a1-sol - Solution to CSE 489/589Homework Assignment 1...

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Solution to CSE 489/589Homework Assignment 1 Please let me know of any typo/mistake ASAP. October 9, 2010 Problem 1. Surf the net or read the textbook find out what the OSI reference model is. Give a very brief description of the OSI reference model (half a page). List two ways in which the OSI model is different than the TCP/IP model. List two ways in which they are the same. Answer. The OSI reference model is an abstract layered model for computer network design, developed by the Open System Interconnection initiative. This model divides the design space into 7 layers (as opposed to the 5 layers of the TCP/IP reference model): application, presentation, session, transport, network, data-link, and physical. The OSI application layer is more or less the same as the TCP/IP application layer. The OSI presen- tation layer is responsible for converting between different data presentation formats. The OSI session layer deals with connection management between computers. The OSI transport layer does flow control, segmentation, and error control for connections. The network layer routes data in the network. The data-link layer deals with single-hop communication issues such as flow control. And, the physical layer defines the physical and electrical specifications for devices. TCP/IP and OSI models have several features in common, including: Both are abstractions for modularizing the design of a data communication network. Both have a network, transport, and application layer. The transport service in both models can provide a reliable end-to-end byte-stream. They also differ in several aspects, including: The number of layers is different. TCP/IP does not have session or presentation layer. TCP/IP does not separate data-link and physical layers. OSI has both connection oriented and connectionless services in the network layer. Problem 2. Consider a network with just four nodes connected as a square. Thus, there are only four links. Each link can carry up to n circuits simultaneously. Suppose n is an even number. A connection is a path between two different nodes. Suppose the network’s switching mode is circuit switching. 1. At the maximum, how many simultaneous connections can be established? 2. How many length- 2 connections can be established at the same time? Briefly argue why your answers are correct. Answer. (The “even n ” fact was not needed.) 1
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1. 4 n . Each connection uses at least one circuit on some link. There are totally 4 n possible circuits on 4 links. This is achievable with 4 n length- 1 connections, n per link. 2.
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This note was uploaded on 12/03/2010 for the course CS 489 taught by Professor Hungngo during the Fall '10 term at SUNY Buffalo.

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a1-sol - Solution to CSE 489/589Homework Assignment 1...

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