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CORK INSTITUTE OF TECHNOLOGY
INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ
Semester 1 Examinations 2008/
Module Title: Communications Network Engineering
Module Code: CTEC 9005
School: Electrical & Electronic Engineering
Programme Title: Master of Engineering in Telecommunications Engineering
Programme Code: ETELT_9-Y
External Examiner(s): Mr. Paul French, Dr. Sean McGrath and Mr. Philip Quinlan
Internal Examiner(s): Dr. Susan Rea, Mr. Aidan McDonald, Ms. Olivia Brickley
Instructions: Use separate answer books for each section Answer any three questions for full marks from any section Maximum available marks is 100 Note: The exam is Open Book and you may use all of your lecture notes
Duration: 2 Hours
Sitting: Winter 2008
Requirements for this examination: Students are allowed calculators
Note to Candidates: Please check the Programme Title and the Module Title to ensure that you have received the correct examination paper. If in doubt please contact an Invigilator.
Section A
Q1.
a. ATM offers five service categories. Name and describe the characteristics of each service category, identifying the relevant traffic and QoS parameters and providing example applications. [15.33 marks] b. Explain the function and importance of connection admission control in ATM networks. [4 marks] What is CLP? How is it used in QoS provisioning? [4 marks] c. What is a traffic contract? Identify the typical parameters used in such a contract. [7 marks] d. Briefly describe the congestion control method Intelligent Packet Discard as used in ATM. [3 marks] [Total: 33.33]
Q2. a. Consider a transmission link with fixed capacity C=1.5Mb/s, an infinite buffer, and a Poisson arrival process with rate λ = 1000 p/s. assume that the packet length distribution is exponential with mean L = 1000 b/p.
- Compute the mean number of packets in the system (including the transmitter). Compute the mean delay for a packet.
- Now assume the arrival rate of packets has risen to λ = 2000 p/s so we double the transmission capacity to C=3 Mb/s. what happens to the mean number of packets in the system? What happens to the mean delay for a packet? [10 marks]
b. For the queuing network shown in Figure 1 calculate the average queue length and average queuing delay for each of the four queues. The parameter values shown are as follows: r 1 = 4/sec, all other r (^) i = 0. μ 1 = 25/sec, μ 2 = 33/sec, μ 3 = 16/sec, μ 4 = 20/sec p12 = p 13 = 0.5, p 41 = p 21 = 1, p 31 = 0.6, p 30 = 0.4, all other pij = 0.
Section B
Q3.
a. Outline the SIP client-server architecture, describing in detail the function of each entity. [7.33 marks]
b. SIP is a request response protocol; describe and illustrate the call setup procedure using a proxy server. [8 marks]
c. A fundamental QoS building block for network traffic is classification. Discuss what characteristics are generally used to classify data? [6 marks]
d. End-to-end delays experienced when traversing a WAN can have a serious impact on VoIP connections. Outline three sources of such delay. Describe in detail, techniques which can limit these phenomena. [12 marks]
Section C
Q4.
a. If all codes are breakable, what is the significance of a code been computationally secure? Discuss this. (5 marks) b. Outline the basic properties of the following algorithms: i. Secure HASH function; ii. Digital signature; Explain how these and encryption can be used to provide a secure email application. (12 marks) c. According to Bellovin and Cheswick, what are the design goals of a firewall? Outline the operation of two types of firewall (8 marks) d. In IPSec, what is a security association? Illustrate the two modes of operation for ESP in IPSec? (8.33 marks) (Total: 33.33 marks)
