Overview of Cable Data Networks DOCSIS Technology Primer

Overview of Cable Data Networks — DOCSIS Technology Primer May 16, 2006 Greg White Lead Architect - Broadband Access Cable Television Laboratories, Inc. www. cablelabs. com

Topics • Overview of the cable data network • DOCSIS Technical Overview – Basics – Physical (PHY) layer technology – Media Access Control (MAC) layer technology • Future Developments © Cable Television Laboratories, Inc. 2006. All Rights Reserved.

Overview of the Cable Data Network

Broadband Trends • IP-based broadband networks have revolutionized wireline communications – Number of U. S. broadband subscribers expected to hit 80 M by 2009 (Sanford & Bernstein) • Customers value broadband for a wide range of real-time communication and entertainment services – – – Vo. IP and video telephony Online-gaming Music and content acquisition and distribution Instant Messaging Video content delivery (IPTV) • Cable operators, telephone companies, and independent service providers are competing to offer new services to broadband customers • Vo. IP has become a ‘killer’ application and created a multibillion dollar market opportunity • Many MSOs are dabbling in IPTV types of video services. © Cable Television Laboratories, Inc. 2006. All Rights Reserved.

illi on Over 64 Million DOCSIS® Modems Shipped Worldwide Source: Cable Datacom News, Kinetic Strategies, September 2005 © Cable Television Laboratories, Inc. 2006. All Rights Reserved.

Terms • DOCSIS – Data-Over-Cable Service Interface Specification – Set of standardized protocol specifications that allow multi-vendor interoperability for CM & CMTS • CM – Cable Modem – Device at the customer’s premises • CMTS – Cable Modem Termination System – Device at the operator’s headend • HFC – Hybrid-Fiber Coax – The physical media that separates the CM & CMTS • MSO – Multiple System Operator – Synonymous with cable operator © Cable Television Laboratories, Inc. 2006. All Rights Reserved.

Cable Architecture Packet. Cable Services MPEG Services • HVAC control • Fire sense & control • Security • Air quality monitoring • Child monitoring • Energy management, etc. Operator Core Backbone IP Services DOCSIS • Remote file sharing • Shared calendar • Unified messaging • Managed services Core Network Cable. Home CM CMTS Operator Aggregation network CM CM CMTS Aggregation Network CM CM CM Access Network Operator administered Backend Headend © Cable Television Laboratories, Inc. 2006. All Rights Reserved. CPE

Modern Cable Data Network (Aggregation Network) Interne t Distribution Hub mux Regional Data Network DWDM Master Headend DWDM Distribution Hub Gig. E/IP PSTN Distribution Hub © Cable Television Laboratories, Inc. 2006. All Rights Reserved. HFC (access network)

Hybrid Fiber-Coaxial Network Coax (Access Network) Fiber Node Fiber Tx Modem CMTS Fiber Rx Fiber Node Modem Bi-Directional Amp High-Pass (50 -860 MHz) H H L L © Cable Television Laboratories, Inc. 2006. All Rights Reserved. Low-Pass (5 -42 MHz)

Extending into the home network Printer Entertainment Device PC Mobile Device Coax Cable Residential Gateway IP Audio MP 3 Player Home Security © Cable Television Laboratories, Inc. 2006. All Rights Reserved.

DOCSIS® Technical Overview

What is DOCSIS ? • DOCSIS defines the PHY & MAC layer protocol for communication and Ethernet frame carriage between the CMTS and the CM. • DOCSIS also defines a provisioning and management framework • Three published versions: * – DOCSIS 1. 0 (ca. 1996) (ITU-T J. 112 -B (3/98)) – DOCSIS 1. 1 (ca. 1999) (ITU-T J. 112 -B (3/04)) – DOCSIS 2. 0 (ca. 2001) (ITU-T J. 122 (12/02)) • Next generation in progress: – DOCSIS 3. 0 (ca. 2006) *available at www. cablemodem. com © Cable Television Laboratories, Inc. 2006. All Rights Reserved.

Cable Modem Protocol Stack Application Layer SNMP, TFTP, DHCP, To. D, IGMP Presentation Layer Session Layer Transport Layer TCP/UDP Network Layer IP, ICMP, ARP Link Layer Control 802. 2 LLC Media Access Control DOCSIS MAC 802. 3 MAC Physical Layer DOCSIS PHY 10/100 Base-T, USB OSI Ref. Model Cable Interface Customer Interface Data Link Layer 802. 1 d Bridge 802. 2 LLC © Cable Television Laboratories, Inc. 2006. All Rights Reserved.

DOCSIS Physical Layer

HFC Spectrum Allocation AWGN (~1/f) Downstream … ~ ~ DOCSIS … DOCSIS ~ ~ Upstream 5 42 54 Analog Video Digital Video (NTSC/PAL) (MPEG/DVB) © Cable Television Laboratories, Inc. 2006. All Rights Reserved. 860 f (MHz)

Downstream Physical Layer Region Standard North America Europe ITU-T J. 83 -B ETSI EN 300 429 (DVB) Modulation 64 QAM 256 QAM Channel Spacing 6 MHz 8 MHz Symbol Rate (Mbaud) 5. 057 5. 361 6. 952 Raw Data Rate (Mbps) 30. 34 42. 88 41. 71 55. 62 TCM rate 14/15 19/20 N/A (128, 122) (204, 188) 26. 97 38. 80 38. 44 51. 25 Reed-Solomon FEC Post-FEC Data Rate (Mbps) © Cable Television Laboratories, Inc. 2006. All Rights Reserved.

Upstream Physical Layer Version DOCSIS 1. x DOCSIS 2. 0 Format Bursted F/TDMA, F/S-CDMA QPSK, 16 QAM QPSK, 8 QAM, 16 QAM, 32 QAM, 64 QAM, 128 QAM Channel Width (MHz) 0. 2, 0. 4, 0. 8, 1. 6, 3. 2, 6. 4 Symbol Rate (Mbaud) 0. 16, 0. 32, 0. 64, 1. 28, 2. 56, 5. 12 Raw Data Rate (Mbps) 0. 32 – 10. 24 0. 32 – 35. 84 Pre-Equalization 8 -tap FIR (opt. in 1. 0) 24 -tap FIR Trellis Coded Modulation Rate N/A Optional: n/n+1 Reed-Solomon FEC T=0 -10; k=16 -253 T=0 -16; k=16 -253 Post-FEC Data Rate (Mbps) 0. 14 – 10. 24 0. 11 – 30. 72 Modulation © Cable Television Laboratories, Inc. 2006. All Rights Reserved.

DOCSIS Upstream PHY Modes • Time Division Multiple Access (TDMA) – CMs take turns transmitting, one at a time, each occupies the entire upstream channel during transmission. – Tranmissions consist of: preamble, data burst, guard time – Better immunity to narrowband interferers • Synchronous Code Division Mult. Access (S-CDMA) – – – DOCSIS 2. 0 only Direct Sequence Spread Spectrum Multiple CMs can transmit simultaneously Much shorter preamble, no guard time Slightly more efficient, better immunity to burst noise © Cable Television Laboratories, Inc. 2006. All Rights Reserved.

S-CDMA Basics • S-CDMA is a multiple access modulation technique which uses direct-sequence spread-spectrum and a set of 128 orthogonal codes. • Orthogonality is maintained by aligning and synchronizing the transmitted waveforms. • Multiple access is supported through both time and code domain allocation (more than one CM can transmit at a time). © Cable Television Laboratories, Inc. 2006. All Rights Reserved.

S-CDMA System © Cable Television Laboratories, Inc. 2006. All Rights Reserved.

Ranging • Ranging is used to synchronize CMs and align them with the CMTS receiver. – – TDMA requires coarse alignment (± 800 nsec) S-CDMA requires accurate alignment (± 1 nsec). CM sends a RNG-REQ message CMTS responds with a RNG-RSP message • Contains Timing Adjust (Resolution = 0. 3815 nsec. ) • also Power adjust, Frequency adjust, Pre-EQ params. • Ranging is a two-step process: – Initial maintenance (coarse time alignment). – Periodic station maintenance (fine time alignment). © Cable Television Laboratories, Inc. 2006. All Rights Reserved.

DOCSIS MAC Layer

DOCSIS MAC • Media Access Control (MAC) Sub-Layer – Controls access to the Physical Layer (the channel) – Allows multiple users to share a communications channel • One-to-many architecture • Two physical channels (upstream/downstream) both controlled by the CMTS • No direct peer-to-peer (CM-to-CM) communication © Cable Television Laboratories, Inc. 2006. All Rights Reserved.

DOCSIS Downstream MAC • • Only one transmitter - the CMTS Multiple receivers - the CMs CMTS manages its own transmissions. Quality of Service can be assured by: – Token bucket rate limiting – Reserved data rates – Traffic Priority © Cable Television Laboratories, Inc. 2006. All Rights Reserved.

DOCSIS Upstream MAC • Multiple transmitters - the CMs • One receiver - the CMTS • The CMTS arbitrates access to the channel – Upstream channel is described in minislots • 2 n*6. 25µs in TDMA mode – “MAP” messages are broadcast downstream to describe who gets to transmit and when – One MAP message per upstream channel per MAP interval (chosen by CMTS, 2 -5 ms typical) • Access Control is Reservation based – Reservation requests are sent in contention (“Slotted-Aloha”) – Reservations can also be pre-scheduled at periodic intervals © Cable Television Laboratories, Inc. 2006. All Rights Reserved.

MAPs are broadcast by the CMTS on the downstream channel Downstream Channel MAP Upstream Channel (TDMA) Transmit Opportunities mini-slots CM tx opportunity previous map request contention area CM tx opportunity ranging minislots described by the current map © Cable Television Laboratories, Inc. 2006. All Rights Reserved. as-yet unmapped minislots

S-CDMA Mini-slot Mapping • Mini-slots are one-dimensional (transmission in time only). • S-CDMA transmissions are two-dimensional (transmissions in time and code domains). – S-CDMA frame is up to 128 codes by K spreading intervals. – Frame size parameters are configurable. • The PHY layer maps the mini-slots to frames. © Cable Television Laboratories, Inc. 2006. All Rights Reserved.

S-CDMA Framing Structure © Cable Television Laboratories, Inc. 2006. All Rights Reserved.

Mini-slot Numbering and Timestamp Snapshot In this example, 126 codes are active. © Cable Television Laboratories, Inc. 2006. All Rights Reserved.

Ranging, again • Initial Ranging –First upstream transmission by CM –To lock-in time sync, frequency, and power • Periodic Ranging –a. k. a. Periodic Maintenance, Station Maintenance –CMTS must offer to each CM at least once every 35 seconds • generally much more often • If not offered by CMTS (or missed by CM), CM declares T 4 timeout –To maintain sync, frequency, and power settings over daily plant variations • Temperature change • Cable stretch, etc. © Cable Television Laboratories, Inc. 2006. All Rights Reserved.

The Reservation Mechanism – Requests and Grants • When a CM has data to send, it: – Waits for a Request contention interval in downstream MAP messages – Randomly selects a sub-interval – Transmits a 6 -byte REQ message to the CMTS, which: • identifies the CM (via Service ID) • specifies the number of minislots needed – Retransmits request, if no response from the CMTS • The CMTS then: – Queues/prioritizes REQs – Reserves future minislots for the requesting CMs – Communicates the “Grants” to the CMs via MAP messages. • The CM can have only one request outstanding at a time (per SID) © Cable Television Laboratories, Inc. 2006. All Rights Reserved.

Piggybacking • Suppose the CM has sent a REQ to transmit Pkt #1. • Before the grant time arrives, Pkt #2 is enqueued. • The CM can “piggyback” a REQ for Pkt #2 in the MAC header of Pkt #1. • Avoids delay/backoff waiting for a contention interval, and possibility of collision. Pkt #1 REQ for Pkt #2 © Cable Television Laboratories, Inc. 2006. All Rights Reserved.

Concatenation • Suppose the CM has multiple small packets waiting in the queue. • The CM can pack them together into a large frame, and send one REQ to transmit the concatenated frame • CMTS unpacks the concatenated frame and forwards the individual packets normally • Avoids multiple REQ-grant latency cycles, collisions, minimizes PHY overhead. © Cable Television Laboratories, Inc. 2006. All Rights Reserved.

CM Provisioning • During initialization, the CM downloads (via TFTP) a configuration file from the cable operator • Config file defines: – Quality of Service (Qo. S) Parameters • Rate limiting, bandwidth guarantees, etc. – Filters • e. g. block Windows file sharing (net. BIOS, SMB, CIFS) – Privacy (encryption) parameters • The CM then sends a Registration Request message to the CMTS containing the Qo. S parameters, and begins a key exchange to initialize encryption. © Cable Television Laboratories, Inc. 2006. All Rights Reserved.

CM Initialization Sequence 1. Downstream Channel Acquisition – Scan for digital channels, acquire QAM, FEC, MPEG lock, identify DOCSIS PID (program ID) 2. Upstream Channel Acquisition – Select upstream channel based on Upstream Channel Descriptor messages – Initial Ranging • Find Initial Maintenance interval in MAP messages • Send RNG-REQ, receive RNG-RSP, adjust transmitter, repeat if necessary 3. Establish IP Communications (DHCP) 4. Download Configuration File (TFTP) 5. Registration – Send REG-REQ, receive REG-RSP, send REG-ACK 6. Initialize Encryption – CM Authentication & Key exchange with CMTS © Cable Television Laboratories, Inc. 2006. All Rights Reserved.

Future Developments

DOCSIS 3. 0 Features • Much higher bandwidth through channel bonding – Starts at 160 Mbps Downstream, 120 Mbps Upstream & goes up from there – Multiple physical channels are bound, treating them logically as one – Channel bonding in both upstream and downstream • IPv 6 for advanced networking capabilities – Expanded address space • 667, 000 per square nanometer of the earth’s surface vs. 22 per sq. mile today – Improved operational capabilities • IP Multicast to support IPTV-type applications – Use existing standard protocols to manage IP video service – Efficient “switched-video-like” bandwidth usage • Programs are only delivered when viewers are present. – Quality-of-Service so network congestion doesn’t impact video quality • Stronger Traffic Encryption (128 bit-AES instead of 56 bit-DES) © Cable Television Laboratories, Inc. 2006. All Rights Reserved.

DOCSIS Roadmap DOCSIS Version DOCSIS 1. 0 DOCSIS 1. 1 DOCSIS 2. 0 DOCSIS 3. 0 X X X X X X X X 40 5[1] 160 minimum[2] 5[1] 10 80[3] 30 170[4] 120 minimum[5] 170[4] Services Broadband Internet Tiered Services Vo. IP Video Conferencing Commercial Services Entertainment Video Consumer Devices Cable Modem Vo. IP Phone (MTA) Residential Gateway Video Phone Mobile Devices IP Set-top Box Downstream Bandwidth Mbps/channel Gbps/node Upstream Bandwidth Mbps/channel Mbps/node [1] [2] [3] [4] [5] Assumes 750 MHz of available downstream spectrum (125 channels) Aggregation of four 6 MHz channels. With 256 QAM = 160 Mbps Assumes ~25 MHz of useable upstream spectrum © Cable Television Inc. 2006. Assumes ~35 MHz of useable upstream. Laboratories, spectrum Aggregation of four 6. 4 MHz channels All Rights Reserved.

Thank You! Cable. Labs ® Cable Television Laboratories, Inc. Greg C. White Lead Architect Broadband Access 858 Coal Creek Circle Louisville, Colorado 80027 -1266 Phone: 303 -661 -9100 Direct: 303 -661 -3822 Fax: 303 -664 -8192 Email: g. white@cablelabs. com http: //www. cablelabs. com © Cable Television Laboratories, Inc. 2006. All Rights Reserved.