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]
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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
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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]

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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

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