in radio transmission, so WiFi attempts to avoid collisions to a greater extent. One method is: Distributed Coordination Function (DCF) - each frame is sent using stop and wait ARQ
IEEE 802.11B - this standard provides moderate speed wireless networking int he 2.4 GHz range. It is a legacy technology, and no new products are being developed, but some firms still use it. It provides three channels for indoor use in the US. Each channel provides a maximum data range of 11Mbps. Only when there is significant interference, or the signal begins to weaken because the user is moving so far from the WLAn does the data range change in attempt to improve singal quality. The advantage of this standard is the frequency range, as it suffers less attenuation and thus the signal has greater range.
IEEE 802.11A - This standard provides high speed wireless networking in the 5GHz range. It is a legacy technology, and no new products are being developed. It provides eight channels for indoor use int he US, and has fewer channels inother parts int he world. Each channel provides speeds of 54 MBps udner perfect conditions.
IEEE 802.11G - This standard provides high speed wireless networking in the 2.4 GHz range. It will soon be replaced by 802.11N, so it too will be a legacy technology. I tprovides three channels for indoor use in the US. This standard provides for more or fewer channels in other parts of the world. Each channel provides a maximum data range of 54Mbps in ideal conditions of 300 feet. It is also backward compatible.