Cable Basics

Week 14

ICS 620

CABLE BASICS

ICS 620

Week 14

Overview — Cable TV Systems

• History

• Two-Way vs. Broadcast

• HFC – Digital Systems

History

• 1948

• Rebroadcast of basic TV channels

• Premium Channels (HBO)

• Pay per View (WWF, Rock Concerts)• Local Origination (PEG Channels)

• Data (ISP; IP telephony; IP video))

Frequency Allocation

Cable TV Frequencies

Cable TV Frequency Allocation

5 - 50 MHz Sub band Upstream Cable

54 - 88 MHz VHF-Lo Ch. 2 – 6

88 – 108 MHz FM Radio FM radio

90 – 174 MHz Mid band Downstream Cable

174 – 216 MHz VHF-Hi Ch. 7-13

216 – 300 MHz Super band Downstream Cable

300 – 1002 MHz Hyper band Downstream Cable

470 - 806 MHz UHF Ch. 14-69

Cable System Architecture• Antenna Systems

•Off-air; microwave, satellite

•Headend•Signal reception, processing and conditioning, scrambling (analog) or encryption (digital)

• Distribution Plant•Amplifiers, Traps, Trunk, Feeder, Multi-taps and Drop

• Subscriber Equipment – “The Box”•De-scrambling or de-encryption

Cable TV Tower

Cable System

CATV Headend

Analog CATV Headend

Spectrum Allocation with Sub band Reverse

Basic Coaxial CATV System

CATV Distribution Map

Strand Map

Distribution Cables

Trunk Lines - 3/4” to 1” in diameter

Feeder Lines - 1/2” in diameter

Drop Lines - 1/4” in diameter

Trunk Amplifiers - Every 2000 feet

Bridger Amplifiers - Every .35 to .5 miles

Coaxial Cable Signal Loss

The principal negative of coaxial cable is its relatively high loss over distance. Coaxial cable signal loss is a function of its diameter, dielectric construction, temperature, and operating frequency. A ballpark figure is 1 dB of loss per 100 feet.

Coaxial Cable Signal Loss

Ch. 2

Ch. 13

Coaxial Cable Signal LossExample

The logarithm of the attenuation of cable (in dB) varies with the square root of the frequency. The attenuation at 216 MHz (Ch. 13) is twice that of 54 MHz (Ch. 2) since the frequency is four times as great. Thus, if Ch. 2 is attenuated 10 dB in 1,000 feet, Ch. 13 will be attenuated 20 dB.

Two-Way vs. One-Way

• Splits (sub band v. mid band)

• Change in perspective by user

– New services

• Digitization

CATV Multiplexing

t1 t2 t3 t4

f2

f1

FREQUENCY

TIME

Time Division Multiplexing

Feeder Network

CATV Trunk Station

CATV Trunk Station

Code Operated Switch

Two Way Distribution Network

Subscriber Pedestal

Multi-Tap

CATV Set-Top Box

Problems with Broadband Tree and Branch

• Most Cost Effective with Broadcast• Limited Serving Area

– Amplifier Cascades Limit Performance– Serial String Reliability

• Serving Area Shrinks as Bandwidth Increases• Reliability of Local Powering• Security (traps; scrambling)

BREAK

10- minute break

Modern Cable Plant Architecture

Hybrid Fiber Coax (HFC)

Analog Headend with AM Fiber

AM Fiber to the Bridger

From Analog to Digital

1989 (General Dynamics)

MPEG Compression

10 channels of video in the 6 MHz bandwidth

Amplifier cascades reduced from 30+ to six or fewer.

Given 550 MHz of bandwidth, nearly 1,000 channels of digital video are possible.

Today’s Typical CATV System

• Fiber/Coax Fiber to the Bridger Architecture

• Serving Nodes 500 - 2000 House holds passed

• Downstream Bandwidths 550 - 750MHz, a few 1GHz - Actives– Most use or consider 1GHz passives and spacing of

apparatus. The media is capable of transmitting frequencies up to 3 GHz.

• Upstream Capability in 5 - 50 MHz band– Some systems have High reverse

Fiber Optics

Fiber Optic

Total Internal Reflection

CATV Fiber Network

CATV Digital Headend

Digital CATV Spectrum Allocation(ANSI/EIA-542-1997)

Analog Channels: Ch. 2-78 55 MHz to 547 MHz

Digital Channels: Ch. 79-136 553 MHz to 865 MHz

Digital CATV Spectrum Allocation

Fiber in the CATV Network

• Fiber Optic will increase quality, reliability, and operational savings.

• Fiber Optic is economically competitive in comparison with coaxial cable.

• Fiber Optic offers the opportunity of two-way services, fact that will increment revenues for the company.

• Fiber Optic networks are fully expandable, with large capacities to provide countless services.

What about data?

Inside the Cable Modem

• Tuner

• Demodulator

• Modulator

• Media Access Control (MAC) device

• Microprocessor

Cable ModemsWhat’s Inside?

DOCSIS

Developed by Cable Labs and approved

by the ITU in March 1998, Data Over

Cable Service Interface Specification

defines interface standards for cable

modems and support equipment.

Cable Modems

DOCSIS specifies downstream traffic

rates between 27 and 36 Mbps over RF

paths in the 50 MHZ to 750 MHz range,

and upstream traffic at between 320 Kbps

and 10 Mbps over an RF path between 5

and 42 MHz.

Cable ModemsWhat is Downstream?

•What the Cable Modem receives

•Frequency 50-750 MHz

•Bandwidth 6 MHz (USA); or 8 MHz (EU)

•Modulation 64-QAM (or 256 QAM)

•Data-rate 27-56 Mbit/s (4-7 Mbyte/s)

•Continuous stream of data

•Received by all modems

Cable ModemsWhat is Upstream?

•What the Cable Modem transmits

•Frequency 5-42 MHz (5-42 MHz)

•Bandwidth e.g., 2 MHz

•Modulation QPSK or 16-QAM

•Data-rate e.g., 3 Mbit/s (~400 KB/s)

•Transmit bursts of data in timeslots (TDM)

•Reserved and contention timeslots

What does Cable Modem mean?

• “CABLE” is short for Cable TV (CATV) Network

• “MODEM” is MOdulator-DEModulator

• Actually more like a network adapter than a modem

CMTS (Head-End)

Upstream DemodulatorQPS K/16-QAMF: 5-65 MHz BW: eg 2 MHzRate: eg. 3 Mbit/s

Downstream Modulator64-QAM/256-QAMf:65-850 MHz BW: 6/8 MHzRate: 27-56 Mbit/s

Cable Modem

Upstream ModulatorQPS K/16-QAMF: 5-65 MHz BW: eg 2 MHzRate: eg. 3 Mbit/s

Downstream Demodulator64-QAM/256-QAMf:65-850 MHz BW: 6/8 MHzRate: 27-56 Mbit/s

What is a CMTS?

A CMTS is a Cable Modem Termination

System, or router, which is a device located

in the cable head-end that allows cable

television operators to offer high-speed

Internet access to home computers.

CMTSThe Cable Modem Termination System

Cable’s Future

• Integrated Carrier (Voice, Data, Video)

• High Bandwidth (Ultra Wideband)

• HDTV (Next Week)

• IP Telephone (VoIP)

• PCS Provider (Wireless)

Ultra Wideband

Previously classified military technology, Ultra Wideband radio broadcasts digital pulses that are timed very precisely, on a signal occupying a very wide spectrum at the same time. UWB can peacefully co-exist with broadband cable technology without interference.

Ultra Wideband

Ultra Wideband

Experiments have achieved 1.2 Gb/s downstream and 120 Mb/s upstream per node. UWB technology could easily double the capacity of existing copper or hybrid fiber-coax systems today.

Ultra Wideband

UWB signals are injected into existing cable systems. Because these pulse code transmissions are very low amplitude, the signals ride below but do not interfere with existing digital or analog cable signals. A typical 500 MHz UWB signal can easily propagate throughout a cable TV network, both copper and hybrid fiber-coax.

UWB in Cable TV

Ultra Wideband

Voice over IP (VoIP)

VoIP Business Case

VoIP Models

Video Phones

Questions

and

Answers