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(Explain the principle of DMT and QAM.)
k (Afkortingen: phy)
Regel 515: Regel 515:
** IDFT: Inverse Discrete Fourier Transform
** IDFT: Inverse Discrete Fourier Transform
** DAC: Digital Analog Conversion
** DAC: Digital Analog Conversion
** PHY: Physical Layer
* ONU: Optical Network Unit
* ONU: Optical Network Unit
* TE: Traffic Engineering
* TE: Traffic Engineering

Versie van 8 jun 2006 om 17:31


“Broadband Communication” Francqui KULeuven 2005-2006 [1] by Piet Demeester


General information on examination

Material for the examination

All the lectures

  • Inaugural lecture
  • Internet support for multimedia flows
  • Access Networks
  • Optical Networks
  • Mobile Networks
  • Grid Computing
  • Reliability of Communication Networks


  • Internet support for multimedia flows:
    • The Session Initiation Protocol: Internet-Centric Signaling (Schulzrinne, Rosenberg)
    • On the building blocks of quality of service in heterogeneous IP networks(Soldatos, Vayias, Karmentzas)
  • Access Networks:
    • Media Access Control for Ethernet Passive Optical Networks: An Overview(Zheng, Mauftah)
  • Mobile Networks:
    • IP Micro-Mobility Protocols (Reinbold, Bonaventure)
  • Grid Computing:
    • A Gentle Introduction to Grid Computing and Technologies (Buya, Venugopal)
  • Reliability of Communication Networks
    • Benefits of GMPLS for Multilayer Recovery (Puype


  • Closed book exam: 70% from list of questions (see below), 30% not from list
  • Open book (slides, notes, publications allowed): e.g. questions that link different subjects together or small exercises
  • Evaluation: roughly 70% closed book, 30% open book
  • Duration: 3 hours
Illustrate your answers with clear figures (when appropriate)

List of Questions

  • The whole question or a part of a question may be asked
  • Some questions are related to the publications that are listed above (they are indicated in italic)

Internet support for multimedia flows


Explain the principle of and relation between a user plane and a control plane in classical telephony.

slides 5-10

  • User plane: talk, send voice data
  • Control plane: administration of the network, eg. Setting up the connection, routing, ... : overlay

Describe 3 cases where VoIP is used.

slides 15-17

  • PSTN to IP (eg. Calling a skype user)
  • VoIP on the Intranet: Local phone use, external is sent to PSTN
  • IP in the core (backbone) of Telephony providers, also carrying voice

What is SDP.

slides 19-22

Explain the general principle of SIP and give the basic building blocks.

slides 24-27

An example of a SIP message is given during the exam: explain.

slides 33-39

Give 2 specific problems when the Internet is used for voice. What are (partial) solutions to these problems.


  • packet loss (43)
  • jitter (44-45) [in the extreme: generates packet loss]

Solutions: (Notes on slide 42)

  • error recovery: FEC, interleaving, adding sequence numbers, adding timestamps

Solutions on receiver side: (Notes on slide 42)

  • Dejitter buffer
  • Packet concealment: (fill with noice or interpolation)

Other information...

  • Other problems: link delay (46)
    • transmission delay --> use faster access lines (higher bandwidth)
    • propagation delay (lightspeed) --> use shorter, faster path (transatlantic fiber vs. satellite)

Terminal actions 49

  • CODEC 50-60
  • Timing: RTP 61-63
  • de-jitter buffer 64
  • packet concealment 65

Network actions 66-68

  • QoS Router 69-82
  • Network coordination 84-96

How does RTP resolve timing problems encountered when transporting voice or video over internet.

slides 61-63 +64 +65 ! Lees ook de notes

RealTime mijn poep, dit is niet real-time as you probably know it: Steekt extra info in packet (type, seq. nr, timestamp & conn ident.) Het hele idee is dat UDP packet nrs te weinig zijn om iets te kunnen doen (eg dejitter of packet concealment).

==> in deze context Real-Time te lezen als: het gaat over gelijklopende klokken, niet over logische volgorde.

Met die extra info kan er op de client side 'slim' omgesprongen worden met de UDP packets (vb: als packages om de 160, en 400 lang geen packet meer ontvangen; jitter/loss of niet ? volgend package heeft SQ+1 en TS+400: geen jitter maar de bedoeling).

Dankzij die extra RTP info is Dejitter en Packet Concealment mogelijk.

==> inderdaad. De RTP informatie is nodig om de "tijds-synchronisatie" van de pakketten juist te kunnen krijgen. (De volgnummers van UDP geven enkel informatie over de logische volgorde.) Een extra voordeel is dat pakketten die enkel stilte bevatten expliciet niet uitgezonden hoeven te worden, wat minder netwerkbelasting veroorzaakt. (die pakketten worden eigenlijk niet geconcealed, want via de UDP nummers weet de ontvanger dat er daartussen inderdaad een stilte was)

Explain the principle of a QoS aware IP router.

slides 69-82

Explain classification, shaping, policing, queueing, scheduling, buffer management as used in a QoS aware IP router.

slides 69-82

  • classification (70) :
    • identification of the flows (voice, file transfer, ...) on entering the buffers
    • enable a different treatment for different flows
    • identifiers:
      • source/destination IP address (+ ports)
      • dedicated classifier / label
  • policing (71): "the process of discarding packets (by a dropper) within a traffic stream in accordance with the state of a corresponding meter enforcing a traffic profile."
    • Why?
      • Control incoming flow against certain specification
    • How?
      • e.g. Token Bucket Algorithm (72-73)
      • discard | mark packet | make best-effort packet (= worst effort)
  • shaping (74): "the process of delaying packets within a traffic stream to cause it to conform to some defined traffic profile."
    • Why?
      • Obtain a smooth flow of packets( reduce burst size)
    • How?
      • e.g. Token Bucket Algorithm (75-76)
  • queuing (77)
    • one queue for all flows
    • one queue for one class of flows
    • one queue for each individual flow
  • scheduling
    • priority (81)
      • easy to implement
      • high priority queues have very low delay
      • low priority queues can have very bad behavior (starvation)
    • weighted round robin (82) (WFQ)
      • easy to implement
      • different bandwidths possible
      • also low priority traffic is served
      • can become very complex with many queues
  • buffer management (79-80)
    • When should a packet be dropped?
    • Which packet should be dropped?
      • RED
      • W-RED

Explain the principle of 2 techniques used to support flow differentiation in IP networks.

slides 84-88

  • IntServ (Integrated Services)
  • DiffServ (Differntiated Services)

Explain the operation of MPLS.

slides 92-96

Explain the principle of VOQ (Virtual Output Queue) and why is it used.

Paper: On the building blocks of quality service in heterogeneous IP networks p. 78

Access Networks


Explain the evolution of a classical telephone access network towards a triple play enabled access network.

Triple play: telephone, tv, internet 19

Explain the ADSL architecture (figure from ITU-T rec G.992.1 will be given).

slides 30-35

Explain the principle of DMT and QAM.

  • Discrete Multi Tone 39-42
    • Way of using the available bandwidth, by splitting it up in descrete frequency (tone) bands. For each discrete band, the SNR is being determined.
  • Quadrature Amplitude Modulation 43-46
    • Using the bands of DMT by means of complex modulation technique, where amplitude and phase are used to encode the information. Depending on the SNR of the individual bands, a more complex modulation can be used, (more information per frequency band).

Explain the basic principles of : CRC, scrambling, FEC.

  • Cyclic Redundancy Check 59-62
  • Scrambling 63-64
  • Forward error correction 65-69

Explain in detail FEC (coding and decoding).

  • Forward error correction 65-69

Explain the evolution of a classical coax access network (CATV) towards a triple play enabled access network.

slides 80-83

Explain the basic principle of MPCP in E-PON. Give 3 polling policies.

  • Ethernet-Passive Optical Network 96-105
  • Multi Point Control Protocol 106-108
  • Polling policy: Interleaved Polling with Adaptive Cyclic Time 110-111

Paper: Media Access Control for Ethernet Passive Optical Networks: An Overview

  • E-PON p. 145-146
  • MPCP p. 147
  • Polling policies p. 148
    • Poll-and-stop polling
    • Interleaved polling
    • Interleaved polling with stop

Explain DBA in E-PON.

Dynamic Bandwidth Allocation 109

Paper: Media Access Control for Ethernet Passive Optical Networks: An Overview

  • DBA p. 149

Optical Networks

Optical Packet Switching is not part of the examination subject matter

Useful Fiber Optic glossary:

Explain the difference between logical and physical topology. Give an example.

slides 5

Explain the principle of WDM and OTDM.

slides 9-17

  • Wavelength Division Multiplexing
  • Optical Time Division Multiplexing

Wavelength Division Multiplexing (WDM) and Optical Time Division Multiplexing (OTDM) are the two multiplexing techniques to increase the bit rate transmitted over a fibre above the bit rates which can be generated electronically using Electric Time Division Multiplexing. The limit for ETDM is now 40 Gbit/s and might be shifted up to 80 Gbit/s in the future.

WDM modulates the electric signals on optical carriers with different wavelengths. The spacing of the wavelengths in practical systems is usually 100 GHz and the bit rate per channel 10 Gbit/s, which as mentioned will be increased to 40 or even 80 Gbit/s. The total bit rate per fibre is limited by the useable spectrum, which in turn is limited by the bandwidth of the optical amplifiers used. The bandwidth of the C-band EDFA is about 4 THz. The band width can be increased by using other amplifiers (L-Band, Raman and hybrid solutions). The total bit rate can also be increased by increasing the spectral efficiency, the ratio between single channel bitrate and the channel spacing. It might be possible to increase the spectral efficiency well above 1 bit/s/Hz by using special modulation and coding techniques. In laboratory systems a total bit rate of more than 10 Tbit/s has already been demonstrated. Optical Time Division Multiplexing instead uses the potential to generate very narrow optical pulses. These are multiplexed by using suitable delay lines. One major challenge is the demultiplexer which needs operate at speeds of the multiplexed bit rate. 1.28 Tbit/s have already been achieved, using this technique [M. Nakazawa et al.: 1.28 Tbit/s – 70 km OTDM transmission using third- and fourth-order simultaneous dispersion compensation with a phase modulator, PD 2.6, ECOC 2000]. It might be hard to overcome this result, due to problems with spectral and polarisation mode dispersion (PMD) at these high bit rates.

Explain the principle of dispersion, attenuation, 3R regeneration, space switching, wavelength switching, optical memory.

slides 19-25

Dispersion, absorption, and scattering are the three properties of optical fibers that cause attenuation, or a marked decrease in transmitted power, and therefore, have limited progress in areas of high-speed transmission and signal efficiency over long distances. Dispersion occurs when the light traveling down a fiber optic cable “spreads out,” becomes longer in wavelength and eventually dissipates. Two other major mechanisms of attenuation in optical fibers are absorption and scattering.
3R regeneration:

Give the basic structure of an OXC and OADM.

slides 27-31

Explain the difference between an optical network with or without wavelength conversion.

slides 32-33

Explain the principles of control planes in optical networks: static versus dynamic, dynamic overlay versus dynamic peer.

slides 35-39

Mobile Networks

Explain: FDMA, TDMA, SDMA and CDMA.

slides 6-14

  • Frequency Devision Multiple Access
  • Time Devision Multiple Access
  • Space Devision Multiple Access
  • Code Devision Multiple Access

Explain: TDD, FDD.

slides 15

  • Time Division Duplex
  • Frequency Division Duplex

Explain: hidden terminal problem, exposed terminal problem.

slides 16-22

Explain RTS/CTS principle.

slides 20-21

  • Request To Send
  • Clear To Send

Explain FHSS and DSSS.

slides 23-25

  • Frequency Hopping Spread Spectrum
  • Direct Sequence Spread Spectrum

Describe the basic architecture of a GSM network.

slides 28-31

Explain roaming in GSM.

slides 30

Explain the evolution towards 3G (briefly explain the different technologies/enhancements).

slides 42-47

Explain the principle of DFWMAC-DCF using CSMA/CA using an example.

slides 57-59

  • Distributed Foundation Wireless Medium Access Controll-Distributed Coordination Function
  • Carrier Sense Multiple Access with Collision Avoidance

Explain the principle of Mobile IP.

slides 75-78

Make a comparison between GSM and Mobile IP.

slides 79

Explain the figure 5 from the paper “IP Micro-Mobility Protocols (Reinbold, Bonaventure)”. The figure will be given.

Explain the principle of Hierarchical Mobile IP and Fast Handoff.

Paper IP Micro-Mobility Protocols p. 49-50
Duidelijker uitgelegd (vind ik - Kurt), mét tekening:
Hierarchical: 36-37
Fast Handoff: 38

Grid Computing

Explain the evolution towards grid computing from 2 different perspectives.

  • Historical 3-16
  • Network: 42

Give 4 types of grids and explain the principles.

slides 46 (use a mirror)-56

  • Cycle scavenging grids
  • Computational grids
  • Data grids
  • Service grids

Describe the building blocks of a grid architecture.

slides 59-64

What is grid middleware.

slides 65-66

Explain grid scheduling.

slides 70-71

What is application gridification. Give two examples.

slides 75, 82-87

Application gridification is the term given to the process of enabling an existing application for its execution on a grid infrastructure.
Zie bundeltje 'Six strategies for grid application enablement'

What is network aware grid scheduling. When is it important.

slides 94

Reliability of Communication Networks

Explain defect, repair, fault, failure.

slides 9-15 Network element defect
Decrease of network element ability to perform a required function
E.g. a link defect -> poor link quality -> error detection -> packet/frame retransmissions

Network element failure
Termination of network element ability to perform a required function
Happens at one particular moment in time
E.g. a cable cut by an excavator

Fault or outage
Inability of a network element to perform a required function
Lasts until repair of the network element
Covers a time interval

Explain: protection and restoration, dedicated and shared protection, recovery scope.

slides 17-18

How does the classical TCP/IP protocol stack cope with network element failures?

slides 26-31

Explain the principle of facility backup in MPLS.

slides 35-37

Explain 1+1, 1:1, 1:1 with preemption and OMS-SPRing (in optical networks)

slides 39-46

  • Optical Multiplex Section-Shared Protection Ring

Explain single layer recovery in the IP/MPLS over OTN case.

slides 50-52

What are secondary failures and what is the impact on single layer recovery.

slides 51-53

Explain the problem of uncoordinated multi-layer recovery. Give a solution.

slides 57-62

Explain Static versus Dynamic multilayer recovery.

slides 69


  • PSTN: Public Switched Telephone Network (ook POTS)
  • POTS: Plain Old Telephone Service
  • IP: Internet Protocol
  • VoIP: Voice over IP
  • QoS: Quality of Service
  • UNI: User Network Interface
  • NNI: Network Node Interface of Network Network Interface
  • LEX: Local EXchange
  • TEX: Transit EXchange
  • LD: Loop Disconnected
  • DTMF: Dual Tone Multi Frequency
  • TS: Time Slots
  • SS7: Signal System 7
    • SP: Signaling Points
    • SL: Signaling Links
    • SSP: Service Switching Point
    • STP: Signal Transfer Point
    • SCP: Service Control Point
    • LNP: Local Number Portability
  • ITU: International Telecommunication Union
    • ITU-T: ITU - Telecommunication standardization sector
  • S/D: Source/Destination
  • IN: Intelligent Networks
  • NGN: Next Generation Networks
  • SDP: Session Description Protocol
  • SIP: Session Initiation Protocol
  • CODEC: COder/DECoder
  • GW: GateWay
  • MG: Media Gateway
  • SG: Signaling Gateway
  • MGC: Media Gateway Controller
  • GK: Gate Keeper
  • BS: Billing Server
  • MEGACO: Media Gateway Control protocol
  • IETF: Internet Engineering Task Force
  • TDM: Time Division Multiplexing
  • UDP: User Datagram Protocol
  • ITSP: Internet Telephony Service Provider
  • RTP: Real-time (Transport) Protocol
  • RTCP: RTP Control Protocol
  • AVP: Audio Video Profile
  • TTL: Time To Live
  • PCM:
  • GSM: Global System for Mobile Communications
    • FR: Full Rate (zie Codec)
    • HR: Half Rate (zie Codec)
  • NTP: Network Time Protocol
  • UA: User Agent
  • UAC: User Agent Client
  • UAS: User Agent Server
  • HLR: Home Location Register
  • TLS: Transport Layer Security
  • DNS: Domain Name System
  • SRV: Service Record (zie DNS)
  • URI: Uniform Resource Identifier
  • MIME: Multipurpose Internet Mail Extensions
  • ISUP: ISDN User Part
  • ISDN: Integrated Services Digital Network
  • CR/LF: Carriage Return/Line Feed
  • 3GPP: Third Generation Partnership Project
  • IMS: IP Multimedia core network Subsystem
  • FEC: Forward Error Correction
  • A/D: Analog/Digital
  • OSPF: Open Shortest Path First
  • GEO: Geostationary Earth Orbit Satellites, Geosynchronous Earth Orbit
  • MOS: Mean Opinion Score
  • PESQ: Perceptual Evaluation of Speech Quality
  • PSQM: Perceptual Speech Quality Measure
  • PEAQ: Perceptual Evaluation for Audio quality
  • SSRC: Synchronization SouRCe
  • CSRC: Contributing SouRCe
  • CAC: Customer Access Control
  • ER: Edge Router
  • CR: Core Router
  • SLA: Service Level Agreement
  • WFQ: Weighted Fair Queuing
  • RED: Random Early Detection
  • W-RED: Weighted-RED
  • RIO: RED with In-Out
  • DFWMAC-DCF: Distributed Foundation Wireless Medium Access Controll-Distributed Coordination Function
  • CSMA/CA: Carrier Sense Multiple Access with Collision Avoidance
  • IntServ: Integrated Services
  • DiffServ: Differentiated Services
  • BE: Best Effort
  • TOS: Type Of Service
  • DSCP: DiffServ Code Point
  • RSVP: Resource Reservation Protocol
  • PHB: Per Hop Behaviour
  • EF: Expedited Forwarding
  • AF: Assured Forwarding
  • BB: Bandwidth Broker
  • (Q-)OSPF: (QoS-)Open Shortest Path First
  • MPLS: Multi-Protocol Label Switching
  • LSR: Label Switched Router
  • LIB: Label Information Base
  • LSP: Label Switched Path
  • ATM: Asynchronous Transfer Mode
  • LDP: Label Distribution Protocol
  • VOQ: Virtual Output Queue
  • CATV: Community Antenna TeleVision
  • MSC: Mobile Switching Center
  • TP: Twisted Pair
    • STP: Shielded TP
    • UTP: Unshielded TP
  • BER: Bit Error Rate
  • SNR: Signal to Noise Ratio
  • SDM: Space Division Multiplexing
  • QAM: Quadrature Amplitude Modulation
  • DSL: Digital Subscriber Line
    • DSLAM: DSL Access Multiplexer
    • ADSL: Asymetric DSL
    • HDSL: High speed DSL
    • VDSL: Very high speed DSL
    • EC: Echo Cancellation
    • BRAS: Broadband Remote Access Server
    • ATU-R: ADSL Tranceiver Unit - Remote
    • ATU-C: ADSL Tranceiver Unit - Central Office
    • SM: Service Module
    • NT#: Network Termination (number)
    • PABX: Private Automatic Branch eXchange
    • NTR: Network Timing Reference
    • OAM: Operation Administration and Maintenance
    • EOC: Embedded Operations Channel
    • AOC: ADSL Overhad Control Channel
    • Cell TC: Cell Transmission Convergence (ATM-Cells ~ Ethernet-Frame)
    • CRC: Cyclic Redundancy Check
    • IDFT: Inverse Discrete Fourier Transform
    • DAC: Digital Analog Conversion
    • PHY: Physical Layer
  • ONU: Optical Network Unit
  • TE: Traffic Engineering
  • FFT: Fast Fourier Transform
  • EOC: Embedded Operations Channel

--SCIFFY en Cube 5 juni 2006

--Jeroentrappers 7 jun 2006 17:22 (CEST)

--Kurt 8 juni 2006