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辅导案例-EL873 /

By May 21, 2020No Comments

UNIVERSITY OF KENT EL873 / 2020 FACULTY OF SCIENCES LEVEL 7 EXAMINATION SCHOOL OF ENGINEERING AND DIGITAL ARTS ADVANCED NETWORKING SYSTEMS AND TECHNOLOGY (2 hours) Instructions There are FOUR questions. Candidates must answer THREE questions. turn over Q1 (i) In your own words, explain why synchronisation and ranging are required for upstream data transmission using (co-axial) cable modems. Describe the synchronisation and ranging procedures used in the Data Over Cable Service Interface Specification (DOCSIS) standard. [7 marks] (ii) Describe, in your own words, the principles involved in the scheduling for upstream transmissions in DOCSIS. [3 marks] (iii) A 5G (5th Generation) Fixed Wireless Access (FWA) system operates with the parameters shown in Table 1.1. Table 1.1 System nominal bandwidth BW = 100 MHz FFT size 4096 Oversampling factor n = 1.2288 Guard period ratio G = 1/14 Data subcarriers Ndata = 3300 Pilot subcarriers Npilots= 256 (a) What is the subcarrier spacing? (b) How many guard and null subcarriers are there? (c) What is the useful symbol time? (d) What is the total symbol duration? (e) What is the raw data rate in this system for 64 Quadrature Amplitude Modulation (QAM)? [6 marks] (iv) Referring to your answers for (iii), discuss the resilience of the system to multipath and Doppler effects. [4 marks] 2 EL873 / 2020 Q2 (i) With reference to Synchronous Digital Hierarchy (SDH) networks, describe, in your own words, the operation of: (a) add-drop multiplexers (b) cross-connects. [6 marks] (ii) In your own words, describe the reasons why the Optical Transport Network (OTN) standard specifications were developed, instead of simply extending SDH to higher rates. Your discussion should include the use of forward error correction (FEC) and tandem connection monitoring (TCM). [9 marks] (iii) Sketch the wavelength (virtual) topology for the unidirectional optical ring network shown in Figure 2.1, where the nodes are optical (wavelength) add-drop multiplexers at which the labelled wavelengths are added and dropped. [5 marks] Figure 2.1 A B C D 2, 3, 4 1, 4, 5 2, 5, 6 1, 3, 6 3 EL873 / 2020 tun over Q3 (i) Contrast the Expedited Forwarding and Assured Forwarding standard Differentiated Services (DS) approaches. [3 marks] (ii) In your own words, discuss how different switch/router queuing disciplines, such as weighted fair queuing and strict priority queuing, can help provide for different quality of service for different traffic flows or classes. [4 marks] (iii) Describe, in your own words, why Content Distribution Networks (CDNs) are needed by content providers, such as video-on-demand service providers. What are the trade-offs involved in distributing content to greater numbers of local data centres? How can IP Anycast addresses be used in server cluster selection? [7 marks] (iv) In Multi-Protocol Label Switching (MPLS), state two ways in which label-switched paths can be set up. [2 marks] (v) In Multi-Protocol Lambda Switching (MPS), describe the equivalence of the functions in an optical cross-connect (OXC) with those provided in a label switch router (LSR). Discuss the two levels of operation that should be provided in a MPS OXC. [4 marks] 4 EL873 / 2020 Q4 (i) Describe, in your own words, the processes involved in call setup and information transfer in a voice/video over IP call using Session Initiation Protocol (SIP). How is a user permitted to move to different locations? [4 marks] (ii) State the advantages and disadvantages of using Hypertext Transfer Protocol (HTTP) for video streaming instead of Real-Time Transport Protocol/Real-Time Transport Streaming Protocol (RTP/RTSP). Refer specifically to the use of Dynamic Adaptive Streaming over HTTP (DASH). [5 marks] (iii) Describe, in your own words, the upstream channel access in current Passive Optical Networks (PONs). What is the key difference between downstream and upstream transmission and channel access in IEEE and ITU-T PONs? [6 marks] (iv) How can wavelength be used to provide a point-to-point logical overlay in a (point-to-multipoint) PON? Describe, in your own words, how different generations of PON technologies can thereby co-exist. [5 marks] Note: IEEE: Institute of Electrical and Electronics Engineers ITU-T: International Telecommunications Union – Telecommunications Standardisation Sector End of Examination Paper 5 EL873 / 2020


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