FTTxtra » VDSL2

Whither VDSL2, DOCSIS, and FTTH?

John Bartell — Thu, 24 Sep 2009 19:40:38 +0000

Choosing a new broadband network technology is no small task for a carrier. When moving to a better broadband technology, a carrier must consider what access infrastructure is available and already deployed. There are many factors to be considered, but by far, what a carrier has already deployed tends to be the biggest consideration. Using existing network infrastructure is imperative to keep installation costs down. It eliminates the most expensive part of installing a new service, which is trenching the ground to install new cables.

The cost to trench new cable for a single subscriber can be as high as $500 to $1500 per subscriber or more, and it can be especially high in rural areas. This cost can often be justified in new installations, but where other access facilities are available, such as coax or twisted pair copper, a carrier rationally must leverage these already installed access facilities.

Telcos have many billions of dollars of copper local loop installed, so they will gravitate to VDSL2 and ADSL2+, at least in the short term. Cablecos have invested tremendous capital in Hybrid Fiber Coax (HFC) networks, so they will continue with their DOCSIS upgrades (1.1 to 2.0 to 3.0) for quite a while. And those carriers with no infrastructure, like many municipalities, will make the leap to Fiber to the Home (FTTH), like Lafayette, LA (my home town), famously did. There are very few arguments for deploying any technology but FTTH in brand new wireline access networks.

VDSL2

Telcos have local loop copper, billions and billions of dollars worth, so they are keen to deploy Digital Subscriber Line (DSL) technologies like ADSL2+ and VDSL2. Many people complain that these are deficient when compared to FTTH, and they are right in many ways. Practically, VDSL2 delivers perhaps 50 Mbps at reasonable distances, and ADSL2+ substantially less.

The cost to deploy DSL where copper is already available is probably under 20% of the cost to deploy new fiber facilities along with splitters and the FTTH Optical Network Terminal (ONT) and Optical Line Terminal (OLT) electronics. This substantially lower cost for DSL makes the likelihood of a subscriber getting any broadband at all much more likely when this option is available. Telcos will still deploy FTTH in greenfield buildouts where they have no existing copper local loops. Over time, with competition from cablecos and munipalities, telcos will deploy FTTH networks in brownfield areas as well.

DOCSIS

Over the last decade or so, Cable TV companies (also know as MSOs) have installed billions of dollars of Hybrid Fiber Coax (HFC) access networks. They do not need a new broadband technology to deliver quite good broadband rates. DOCSIS 3.0 allows bonding of multiple HFC analog channels to provide rates of over 100 Mbps, though this is shared among a number of subscribers. However, most subscribers use only a very small fraction of their available bandwidth, so this is not too much of a constraint.

For an MSO to move to DOCSIS 3.0, it is usually just an upgrade to the Cable Modem Termination System (CMTS) in the headend and new DOCSIS 3.0 cable modems in subscriber residences. One requirement for DOCSIS 3.0 upgrades is that several analog TV channels must be sacrificed for broadband, but this is a much easier sacrifice than investing in an entirely new fiber access network.

Broadband is delivered to my house over an HFC network. The picture below (click to enlarge) shows the gray coax NID installed on the outside of my house. This NID delivers voice, analog TV, and cable modem service to my house.

The Cable TV companies will probably be the slowest to migrate to FTTH. Their HFC networks can easily deliver broadband services at rates in the hundreds of megabits per second. One issue they have is that their HFC networks do not reach many business customers they would like to serve, so their initial access fiber deployments will serve their business customers.

FTTH

Fiber to the Home (FTTH) (a subset of Fiber to the Premises or FTTP) is seen by many as the ultimate broadband delivery platform for residential subscribers, and they are correct. Nothing compares with the bandwidth capabilities of FTTH. However, in brownfield areas, nothing is as expensive as deploying a new FTTH network. Interestingly, all wireline carriers, including munipalities, cablecos, and telcos, are moving to FTTH architectures, each at their own pace. FTTH is a broadband access architecture common to all these carriers. Once one carrier in an area deploys FTTH, other carriers will have to respond, and often this will be with another FTTH network.

FTTH, although capable of tremendous broadband rates, is not a perfect solution. Unlike coax and twisted pair copper, fiber is unable to deliver electrical power of any useful magnitude (there is technology for delivering photovoltaic power over fiber, but it only delivers a very small amount of power, and very inefficiently at that, over the single mode fiber used in FTTH). Most carriers do not leave or install any copper local loop along with the fiber, so subscribers must deal with a battery to ensure lifeline access for FTTH services.

Almost everyone agrees that FTTH is the future for all wireline access carriers. Each carrier will proceed to this ultimate broadband destination at their own pace, a pace determined largely by the alternative networks already in place and the level of local broadband competition.

VDSL2 Versus DOCSIS Smackdown

John Bartell — Fri, 04 Sep 2009 12:23:51 +0000

Light Reading is reporting that Cox is offering 50 Mbps DOCSIS cable modem service in Arizona on Cisco gear to counter Qwest’s 40 Mbps VDSL2 service offering. Prices are $89.99 per month for Cox’s DOCSIS-based offering and $109.99 per month for Qwest’s VDSL2-based offering. The informal poll on FTTxtra indicated that the majority of participants were willing to spend as much as $100 per month on broadband access service, so the prices Cox and Qwest are charging make sense as initial conditions.

The bulk of HFC electronics are deployed in OutSide Plant (OSP) cabinets serving a neighborhood or portions of a large neighborhood, and with DOCSIS, all of this substantial investment is retained by the MSO. These node cabinets are fed with fiber and serve many homes with telephone, DOCSIS cable modem, and television services over coax. A typical HFC node cabinet (this is the actual one serving my neighborhood) is shown below.

HFC Cabinet

The picture below shows the power, telephone, and cable connections into my house. The grey box is the HFC coax NID, which is span powered from the cabinet above. The HFC NID has a coax connection to a three-way splitter installed above the NID and a two-wire telephone connection to the brown box on the top right.

Telcos often deploy VDSL/VDSL2 services in FTTN (at the node) or FTTC (at the curb) architectures. The length of some copper local loops served from a FTTN node (typically up to 5000 feet or so, depends on the telco) tend to be a bit long for VDSL2, but sometimes FTTN is a telco’s only feasible option for installing VDSL2.

FTTN VDSL2 nodes are installed in locations with access to the copper local loop, usually through what is called a Feeder Distribution Interface or FDI, shown below. The DSL electronics accessing the loops at this FDI are housed in the beige boxes located behind the FDI. The FDI houses no electronics, just cables and cross-connects. A typical concentration level at an FDI is one upstream copper pair (feeder pair) for two downstream (distribution) copper pairs, so on average, before any electronics are installed at the node, only perhaps half of the local loops delivered to subscribers are already in use.

DSL Feeder Distribution Interface (FDI)

If you want to see what an HFC network can do with broadband, do not miss the video at the end of the article on DOCSIS 3.0 showing a speed test on a Comcast DOCSIS 3.0 network.

VDSL2 Overview and Tutorial

John Bartell — Tue, 01 Sep 2009 18:24:56 +0000

VDSL2 (Very high bit rate Digital Subscriber Line 2), a performance-improved version of the original VDSL now known as VDSL1, is standardized by the ITU in G.993.2. A relatively new local loop access technology, VDSL2 provides broadband access rates up to 100 Mbps over twisted pair copper. VDSL2 is important mainly because it leverages all that expensive copper local loop in the ground to provide a compelling broadband Internet service. It is well suited to deployments on the curb (FTTC) or in a building (FTTB) and can be used for Fiber to the Node (FTTN). The diagram below shows a typical VDSL FTTC network architecture.

VDSL2 faces a rather large challenge, however, because many copper local loops are too long to make effective use of all the capabilities of VDSL2, which relies on higher frequencies that are filtered out on longer local loops. VDSL2 chipsets provide a fallback mode to ADSL2+ because of this. ConvergeDigest offers the graph below showing a comparison of ADSL2+ and VDSL2 performance over distance. According to this graph, it is obvious that VDSL2 provides only marginal benefits over ADSL2+ beyond 4000 feet and no benefit beyond 7000 feet.

VDSL2 will often be deployed at a Feeder Distribution Interface (FDI) because of easy access to local loops at this point, though some of the local loops can be a bit long for optimal VDSL2 performance. A picture of an FDI (just about a mile from my house) is shown below.

When VDSL2 is deployed at an FDI, this architecture is called Fiber to the Node or FTTN. A typical FTTN network architecture is shown in the drawing below.

VDSL2 is implemented with what are called profiles, which specify what subset of VDSL2’s total capabilities are to be used in a particular installation. Differerent profiles are optimized for different situations. Some profiles are for Central Office (CO) VDSL2 deployment, some are for OutSide Plant (OSP) cabinet deployments of VDSL2, and some are for in-building deployments of VDSL2, especially the higher rate ones. VDSL2 profiles 8a, 8b, 8c, and 8d use 8 Mhz to provide data rates up to 50 Mbps. Profiles 12a and 12b use 12 Mhz to provide bandwidths up to 68 Mbps. Profiles 17a (17 Mhz) and 30a (30 Mhz) provide bandwidths up to 100 Mbps, but are intended only for very short distances such as those common with in-building (FTTB) VDSL2 installations (see below).

VDSL2 is expected to be more successful than VDSL1, which has been around a while but has seen only limited deployments. The following table, from RubyTech, compares VDSL1 and VDSL2.

VDSL and VDSL2 Comparison

Sunrise Telecom offers this screenshot below from their MTT – ACM II to show how VDSL2 is susceptible to bridge taps. The screenshot also shows how other technologies like ADSL and ADSL2+ do not require the same range of frequencies as VDSL2 does, though VDSL2 can operate at higher levels of attenuation. A bridge tap 15 feet in length created the notch shown and centered at about 9.7 MHz.

Sunrise Telecom MTT - ACM II Screenshot

The following companies are prominent manufacturers of VDSL2 chipsets.

Ericsson provides more technical information in this article on VDSL2.

PON, VDSL, and DOCSIS 3.0 Demand Up

John Bartell — Wed, 26 Aug 2009 15:44:17 +0000

From a Dell’Oro Group press release issued today…

“Two important factors impacting demand for Access equipment are broadband subscriber additions and network upgrades,” said Tam Dell’Oro, President of Dell’Oro Group. “Total broadband subscriber additions have been lower since the peak year of 2006, and are having a negative impact on equipment demand, especially for a slower-speed technology such as ADSL. On the positive side are the upgrade projects that are being driven by competition, increasing internet traffic, government incentives, and the desire by operators to enable new revenue-generating services such as TV over broadband. These upgrade projects increasingly drive demand for higher-speed PON, VDSL, and Cable DOCSIS 3.0 equipment,” Dell’Oro added.

BT Counters Competition with Free DSL Upgrade

John Bartell — Wed, 19 Aug 2009 16:47:22 +0000

Pocket-Lint and FierceTelecom are both reporting that BT is providing a free upgrade to 20 Mbps from 8 Mbps in 40% of their service area. Virgin Media, one of BT’s cable competitors, is already offering 50 Mbps.

BT is planning an extensive FTTC and FTTH rollout over the next few years. By 2012, they plan nine million homes served by FTTC (and perhaps VDSL2) along with 1 million homes served with GPON. (also from FierceTelecom)

In the UK, the access speeds are ramping up quickly. BT will have to spend some money upgrading their access facilities to support these higher rates, but the nice thing is that their recurring costs on the backbone will not increase nearly as quickly as they are increasing access speeds. People tend to get the same things done over faster access facilities. They just get them done quicker. Yes, over time they discover new things to do with the increased bandwidth, but never expect a proportionate increase in backbone bandwidth requirements when access speeds are increased (I remember reading an article about when speeds went from 10 Mbps to 50 Mbps in Japan, backbone utilization only increased 6%). What is interesting is access speeds delivered to subscribers depend more on the state of competition and the hardware for providing high speed access and much less on the costs of Internet backbone bandwidth.

Additional insights and comments are welcomed. Just provide them in the comment box below.

DOCSIS 3.0, a DSL nightmare

John Bartell — Mon, 10 Aug 2009 21:33:57 +0000

As much as the DSL folks would like to disbelieve, DOCSIS 3.0 is here today, works quite well, and will be ubiquitous in just a few years. Below are a few quotes indicating progress and expected penetration for DOCSIS 3.0.

From Broadcom’s 2Q09 earnings call (he means DOCSIS 3.0 when he refers to DOCSIS),

Scott McGregor, Broadcom’s CEO, said “Absolutely, I do believe we were seeing continued move over to DOCSIS. That’s more next year phenomena, but HD continues to be a phenomenon. People will buy a new TV set and they really want to get the better picture quality.”

Pike and Fisher have released a report covering DOCSIS 3.0, and they predict universal coverage in a few years. From their report summary…

We conclude that the top cable operators will have DOCSIS 3.0 covering 100% of homes passed by the end of 2013, and that MSOs can significantly shorten the time to achieve a return on their DOCSIS 3.0 investments by aggressively targeting business customers.

Comcast is going full speed ahead with DOCSIS 3.0. From DSLReports…

“We have raised our goal to roll out DOCSIS 3.0 to nearly 80% of our national footprint before the end of this year,” Comcast spokesman Charlie Douglas tells us. “That would mean passing about 40 million homes and businesses with the new wideband offerings Extreme 50 and Ultra 22, in addition to doubling speeds for existing Premier customers for no additional cost,” he notes.

And finally, the following is a video of an internet speed test over a Motorola DOCSIS 3.0 modem.

[youtube MLAvj6S0zCY&]