Evolution of Access Networks

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Evolution of Access Networks

• kramer_at_cs.ucdavis.edu

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

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Access Network Technologies

• Dial-up
• ISDN
• T1/E1
• DSL
• Cable
• What is next?

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Analog Dial-up line

• 2.4 / 4.8 / 9.6 / 14.4 / 28.8 / 56 Kbps
• Uses one voice channel (64 Kbps) to reach ISPs
  modem across telephone network
• Analog from user to Central office, then digital
  (DS0)
• Actual speed depends on distance
• Charged per minute

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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

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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)

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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.

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Cable Modem

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

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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

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Point-to-Point vs. PON
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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

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PON topologies
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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

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Single-Fiber PON

• Use 2 wavelength, but save fiber (repair and
  maintenance)
• Use TDM in the upstream to avoid collisions

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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

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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
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IPACT Dynamic Bandwidth Allocation Scheme
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SBA vs. DBA
IPACT Interleaved Polling with Adaptive Cycle
Time (Photonic Network Communications, vol. 4,
no. 1, January 2002)
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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 -gt 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

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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