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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
2
Local Loop
The “last mile” or “first mile”: connection between
customer premise and central office (CO) of
telephone company
3
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.
4
ADSL
Asymmetric Digital
Subscriber Line
Modulation
technique:
- DMT (discrete multitone)/OFDM (Orthogonal
Frequency Division
Multiplexing)
Data rate as a
function of distance
5
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
6
FTTx
Fiber-to-the-node (FTTN)
Fiber-to-the-curb (FTTC)
Fiber-to-the-building (FTTB)
Fiber-to-the-home (FTTH)
7
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/
8
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)
9
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
12
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
13
Call Handoff
Calls need to be seamlessly handed off from one base
station to another to support mobility
14
Umbrella Cells
Supporting users with different mobility
rates
Source: Rappaport, Wireless Communications, Prentice Hall
15
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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