final docsis
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DOCSIS : DATA OVER CABLE SERVICE INTERFACE SPECIFICATIONS
International Standard developed by Cable Labs
A set of standards for sending data over cable and managing
the supporting equipment
It is used for transporting data over a cable (CATV) plantutilizing QAM &/ or QPSK RF Modulation.
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CableLabs is a non-profit research and development
consortium founded in 1988 by cable operatingcompanies.
It is dedicated to pursuing new cabletelecommunications technologies and to helping its
cable operator members integrate those technicaladvancements into their business objectives.
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1984: DICK LEGHORN (FATHER OF CableLabs)
Wrote a memorandum entitledAn R&D Entity for the CableIndustry?
(~1994 1998) 1st generation were
Proprietary systems
Lancity
Terayon
Motorola (1998 Present) 2nd generation moved to open standard
(DOCSIS)
Contributing companies include ARRIS, BigBand Networks,
Broadcom, Cisco, Conexant, Correlant, Harmonic, Intel, Motorola,Net ear, Tera on, and Texas Instruments
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Simplification to cable Technology.
Offers communication and operation support
Addition of High Speed data over existing cable Tv(CATV).
Employed by Cable operators over the existing Hybrid
Fiber Coaxial.
Multiple suppliers
85+ Vendors to date have received certification or
qualification
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DOCSIS 1.0 DOCSIS 1.1 DOCSIS 2.0 DOCSIS 3.0
March 1997 April 1999 Jan 2002 Aug 2007
Data
transmission was
asymmetric.
Improved
operational
flexibility.
Increased upstream
reliability and
throughput.
It provides
channel
bonding
- Improved
security.
- Support for
IPTV.
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Modem in the true sense of the word
Modulates and demodulates signals
It simply uses the increased bandwidth of the TV cable
instead of an ordinary phone line
Cable modem
Client device for providing 2 way communication(data,voice and video) over the ordinary cable TV networkcables
Downstream - Data flowing from the CMTS to the cablemodem
Upstream - Data flowing from the cable modem to theCMTS
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They typically have two connections
One to the cable wall outlet and the other to a PC
Online access via cable modems provides PC users faster
access to online information
Up to 1000 times faster than todays fastest telephone
modems
Cable modem speeds range from 500 Kbps (500,000 bitsper second) to 10 Mbps (10 million bits per second)
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Connect the Cable Modem to the TV outlet for your cableTV
The cable TV operator connects a Cable ModemTermination System (CMTS) at their end (the Head-End)
The CMTS is a central device for connecting thecable TV network to a data network like the Internet
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DOCSIS - Data Over Cable Service Interface Specification
The dominating cable modem spec that defines thetechnical specs for both the cable modem and the CMTS
Architecture Tuner, transceiver (modulator/demodulator), MAC, CPU,interface
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Tuner
Connects directly to the CATV outlet
Converts TV channel to a fixed lower frequency (6-40
MHz)
Normally a tuner with build-in diplexer is used, to provideboth upstream and downstream signals through the same
tuner
Must be of sufficiently good quality to be able to receivethe digitally modulated QAM signals
A new concept of a silicon tuner is in the works
Tuner on a chip
Expected to cut the cost down quite a bit compared toa more conventional tuner module
Companies (Sharp, Temic, Panasonic)
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Demodulator
Performs analog-to-digital (A/D)conversion,demodulation (QAM-64/256), Reed Solomon
error correction and MPEG frame synchronization
In the receive direction, the interface signal feeds a
demodulator
Companies
Broadcom, Conexant Systems, SGS Thomson, VLSITechnologies/Philips, LSI Logic, Fujitsu
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Burst modulator Performs Reed Solomon encoding, modulation(QPSK/16-QAM), frequency conversion, digital-to-analogconversion
In the transmit direction, a burst modulator feeds the tuner
The output signal is fed through a driver with variableoutput level, so the signal level can be adjusted tocompensate for the unknown cable loss
Companies
Broadcom, Conexant Systems, Analog Devices, SGSThomson
Combined demodulator and burst modulator chips are
also available
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MAC (Media Access Control) sub-layer in the networkstack (runs on both the cable modem and head-end)
Extracts data from MPEG frames, filters data, protocol
execution, times transmission of upstream bursts Sits between the receive and transmit paths
Can be implemented in hardware or split between
hardware and software
Assigns upstream frequency & data rate
Allocates time-slots (upstream bandwidth)
Requires CPU to handle MAC layer functions
Companies: Broadcom, Texas Instruments, Conexant
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Interface
Data passes through the MAC and goes into thecomputer interface of the cable modem
PCI bus, USB, Ethernet, HomePNA
CPU - microprocessor
Required for external cable modems
Single-chip cable modem are emerging
Combines the MAC, demodulator, burst modulator,CPU,Ethernet/HomePNA/PCI/USB interfaces
Additional parts such as memory, tuner, analog, powersupply will not be within the single-chip cable modem
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Cable Television Laboratories, Inc. 2005. All Rights Reserved. Proprietary/Confidential
22
CM
CM
CM
CM
CM
CM
CM
CM
Operator CoreBackbone
CMTS
CMTS
CMTS
Aggregation Network Access Network
CM
CM
OperatorAggregation
network
Core Network
Operator administered
New Services
Opportunities DOCSIS CableHome
Remote filesharing
Shared calendarUnifiedmessagingManagedservices
CM
HVAC controlFire sense & controlSecurityAir quality monitoringChild monitoring
Energy management, etc.
PacketCable
MPEG Services
IP Services
CPEHeadendBackend
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Cable ModemTermination System(CMTS) and Cable
Modem
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Transfer bi-directionaldata traffic betweenservice providers head
end(CMTS) and
customers cable modem CATV tree-and-branch
infrastructure provides
data conduit: fiber andcoax cables with
amplifiers -- hybrid-fiber/coax (HFC)
Wide BW and fast datarate for DS
Allocated BW and lower
data rate for US ascom ared to Euro e.
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IEEE 802.2 is the IEEE 802 standard defining Logical LinkControl (LLC), which is the upper portion of the data linklayer of the OSI Model.
The LLC sub-layer acts as an interface between the MediaAccess Control (MAC) sub layer and the network layer.
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Physical Medium Dependent : Generates electrical or opticalsignals depending on the nature of the physical mediumconnected.
In layer 1 of the (OSI) 7-layer internetworking model, PMDrepresents the part of the physical layer (PHY) that dictatesthe way bits are converted to physical signals, such as light inthe case of fiber.
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Medium Access Control, is a sublayer ofthe Data Link Layer.
It provides addressing and channelaccess for several terminals, typically alocal area network (LAN) or metropolitanarea network (MAN).
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Registration of CM into Network
Acquiring upstream and downstream channels and
encryption keys from the CMTS and an IP address from theISP.
CM also determines propagation time from the CMTS inorder to synchronize itself with the CMTS
Multiple handshakes between the CMTS and each CM
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The upstream channel is divided into a stream of timedivision multiplexed mini-slots contain from 8 to 32 bytesof data.
Each CM must learn its distance from the CMTS.
This is called ranging.
DATA RATE : 320 Kbps 10 Mbps
Bandwidth/ Channel : 2 MHz for a 3Mbps QPSK Channel
Frequency : 5-65 MHz
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188 byte MPEG frames
With 4 bytes of header and a 184 byte payload
Data rates 27-56 Mbps
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It is a telecommunications industry term for a broadband
network which combines optical fiber and coaxial cable.
It is employed globally by all Cable TV operators and itsInfrastructure is shown below.
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High Speed Internet Access.
Downstream traffic transfer rates between 27 and 36 Mbps
Upstream traffic transfer rates between 320 Kbps and 10Mbps (Average 5 Mbps)
But, because data over cable travels on a shared loop,individuals will see transfer rates drop as more users gainaccess.
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Support for multiple service flows per cable modem allowsa single modem to support a combination of video, voiceand data packets.
Dynamic service establishment to dynamicallycreate,modify and delete traffic flows.
Fragmentation allows fragmenting larger data packet.
Fragmentation and concatenation improve throughput.
Enhanced Security
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Upstream Capacity
Higher Modulation
Impairment Protection
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DOCSIS 3.0 provides the number of enhancements.
10 bonded 6 Mhz channels as spectrum allocation forDOCSIS 3.0
Downstream speed=171.52 Mbit/sec.
Upstream speed= 122.88 Mbit/sec.
Channel bonding.
Support for IPTV.
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DOCSIS 1.0 provides the cable industry-platform thedelivery of high-speed data on cable modems.
DOCSIS 1.1 provides high-quality digital voice, interactivegaming.
DOCSIS 2.0 increases upstream throughput resulting in anincrease in the capacity to deliver high-speed data.
DOCSIS 3.0 provides a platform for the evolution of thecable video business into IPTV.
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FEATURES DOCSIS 1.0/1.1 DOCSIS 2.0 DOCSIS 3.0
PHYSICAL LAYER CHANNEL
WIDTH
200 KHz 3.2
MHz
6.4 MHz 10 bonded 6
Mhz
MODULATION Downstream:
27-36 Mbps
(approx)
Upstream :10
Mbps (approx)
Downstream: 52
Mbps (approx)
Upstream :30
Mbps (approx)
Downstream:
170 Mbps
(approx)
Upstream
:120 Mbps
(approx)
MAC LAYER DETERMINISTIC
ACCESS
METHODS
TDMA TDMA & S-
CDMA
TDMA
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Request-Grant arbitration mechanism
CM makes requests to the CMTS
Requests can be made in Contention or as Piggybacks Contention is resolved using combination of Binaryexponential back off and Ack-Timer
Piggyback is a request for additional bandwidth sent in adata transmission
Only one unresolved request allowed per priority per CM
CMTS issues grants using a MAP message
CM transmits data during its Grant period
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Phase Shift Keying(PSK) changes the phase of the carrier instep with the digital message.
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For binary phase shift keying(BPSK) ,each symbol couldindicate two different states or one bit per symbol. In otherwords, 0=0 , 180=1.
QPSK adds two more phases: 90 and 270 degrees. Nowtwo symbols per bit can be transmitted. Each symbols
phase is compared relative to the previous symbol; so, ifthere is no phase shift (0 degrees), the bits 00 arerepresented. If there is a phase shift of 180 degrees, thebits 11 are represented.
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ASK and PSK can be combined to create QAM where
both the phase and amplitude are changed.
The receiver then receives this modulated signal, detectsthe shifts and demodulates the signal back into theoriginal data stream.
16-QAM, each symbol can now represent four bits insteadof just the two bits per symbol with QPSK.
Each point indicates a unique amplitude and phase ofthe wave (for example, point (1,1) indicates 90 degreesand amplitude of 1).
Table : Quadrature Phase Shift Keying
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The Goal of DOCSIS security
To provide CM users withdata privacy across theNetwork .
To provide cable operatorswith protection from theft ofservice .
To provide security to all ofthe CPE attached to theDOCSIS Network.
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Security of Data Transport Services .
Security of CPE devices, which use cable modems to attach
to public data networks.
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An Encapsulation Protocol
A Key Management protocol
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Frame Format for carrying encrypted packet data.
Data Encryption and Authentication Algorithms.
Rules for applying the Cryptographic Algorithms to aDOCSIS MAC frames packet data.
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FACTORS DOCSIS DSL
SPEED 2 TIMES FASTER THAN
DSL
1.5Mbps
COST CHEAPER (LOW COST OFCABLE MODEMS)
EXPENSIVE
SECURITY SECURITY BUNDLED IN
HARDWARE MODEM
PROVIDED
LESS SECURE
ON CONNECTION PRESENT PRESENT
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Superior performance, voice.
To provide real time digital video broadcast.
Incredible Speed.
Emerging markets get access to broadband
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Infrastructure Problems- ISPs
Present Stats :
25 Million Indian homes Cable TV(more than phone lines inthe country)
Total population : 1 billion
Estimated Phone Lines : 19.1 million
Estimated PCs : 3 million
Cable Operators :600,000
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