DOCSIS Channel Bonding Enables Higher Bandwidth Multimedia

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 Inc

www.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.

Beyond VoIP: DOCSIS Based Options
for Higher Bandwidth Multimedia Applications
Publication History
Version Date Prime(s) Description

1.0 August 24, 2004 M Harrington Released under license to SCTE

1.1 August 25, 2004 S Brovont Modified per SCTE requests

Table of Contents

Publication History ........................................................................................................................................ 2
Table of Contents.......................................................................................................................................... 2
1.0 Summary.......................................................................................................................................... 3
2.0 Target Services and DOCSIS .......................................................................................................... 3
3.0 Channel Bonding Concept ............................................................................................................... 4
3.1 Candidates for Combination ........................................................................................................ 6
3.2 Beneficial Effects of Channel Bonding ........................................................................................ 7
4.0 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) .................................................. 11
5.0 Conclusions.................................................................................................................................... 12

www.arrisi.com Page 2 of 12 August 2004


1.0 Summary
Cable 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-top
Gateway are enabling additional services such as video conferencing and network gaming. All digital cable
networks facilitate an “Everything on Demand” model of service. New, advanced, converged multimedia
services are facilitated in cable networks by additional downstream bandwidth.

DOCSIS provides an excellent platform for adding downstream bandwidth on HFC networks in a technically
effective and economically viable way. Two ways of increasing the maximum potential bandwidth per
subscriber using currently available RF standards for HFC are DOCSIS channel aggregation and DOCSIS
channel bonding. Channel aggregation is a technique used to split content flow across two or more channels
for the purposes of load balancing or peak load bandwidth management. In this case, the RF channels need
not be bonded or even spectrally adjacent. In fact, in many cases this would place too many constraints on
deployment architectures. Channel aggregation allows very high data rates from one source to traverse as
many 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 QAM
channel bonding. Two or more QAM channels are grouped together in an adjacent frequency range, such that
they share the same up-conversion and other hardware stages, reducing hardware cost in the CMTS and
headend HFC network. Like channel aggregation, channel bonding ensures backwards compatibility with set
tops and cable modems. Channel aggregation and bonding also provide growth options for cable operators, in
that additional access devices with greater than 100Mbps throughput can be provided economically without
cable HFC plant upgrades. New headend and access-side silicon solutions and products are now becoming
available, which enable the use of multiple DOCSIS channels, to enable cable operators to compete with the
threats posed by advanced DSL and other alternative broadband services. Similarities in specification between
digital video and DOCSIS downstreams can be leveraged to provide devices which can simultaneously
transport native-digital-video as well as Internet Protocol traffic, enabling operators to bundle multimedia
services using common access devices.

2.0 Target Services and DOCSIS
Cable operators have held dominant positions in the provision of television to subscribers and have led in the
deployment of broadband access and, of late, through the deployment of Voice over IP services, in many
countries and territories. This paper proposes that DOCSIS downstream bonded channel technology provides
a viable and economical mechanism for delivery of further advanced services, to compete with present and
emergent competitive threats to that dominance.


Satellite has appeared as a compelling option to subscribers for TV service, and in some cases has led in the
deployment of HDTV. Broadband over satellite is also viable, though only for services where transmission
delay 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 the
point where, depending on distance of the subscriber’s premises from the DSLAM, available bitrates greater
than 50MBps are technically possible and economically viable.

The bundling of data, voice and video services over coaxial networks is still an attractive business proposition to
attract new customers and reduce churn. Additional services can also be offered economically, to enhance the
bundle. 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
services

The common denominator in many of these services is the need for higher available bitrates in the downstream
direction. A switch from a predominantly broadcast based network to a model where peer to peer or unicasted
traffic 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 services
have been deployed, coexistent with Voice-over-IP (G711 codec based) and high speed traffic (typical 1Mbps
down, 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, assuming
various levels of service penetration and concurrent usage.

3.0 Channel Bonding Concept
Digital-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). In
particular the modulation (channel coding) and subsequent baseband channel format, and upconversion basic
technologies are common.



Figure 3 1, Channel Combination Basic Concept

In the unbonded case, DOCSIS data and digital video streams are carried at baseband as an MPEG formatted
sequence of data. This data format must then be converted into a form which can be transmitted on the coaxial
cable, 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 advantageous
mechanism of creation of these channels which leads to both lower cost and better RF characteristics?


Channel combining, using the concept of bonded channels, is a straightforward and economical means of
achieving 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 higher
bandwidth 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.


• 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 and
current set-tops and cable modems. If backwards compatibility is a requirement, then channel bonding offers a
viable 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 set

4.0 DOCSIS as a Mechanism for High Bandwidth Converged Services

4.1 Relative Costs of DOCSIS Downstreams versus Video-QAMs
A DOCSIS “downstream” carries a higher price than the equivalent QAM modulator and up-convertor for digital
video, even though these use similar technologies. However, a DOCSIS headend has quite a number of
additional 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 and
return-channel headend for video services, integrated in one device.

The channel bonding concept may indeed be applied to a CMTS, in order to increase the downstream capacity
available by addition of extra downstream channels. It is worthy of note that the cost of a multi-downstream
CMTS does not increase linearly with the number of downstreams, since most of the other elements are
unchanged.

4.2 DOCSIS as a Basis for Bonded Channels
Besides the modulation specified in Annex B, there are no RF standards applied to digital video delivery, except
those generally accepted as industry practice. Since DOCSIS and digital video transmission characteristics are
so similar in nature, and since services may converge over the same transmission fabric, DOCSIS is a good
reference point for such an RF standard.

DOCSIS provides a tough specification for downstream RF transmissions to ensure that DOCSIS data
channels do not corrupt legacy analog and other signals already transmitted on the cable. In particular the
DOCSIS 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 controlled

Compliance 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 original
motivating 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..


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 the
extra bandwidth capacity available through bonded channels. Presently deployed digital set-top boxes typically
have 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 all
video-demodulation and DOCSIS functions in a single low cost device. In this case set-tops are already on the
market 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 channel
approach has a very significant advantage as well for the demodulation process, in that if channels are allocated
contiguously, 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.

4.5 Modifications to DOCSIS Medium Access Control
The DOCSIS standard has been architected with primarily a single QAM-channel data delivery in mind. If a
receiving device needs to access multiple QAM channels simultaneously (e.g. a fast FTP session for PVR
services), 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 Channels
A 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.



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 DMTS
concentrates 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 48
downstreams in a 2RU rack-mountable form-factor. The Q5 can contain up to 24 DOCSIS-2.0 upstream
channels to facilitate DOCSIS return channel interactivity. In future software releases, Q5’s will be able to be
grouped in clusters, so that DOCSIS downstreams and upstreams can be flexibly allocated to MAC-domains
and interconnected.

One of the fundamental dilemmas facing cable operators is how to allocate enough cable bandwidth for
concurrent transmission of both legacy analog and digital video formats. However, there may well be another
such similar dilemma in the future: how to provide for a migration from the current digital-video (i.e. the current
native MPEG2) format to a future Video-over-IP transport paradigm. The Q5 helps to resolve this question, at
least in the deployment of the headend equipment, to facilitate that migration.


Within 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 channel

The 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, since
it can seamlessly operate in both modes, in a cost effective and upgradeable manner.

5.0 Conclusions
Channel bonding provides a viable, economic and operationally convenient solution for additional downstream
cable bandwidth. Channel bonding can be provided in a DOCSIS environment in an incrementally cost-efficient
manner.

DOCSIS is a suitable transport mechanism for advanced and high bandwidth services, because it provides the
Quality 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, the
ARRIS logo and Cadant® are all trademarks of ARRIS International, Inc. Other trademarks and trade names may be used in this document to refer to
either 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 ARRIS
International, Inc., is strictly forbidden. For more information, contact ARRIS.

Issue: 1.1
Status: Approved
Date: August 25, 2004
Principal Author: Michael Harrington, R&D Engineering Director, ARRIS Inc
Contributing Authors: Stan Brovont, Vice President Marketing, ARRIS Inc
Mike Caldwell, Sr. Director PLM, ARRIS Inc

© 2004 ARRIS International, Inc. All Rights Reserved

ARRIS Security Notice:
Provided under license to The Society of Cable Television Engineers.
FRM0063v2.0 11/5/01 Refer to QMS0071


DOCSIS Channel Bonding Enables Higher Bandwidth Multimedia

Recommended

Recommended

More Related Content

What's hot

What's hot (19)

Viewers also liked

Viewers also liked (14)

Similar to DOCSIS Channel Bonding Enables Higher Bandwidth Multimedia

Similar to DOCSIS Channel Bonding Enables Higher Bandwidth Multimedia (20)

More from herooftit

More from herooftit (6)

Recently uploaded

Recently uploaded (20)

DOCSIS Channel Bonding Enables Higher Bandwidth Multimedia