FTTxtra » PON

GPON’s Dynamic Bandwidth Assignment (DBA)

John Bartell — Wed, 16 Dec 2009 22:11:01 +0000

Dynamic Bandwidth Assignment (DBA) is used on Passive Optical Network’s to allow better use of upstream bandwidth, and it is especially good for dealing with bursty upstream traffic. GPON and many other PON technologies use Time Division Multiple Access (TDMA) for managing upstream access by ONUs, and at any one point in time, TDMA provides unshared timeslots (fraction of the upstream bandwidth over time) to each ONU for upstream transmissions.

DBA allows upstream timeslots to grow and shrink based on the distribution of upstream traffic loads and operates on a timescale of milliseconds. Of course, the total of all timeslots on a PON cannot be greater than the length of a single upstream frame.

DBA functions on Transmission Containers (T-CONTs), which are upstream timeslots, and each is identified by a particular AllocID. An ONU must have at least one T-CONT, but most have several T-CONTs, and each corresponds to a particular upstream time slot on the PON. Without DBA support in the OLT, upstream bandwidth is statically assigned to T-CONTs, cannot be shared, and can be changed only through a management system.

There are two methods to determine the bandwidth requirements of ONTs. The first, called Status Reporting (SR) DBA, involves explict T-CONT buffer status provided by the ONTs. With this method, the OLT solicits T-CONT buffer status, and the ONUs respond with a report for each assigned T-CONT. The other method is known as Traffic Monitoring (TM). With TM DBA. the OLT imputes how much bandwidth is required by monitoring the number of idle frames sent in a particular T-CONT. A GPON OLT must support both methods, but ONUs need not provide any support for DBA; the OLT will just use Traffic Monitoring DBA for ONUs that provide no support for DBA.

DBA provides a way for an OLT to oversubscribe its upstream bandwidth and provides an effective increase to average bandwidth available to each of its ONTs. But DBA brings with it the possibility of a carrier not being able to satisfy all the upstream bandwidth granted to ONTs. Static bandwidth assignment does not have this problem, but it does not allow for any more than the 1.244 Gbps of the upstream to be assigned to the ONTs. The bottom line is that DBA allows more ONUs on a single GPON, and it allows more bandwidth to be assigned to each ONU, with no changes to the optics in the OLT or the ONUs.

ONU or ONT?

John Bartell — Thu, 03 Dec 2009 20:51:33 +0000

In the ITU-T standards, ONU is the generic name for devices installed at subscriber premises to convert PON interfaces to Ethernet, POTS, and other interfaces, whether the device is serving one or more subscribers. The current version of G.984 does acknowledge the need to differentiate between single user and multi-user devices.

In this book, to avoid ambiguity, ONU is used to describe a device that serves multiple subscribers, such as a DSLAM with a PON uplink. ONT describes a device serving a single subscriber such as one that is installed on a single family home. An ONT is typically a device highly cost-optimized to serve a single subscriber. An ONU typically has a radically different architecture and is often more similar to a DSLAM or Ethernet Switch than a single family ONT.

In the ITU-T standards, Optical Network Unit (ONU) is the generic name for a device installed at a subscriber’s premises to convert fiber access interfaces to Ethernet, POTS, and other interfaces, whether the device is serving one or more subscribers. The current version of the G.984 GPON standard does acknowledge the need to differentiate between single-user and multi-user devices.

In common usage, an Optical Network Terminal (ONT) serves a single subscriber premises such as a stand alone house. An ONT has no need for security between its few interfaces and sells for perhaps a few hundred dollars. A typical indoor ONT is shown below.

ONU is used to describe a device serving multiple subscribers such as those in an apartment building or shared office building. It has a radically different architecture and is more similar to a DSLAM or Ethernet Switch than a single family ONT. An ONU can sell for several thousand dollars, depending on subscriber density, but often offers a lower per-subscriber cost than an ONT because common components are shared.

10G GPON Tutorial

John Bartell — Mon, 26 Oct 2009 13:07:46 +0000

10G GPON (Gigabit Passive Optical Network) is an important 10 Gbps Passive Optical Network (PON) technology that is being standardized by the ITU-T and FSAN for use on Fiber To The Premises (FTTP) shared access fiber optics. 10G Ethernet PON (10G EPON) is another contender for the next gen of PON networks, and this FTTxtra tutorial provides background on 10G EPON for the comparisons in this article.

The diagram below shows a typical 10G GPON Fiber to the Home (FTTH) network. In 10G GPON, the downstream rate on the fiber is 10 Gbps. Upstream could be 1.25 (current GPON upstream rate, not shown), 2.5, or 10 Gbps, and the higher the upstream rate, the higher the cost of the optics in the Optical Network Terminals. Current GPON networks use ONT optics transmitting at 1.25 Gbps upstream, and this will be by far the cheapest alternative for a 10G GPON ONT transceiver, which is usually the most expensive component in the ONT. Dynamic Bandwidth Assignment (DBA), as specified in G.984.3, allows over subscription in the upstream direction, and this eliminates much of the requirement for higher upstream rates.

The number one electronics cost in a PON network is the unshared ONTs, though the cost of installing the fiber optics generally drives the complete cost equation. There could easily be thousands of ONTs per single moderate-sized OLT. A critical element to keeping the cost of the ONT down is an inexpensive optical transceiver, and 10G GPON transceivers capable of transmitting 10G upstream are considerably more expensive than 2.5G and 1.25G upstream capable transceivers. Although upstream has been getting a lot of attention lately, the cost of the ONT gets a lot of attention by the carriers, so expect 10G GPON upstream rates on the lower end initially and for quite a while in FTTH networks.

According to Fierce Telecom, Alcatel-Lucent is an advocate of 10G GPON versus WDM PON. Their argument is that 10G GPON is a natural progression from the current GPON as specified in ITU G.984. 10G GPON will bring virtually all the factors that have made GPON successful so far in FTTH deployments (cost is the big question at this point), and it adds greater rates in both downstream and upstream directions.

10G EPON and 10G GPON are compared in this article from OSP Magazine.

10G GPON standardization is about a year behind the 10G EPON standardization effort. However, given its close relationship to GPON, expect 10G GPON to succeed as a higher speed FTTP alternative. It will likely be popular in the same places GPON has succeeded even though its standardization is lagging that of 10G EPON.

PON Splitter Technology

John Bartell — Tue, 22 Sep 2009 11:25:56 +0000

Passive Optical Network (PON) splitters play an important role in Fiber to the Home (FTTH) networks by allowing a single PON network interface to be shared among many subscribers. Splitters contain no electronics and use no power. They are the network elements that put the passive in Passive Optical Network and are available in a variety of split ratios, including 1:8, 1:16, and 1:32.

Splitters are installed in each optical network between the PON Optical Line Terminal (OLT) and the Optical Network Terminals (ONTs) that the OLT serves. Networks implementing BPON, GPON, EPON, 10G EPON, and 10G GPON technologies all use these simple optical splitters. In place of an optical splitter, a WDM PON network will use an Arrayed WaveGuide (AWG).

A PON network may be designed with a single optical splitter, or it can have two or more splitters cascaded together. Since each optical connection adds attenuation, a single splitter is superior to multiple cascaded splitters. One net additional coupling (and source of attenuation) is introduced in connecting two splitters together.

A single splitter is shown in the GPON network diagram below. Note that the splitter can be deployed in the Central Office (CO) alongside the OLT, or it may be deployed in an OutSide Plant (OSP) cabinet closer to the subscribers. A splitter can also be deployed in the basement of a building for a Multiple Dwelling Unit (MDU) installation (not shown).

Splitter in GPON Network

An interesting (and strange) fact is that attenuation of light through an optical splitter is symmetrical. It is identical in both directions. Whether a splitter is combining light in the upstream direction or dividing light in the downstream direction, it still introduces the same attenuation to an optical input signal (a little more than 3 dB for each 1:2 split).

There are two basic technologies for building passive optical network splitters: Fused Biconical Taper (FBT) and Planar Lightwave Circuit (PLC). Fused Biconical Taper is the older technology and generally introduces more loss than the newer PLC splitters, though both PLC and FBT splitters are used in PON networks.

A Fused Biconical Taper 1:2 optical splitter is diagrammed below. A Fused Biconical Taper (FBT) splitter is made by wrapping two fiber cores together, putting tension on the optical fibers, and then heating the junction until the two fibers are tapered from the tension and fused together. FBT attenuation tends to be a bit higher than attenuation from PLC splitters.

Fused Biconical Taper Optical Splitter

A 1:8 Planar Lightwave Circuit (PLC) splitter is diagrammed in the figure below. A PLC splitter is made with techniques much like those to manufacture semiconductors, and these optical splitters are very compact, efficient, and reliable. A single 1:32 PLC splitter may be no larger than 1 cm x 2 cm.

Planar Lightwave Circuit (PLC) Optical Splitter

The loss to be expected from a 1:8 splitter like the one diagrammed above is less than one dB greater than what would be expected from a perfect splitter, which has exactly 9 dB of loss (3dB for each 1:2 split). A good 1:32 PLC splitter has an attenuation in both directions of less than 17 dB or even 16 dB (a perfect 1:32 splitter would introduce 15 dB of loss).

GPON Tutorial

John Bartell — Sun, 20 Sep 2009 23:30:14 +0000

Gigabit Passive Optical Network (GPON) is a high bandwidth shared fiber access technology that is used around the world for Fiber to the Home (FTTH) and, at least in North America, is thought by many to be the successor to BPON. GPON technology is especially popular with large US-based telcos, especially Verizon, though it is used by the MSOs as well (often for serving business customers as a complement to their Hybrid Fiber Coax (HFC) networks). 10G GPON is a higher speed version of GPON that has yet to be standardized by the ITU-T. EPON, 10G EPON, WDM PON, and BPON are Passive Optical Network (PON) technologies that are also vying for carrier attention.

GPON is standardized by the ITU-T in its G.984 series (see end of this article for details), but widespread interoperability between different vendors’ equipment has not materialized. Basic data transmission is readily achievable. Managing a multi-vendor GPON solution is quite an operational challenge, however.

GPON Architectures

There are three main components in a GPON access network (other than the fiber itself). The GPON Optical Line Terminal (OLT) is the network concentrator, usually installed in a Central Office (CO). The splitter (or splitters) allows a single fiber from the CO to be shared among a number of subscribers. The Optical Network Terminal (ONT) serves a single residence, converting optical signals to electrical signals that can be used within the home. Note that the ITU standards call the subscriber device an Optical Network Unit (ONU), and many use ONU to mean an ONT serving several subscribers, which would be common in an installation serving a number of apartments in the same building.

GPON is specified to be a single or dual fiber system, but almost all GPON systems are single fiber like virtually all popular FTTH technologies. There is little reason to use dual fibers, although this option is indeed allowed in the standard.

G.984 allows for 60km maximum reach with 20km differential reach and up to 128 subscribers on a single GPON network. However, GPON systems typically provide only 0-20km reach owing to the cost of the optics. G.984.6 is a new ITU-T specification that provides for a Mid-Span Extender that can increase the reach of GPON beyond 20km to as much as 60km.

Many carriers use a maximum of 32 subscribers on a single GPON segment. B+ optics provide for 32x split with 20km reach. C+ optics, newly available and expensive, provide for 64x split with the same 20km reach. GPON wavelengths are 1490 nm down and 1310 nm up. RF Overlay is carried downstream on 1550nm. Forward Error Correction (FEC) potentially allows for cheaper optical transceivers, though this cost advantage in the optics comes at the cost of extra complexity and overhead (almost 10% extra overhead) to support FEC.

A GPON network can have two, three, or four wavelengths in use. Two and three wavelength systems are covered below. See my article on RFoG for a description and diagram of a four wavelength system combining GPON and RFoG.

Two Wavelength System

The following diagram shows the architecture of a basic two wavelength GPON network, which is probably the most common implementation. The downstream wavelength is 1490nm and transmits data at 2.488 Gbps. The upstream wavelength is 1310nm and transmits data at 1.244 Gbps.

GPON Network Diagram (Two Wavelengths)

The GPON Optical Line Terminal (OLT) is typically installed in a Central Office (CO), though it could be installed elsewhere. The optical splitter is installed somewhere between the CO and the subscribers. And a GPON Optical Network Terminal (ONT) is installed at each subscriber’s home. Voice, video, and data traffic must all be delivered across the single GPON downstream wavelength. A nice facet of GPON for IP video support is that its downstream is naturally a broadcast medium, and it is very efficient for delivering multicast traffic.

The optics in the GPON ONT for a two wavelength implementation is called a diplexer. See the diplexer diagram below. Diplexers can be implemented with a three dimension bulk optic design (discrete components aligned and welded together manually) or with a Planar Lightwave Circuit (PLC) design (link to a good article by Enablence explaining bulk optics and PLCs). A PLC puts all its optical components on a silicon substrate for a two dimension design, eliminates all the complexity of dealing with a third dimension, and allows for low-cost automated manufacturing.

GPON Diplexer

Three Wavelength System

The architecture of a GPON three wavelength system is identical to that of a two wavelength system with the addition of a third downstream video wavelength on the fiber and the equipment to insert this signal into the fiber. The following diagram shows the architecture of a three wavelength RF Overlay GPON network.

GPON RF Overlay Network Diagram

Note that only up to 32 GPON ONTs are indicated for a single GPON OLT port. This is because of the RF Overlay video signal and not the GPON signal. For 20km reach and 32 subscribers on a single network, the maximum amount of light that a fiber will accept (20 dBm or 100 mW) must be inserted into the fiber by the RF Overlay video equipment, and any additional optical power is just wasted. New C+ optics allow for 64x splits and 20km reach for the GPON signal, but this is no help for the RF Overlay video signal. The RF Overlay transmit signal is already at maximum for 32x split and 20km and only the receiver sensitivity can be improved. This may come in time.

The transceiver in the GPON ONT for a GPON RF Overlay video implementation is called a triplexer (see diagram below). Triplexers are more expensive than diplexers and generally are implemented with a three dimensional bulk optic design (discrete components aligned and welded together manually). PLC circuits not as common for triplexer implementations though Enablence describes a PLC triplexer.

GPON Triplexer

The OLT does nothing with the third RF Overlay wavelength other than filter it out. The ONTs merely convert the 1550nm optical signal to an electrical signal for delivery throughout the home over 75 ohm coax. The thorniest issue to solve with a three wavelength signal is how to get the upstream data for controlling the RF Overlay signal to the headend. One option is to convert the traffic into IP and send it upstream on the 1310nm upstream wavelength, though this method has some limitations. A more robust (and more expensive) option is RFoG, which is described in my article on RFoG.

Transmission

The ITU GPON standard allows up to 2.488Gbps symmetric transmission, but almost all GPON systems are 2.488Gbps down/1.244Gbps up. Both downstream and upstream bandwidth is shared although in different ways.

Downstream from the OLT to the ONTs is broadcast with an ONT grabbing only traffic addressed to it. Upstream is Time Division Multiple Access (TDMA) with each ONT transmitting in turn (with perhaps multiple turns per ONT). A single ONT can have multiple upstream timeslots, and each timeslot can be a different size. Additionally, Dynamic Bandwidth Assignment (DBA) allows for real-time changes in upstream timeslot sizes to accommodate varying traffic conditions. A typical implementation has one upstream timeslot for management, one for voice, and one for data traffic for each ONT. A GPON network with 32 ONTs may have about 100 upstream timeslots in use.

GPON natively supports Ethernet (GFP), ATM, and TDM, but most systems run just Ethernet (sort of like a souped up EPON). Upstream and downstream frames are transmitted 8000 per second (the downstream frame is twice the size of the upstream frame), which provides a nice 8 kHz signal to the ONTs for POTS service (required for good fax speeds).

OMCI

ONT Management and Control Interface (OMCI) is the management protocol used between the OLT and the ONTs. With OMCI, external management systems do not have to communicate directly with the ONTs. OMCI allows a single IP address to be used to manage an OLT and, through OMCI, all of its associated ONTs. This is very efficient for IP address conservation, and it reduces the load on a management system, but it does require the implementation of a technology-specific management protocol. If there is a VoIP implementation in the ONTs, it is likely they will require separate management and IP addresses anyway. Owing to the popularity of VoIP in these systems, IP address conservation with OMCI is of dubious benefit in many GPON implementations.

Standards

GPON is standardized by the ITU-T in its G.984 series. The list below provides links to the relevant ITU-T GPON standards.

G.984.1, General characteristics, [A general overview. Easy reading.]
G.984.2, Physical Media Dependent (PMD) layer specification, [Optics, mostly irrelevant.]
- G.984.2 Amendment 1, [B+ optics, most common implementation.]
- G.984.2 Amendment 2, [C+ optics and some tweaks. Allows 64x splits with 20km reach.]
G.984.3, Transmission convergence layer specification, [The protocols. Pretty darn technical.]
- G.Imp.984.3, Implementators’ Guide for ITU-T Rec. G.984.3,
G.984.4, ONT management and control interface specification, [OMCI. Yawn.]
- G.Imp.984.4, Implementor’s Guide for ITU-T Rec. G.984.4,
G.984.5, Enhancement band, [Next generation PON compatibility.]
G.984.6, Reach extension. [Increased range using an active mid-span extender.]

Three Fundamental Architectures for FTTH

John Bartell — Thu, 10 Sep 2009 06:00:58 +0000

Essentially, there are three fundamental architectures for delivering fiber directly to a subscriber’s house: point-to-point, switched, and Passive Optical Network (PON). All three Fiber to the Home (FTTH) architectures require an aggregation device in the CO (the Optical Line Terminal or OLT), and all three require an optical to electrical converter (Optical Network Terminal or ONT) in or on the house. These three architectures differ mainly in what type of device (if any) is installed between the CO and the house.

One common characteristic of Fiber to the Home network architectures is the use of bidirectional transceivers (BIDI) allowing the use of a single fiber to serve each home. One wavelength is used for downstream (CO to home), and another wavelength is used for upstream transmissions. Bidirectional transmission on a single fiber increases the cost of optical transceivers somewhat, but it reduces the quantity of fiber (and labor to splice the fiber) needed to serve a home by half.

Point-to-Point FTTH

Point-to-Point (P2P, also known as Active Fiber) is the simplest of all three FTTH fundamental architectures. With a P2P 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). The CO contains a high port count aggregation device (one port per subscriber) known as an Optical Line Terminal or OLT. 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). P2P has an advantage that no port is shared in any way, thus troubleshooting problems on the network is greatly simplified. With P2P, 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.

Switched FTTH

A switched FTTH architecture (commonly Active Ethernet) has many of the advantages of P2P, but it dramatically reduces the number of fibers terminated in the CO. Of the three architectures, it has the potential to have the fewest fiber terminations in the CO, but it requires the largest investment in the OutSide Plant (OSP). To aggregate fibers delivered directly to subscribers, a switched architecture requires switches be installed in secured cabinets between the CO and the subscriber homes.

Passive Optical Network FTTH

A Passive Optical Network or PON network architecture is similar to the switched architecture, but it requires no OSP electronics. Instead, an optical splitter is used in place of the OSP switch. The splitter divides the light coming from the OLT, and it combines the light coming from the ONTs. This greatly reduces the cost of OSP aggregation since the splitter is inexpensive, requires no power and very little, if any maintenance. Maximum concentration of subscribers is generally limited to 32 per fiber (with a 32 port splitter) delivered to the CO, though up to 64x and even 128x splits are possible. BPON, EPON, and GPON are common types of PON networks in use today. 10G EPON and 10G GPON are new technologies to be deployed in the next few years. WDM PON is similar, but instead of a splitter, it requires an Arrayed WaveGuide (AWG) to divide wavelengths for individual delivery to subscribers. Note that a PON may support RF overlay analog video, which is generally not feasible in the other two architectures.

Which Vendors Have WDM PON products?

John Bartell — Fri, 04 Sep 2009 15:07:27 +0000

Optiblue WDM PON Systems

WDM PON provides the dedicated bandwidth of a point-to-point network with the fiber sharing inherent in PON networks. The WDM PON physical architecture is identical to that of EPON and GPON. However, instead of a traditional PON splitter, WDM PON uses an Arrayed WaveGuide (AWG) that separates the wavelengths for individual delivery to subscribers’ ONTs.

The following vendors have WDM PON products or appear to be working on them.

ADVA Optical

Alcatel-Lucent

Applied Optoelectronics Inc. (AOI)

Ericsson

Genexis B.V.

Ignis

LG Nortel

Optiblue

Pirelli Broadband Solutions

Teldat

Tellabs

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.

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.

Vendors of GPON Optical Transceivers

John Bartell — Fri, 21 Aug 2009 16:36:06 +0000

AOI transceiver-pon

GPON transceivers are used in the OLT and in the ONT to interface to the optical fiber used to connect the two. Even though GPON is specified to support both dual and single fiber implementations, I have yet to encounter a dual fiber implementation. A single fiber implementation uses BIDI or bidirectional GPON transceivers that both transmit and receive on the same fiber. Obviously, the OLT transmit wavelength is the receive wavelength for the ONT and vice versa. The OLT transceiver has no role in RF video support other than rejecting the 1550nm wavelength (which is a very high power signal).

The ONT transceiver is a diplexer when it supports two wavelengths, and it is a triplexer when it supports the third, RF overlay wavelength. Diplexers and triplexers are typically very different designs, and one vendor may provide only diplexers or triplexers.

Diiplexer and Triplexer

The following vendors all provide GPON ONT and/or OLT transceivers.