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8/7/2019 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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Documents

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