While DOCSIS 2.0b has had the proverbial fork stuck in it since mid-summer, that doesn’t mean that cable operators aren’t looking for other means of boosting bandwidth while getting a jump on DOCSIS 3.0 capabilities. The modular cable modem termination system (M-CMTS) specification published by CableLabs in 2005 is separate from the DOCSIS 3.0 specs, but M-CMTS is still a part of most MSOs’ 3.0 game plan for competitive reasons and because it can separate CMTS upstreams and downstreams. On the competitive front, M-CMTS, along with the edge QAMs, will help operators combat competition, such as from Verizon’s FiOS deployment, and help overseas operators battle advanced DSL deployments.  The Next Generation Network Architecture, defined in 2004 by Comcast, Cox and Time Warner Cable in 2004, determined that CMTSs should be modularized in order to compete with fiber, DSL and other technologies. Prior to the release of the M-CMTS specs, the integrated CMTS (I-CMTS) contained DOCSIS MAC and PHY functions, as well as other types of upper layer protocols, in one chassis. In one scenario, M-CMTS architecture splits the components into an M-CMTS core that is connected via an interface to an edge, or universal, QAM.  The other option is to upgrade the required interfaces to the I-CMTS so it could operate as an M-CMTS edge QAM and upstream receiver. Like almost any other specification, there is some leeway allowed for how vendors will implement the M-CMTS specification. Here’s a look at how several vendors are approaching M-CMTS and how operators can use it in phases en route to an eventual DOCSIS 3.0 deployment.  (For a further look at how the M-CMTS falls strategically within a convergence of IP-based services, see this article from the October issue of Communications Technology by John Treece of Juniper Networks and Michael Patrick of Motorola.) Cisco Cisco’s John Mattson, senior director of product marketing for Cisco’s access and aggregation business unit, said his company’s strategy differs from the competition because “we’re actually deploying kind of a modular CMTS architecture with our wideband solutions.”  “What most people are doing is bonding channels on an existing CMTS line card,” Mattson said. “To us, this is a double-sided problem; one side is more bandwidth, and the other side is lower cost per bit. You want to solve both sides of that equation if you’re an MSO. Just adding more bandwidth to be able to go 50 Mbps per subscriber is a good thing, but if it costs you the exact same amount per bit as it did before, then you’re piling up a lot of infrastructure.” In the wide area network (WAN) interface on its uBR series chassis, Cisco added in an additional line card that pipes over bandwidth to an edge QAM. Mattson said adding an existing edge QAM is much cheaper cost per QAM than adding a CMTS QAM. “The way the other guys are dong it is just by adding more line cards to build more smaller pipes to make a bunch of smaller pipes equal a few fat pipes,” Mattson said. “What we said is, ‘Let’s keep the existing infrastructure you have with your existing line cards in place, and instead of doubling it, lets find a way to add more downstream at a much lower cost per downstream.’” Cisco announced a trial in September for its wideband solution with UPC Broadband in Europe. Cisco will use its uBR10012 for its DOCSIS 3.0 solution. “The next step beyond what we’re doing today is the introduction of the universal or edge QAM, which is what M-CMTS is all about,” Mattson said. “For us, it’s a fairly simple step to go from an architecture that exports downstream traffic to an existing edge QAM to adding the interfaces and other pieces of the M-CMTS specification that turns it into a pipeline that shares a universal QAM.” Arris On the wideband front, Arris is in trials with several companies, NTL in the UK and JEJU Broadcasting in South Korea, with its FlexPath solution. Stan Brovont, Arris’ VP of marketing, said that FlexPath uses DOCSIS 3.0 channel bonding techniques to bond the downstreams. Arris also had to create its own software for cable modems so they can communicate with its Cadant C4 CMTSs to enable the wideband solution. “DOCSIS 3.0 will be an evolutionary process,” Brovont said. “What we’re allowing people to do is selectively use some of the features in DOCSIS 3.0, like wideband with our FlexPath, without them having to fully commit to or wait for M-CMTS or DOCSIS 3.0.” For DOCSIS 3.0, Arris is doubling down its bets by offering both M-CMTS and I-CMTS implementations on its existing C4 chassis. “We obviously think that gives us a competitive advantage, as well,” Brovont said. “Some of our competition has no upgrade path for their installed base, and they’re expecting people to replace all of the equipment.” BigBand While not ruling out I-CMTS, BigBand has been demonstrating an M-CMTS solution since the CableLabs Summer Conference in 2005. BigBand is working on an M-CMTS solution that uses its existing cards with its BEQ6000 edge QAM. The BEQ6000 is based on BigBand’s BME50, with the addition of DOCSIS Timing Interface. “You need to find a way to do the downstreams much cheaper, and we have a unique aspect to our design; we don’t have any switched architecture that that traffic has to flow through” said Roger Slyk, BigBand’s director of product marketing. “We’ve taken our completely distributed architecture, which has a lot of additional power, and increased the processing capability in those cards,” Slyk said. “We have FPGAs (field programmable gate arrays) in those boards, and we’ve programmed them to do a lot more of the DOCSIS processing in the FPGAs and in the microcode of the communications processors than they’ve ever done before.” Slyk said BigBand is able to take a 2X8 card and increase the downstreams to 8X8 by using edge QAM. The DOCSIS processing is done on the CMTS core with QoS, encryption, filtering and compression functions done on the card. The data is then encapsulated into an IP frame and sent over to the edge QAM, which strips off the IP header before doing the modulation and upconversion en route to the HFC plant. “We know it takes a lot of time and effort to create these new cards, so we’re going to use the exact same cards we have today,” Slyk said. “We’re going to use edge QAM to gain access to those additional downstreams, and cost per downstream with edge QAM is considerably less than in the CMTS.” Bigband’s M-CMTS solution is currently in trials with operators in North America, Europe and Asia, with a full release slated for early next year. – Mike Robuck

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