ICT210E Computer Communication

This question aims to explain WAN and routing, and their implementations. Implement different communication options. (a) Consider the transfer of a message in a packet-switching network as shown below from node X to node Y passing through three intermediate nodes, a, b, and c. Assume a datagram approach.The message consists of 66 octets of data.Each packet in the network has a 4-octet header that contains the control information. Consider the transmission of the message from X to Y in each of the following cases:

(i) The entire message is sent as a single packet.

(ii) The message is sent by dividing it into 6 packets.

(iii) The message is sent by dividing it into 22 packets. Determine the total time of transmission (in terms of octet time) of the message in each of the above cases. What conclusion can you draw from the above observation?

(b) Analyse routing techniques and least-cost paths for the packet-switching network.

(i) Apply Dijkstra�s routing algorithm to the network below to determine the least cost paths from node E to all other nodes. The number on each link indicates the least cost of the link. Use a table to show clearly the cost and path at each iteration of the algorithm.

This question aims to analyse packet-switching networks and LAN. (a) Consider a 100Base-T Ethernet LAN where stations A and B are attached to a storeand-forward switch 100 m away. The data rate of the LAN is 100 Mbps and the propagation speed is 2x108 m/s. Station A wants to send a file containing five thousand 8-bit characters to station B. The file is divided into frames for transmission. Each frame is 1000 bits including 80 bits overheads. Each frame is acknowledged with a 120-bit frame before the next is sent.

Analyse the above network description and answer the following:

(i) Calculate the data frame transmission time, acknowledgement frame transmission time and one-way propagation delay.�

(ii) What is the total elapsed time for transmitting one data frame and getting back one acknowledgement frame?�

(iii) What is the total elapsed time for transmitting the entire file?�

(iv) What is the effective throughput of the system?

(b) Review TWO (2) weaknesses of a layer-2 switch. How do you overcome these weaknesses?

(c) Consider a bus CSMA/CD network with a data rate of 100 Mbps. Suppose the maximum one-way propagation time is 15 ms, what is the minimum size of the frame?

This question aims to discuss/illustrate LANs and wireless LAN. (a) Wireless LAN defines a superframe structure. Outline the operation of the superframe structure. Why is it needed?�

(b) Illustrate the operation of a bridged LAN below: Consider a bridged network consisting of 8 transparent bridges and 5 Ethernet segments as shown in the Figure below. Apply the standard spanning tree algorithm (STA) to construct the spanning tree for the network. The costs associated with individual segments are indicated in the Figure. In your answer, state clearly the

(i) root bridge,

(ii) root ports,

(iii) designated bridges/ports

(iv) disabled bridges/ports. Draw the network topology for the final spanning tree.

This question aims to (a) outline IP and TCP protocols, and (b) Analyse and design networking application.

(a) Consider three LANs interconnected by router1 and router2 as shown in the Figure Q4(a) below. The IP addresses for all LANs and the Ethernet MAC addresses for all adapters are indicated. Assume routing tables and ARP tables are all available. Suppose host A sends a datagram to host F. Outline and determine the source and destination MAC addresses as well as the source and destination IP addresses as the frame is transmitted

(i) from host A to router1;

(ii) from router1 to router2;

(iii) from router2 to host F. (12 marks) Figure Q4(a)

(b) An organization is granted the block of Class B address 141.60.0.0. Suppose 7 bits subnetting is used, analyse and assign IP addresses by answering the following:

(i) What is the subnet mask? (ii) How many subnets can be formed?

(iii) How many hosts can be formed in each subnet?

(iv) What is the range of subnet addresses? Give first TWO (2) and last TWO (2) subnet addresses.

(v) What is the subnet address for the first subnet in the network?

(vi) What is the host address range for the first subnet?

Give first TWO (2) and last TWO (2) host addresses. Exclude all �0� and all �1� subnet addresses as well as host addresses.