FTTx
#1

ABSTRACT
FTTx is a network where an optical fiber runs from the telephone switch to the subscriber's premises - business or home. For the past few years, telecom companies have been working diligently to provide us with pseudo-broadband Internet connections over copper (DSL) and cable (cable modem), with practical speeds of up to 1.5 Mbps. No doubt improvements will be made over the next few years to squeeze more out of copper and cable, but it doesn't matter, because fiber to the home is coming, and it will be here faster than most people predict providing download speeds of up to 155 Mbps. Such speeds will enable instantaneous data transfer and video on demand. It also provides a future-proof network in that one does not have to upgrade from ADSL to xDSL to digital co-ax to digital wireless.
Optic fiber has higher reliability and does not need electric powering and is immune to lighting and other transients. These properties of the fiber lead to lowest powering costs and operational costs (such as maintenance, provisioning, and facilities planning). However, challenges such as making FTTx cost effective will create stumbles along the way to providing FTTx. Also the lack of product standardization and the lack of greater bandwidth demand from consumer and business applications have so far made FTTx deployment impractical.



1. INTRODUCTION
Just as the unsettling but always fascinating X Files television series comes to an undoubtedly eerie end, a previously unimaginable reality may be taking shape in broadband telecommunications.Fiber-to-the-curb (FTTC), fiber-to-the-home (FTTH), even fiber-to-the-user (FTTU) systems are gaining renewed attention from local telcos, utilities and municipalities across North America and around the world. This unrelenting activity seems to have created a weird trickle-up theory of deep-fiber deployment The most important factor thatâ„¢s giving life to such approaches as fiber-to-the-home is the Internet .Like any new or advanced method, fiber-to-the-home started out as a Ëœsomething we (service providers) can do, but itâ„¢s really expensiveâ„¢ approach. But, theyâ„¢ve been chipping down the price ever since.
In the meantime, there™s this other revenue stream that™s popped up that could potentially pay for the investment“high-speed data. That™s because when they first started doing this, there wasn™t any Internet. There was only voice and video, and those don™t add up to pay off the costs. If it weren™t for the Internet, fiber-to-the-home would be pushed back at least another 20 years.Factors that may accelerate this thirst for all things fiber, says the report, and would be faster-than-expected cost reductions or applications that drive bandwidth demand beyond what non-fiber-based technologies can provide. However, the report cautions, factors that may hinder the rollout of deep fiber solutions include slower cost reductions or improvements in non-fiber-based technologies that keep pace with future bandwidth demands.The breakthrough for FTTH was the result of two factors“cheaper equipment costs and better technology.
The cost of fiber came down a good 15 percent or maybe even 25 percent. Splitters and couplers are down very significantly. Today, you can get glass splitter/couplers that two years ago would have cost $100 to $150 a port, for $35 a port now. Labor is down a bit because of the recession as well.The optics costs have come down as well. In fact, today we pay 25 percent of what we did for optics two years ago. And then, we also get to enjoy all the normal Mooreâ„¢s Law-type associations with higher integration of the new generation of network processors that are out there.


2. OPTICAL FIBER ACCESS OVERVIEW




There are mainly two types of architectures used in Optical Fiber Access namely
1. PON Architecture
2. Point-to-Point Architecture

In PON Architecture passive splitters are used.There are no active electronics like regenerators between the OLT & ONU/ONT, where OLT is the Optical Line Terminal,ONU is the Optical Network Unit and ONT is the Optical Network Terminal.Splitters are used to split the incoming signals to different ONTs.
In Point -to-Point Architecture the fibers from the P2P transceiver directly connects to the Media Converter.Here passive splitters are not used.


3. PON ARCHITECTURE
In PON Architecture passive splitters are used.There are no active electronics like regenerators between the OLT & ONU/ONT, where OLT is the Optical Line Terminal,ONU is the Optical Network Unit and ONT is the Optical Network Terminal.Splitters are used to split the incoming signals to different ONTs.

3.1 PON (PASSIVE OPTICAL NETWORK)
A passive optical network (PON) is a system that brings optical fiber cabling and signals all or most of the way to the end user. Depending on where the PON terminates, the system can be described as FTTx. The passive simply describes the fact that optical transmission has no power requirements or active electronic parts once the signal is going through the network. To understand how PONs work it is best to go back to basics. Essentially, carriers want to connect each customer site with a wavelength of light, but they

want to avoid having to dedicate a fiber to every wavelength. PONs address this issue by bundling together multiple wavelengths (up to 32 at present) so they can be carried over a single access line from the carrier's central office (CO) to a manhole or controlled environmental vault close to a cluster of customer sites. At that point, the wavelengths are broken out and each one is steered into a different short length of fiber to an individual site. A different scheme is used for collecting traffic traveling in the opposite direction - from user sites to the CO. In this case, each site is given a specific time slot to transmit, using a polling scheme similar to the one used in old networks.
PONs share the costs of fiber and much of the equipment located with the service provider among several customers, while also eliminating expensive, powered equipment between the service provider and these customers. The optical path is "transparent" to bit rate, modulation format (e.g., digital or analog), and protocol (e.g., SONET/SDH, IP, Ethernet). Such transparency results from nothing being installed between the service provider and the customer which is specific to the bit rate, modulation format, etc., allowing services to be mixed or economically upgraded in the future as needed. New services and/or new customers can be added by changing service-specific equipment only at the ends of the network, and only for those customers affected. Such flexibility is not the case in most of today's other access network architectures.
Despite their advantages, PONs face significant obstacles on the road to success. The facts that Pons share bandwidth among multiple subscribers lowers service costs and helps carriers efficiently amortize the equipment and operations expenses. However, any amount of upstream bandwidth transmitted over a PON will be divvied up among the number of users at the customer site. Therefore, on a 155-Mbit/s PON page link with four splits, each subscriber will receive 38.75 Mbps. Addition of splitters to links that have already been split leads to lowering of the final available bandwidth. Also, the fact that PONs does not regenerate or convert optical signals mid-network makes them cheaper, but it also limits their reach. Without regeneration, light signals lose power quickly, consequently losing transmission capability. Due to these disadvantages and the availability of other broadband access alternatives the market for PONs will remain relatively small for the next few years.


4. DIFFERENT PON STANDARDS
The different PON standards are
1. APON (ATM PON)
2. BPON (Broadband PON)
3. GPON (Gigabite PON)
4. EPON (Ethernet PON)

4.1 APON
The first PON standard was APON (ATM PON), which used ATM encapsulation of the transported data and was aimed primarily at business applications. APON was quickly followed by BPON.
APONs were developed in the mid 1990s through the work of the full-service access network (FSAN) initiative. FSAN was a group of 20 large carriers that worked with their strategic equipment suppliers to agree upon a common broadband access system for the provisioning of both broadband and narrowband services. British Telecom organized the FSAN Coalition in 1995 to develop standards for designing the cheapest, fastest way to extend emerging high-speed services, such as Internet protocol (IP) data, video, and 10/100 Ethernet, over fiber to residential and business customers worldwide.
At that time the two logical choices for protocol and physical plant were ATM and PON: ATM because it was thought to be suited for multiple protocols, PON because it is the most economical broadband optical solution. The APON format used by FSAN was accepted as an International Telecommunications Union (ITU) standard (ITU“T Rec. G.983). The ITU standard focused primarily on residential applications and in its initial version did not include provisions for delivering video services over the PON. Subsequently, a number of start-up vendors introduced APON“compliant systems that focused exclusively on the business market.



BPON
BPON (Broadband PON) is the form of PON being almost exclusively rolled out today. It has largely replaced APON in PON deployments because of its superior features. For example, it has survivability, WDM support for video overlay, higher upstream bandwidths, and dynamic upstream bandwidth allocation, which APON does not. BPON can be run at 622 Mbit/s or 1.2 Gbit/s.BPON making up 84 percent of all PON subscribers in Asia in 2004. However, EPON is being rolled out so fast in market-leading Japan that it will overtake Japanâ„¢s BPON subscriber base in 2005.BPON is the PON technology gorilla in North America, making up 81 percent of North American PON revenue in 2004, and will continue its reign through 2006, when its successor, GPON, becomes more available


MAX3690
The MAX3690 serializer is ideal for converting 8-bit-wide, 77Mbps parallel data to 622Mbps serial data in ATM and SDH/SONET applications. Operating from a single +3.3V supply, this device accepts TTL clock and data inputs, and delivers a 3.3V differential PECL serial-data output. A fully integrated PLL synthesizes an internal 622MHz serial clock from a low-speed crystal reference clock (77.76MHz, 51.84MHz, or 38.88MHz). The MAX3690 is available in the extended-industrial temperature range (-40°C to +85°C) in a 32-pin TQFP package.

MAX3738
The MAX3738 is a +3.3V laser driver designed for multirate transceiver modules with data rates from 1Gbps to 2.7Gbps. Lasers can be DC-coupled to the MAX3738 for reduced component count and ease of multirate operation.
Laser extinction ratio control (ERC) combines the features of automatic power control (APC), modulation compensation, and built-in thermal compensation. The APC loop maintains constant average optical power. Modulation compensation increases the modulation current in proportion to the bias current. These control loops, combined with thermal compensation, maintain a constant optical extinction ratio over temperature and lifetime.
The MAX3738 accepts differential data input signals. The wide 5mA to 60mA (up to 85mA AC-coupled) modulation current range and up to 100mA bias current range, make the MAX3738 ideal for driving FP/DFB lasers in fiber optic modules. External resistors set the required laser current levels. The MAX3738 provides transmit disable control (TX_DISABLE), single-point fault tolerance, bias-current monitoring, and photocurrent monitoring. The device also offers a latched failure output (TX_FAULT) to indicate faults, such as when the APC loop is no longer able to maintain the average optical power at the required level. The MAX3738 is compliant with the SFF-8472 transmitter diagnostic and SFP MSA timing requirements. The MAX3738 is offered in a 4mm x 4mm, 24-pin thin QFN package and operates over the extended -40°C to +85°C temperature range
MAX3656
The MAX3656 is a burst-mode laser driver that operates at data rates from 155Mbps up to 2.5Gbps. The laser driver accepts either positive-referenced emitter coupled

logic (PECL) or current-mode logic (CML) data inputs and provides bias and modulation current for the laser diode. The device can switch the laser diode from a completely dark (off) condition to a full (on) condition (with proper bias and modulation currents) in less than 2ns. The MAX3656 incorporates DC-coupling between laser driver and laser diode and operates with a single supply voltage as low as +3.0V.
A digital automatic power-control (APC) loop is provided to maintain the average optical power over the full temperature range and lifetime. The APC loop is functional for a minimum burst on-time of 576ns and minimum burst off-time of 96ns, with no limit on the maximum burst on- or off-time. A fail monitor is provided to indicate when the APC loop can no longer maintain the average power. The MAX3656 can be configured for nonburst-mode applications (continuous mode) by connecting burst enable (BEN) high. For power saving, the MAX3656 provides enabling and disabling functionality. The modulation current can be set from 10mA to 85mA and the bias current can be set from 1mA to 70mA.
The MAX3656 is packaged in a small, 24-pin, 4mm x 4mm thin QFN package and consumes only 132mW (typ), excluding bias and modulation currents.
MAX3681
The MAX3681 deserializer is ideal for converting 622Mbps serial data to 4-bit-wide, 155Mbps parallel data in ATM and SDH/SONET applications. Operating from a single +3.3V supply, this device accepts PECL serial clock and data inputs, and delivers low-voltage differential-signal (LVDS) clock and data outputs for interfacing with high-speed digital circuitry. It also provides an LVDS synchronization input that enables data realignment and reframing. The MAX3681 is available in the extended-industrial temperature range (-40°C to +85°C), in a 24-pin SSOP package

MAX3872
The MAX3872 is a compact, multirate clock and data recovery (CDR) with limiting amplifier for OC-3, OC-12, OC-24, OC-48, OC-48 with FEC SONET/SDH, and Gigabit Ethernet (1.25Gbps/2.5Gbps) applications. Without using an external reference clock, the fully integrated phase-locked loop (PLL) recovers a synchronous clock signal from the serial NRZ data input. The input data is then retimed by the recovered clock, providing a
clean data output. An additional serial input (SLBI±) is available for system loop back diagnostic testing. Alternatively, this input can be connected to a reference clock to maintain a valid clock output in the absence of data transitions. The device also includes a loss-of-lock (LOL-bar) output.
The MAX3872 contains a vertical threshold control to compensate for optical noise due to EDFAs in DWDM transmission systems. The recovered data and clock outputs are CML with on-chip 50 back termination on each line. Its jitter performance exceeds all SONET/SDH specifications. The MAX3872 operates from a single +3.3V supply and typically consumes 580mW. It is available in a 5mm x 5mm 32-pin thin QFN with exposed-pad package and operates over a -40°C to +85°C temperature range.
MAX3654
The MAX3654 analog transimpedance amplifier (TIA) is designed for CATV applications in fiber-to-the-home (FTTH) networks. This high-linearity amplifier is intended for 47MHz to 870MHz subcarrier multiplexed (SCM) signals in passive optical networks (PON). A gain-control input supports AGC operation with optical inputs having -6dBm to +2dBm average power. With 62dB maximum gain at 47MHz and 18dB gain control range, the minimum RF output level is 14dBmV/channel at -6dBm optical input. A compact 4mm x 4mm package includes all of the active RF circuitry required to convert analog PIN photocurrent to a 75 CATV output. This 700mW SiGe RF IC provides a low-cost, low-power integrated analog CATV receiver solution for FTTH ONTs

GPON
GPON (Gigabit PON) is under development by the same ITU and FSAN groups that developed BPON, and there are a couple of suppliers delivering early versions of GPON today. It looks as if North America, where there is a lot of BPON being rolled out, will favor GPON, because it is an evolution of BPON. GPON will support Ethernet in addition to ATM for the Layer 2 data encapsulation, and it will offer enhanced security.GPON is really the continuation of the work done for BPON by the FSAN Group, says Sayeed Rashid, senior manager of marketing at Alcatel (NYSE: ALA - message board; Paris: CGEPTongueA), Access Network Division, North America. The specifications are really based on the premise that efficient IP transport and bandwidth scaleability are key for the PON in the future. In GPON you have twice the bandwidth scaleability “ up to 2.5 Gbit/s symmetric “ that you have in the other PONs. With GPON you also have highly efficient IP transport capability compared to other PONs.The introduction of the ONT management and control interface (OMCI) specification, adopted in April 2004, largely completes the work for the basic set of GPON specifications. So standards-compliant products should start appearing in 2005, and mass-market deployment should begin in 2006.
NTT East and NTT West together have more than a million subscribers “ more than two thirds of the world™s PON subscribers “ and these providers are now switching to Gigabit Ethernet PON (GEPON, a form of EPON) almost exclusively.BPON is the PON technology gorilla in North America, making up 81 percent of North American PON revenue in 2004, and will continue its reign through 2006, when its successor, GPON, becomes more available. GPON is a flexible option for providers because it is designed to handle Ethernet, IP, and ATM traffic, and can stream video over IP or a separate analog wavelength. GPON offers roughly twice the capacity of EPON.EPON is firmly entrenched in much of Asia, but GPON is gaining momentum in North America, Europe, and several Asian countries, with China a good possibility, where analog video is an issue. By 2008, North America will account for 43 percent of worldwide PON revenue (where GPON dominates), and Asia will account for 39 percent of worldwide revenue (where EPON dominates).

EPON
EPON (Ethernet PON) was standardized in mid-2004 and is the Institute of Electrical and Electronics Engineers Inc. (IEEE) Ethernet in the First Mile (EFM) standard. It runs at 1.25 Gbit/s symmetric and is suitable for data services. And, of course, it uses Ethernet rather than ATM data encapsulation.
The development of EPONs has been spearheaded by one or two visionary start-ups that feel that the APON standard is an inappropriate solution for the local loop because of its lack of video capabilities, its insufficient bandwidth, its complexity, and its expense. Also, as the move to fast Ethernet, gigabit Ethernet, and now 10-gigabit Ethernet picks up steam, these start-ups believe that EPONs will eliminate the need for conversion in the wide-area network (WAN)/LAN connection between ATM and IP protocols. EPON vendors are focusing initially on developing fiber-to-the-business (FTTB) and fiber-to-the-curb (FTTC) solutions, with the long-term objective of realizing a full-service fiber-to-the-home (FTTH) solution for delivering data, video, and voice over a single platform. While EPONs offer higher bandwidth, lower costs, and broader service capabilities than APON, the architecture is broadly similar and adheres to many G.983 recommendations.


MAX3748, MAX3748A
The MAX3748/MAX3748A multirate limiting amplifier functions as a data quantizer for SONET, Fibre Channel, and Gigabit Ethernet optical receivers. The amplifier accepts a wide range of input voltages and provides constant-level current-mode logic (CML) output voltages with controlled edge speeds.
A received-signal-strength indicator (RSSI) is available when the MAX3748/MAX3748A is combined with the MAX3744 SFP transimpedance amplifier (TIA). A receiver consisting of the MAX3744 and the MAX3748/ MAX3748A can provide up to 19dB RSSI dynamic range. Additional features include a programmable loss-of-signal (LOS) detect, an optional disable function (DISABLE), and an output signal polarity reversal (OUTPOL). Output disable can be used to implement squelch. The combination of the MAX3748/MAX3748A and the MAX3744 allows for the implementation of all the small-form- factor SFF-8472 digital diagnostic specifications using a standard 4-pin TO-46 header. The MAX3748/ MAX3748A is packaged in a 3mm x 3mm 16-pin QFN package with an exposed pad.


POINT TO POINT ARCHITECTURE
In Point -to-Point Architecture the fibers from the P2P transceiver directly connects to the Media Converter.Here passive splitters are not used.In this Architecture we have to dedicate a fiber for each connection.

MEDIA CONVERTER
125 Mbps media converter for P2P access

MAX3669
The MAX3669 is a complete, +3.3V laser driver with automatic power control (APC) circuitry for SDH/SONET applications up to 622Mbps. It accepts differential PECL inputs, provides bias and modulation currents, and operates over a temperature range from -40°C to +85°C.
An APC feedback loop is incorporated to maintain a constant average optical power over temperature and lifetime. The wide modulation current range from 5mA to 75mA and bias current of 1mA to 80mA are easy to program, making this product ideal for use in various SDH/SONET applications. Two pins are provided to monitor the current levels in the laser: BIASMON with current proportional to laser bias current, and MODMON with current proportional to laser modulation.
The MAX3669 also provides enable control and a failure-monitor output to indicate when the APC loop is unable to maintain the average optical power. The MAX3669 is available in 4mm x 4mm 24-pin thin QFN and 5mm x 5mm 32-pin TQFP packages as well as dice .
MAX3657
The MAX3657 is a transimpedance preamplifier for receivers operating up to 155Mbps. The low noise, high gain, and low-power dissipation make it ideal for Class-B and Class-C passive optical networks (PONs).
The circuit features 14nA input-referred noise, 130MHz bandwidth, and 2mA input overload. Low jitter is achieved without external compensation capacitors. Operating from a +3.3V supply, the MAX3657 consumes only 76mW power. An integrated filter resistor provides positive bias for the photodiode. These features, combined with a small die size, allow easy assembly into a TO-46 header with a photodiode. The MAX3657 includes an average photocurrent monitor.
The MAX3657 has a typical optical sensitivity of -38dBm (0.9A/W), which exceeds the Class-C PON requirements. Typical overload is 0dBm. The MAX3657 is available in die form with both output polarities (MAX3657E/D and MAX3657BE/D.) The MAX3657 is also available in a 12-pin, 3mm x 3mm thin QFN package
MAX3964, MAX3965, MAX3968
The MAX3964 limiting amplifier, with 2mVP-P input sensitivity and PECL data outputs, is ideal for low-cost ATM, FDDI, and Fast Ethernet fiber optic applications.
The MAX3964 features an integrated power detector that senses the input-signal power. It provides a received-signal-strength indicator (RSSI), which is an analog indication of the power level and complementary PECL loss-of-signal (LOS) outputs, which indicate when the power level drops below a programmable threshold. The threshold can be adjusted to detect signal amplitudes as low as 2.7mVP-P. An optional squelch function disables switching of the data outputs by holding them at a known state during an LOS condition.


The MAX3965 provides the same functionality, but offers TTL-compatible LOS outputs. The MAX3968 pro-vides the same functionality as the MAX3964, but has data-output edge speed suitable for ESCON and 266Mbps fibre channel applications. The MAX3964/MAX3965/MAX3968 are available in die form, as tested wafers, and in 20-pin QSOP packages. The MAX3964ETP is available in a 20-pin thin QFN package

6. PON & FTTx
The X in FTTx can stand for a lot of things, often not very different, but for practical purposes they can all be grouped in any of three basic approaches:
1) Fiber all the way to the residential or business customer by using PON or Ethernet
These are:
¢ Fiber to the Home (FTTH)
¢ Fiber to the Building (FTTB)
The distinction is basically between single homes or apartments and business or multitenant buildings.
2) Fiber all the way to the customer by using PON only
This is:
¢ Fiber to the Premises (FTTP)
3) Fiber partial
These all use copper from the partial point on to the customer:
¢ Fiber to the Neighborhood (FTTN)
¢ Fiber to the Node (also FTTN)
¢ Fiber to the Curb (FTTC, also FTTK for those who spell, usefully, curb as kerb)
¢ Fiber to the Cabinet (also FTTC)
Fiber partial means fiber goes to some point near to the customer, and then another mechanism (usually copper pairs supporting ADSL or VDSL) takes over for the final page link to the customer.
The two FTTNs “ FTTNeighborhood and FTTNode “ mean basically the same thing: fiber is run out to a point close to the customers. Typically in North America this is a node in a remote terminal, or even closer to the customer in a crossconnect or similar box. The main deployments in North America for FTTN usually have a node that can handle 400 to 600 customers or homes.FTTCabinet is pretty similar to the FTTNs, and FTTCurb refers to fiber deployments that go even closer to the customer, and usually serve eight to 24 customer drops (copper).
Figure shows how some of these main varieties of FTTx are differentiated when using PON fiber.The big attractions for telcos in deploying PONs as the basis of a mass-market fiber rollout are:
¢ All-optical passive loop plant
¢ Significantly reduced CO wiring and space requirements
¢ Reduced plant operational expenditures



7. CONCLUSION

The Technologies Behind the Networks -- FTTx is a network where an optical fiber runs from the telephone switch to the subscriber's premises - business or home. For the past few years, telecom companies have been working diligently to provide us with pseudo-broadband Internet connections over copper (DSL) and cable (cable modem), with practical speeds of up to 1.5 Mbps. No doubt improvements will be made over the next few years to squeeze more out of copper and cable, but it doesn't matter, because fiber to the home is coming, and it will be here faster than most people predict - providing download speeds of up to 155 Mbps. Such speeds will enable instantaneous data transfer and video on demand. It also provides a future-proof network in that one does not have to upgrade from ADSL to xDSL to digital co-ax to digital wireless.
Several new technologies are leading to cost reduction of FTTH. Previously a single fiber was needed to connect to each home separately. Technology advances permit N-way distribution of the bits to many homes through resource sharing circuits (Passive Optic Network based FTTx). Recent advances in loop lasers, fiber and other components, and chips for compressing digital video greatly reduce the system cost and will bring FTTx as the forefront broadband access technology. It will provide service providers with a potential to increase revenues from applications such as interactive access, pay-per-view, video on demand, and subscription services
Fiber-to-the-Curb and Fiber-to-the-Home, predicted FTTH systems in the United States will reach 2.65 million homes by 2006, after starting from just 89,000 homes in 2001. As a result, says the report, the FTTH equipment market will grow from just $100 million in 2001 to nearly $1 billion in 2006.In the next four to five years, increased market demand and decreasing cost factors are expected to drive most or all of the RBOCs (Regional Bell Operating Companies) to begin FTTH deployment in new housing developments, then in network rebuilds.
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[attachment=4890]
This article is presented by:
Wayne Sorin
FTTx -Next Generation Broadband Access


Outline
-Motivation and Background
-FTTx approaches
*Point-to-Point
*AON
*TDM-PON (BPON, EPON, GPON)
*WDM-PON (wavelength-locked solution)
-Summary


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