Access Network Technologies

IS250Spring 2010

chuang@ischool.berkeley.edu

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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- Integrated Services Digital Network (ISDN)- Supports voice and data

- Digital Subscriber Line (DSL)- Several variants, e.g., ADSL, VDSL, SDSL, …

QuickTime™ and a decompressor

are needed to see this picture.

Location of CO’s in U.S.

A Central Office

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ADSL

Asymmetric Digital Subscriber Line

Modulation technique: - DMT (discrete multi-tone)/OFDM (Orthogonal Frequency Division Multiplexing)

Data rate as a function of distance

http://www.maxim-ic.com/images/appnotes/3638/3638Fig02.gif

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Cable Plant

Headend

Home

Drop Loop

Node

Feeder (Fiber)

Active

FROMBROADCASTSOURCES

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

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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

Complements 802.11 Competes against 3G/4G (cellular-based)

http://en.wikipedia.org/wiki/Image:30WiMAX.gif

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Cellular Communications

Source: Rappaport, Wireless Communications, Prentice Hall

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”

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Cellular Communications

Source: Rappaport, Wireless Communications, Prentice Hall

Mobile switching center Public switched telephone network

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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