1. Cable Modem Overview EEL 4930 – Computer Networks Fall 2002 Bradley C. Spatz

2. Agenda for Today Review national/regional/HFC networks Intro to DOCSIS CM Operation Protocol Layers, RF overview Future of DOCSIS Questions

3. HFC Architecture Hybrid Fiber Coax Broadband signal is transmitted over fiber to a local neighborhood “node” Node connects to a small coax network 500 or less homes passed per node Each node is conceptually a subnet or collision domain

4. Cox Hybrid-Fiber Coax (HFC) MTC/Hub node Ring-in-ring fiber neighborhood coax

5. What is DOCSIS? Data Over Cable Service Interface Spec. Developed by cable industry, including Cox CableLabs is R&D Ensures vendor interoperability Internet-track standards Baseline Privacy Security (public key, DES) External modem: ethernet/USB

6. DOCSIS Players Broadband Router (CMTS) Cable Modem (CM)

7. DOCSIS Architecture transparent IP through system

8. CM Initialization 1.Scan downstream (DS), sync, listen for DOCSIS 2.Listen for upstream descriptor(s) 3.Upstream (US) connectivity: power ranging 4.Establish IP connectivity: DHCP 5.Determine Time of Day (RFC 868) 6.Download operational params (TFTP) 7.Register with CMTS 8.Establish Baseline Privacy (public key, DES) 9.Surf!

9. DOCSIS Protocol Stack

10. IP Forwarding Not your traditional LAN: DS and US are at different frequencies Each channel is simplex DS is a shared media US is point-to-point Conceptual MAC forwarder connects DS+US

11. Protocol Layers Network+: DHCP, TFTP, TOD, SNMP Network: IPv4 Data Link: structured as IEEE 802 Logical Link Control (LLC) sublayer Link-Layer Security sublayer (DOCSIS) Media Access Control (MAC) sublayer

12. Protocol Layers: MAC CMTS controls bandwidth (collision-free) stream of mini-slots in the upstream dynamic mix of contention/reservation efficiency via variable length packets extensions for ATM (Europe) or other PDU format class of service support (e.g. VoIP) wide range of data rates

13. Protocol Layers: Physical DS Transmission Convergence sublayer 188-byte MPEG-2 packets (4-5 byte header) Physical Media Dependent (PMD) sublayer DS: 64, 256 QAM in 6 MHz carrier (27 or 38 Mbps) Frequency agility Programmable Reed-Soloman FEC, interleaver US: TDMA US: QPSK, 16 QAM, 200-3200 kHz carrier (up to 10 Mbps) US: multiple symbol rates

14. Modulation Tradeoffs

15. RF Spectrum Intro analog TVdigital V C A 6 MHz Each TV channel is 6 MHz analog signal Includes video, color, and audio sub-carriers

16. RF Spectrum Layout 5 MHz 42 MHz 54 MHz Downstream 750/860 MHz Upstream Two - - Way "Broadcast" Two - - Way 550 MHz Voice & & Data Svcs Digital TV Services Analog TV Services 650 MHz 30 MHz Spare HDTV, VOD Reserve I I m m p p u u l l s s e e Voice & & Data

17. DOCSIS Future DOCSIS 1.1 Interoperable with 1.0 QoS: data rate and latency guarantees (VoIP) Improved security Transmit pre-equalization DOCSIS 2.0 Interoperable with 1.0/1.1 Wider upstream (6.4 MHz) New modulation formats: A-TDMA, S-CDMA: Symmetric services (30 Mbps upstream)

18. DOCSIS Future DOCSIS in everything Integrated into set-top boxes, home gateways VoIP modems (“MTAs”) DOCSIS adapters for gaming consoles Data Over Cable  Cable Over Data The triumph of IP!

19. brad.spatz@cox.com www.cox.com