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Access Network Technologies
IS250
Spring 2010
[email protected]
Access Network Options




Copper: DSL, cable, power line (PLC/BPL)
Silicon: FTTH
Copper/Silicon Hybrid: HFC, FTTC
Wireless: WiFi, WiMax, cellular (2G, 3G),
satellite
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Local Loop
 The “last mile” or “first mile”: connection between
customer premise and central office (CO) of
telephone company
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POTS to PANS
 Originally for analog
POTS (plain old
telephone service)
 Also used for digital
service
QuickTime™ and a
decompressor
are needed to see this picture.
A Central Office
- Integrated Services Digital
Network (ISDN)
- Supports voice and data
- Digital Subscriber Line
(DSL)
- Several variants, e.g.,
ADSL, VDSL, SDSL, …
Location of CO’s in U.S.
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ADSL
 Asymmetric Digital
Subscriber Line
 Modulation
technique:
- DMT (discrete multitone)/OFDM (Orthogonal
Frequency Division
Multiplexing)
 Data rate as a
function of distance
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http://www.maxim-ic.com/images/appnotes/3638/3638Fig02.gif
Cable Plant
 Cable plant originally designed for one-way delivery of CATV
programming; upgraded to support two-way data communication
- Groups of subscribers in neighborhood share network
 Hybrid Fiber Coax (HFC):
- Optical fiber from cable headend to neighborhood concentration points
- Coax cable to subscriber premises
 Cable modem: uses FDM + TDM
Active
Node
Home
FROM
BROADCAST
SOURCES
Headend
Feeder (Fiber)
Drop Loop
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FTTx




Fiber-to-the-node (FTTN)
Fiber-to-the-curb (FTTC)
Fiber-to-the-building (FTTB)
Fiber-to-the-home (FTTH)
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WiFi Access Networks
 Different scales, different
economic models
- Wireless ISPs (e.g., Boingo)
- Municipal WiFi networks (e.g.,
Philadelphia, Taipei, Mountain View)
- Community mesh networks
- Private Access Points
 Interference between provider,
public and private APs an
unresolved issue
- WiFi operates in unlicensed spectrum
Source: http://www.wigle.net/
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Wi-Max (802.16)
 WMAN standard
supporting
point-to-multipoint
wireless broadband
access (WBA)
- Up to 30 miles range
- Up to 70 Mbps data rate
- 802.16e provides mobility support
http://en.wikipedia.org/wiki/Image:30WiMAX.gif
 Complements 802.11
 Competes against 3G/4G (cellular-based)
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Cellular Communications

1st generation (1G): analog,
circuit switched, voice

2nd generation (2G): digital,
circuit switched, voice

2½ generation (2.5G): digital,
packet switched, voice and
narrowband data

3rd generation (3G): digital,
packet switched, voice and
broadband data

4th generation (4G): “beyond
3G”
Source: Rappaport, Wireless Communications, Prentice Hall
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Cellular Communications
Mobile switching center
Public switched telephone network
Source: Rappaport, Wireless Communications, Prentice Hall
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Frequency Reuse
 Cells with same letter use
the same set of frequencies
 Cell cluster (outlined in
bold) replicated over
coverage area
 Example: cell cluster size,
N=7
 Frequency reuse factor =
1/N
Source: Rappaport, Wireless Communications, Prentice Hall
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Cell Splitting
 Cell splitting allows
channels to be
added with no new
spectrum usage
 Note: vertices are
locations of cell
towers
Source: Rappaport, Wireless Communications, Prentice Hall
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Call Handoff
 Calls need to be seamlessly handed off from one base
station to another to support mobility
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Umbrella Cells
 Supporting users with different mobility
rates
Source: Rappaport, Wireless Communications, Prentice Hall
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Local Loop Economics
 Cost to deploy new wire: ~$1000 per home
- Depends on population density (higher in rural areas)
- Example: Verizon FiOS $23B for 18 mil homes
- Cost per subscriber is higher
 Number of households in U.S.: 100 million
 Total cost: at least $100 Billion
 Wireless:
- AT&T wireless capital investment $20B in 2010
- Number of wireless subscribers 85Mil
- Wireless revenue $50B
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