FTTxtra » Broadband

Active Fiber Overview

John Bartell — Fri, 30 Oct 2009 12:27:44 +0000

Point-to-Point (P2P, also known as Active Fiber) is the simplest of all three Fiber To The Home fundamental architectures. With a point-to-point network architecture, a fiber (typically only a single fiber) is installed from each subscriber’s house directly into the Central Office serving that subscriber. This architecture has the advantage of simplicity, but it does require terminating lots of fiber cables in the Central Office (CO).

Active Fiber Architecture

With Active Fiber, the CO contains a high port count aggregation device (one port per subscriber) known as an Optical Line Terminal or OLT. A single optical fiber connects each subscriber’s house to the Central Office. An Optical Network Terminal (ONT) is installed either on the side of the subscriber’s house (typical in the US) or inside the subscriber’s house (not typical in the US).

Advantages

Active Fiber has an advantage in that no port is shared in any way, thus troubleshooting problems on the network is greatly simplified. With this simple architecture, optical problems can be easily isolated. Additionally, this architecture has the highest bandwidth potential. Links are easily upgraded to higher rates (requires new optics and electronics on both ends however), and each additional fiber linearly adds more aggregate bandwidth to the network.

Broadband Access Carriers Need Net Neutrality Too

John Bartell — Thu, 22 Oct 2009 14:01:39 +0000

Net Neutrality (or Network Neutrality or Internet Neutrality), as proposed recently by the FCC, is good for the broadband access carriers. Though this is counter to almost all of the discussion around Net Neutrality, carriers have much to gain from FCC regulation that guarantees unrestricted access to all the wonderful content sources on the Internet. Without Net Neutrality, access to this content will no longer be assured, and carriers could be forced to negotiate with the major content providers.

Broadband is Important, but Content is King

Good content is precious on the Internet, and access is, unfortunately, largely a commodity. But what I suspect these carriers are missing is that, without Net Neutrality regulated by an organization like the FCC, the quality content providers (whose networks and servers are an integral part of the Internet) could discriminate just like the broadband access providers. And it does not matter whether Net Neutrality regulation directly affects content providers, because the content providers could own, influence, or select their own access networks to discriminate. I suspect regulation could address this somehow.

Note that there is nothing fundamentally different about what the large content providers do and what any Internet user does at home. The difference is really just a matter of degree (admittedly a rather large difference in degree, but still one of degree and not fundamentally different). Both can act as sources and sinks for information.

With competition, subscribers have a choice. Without Net Neutrality regulations, broadband subscribers may be forced to choose their service provider based on content. Many would rather have 1 Mbps broadband service and unfettered access to all content than 100 Mbps service without this.

An Analogy

I have yet to run across a good analogy for discrimination on the Internet, so I came up with my own. Words are clumsy here, so the diagram below represents how an access provider and a content provider could discriminate.

Note that there are two access networks involved, and rarely would the content provider and the broadband subscriber be on the same access network. If one access provider can discriminate, then so can the other. Who does this hurt more? Obviously, Carrier A has the most to lose. If a broadband subscriber highly values a content provider (e.g., Facebook for which there is no direct substitute), this subscriber will change broadband access provider and drag along the entire triple or quadruple play of services.

FCC Regulations Will Benefit Carriers

Broadband access carriers should not dread FCC regulation that enforces Net Neutrality. These carriers have much to gain from free access to everything on the Internet.

Fiber in Broadband Access Networks

John Bartell — Tue, 20 Oct 2009 12:18:26 +0000

The most expensive element in delivering broadband Internet services over fiber optic cable is the access network, and its architecture largely determines how much bandwidth can be delivered to a subscriber. In brownfield installations (with copper local loop already installed), the most expensive element is the labor to install fiber.

There are three elements to a typical broadband fiber access network: the feeder portion, the distribution portion, and the drop cables to the subscribers’ premises. Where fiber is deployed in place of copper determines the fundamental architecture of the access network. For telcos, the three major architectures are Fiber to the Node (FTTN), Fiber to the Curb (FTTC), and Fiber to the Premises (FTTP), and each has a different proportion of fiber. FTTN and FTTC are hybrids combining fiber with copper local loops and are attractive owing to their cost-efficiency in brownfield installations. FTTP is entirely fiber from the wire center to the subscriber.

FTTN

If only the feeder portion of the access network has fiber optic cables, and copper local loops are served with DSL (Digital Subscriber Line) from the Feeder Distribution Hub, then the architecture is known as Fiber to the Node or FTTN (BT confusingly refers to this architecture as Fiber to the Cabinet or FTTC). The feeder portion of the access network is from the wire center (or Central Office) to a Feeder Distribution Hub. A typical network architecture for FTTN is shown below.

The picture below is of a FTTN installation about one mile from my house. TThe rear beige cabinet is a Digital Loop Carrier (DLC) system, which houses telephony electronics. The two beige cabinets in front of the DLC house adjunct DSLAMs providing DSL services. The green cabinet to the right is the Feeder Distribution Interface, which provides copper pair concentration (typically 2 distribution pairs for each feeder pair, which in this case are only a few feet in length).

Click to Enlarge

FTTC

If fiber is installed in the feeder and distribution portions of the access network, and DSL copper from there to businesses and homes, then this architecture is known as Fiber to the Curb or FTTC. The distribution portion of the broadband access network distributes fiber from the Fiber Distribution Hub to the drop portion of the network, which usually begins at the curb. The diagram below represents a typical FTTC network architecture.

FTTP

If fiber is installed in the feeder, distribution, and drop portions of the broadband access network, then the architecture is known as Fiber to the Premises or FTTP. FTTP is known as Fiber to the Home (FTTH) when serving residential subscribers and as Fiber to the Building (FTTB) when serving buildings such as multi-tenant office buildings. With FTTB, fiber enters the building, but subscribers are served directly with DSL or Ethernet. FTTB is especially common in Japan and Korea, which lead in broadband rates.

Common FTTP technologies include the various PON alternatives (Broadband PON or BPON, Gigabit PON or GPON, Ethernet PON or EPON, and Wave Division Multiplex PON or WDM PON), Active Ethernet, and Active Fiber. With PON, an optical splitter (Arrayed WaveGuide with WDM PON) is installed at the Feeder Distribution Hub with possibly another splitter at the curb. With Active Ethernet, an OutSide Plant (OSP) Ethernet switch is installed at the Fiber Distribution Hub. With an Active Fiber network, only fiber cables and cross-connects are installed in the access network between the wire center and subscribers’ premises.

In brownfield applications, FTTP is the most expensive alternative for a broadband access network. The most costly element per subscriber is the fiber drop cable serving that subscriber’s premises, and the attraction of FTTC is that it avoids this cost. In greenfield installations, FTTP is not significantly more expensive (if at all) compared to copper or coax. A representative FTTP architecture is shown in the diagram below.

Hybrid Versus FTTP

All three fiber access architectures can deliver broadband rates to subscribers. The two hybrid alternatives are generally less expensive, especially in brownfield installations, but also less capable. With fiber rates measured in Gbps, and DSL in Mbps, more fiber equates to greater potential broadband rates. FTTP, of course, provides the ultimate in broadband access.

The Death of Telephony

John Bartell — Mon, 12 Oct 2009 11:46:51 +0000

The era of voice driving network investment is over. Voice is here, it is still useful, but it is almost invisible in the design of most networks being built today. Telephony Magazine had it right in changing its name to Connected Planet after more than 100 years. Telephony has become incidental, almost a free rider on the primary communications medium of today and the future–the broadband Internet. Is there any such thing as a Telephone Company anymore?

Because just about everyone had a phone, voice’s value has been its ubiquitous nature, and for the last 100 years or so it was the default means of contacting someone at a distance. Today, the Internet has seeped into virtually everyone’s life, and even my mother and my in-laws surf the web and use email. Over 2/3 of homes in the US have broadband access, and even more have some form of Internet access either through dial-up or smartphones. And with businesses, Internet access has been a staple for years, and many have migrated their phone systems to VoIP. Cisco has had great success selling VoIP phones and VoIP PBX systems to businesses large and small.

Those devices we strap to our hips and use for text, social media, email, and yes voice, are they really primarily phones anymore? I use mine far more for Internet access than for voice, though I am not known to be especially chatty. Smartphones are becoming more and more popular, and I suspect that many people use their smartphones similarly to the way I use mine. Voice over IP (implemented as SIP, MGCP, or H.248) is even becoming common on these devices with support for Skype and Google Voice VoIP applications.

Because people use its data capabilities so much, the iPhone is giving AT&T broadband wireless network fits. I suspect AT&T thought they were selling phones (it is called the iPHONE) to people, not IP data terminals. The super-sizing of the iPhone screen should have been a dead giveaway. Those flashy screens are surely not to improve voice communications. They are, of course, for displaying documents and pages sent over the Internet and for typing in messages.

Because we tend to gravitate to those communications methods that require the least energy, computer-based communications like email, text, and Twitter have trumped voice and paper. We send email instead of snail mail (when was the last time you wrote a letter?). We text someone rather than call them, and ironically the text message is often delivered to something called a “cellular telephone”. We send an attachment rather than printing it out and mailing or faxing it.

Interactive video is the worst energy drain and is almost completely a non-starter. We love to see the other person while they talk. We hate for someone else to see us, and that asymmetry is the sting of death for video “telephony”. Why would you ever want to have to dress and comb your hair just to let your plumber know your toilet is leaking? Sure, video could be useful for a job interview, but how often is that necessary?

Interactive voice is the next most expensive in terms of energy requirements. I can send probably ten meaty emails with the same energy required for a single ten minute conversation with someone. And on Twitter, I can send a message that will be read by hundreds with about 10 seconds of effort. No way voice can compete with that, though it definitely has its place.

When I do have to talk to someone, I use Skype’s VoIP service to communicate through my computer, and I prefer their VoIP network for voice to anything else I use for this purpose. The voice quality is better, I can talk just about anywhere in the world for free, and I can combine talking with text and other electronic methods of communications. Voice is an important part of my use of Skype’s network, but it is not the primary reason Skype is so attractive to me.

Ironically, all these new digital communications methods are faulted for taking up too much of our lives. The reality is that they are much better at leveraging our time and energy, and this is the driver for their victory over voice. Workers may claim that smartphones and email are consuming their work lives. However, without email and other electronic communications, many workers would be much less valuable and therefore paid less. Few workers would trade in their Blackberry for reduced compensation.

Is Latency the Bane of Broadband?

John Bartell — Mon, 05 Oct 2009 11:37:01 +0000

Defined as the time from a stimulus to the completion of its response, latency is an often under-appreciated aspect of the broadband experience. When considering broadband, most people ignore network latency and focus almost exclusively on download performance, repeatedly measuring their download rate with Internet speed tests like Speedtest.net. Although download rate is very important, it is certainly not the only thing that contributes to a good broadband experience. The Internet is becoming a very social medium, and high network latency’s major adverse affect on interactively limits the social value of the Internet.

The Internet was not designed for low latency transmission, so reducing latency to better serve interactive communications is quite difficult. With the current architecture of the Internet, some factors cannot be improved as they require changes to the laws of physics. No one will increase the speed of light, and the speed of light is rather slow when packets are routed around the world to serve a request. A single trip from the east coast to the west coast of the US requires about 25 ms just owing to the speed of propagation (about 2/3 the speed of light in a vacuum for transmission of electrical signals in copper, faster in fiber), and there is nothing that can be done to significantly reduce this. Other factors can be improved, but there is certainly a limit.

Latency’s effects depend on the application. These are discussed below by application.

Broadcast Media

Network latency has very little effect on broadcast communications. Examples of broadcast communications include watching video on YouTube and Hulu, listening to a podcast, or watching a recorded slide presentation. There is no interaction between the originator of the content and the user of the content, so if the content delivery is delayed by even a second or so, there will be little effect on the value of the communications.

Where latency can be a problem for broadcasting is in its variance, a value known as jitter . To compensate for changing latencies, a client receiving the broadcast stream will buffer the arriving packets and then steadily feed them to the user. However, if the jitter buffer is too small, and the latency variation is larger than the buffer’s capacity, then the user experience will suffer from jerky video and/or stuttering audio. The jitter buffer must be as least as large as the largest variance in delay experienced by a connection. Ultimately, the size of the jitter buffer is just an educated guess. Latencies can increase suddenly, and occasional problems are possible.

Interactive Media

Latency adversely affects interactive communications, both audio and video communications. Quality interactive Voice over IP (VoIP) communications requires low latency, and for the latency to be undetectable, it needs to be less than 50 ms. With higher latencies, interactive conversation with VoIP is difficult because a user has a hard time determining when to start talking. Arguing or having a heated discussion with someone is almost impossible. One party begins talking without realizing that the other party is also talking, so the two talk over one another and have to restart. Skype is a common interactive voice application used on the Internet.

Interactive video has even higher requirements for low latency. For someone to appear as though they are truly listening, their visual and audio feedback (nodding, uh huh, etc.) needs to be immediate and certainly less than 50ms. Longer latencies make it impossible for someone to properly convey that they are listening, and video becomes a distraction and a hindrance rather than an enabler. Interactive video with audio has the same audio problems that voice-only communication does.

Surfing the web is another interactive broadband Internet experience that is adversely affected by latency. A single web page is typically composed of tens of different files that must all be downloaded to display a single page. Serially downloading these files, even across very fast broadband, can tax the patience of almost anyone. For example, NYTimes.com requires 87 files to fully display its home page. If roundtrip latency is 200ms, serially downloading the home page requires at least 17 seconds just for the roundtrip latency, and other factors will make an actual download of NYTimes.com take even longer. Many viewers are lost once a page load exceeds 10 seconds, so parallel downloads are used by web browsers to optimize the user experience.

File Downloads

File downloads are largely unaffected by network latency owing to the windowing capability of TCP (the end-to-end layer four protocol that runs on top of IP). The most important factor is the TCP receive window size, which determines the amount of received data can be buffered in the client (typically a PC) before the sender (server) requires an acknowledgement to continue sending. By adjusting its receive window size, TCP allows the server to send packets to completely “fill the pipe” so that the it does not have to wait for acknowledgements from the client to continue sending.

For a server to use the entire bandwidth available, the client must have a receive window size equal to the bandwidth delay product. The bandwidth delay product is calculated as follows: (lowest link bandwidth on a connection) x (roundtrip delay). For a connection with the slowest link being a T1 (1.536 Mbps), and roundtrip delay of 200 ms, the bandwidth delay product is 307200 bits. The TCP window size on the connection must be equal to at least (307200 bits) / (8 bits/byte) = 38400 bytes for the full 1.536 Mbps to be used for a single download, and this is well within TCP’s maximum receive window size of 64k bytes.

To get beyond the 64k byte limit, Vista supports a feature called TCP Window Scaling to efficiently handle higher latency and higher bandwidth connections (both affect the bandwidth delay product). With scaling, an option is sent in synchronize (SYN) segments during the TCP connection establishment process. The option scales the TCP receive window to support up to a quite large value of about one gigabyte.

XP’s handling of TCP’s receive window is rather crude, but Vista includes a feature called Receive Window Auto-Tuning that automatically optimizes TCP throughput, and it is especially effective on paths with a high bandwidth delay product. Receive Window Auto-Tuning measures the bandwidth delay product and the rate at which data is cleared from the receive buffer and then periodically adjusts the receive window size for optimum throughput. Windows XP is much less sophisticated and requires manual configuration of the receive window size, which applies identically to all connections. Vista’s Receive Window Auto-Tuning works on each connection separately, individually tuning the receive window for maximum throughput.

Supporting a maximum scaled receive window size of 16 megabytes, which is 256 times larger than TCP’s unscaled receive window, Vista will accept around 600 Mbps on a single TCP connection having a roundtrip delay of 200ms. This is well beyond the capabilities of most PCs to digest.

Testing Network Latency

The easiest way to measure latency is to use the ping command, which is a tool built into many operating systems like Windows and Linux to assist in network performance management. On Windows, bring up a command prompt window and just type “ping google.com” to try it out (Note that not all websites will respond. Google.com and Yahoo.com will both respond.). Windows will send out several pings and report on the latency for each (mostly network latency usually). The diagram below (click to enlarge) shows a representative path of a test with the ping utility from a residence to google.com and back. Note that every element in the connection contributes to latency.

On links, the contributors to latency are the serialization delay and transmission delay. Serialization delay is the time required for a link to assimilate a packet and depends on the speed of the link. Transmission delay has to do with the time required for bits to travel a link, which could be as much as 25 ms should the link cross the US or the Atlantic ocean. Transmission delay has nothing to do with the speed of the link. Additional delay is introduced in the various routers, in the server processing the request, and even some in the local PC.

Other options for latency testing include tools available from Speedguide.net and Pingdom.com. Speedguide.net offers a ping utility as well as a traceroute tool that allow you to monitor latency on the connection from their site to your PC or any IP address. Their tools allow more net latency testing options beyond just the latency from your PC to a server on the Internet.

Pingdom.com provides a good test of website latency, and its tool also shows all the files downloaded to display a page. In web page response time, the number of files is more important than the size of the files unless they are unreasonably large; browsers are limited in the number of files they will download at one time. A web page requiring 40 files, and accessed with a browser supporting only 4 file downloads at a time, may require 10 separate sets of downloads to render a page. Note that many web pages are viewable well before all the data describing it is delivered to the client PC, and this reduces the problem.

To Sum Up

No, network latency is not the bane of broadband, but it is the adverse factor of broadband performance that is by far the most difficult to improve. In the coming years, we will have hundreds of megabits per second of broadband delivered to our homes, but the latency of our connections likely will not improve much at all. The Internet was originally designed to carry non-real time data traffic, and it has done a fine job of that along with many other things it was never designed to do. Without radical changes to the Internet’s architecture, interactive communications will forever suffer from the latency inherent in the current design of the broadband Internet.

For more, see this ACM article, Latency Lags Bandwidth (registration required), and this GigaOM article, Pain at the Pipe: Latency Matters.

Light Peak Revealed

John Bartell — Tue, 29 Sep 2009 23:23:46 +0000

Light Peak is a new fiber optic technology for interconnecting peripherals to personal computers and portable devices. Apparently it was conceived by Apple and is being implemented by Intel at Apple’s behest. It sounds like an Apple idea to me (simple, elegant, wish I would have thought of that first), and expect to first see this fiber networking technology integrated into Apple’s products.

Light Peak is elegant in its simplicity, and with PC peripheral interconnects, simplicity is a definite virtue. The situation today is far from optimal, with a variety of different technologies in use including various versions of USB and Firewire. Light Peak has the potential to be a universal technology for networking PC peripherals, though its use of fiber optic cable will bring some challenges.

Intel already has early 10 Gbps Light Peak modules and is predicting 2010 for its first production shipments. Intel is anticipating eventual 100 Gbps versions. The picture below (click to enlarge; from Intel) shows a multi 10G fiber Light Peak module mounted on a PCB with four different interfaces.

What does this have to do with broadband? Well, broadband rates follow behind home Ethernet networking rates, which follow behind the PC peripheral rates. So I guess you could say Light Peak is future broadband’s distant relative. As Light Peak drives up the rates for PC peripheral interconnects, local networking bandwidth should increase with Gigabit Ethernet becoming even more popular. And with Gigabit Ethernet, rates delivered with fiber broadband technologies like Passive Optical Network (PON) can be fully utilized.

Even today, GPON Optical Network Terminals (ONTs) are capable of delivering broadband rates of up to 1 Gbps to residential subscribers. But, subscribers who cannot take advantage of these rates will not be very interested in paying more for this level of broadband bandwidth.

Engadget broke the news and has three articles on Light Peak. Scroll down to see the articles.

CNET has a good comprehensive article on Light Peak.

And Intel has several pages on their website devoted to Light Peak.

10g fiber

ethernet networking

fiber optic

fiber optic network

fiber optic networking

fibre optic cable

networking

optical fiber cable

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.

Fiber to the Node (FTTN) Overview

John Bartell — Wed, 09 Sep 2009 15:43:27 +0000

Fiber to the Node (FTTN) is a fiber and copper local loop architecture for delivering broadband Internet to subscribers. With FTTN, fiber is installed only to copper local loop aggregation points known as Feeder Distribution Interfaces (FDIs). FTTN has the advantage that, compared to FTTH, it dramatically reduces the amount of fiber that must be installed to serve a subscriber and requires substantially less capital to install. However, FTTN does not provide the bandwidth potential of network architectures like FTTH or even Fiber to the Curb (FTTC).

A typical FTTN network architecture is shown in the drawing above. Fiber from a CO (or could be from an RT DLC cabinet, not shown) serves a DSLAM or BBDLC installed adjacent to a Feeder Distribution Interface, which provides copper loop concentration (typically 2:1) and cross-connect functions. Local loops from the FDI to its subscribers are typically less than 5000 feet, which is a reasonably good match to the distances over which VDSL2 provides bandwidth advantages over ADSL2+. The picture below shows what a typical FDI looks like, though this cross-connect cabinet is installed next to a DLC (beige cabinet to the right).

FDI

AT&T and Qwest are big proponents of FTTN. AT&T’s U-verse service offering is based on an FTTN architecture. In 2007, Qwest committed $300 million to delivering broadband services across an FTTN architecture.

FTTH Overview and Update

John Bartell — Thu, 03 Sep 2009 16:19:56 +0000

Fiber To The Home (FTTH) is one of several methods for delivering Broadband to residential subscribers. With FTTH, the architectural distinctions between types of carriers (like Telco, Muni, Cableco, Utility) disappear. All these carriers deploy virtually identical architectures once they are delivering services with FTTH, and the only remaining differences are largely due to legacy system support. Other forms of Broadband bring fiber to an aggregation point and use either wireless (e.g., WiMAX and LTE) or some form of wireline (twisted pair, coax, or powerline) to serve a subscriber.

Other versions of FTTx that are commonly used are as follows:

FTTB – Fiber to the Building, usually a multi-tenant building, with Digital Subscriber Line (DSL) or Ethernet delivered to each subscriber,
FTTC – Fiber to the Curb, typically with some form of DSL connecting to the subscribers,
FTTN – Fiber to the Node, typically with ADSL2+ or VDSL2 from an OutSide Plant (OSP) cross-connect to the subscribers,
FTTP – Fiber to the Premises, where the premises could be a business or a residence. (Note that “Premises” is ALWAYS spelled plural (but used as singular) and means building(s) and land taken together as one piece of property. Premises derives from the descriptions of property at the beginning of a deed, and these descriptions are known as premises because they are taken as a given.)

BroadbandSoho.com offers an excellent set of images of FiOS BPON deployment, which is Verizon’s original Fiber to the Home technology. Note that Verizon is a fan of aerial fiber, and fiber shown in this series of images is all aerial fiber. Aerial fiber is cheaper to install than buried fiber in an overbuild, and most installations of Verizon FiOS are overbuilds.

The Optical Network Terminal (ONT, but ITU-T standards refer to it as an ONU), installed at the subscriber’s home, converts optical signals to electrical signals for transmission to phones, routers, computers, and Set Top Boxes (STBs) within the home. The ONT can be installed outside the home (an outside ONT is shown in the FiOS pictures above), or it can be installed inside. Inside ONTs are rare in the US because, on existing homes, generally all telephone and cable connections terminate outside, and installing the ONT outside allows technicians easy access for repairs and upgrades (no appointment necessary with the owner). The picture below shows where power, cable, and telephone connections are installed on the outside of my house. I do not have FTTH as a service option, and the gray box is an HFC coax NID providing TV, telephone, and DOCSIS cable modem service. An FTTH ONT would replace this HFC NID.

Indoor FTTH ONTs are less expensive than outdoor ones, but most homes have no interior fiber, and installing it is expensive. One reason indoor ONTs are less expensive is that they do not have to operate in the wide temperature range (-40C to +65C) that the outdoor ones have to deal with, and this allows the indoor units to be built with cheaper components (especially the optical transceiver, typically rated 0 to +50C for indoor units). Additionally, the enclosure is a large part of the ONT cost, and indoor units can be built with a much less expensive enclosure. An indoor ONT is shown below.

Even though Fiber to the Home is typically a substantial investment for a carrier, the recession does not seem to have substantially dampened the expansion of FTTH. With other carrier(s) offering FTTH services in a market, a carrier may not have a choice when it comes to installing FTTH. Competition will force a carrier to upgrade to remain competitive. The following graphic, from Yankee Group, shows the FTTH payback period for various combinations of ARPU (Average Revenue Per User) and percent takeup. Because it does not discount future cash flows, this analysis provides an optimistic set of payback periods. Regardless, high ARPUs and high take rates are necessary to make the payback period reasonable.

Today, Fiber to the Home penetration is approximately 40 million homes worldwide. In the US, Verizon’s FiOS is the largest installation of FTTH. According to Fiberforall.org

In total, Verizon FiOS is available to 11 million premises within those states as of July 2009. This equates to about 34 percent of the households in Verizon’s wireline network footprint. Verizon has plans to keep FiOS deployment on a fast track with deployment reaching over 17 million homes by the end of 2010.

Note that there is a big difference between subscribers passed and subscribers served. With FiOS, approximately 30% of homes with available FiOS service actually subscribe to the service.

FTTH penetration varies greatly by country and tends to be more common in wealthy countries with high subscriber densities like Japan and Korea. The US is not a leading country in FTTH penetration as is shown in the graphic below (data for end of 2008). For each country listed, the orange part of the bar shows Fiber to the Building FTTB penetration and the blue shows actual FTTH. In FTTB, a fiber is terminated in the building, but subscribers are served with DSL or Ethernet.

WiMAX Tutorial

John Bartell — Wed, 02 Sep 2009 20:20:25 +0000

WiMAX (Worldwide Interoperability for Microwave Access) is a form of broadband wireless Internet access standardized by the IEEE in its 802.16 series of standards. WiMAX can support rates of 15 Mbps and even higher, but commercially offered speeds are generally only up to 6 Mbps. There is a distance/data rate tradeoff with WiMAX, and subscribers closer to a base station potentially can receive higher WiMAX rates. WiMAX-m, standardized by the IEEE as 802.16m, pushes the maximum rate of WiMAX to 1 Gbps, but it maintains compatibility with previous versions.

The IEEE produced the WiMAX standard as 802.16 in 2004 and 802.16e in 2005. The original standard was created by the 802.16d working party and is sometimes called 802.16d. 802.16e adds, among other things, support for mobility in WiMAX networks, and the original 802.16 standard provided only fixed operation. Interoperability and certification of products is furthered by the WiMAX Forum, which has the goal to increase acceptance of products based on WiMAX 802.16 standards..

Subscribers can use WiMAX service with either an indoor (typically integral to the WiMAX modem) antenna or with a separate outdoor antenna as shown above. Indoor antennas place greater demands on the carrier’s network because of additional losses experienced within a structure. To support indoor antennas, a carrier typically requires more base stations for ubiquitous coverage or has limited coverage where indoor antennas can be used. Asus, Acer, Dell, Lenovo, and Toshiba have built laptops with integral WiMAX. The following is an image of a WiMAX USB adaptor from Motorola followed by images of two stand-alone WiMAX modems (Alvarion and Motorola).

An outdoor antenna provides better reception over longer distances from a base station and higher possible data rates. The following is a picture of a WiMAX outdoor antenna on a subscriber’s house.

Prominent vendors of WiMAX base station equipment include Alcatel-Lucent, Alvarion, Cisco, Huawei, Motorola, NEC, Nokia Siemens Networks, Samsung, and ZTE, among others. Japan Radio Company, Ltd. (JRC) provides the integrated mobile WiMAX base station shown below.

Clearwire is a major provider of WiMAX services in the US and offers downstream rates of up to 2 Mbps. Serving almost 50 markets, Clearwire offers service for as low as $29.99 per month according to the Clearwire website, which provides information on service plans. The following is a recent Clearwire WiMAX coverage map.

Clearwire Coverage Map

And Intel, a big supporter of WiMAX, has this video on WiMAX.

[youtube ujbFwiPUvUc]