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  • 1. Broadband Communications: Myth and Reality Professor Stephen McLaughlin School of Engineering & Electronics University of Edinburgh

2. 3. Contents of Presentation

  • What do we mean byBroadband ?
  • Some Broadband Myths
  • Flavours ofBroadbandCommunication
    • Fibre to the Home
    • DSL
    • Wireless LAN
  • Future Technologies
  • Conclusions

4. What willImean byBroadband ? A transmission facility having a bandwidth sufficient to carrymultiplevoice, video or data channels simultaneously. Each channel occupies (is modulated to) a different frequency bandwidth on the transmission medium and is demodulated to its original frequency at the receiving end; NB used originally to describe a channel with more bandwidth than a standard 48 KHz voice grade channel. 5. What is commonly meant byBroadband ? At present, there is no internationally agreed definition of broadband. In general,broadbandoften refers to internet access service with transmission speed from hundreds of kbps (kilobits per second) to several Mbps (Megabits per second)Note that 'dedicated bandwidth' or 'shared bandwidth' services advertised by ISPs normally refers to the transmission speed of the customer access circuit between the customer's premise and the nearest exchange. The active usersstill have to sharethe public network resources outside the exchange, including local and external transmission circuit. 6. Some Broadband Myths

  • You can never have too much bandwidth.
    • i.e.If you build it, they will come
  • Internet traffic is doubling every three months.
  • Everyone needs more bandwidth because of the new killer applications!

7. You can never have too much bandwidth

  • If you build it, they will come.
    • Q: How quickly will they come?
    • A: Not as quickly as many had hoped.

8. Internet Traffic doubles every 3 months

  • The reality.?
    • Backbone traffic growth:
      • about 100% per year in 1990 through 1994
      • about 1,000% per year in 1995 and 1996
      • about 100% per year in 1997 through 2000
    • Overall data traffic growth:
      • around 20 to 30% per year in the 1980s
      • 30 to 40% per year in 1990 through 1998
      • accelerating towards 100% per year

9. SWITCH traffic and capacity across the Atlantic 10. We need more bandwidth

  • Traffic is not the same as bandwidth!
    • Factors decreasing bandwidth demand:
      • Elimination of SONET rings, ATM cell tax, etc.
      • VPNs over public network replacing private lines
    • Factors increasing bandwidth demand:
      • Optical switching
      • Demand for low transaction latency
  • DWDM is doubling transmission capacity each year!
    • However, magnetic storage is also doubling each year!
      • So location matters

11. Some reasonable conclusions

  • Transmission capacity is growing at about the same rate as traffic
  • Magnetic storage is doubling each year
  • Streaming media traffic is unlikely to be a dominant factor
    • local store and replay will have a strong role

12. Flavours of Broadband Communications

  • Fibre optics
    • Fibre to the home?
  • DSL/Cable Modems
    • Data rates cost etc
  • Wireless
    • IEEE802.11
  • Mobile
    • 3G and beyond

13. What about Fibre to the Home?

  • For 25 years researchers and telcos have been talking about delivering fibre to the home
    • Currently connection costs to premises are $1500 for fibre and $200 for copper DSL (assuming large scale deployments)!
    • Fibre to the home is a long term goal but in the near and medium term DSL and developments thereof will be the main delivery mechanism for broadband services to the home.

14. What is Digital Subscriber Line?

  • DSL is a generic name for a group of technologies which transport data at high rates over the access part of the network.
  • DSLs are distinct from conventional modems in that the data is only transmitted as far as the local exchange.
  • The signal bandwidth greatly exceeds 4kHz
  • Based on secondary use of existing cables

15. DSL:The Access Network

  • Construction and Topology
  • Signal Degradation
  • Noise and Interference

NTE Street Cabinet orPCP Switch Overhead DP NTE Underground DP Exchange to flexibility point 1-3km Flexibility point to DP 0.5 to 1km DP to customers premises 50m Fibre optics is only In the core 16. Flavours of DSL

  • ADSL operates in 300kHz to 1.1MHz band
    • 1.5Mbits/s to 6Mbits/s downstream, 640kbits/s downstream
    • Always on (operates above baseband)
    • Single line 1Mb/s symmetric service
  • VDSL potentially operates up to 30MHz
    • 52Mbits/s@ 300m, 26Mbits/s@ 900m, 13Mbits/s@ 1.5km


  • Both ADSL and VDSL use DMT modulation(Discrete Multi-Tone)

18. DSL Bit rates vs Reach 19. 5.2 1,820,230 UK 10 10.9 2,170,243 Canada 9 8.3 2,280,000 Italy 8 21.4 2,800,000 Taiwan 7 9.6 3,262,700 France 6 8.4 4,500,000 Germany 5 27.7 6,435,955 South Korea 4 4.8 9,119,000 USA 3 14.4 10,272,052 Japan 2 5.1 10,950,000 China 1 DSL per 100 phone lines 31 December 2003 DSL Subscribers 31 December 2003 Country Global Ranking 20. 21.

  • Problem of crosstalk in the network
  • DSM = Dynamic Spectrum Management
    • Adapt transmit spectrum dynamically
    • Reduce crosstalk (=noise) for other users in the network.
    • DMT is very suited to apply DSM (flexible spectrum allocation)

Future enhancements to DSL Central Office User Modem User Modem Central Office 22. DSM principles 23. Wireless Technologies

  • WLAN
    • IEEE 802.11b and 802.11g standards transmit at 2.4 GHz, while those that comply with the 802.11a standard transmit at 5 GHz offering data rates of 11-54Mbits/s.
    • Limited range of around 30m with discontinuous coverage.
    • Frequency bands are unlicensed Interference!
  • Mobile
    • Operates between 1-2GHz in licensed bands
    • Moderate data rates around 64kbits/s
    • Extensive coverage and range

24. Wireless LAN and DSL

  • Wireless routers with an inbuilt ADSL modem are available for around 70
  • So wireless LAN avoids having to wire your house with CAT5 cable!

25. Wireless LAN:What is the underlying technology?

  • Orthogonal frequency division multiplexing (OFDM) is a communications technique that divides a communications channel into a number of equally spaced frequency bands. A subcarrier carrying a portion of the user information is transmitted in each band. Each subcarrier is independent of each other.
  • OFDM is the modulation technique for DSL, wireless LANs, Digital Audio Broadcast and Digital Video Broadcast systems and a candidate for future mobile systems.

Useri Userj Userk Userl Userm Subcarriers 1 2 3 4 5 N 26. The Future..

  • So what does the future hold..?

27. The Drivers VOICE (A) VOICE (D) MULTIMEDIA WIRELESS WORLD (WW) Digital - Quality - Security - Reliability - Capacity - Roaming Services - Mixed services - Capacity - Flexible billing - Personalisation Integrated WW - Mixed networks (WAN,WLAN,DVB,etc.) - IP based/connected - Ambient awareness - Ubiquity/flexibility - Always connected 1G 2G 3G B3G 28. B3G Design Challenges

  • Although 3G is an important first step, several basic issues still need to be addressed for next generation wireless systems:
    • Fast/reliable broadband radios (PHY/MAC) with QoS
      • ~100 Kbps 1-10 Mbps with adaptivity, link reliability & QoS
    • Scalable system capacity for mass-market services
      • high service penetration implies ~Gbps/Sq-Km