Circuit and Packet Switching, Concept of Quality of a Service for Network | CSC 401, Assignments of Computer Systems Networking and Telecommunications

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Homework 1

Issued 8/29/02, due date: 9/9/ All questions have equal weightage.

1. (a) Define circuit- and packet-switching. (b) What are the tradeoffs involved in these two transport orientations?
2. What are the elements of a protocol? Define each in a single sentence.
3. Define the concept of Quality of Service for a network in a single sentence.
4. (a) Which of the following networks are hierarchical and which are not? (In this context, hierarchy is defined as in class) POTS, Ethernet, Internet. (b) For the same three networks, which are scalable and which are not?
5. List the 7 layers of the OSI protocol stack and define the function of each in a single sentence.
6. Answer Q19 of Chapter 1 of the text.
7. Answer Q20 of Chapter 1 of the text.
8. Answer Q24 of Chapter 1 of the text.
9. Answer Q26 of Chapter 1 of the text.
10. Consider the postal system, which we considered as a real-life analogy of computer networking in light of the OSI layers. Assume that the application, presentation and session layers are merged into one and are implemented in the user of the postal system (whoever sends or receives a letter). Try to find answers to the following questions that satisfy you. a. What is the application layer PDU? b. Does it make sense to talk about the lowest layer as the “physical layer”? c. What are the “links” the “DLC layer” implements? d. What are the “components” that exist at the “network layer”? e. What are the PDUs of that layer? f. Many letters go into the same mailbag: this introduces the concept of consolidation, which is not obvious from the OSI layers. To simplify the issue, assume it is a really really lazy day at the USPS and at any time there is no more than one piece of mail waiting to be processed at any PO, and it cannot be kept waiting for consolidation. Trace the encapsulation process from the highest to the lowest layer. g. Does the concept of layering or the OSI layers fit this system well?