Access and Interconnection Technologies. Overview Two important Internet facilities – Access technologies used to connect individual residences and businesses.

Access and Interconnection Technologies

Overview

• Two important Internet facilities– Access technologies used to connect individual

residences and businesses to the ISP (last mile)• ADSL, Cable Modem, Hybrid Fiber Coax, Wireless

– High-Capacity Connections at the Internet Core

• Telecommunication-based networking technologies– Know the jargons

Upstream and Downstream • Internet access through an Internet Service Provider (ISP) – An asymmetric pattern

• Downstream: data traveling from an ISP– E.g., a streamed movie

• Upstream: data traveling to an ISP– E.g., upload personal photo

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Narrowband and Broadband

• Two broad categories on data services based on data rate – Narrowband: up to 128 kbps– Broadband: about > 1 Mbps

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Local Loop

• Local loop– Physical connection between a telephone

company Central Office (CO) and a subscriber– Twisted pair connections– Dialup call: 4 kHz of bandwidth– Potential bandwidth: about 1MHz

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Digital Subscriber Line (DSL)• DSL– High-speed data communication services over a local

loop

AT&T U-Verse , Verizon FiOS, CenturyLink

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ADSL• ADSL is the most widely deployed variant.– May not be so soon.

• ADSL uses FDM to divide the bandwidth of the local loop into three regions– POTS: Plain Old Telephone Service– Two regions provide data communication

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Local Loop Characteristics and Adaptation

• ADSL technology is complex – No two local loops have identical electrical characteristics

• FDM is implemented by dividing the bandwidth into 286 separate frequencies– 255 sub-channels allocated for downstream data transmission– 31 allocated for upstream data transmission– Not using the bandwidth below 26 kHz.

• ADSL is adaptive– Negotiation between two ends regarding data rate.

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Data Rate of ADSL • ADSL does not guarantee a data rate– do as well as line conditions allow

• Downstream rate: up to 8.448 Mbps– Depends on how far away from the central office or local

offices.

• Upstream rate: up to 640 kbps– Network control channel: 64 kbps– Effective upstream rate for user data: 576 kbps

• ADSL2 is better.– Downstream: close to 20 Mbps

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ADSL Splitters • An FDM device to divide bandwidth – Low frequencies to phone– High frequencies to modem– Passive: require no power.– Installed locally.

Compare ADSL with Other DSLs

• SDSL– Equal downstream and upstream

• HDSL– Addressing the distance problem of ADSL.

• VDSL/VDSL2– FiOS and U-Verse– No longer limited to copper wires.– DSL: only means that the service still relies on the

phone infrastructures.

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Cable Modem • High bandwidth & less susceptible to

electromagnetic interference than twisted pair.

• Use FDM to deliver TV signals over coaxial cable– 6 MHz per channel– Shared by all users.

• From 55MHz (Channel 2) to 1GHz (Channel 158)

– Internet services consume the bandwidth of one channel

Digital TV

• Still use the channel frequencies of analog channels.

• Why are there more than 150 channels?– Compression: more efficient use of frequency

resources.

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Data Rate of Cable Modems• In theory– Downstream: 52 Mbps– Upstream: 512 kbps upstream

• In practice, the rate can be much less– Shared among a set of N subscribers via statistical

multiplexing• About 44 Mbps at my home at 1am Saturday morning

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Cable Modem Installation

• Attach to the cable wiring directly– FDM hardware guarantees that data and

entertainment channels will not interfere with one another

Hybrid Fiber Coax

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• A combination of optical fibers and coaxial cables– Optical fibers: higher speed connection to central

facilities– Cables: lower speed connection to subscribes

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Access Technologies With Optical Fiber

From Wikipedia

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FiOS: FTTP Service by Verizon

• FiOS: Fiber Optic Service– 3-in-1: Internet, TV and phone service

• TV: 200 channels, including high-definition• FiOS Internet: up to 50 Mbps downstream and up to 5 Mbps upstream

• Three wavelength bands– One for TV– Two for data: one upstream and one downstream

• Phone service is just like regular phone service, but uses fiber.

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Installation of FiOS

• Requires new equipment outside and inside a premise.– http://www.bricklin.com/fiosinstall.htm

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Cable Modem VS. DSL

• Speed– Usually cable modem is better than DSL.– FiOS and U-Verse have changed the game.

• Availability– In US, cable is more popular. – Outside US, DSLs dominate.

• Installation– Cable model and regular DSL are simple– VDSL, HDSL are more complicated

High-Capacity Connections

• What if a company needs more bandwidth, say 10 Gbps?– A point-to-point digital circuit leased from carriers.

Wired networking still faces problems

• Remote farms and villages– No cable services

• Outdated wires and equipment– impossible to use high frequencies on telephone lines

that contain loading coils, bridge taps, or repeaters

Wireless Access Technologies • Wireless from cellular service providers– 3G or 4G

• Wifi– Different versions

• a/b/g/n/ac• 2.4G, 3.7G, 5G

– Municipal wifi• Challenges in finance and policy

– Google Loon Project• http://www.google.com/loon/

• Satellite– Long-delay is problematic