BEng (Hons) Telecommunications Cohort: BTEL/10A/FT Examinations for 2011 2012 / Semester 1 MODULE: IP Telephony MODULE CODE: TELC3107 Duration: 2 Hours Reading time: 15 Minutes Instructions to Candidates: 1. This paper contains FOUR questions 2. Answer all four questions 3. Total marks 100 4. Always start a new question on a fresh page 5. Questions may be answered in any order but your answers must show the question number clearly This question paper contains 4 questions and 6 pages. Page 1 of 6
SECTION A: COMPULSORY QUESTION 1: (25 MARKS) (a) What is a Voice Codec? (4 marks) (b) Why is a Voice Codec required? (6 marks) (c) Explain in detail: i. G.729 ii. G.711 (10 marks) (d) What is the importance of QoS in IP telephony? (5 marks) Page 2 of 6
SECTION B: ANSWER ALL QUESTIONS QUESTION 1: (25 MARKS) a) When talking about unified communication there are two very important concepts that need to be understood: i. Concept of Presence ii. Single number reach Explain both of them in detail (10 Marks) b) Since we are speaking of integration, just everything at the service of communication can be integrated. List and explain the four common things that can be integrated.. (8 Marks) c) How can unified communications be useful? Describe four examples that would show the usefulness of unified communication. (7 Marks) Page 3 of 6
QUESTION 2: (25 MARKS) (a) What are the pros and challenges of having an IP telephony network? (8 Marks) (b) What is the technical difference between Internet Protocol Telephony and PSTN networks? (5 Marks) (c) Can two IP phones on the same network have same IP address? (5 Marks) (d) How is Reliability different from Availability in a voice system? Your answer must be supported with examples and appropriate use of formulae. (7 Marks) Page 4 of 6
QUESTION 3: (25 MARKS) Read the Case Study below and answer the questions that follow. Case Study Recently Voice over IP (VoIP) is experiencing a phenomenal growth. Being a realtime service, VoIP is more susceptible to attacks. Moreover, VoIP uses multiple protocols for call control and data delivery, making it vulnerable to various attacks at different protocol layers. An attacker can easily disrupt VoIP services by flooding TCP SYN packets, UDP-based RTP packets, or SIP-based INVITE messages, which pose a critical threat to IP telephony. Attack to an IP telephony network is not a new concept. However, the manifestation of attacks, their targets, and how they are executed has evolved over the past decade. To date, most Internet originated attacks have targeted the transport and network layers of the TCP/IP protocol stack. Typically, the goal of these attacks is either to overwhelm a particular machine or to saturate the communication link. However, as the Internet evolves and enterprises deploy multiple connections to the Internet, attacking the infrastructure has become less critical. Certain attacks are being targeted at specific services that consumers demand and rely upon, e.g., e- mail and web. This trend will continue as new complex services are deployed and gain widespread adoption. IP telephony is one such complex service that is gaining rapid momentum and has the potential for becoming a strategic new technology in coming decades. In turn, it is a prime target for new forms of attacks. In order to support IP telephony in an enterprise network, new network elements must be deployed and existing network elements must be modified. To support calls between endpoints connected to the IP network, referred to as Net-to-Net calls, SIP (Session Initiation Protocol) Proxy and Registrar/Location Server (RLS) must be deployed. To support call between endpoints in the Public Switched Telephone Network (PSTN) and endpoints connected to the IP network, referred to Net-to- PSTN and PSTN-to-Net calls, it is necessary to deploy a Media/Signal Gateway (MSG) that can act as an application level proxy between the IP network and the PSTN. Besides these new network elements, supporting IP telephony requires Page 5 of 6
modifications in the enterprise firewall to allow dynamic protocol ports to be opened at the clients to send and receive audio and/or signaling and control messages. a) The case study says that different attacks are possible on an IP telephony network. Explain in detail the famous attacks on an IP telephony network. (10 Marks) b) From the case study we can deduce that there is a need to have vulnerabilities for a hacker to break into the system. Hence, what are the different important steps that need to be followed to mitigate the vulnerabilities associated in a VoIP network? (7 Marks) c) When a hacker performs a DoS attack on IP telephony network, the two main protocols that he might use are namely: i. ICMP ii. TCP/SYN Explain how the hacker would use the above protocols to perform his attack. (8 Marks) ***END OF QUESTION PAPER*** Page 6 of 6