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Evolution of Access Networks

Evolution of Access Networks

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Evolution of Access Networks

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  1. Evolution of Access Networks kramer@cs.ucdavis.edu

  2. What is Wide Area Network (WAN)? MCI Network http://www1.worldcom.com/global/about/network/maps/northam/

  3. What is Metropolitan Area Network (MAN)? Metromedia Fiber Network, Inc. San Francisco Bay Area MAN (dark fiber) http://www.mfn.com/network/map_bayarea.shtm

  4. What is Access Network? • Access network in Davis (imaginary) • Connects Central Office to end customers (subscribers) • Also called subscriber network, “last mile”/”first mile”, local loop

  5. Access Network Technologies • Dial-up • ISDN • T1/E1 • DSL • Cable • What is next?

  6. Analog Dial-up line • 2.4 / 4.8 / 9.6 / 14.4 / 28.8 / 56 Kbps • Uses one voice channel (64 Kbps) to reach ISP’s modem across telephone network • Analog from user to Central office, then digital (DS0) • Actual speed depends on distance • Charged per minute

  7. Integrated Services Digital Network (ISDN) • 2 bearer channels (B channels) – 64 Kbps each. B channel can be used for voice or data • 1 data channel (16 Kbps) for signaling. • Total 144 Kbps. • Digital all the way. • Charged per minute

  8. T1/E1 • T1 – 24 D0 channels (1.544 Mbps) • E1 used in Europe (30 D0 channels) • Uses 4 wires and customer switching unit (CSU) • Must be provisioned be network operator (very difficult and expensive) • Permanent circuit! (always on)

  9. Digital Subscriber Line (DSL) • Uses one twisted pair for voice and data (different frequency) • Data rates from 144 Kbps to 1.5 Mbps (depends on distance and line quality) • Distance limited to 18000 ft (5.5km). In most cases is not available if distance from CO exceeds 12000 ft.

  10. Cable Modem • Tree-like cable network • Serves many subscribers (~2000) • Requires cable modem and CM terminating system (CMTS) • Always on

  11. Fiber-to-the-Home/Business (FTTH/B) • Fiber constantly reaching deeper into the subscriber area • Remote DSLAMs use fiber feeds • CATV uses fiber from head end to remote nodes (HFC architecture) • Next generation of access networks will bring fiber all the way to the customer

  12. Point-to-Point vs. PON

  13. Passive couplers • Fused fiber or waveguide technology • NxN coupler created by combining multiple 2x2 couplers • Splitter: coupler with only one input used • Combiner: coupler with only one output used

  14. PON topologies

  15. WDM vs. TDM PON • Non-traditional connectivity • Downstream: broadcast • Upstream: Point-to-point, but collisions possible • Upstream channels must be separated • WDM • each ONU must have different  • OLT must have a receiver array • TDM • Receiver and electronics run at higher speed • time synchronization

  16. Single-Fiber PON • Use 2 wavelength, but save fiber (repair and maintenance) • Use TDM in the upstream to avoid collisions

  17. ATM Passive Optical Network (APON) • Uses ATM cells to carry data traffic • Full Service Access Networks (FSAN) Initiative - 1995 • Too expensive • Too complicated • Less efficient (than Ethernet) • Example: For 44-byte IP datagram, Ethernet will use 64-byte frame + 8-byte preamble + 12-byte IFG = 84 bytesATM will add 12-byte AAL5 and will use 2 cells = 106 bytes • For tri-modal packet distribution (CAIDA.org) cell tax is 13%

  18. Ethernet Passive Optical Network (EPON) • Use Ethernet frames to carry the data • Static bandwidth allocation (SBA) – each user gets fixed slot size • Dynamic bandwidth allocation (DBA) – slot size depends on queue length(request/grant scheme) Downstream traffic Upstream traffic

  19. IPACT – Dynamic Bandwidth Allocation Scheme

  20. SBA vs. DBA IPACT: Interleaved Polling with Adaptive Cycle Time (Photonic Network Communications, vol. 4, no. 1, January 2002)

  21. Upgrade scenarios • Wavelength upgrade • Move premium ONUs to separate wavelengths • Less ONUs per  = more bandwidth per ONU • Inventory problem (ONUs are different) • Receiver array in OLT • Rate upgrade • Increase rate of EPON (1 Gbps -> 10 Gbps) • OLT should receive new rate (from premium ONUs) and old rates (from non-premium ONUs) • Dispersion penalties affect maximum distance • Spatial upgrade • Split 32-user EPON into two 16-user EPONs • Deploy multiple trunks or splitter in the CO • Eventually becomes point-to-point topology

  22. Conclusion • Advantages of PON • Allows longer distances between CO and customer premises. • Minimizes fiber deployment • Provides higher bandwidth • Allows downstream video broadcasting. • Eliminates multiplexers and demultiplexers in the field • Transparent. Easy upgrades to higher bit rates or additional wavelengths