Fast Net News, DSL Prime, DOCSIS Report

Standard cable coax systems have a total capacity of 4.7 gigabits when used just for data. Most of the bandwidth today is used for TV. As the TV side goes all digital, data can claim more of the pipe.

First generation cable modems shared a single 6 MHz or 8 MHz channel for a maximum speed of 35-50 megabits, shared.

DOCSIS 3 initially bonded 4 channels for 150-200 megabits downstream. The systems now coming out of the labs bond 25 channels for a shared gigabit. The typical cable system has 132 6 MHz channels, but carrying 100 HD TV channels and the remaining analog TV takes up many of those. Upstream is typically limited and offered to customers as no more than 5-6 megabits. Higher upstream speeds are practical, but would require more changes to the system and are very rarely implemented.

  Intel began sampling gigabit chips in 2012 and Arris has shown working gear at trade shows.  Kabel Deutschland CTO Glanz  is optimistic he’ll begin serving customers by the end of 2013.

  DOCSIS 3.1 is expected to be 1 gigabit (shared) upstream and 10 gigabits downstream, according to John Chapman, Cisco’s chief cable architect and a member of the committee. Manufacturers are targeting 2015 but were two years late with DOCSIS 3.0. It uses more efficient OFDM coding and I believe will use higher frequencies as well. Most systems will require (modest) upgrades to CMTS, amplifiers and other gear. The cost should be moderate (? < $200 most places) but real.

Simple, straightforward, and not terribly expensive John Chapman has been promising since 2005 to deliver a gigabit over cable. Nobody but the engineers believed him then and even John knew it would be years away. Production systems were 36 megabits (shared) and DOCSIS 3.0 still years away. (John played a key role on DOCSIS 3, incidentally, using some of these concepts.) By 2008, CableLabs CEO Dick Green made a trip to Singapore to see whether cable could meet the requirements of Singapore’s planned gigabit network. He confirmed to me a gig was definitely possible but the needed processing power was too expensive back then. DOCSIS 3 was reaching the field, sharing 160-200 megabits by bonding 4 channels. Working with some of the best engineers, John has authored “Mission is Possible: An Evolutionary Approach to Gigabit-Class DOCSIS.” Abstract below, complete paper available for free here  or here

     The basic concept is very simple. A common 860 MHz cable system if used all for data can carry 4-6 gigabits. Until recently, 80 channels, (480 MHz in U.S.) was used for analog TV and the digital TV required most of the remaining space, especially with HD. There simply wasn’t enough room for a gigabit of data. Switched digital frees some room and is widely deployed. Giving the remaining analog TV viewer a cheap DTA box allows a full digital conversion, freeing half the spectrum. With DTA prices around $30, many systems have shut off analog and have plenty of new capacity. The 36 megabits of early U.S. DOCSIS used only one 6 MHz channel. The 160 megabits of today's U.S. DOCSIS 3.0 bonds four of those channels and adds some efficiency improvements. By 2012, DOCSIS 3 modem chips bond eight channels, raising the  the download speed to 400 megabits (shared) in Europe although that’s just beginning to be distributed. 

     Use 25 of the 120 channels for data, and a gig is possible. 25 channels are easily found after the analog switchover in Europe, where they carry fewer TV channels. (Note U.S. DOCSIS uses 6 MHz per channel, EURO DOCSIS 8 MHz. On most modems in use, that's about 36 megabits per channel in the U.S. but about 48 megabits in Europe. We all get confused on these numbers.)

     May 2012, Kabel Deutschland, working with Arris, showed 4+ gigabit (shared) speeds in production-type gear. They used twelve ARRIS 8 channel bonded modems to achieve the 4 gigabits, the maximum today. Broadcom, Intel and perhaps others are racing to make chips that can bond more than 8 channels. Word just came in from Arris that they will show a 24 channel bonded modem capable of 800+ megabits at IBC in September. They aren’t shipping soon but see no obstacles to going into production soon. Initially, price will be high for a cable modem, but recoverable with just a few months of customer service. I’ve posted the press releases below.

   There’s a slew of work required before gigabit cable becomes a regular product. Decisions have to be made about allocations to upstream and downstream. Should the spectrum in use be extended to 1 GHz or perhaps higher? Should new error corrections and modulation methods be included? There are many more questions. Chapman of Cisco was joined was joined by Mike Emmendorfer of Arris, Robert Howald of Motorola and Shaul Shulman of Intel for the crucial discussion paper.

Hitron’s ready for CableLabs Certification. By this time next year, some cable companies will be offering 600 megabit-1 gigabit (shared) downloads. ARRIS and Hitron both showed 16-24 channel modems at SCTE, promising samples in a few months and volume production sometime next year. Both use the Intel Puma 6 chip and 3x3 MIMO for WiFi performance. Intel offers a reference design they all but promise will pass CableLabs, so numerous vendors should be on the market soon. In early days, the price will likely be high but that shouldn't last very long.

ARRIS also is ready to upgrade their best-selling C4 CMTS with software and a System Control Module. No word from lead competitor Cisco on when they will match, but they certainly are working hard. The main limit, once the gear is field-proven, will be bandwidth. Most U.S. systems don't have a spare dozen channels. Some Europeans, where they carry fewer TV channels, will be able to jump on early. SK in Korea has announced they will be upgrading as soon as possible; they face tough competition from fiber.

Sharing on cable works remarkably well. I'd estimate actual performance will be better than 500 megabits 95+% of the time. More than 99% of the time users are likely to achieve 200 megabits. If anything, those are low estimates. Speeds may occasionally go down as bandwidth demand increases over time. But the new gear should reliably deliver 100 megabits for the rest of this decade.

More on gigabit cable.  Here's the product sheet from Hitron and the press releases from ARRIS and Intel.