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Introduction

Surfing the World Wide Web typically of-

fers residential Internet users a click-and-

wait experience rather than an interactive

extravaganza. Because connection speeds are

typically limited to 53 kbit/s or less, frus-

trated residential online users are demand-

ing higher-speed connections. However, in

spite of the slow narrowband speeds cur-

rently available through existing dial-up

telephone modem connections, residential

Internet and online usage continues to grow

rapidly.

Local service providers currently offer res-

idential ISDN services that provide connec-

tion speeds up to 128 kbit/s. To offer down-

stream speeds in excess of 1.5 Mbit/s, ser-

vice providers will have to look to alterna-

tive solutions, such as digital subscriber line

(DSL) technologies, faster downstream data

connections from direct broadcast satellite

(DBS), fixed wireless access, and high-speed

cable modems.

Broadband coaxial cable passes by more

than 105 million homes in North America,

and more than 75 million of these subscribe

to cable TV. Coaxial cable connections offer

nearly universal coverage and a powerful

platform for providing high-speed data ac-

cess to residences and small businesses.

However, to support advanced communica-

tions services, one-way cable television sys-

tems must be upgraded into modern two-

way networks. This is a technically complex

and capital-intensive proposition.

Cable systems were originally designed to

deliver broadcast television signals effi-

ciently to subscribers’ homes. To ensure that

consumers obtain cable service via the same

TV sets with which they receive over-the-

air broadcast TV signals, cable operators

recreate a portion of the over-the-air radio

frequency (RF) spectrum within a sealed

coaxial cable line or CATV network de-

signed and used for cable TV distribution.

The system must be upgraded with

bidirectional amplifiers in the cable-

distribution or CATV network before sig-

nals can flow in two directions. Most CATV

networks are a hybrid of fiber and coaxial ca-

bles. Signals are passed through fiberoptic

cables from the head-end center to locations

near the subscriber. The signals are then

transmitted in coaxial cables that run to the

subscriber premises. Higher-frequency sig-

nals flow toward the subscriber and lower-

frequency signals flow toward the broad-

casting head-end.

Cable plant architecture

Several elements are required to bring high-

speed data over cable (Figure 1). A cable

plant consists of a hub or ring of hubs. In a

typical cable plant, one or more of these hub

facilities serve as the collection points. The

head-end hub gathers television signals

from various sources—primarily satellite

TV transponders. The TV signals are picked

up, decoded, and down-converted to select-

ed channels. These channels are then com-

bined into a local fiberoptic network for

local distribution or placed on a higher-

capacity optical network between the re-

gional hubs. One or more of these hubs also

serve as the main interface to the Internet

and are tied to it via high-speed optical

links.

Each hub has a head-end that uses small-

er fiber bundles to distribute the television

Ericsson Review No. 1, 2001

Cable modems—Broadband highway to the home

Juan Figueroa and Bill Guzek

Cable operators are eyeing a huge business opportunity in providing resi-

dential customers with high-speed Internet access. The market for cable

modems is expected to increase dramatically over the next few years.

This increase will be the result of rising user demands for access to the

services and capabilities made possible by greater speed, such as high-

quality voice, video on demand, and a variety of entertainment services.

The authors describe the technology of using cable plants to bring

high-speed Internet access into the home.

ADC Analog-to-digital converter

ARP Address resolution protocol

ATM Asynchronous transfer mode

BER Bit error rate

BPI Baseline privacy

Cable net- Refers to the cable television plant

work that would typically be used for

data-over-cable services.

CATV Cable TV

CM Cable modem

CMCI Cable modem-to-CPE interface

CMTS Cable modem termination system

CPE Customer premises equipment

DBS Direct broadcast satellite

DHCP Dynamic host configuration protocol

DOCSIS Data-over-cable service interface

specification

DSL Digital subscriber line

DSP Digital signal processor

FEC Forward error correction

Head-end Central distribution point for a CATV

system

HFC Hybrid fiber-coaxial

ICMP Internet control message protocol

IEEE Institute of Electrical and

Electronics Engineers

IF Intermediate frequency

IP Internet protocol

ISDN Integrated service digital network

ISP Internet service provider

LAN Local area network

LLC Logical link control

MAC Media access control

MCNS Multimedia Cable Network System

Partners Ltd.

MSO Multiservice operator

NAT Network address translation

NSI Network-side interface

OSI Open systems interconnection

PC Personal computer

PDU Packet data unit

QAM Quadrature amplitude modulation

QoS Quality of service

QPSK Quadrature phase-shift keying

RF Radio frequency

RFC Request for comments

RFI RF interface

RISC Reduced instruction set computing

SID Service ID

SNAP Subnetwork access protocol

SNMP Simple network management protocol

SU Subscriber unit

TFTP Trivial file transfer protocol

UDP User datagram protocol

USB Universal serial bus

VoIP Voice over IP

BOX A, TERMS AND ABBREVIATIONS

1 2 3 4 5 6 ... 11 12

Resumo do Conteúdo

Página 1 - Cable plant architecture

IntroductionSurfing the World Wide Web typically of-fers residential Internet users a click-and-wait experience rather than an interactiveextravaganza

Página 2 - Figure 1

Ericsson Review No. 1, 200141Signals from various sources, includingbroadcast transmissions, satellite-deliveredprogramming, and local television broa

Página 3 - The cable modem

IP traffic, can be seamlessly delivered to end-users over the cable modem platform. StandardizationIn the US, cable operators formed a consor-tium cal

Página 4 - Cable modem

Ericsson Review No. 1, 200143Some of the enhancements are • configuration and registration for cable-modem-based QoS;• fragmentation of upstream packe

Página 5 - Cable modem details

Ericsson Review No. 1, 200133signal to smaller local distribution ampli-fiers. The fiber is then terminated and thesignal is converted back into elect

Página 6 - Operation

comparison of DOCSIS and Euro-DOCSIS,see Tables 1, 2 and 3).The cable modemtermination systemA CATV network consists of six major parts:• a cable mode

Página 7 - Generic frame format

Ericsson Review No. 1, 200135system with 400 MHz of downstream band-width can carry the equivalent of 50 to 60analog TV channels, and a modern hybridf

Página 8 - Upstream traffic

Depending on the network architectureand traffic load, an individual subscribermight experience access speeds from 500 kbit/s to 1.5 Mbit/s or more. C

Página 9 - Basic operation of the

Ericsson Review No. 1, 200137tention- and reservation-based transmissionopportunities. Each cable modem has aunique 48-bit MAC address that is used fo

Página 10 - Figure 14

The time-division multiple access (TDMA)transmissions from cable modems at variousdistances from the head-end must be coor-dinated so that all transmi

Página 11 - Standardization

Ericsson Review No. 1, 200139comes operational. The CMTS must autho-rize the cable modem before it can send traf-fic into the network.Each cable modem

Página 12 - Conclusion

In the upstream direction, the digital sig-nal is encoded to QPSK or 16 QAM, con-verted into an analog signal, and sent to thetuner for transmission i

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Ericsson HM200c/HM201c Manual do Utilizador

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