1. Data Over Cable & DOCSIS Tom 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

2. Cable 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

3. Cable 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

4. Cable 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

5. Cable 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

6. Cable 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

7. Cable 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

8. Cable 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

9. DOCSIS 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

10. DOCSIS 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

11. Sources 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.