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Broadband Overview
1
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Why Broadband?
High-speed Access
Rich Voice and Video Services
Always On
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Cable Options
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DSL Options
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Cable Technology
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What IsCable?
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How a Cable System Works
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How a Cable System Works (Cont.)
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Cable Modem?
Traditional dial-up modems provide online accessthrough the public telephone network at up to 56 kbps .Acable modem, on the other hand, gives users high-speedInternet access through a cable TV network at more than1 mbps about 20 times faster.
When a cable modem unit is installed next to yourcomputer, a splitter also is placed on the side of yourhousehold. It separates the coaxial cable line serving thecable modem from the line that serves your TV sets. A
separate coaxial cable line is then run from the splitter tothe cable modem.
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Cable Modem?
Cable modems typically connect to computersthrough a standard 10Base-T Ethernet interface.
"Category 5 cabling," is run from the cablemodem to an Ethernet card in the computer.
Cable modem termination system (CMTS),located at the local cable operator's networkhub, controls access to cable modems on thenetwork. Traffic is routed from the CMTS to thebackbone of a cable Internet service provider(ISP), such as Road Runner, which, in turn,
connects to the Internet.
With newer cable modem systems, all trafficfrom the CMTS to the cable modem is encryptedto ensure privacy and security for users.
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What is inside a Cable Modem?
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DOCSIS
Data over cable service interface specification.
Definestechnical specification for equipment atCPE and CO
Version 1.0, 1.1 and Current is 2.0
Managed byCable labs,founded in 1998
Most vendors currently use version 1.1
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DOCSIS components & Architecture
Cable Modem Termination System (CMTS).
Device that modulatesthe signal to the CM and demodulate
the CM response.CMTS resides in head end.
Cable Modem (CM)
Device thatterminates as well asperforms modulation and
demodulation ofsignalsto and from CMTS
Back office services.
Service such as TFTP for configuration file.DHCP for
dynamic ip assignment
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Cable System Components
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Hybrid Fiber-Coaxial Architecture
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Digital Signals overRF Channels
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Digital Singals overRF Channels(Cont.)
Data-over-Cable Service Interface Specification (DOCSIS)
RF interface specification of minimum recommended technical
performance requirements for data
Cable modem termination system (CMTS) and cable modem (CM)vendors mustpass certification
CableLabstests and grants (or withholds)DOCSIS Certified orQualified status
Cable operatorspurchase certified/qualified equipmentto ensureinteroperability with vendors
A variation isEuro-DOCSIS standardsthat use 7 MHz and 8 MHz forcable plants
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Identifying Cable Technology Terms
Basic Cable Terms
Broadband CATV: Originally community antenna television
Coaxial cable
Headend
Downstream (DS)
Upstream (US)
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Identifying Cable Technology Terms(Cont.)
Carrier orRF carrier
Spectrum reuse
FDM: Frequency-division multiplexing
QPSKQuadrature phase shift keying
QAMQuadrature amplitude modulation
Carrier-to-noise: C/N (also CNR)
Signal-to-noise: S/N (also SNR)
Ingress noise
FEC: Forward error correction
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Satellite Options
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Types ofsatellite Orbits.
GEO.
Fixed over earthssurface because it completes an
orbit every 24 hrs.The Altitude to achieve this orbit is
35,800km.
LEO
Circular orbit at an altitude lessthan 2000 km above the
surface of earth.
MEO
circular orbit at an altitude of 10000km
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Wireless Options
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Wireless LAN Standards
IEEE 802.11 :
Define rules for communication in a wireless LAN
Standard that specifies the slowest data transferrates in both RF and light-based transmissiontechnology
IEEE 802.11b :
Faster data transfer data rate and a more restrictivescope of transmission technology.
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Wireless LAN Standards
IEEE 802.11a :
Faster data transferthan (backwards compatibility with)
IEEE 802.11b, uses 5 GHz
IEEE 802.11g :
Standard that describes data transfer rates equally as fastas IEEE 802.11a and boaststhe backward compatibilityto
IEEE 802.11b req.to make inexpensive upgrade
Offer 54Mbps data transfer rate.
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AccessPoints
onlythe basic wirelessPC card,the accesspoint, orAP, isprobablythe most common wireless LAN devicewith whichyou will work as a wireless LAN administrator
Provide clients with a point or access into a network.
An accesspoint is a half-duplex device with intelligenceequivalentto that of a sophisticated Ethernet Switch
Fig. 1 shows an example of an access-point and fig. 2
illustrates where the accesspoint is used on a wirelessLAN
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AccessPoint Modes
There are 3 modes in which an accesspoint canbe configured:
Root Mode
Repeater Mode
Bridge Mode
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In bridge mode, accesspoints act exactly like wirelessbridge.
In fig.that clients do not association to bridges, but
rather, bridges are used to link two or more wiredsegmentstogether wirelessly.
Bridge Mode
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In repeater mode, accesspointhave the abilityto provide awireless upstream link into the wired network ratherthan thenormal wired link.
Using an accesspoint in repeater mode is notsuggested unlessabsolutely necessary because cells around each accesspoint inthisscenario must overlap by a minimum of 50%.
Repeater Mode
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Putting Cable Technology AllTogether
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Process forProvisioning a CableModem
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A cable modem can provide upto 90timesthe
speed of a dial-up connection.
DSL usesthe unused bandwidth on a phoneline to deliver fast digital data transmission.
Satellite delivers downstream data in bursts up
to 400 kbps, with upstream speeds of upto 125
kbps.
Wirelessprovides bridging at 2 Mbps
throughput at distances of upto 25 miles.
Summary
