Docsis® based options for higher bandwidth

1,001 views

Published on

Published in: Technology, Business
0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total views
1,001
On SlideShare
0
From Embeds
0
Number of Embeds
2
Actions
Shares
0
Downloads
32
Comments
0
Likes
0
Embeds 0
No embeds

No notes for slide

Docsis® based options for higher bandwidth

  1. 1. Beyond VoIP: DOCSIS® Based Options For Higher Bandwidth Multimedia Applications Author: Michael Harrington, R&D Engineering Director, ARRIS Inc Contributing Authors: Stan Brovont, Vice President Marketing, ARRIS Inc; and Mike Caldwell, Sr. Director PLM, ARRIS Incwww.arrisi.com Page 1 of 12 July 2004 From North America, Call Toll Free: 1-866-36-ARRIS • Outside of North America: +1-678-473-2000 All contents are Copyright © 2004 ARRIS International, Inc. All rights reserved.
  2. 2. Beyond VoIP: DOCSIS Based Options for Higher Bandwidth Multimedia ApplicationsPublication HistoryVersion Date Prime(s) Description1.0 August 24, 2004 M Harrington Released under license to SCTE1.1 August 25, 2004 S Brovont Modified per SCTE requestsTable of ContentsPublication History ........................................................................................................................................ 2Table of Contents.......................................................................................................................................... 21.0 Summary.......................................................................................................................................... 32.0 Target Services and DOCSIS .......................................................................................................... 33.0 Channel Bonding Concept ............................................................................................................... 4 3.1 Candidates for Combination ........................................................................................................ 6 3.2 Beneficial Effects of Channel Bonding ........................................................................................ 74.0 DOCSIS as a Mechanism for High Bandwidth Converged Services............................................... 7 4.1 Relative Costs of DOCSIS Downstreams versus Video-QAMs .................................................. 7 4.2 DOCSIS as a Basis for Bonded Channels .................................................................................. 8 4.3 Hardware Implementation Issues ................................................................................................ 8 4.4 Implications for Set-Top boxes, Cable-Modems and Residential Gateways. ............................. 9 4.5 Modifications to DOCSIS Medium Access Control.................................................................... 10 4.6 Data Transmission Options on Bonded QAM Channels ........................................................... 10 4.7 ARRIS Q5™ Digital Multimedia Termination System (DMTS) .................................................. 115.0 Conclusions.................................................................................................................................... 12www.arrisi.com Page 2 of 12 August 2004 From North America, Call Toll Free: 1-866-36-ARRIS • Outside of North America: +1-678-473-2000 All contents are Copyright © 2004 ARRIS International, Inc. All rights reserved.
  3. 3. Beyond VoIP: DOCSIS Based Options for Higher Bandwidth Multimedia Applications1.0 SummaryCable operators around the world are rapidly deploying digital services, including High Definition Television,High Speed Data, and Voice over IP. New protocols including PacketCable™ Multimedia and DOCSIS Set-topGateway are enabling additional services such as video conferencing and network gaming. All digital cablenetworks facilitate an “Everything on Demand” model of service. New, advanced, converged multimediaservices are facilitated in cable networks by additional downstream bandwidth.DOCSIS provides an excellent platform for adding downstream bandwidth on HFC networks in a technicallyeffective and economically viable way. Two ways of increasing the maximum potential bandwidth persubscriber using currently available RF standards for HFC are DOCSIS channel aggregation and DOCSISchannel bonding. Channel aggregation is a technique used to split content flow across two or more channelsfor the purposes of load balancing or peak load bandwidth management. In this case, the RF channels neednot be bonded or even spectrally adjacent. In fact, in many cases this would place too many constraints ondeployment architectures. Channel aggregation allows very high data rates from one source to traverse asmany separate DOCSIS downstream data channels as required to meet the overall bandwidth requirements.Data streams split out in several such channels can be reassembled at the subscriber device.Downstream bandwidth can potentially be made available more economically using the concept of QAMchannel bonding. Two or more QAM channels are grouped together in an adjacent frequency range, such thatthey share the same up-conversion and other hardware stages, reducing hardware cost in the CMTS andheadend HFC network. Like channel aggregation, channel bonding ensures backwards compatibility with settops and cable modems. Channel aggregation and bonding also provide growth options for cable operators, inthat additional access devices with greater than 100Mbps throughput can be provided economically withoutcable HFC plant upgrades. New headend and access-side silicon solutions and products are now becomingavailable, which enable the use of multiple DOCSIS channels, to enable cable operators to compete with thethreats posed by advanced DSL and other alternative broadband services. Similarities in specification betweendigital video and DOCSIS downstreams can be leveraged to provide devices which can simultaneouslytransport native-digital-video as well as Internet Protocol traffic, enabling operators to bundle multimediaservices using common access devices.2.0 Target Services and DOCSISCable operators have held dominant positions in the provision of television to subscribers and have led in thedeployment of broadband access and, of late, through the deployment of Voice over IP services, in manycountries and territories. This paper proposes that DOCSIS downstream bonded channel technology providesa viable and economical mechanism for delivery of further advanced services, to compete with present andemergent competitive threats to that dominance.www.arrisi.com Page 3 of 12 August 2004 From North America, Call Toll Free: 1-866-36-ARRIS • Outside of North America: +1-678-473-2000 All contents are Copyright © 2004 ARRIS International, Inc. All rights reserved.
  4. 4. Beyond VoIP: DOCSIS Based Options for Higher Bandwidth Multimedia ApplicationsSatellite has appeared as a compelling option to subscribers for TV service, and in some cases has led in thedeployment of HDTV. Broadband over satellite is also viable, though only for services where transmissiondelay and return path are not issues. Telcos now provide a potent threat, especially since low latency voice,data and video services can also be provided via DSL on twisted pair lines. DSL technology has evolved to thepoint where, depending on distance of the subscriber’s premises from the DSLAM, available bitrates greaterthan 50MBps are technically possible and economically viable.The bundling of data, voice and video services over coaxial networks is still an attractive business proposition toattract new customers and reduce churn. Additional services can also be offered economically, to enhance thebundle. For example: • Video on Demand (and variants nVoD, iVoD etc) has yet to become pervasive, but is gaining customers • PVR based services. For example low cost high capacity disk drives in set-top-boxes allow videos to be downloaded in off-peak hours, and played back on demand. • Video conferencing, various streaming (for example gaming) and other interactive entertainment servicesThe common denominator in many of these services is the need for higher available bitrates in the downstreamdirection. A switch from a predominantly broadcast based network to a model where peer to peer or unicastedtraffic is more prevalent, puts heavy pressure on the bandwidth capacity of the operator’s networks.A simple example can illustrate the point. Consider the case of a future deployment where multimedia serviceshave been deployed, coexistent with Voice-over-IP (G711 codec based) and high speed traffic (typical 1Mbpsdown, 256kbps up service). The advanced service is a high speed movie download to a PVR based home-movie system. A VoD service is offered as Video over IP. It is assumed that at some point during the day,concurrent video usage will clearly peak (for example, after an evening meal).A Fiber-Node size of 500HHP has been used. The table below illustrates the bandwidth-utilization, assumingvarious levels of service penetration and concurrent usage.3.0 Channel Bonding ConceptDigital-video and DOCSIS downstream channels share common downstream channel inband characteristics(ITU J83 Annex-B for North American 6MHz channelisation, Annex A for European 8MHz channelisation). Inparticular the modulation (channel coding) and subsequent baseband channel format, and upconversion basictechnologies are common.www.arrisi.com Page 4 of 12 August 2004 From North America, Call Toll Free: 1-866-36-ARRIS • Outside of North America: +1-678-473-2000 All contents are Copyright © 2004 ARRIS International, Inc. All rights reserved.
  5. 5. Beyond VoIP: DOCSIS Based Options for Higher Bandwidth Multimedia Applications Figure 3 1, Channel Combination Basic ConceptIn the unbonded case, DOCSIS data and digital video streams are carried at baseband as an MPEG formattedsequence of data. This data format must then be converted into a form which can be transmitted on the coaxialcable, through the processes of: • Modulation. The baseband signal is transformed (“channel coding”) such that it can withstand the noise and other degradation characteristics inherent in coaxial cable networks. It is also converted into a sequence of QAM symbols, which, when digitally modulated and filtered, will occupy a certain limited frequency band. This process is almost entirely high speed digital in nature, though the final digital stream is then usually converted to analog, by a D/A convertor, into an intermediate “IF” frequency. This IF frequency is simply a replica of the QAM channel at a conveniently lower frequency • Up-conversion. The IF output of the modulator is transformed, such that it then occupies a unique frequency band on the coaxial cable, as programmed by the operator. The upconversion process is usually analog in nature, though through the latest Direct Digital Synthesis approaches, an almost all digital upconversion may well be possible in several years time.It is also quite typical that an operator will allocate the outputs of many channels, which carry similar content(e.g. video or data), to be contiguous in frequency. This begs the question: is there a more advantageousmechanism of creation of these channels which leads to both lower cost and better RF characteristics?www.arrisi.com Page 5 of 12 August 2004 From North America, Call Toll Free: 1-866-36-ARRIS • Outside of North America: +1-678-473-2000 All contents are Copyright © 2004 ARRIS International, Inc. All rights reserved.
  6. 6. Beyond VoIP: DOCSIS Based Options for Higher Bandwidth Multimedia ApplicationsChannel combining, using the concept of bonded channels, is a straightforward and economical means ofachieving these goals.3.1 Candidates for Combination 1. Modulation. Since modulation is implemented primarily in the digital domain, it is a prime candidate to take advantage of higher density digital logic. This can lower costs and power consumption and increase hardware density. In particular, channels can be combined digitally, such that only one D/A conversion component is needed to create an analog output. 2. Up-conversion.. Channels can be up-converted in already digitally pre-combined groups, using the same RF technologies as a single channel approach. In this case only one RF up-convertor line- up is needed. Extensive tuning of the design is needed, including use of wider band components (in particular SAW’s), paying particular attention to distortion and compression effects, given the higher aggregate power now being transmitted. Again, cost and power consumption is reduced, while density is effectively improved by the number of channels being combined. Figure 3 2, Spectral Shape for 4 Channel Bonded Channel.An alternative is to opt for a completely different approach altogether, especially where a much higherbandwidth capacity transmission channel is needed. Different approaches include • Wide channel modulation. Occupy a wider spectrum using an extension of Annex B (or A) i.e. typically a multiple of 6 or 8MHz such that additional data can be transmitted at a higher symbol rate in the same modulated channel.www.arrisi.com Page 6 of 12 August 2004 From North America, Call Toll Free: 1-866-36-ARRIS • Outside of North America: +1-678-473-2000 All contents are Copyright © 2004 ARRIS International, Inc. All rights reserved.
  7. 7. Beyond VoIP: DOCSIS Based Options for Higher Bandwidth Multimedia Applications • Utilize a completely different modulation approach, such as Ultra-Wide-Band, Orthogonal Frequency Division Multiplexing or other.Unfortunately all of these alternatives suffer from the lack of backwards compatibility with already deployed andcurrent set-tops and cable modems. If backwards compatibility is a requirement, then channel bonding offers aviable solution, while providing higher bandwidths needed for future services.3.2 Beneficial Effects of Channel Bonding • Legacy-Compatibility. Already deployed cable modems and digital set-tops can still function seamlessly in a bonded channel scenario, given that each of the channels is Annex-B (A) compliant. If individual channels in a bonded set can be disabled, then the group can also be superimposed on an existing legacy network, until those legacy services are moved or discontinued. • Costs of Acquisition. Costs of delivery of multiple QAM channels can be reduced, in line with the the reduction in the hardware count, in particular in the sharing of the up-convertor RF circuitry . • RF Performance. Where the DOCSIS RFI standard is used as the basis for the bonded channels, the operator has a reassurance that RF fidelity is maintained in his cable plant. • System Level: Channels are now more naturally aligned in terms of timing and synchronization, given that the modulation mechanism shares common clock and other resources. This can lead to beneficial effects for redundancy management and faster, hitless load balancing of modems across the downstreams within the same bonded set4.0 DOCSIS as a Mechanism for High Bandwidth Converged Services4.1 Relative Costs of DOCSIS Downstreams versus Video-QAMsA DOCSIS “downstream” carries a higher price than the equivalent QAM modulator and up-convertor for digitalvideo, even though these use similar technologies. However, a DOCSIS headend has quite a number ofadditional value-adding functions besides downstream signal conditioning, including. • Downstream channel management and per-subscriber service-policing functions • Upstream channel physical-reception and management, including complex PHY and MAC functions for DOCSIS 2.0’s TDMA/SCDMA operation. • Networking and routing functions • Extensive management and diagnostics, as well as other value add features (e.g. embedded DHCP/TFTP servers)In effect, a DOCSIS CMTS headend for data services can be equivalent to a router, statistical multiplexer andreturn-channel headend for video services, integrated in one device.www.arrisi.com Page 7 of 12 August 2004 From North America, Call Toll Free: 1-866-36-ARRIS • Outside of North America: +1-678-473-2000 All contents are Copyright © 2004 ARRIS International, Inc. All rights reserved.
  8. 8. Beyond VoIP: DOCSIS Based Options for Higher Bandwidth Multimedia ApplicationsThe channel bonding concept may indeed be applied to a CMTS, in order to increase the downstream capacityavailable by addition of extra downstream channels. It is worthy of note that the cost of a multi-downstreamCMTS does not increase linearly with the number of downstreams, since most of the other elements areunchanged.4.2 DOCSIS as a Basis for Bonded ChannelsBesides the modulation specified in Annex B, there are no RF standards applied to digital video delivery, exceptthose generally accepted as industry practice. Since DOCSIS and digital video transmission characteristics areso similar in nature, and since services may converge over the same transmission fabric, DOCSIS is a goodreference point for such an RF standard.DOCSIS provides a tough specification for downstream RF transmissions to ensure that DOCSIS datachannels do not corrupt legacy analog and other signals already transmitted on the cable. In particular theDOCSIS Radio Frequency Interface (RFI) standards insist on the following. • A relatively high output power capability (programmable from 61dBmV down to 51dBmV when driving into a 75 Ohms impedance cable load ) to ensure reliable reception in a high plant attenuation and/or high levels of noise • A low broadband noise floor specification (73 dBc lower than the peak output power specification), in order that the combined noise floor of several or many such new RF channels does not interfere with legacy analog channels. • Tough narrowband noise characteristics (of less than 60 dBc of the peak output power if less than 10kHz bandwidth) again intended to avoid other-channel interference • Adjacent channel noise (i.e. noise introduced in the 6/8MHz channels immediately adjacent to the DOCSIS channel) is also tightly controlledCompliance with DOCSIS RF standards imposes tough technical requirements on an up-convertor in particular.These requirements are examined below in order to ensure that a bonded channel solution meets the originalmotivating requirements of DOCSIS, while providing significant cost benefits to operators.4.3 Hardware Implementation Issues • RF Signal Quality. A bonded QAM channel solution should be designed to be DOCSIS-certifiable. As outlined above, DOCSIS provides guarantees of RF signal quality and low interference, such that extensive deployment of DOCSIS-compliant bonded channels is unlikely to affect legacy operations. • Maximum Numbers of QAM Channels. There are some practical limits on the number of channels which can and should be bonded together..www.arrisi.com Page 8 of 12 August 2004 From North America, Call Toll Free: 1-866-36-ARRIS • Outside of North America: +1-678-473-2000 All contents are Copyright © 2004 ARRIS International, Inc. All rights reserved.
  9. 9. Beyond VoIP: DOCSIS Based Options for Higher Bandwidth Multimedia Applications o The more channels are bonded, the greater the number of subscribers who are likely to use that channel. Service impacts are greater upon device software or hardware failure. o The more channels, the lesser the possibility that a contiguous frequency band is available within an operator’s available spectrum. o Practical experience and feedback from operators suggests that 2 to 8 channels are viable from such an operational viewpoint. • Maximum Output Power Equivalence: When combined digitally, channels need not be combined using lossy external RF combiners, which typically lose in excess of 3 dB per 2:1 combination. One intuitive relaxation is to allow the peak output power (per QAM channel) to be dropped by that 3dB amount, for every doubling of the quantity of such bonded channels. • A bonded channel implementation should allow the flexibility to disable one or several of its QAM channels, such that the bonded channel set may be superimposed upon a legacy network without disruption on channels in the same frequency bands. This implies that the inband noise (present within a bonded set, when one of the channels have been disabled) should not cause interference with that other channel.4.4 Implications for Set-Top boxes, Cable-Modems and Residential Gateways.Clearly, additional demodulation abilities are needed in a cable-modem or other device, to provide access to theextra bandwidth capacity available through bonded channels. Presently deployed digital set-top boxes typicallyhave either: • Single tuner which is dedicated for digital video demodulation, and no interactive ability over the HFC network, possibly with a telephony based return channel for subscription based services, PPV etc • Dedicated video tuner, plus additional tuner for an Integrated Out of Band signaling channel e.g. DAVIC-compatible signaling channel or • Dedicated video tuner, plus an integrated DOCSIS cable modem, with integrated upstream return channel capability.Increasingly the trend is towards the last option. Silicon providers have fielded solutions, which integrate allvideo-demodulation and DOCSIS functions in a single low cost device. In this case set-tops are already on themarket which include two separately demodulated Annex B (or A) downstream channels.This principle may be readily extended to cover the concept of bonded QAM channels. The bonded channelapproach has a very significant advantage as well for the demodulation process, in that if channels are allocatedcontiguously, these can also be down-converted in a single block, obviating the need for multiple tuners.Multiple-QAM-channel demodulation ability is then needed in the silicon of the cable modem or set-top.However, cost increases here are more readily obviated by ever decreasing costs of silicon integration.www.arrisi.com Page 9 of 12 August 2004 From North America, Call Toll Free: 1-866-36-ARRIS • Outside of North America: +1-678-473-2000 All contents are Copyright © 2004 ARRIS International, Inc. All rights reserved.
  10. 10. Beyond VoIP: DOCSIS Based Options for Higher Bandwidth Multimedia Applications4.5 Modifications to DOCSIS Medium Access ControlThe DOCSIS standard has been architected with primarily a single QAM-channel data delivery in mind. If areceiving device needs to access multiple QAM channels simultaneously (e.g. a fast FTP session for PVRservices), some relatively simple enhancements are desirable.. 1. Device Capabilities Registration It is useful for the CMTS to know the downstream- demodulation channel-capacity of the access device. For example, the CMTS may generate one or several channels in which DOCSIS MAC and data messages are transmitted. The CMTS then transmits data only on the remaining channels of the bonded set. This is because there is a certain, though limited, overhead in throughput due to the DOCSIS MAC messages. The data-only channels are more efficient in the use of their throughput. The CMTS can decide to move single- QAM-channel-capable-only devices to the downstream(s) channel upon which the CMTS includes the DOCSIS MAC messaging. The multiple-QAM-channel-capable devices have access to the other higher throughput data-only channels of the bonded set. 2. Packet Sequencing. Packets being transmitted within the same service session, may be transmitted across multiple QAM’s in order to multiply the effective bitrate available to that service. Packets typically need be received in the proper sequence, especially for connections which have high QoS requirements. In that case, extra packet sequencing headers will help to re-order the packets at the receiver end.4.6 Data Transmission Options on Bonded QAM ChannelsA bonded-channel CMTS can opt to spread data transmission bursts in several ways. 1. Limit the overall throughput to one modem or set-top, to the capacity or fraction of the capacity, depending on Quality of Service agreements, of one downstream channel. This is clearly necessary when dealing with legacy devices. However, legacy devices will benefit from the overall increase in available downstream capacity anyway. 2. Connect via several QAM channels concurrently, so the peak bandwidth available to that device for advanced services can be increased. For example, an FTP session can simultaneously utilize 4 QAM-channels within a bonded set, to increase effective bitrate to well over 100 MBps.www.arrisi.com Page 10 of 12 August 2004 From North America, Call Toll Free: 1-866-36-ARRIS • Outside of North America: +1-678-473-2000 All contents are Copyright © 2004 ARRIS International, Inc. All rights reserved.
  11. 11. Beyond VoIP: DOCSIS Based Options for Higher Bandwidth Multimedia Applications Figure 4 1, FTP Simulation: 4 DOCSIS QAM Channels versus One, courtesy Broadcom Corp.4.7 ARRIS Q5™ Digital Multimedia Termination System (DMTS)The Q5 DMTS is the latest in a series of advanced digital headend solutions from ARRIS. The Q5 DMTSconcentrates numerous Annex B (or A) DOCSIS compliant downstream QAM channels in a small form factor.Downstream channels are grouped as 4 bonded QAM channels.The ARRIS Q5 DMTS combines the ability to transmit native MPEG2 video programming (VoD and Broadcast)and DOCSIS data in the same downstream channels. Each Q5 DMTS device may be configured with up to 48downstreams in a 2RU rack-mountable form-factor. The Q5 can contain up to 24 DOCSIS-2.0 upstreamchannels to facilitate DOCSIS return channel interactivity. In future software releases, Q5’s will be able to begrouped in clusters, so that DOCSIS downstreams and upstreams can be flexibly allocated to MAC-domainsand interconnected.One of the fundamental dilemmas facing cable operators is how to allocate enough cable bandwidth forconcurrent transmission of both legacy analog and digital video formats. However, there may well be anothersuch similar dilemma in the future: how to provide for a migration from the current digital-video (i.e. the currentnative MPEG2) format to a future Video-over-IP transport paradigm. The Q5 helps to resolve this question, atleast in the deployment of the headend equipment, to facilitate that migration.www.arrisi.com Page 11 of 12 August 2004 From North America, Call Toll Free: 1-866-36-ARRIS • Outside of North America: +1-678-473-2000 All contents are Copyright © 2004 ARRIS International, Inc. All rights reserved.
  12. 12. Beyond VoIP: DOCSIS Based Options for Higher Bandwidth Multimedia ApplicationsWithin each of these channels, bandwidth may be allocated to 1. MPEG-2 only (Multiple Program Transport Stream) for set-top box digital-video services 2. DOCSIS only, for cable modem or set-top DSG data services 3. Mix of DOCSIS and MPEG-2, such that a single tuner capable set-top may extract both video and data from the same QAM channelThe Q5 DMTS contains a full suite of L2 VLAN based, L3 routing protocols of a state of the art CMTS solution.The Q5 DMTS facilitates an operator’s migration from the current digital video solution to an all-IP solution, sinceit can seamlessly operate in both modes, in a cost effective and upgradeable manner.5.0 ConclusionsChannel bonding provides a viable, economic and operationally convenient solution for additional downstreamcable bandwidth. Channel bonding can be provided in a DOCSIS environment in an incrementally cost-efficientmanner.DOCSIS is a suitable transport mechanism for advanced and high bandwidth services, because it provides theQuality of Service, management tools (through PacketCable “Voice” and PacketCable Multimedia), and now,the high bandwidth, at economical cost, necessary for such services .The capabilities, system requirements and/or compatibility with third-party products described herein are subject to change without notice. ARRIS, theARRIS logo and Cadant® are all trademarks of ARRIS International, Inc. Other trademarks and trade names may be used in this document to refer toeither the entities claiming the marks and the names of their products. ARRIS disclaims proprietary interest in the marks and names of others. ©Copyright 2004 ARRIS International, Inc. All rights reserved. Reproduction in any manner whatsoever without the express written permission of ARRISInternational, Inc., is strictly forbidden. For more information, contact ARRIS.Issue: 1.1Status: ApprovedDate: August 25, 2004Principal Author: Michael Harrington, R&D Engineering Director, ARRIS IncContributing Authors: Stan Brovont, Vice President Marketing, ARRIS Inc Mike Caldwell, Sr. Director PLM, ARRIS Inc© 2004 ARRIS International, Inc. All Rights ReservedARRIS Security Notice:Provided under license to The Society of Cable Television Engineers.FRM0063v2.0 11/5/01 Refer to QMS0071www.arrisi.com Page 12 of 12 August 2004 From North America, Call Toll Free: 1-866-36-ARRIS • Outside of North America: +1-678-473-2000 All contents are Copyright © 2004 ARRIS International, Inc. All rights reserved.

×