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  • 1. THE EVOLUTION TO IPTV OVER DOCSIS 3.0 AND MODULAR-CMTS Howard Abramson, Director Advanced Engineering Roger Slyk, Director Product Marketing BigBand Networks INTRODUCTION While DOCSIS 3.0 provides cable operators with the necessary bandwidth enhancement, multicasting and other tools to enable the delivery of IPTV over the cable HFC network, it is an M-CMTS (modular cable modem termination system) architecture that allows DOCSIS 3.0 to be delivered in a scalable and economical manner. This paper discusses the trends leading to the development and eventual deployment of IPTV over DOCSIS and then goes on to explain what parts of the CableLabs DOCSIS 3.0 specification are particularly targeted towards services such as IPTV, and how these capabilities are applicable in an IPTV solution. The authors also describe how the M- CMTS specification enables cable operators to smoothly transition to IPTV services with the lowest possible costs. Employing an M-CMTS architecture provides the following advantages: Optimization of bandwidth used between traditional video (including broadcast, PPV, VoD and switched broadcast) and smooth expansions to broader implementations of IPTV; Significant reductions in capital equipment costs and operational costs; Seamless transition from DOCSIS 2.0 to full DOCSIS 3.0 functionality; Ability to expand capacity without requiring node splits, rewiring or wholesale replacement of existing hardware; Flexible allocations of upstream and downstream bandwidth. After describing the details of M-CMTS, the authors examine PSP (packet streaming protocol) and D-MPT (DOCSIS MPEG protocol transport), two possible universal Edge QAM protocols for M-CMTS, contrast the advantages of each and provide a recommendation for deployments today. TRENDS FOR VIDEO TODAY It is an unavoidable fact that consumers are blurring the line between lean-back consumption of TV-based entertainment and lean-forward multimedia activities on their personal computers. A rich array of innovative technologies provide cable operators with the opportunity to expand program line-ups to include hundreds of high definition channels, increasingly personalized content and advertising that more closely matches the interests of viewers. The ability to offer any media to anyone, at any time, anywhere is moving from a concept to a reality. 1
  • 2. Figure 1: Bandwidth-intensive services require increases in network capacity Recognizing that IP provides benefits spanning greater service flexibility and openness, cable operators are looking towards technologies that boost network capacity for IP- based traffic. One of the attributes required to support increases in IP-based applications is bandwidth. However, not only are higher speeds required in downstream directions, applications such as peer-to-peer file swapping require flexible allocations of upstream to downstream capacity ratios. As will be explained later in this paper, traditional I-CMTS (integrated cable modem termination systems) designs are unsuitable for this role. Most I-CMTS solutions available today only support the combination of a single shared downstream channel, associated with four to six independent upstream channels, within a service group. Although the DOCSIS protocol defines more flexible downstream and upstream channel associations, early requirements for symmetrical bandwidth and capabilities of early DOCSIS silicon has resulted in limited combining ratios. Even though significant investment was made in DOCSIS 2.0 by the industry to improve noise mitigation and increase bandwidth capacity in the upstream frequency spectrum (up to 30 Mbps per channel), the unspoken truth has been that this capacity either goes unused or results in under-utilized upstream CMTS receivers. In fact, the improvements in DOCSIS 2.0 upstreams create such an imbalance between upstream and downstream capacity that real networks are prevented from capitalizing on DOCSIS 2.0 improvements. While the existing problem and future DOCSIS 3.0 requirements may be solved using integrated CMTS devices, the imperative of offering IPTV services demands a more modular and flexible approach to expanding upstream and downstream capacity. Fortunately, opportunities exist for an expansion of CMTS capacity by adoption of M- CMTS architectures. This type of platform physically separates once-integrated CMTS functionality for best-of-breed performance. In an M-CMTS architecture, the function of adding DOCSIS information to IP packets that are being transmitted to the user is still the responsibility of the CMTS (called the CMTS Core in this model), while responsibility for 2
  • 3. changing the packets to more closely resemble television signals is moved to a separate Edge QAM chassis. M-CMTS DOCSIS 3.0 CMTS Core Channel Bonding Modem Edge QAM Broadband speeds GigE GigE > 100 Mb/s to IP Network Upstream paths Broadband speeds > 25 Mb/s Legacy DOCSIS 1.x or 2.0 Modems Figure 2: M-CMTS with disaggregated CMTS Core and Edge QAM functionality M-CMTS also addresses the limitation of fixed allocations of downstream and upstream capacity. Increasingly an issue for cable operators faced with the need to accommodate asymmetrical traffic patterns such as streaming video, and symmetrical ones like VoIP (voice over IP), fixed configurations restrict performance, and can lead to operating costs. Fortunately, M-CMTS platforms can provide cable operators the flexibility to assign all capacity to downstream traffic, upstream traffic, or any ratio in between. DEFINING THE REQUIREMENTS FOR THE DELIVERY OF IPTV What is IPTV? In broad terms it is a cable service delivered to an end user over an edge network capable of transporting IP. It could be a traditional video service that an operator offers today such as a linear TV program, a video clip from an Internet source like Googles YouTube, a PPV (Pay Per View) episode, and so on. In general IPTV will exhibit some, or all, of the following characteristics: An expansion of programming choices by broadening the universe of content to include long tail content economically delivered using switched broadcast, richer on-demand choices, and video obtained from the Internet; Bundled video, voice and data services delivered over IP connections; Increasing personalization of content that includes addressable advertising, customized new bulletins, music networks, and more; Time-shifting and device-shifting, and place-shifting as appropriate; Based on the characteristics above, the IPTV ecosystem is becoming both large and complex, and needs to address important services such as content management, content encoding, advertising, billing systems, digital rights management and more. 3
  • 4. This paper focuses on the last mile network architecture which comprises the plumbing technologies for the successful implementation of IPTV. The basic functions provided over the last mile are invisible to subscribers. Rather than providing services that users directly interact with (e.g. selection of a PPV movie) the last mile network provides the necessary functionality to enable various IPTV features and services. This is much like the difference between obtaining television service today over cable versus satellite. This last mile delivery is not critical to the viewer, and the television viewing experience is intended to be essentially the same on both technologies. Before describing the various functions that the cable network needs to support for successful IPTV delivery, lets outline some of the key requirements and assumptions that are associated with the migration to IPTV and the subscriber viewing habits. These requirements and assumptions drive the functions of the last mile network. Firstly, it is widely accepted that the move to IPTV will not be an instantaneous and revolutionary change. Instead, the change will be deliberate and evolutionary. The existing infrastructure and installed base of subscriber set top boxes demands that the existing methods for video delivery over the HFC network will be in use for some time. Secondly, subscriber behaviour while consuming video content will be augmented and enhanced by personalization and time-shifting technologies, but will not be changed completely. Specifically, there will still be a tremendous demand for broadcast video content which is consumed by a large percentage of the subscriber population at specific times of the day. For social and psychological reasons, people will still want to watch various