11-specific system docsis - ku ittc · signals, and rebroadcast onto the hfc plant. •mso:multiple...

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Victor S. FrostDan F. Servey Distinguished Professor

Electrical Engineering and Computer ScienceUniversity of Kansas2335 Irving Hill Dr.

Lawrence, Kansas 66045Phone: (785) 864-4833 FAX:(785) 864-7789

e-mail: [email protected]://www.ittc.ku.edu/

Specific Systems:

Data-Over-Cable Interface SpecificationDOCSIS

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All material copyright 2006Victor S. Frost, All Rights Reserved

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Outline

• DOCSIS Overview• Protocol Stack - IP focused• MAC

– Timing issues– Packet formats– Access protocol– QoS support

• Evolution

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Topology and FDM

Modified from: “Computer Networks, 3rd Edition, A.S. Tanenbaum. Prentice Hall, 1996

FDM on the Cable

500 to 2000 homesDistances up to 100 Km

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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 arereceived here from satellites and maybe other sources, frequencyconverted 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(US): The data flowing from the Cable Modem to the CMTS.• Downstream(DS): 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.

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Data Rates: DOCSIS 1.0/1.1

Carriers limit down and upstream rates, e.g., New Zealand operator TelstraClearprovides:

- downstream speeds of 10Mbit/s and 2Mbit/s - upstream speed of 2Mbit/s.

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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

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DOCSIS Protocol Stack

Modified from: www.cablemodem.com/downloads/specs/SP-CMCI-I09-030730.pdf

Can also be Ethernet between theHost CPE and external CM

NSI=NetworkSide Interface

Convergence Sublayer:Interface between the MAC layer and

Physical Media Dependent Layer (PMD) or PHY

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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 (RNG-

REQ) at initialization• CMTS responses with a Ranging Response

(RNG-RSP) with timing and additional information

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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 boundariesand 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

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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


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DOCSIS Packets• Downstream DOSCIS Frame Format• Enables TDM of digital video (MPEG frames) and the data frames

(DOCSIS)• Payload

– MPEG Video– Data

MCNS=Multimedia Cable Network SystemPID=Program identifier

From: http://www.nextgendc.com/index.htm

4 Bytes

16 Bytes

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DOCSIS Packets

• Upstream format– Variable length (18-1518 Bytes)

compatible with Ethernet frames– ATM (53 Bytes) fixed length– MAC specific, i. e., control– Reserved

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Upstream format

• Example

From: http://www.nextgendc.com/index.htm

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DOCSIS Segmentation

From: http://www.jlsnet.co.uk/index.php?tab=3&page=projects_docsis_chap3c

Convergence Layer

Ethernet Packet

MPEG2

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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 (10.24 – 40Mb/s)

• CM will get assigned a group (or burst) of minislotsto transmit packets, – Match to transmit opportunity to the packet to be

transmitted– Increases upstream efficiency

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• 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– 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


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• Conceptual view of MAP allocation

6.25us

Minislots are assigned numbers4096 minislots/MAP

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• Timing of MAP messages and CM opportunities to transmit

CMTS

CM

t1

CMTS transmitsMAP1 all CM hear this

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CMTS

CM

t1

CMTS transmitsMAP1 all CM hear this

t2CMi receives MAP1 looks for request opportunities

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CMTS

CM

t1

Transmissions based onMAP1 start

t3

t2

Time for all CM’s toReceive and process MAP

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CMTS

CM

t1


t3

t2 t4

t5

- CM transmits a request for a specific number of minislotsto accommodate a packet-This is transmitted in contentionminislots-Contention algorithm later- t4 selected so that request will be received at t5

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CMTS

CM

t1


t3

t2 t4

t5

- t5 the CMTS can schedule the upstream transmissions to satisfy the request

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CMTS

CM

t1


t3

t2 t4

t5

At t6 CMTS transmitsMAP2 all CM hear this

t6

t7

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CMTS

CM

t1


t3

t2 t4

t5 t6

t7

t8


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CMTS

CM

t1 t3

t2 t4

t5 t6

t7

t8 t10

Transmissions of minislot from CM scheduled to be received

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CMTS

CM

t1 t3

t2 t4

t5 t6

t7

t8 t10

Transmissions ofminislot from CM

t9

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Minislots and MAP messgesMinislot numbers

Minislot with identification of Regions

MAP InformationUpstream Channel ID

MAP start time = 1099ACK time=0800

Request Region Offset=0Grant for CM20 Offset=5Grant for CM90 Offset=9

Null Offset=19

Grant for CM20 Offset=5

Grant for CM90 Offset=9

Contention Minislots

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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

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• 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


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• Send the request at minislot R• If do not see grant in next MAP then

– k= number of collisions

– If request not received, i.e., no minislotallocations in the next MAP message the k=k+1 and retry

– Maximum backoff attempt = 16


),0(12 ),1min(

NURN mi WkW

=−= −+

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• Example– Let initial backoff window Wi = 5

• Range = 0…15– Let maximum backoff Wm=10

• Range = 0…1023– A packet arrives– R = 11 (wait 11 contention slots, like non-persistent CSMA)– Assume next MAP has 6 contention slots 6<11 so keep waiting– Assume next MAP has 2 contention slots 8<11 so keep waiting– Assume 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

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DOCSIS Bandwidth Request PDU Format

*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

IE’s Describe Minislots

*

IE = Information ElementIEs define -individual grants-14 bit SID-4 bit IUC-14 bit minislot offset

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Increasing the Efficiency of Bandwidth Requests

• Piggybacked – Request for future grants for upstream transmissions

can be made in current upstream data transmissions– Do not send a separate request packet– No contention

• Concatenated requests– Allows more than one packet per transmission

opportunity, like asking more than one packet/minslot– CMTS receiving a MAC packet with Concatenation MAC

header must unpack the packets.– This process uses up the header so piggybacking request

is not possible– Can not do both concatenation and piggybacking in

DOCSIS

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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 • One MAC can have multiple SID’s, provides another layer of

multiplexing



*

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QoS



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Best Effort DOCSIS 1.0

From: Data Over Cable Service InterfaceSpecifications (DOCSIS) Manish Mangal, Sprint, TP&I

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DOCSIS 1.1 Real Time Polling Mode


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DOCSIS MAC -- DOCSIS 1.1


Circuit Switched Emulation “Unsolicited Grant Mode”

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DOCSIS QoS Services

An Investigation into HFC MAC Protocols:Mechanisms, Implementation, and Research Issues


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Access algorithm

An Investigation into HFC MAC Protocols:Mechanisms, Implementation, and Research Issues


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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+_I06-001215.pdf


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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-of-Service (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/

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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/

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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 1.1Up to 6x better upstream performance than DOCSIS 1.0


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Evolution of DOCSIS

• DOCSIS 3.0: specifications are currently in development at CableLabsand 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.

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The DOCSIS Roadmap

Consumer Devices

Services

XXXXXX

XXXX

XXX

XCable ModemVoIP Phone (MTA)Residential GatewayVideo PhoneMobile DevicesIP Set-top Box

XXXXXX

XXXXX

XXX

XBroadband Internet Tiered ServicesVoIPVideo ConferencingCommercial ServicesEntertainment Video

DOCSIS 3.0DOCSIS 2.0DOCSIS 1.1DOCSIS 1.0DOCSIS Version


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Evolution of DOCSIS

• Embedded DOCSIS: eDOCSIS device contains– CM– One or more embedded Service/Application

Functional Entities (eSAFEs)• Telephone• Video• Audio• Digital video recorders• Multiple TV tuners

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Evolution of DOCSIS

eDOCSIS Referece Model

From: Data-Over-Cable Service Interface SpecificationseDOCSIS™ Specification CM-SP-eDOCSIS-I08-060407

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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-SP-

eDOCSIS-I08-060407

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References

“Computer Networks, 3rd Edition, A.S. Tanenbaum. Prentice Hall, 1996

• DOCSIS Overview, Ajay Gummalla, www.ieee802.org/3/efm/public/jul01/presentations/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

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