|Quick: 1 and 4.5 Gig DOCSIS Explained|
|Thursday, 16 June 2011 14:03|
I've been reporting since 2005 that (shared) gigabit cable would come so this is no surprise. John Chapman and Anton Wahlman provided the roadmap at Fast Net Futures. ARRIS at the 2011 cable show demo'd 4.5 gig down by eliminating any TV programming and using the full bandwidth (128 6 MHz channels) for data. Comcast bonded more than 25 channels and showed 1 gig down and 300 meg up. These are improvised demos, not close to production equipment. It will take two to five years for gear that would make this practical for regular customers; lots of other obstacles beside the technical mean you will not see these speeds at home for a very long time.
Here's how it works.
Coaxial cable by design carries robust signals, divided in the U.S. into typically 128 channels. In DOCSIS 3.0, every 6 MHz channel delivers about 40 megabits downstream.
Takeaway: Coax can carry gigabits, although that will rarely be a commercial product. The gigabit (shared) capacity will become important later this decade as data usage grows. Raising the shared capacity to a gigabit can maintain solid performance for all users at 50 and 100 megabits well. My guess is some nodes will need upgrading 2015-2018 and the increased capacity will support 50 meg service well into the 2020's.