Data Communications and Networking Free-Samples for Students

Questions: 1.Discuss the advantages and disadvantages of star, bus, and mesh Physical topologies. Provide real examples of each type. 2.Explain encapsulation and decapsulation in a five layer TCP/IP protocol suite. How does multiplexing and de-multiplexing differ from encapsulation and decapsulation? 3.Calculate the approximate bit rate and signal level(s) for a 6.8 MHz bandwidth system with a signal to noise ratio of 132. 4.Explain why the OSI model is better than the TCP/IP model. Why hasn't it taken over from the TCP/IP model? Discuss the advantages and disadvantages of both models. Answers: 1.A network consists of nodes and communication channels connecting the nodes. The physical topology of a network is determined by the structure of the physical communication channels connecting the nodes together. Physical communication channels can be wired or wireless. The advantages and disadvantages of star, bus, and mesh physical topologies have been summarized in the following table (Forouzan, 2012). Advantages Disadvantages Example Star There is a central control over the network. Simple and easy to maintain. If any node malfunctions, it is easy to disconnect the node and troubleshoot without affecting the rest of the network. Performance depends on the number of nodes connected to the central hub. The nodes may have to wait for some time before communicating with another node. The network may go down if the central hub crashes. The switches/ hubs connected in a LAN network. Bus Simple and easy to implement. Low-cost solution. If any node malfunctions, it is easy to disconnect the node and troubleshoot without affecting the rest of the network. Performance depends on the number of nodes connected to the backbone channel. At a time, only two nodes can exchange data. The network may do down if the backbone channel goes down. The average waiting time for the nodes to communicate with one another is high. The computers or end user devices connected to the LAN network. Mesh Robust and offer high performance. Each two node has their own dedicated communication channel. The waiting time for nodes to communicate is very low. Complex and hard to maintain. Costly solution. There is no central control, the structure is highly distributed. A personal area network using Bluetooth or wireless channel having more than two devices. 2.There are five layers in the TCP/IP protocol suite as shown below. When an end user sends a message, then it starts from the application layer on the site A. the message goes down below the protocol stack. At each layer, control information is added to the message coming from the last layer. Then the message and the control information are encapsulated and forwarded to the next layer. When the final encapsulated message is received at the site B, it starts from the physical layer and goes upward in the TCP/IP protocol stack. At each layer, it is de-capsulated, the message and control information are separated and only the message is forwarded to the next layer. In this way, the original message reaches to the end user at the site B. Source: (TechnologyUK, 2017) Encapsulation and decapsulation are different than multiplexing and de-multiplexing. Encapsulation and decapsulation are applicable to the structure of a message passing through the TCP/IP protocol stack. On the other hand, multiplexing and de-multiplexing are applicable for the physical channel that carries data from sender to receiver. When there are multiple senders trying to send their data to multiple users through the same channel, then the bandwidth of the channel is distributed among all sender and data is multiplexed to fit into the packet size allowable for the channel. At the receiving end, the packet is de-multiplexed and the chunks of data go to the intended receivers. There are different types of multiplexing schemes depending on the attributes of the communication channel, for example, TDM or Time Division Multiplexing, FDM or Frequency Division Multiplexing and so on (Forouzan, 2012). 3.Following information have been provided in the question. The SNR or S/N = 132. The bandwidth = B = 6.8 MHz. The assumptions are, C = channel capacity M = Maximum number of signal levels. By combining the Shannon-Hartley and Nyquist formulas, Now, putting the value of M, 4.OSI stands for Open Systems Interconnection model. It is a standard for a network connecting nodes and allowing data transmission. On the other hand, TCP/IP is not any standard, it is a protocol suite. So, OSI and TCP/IP models are fundamentally different. OSI is better than TCP/IP model as its applicable for any network. It gives a modular abstraction for the developers so they can implement the functionalities of each layer separately and connect those together. Each layer is loosely coupled with the adjacent layer (Forouzan, 2012). So, the changes on one layer do not affect the rest of the part. Compared to that, the TCP/IP model shows how different protocols can be used for different purposed for an IP-based network like the Internet. It is not applicable for all types of networks. Hence, the scope of TCP/IP model is limited compared to OSI. On the contrary, OSI model cannot replace the TCP/IP model as OSI does not focus on the protocols of a communication network. It focused o n the functions of a network. Basically, OSI and TCP/IP models are complimentary to one another. The advantages and disadvantages of the models Advantages Disadvantages OSI It is an international standard for any communication network. It gives an abstraction and breaks down the complexities of the implementation part of a network. It does not give any information about the actual implementation part. It does not give any information about the protocols and technologies to be used at each layer. TCP/IP It gives information about the protocols for each layer of an IP-based network. It has simplified the implementation part. It has limited scope for IP-based networks only. 5.Following information have been given in the question, There are 10 routers. The propagation delay of each router is 3.5 microseconds. The queuing delay of each router is 1.8 microseconds. The bandwidth is 8Mbps. The length of the communication link is 1900km The speed of light is, meters/second The frame size is 5 million bits or . The calculation is, Total delay = Propagation delay + Transmission delay + Queuing Delay + Processing Delay. = + + + = + + + = () + + (+ seconds = 0.633693 Seconds Hence, the dominant components are propagation delay and transmission delay. The processing delay and queuing delay are negligible 6.POP3 or the Post Office Protocol version 3 is used as a mailbox and works on the client-server model. It allows a client to access mailbox hosted on a server. The client can retrieve emails from a server. The can be implemented by following the RFC 1939. The commands and responses between a client and server for POP3, are defined in the RFC 1939 documentation. However, a POP3 session can be in any of the states, closed, authorization, transition or update. A state of a POP3 session helps to understand the current context of the session. When a request from a client is submitted, the session goes into the authorization state. Once authorized, it goes to transaction or update state. When the transaction is completed, it goes to the closed state (Microsoft MSDN, 2017). During the authorization, a client can force it to close by using the QUIT command. References Forouzan, B. A. (2012). Data Communications and Networking: McGraw-Hill Education. Microsoft MSDN. (2017). How POP3 Service Works. Retrieved from https://technet.microsoft.com/en-us/library/cc737236(v=ws.10).aspx#w2k3tr_pop3_how_cjzh TechnologyUK. (2017). The TCP/IP Protocol Stack. Retrieved from https://www.technologyuk.net/internet/internet-technology/tcp-ip-stack.shtml