MCS-042 DATA COMMUNICATION AND COMPUTER NETWORKDS

                                      M. C. A. (Revised) 

                         Term-End Examination June, 2019 

                MCS-042 : DATA COMMUNICATION AND COMPUTER NETWORKS

1. (a) How does 802.11 deal with the problem of a noisy channel ? Explain with an example.

Ans.  The wireless LAN is based on a cellular architecture where the system is subdivided into cells as shown in Figure1. Each cell (called basic service set or BSS, in the 802.11) is controlled by a base station (called access point or AP). Wireless LAN may be formed by a single cell, with a single access point (it can also work within an AP), most stations will be formed by several cells, where the APs are connected through some kind of backbone (called distribution system or DS). This backbone may be the Ethernet and in some cases, it can be the wireless system. The DS appears to upperlevel protocols (for example, IP) as a single 802 network, in much the same way as a bridge in wire 802.3. The Ethernet network appears as a single 802 network to upperlayer protocols.

Stations can also group themselves together to form an ad hoc network: a network with no central control and with no connections to the “outside world.” Here, the network is formed “on the fly,” simply because, there happens to be mobile devices that have found themselves in proximity to each other, that have a need to communicate, and that find no preexisting network infrastructure. An ad hoc network might be formed when people with laptops meet together (for example, in a conference room, a train, or a car) and want to exchange data in the absence of a centralised AP. There has been tremendous interest in ad hoc networking, as communications between devices continue to proliferate.