Specific Systems: Data-Over-Cable Interface Specification DOCSIS #10 Victor S. Frost Dan F. Servey Distinguished Professor Electrical Engineering and Computer Science University of Kansas 2335 Irving Hill Dr. Lawrence, Kansas 66045 Phone: (785) 864-4833 FAX:(785) 864-7789 e-mail: frost@eecs.ku.edu http://www.ittc.ku.edu/ All material copyright 2006 Victor S. Frost, All Rights Reserved #10 1 Outline • DOCSIS Overview • Protocol Stack • MAC – – – – Timing issues Packet formats Access protocol QoS support • Evolution #10 2 Topology and FDM 500 to 2000 homes Distances up to 100 Km FDM on the Cable Modified from: “Computer Networks, 3rd Edition, A.S. Tanenbaum. Prentice Hall, 1996 #10 3 Some Terminology • • • • • • • CMTS: Cable Modem Termination System. Central device for connecting the cable TV network to a data network like the internet. Normally placed in the headend of the cable TV system. Downstream: Headend: Central distribution point for a CATV system. Video signals are received here from satellites and maybe other sources, frequency converted to the appropriate channels, combined with locally originated signals, and rebroadcast onto the HFC plant. MSO: Multiple Service Operator. A cable TV service provider that also provides other services such as data and/or voice telephony. Upstream: The data flowing from the Cable Modem to the CMTS. Downstream: The data flowing from the CMTS to the cable modem. Ranging: The process of automatically adjusting transmit levels and time offsets of individual modems, in order to make sure the bursts coming from different modems line up in the right timeslots and are received at the same power level at the CMTS. SID (Service ID): Used in the DOCSIS standard to defines a particular mapping between a cable modem (CM) and the CMTS. The SID is used for the purpose of upstream bandwidth allocation and class-of-service management. #10 4 Data Rates: DOCSIS 1.0/1.1 Carriers limit down and upstream rates, e.g., New Zealand operator TelstraClear provides: - downstream speeds of 10Mbit/s and 2Mbit/s - upstream speed of 2Mbit/s. #10 5 Issues • Link management – Upstream synchronization (timing adjustment) – Ranging (offset adjustment) (Periodic and Initial) – Power adjustment – Burst transmission and reception • Bandwidth management – – – – Bandwidth allocation Contention resolution Prioritization/classification of traffic Supports unsolicited grant service (voice/T1 ckts) • Subscriber management – Authentication – Security – Registration Modified from: DOCSIS Overview, Ajay Gummalla, www.ieee802.org/3/efm/public/jul01/presentations/gummalla_1_0701.pdf #10 6 DOCSIS Protocol Stack Convergence Sublayer: Interface between the MAC layer and Physical Media Dependent Layer (PMD) or PHY Can also be Ethernet between the Host CPE and external CM NSI=Network Side Interface Modified from: www.cablemodem.com/downloads/specs/SP-CMCI-I09-030730.pdf #10 7 Timing issues • DOCSIS 1.0/1.1 and 2.0 – Uses burst TDMA system on upstream – Continuous TDM transmission on the downstream • CM must transmit at the “right” time • CM transmits a Ranging Request (RNGREQ) at initialization • CMTS responses with a Ranging Response (RNG-RSP) with timing and to the information #10 8 Ranging Process -Before initial transmission, CM loads it’s ranging offset register with a value to compensate for the known delays (DS interleaver, implementation delays, etc.) – The CM the adjusts it’s 32-bit sync counter by the amount in the ranging offset. – The CM then selects an initial ranging slot and transmits. – The CMTS measures the difference between the received and expected transmission boundaries and sends that back to the CM as a ranging adjustment. It also communicates the power level, frequency offset and delay adjustment to the CM. From: DOCSIS Overview, Ajay Gummalla, www.ieee802.org/3/efm/public/jul01/presentations/gummalla_1_0701.pdf #10 9 CM Initialization • • • • • • Downstream synchronization for TDM Obtain upstream parameters Ranging and automatic adjustments Establish IP connectivity Establish time of day Transfer operational parameters (TFTP download of configuration parameters) • Registration – Assigns a Service ID (SID) • Baseline privacy initialization From: DOCSIS Overview, Ajay Gummalla, www.ieee802.org/3/efm/public/jul01/presentations/gummalla_1_0701.pdf #10 10 DOCSIS Packets • • • Downstream DOSCIS Frame Format Enables TDM of digital video (MPEG frames) and the data frames (DOCSIS) Payload – MGEG Video – Data MCNS=Multimedia Cable Network System From: http://www.nextgendc.com/index.htm #10 11 DOCSIS Packets • Upstream format – Variable length (18-1518 Bytes) compatible with Ethernet frames – ATM (53 Bytes) fixed length – MAC specific, i. e., control – Reserved #10 12 Upstream format • Example From: http://www.nextgendc.com/index.htm #10 13 DOCSIS Segmentation Convergence Layer From: http://www.jlsnet.co.uk/index.php?tab=3&page=projects_docsis_chap3c #10 14 How do CM request opportunities to transmit? • Upstream channel is divided into stream of TDM “mini slots” • Each “minislot” is the unit of granularity for upstream opportunities to transmit • Minislots – Must be multiples of 6.25 us – Typically 8 to 32 Bytes • CM will get assigned a group of minislots to transmit packets, – Match to transmit opportunity to the packet to be transmitted – Increases upstream efficiency #10 15 How do CM request opportunities to transmit? • Each mini slot is assigned a minislot number (wraps around) • Ranging is used so all CM and the CMTS have common view of the minislots • The CMTS send a variable length Bandwidth Allocation Map (MAP) message downstream that identifies – Describes the permitted use of the upstream channel – Specific CM with timing for grants to transmit if the next MAP time interval – Opportunities for CM’s to request opportunities to transmit – System overhead #10 16 How do CM request opportunities to transmit? • Conceptual view of MAP allocation #10 17 How do CM request opportunities to transmit? • Timing of MAP messages and CM opportunities to transmit CMTS t1 CMTS transmits MAP1 all CM hear this CM #10 18 How do CM request opportunities to transmit? • Timing of MAP messages and CM opportunities to transmit CMTS t1 CMTS transmits MAP1 all CM hear this CM t2 CMi receives MAP1 looks for request opportunities #10 19 How do CM request opportunities to transmit? • Timing of MAP messages and CM opportunities to transmit CMTS t1 Transmissions based on MAP1 start t3 Time for all CM’s to Receive and process MAP CM t2 #10 20 How do CM request opportunities to transmit? • Timing of MAP messages and CM opportunities to transmit CMTS CM t1 Transmissions based on MAP1 start t5 t3 - CM transmits a request for a specific number of minislots to accommodate a packet -This is transmitted in contention minislots -Contention algorithm later - t4 selected so that request will be received at t5 t2 t4 #10 21 How do CM request opportunities to transmit? • Timing of MAP messages and CM opportunities to transmit CMTS t1 Transmissions based on MAP1 start t5 t3 - t5 the CMTS can schedule the upstream transmissions to satisfy the request CM t2 t4 #10 22 How do CM request opportunities to transmit? • Timing of MAP messages and CM opportunities to transmit CMTS t1 Transmissions based on MAP1 start t5 t3 t6 At t6 CMTS transmits MAP2 all CM hear this CM t2 t4 t7 #10 23 How do CM request opportunities to transmit? • Timing of MAP messages and CM opportunities to transmit CMTS CM t1 Transmissions based on MAP1 start t5 t3 t2 t4 t6 Transmissions based on MAP2 start t8 t7 #10 24 How do CM request opportunities to transmit? • Timing of MAP messages and CM opportunities to transmit CMTS CM t1 t5 t3 t2 t4 Transmissions of minislot from CM scheduled to be received t6 t8 t10 t7 #10 25 How do CM request opportunities to transmit? • Timing of MAP messages and CM opportunities to transmit CMTS t1 t5 t3 t6 t8 t10 Transmissions of minislot from CM CM t2 t4 t7 t9 #10 26 Minislots and MAP messges Minislot numbers Minislot with identification of Regions Contention Minislots Grant for CM20 Offset=5 MAP Information Upstream Channel ID MAP start time = 1099 ACK time=0800 Request Region Offset=0 Grant for CM20 Offset=5 Grant for CM90 Offset=9 Null Offset=19 Grant for CM90 Offset=9 #10 27 Contention of bandwidth requests • Unallocated minislots can be designated for request (contention) minislots • All upstream CM gain access to a request mini slots using a random access protocol #10 28 Contention of bandwidth requests • Operation of the access protocol – The CMTS sets • Initial backoff window Wi • Maximum backoff Wm – Packet arrives at CM for transmission – CM calculates # minislots (including overhead) needed to send the packet. – Let R= number of contention minislots to skip before sending the request #10 29 Contention of bandwidth requests • Send the request at minislot R • k= number of collisions max(Wi k 1,Wm ) N 2 R U (0, N ) 1 • If request not received, i.e., no minislot allocations in the next MAP message the k=k+1 and retry • Maximum backoff attempt = 16 #10 30 Contention of bandwidth requests • Example – Let initial backoff window Wi = 4 • Range = 0…15 – Let maximum backoff Wm=10 – – – – – • Range = 0…1023 A packet arrives R = 11 Next MAP has 6 contention slots 6<11 so keep waiting Next MAP has 2 contention slots 8<11 so keep waiting Next Map has 8 contention slots so wait 3 minislots and transmit request – If no Data Grant (or Data Ack) the assume a collision and repeat – Quit after 16 collisions #10 31 DOCSIS Bandwidth Request PDU Format * IE = Information Element IEs define -individual grants -14 bit SID -4 bit IUC -14 bit minislot offset *From: An Investigation into HFC MAC Protocols: Mechanisms, Implementation, and Research Issues Ying-Dar Lin, Wei-Ming Yin, and Chen-Yu Huang, National Chiao Tung, IEEE Communications Survey and Tutorials #10 32 Increasing the Efficiency of Bandwidth Requests • Piggybacked – Request for future grants for upstream transmissions can be made in current upstream data transmissions – No contention • Concatenated requests – Allows more than one packet per transmission opportunity – CMTS receiving a MAC packet with Concatenation MAC header much unpack the packets. – This process uses up the header so piggybacking request is not possible #10 33 QoS • QoS is provided by the CMTS – scheduling upstream transmission via the MAP – Scheduling downstream transmission • QoS is provided on an Service ID (SID) basis * *From: An Investigation into HFC MAC Protocols: Mechanisms, Implementation, and Research Issues Ying-Dar Lin, Wei-Ming Yin, and Chen-Yu Huang, National Chiao Tung, IEEE Communications Survey and Tutorials #10 34 QoS *From: An Investigation into HFC MAC Protocols: Mechanisms, Implementation, and Research Issues Ying-Dar Lin, Wei-Ming Yin, and Chen-Yu Huang, National Chiao Tung, IEEE Communications Survey and Tutorials #10 35 Best Effort DOCSIS 1.0 From: Data Over Cable Service Interface Specifications (DOCSIS) Manish Mangal, Sprint, TP&I #10 36 DOCSIS 1.1 Real Time Polling Mode From: Data Over Cable Service Interface Specifications (DOCSIS) Manish Mangal, Sprint, TP&I #10 37 DOCSIS MAC -- DOCSIS 1.1 Circuit Switched Emulation “Unsolicited Grant Mode” From: Data Over Cable Service Interface Specifications (DOCSIS) Manish Mangal, Sprint, TP&I #10 38 DOCSIS QoS Services An Investigation into HFC MAC Protocols: Mechanisms, Implementation, and Research Issues Ying-Dar Lin, Wei-Ming Yin, and Chen-Yu Huang, National Chiao Tung, IEEE Communications Survey and Tutorials #10 39 Access algorithm An Investigation into HFC MAC Protocols: Mechanisms, Implementation, and Research Issues Ying-Dar Lin, Wei-Ming Yin, and Chen-Yu Huang, National Chiao Tung, IEEE Communications Survey and Tutorials #10 40 Security- Baseline Privacy • Two component protocols: – Encapsulation protocol for encrypting packet data across the cable network – BPKM (Baseline Privacy Key Management) protocol for providing secure distribution of keying material from the CMTS to CM • Encapsulation protocol defines – the frame format for carrying encrypted data within DOCSIS MAC frames – set of supported cryptographic suites (pairings of data encryption and authentication algorithms) – rules for applying these algorithms to a DOCSIS frame’s packet data • DOCSIS frame header is not encrypted to facilitate registration, ranging and normal operation of the DOCSIS MAC sublayer • Ref: – http://www.cablemodem.com/Security_in_DOCSIS.pdf – BPI has been enhanced in DOCSIS1.1 to add authentication and Multicast support. http://www.cablemodem.com/BPI+_I06001215.pdf From: DOCSIS Overview, Ajay Gummalla, www.ieee802.org/3/efm/public/jul01/presentations/gummalla_1_0701.pdf #10 41 Evolution of DOCSIS • DOCSIS 1.0: specifications include technology that was available in the 1995–1996 timeframe, and have become very widely deployed around the world. – Internet access • DOCSIS 1.1: specifications provide improved operational flexibility, security, and Quality-ofService (QoS) features that enable real-time services. – Telephony, – Gaming, – Streaming Media • DOCSIS 2.0: specifications provide dramatically increased upstream throughput for symmetric services. Modified from: http://www.cablemodem.com/primer/ #10 42 DOCSIS 1.1 Overview • Interoperable with DOCSIS 1.0, plus more… – Access to bandwidth at high data rates or lower latency adds more value • Enhanced “Quality of Service” (QoS) – Guarantees and/or limits for data rates – Guarantees for latency • Improved security - designed to reduce possibility of “theft of service, provide secure software downloading.” • Interoperability - DOCSIS 1.0 and DOCSIS 1.1 cable modems and CMTSs on the same plant. Better operation and OSS features • Transmit Equalization - more robust transmission Modified from:http://www.cablemodem.com/primer/ #10 43 DOCSIS 2.0 Overview (100% backward compatible with DOCSIS 1.0/1.1) • Symmetrical services are enabled by DOCSIS 2.0 – 1.5x greater efficiency • operates at 64 QAM – 2x wider channels • new 6.4 MHz wide channel • DOCSIS 2.0 widens the pipe for IP traffic, allowing cable providers to create more and better services for voice, video, and data • It does this by using enhanced modulation and improved error correction • Superior ingress and impulse noise performance Up to 3x better upstream performance than DOCSIS 1.1 Up to 6x better upstream performance than DOCSIS 1.0 Modified from:http://www.cablemodem.com/primer/ #10 44 Evolution of DOCSIS • DOCSIS 3.0: specifications are currently in development at CableLabs and will include a number of enhancements, most notably, channel bonding and support for IPv6. Channel bonding provides cable operators with a flexible way to increase upstream and downstream throughput to customers, with data rates in the hundreds of megabits and potentially gigabits per second. #10 45 The DOCSIS Roadmap DOCSIS Version DOCSIS 1.0 DOCSIS 1.1 DOCSIS 2.0 DOCSIS 3.0 X X X X X X X X X X X X X X X X X X X X X X X X X X X X X Services Broadband Internet Tiered Services VoIP Video Conferencing Commercial Services Entertainment Video Consumer Devices Cable Modem VoIP Phone (MTA) Residential Gateway Video Phone Mobile Devices IP Set-top Box Modified from:http://www.cablemodem.com/primer/ #10 46 Evolution of DOCSIS • Embedded DOCSIS: eDOCSIS device contains – CM – One or more embedded Service/Application Functional Entities (eSAFEs) • Telephone • Video • Audio #10 47 Evolution of DOCSIS eDOCSIS Referece Model From: Data-Over-Cable Service Interface Specifications eDOCSIS™ Specification CM-SP-eDOCSIS-I08-060407 #10 48 References • • • • • • • • • • Bartoš, R., C.K. Godsay, and S. Fulton. Experimental Evaluation of DOCSIS 1.1 Upstream Performance. in Parallel and Distributed Computing and Networks. 2004. Innsbruck, Austria. Fellows, D. and D. Jones, DOCSIS cable modem technology. Communications Magazine, IEEE, 2001. 39(3): p. 202-209. Hawa, M. and D.W. Petr. Quality of service scheduling in cable and broadband wireless access systems. in Tenth IEEE International Workshop on Quality of Service, 2002. 2002. Lin, Y.-D., W.-M. Yin, and C.-Y. Huang, An Investigation into HFC MAC Protocols: Mechanisms, Implementation, and Research Issues. IEEE Communications Surveys, 2000. Martin, J. The Impact of the DOCSIS 1.1/2.0 MAC Protocol on TCP. in Second IEEE Consumer Communications and Networking Conference. 2005. Las Vegas, NV. Martin, J. and N. Shrivastav. Modeling the DOCSIS 1.1/2.0 MAC Protocol. in Proceedings of the 2003 International Conference on Computer Communications and Networks. 2003. Dallas TX. Shah, N., et al. A tutorial on DOCSIS: protocol and performance models. in Proceedings of the International Working Conference on Performance Modeling and Evaluation of Heterogeneous Networks. 2005. Ikley, UK. Zhenglin, L. and X. Chongyang, An Analytical Model for the Performance of the DOCSIS CATV Network The Computer Journal 2002. 45(3): p. 278-284. http://www.cablemodem.com/primer/ Data-Over-Cable Service Interface Specifications eDOCSIS™ Specification CM-SPeDOCSIS-I08-060407 #10 49 References “Computer Networks, 3rd Edition, A.S. Tanenbaum. Prentice Hall, 1996 • DOCSIS Overview, Ajay Gummalla, www.ieee802.org/3/efm/public/jul01/pres entations/gummalla_1_0701.pdf • www.cablemodem.com/downloads/specs/SP -CMCI-I09-030730.pdf • http://www.nextgendc.com/index.htm • http://www.jlsnet.co.uk/index.php?tab=3&p ge=projects_docsis_chap3c #10 50 References #10 51