DOCSIS 3.0 (sometimes DOCSIS 3) is a standard developed by CableLabs to upgrade Hybrid Fiber Coax (HFC) networks to deliver high bandwidth broadband Internet service. It is used by MSOs (cable TV companies) to compete against Telcos using FTTH and FTTN/FTTC with VDSL2. DOCSIS 3 is estimated to cost approximately $70 per subscriber in addition to the cost of a new DOCSIS 3 compliant cable modem required on the subscriber premises, which is inline with the cost of installing DSL in an existing OutSide Plant (OSP) cabinet. What DOCSIS avoids is drastic upgrades to an HFC network, and this is its fundamental appeal. Cable companies can deliver very high Internet access bandwidth for very little additional investment with the various DOCSIS standards, especially DOCSIS 3.
The most important thing about DOCSIS 3.0 is bonding cable TV channels for more bandwidth. Previous versions of DOCSIS only used a single channel and were limited in their throughput. With 4 channels, rates of about 160/120Mbps are possible. With 8 channels, rates of 320/120Mbps are possible. Of course, the cable companies with have to give up these analog video channels to devote them to DOCSIS 3.0, but this can be done incrementally, and it does not have to be done throughout the network all at once.
The equipment required to deliver DOCSIS 3.0 services is the Cable Modem Termination System (CMTS) and the DOCSIS 3.0 cable modems on each subscriber premises. Both must be upgraded to support DOCSIS 3.0 over an existing HFC network, shown below before an upgrade. Note that the HFC network is unchanged with the upgrade to DOCSIS 3.0. The only change is in equipment that is installed in the headend and on the subscriber premises.
Source: fttxtra
Comcast can now put another point in its DOCSIS 3.0 upgrade wins column. The MSO announced this week that it completed its DOCSIS 3.0 upgrade in its greater Chicago area market, including Northwest Indiana. In July, Comcast reported it had upgraded about 50 percent of its nationwide HFC network to DOCSIS 3.0, and it remains confident it will pass 80 percent of its total homes and businesses with DOCSIS 3.0 by the end of 2009. This projection is up from the initial 65 percent target Comcast set in February.
And it appears that Comcast is well on the path of achieving its 80 percent penetration goal. The MSO’s DOCSIS 3.0-based service is currently available in 11 U.S. cities, including: Atlanta, Baltimore, Boston, parts of Connecticut, Fort Wayne, parts of New Jersey, Philadelphia, Pittsburgh, Portland, the Twin Cities and Seattle. Subscribers can choose from two DOCSIS 3.0 service sets.
Cable’s DOCSIS 3.0 race is certainly on. Comcast’s fellow cable brothers Cox Communications, Canadian operator Rogers and the U.K.’s Virgin Media have been making DOCSIS 3.0 waves lately. Similar to Comcast, Cox has also taken a tactical approach to its DOCSIS 3.0 rollouts by launching its wideband service in not only Verizon’s FiOS territories (Fairfax County, Virginia and Rhode Island), but more recently Qwest’s FTTN territories in Phoenix. Meanwhile, Rogers launched its wideband service in parts of Toronto last week.
Of course, DOCSIS 3.0 is not just a large MSO’s game. With its conversion to all-digital video complete in its major metro markets, competitive cable operator RCN said it will begin rolling out DOCSIS 3.0-based services initially in its New York and Boston markets this fall.
source: fiercetelecom
This week we’ve been looking at why cable companies are kicking the tires on fiber-based passive optical networks, even though they have a heavy investment in hybrid fiber coax (HFC) networks. Today, we’ll look at the DOCSIS architecture and its skinny upstream data path, and how this decreases the longevity of the DOCSIS architecture.
I’m going to condense a whole lot of history and summarize a lot of detail in only a couple paragraphs, so if I leave out some details you are looking for, please comment on this post and I’ll circle back to try to get answers in future posts.
When looking at the DOCSIS architecture as defined by CableLabs, it is important to remember that DOCSIS was rooted in the history of broadcast television networks. Cable networks were originally designed for one thing: distributed television signals in one direction – from the headend (imagine it as a bunch of electronic gear sitting beside a big satellite dish picking up a bunch of television signals) downstream to your house. Originally, the main reason to have a return (upstream) path at all was to allow network elements to report errors and anomolies back to a network management system, so not a lot of bandwidth was necessary for the upstream direction.
Since the cable networks were designed to distribute TV signals, they were designed just like over-the-air broadcast television signals, using radio frequency spectrum in 6 MHz channel sizes. A typical HFC plant is designed around 870 MHz of radio frequency spectrum, with 800 MHz of the spectrum allocated for downstream TV channels. The bottom of the spectrum is used for upstream capacity, but a lot of the bottom part of the spectrum is allocated for the DOCSIS operating system, and some of the rest is poor quality spectrum and unusable for data services. In the end, only about 20 MHz is used for the upstream data channel in a DOCSIS 2.0 deployment. That amounts to about 80 Mbps of upstream bandwidth to be shared across 250 customers per node, or about 320 Kbps per customer. If there are 500 customers on your node, then your upstream bandwidth is about 160 Kbps.
That’s not a lot of bandwidth in the upstream direction, so you can understand why cable companies are very concerned about applications like BitTorrent that use tons of upstream capacity. These kinds of peer-to-peer applications work much better when there is a bunch of upstream capacity available. On an upstream-constrained cable network, peer-to-peer applications have the potential to suck up all of the already-limited upstream capacity.
DOCSIS 3.0 was supposed to help with this problem by allowing multiple channels to be “bonded”, so that bandwidth can be multiplied. However, in an effort to accelerate DOCSIS 3.0 certification efforts, the cable industry deferred upstream channel bonding certification til 2009, so that they could provide downstream channel bonded services earlier in 2008. What that means is that in 2008 the top downstream speed may be able to hit 160 Mbps under ideal conditions, but the upstream speeds are still stuck at DOCSIS 2.0 speeds.
Also, while DOCSIS 3.0 grabs headlines with numbers like 160 Mbps or 100 Mbps downstream, it is likely that this capacity will be shared across multiple customers, just like today’s cable Internet services, so a cable customer may not really be able to buy a service as fast as 160 Mbps downstream.
So, in 2008 at least, while a Verizon FiOS customer is enjoying a 5 Mbps upstream connection, a cable customer is likely to be stuck with a 360 Kbps upstream connection, even on DOCSIS 3.0. It won’t be til sometime in 2009 that the cable customer really starts to see upstream speeds on par with Verizon FiOS.
As time goes on, even with DOCSIS 3.0, the upstream direction is likely to remain the bottleneck in cable Internet services, and it will remain a serious disadvantage for cable Internet service providers until they finally break the tie with HFC architecture.
source: ikeelliott.typepad.com