I think that some "equal time" for the cable tv/cabalemodem camp is only fair here, since for the past couple of days we've been focusing on wireless and fiber access schemes to the greater extent.
This snip is from a report that I receive periodically from BroadBand Home. I recommend this publication to anyone interested in last mile and residential/so-ho networking developments:
broadbandhomecentral.com
I have comments on some of these observations, but I'll defer those until some other time. In the meantime, how about some comments from you all?
FAC
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"Cable's Magic Trick: How Bandwidth Keeps Growing"
How much life is left in the cable plant? There's been lots of discussion, both in this newsletter and in debates with fiber providers who think that fiber to the home is the only way to offer the full range of digital services in the future. While we remain convinced that anyone building in a greenfield environment should have their heads examined if they don't use fiber, the reality in North America is that cable passes the vast majority of residences and that over the past five years, cable operators have made large investments in upgrading and rebuilding their physical plants. Although fiber deployments are happening in new communities, it's hard to see how anyone could get the funding to build a new FTTH plant in North America, where telephone and cable company wires each pass almost all homes and most families already subscribe to both.
But how will cable operators deploy all the new services and accommodate the growing traffic which eat up their bandwidth resources? How will they carry increasingly symmetrical services in the face of limited upstream bandwidth?
While we were at the Western show, we looked at several developing technologies designed to expand the digital carrying capacity of existing cable plants and came away thinking that cable operators may be able to get enough extra capacity to phase in a lot more digital services over their existing cables.
This magic trick of creating more bandwidth comes from three technologies, and have a multiplicative effect. The first (BigBand) addresses broadcast video and increases the channel carrying capacity of existing digital multiplexes; the second (Narad) moves data services away from the traditional cable bandwidth and claims to carry additional gigabits per second over the existing physical plant; and the third (Rainmaker) claims to double the efficiency of any service through wavelet modulation.
BigBand - Squeezing more video into existing channels
At the show, we met with Sylvain Riviere of BigBand Networks, which provides technology to make better use of the bandwidth assigned to current digital broadcast multiplexes.
Today's digital cable multiplexes are created by taking existing multiplexes from satellites and combining them with individual digital and encoded analog channels. With today's technology, this requires separate boxes for each incoming and outgoing multiplex, and complex and often manual systems to keep track of the channel assignments.
BigBand has a line of "broadband multimedia-service routers" which cable operators use to carry broadcast-quality video, audio and data throughout a cable system's backbone network. These routers move all the de-multiplexing and re-multiplexing into a single box, with a management software suite that includes dynamic control of variable bitrate encoding to fit more channels in a fixed bandwidth, and scheduled changes of channel assignment.
Sylvain discussed with us some additional methods they plan to add to their software. These promise to further increase the carrying capacity of existing channels for broadcast and on-demand video.
( www.bigbandnet.com )
Narad - Taking advantage of unused bandwidth
While BigBand squeezes more digital video into the existing channels, Narad Networks moves other IP services out of the bandwidth assigned for traditional cable delivery and into unused portions of the cable frequency spectrum.
In North America, the typical "hybrid fiber-coax" (HFC) cable plant assigns the bandwidth from 50 to 750 or 860 MHz to "downstream" delivery (from the cable system to the home) and assigns 5 to 35 or 42 MHz to "upstream" delivery (from home to the cable system). This bandwidth allocation works fine for television services, but is a problem for data services (which share the bandwidth with other cable services). The allocation is not only highly asymmetric (much more bandwidth is downstream than upstream), but even worse the upstream bandwidth is comparatively noisy; thus fewer bits can be transmitted per Hertz upstream than downstream. As more homes install cable modems, cable operators are forced to limit the upstream data rates even as users want to share music, digital photos and videos with their family and friends.
Narad's approach is to carry switched IP services in the bandwidth above the high end (750 or 860 MHz). Since cable amplifiers don't transmit the higher frequencies, Narad replaces them with combined amplifiers and GigaBit Ethernet switches. The amplifiers handle the lower frequencies in the traditional way, while the switches handle bidirectional data.
Narad's "Virtual Fiber Architecture" offers two options for switched IP services. The first uses the bandwidth from 860 MHz to 1 GHz to derive bidirectional 100 Mbps ("Fast Ethernet") service; the second uses 1 to 2 GHz to derive bidirectional 1 Gbps ("Gigabit Etherner") service. They claim that both will operate on existing cable plants without any effect on existing cable services running below 860 MHz.
Narad's approach, when and if proven by upcoming field trials, promises cable operators that they will be able to provide switched Ethernet services to business and residential customers without having to rebuild the physical cable plant (but needing to replace the amplifiers and other boxes between cable segments).
( www.naradnetworks.com )
Rainmaker Technologies -- Getting more bits out existing bandwidth
Any approach to transmitting data -- whether video, voice, or data -- depends on a modulation scheme. In North American cable systems, the downstream modulation is either 64 QAM or 256 QAM, which operate in 6 MHz channels at 30 and 40 Mbps respectively. The ratio of bits per second to Hertz is the "efficiency" of the modulation scheme - thus their efficiency is about 5 and 6.5 bits per Hertz, respectively.
At the show, we met with Paul Chin and Mark Laubach of startup Rainmaker Technologies. Rainmaker proposes to use wavelet modulation rather than the traditional QAM modulation, and to operate digital services in wider channels than the traditional 6 MHz allocation. They claim that this approach will provide 170 Mbps downstream in 18 MHz (combining three 6 MHz channels) and 100 Mbps upstream - at a cost similar to today's DOCSIS modems operating at much lower data rates. This provides an efficiency gain of nearly 2:1 downstream and 4:1 upstream.
Rainmaker's modulation approach, when and if proven, applies both to traditional services carried in the existing bandwidth, as well as to new services such as those proposed by Narad. While their emphasis to date has been on cable, they are agnostic as to type of broadband access - the same modulation approach could be applied to DSL, fixed wireless, and satellite delivery of broadband services.
( www.rainmakertechnologies.com )
A note of caution: Narad is just about to roll out its first trial systems so we'll need to stay tuned on how well they actually do in the field. Rainmaker is even further from actualization -- they are seeking funding to build units and run trials. Other companies are also active in this "bandwidth magic" space and we'll be tracking how they do in the harsh real physical world.
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