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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. 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. 5.What is the total delay (latency) for a frame of size 5 million bits that is being sent on a link with 10 routers each having a queuing time of 3.5 s and a processing time of 1.8 s. 6.According to RFC1939, a POP3 session is one of the following states: closed, authorization, transaction or update. Draw a diagram and explain to show these four states and how POP3 moves between them. Answers: 1.Advantages of Star Topology 1) the performance of the star topology is better than many of the counterparts topologies using the intelligent switches in place of hubs to increase the performance of the network. The signal directly reaches the require destination from the single station to the final destination. The capacity of the channel and network is dependent upon the central device node that is installed which is much higher in the case of Switch than the hubs. 2) If adding any new device to the network is needed, it is quite easy and it doesnt even affect rest of the network, in the similar manner the any device can be removed from the network without affecting the remaining network. 3) the entire network management is done centrally with entire network traffic is passing through the single station device hence managing the bandwidth aspects, firewall etc. all needed to be done at the central station only. 4) Failure of any node doesnt affect the network and finding faults in the network is quite easy to detect and then troubleshoot the issues associated with the network. (Abbagnale, Cipollone, Cuomo, n.d.) Disadvantages of Star Topology 1) The overall network depends upon the central node hence it has high dependency on it so this means if the central node goes down so will the entire network. 2) Smarter the device for the central node costlier it is for the network hence it is quite costly to implement. 3) Performance of entire network depends upon the central node hence high demanding networks do not favor star topologies. (Abbagnale, Cipollone, Cuomo, n.d.) Advantages of Bus Topology It is quite easy to connect and joins the peripheral devices accordingly. Requirements of cables is quite low as compared to the star topology Disadvantages of Bus Topology Any issue with the cable would mean entire network connectivity to go down. Terminators at both ends are to be installed It cannot be used as the solution for the entire network of any organization. Advantages of Mesh Topology All the nodes are connected to each other hence there are number of ways by which one node can reach out to the other node if in case the nodes connected link doesnt work. Hence, we can say that broken link doesnt hamper the network and it works as it is. Adding new devices doesnt hamper the network performance as new nodes provides new paths hence lesser congestion that would make the network more robust in nature. (Abbagnale, Cipollone, Cuomo, n.d.) Disadvantages of Mesh Topology Management of the network in mesh topology is quite annoying and expensive. It requires monitoring at all the nodes in order to check of any issues associated, a highly skilled network administrator is needed to perform the task and manage the overall mesh network ("Diagram Physical Topologies", 2017) 2.The process of encapsulation is to provide the data wrapped up in a shell that can be accessed from the authorized layer of the network, the capsulated form is protected from any of the outside intrusion and is also out of the misuse of the packet hence it simplifies the overall use of the packet by the system. It also transforms the data packet from one form to another so that it can be understood by different layers of networking nodes. ("Encapsulation", 2017) The process of encapsulation occurs when the packet from higher layer goes down to the layer below, the lower layer only understands the encapsulated form of the packet hence encapsulation is termed to be as necessary. The Encapsulation is nothing but the header information attached to the packet when it travels down the layers. The lower layer just reads the information from the header and passes the required information to the client. ("Encapsulation", 2017) The Decapsulation of the packet is just the reverse of the encapsulation process the packet travels from lower to higher layer and each layer removes the header information belonging to the packet and send it to the layer above 3.C = B log2(1+SNR) = 6.8 log(1+132) = 6.8 * 2.12 = 14.442 Mbps This is the upper limit of the channel for easier calculations we use 10 Mbps as capacity 2 * B * log L = 10 2 * 6.8 * log L = 10 log L = 0.735 L = 1.66 (Channels) 4.The OSI model is the suite that was proposed in order to fulfil the shortcomings of the TCP/IP layer protocol suite. It is better than the TCP/IP suite is a question of debate but we can list down certain aspects by which we can say that the OSI model was better. First it was the open layer architecture hence any device can be built on this model and it can communicate with the rest of the devices around the globe if they are too built on this model. This open layer architecture feature was not available in the TCP/IP suite as the devices following the TCP/IP model were wired to the core using the TCP or UDP based protocols only and were not flexible enough for the protocol development and its overall enhancement. (Meyer, Zobrist, 1990) The reason for the OSI didnt became popular according to Tannenbaum was the timing of the launch of the OSI model, lots of money was invested in the research of the OSI along with lot of people were included for the research as well. The bad politics was another reason due to which the OSI didnt become much popular. The timing was bad as it took way too long to finish up and with lot of resources being used the model was still lot complex than TCP/IP and require more complex structure to develop the required hardware. Till then manufacturers already invested lot of money in TCP/IP hence no one was willing to take the risk. It was not balanced as well as the layers of the Session and Presentation were almost empty and other layers were over populated with number of protocols. With the earlier implementation failing the OSI soon became the synonym for the poor and less reliability. Finally, the politics, the major devices were available in the market was built for Unix and earlier netw ork and computer implementation and adaptations were done by academicians which preferred Unix and it had strong association with TCP/IP but OSI on the other hand didnt had any such associations. (Tanenbaum, Wetherall, 2014) Advantages of OSI: It provides open architecture hence choice of implementing is provided It is open architecture hence it is not bounded to any system or specific breed of systems It understands the product development at each stage hence better implementation. It encrypts the entire data for security purposes Multiple models can be worked upon simultaneously. Disadvantages of OSI: Many applications do not need data integrity hence it is burden for many applications to use the OSI model It is quite complex than the TCP/IP to implement It is not adapted to all the communication applications. (Tanenbaum, Wetherall, 2014) Advantages of TCP/IP: It can be built to perform communication b/w two different types of systems Operating System independent It supports many routing protocols Devices internetworking and their organization is done quite efficiently. It has the scalable nature hence preferred by Client-Server Architecture. Disadvantages of TCP/IP: It is complex for initial setup and management Its overhead for communication is large (Tanenbaum, Wetherall, 2014) 5.Propagation time = distance / propagation speed = 1900 Km /2.2 x 108 m/s = 8.63 ms Transmission time = Message size / Bandwidth = 5 x 106 bits/ 8 Mbps = .625 s = 6250 ms Queuing time = 10 routers * 3.5 us = 35 us Processing Delay = 10 routers * 1.8 us = 1.8 us Total delay (latency) = 8.63 + 6250 + 0.035 + .0018 = 6258.6668 ms = 0.62586 sec 6.Figure 1POP3 state References Abbagnale, A., Cipollone, E., Cuomo, F. Constraining the network topology in IEEE 802.15.4.Advances In Ad Hoc Networking, 167-178. https://dx.doi.org/10.1007/978-0-387-09490-8_15 Encapsulation. (2017).Study-ccna.com. Retrieved 7 May 2017, from https://study-ccna.com/encapsulation/ Meyer, D., Zobrist, G. (1990). TCP/IP versus OSI.IEEE Potentials,9(1), 16-19. https://dx.doi.org/10.1109/45.46812 Tanenbaum, A., Wetherall, D. (2014).Computer networks(1st ed.). 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