7326144 wk14 cable basics
TRANSCRIPT
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