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1. Networks (25 Marks) (a) Briefly explain the operations of the CSMA/CA protocol and explain why this protocol is needed for a wireless LAN access. [3 Marks] (b) Describe each of the overhead factors in an Ethernet and a in a token ring Network and briefly explain how these factors affects the performance of a network. [4 Marks] (c) The Figure below shows a bridge that connects two LAN segments, each containing three computers. The table lists a sequence of events. Each event involves one of these computers transmitting a packet to another. This table also contains two columns to summarise the knowledge that the bridge has accumulated up to that point about which computers are on which segments. Assuming that the packets are transmitted in the order they appear in the table, write down a completed version of this table. [6 Marks] LAN segment 1 LAN segment 2 bridge computer A computer B computer C computer D computer E computer F Knowledge of bridge Knowledge of bridge about which computer is about which computer on segment 1 is on segment 2 Event (transmission of a packet) B sends packet to A D sends packet to F E broadcasts Csends packet to D A broadcasts F sends packet to B (d) You need to connect two buildings across a public road, and it is not feasible to use a direct cable connection. When would you use the following links? (i) Leased line link (ii) Satellite link [2 marks] (e) The graph in the Figure below summarises the connection between six packet switches that form the backbone of a wide area network, including the communication distances between them. 7 S1 S2 1 S3 4 7 1 3 5 S4 2 S5 1 S6 (i) Write down the route of the shortest path between switch S3 and switch S1. Write down the total distance travelled along this path. [1.5 Marks] (ii) Write down the next hop routing table for Switch 2. [2.5 Marks] (f) One function of a routing protocol is to determine the "best" path between sending and receiving nodes. List and briefly explain any two criteria used to consider a "best" path? [2 marks] (g) With reference to an Ethernet frame, explain how a host can support multiple a network protocols via a single attachment to the physical transmission medium. [2 marks] (h) Describe two ways how the capacity of a LAN can be increased to accommodate heavier user data traffic. [2 marks]