BROADBAND COMMUNITIES is the leading source of information on digital and broadband technologies for buildings and communities. Our editorial aims to accelerate the deployment of Fiber-To-The-Home and Fiber-To-The-Premises.
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MAY/JUNE 2014 | www.broadbandcommunities.com | BROADBAND COMMUNITIES | 61 systems more efcient. One way to do this is to eliminate duplicate network engineering eforts. Today's lack of convergence between video and DOCSIS (data) engineering teams results in duplicate networks over the same infrastructure. Operators must merge and align service group sizes to fully maximize the benefts of node splits. By eliminating service group separation, operators can simplify their headends. A universal platform capable of supporting carrier channels for both video and DOCSIS maximizes available spectrum and eliminates the need for a large portion of the combiner function in the headend (see Figure 1). Instead of engineering a network with 24 to 32 video QAM channels and a second network with 16 to 32 DOCSIS QAM channels, engineering a single platform that integrates and uses a combined 80- to 120-QAM channel format to support both types of services allows downstream bandwidth to grow to more than 1 Gbps of data services and support a full breadth of video features (video on demand, SDV or IPTV). A single platform also saves signifcant space and power. Tough many in the industry assume this universal platform will be a Converged Cable Access Platform (CCAP), the platform should not be a large CMTS box. Converging internally generated video over the same data channel as Internet-routed trafc creates additional costs. It also eliminates the ability to diferentiate the operator-generated video ofering from the OTT-generated video through Internet portals. Upstream bandwidth will increase. Te biggest limitation of current network architecture is the potential for upstream bandwidth capacity. With the mid-split (the frequency division scheme that allows bidirectional trafc on a coaxial cable) currently locked in at 50 MHz for North America and much of Central and South America, upstream channel capacity is constrained. Deep-fber architectures and unity gain drop amplifers support the use of four-channel confgurations by overcoming the noise foor challenge; however, demand requirements will quickly outstrip total upstream bandwidth capacity, whose theoretical limit is 160 Mbps. Te bottom line is that the mid- split needs to move to free up more upstream capacity to accommodate subscriber demand. Te decision to move the mid-split is not easy and will require signifcant network investment – product costs alone will likely range between $85 and $140 per home as network taps and drop amplifers will need to be replaced and nodes modifed to support the change. Although this requires a substantial investment, it is a cost-efective way to accommodate a steep change in available upstream capacity. One issue is where to make the new mid-split. Te near-term challenges of supporting a wide array of customer- premises equipment makes 85 MHz a popular choice. Tough an 85 MHz split will double the upstream capacity of the network, it leaves a substantial gap between downstream and upstream capacities. It also creates a new complexity in evaluating future technologies and the cost of deployment. If operators want to maximize the capabilities of DOCSIS 3.1 in the future, they must plan in 200 MHz increments rather than 6 MHz channels. A mid-split at 200 MHz accommodates one orthogonal frequency-division multiplexing (OFDM) modulated upstream channel capable of supporting 2 Gbps or 30 256 QAM channels delivering more than 1 Gbps of bandwidth. If operators choose to pursue a smaller frst step by expanding the mid-split, the value and cost of converting to DOCSIS 3.1 becomes an issue. Does 320 Mbps of upstream capacity really support a 6 Gbps downstream capability, or is a DOCSIS 3.0 platform with 1 to 2 Gbps of downstream data with less investment and less complex technology management (mixed modulations schemes) more suitable for the demands of the targeted consumer base? Video formats will evolve. Operators are already starting the evolution from analog and digital MPEG formats to IPTV-based formats capable of supporting multiscreen device and time-shifted viewing. Tough IP video formats can run over DOCSIS channels, operators can also insert additional IP video channels directly into the universal edge QAM or carrier rather than using more costly CMTS ports to alleviate network congestion. Maintaining separate video channels for operator-inserted content also maintains the value of that content by Figure 1: A universal headend platform can maximize available spectrum and eliminate functions. BBC_May14.indd 61 5/29/14 9:19 AM