Data Over Cable & DOCSISData Over Cable & DOCSIS

Tom BahnckTom Bahnck

Cable Architecture

Cable Implementation

Cable vs. DSL

Cable Modems

Cable Television Laboratories

DOCSIS System Scope

DOCSIS/CableLabs Certified Cable Modems protocol

Cable Architecture

Cable Implementation

Cable vs. DSL

Cable Modems

Cable Television Laboratories

DOCSIS System Scope

DOCSIS/CableLabs Certified Cable Modems protocol

5/5/2005

Cable ArchitectureCable Architecture

Bahnck 5/5/2005

Cable modem at client, cable modem termination system (CMTS) at central office.

Downstream data sent to all users, like Ethernet, but encrypted (DOCSIS). MAC absorbs appropriate packets.

Upstream seen only by CMTS.

Downstream FDMA, upstream TDMA. Reflects volume of data passing in each direction.

TDMA - better for bursty data (requests, commands, DNS). FDMA - better for statistical multiplexing.

Cable modem at client, cable modem termination system (CMTS) at central office.

Downstream data sent to all users, like Ethernet, but encrypted (DOCSIS). MAC absorbs appropriate packets.

Upstream seen only by CMTS.

Downstream FDMA, upstream TDMA. Reflects volume of data passing in each direction.

TDMA - better for bursty data (requests, commands, DNS). FDMA - better for statistical multiplexing.

Architecture

Implementation

Cable vs. DSL I

Cable vs. DSL II

Cable Modems

CableLabs I

CableLabs II

DOCSIS

Cable ImplementationCable Implementation

Bahnck 5/5/2005

TV channels transmitted in 6 MHz bands, in 65 MHz - 850 MHz range.

Data allocated two channels, an upstream and downstream. Upstream bandwidth only 2 MHz, range = 5 - 42 MHz. Downstream range= 42-850 MHz.

Downstream 6 MHz capacity = ~1,000 users, data rate = 30 - 40 Mbps.

Users allocated bandwidth as proportional to total concurrent users. 1 user -> 100% BW, 10 users -> 10%.

Cable providers increase capacity by adding data (6 MHz) channels, segment users to new channels.

TV channels transmitted in 6 MHz bands, in 65 MHz - 850 MHz range.

Data allocated two channels, an upstream and downstream. Upstream bandwidth only 2 MHz, range = 5 - 42 MHz. Downstream range= 42-850 MHz.

Downstream 6 MHz capacity = ~1,000 users, data rate = 30 - 40 Mbps.

Users allocated bandwidth as proportional to total concurrent users. 1 user -> 100% BW, 10 users -> 10%.

Cable providers increase capacity by adding data (6 MHz) channels, segment users to new channels.

Architecture

Implementation

Cable vs. DSL I

Cable vs. DSL II

Cable Modems

CableLabs I

CableLabs II

DOCSIS

Cable vs. DSLCable vs. DSL

Bahnck 5/5/2005

Cable: No performance loss with increased distance from client to central office.

DSL: Permanently slower transfer rates with increased distance from central office.

Quality of data reception similar to quality of TV channel: Central office designed to boost signal enough at origin in order to reach client intact.

Strength of data transmission set by client modem modulator programmed with distance to central office, adjusts signal accordingly.

Cable: No performance loss with increased distance from client to central office.

DSL: Permanently slower transfer rates with increased distance from central office.

Quality of data reception similar to quality of TV channel: Central office designed to boost signal enough at origin in order to reach client intact.

Strength of data transmission set by client modem modulator programmed with distance to central office, adjusts signal accordingly.

Architecture

Implementation

Cable vs. DSL I

Cable vs. DSL II

Cable Modems

CableLabs I

CableLabs II

DOCSIS

Cable vs. DSLCable vs. DSL

Bahnck 5/5/2005

Peak downstream data rates for basic service (2004): Comcast Cable 3 Mbps, Verizon DSL 1.5 Mbps.

Price (2004): Comcast Cable ~$45, Verizon DSL ~$35.

Peak downstream data rates for basic service (2004): Comcast Cable 3 Mbps, Verizon DSL 1.5 Mbps.

Price (2004): Comcast Cable ~$45, Verizon DSL ~$35.

Architecture

Implementation

Cable vs. DSL I

Cable vs. DSL II

Cable Modems

CableLabs I

CableLabs II

DOCSIS

Cable ModemsCable Modems

Bahnck 5/5/2005

Tuner: Listens for downstream channel, passes data to demodulator.

Demodulator: 64 or 256 QAM. Frames structured in MPEG format for digital set top MPEG stream modulation compatibility.

Modulator: Inverse of demodulator in the upstream.

MAC: Works with CPU to absorb correct packets.

CPU: Motorola PowerPC.

Tuner: Listens for downstream channel, passes data to demodulator.

Demodulator: 64 or 256 QAM. Frames structured in MPEG format for digital set top MPEG stream modulation compatibility.

Modulator: Inverse of demodulator in the upstream.

MAC: Works with CPU to absorb correct packets.

CPU: Motorola PowerPC.

Architecture

Implementation

Cable vs. DSL I

Cable vs. DSL II

Cable Modems

CableLabs I

CableLabs II

DOCSIS

Cable Television LaboratoriesCable Television Laboratories

Bahnck 5/5/2005

Short CableLabs, R&D consortium for cable telecommunications technology.

Members include Comcast, Time Warner, Cablevision.

Research and document new broadband technology.

Certify data over cable products.

Author specifications.

Own specifications through standardization in ITU in the U.S.

Supported through subscription and certification fees.

Short CableLabs, R&D consortium for cable telecommunications technology.

Members include Comcast, Time Warner, Cablevision.

Research and document new broadband technology.

Certify data over cable products.

Author specifications.

Own specifications through standardization in ITU in the U.S.

Supported through subscription and certification fees.

Architecture

Implementation

Cable vs. DSL I

Cable vs. DSL II

Cable Modems

CableLabs I

CableLabs II

DOCSIS

Cable Television LaboratoriesCable Television Laboratories

Bahnck 5/5/2005

Promote cable over ADSL as better broadband, because idle BW is recoverable (statistical multiplexing).

Publish DOCSIS specifications, adopted by most member companies.

Promote cable over ADSL as better broadband, because idle BW is recoverable (statistical multiplexing).

Publish DOCSIS specifications, adopted by most member companies.

Architecture

Implementation

Cable vs. DSL I

Cable vs. DSL II

Cable Modems

CableLabs I

CableLabs II

DOCSIS

DOCSIS System ScopeDOCSIS System Scope

Bahnck 5/5/2005

Active Directory

Kerberos

Access Token

Descriptors

EFS

Registry

CTMS routes client traffic to ISP servers, operates DOCSIS/CableLabs Certified Cable Modems protocol.

Source: DOCSIS Set-top Gateway (DSG) Interface Specification

DOCSIS ProtocolDOCSIS Protocol

Bahnck 5/5/2005

DOCSIS: Data Over Cable Service Interface Specification. Also known as CableLabs Certified Cable Modems protocol.

Defines interface for cable modems operating over cable television system networks.

Most cable modems certified in DOCSIS – sell to any cable provider.

DOCSIS 1.0: 1995, widely deployed

DOCSIS 1.1: 2003, security, QoS for VoIP, interactive gaming, etc.

DOCSIS 2.0: 2005, upstream for symmetric services increased- 30 Mbps. [end]

DOCSIS: Data Over Cable Service Interface Specification. Also known as CableLabs Certified Cable Modems protocol.

Defines interface for cable modems operating over cable television system networks.

Most cable modems certified in DOCSIS – sell to any cable provider.

DOCSIS 1.0: 1995, widely deployed

DOCSIS 1.1: 2003, security, QoS for VoIP, interactive gaming, etc.

DOCSIS 2.0: 2005, upstream for symmetric services increased- 30 Mbps. [end]

Architecture

Implementation

Cable vs. DSL I

Cable vs. DSL II

Cable Modems

CableLabs I

CableLabs II

DOCSIS

SourcesSources

Bahnck 5/5/2005

Cable Television Laboratories, Inc. Cable Modem/DOCSIS. http://www.cablemodem.com/, various sources. Cable Television Laboratories, Inc., 2000 – 2005.

Cable Television Laboratories, Inc. DOCSIS Set-Top Gateway (DSG) Interface Specification. Cable Television Laboratories, Inc., 2001 – 2005.

Franklin, Curt. How Cable Modems Work. http://computer.howstuffworks.com/cable-modem.htm. HowStuffWorks, Inc., 1998 – 2005.

Lake, Matt. The Promise of More DSL Speed. http://reviews.cnet.com/4520-6028_7-5144462-1.html. CNET Networks, Inc., 2004.