As demand for narrowcast video services grows, cable operators both in the US and Europe face a number of critical technology choices. Stuart Thomson looks at some of the key developments.
US cable giant Comcast is currently pulling the industry towards its vision of the next-generation cable architecture. The focus of its current activity is the CMAP, or Converged Multiservice Access Platform, which grew out of Comcast’s need for a dense headend platform in order to allocate ever-greater amounts of bandwidth for video applications – a need driven in the US by the deployment of switched digital video (SDV) services, HD and online video. The wider project, of which CMAP is a part, is know as the Next-Generation Access Architecture (NGAA).
CMAP is actually a product specification. It is not an attempt to create a new standard for the delivery of IP over cable – the CMAP platform is designed to be fully DOCSIS-compliant. The product specification therefore is for a much denser and more flexible combination of Edge QAM device and cable modem termination system (CMTS) that will work with existing DOCSIS interfaces but will deliver vastly more QAMs per port than existing gear.
Comcast has decided to specify a device with a certain number of ports per rack-unit, leaving it open to vendors to decide on the precise RU configuration.
Because it is not a ‘standard’ as such, CableLabs (and EuroCableLabs) do not really need to get involved (although they are following the project closely). They just need to qualify the products as they would with any CMTS device.
One of the key objectives for cable operators including Comcast is to reduce the amount of space required for CMTS racks (as well as the amount of cabling required) and to reduce energy consumption.
The key cost savings are expected to come from saving space and energy – the cost of the equipment itself is likely to remain relatively high, and it is questionable whether it will prove to be cheaper than the (in any case progressively declining) cost of conventional CMTS and Edge QAM gear. But energy and space are emerging as key concerns for service providers as they address the need to build facilities to serve ever-increasing bandwidth demand.
As Ramin Farassat, vice-president of product marketing at RGB Networks, says CMAP is in a sense an attempt to define what the next-generation CMTS will look like. As such, it comes in variant forms that carry echoes of recent attempts to push a more modular data-over-cable infrastructure.
Charles Cheevers, chief technology officer, Europe at broadband cable specialist Arris, says that CMAP is a “natural evolution of the headend architecture of cable networks” as a growing proportion of traffic becomes unicast. “The first thing about CMAP is that it’s a technology that converges and puts out more capacity on less hardware with greater density,” says Cheevers.
“Each company can focus on their core capabilities. We are opening things up to any strong router vendor on the market.”
Ramin Farassat, RGB Networks
The modular variant of CMAP can be seen in some ways as an alternative to the modular CMTS (M-CMTS) standard, a technology that failed to gain the traction many predicted for it. “M-CMTS was not really good enough,” says Gil Katz, senior director of cable solutions at Harmonic. The essential flaw in the standard, he says, is that it did not go far enough by separating RF technology elements entirely from the IP platform – the CMTS – thus permitting new entrants with purely IP expertise including the likes of Juniper and Alcatel Lucent to enter the market. “What we pushed was a modular approach where the CMTS is really just an IP router in-and-out with no RF,” says Katz. He distinguishes this ‘packet shelf’ from the RF ‘access shelf’ – a platform akin to the existing Edge QAM device – that delivers RF both up and downstream. This separation enables the service provider to keep core CMTS functions, including HTTP servers, Quality of Service monitoring and subscriber management, in a single location and put an Edge QAM-like device out in the network. This is in contrast to M-CMTS deployments, where an RF return path all the way to the headend has been necessary.
For Katz, the combination of an all-IP headend and IP infrastructure between headend and hub, with distributed access shelf devices positioned in each hub, is a “great architecture for Europe” that would allow more vendors to enter the market. “Those companies do not want to deal with RF but DOCSIS is just another protocol that they can run on their routers so there are more vendors that can compete in the CMTS space,” he says. Taking IP all the way to the node would offer further benefits to operators, he says, by making it much simpler for them to segment each node – a key future requirement for many European operators that still operate nodes serving 1,200-1,500 homes.
Brad Ferris, head of portfolio management, TV solutions area at Ericsson, another Edge QAM supplier and supporter of modular solutions, says that CMAP is squarely addressed at addressing the challenge of an increasing number of narrowcast channels. He says that the packet shelf and the access shelf are derivatives of the CMTS and the Edge QAM. At present, integrated CMTS have the lion’s share of the market by far, with M-CMTS having relatively limited take-up to date. “The integrated approach has advantages and disadvantages. From the access shelf perspective we think we can cooperate with people on the packet shelf side,” says Ferris.
RGB’s Farassat says that CMAP is in a sense an attempt to define what the next-generation CMTS will look like. He agrees with Katz that the modular variant is a “bigger idea” than M-CMTS. Farassat says that RGB is building an access shelf that does all upstream and downstream RF transmission both for data and IP-based video as well as traditional QAM-based video delivery. The CMAP access shelf will be able to deliver “hundreds of QAMs”, while a packet or IP shelf, separated from the RF elements, will take care of IP Quality of Service, subscriber management and all the things that routers do well, according to Farassat. “Each company can focus on their core capabilities,” he says. “We are opening things up to any strong router vendor on the market.”
Cisco Systems, a major infrastructure supplier to Comcast, has expertise both in RF and IP of course. Daniel Etman, product manager at Cisco’s cable business unit, says that Cisco is already “85% compliant” with CMAP. He believes that some aspects of the product specification will feed into CableLabs standards, though not things like form factor. “It’s up to CableLabs and the MSOs to make that decision,” he says. “I think if you look at the spec, the key point is that it’s bringing more density and versatility in a smaller form factor.” The more advanced version of the spec, which requires the splitting of the RF elements from IP completely, will likely require CableLabs involvement. “That’s not necessarily the direction Cisco is going,” he says. “We base our products on industry requirements.”
One obstacle to a radical departure in terms of the cable architecture is that operators are organisationally still divided into video and data groups with different procurement responsibilities, says Etman. “Operators need to change their internal approach to procurement,” he says.
Etman also points out that CMAP does not specify the size of the device – only the maximum size (16RU). “If you look at Europe, 16RU is often quite large, especially looking at the densities you can offer with next-generation capabilities,” he says.
According to Harmonic’s Katz, other operators in the US and Europe have been following CMAP discussions closely.
Platforms with limited capabilities should be available next year, with fully functional systems up and running by 2012, according to Katz. Key to the platform’s wider success, he says, will be its ability to “scale down”. Katz (like other Edge QAM vendors) does not believe that the ‘integrated CMAP’ model will win many adherents other than existing CMTS vendors that have little choice in the matter because they do not supply Edge QAMs.
CableLabs has not so far been formally involved in CMAP, but RGB’s Farassat says it is likely to become so at the later stages to cover questions such as how the platform will handle encryption and testing.
Whether variations in the platform will be necessary to handle the requirements of international operators remains a moot point. It is possible, at least in the view of some of the vendors, that an integrated model might be suitable for operators with smaller headends.
North American concerns are clearly driving the initiative, and key to the thinking behind it is the need to support a large installed base of legacy set-tops. “The numbers are big enough to make sure that any initiatives going forward have to support those devices,” says Cheevers. “That’s not the same for Europe or Asia.” European implementations of CMAP would need to accommodate a number of variations in requirements. For example, in the US, each CMAP device is likely to have the capability to support multiple local ad insertion zones, a requirement that doesn’t really exist in Europe where, as well as high interest in switched digital-video to recapture bandwidth. In Europe, on the other hand, there may be high-demand for more narrowcast channels as operators migrate to IP services.
Cheevers believes that European requirements may converge to some extent with North American ones as operators seek to compete with DTH players by offering bandwidth-hungry expanded HD tiers.
As was the case in the debate over modular versus integrated CMTS to accompany the move to DOCSIS 3.0, suppliers of CMTS gear without Edge QAM products, including US cable industry stalwart Motorola, believe that integrated models will be adopted first, for a variety of reasons.
Motorola has for some time been working on its own next-generation product, the Video Edge Services Platform (VESP), which it has more recently said is relatively closely aligned with Comcast’s requirements. “We are in the process of defining our implementation of a CMAP-compliant platform [based on] VESP but one that will also meet the requirements of European operators,” says Mike Gannon, EMEA business development, Motorola. Gannon says Motorola believes in an integrated platform combining IP switching and routing with headend functionality including subscriber management. However, he says that the company’s roadmap is “not finalised” and argues that the density (i.e. number of QAMs delivered per port) being called for by Comcast might not be applicable to all operators’ headends.
Regarding ‘integrated’ versus ‘modular’ implementations, Gannon says Motorola believes that the requirement for RF redundancy will grow as platforms deliver ever greater numbers of QAM channels, meaning that ‘integrated’ is the way to go. “There is a lot more to delivering video over DOCSIS than just pure IP routing,” he says. “It’s an area where experience is invaluable.”
However, he says that such a platform may not necessarily be applicable for smaller headends, and points out that European requirements are different because operators are under different pressures. Switched-digital video, for example, by and large remains a technology that appeals specifically to US operators, which have seen bandwidth-hungry MPEG-2-based HD tiers expand rapidly.
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Arris will also initially produce an integrated product and Cheevers argues that the modular version could be problematic for operators with smaller hub sites. Arris will migrate its C4 CMTS to become an integrated CMAP platform. “We have been successful in the CMTS space with integrated devices and we still see that the integrated version is the right way to launch,” says Cheevers. He argues that the advantages of having devices from multiple vendors in the same facility, which has been made possible by the development of fully standardised interfaces, can cause problems for an operator, which then has a number of different vendors to call for support.
Cheevers makes the salient point that service providers are unlikely to switch off legacy equipment and migrate to an entirely new architecture overnight. “There is a challenge of getting CMAPs into smaller headends,” he says. Moreover, the transition to ‘all-IP’ is fraught with practical problems. “Serving groups for video and DOCSIS do not necessarily have a one-to-one correlation,” says Cheevers. One possible solution could be for operators to subdivide video service groups into separate groups for data.
Because CMAP will have to be deployed alongside existing legacy equipment, at least in the first phase of deployment, it is unlikely that service providers will be able to harvest the full benefit that should be possible in terms of reduced operating expenses.
While cable technologists in the US have focused on the Comcast project, less has been heard recently about a European initiative to solve some of the challenges faced by operators by dramatically increasing the bandwidth available over their networks – the DVB-C2 project. DVB-C2, the next generation of the European DVB for cable standard deploys a range of techniques – notably the use of COFDM rather than single-carrier QAM modulation and 16 up to 4096 QAM modulation schemes rather than the DVB-C range of 16 to 256 QAM – to deliver 30% higher spectrum efficiency and possibly 60% improvements in bandwidth over the existing DVB-C standard.
Unlike CMAP, a product definition created to meet a need by a specific operator, the DVB-C2 standard is an initiative driven primarily by technologists that is in search of operator support. As such the standard may have a diminished chance of success – something that would, in the view of Harmonic’s Katz at least, be a pity. DVB-C2 addresses the legacy of analogue video that forced operators to carve up their available spectrum into 6MHz or 8MHz slices in order to deliver analogue video channels – an entirely wasteful procedure in the digital world. “It’s all about narrowcast services moving forwards,” says Katz. “Cutting the spectrum up makes it less efficient and makes resource management much more complicated – you need multiple tuners [in equipment] to get different frequencies at the same time, which makes management of the boxes more complicated.”
Ericsson’s head of system management, solutions area TV, Paul Stallard, argues that all vendors are currently in much the same position – waiting to find out what the silicon suppliers will do. “We were involved at an early stage in C2 and it was something we supported,” says Stallard. “I think we are in the same position as a lot of other vendors on our side. It will really depend on the availability of chipsets and the pricing of those chipsets in terms of when C2 becomes a market reality.”
While DVB-C2 would overcome this legacy problem, it would require operators to deploy new customer premises equipment – something that those operators with large legacy digital TV subscriber bases would obviously be loath to do. This problem, together with the fact that operator interest has so far largely been confined to Germany (led by Kabel Deutschland) means that silicon suppliers will continue to be cautious about investing in chipsets. This is the crucial problem facing the standard. Introducing DVB-C2 alongside existing DVB-C systems means simulcasting, removing the advantage in bandwidth savings that DVB-C2 was supposed to confer in the first place. This will lead to delays as silicon suppliers hold out to see if the market will take off. But even in Germany, where interest is currently greatest, another couple of years will see existing digital rollouts expand, creating exactly the kind of legacy base that operators in more mature markets already have to content with. “Migration is the great challenge to C2,” says Motorola’s Gannon. “Existing set-tops will not have access to [services]. You either need a C2 overlay network or to replace existing set-tops.”
There is also a question of whether the wider market, even within Europe, requires investment in such a technology to be a priority. Ericsson’s Stallard points out that the related DVB-S2 standard arrived at a time when satellite pay-TV operators were looking to deploy HD. “It was perfect timing,” he says. There were no legacy boxes in the market to speak of. “Cable is in a different situation because [C2] came along after many of them had already made the HD transition.”
Nevertheless, Arris’s Cheevers believes that interest is growing, even if it is from a small base. Cheevers believes that physical layer technologies for cable will have to advance. Addressing one of the key hurdles – the lack of consumer equipment – he points out that set-top providers have an opportunity to leverage the work already done on the closely related DVB-T2 standard, now being deployed for the launch of digital-terrestrial HDTV channels in the UK and Italy. “There is a huge cross-over,” says Cheevers, who adds that companies active in the T2 space will have the ability to make C2 set-tops very quickly. “The question mark is over the commercial viability of carrying that extra overhead in the silicon.” Set-top boxes would have to be rigorously tested and whether vendors could develop a single-chip C2 solution that could be sold across the World is open to question. However, one solution, says Cheevers, is to develop equipment based on a limited subset of the “full” DVB-C2 standard. The technology works by dividing each 8MHz carrier into multiple OFDM sub-carriers, with multiple possible modulation rates of up to 4096QAM. On top of that multiple DVB-C2 tuners can combine carriers to increase the available bandwidth. “The number of permutations is huge,” says Cheevers. Supporting all the elements of the standard could involve a significant investment, but working within a smaller sub-set of parameters could help operators and vendors to manage the cost of deployment, according to Cheevers. For example, initial deployments could be based on a more limited number of modulation schemes, starting say with 256QAM. However, the development of integrated silicon for the set-top box remains key.
The developments in parallel of these technology initiatives point to some of the key challenges cable network operators face as they look to accommodate the shift from broadcast to narrowcast and converged services. There are many technology areas that operators could focus their investment priorities on (not least driving fibre deeper into their access networks). However, the headend and consumer premises equipment choices they make will be crucial in determining their ability to support the kind of new services that their customers will increasingly demand.
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