Telephony Networks - Telecommunications Software Applications - Past Exam Paper, Exams of Software Engineering

Download Telephony Networks - Telecommunications Software Applications - Past Exam Paper and more Exams Software Engineering in PDF only on Docsity! Semester II Examinations 2008/ 2009 Exam Code(s) 4BN121, 4BP121 Exam(s) B.E. Degree Examination (Electronic Engineering) B.E. Degree Examination (Electronic Engineering and Computer Engineering) Module Code(s) EE423 Module(s) Telecommunication Software Applications Paper No. 1 Repeat Paper N External Examiner(s) Professor G. Irwin Internal Examiner(s) Professor G. Ó Laighin Mr. L. Kilmartin Instructions: Answer any five questions (20 marks per question) Duration 3 hours No. of Pages 7 Department(s) Electrical & Electronic Engineering Course Co-ordinator(s) Mr. Liam Kilmartin Requirements: MCQ Handout Statistical Tables Y Graph Paper Y Log Graph Paper Other Material 1. (a) Explain the meaning of the following terms in the context of a modern Public Switched Telephony Network (PSTN): (i) Hierarchical network (ii) E1 Time Division Multiplex (iii) Local Loop (iv) Pulse Code Modulation (PCM) Codec (v) Dual Tone Multi-Frequency [10 marks] (b) Number translation services are widely implemented within telephony networks in order to support many different services such as Premium Rate and Freephone services. Explain what you understand by the terms in bold and, hence, describe how such services can be implemented using (i) a Service Node (SN) model and (ii) an Intelligent Network (IN) model. [6 marks] (c) A company currently has a two circuit leased line supporting all voice calls with the PSTN. Over a period of time, it was noted that approximately 25% of all busy hour call attempts with the PSTN were failing due to insufficient channel capacity over this leased line. Determine the busy hour amount of traffic in Erlangs that was being offered to the leased line and, hence, the corresponding number of call attempts if it is known that the average call duration is 12 minutes. If the company increased its leased line capacity to four channels, determine the GOS that would be provided for the same busy hour traffic. [4 marks] 2. (a) Frequency reuse and trunking are fundamental concepts which are used within all cellular networks to support a very large number of subscribers using a limited frequency spectrum. Explain the meaning of the two terms in bold in the context of the statement above. [4 marks] (b) The basic coverage area in a cellular network is known as a cell. Identify THREE different types of cells that are typically found in a cellular network and clearly explain the scenarios in which such cell types would be used. [6 marks] (c) Describe the purpose of the following functions in the context of the GSM Air Interface. (i) Time Division Duplexing, (ii) Timing Advance, (iii) Adaptive Power Control, (iv) Discontinuous Transmission [6 marks] (d) Explain, using a timing diagram, why in the GSM system the Random Access Burst is substantially shorter than the Normal Burst generated by mobile stations. The random access burst used by GSM mobiles has duration of 88 bits at the GSM transmission bit rate of 270 kbps. Given that a single GSM burst period has duration of 156.25 bits, show that the maximum size of a GSM cell is between 35 and 40 km. [4 marks] 3. (a) Directly after powering on a GSM handset, the handset interacts with a variety of network entities in order to complete its network registration process. With the aid of a diagram, clearly identify the network entities involved in this process, the role which each plays in the registration process and summarise the data which is stored on each of these network entities which is relevant to this registration process. IP P8 P10 f Left circular shift K1 8 bit plaintext 10 bit key 8 bit swap The oper Appendix Point A s 1011100 Outline t mode of preferred (c) Expla equations In a simp code. Ex the result A receiv ciphertex 7. (a) Expla hence, ou have prio (b) A co encrypti sites overP8 IP-1 Left circular shift K2 8 bit ciphertext f Figure 1 – Structure of a simplified DES implementation ational implementation of the functionality in the boxes labeled f in Figure 1 is summarised in A at the end of this paper. Using this information determine the value which would be generated at hown in figure 1,for the case where the 8 bit plain text value is 10001101 and the 10 bit key value is 011. he difference between the Electronic Codebook Mode (ECM) and the Cipher Block Chaining (CBC) operation for the DES algorithm. Your answer should clearly identify why CBC would be the mode of these two modes of operation for DES. [9 marks] in what you understand by the term public key encryption algorithm and hence state the main which define the design and operation of the RSA algorithm. lified version of RSA, the values of p=13, q=11 and e=13 are proposed for use in designing the plain why each of these values are valid and hence determine a suitable value for d and clearly state ant public and private keys which have been designed. ed ciphertext message has a decimal value of 31. Determine the plaintext value that produced this t using the developed RSA algorithm above. [6 marks] in how a basic Keyed MD5 algorithm can be used to implement an authentication protocol and, tline how this basic algorithm can be enhanced so that there is no requirement that both parties to r knowledge of a shared secret key. [6 marks] mpany has private IP networks located at two different geographic locations. Explain how on and Virtual Private Network (VPN) technologies can be used to securely interconnect these a public IP network. [4 marks] Point A (c) Describe the role of a firewall in a corporate network and clearly distinguish between the operation of a filter based firewall and a proxy based firewall. [4 marks] (d) Explain, using diagrams where appropriate, the meaning of the following terms: (i) Network Address Translation (NAT) (ii) Demilitarised Zone (DMZ) (iii) Denial of Service Attack (iv) IPSEC [6 marks] Appendix A Implementation of Simplified DES Algorithm The simplified DES algorithm is implemented using the following table definitions: P10 Input 1 2 3 4 5 6 7 8 9 10 output 3 5 2 7 4 10 1 9 8 6 P8 Input 1 2 3 4 5 6 7 8 output 6 3 7 4 8 5 10 9 IP Input 1 2 3 4 5 6 7 8 output 2 6 3 1 4 8 5 7 IP-1 Input 1 2 3 4 5 6 7 8 output 4 1 3 5 7 2 8 6 Expansion Input 1 2 3 4 5 6 7 8 output 4 1 2 3 2 3 4 1 S-Boxes S0 0 1 2 3 0 1 0 3 2 1 3 2 1 0 2 0 2 1 3 3 3 1 3 2 S1 0 0 1 2 3 1 2 0 1 3 2 3 0 1 0 3 2 1 0 3 P Input 1 2 3 4 output 2 4 3 1