The copperbelt university
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BBF221 FINAL CA - FT
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- [3 marks] An internet is a virtual network system because the communication system is an abstraction. Explain the meaning of this statement. [2 marks]
- . [5 marks] ANSWER
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Q While Q != {} u extract-min(Q) u = node with lowest cost S S plus {u} Within Q: for each node v adjacent to u “relax” the cost of v is it cheaper to go through u? QUESTION TWO Suppose the sender and receiver windows are of size N = 4 and suppose the sequence number space goes from 0 to 15. Show the position of the sender and receiver windows over this sequence number space at time t. [5 marks] Suppose a computer is moved from one department to another. Does the physical address need to change? Does the IP address need to change? Does it make a difference if the computer is a laptop? [3 marks] An internet is a virtual network system because the communication system is an abstraction. Explain the meaning of this statement. [2 marks] Suppose that it take 1 ms to send a packet, with a 10 ms one-way propagation delay between the sender and receiver. The sliding windows size is again N = 4. What is the channel/link utilization? [5 marks] What difference does it make to the network layer if the underlying data link layer provides a connection-oriented service versus a connectionless service? In your answer explain the difference between connection oriented and connectionless oriented services. [5 marks] ANSWER 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 window The physical address does not change (1). It is globally unique to the computer's NIC card. The IP address may need to be changed (1) to reflect a new subnetwork id and host id. The situation is the same for laptops.(1) Virtual network abstraction that is the basic principle of the Internet model. All physical implementation details (ideally even though this is not quite true) are hidden below the IP layer. The IP layer provides an unreliable, connectionless delivery system The utilization is 4/(1+20) or 0.19. If the data link layer provides a connection-oriented service to the network layer, then the network layer must precede all transfer of information with a connection setup procedure (2). If the connection-oriented service includes assurances that frames of information are transferred correctly and in sequence by the data link layer, the network layer can then assume that the packets it sends to its neighbor traverse an error-free pipe. On the other hand, if the data link layer is connectionless, then each frame is sent independently through the data link, probably in unconfirmed manner (without acknowledgments or retransmissions). In this case the network layer cannot make assumptions about the sequencing or correctness of the packets it exchanges with its neighbors (2). The Ethernet local area network provides an example of connectionless transfer of data link frames. The transfer of frames using "Type 2" service in Logical Link Control (discussed in Chapter 6) provides a connection-oriented data link control example. Download 290.5 Kb. Share with your friends:
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