INTRODUCTION
Presently, not only the European Union (EU) but the global community faces a decisive priority to “redesign” its economy and society, in order to meet a variety of challenges imposed by the expansion of innovative technological features, in the scope of the new millennium. The rate of investments performed and the rapid development of electronic communications networks-infrastructures, together with all associated facilities in the scope of broadband evolution, create novel major opportunities for the related market sectors (Chochliouros, & Spiliopoulou, 2005). Modern digital-based technologies make compulsory new requirements for next-generation components and for much wider electronics integration. This critical challenge also raises the issue for considering the “evolution” from current large legacy infrastructures towards new (more convenient) ones, by striking a “balance” between backward compatibility requirements and the need to explore disruptive architectures to appropriately build (and offer) future Internet, broadband, and related service infrastructures. More specifically, for the entire European market a number of evolutionary initiatives, as they currently have been encouraged by the latest EU strategic frameworks, relate first and foremost to the technological expansion and the exploitation of ubiquitous broadband networks, the availability/accessibility of dynamic services platforms, and the offering of “adequate” trust and security, all in the framework of converged and interoperable networked environments (European Commission, 2006).
However the global information society cannot deliver its major benefits without a “suitable” and appropriately deployed infrastructure, able to fulfill all requirements for increased bandwidth. During recent years, optics and photonics have become increasingly pervasive in a broad range of applications. Therefore, photonic components and subsystems are nowadays indispensable in multiple application areas, and consequently they constitute concerns of high-strategic importance for many operators. In this critical extent, fiber is constantly becoming an essential priority for wired access, as it can provide excessive bandwidth and additional advantages, if compared to similar alternativeoptions ofunderlying infrastructures (Agrawal, 2002). There are several market and investment evidences demonstrating that a significant part of next-generation access networks will be based on optical access (Chochliouros, Spiliopoulou, & Lalopoulos, 2005).
This is due to the fact that we are presently witnessing an extraordinary expansion in bandwidth demand, mainly driven by the development of sophisticated services/applications, including video-on-demand (VoD), interactive high-definition digital television (HDTV), IPTV, multi-party videoconferencing, and many more. These facilities require both the existence and the use of a “fitting” underlying network infrastructure, capable of supporting high-speed data transmission rates that cannot be fulfilled by the “traditional” copper-based access networks. In fact, market actors are currently focusing on developing and deploying new network infrastructures (Leiping, 2005) that will constitute future-proof solutions in terms of the anticipated worldwide growth in bandwidth demand (reaching a rate of 50% to 100% annually), but at the same time be economically viable (Prat, Balaquer, Gene, Diaz, & Fiquerola, 2002). To this aim, fiber-access technologies evolve quite rapidly as they can guarantee “infinite” bandwidth opportunities, for all prescribed market needs, either corporate and/or residential.
BACKGROUND
A great majority of users currently benefit from rather high speed communication services offered through DSL (digital subscriber line) access technologies. DSL’s deployment has been widely supported by incumbent operators, as they were able to exploit their already laid copper infrastructure to offer broadband connectivity services to their customers, without being actually obliged to realize severe investments in access infrastructure. However, such schemes are considered as “short-term” market solutions, since the aging copper-based infrastructure is rapidly approaching its essential speed limits, while simultaneously, modern applications definitely “push” data rates beyond the capabilities of such networks. As a consequence, such networks “generate” a type of “limitation”(or a “bottleneck”) concerning requirements of bandwidth and service provision between the operator and the end user. In contrast to this option, optical access architectures allow communication via optical fibers and can provide significant advantages to the customers’ needs mainly by providing a fully practical (and viable) solution to the access network “bottleneck problem,” as they can support extremely high and symmetrical bandwidth to the end user (Green, 2006). Furthermore, they future-proof the network operator’s CA-PEX investment, as they offer simple and low-cost speed upscale, whenever necessary. While the cost of installing optical access networks has been considered as “extremely high” in the past, this has been falling progressively, and such infrastructures currently seem to be the main broadband access technology of the decade (Frigo, Iannone, & Reichmann, 2004). Optical access networks are not a new concept, as they have been considered as a potential solution for the subscriber access network for quite some time. Their deployment costs as well as their corresponding equipment costs have been dramatically reduced in recent years. Current experience has demonstrated that once fiber is installed, no significant additional investments (or reengineering) are likely to be required for the next few decades; in fact, fiber-based networks can offer fast and easy repair, low-cost maintenance, and simple upgrade. The specific category of Passive Optical Networks (PONs)—as explained in detail in the subsequent parts of this article—are now viewed as probably the “best solution” for bringing fiber to the home, since they are composed of only passive elements (fibers, splitters, splicers, etc.) and are therefore very low priced. In addition, a PON can support very high bandwidths and can function at long distances (of up to 20 km) significantly higher than these supported by high-speed DSL variants.
PON ARCHITECTURE AND DEPLOYMENT
The advent of video-on-demand and interactive gaming has prompted the deployment of immense broadband infrastructures. Because of its large bandwidth, passive optical networks are currently seen as a “proper” technology to make this happen. PON technology, nowadays being broadly adopted and deployed in multiple areas all over the world (with remarkable growth rates in North America and Japan where it provides the main solution for fiber-to-the-home (FTTH) exploitation), constitutes a convenient solution for exploiting the “undoubted” and beneficial usage of the broadband perspective (Gumaste, & Anthony, 2004; Cisco Systems, 2007).
PONs allow individual homes, larger residential or office buildings, and wider premises to be connected to public telecommunications networks directly via fiber with a high bit rate. Even across great distances, they provide users with a very high transfer capacity, which is essential for all modern data services such as high-resolution television reception or home entertainment services. PON is a very recent, and still developing, access technology based on the specification originally developed by the Full Service Access Network (FSAN) vendor consortium (http://www.fsanweb.org/) for the APON (ATM (asynchronous transfer mode)- based passive optical network) case. However, as discussed in a subsequent part of this article, several variants have been deployed, with distinct characteristics (Ramas-wami, & Sivarajan, 2002).
A PON is a point-to-multipoint, fiber-to-the-premises network architecture where unpowered optical splitters are used to enable a single optical fiber to serve multiple premises (typically 32 different lines). A relevant configuration reduces the amount of fiber and central office (CO) equipment required, if compared with “traditional” point-to-point architectures. The “deletion” of active components implicates that the access network consists of one bi-directional light source and a number of passive splitters that divide the data stream into the individual links to each customer (Kramer & Mukherjee, 2000; Green, 2006). A PON system typically consists of optical line terminals (OLTs), optical network terminals (ONTs), optical network units (ONUs), and passive splitters, as shown in Figure 1.
The OLT is located in the network operator’s CO in a telecommunications application, or in the CATV (cable TV) provider’s head-end. The OLT can either generate optical signals on its own, or pass optical signals (e.g., synchronous optical network-SONET) from a collocated optical crossconnect or other device, broadcasting them downstream through one or more ports. The OLT provides the interface between the PON and the backbone network. These typically include: standard time division multiplexed (TDM) interfaces such as SONET/SDH (synchronous digital hierarchy) or PDH (plesiochronous digital hierarchy) at various rates, Internet protocol (IP) traffic over gigabit or 100 Mbit/s Ethernet, and ATM UNI (user-network interface) at 155-622 Mbit/s.
The ONU or the ONT terminate the circuit at the far end. An ONT is a single integrated electronics unit, and it is used to terminate the circuit inside the premises in an FTTP (fiber-to-the-premises) scenario, where it serves to interface the optical fiber to the copper-based inside wire. In fact, it presents the native service interfaces to the user.
An ONU is the PON-side half of the ONT, terminating the PON; it may present many converged interfaces (such as xDSL or Ethernet) towards the user. It typically requires a separate subscriber unit to provide native user services such as telephony, Ethernet data, or video. In practice, the difference between an ONT and ONU is frequently ignored, and either term is used generically to refer to both classes of equipment (Mukherjee, 1997). The ONU is used in an FTTC (fiber-to-the-curb) scenario, where the fiber stops at the curb, with the balance of the local loop being provisioned over embedded copper (unshielded twisted pair-UTP) in conventional telecommunications networks and coaxial (coax) in CATV networks. An ONU also is used in an FTTN (fiber-to-the-neighborhood) scenario, in which it is positioned at a centralized position in the neighborhood, with the balance of the local loop being provisioned over embedded coax or UTP. While this scenario maximizes the use of embedded cable plant, and therefore minimizes the costs associated with cable plant replacement, it compromises performance to some extent.
The passive optical splitter “sits” in the local loop between the OLT and the ONUs (or ONTs). The splitter divides the downstream signal from the OLT at the network edge into multiple, identical signals that are broadcast to the subtending ONUs. Each OLT/ONU is responsible for determining which data are intended for it, and for ignoring all others (Keiser, 2006). Upstream signals are supported by a time-division multiple access scheme, with the transmitters in the ONUs operating in burst mode. FSAN supports both symmetric and asymmetric modes.
A PON uses small, inexpensive, low-power optical splitters, rather than the relatively large, expensive, “power-hungry” optical repeaters employed in more traditional optical networks. In particular, the neighborhood switches are replaced by cheap (or reasonably priced) passive (i.e., requiring no electric power) splitters, whose only core function is to split an incoming signal into many identical outputs (Gorshe, 2006).
Downstream signals are broadcast to each premise by sharing a fiber. The OLT sends a single stream of down stream traffic that is “seen” by all ONTs. Each ONT only reads the content of those packets that are addressed to it, while encryption is used to prevent eavesdropping on downstream traffic. Upstream signals are combined using a multiple access protocol, invariably time division multiple access (TDMA). The OLTs “range” the ONUs in order to provide time slot assignments for upstream communication.
PON APPLICATIONS
A PON is a “pure” media network, which circumvents from any impacts caused by electromagnetic interference or lightning. As a consequence, a key reason to deploy it is to decrease the spectral interference created by copper-fed applications like asymmetric DSL (ADSL). Moreover, the fault rate is considerably decreased, bandwidth limitations are removed, reliability is strongly improved, and maintenance cost is significantly cut (as service is less expensive to maintain because there are no active loop devices and because fiber is less expensive to maintain in the long run than copper). In fact, a fiber-based PON solution using passive elements can deliver cost savings, which can add up to a 40-60% lower cash expense for labor. Savings mainly result from lower customer contacts associated with service orders and trouble reporting, outside plant operations, central office operations, and network operations (Rashid, 2004).
Simultaneously, a PON has a fine transparency and wide bandwidth, thus being applicable to a variety of signals of any format and of any bit rate. Moreover, it provides a very good solution for technically and economically supporting “triple-play” services.
Figure 1. Basic passive optical network (PON) architecture
In a PON the entire downstream bandwidth is transmitted to the power splitter, and a portion of the optical power is delivered to each subscriber. Since bandwidth in a passive system is not dedicated to each subscriber, each user shares the total capacity of the system. Thus, potential customers/users have the opportunity to share end-office equipment and optical fibers, thus resulting in lower usage costs with shorter distance of the fiber, and less transmitting/receiving equipment (Nakano, 2006). However, PONs must physically restrict the number of subscribers on a power splitter to achieve higher throughputs. If the total network capacity is exhausted, then the electronics at each end (CO and CPE-customer premises equipment) must be upgraded to a newer technology.
PONs can also be used to backhaul traffic from remote DSLAMs (digital subscriber line access multiplexers) to CO-based DSLAMs, or for wireless backhaul between base station controllers and mobile switching centers. Furthermore, in a short-term, PON networks can be used in conjunction with other gear in the network. One possible configuration can suggest PON equipment to provide the backbone for an expanded DSL network, where PON extends the reach of DSL and brings it closer to the customer, allowing IPTV and VoD services to be deployed over existing copper connections to the home. Services offered can cover a broad range of network requirements like bit rate, symmetry/asymmetry or delay, and range from video distribution, with varying degrees of interactivity, to electronic data transfer, LAN interconnection, transparent virtual paths, and so forth.
PONs are especially attractive to today’s carriers (or network providers) that have to reduce (or minimize) capital and operational costs, while maximizing the overall revenue per customer. These criteria must be achieved without sacrificing performance or network reliability, and a PON has all the ingredients to deliver these goods (Chanclou, Gosselin, Palacios, Alvarez, & Zouganeli, 2006). PONs are therefore considered as a “conformant solution” currently offered in the marketplace for bringing FTTH, since they comprise only passive elements and so they implicate low cost (Green, 2006). Moreover, when providing opportunities of high bandwidths, a PON can quite satisfactorily function at distances of up to 18-20 km in some cases, considerably higher than the distances supported by existing high-speed DSL variants (as shown in Figure 2). Besides, PONs do not engage the existence of any complex equipment (such as multiplexers/demultiplexers) in the local loop, in the proximity of the subscribers; this attribute drastically decreases the rates of installation and maintenance cost, and allows for uncomplicated upgrades to higher speeds, as such kinds of upgrades need only be performed centrally (i.e., at the network operator’s central office) where the appropriate active equipment is established (ITU, 2005a).
Standardization of PONs is of fundamental meaning if they are indeed to be widely deployed and so to constitute a conformant future’s broadband access infrastructure. From a network operator’s perspective, standardization “translates” into cost reduction and adequate interoperability, while for a manufacturer it offers assurance that the products will successfully meet any probable market requirements, in order to be (widely) acceptable in international markets.
Figure 2. A passive optical network
Consequently, well-defined standardization effort provides certainty-guarantee for performing investments in the relevant field.
There are three fundamental PON standards in the marketplace: broadband PON (BPON), gigabit PON (GPON), and Ethernet PON (EPON). The first two generations of standards have been endorsed by the ITU (International Telecommunication Union), while the third is from the IEEE (Institute of Electrical and Electronic Engineers). The most significant differences between each type of PON technology are the supported line rates and the type of packet processing used, as discussed (among other features) in the subsequent sections.
Following the first release of the ATM-based passive optical network (APON) a few years ago, there were several releases of technical standards, all following the tracks of TDMA-based bandwidth sharing. APON was supposed to be a good solution and was intended primarily for business applications; however its use finally faded out, due to its high cost, limited service capacity, low bit rate, low efficiency, and most importantly, the decline of ATM technology in the global arena.
Broadband PON was based on APON (ITU, 2005a, 2005b). It added support for WDM (wavelength division multiplexing), dynamic and higher upstream bandwidth allocation, and survivability. It also created a standard management interface, called “OMCI,” between the OLT and ONU/ONT, enabling mixed-vendor networks. A typical APON/BPON provides 622 Mbit/s of downstream bandwidth and 155 Mbit/s of upstream traffic, although the standard accommodates higher rates. BPON suffers from the very aggressive optical timing of ATM and the high complexity of the ATM transport layer.
The GPON standard (ITU, 2003) represented an improvement in both the total bandwidth and bandwidth efficiency through the use of larger, variable-length packets (PMC-Sierra, 2006). Again, the standard permits several choices of bit rate, but the industry has converged on asymmetrical operation of 2.488 Mbit/s of downstream bandwidth, and 1.244 Mbit/s of upstream bandwidth. The standard, instead of ATM encapsulation, uses GPON encapsulation method (GEM), which allows very efficient packaging of user traffic, with frame segmentation to allow for higher quality of service (QoS) for delay-sensitive traffic (such as voice and video communications). Moreover, GPON uses generic framing procedure (GFP) protocol to provide support for both voice- and data-oriented services. A big advantage over other schemes is that it interfaces to all provided main services while GFP-enabled networks packets belonging to different protocols can be transmitted in their native formats (Sims, 2007). GPON supports ATM, Ethernet, and WDM using a superset “multi-protocol” layer. The standard offers an abundant number of network management functions.
The emergence and deployment of IP technology has forwarded the concept of EPON, where APON’s physical layer has been preserved, while replacing data link layer protocol (ATM) with Ethernet (Kramer, 2005). Thus, EPON was capable of providing a wider range of services with extended bandwidth, lower cost, lower complexity, and simplified timing (Hajduczenia, da Silva, & Monteiro, 2006). By sending and receiving signals within an Ethernet frame, less expensive and more versatile Ethernet parts can be used, thus helping to keep components simple and reduce costs. The basic features of this variant implicate that ATM and SDH layers have been removed. The IEEE 802.3 Ethernet PON standard (EPON or “GEPON” in order to emphasize the “gigabit” aspect of the service) was completed in 2004 (http ://www.ieee802.org/3/) as part of the Ethernet First Mile Project (Beck, 2005). It uses standard 802.3 Ethernet frames with symmetric 1 Gbit/s upstream and downstream rates; however, recently (i.e., starting in early 2006), work began on a very high-speed 10 Gigabit/second EPON (XEPON or 10-GEPON) standard (http://www.ieee802.org/3Zav/). EPON is applicable for data-centric networks, as well as full-service voice, data, and video networks.
However, with various emergent branches of PON technology, it is not yet possible to identify which one will be the most appropriate for next-generation optical access networks. Time to market, technology maturity, system availability, operational considerations, video compression performance, service requirements, engineering rules, and business impacts all need to be taken into account in making decisions regarding how to deploy PON (Nortel Networks, 2004).
The industry is looking at ways to deliver even more bandwidth over longer distances than ever before. Two ways of doing this are by increasing the number of optical wavelengths being used on the PON fiber, and by increasing the bandwidth and bandwidth efficiency of each wavelength. There are currently the following relative options deployed in the international environment: (i) the “traditional” TDMA-PON (Davey et al., 2006), and (ii) the “novel” WDM-PON (Banerjee et al., 2005; Lee, Sorin, & Kim, 2006) and OCDMA-PON.
FUTURE TRENDS
The main disadvantage of PONs is the requirement for complex mechanisms to allow shared media access to the subscribers so that data traffic collisions are avoided. This is due to the fact that although a PON is a point-to-multipoint topology from the OLT to the ONU (i.e., downstream direction), it is multipoint-to-point in the reverse (upstream) direction. This implies that data from two ONUs transmitted simultaneously will go into the main fiber link at the same time, and thus will collide as the OLT is not able to discriminate them. Therefore, it is obvious that there needs to be an appropriate mechanism implemented in the upstream direction, so that data from each ONU can reach the OLT without colliding and getting distorted. An effective way to realize this can be via the usage of a wavelength division multiplexing (WDM) scheme, in which each ONU is allocated a dedicated wavelength to communicate with the appropriate OLT, so that all ONUs can use the main fiber link simultaneously (Park et al., 2004). In a similar way, the time division multiplexing (TDM) scheme can also be used, in which each ONU is allowed to transmit data only at a specific time window dictated by the OLT. The essential PON architecture permits simple service upscale whenever there is a need for more bandwidth, and this can be achieved through a combination of WDM and TDM schemes in the access fiber—that is, where different wavelengths carry different TDM PON streams or even better by using a WDM access scheme, where each subscriber is allocated a different wavelength (ITU, 2005b). In fact, WDM-PONs offer a very exciting perspective: they represent the next generation in PON development and promise to bring extended bandwidth to end users by fully utilizing the fiber’s spectral windows. Although WDM-PONs truly have the potential of supporting enormous bandwidth rates (together with scalable functionality and ease of customization), their actual major drawback is associated with the high costs of the required equipment. Hence, there is currently a significant effort of research interest on finding appropriate ways to lower the high costs of such schemes, mostly by addressing the need for expensive broadband light sources. It should be expected that further progress in the area will entirely “transform” their adoption in the marketplace.
CONCLUSION
Growing demand for high-speed Internet is the primary driver for new access technologies that enable experiencing broadband. Fiber can sustain very high capacity, resulting in a high revenue potential (Hasegawa, Kuritani, Makino, Shimada, & Gorshe, 1990). A PON, utilizing passive splitters and shared-media configuration, can carry a veritable pipe of high bandwidth for users to share downstream, presenting a high-speed and inexpensive access scheme for multimedia service (Davey et al., 2006). The fundamental benefits of PON technology are flexibility, reliability, and simplicity.
The compelling advantages of PON for network operators and their customers are more than simply clear. These include a long-term life expectancy of the fiber infrastructure, lower operating costs through the reduction of “active” components, support for greater distances between equipment nodes, and most importantly, much greater bandwidth. PONs can also enable the use of new applications and services, such as high- resolution television, video telephony, e-learning, or even business applications. Furthermore, the passive splitting of the fibers means that expensive and high-maintenance active network elements are not necessary, while simultaneously the number of optical components is kept to a minimum.
Extended demand for bandwidth and progress in electro-optics have made passive optical networking into an attractive and quite convenient solution for bringing fiber to the customer. Since PONs eliminate active components on the loop, they can provide cost savings up to 10 times that of SONET, and they are now reaching cost equivalence with DSL and hybrid fiber coaxial (HFC). In addition, the combination of PON and WDM increases bandwidth availability and cost advantages even further.
Among the key reasons to deploy PONs is to decrease the spectral interference created by copper-fed applications (like ADSL). This results in a service that is less expensive to maintain, while PONs let operators go into new markets and share fibers among residential and small business customers. Other applications include buildings that are just out of reach of fiber in a metropolitan network, or even in-building networks to bring fiber to additional floors. Either way, once PON is deployed, it offers flexible bandwidth, which is important since business tenants commonly move within or out of buildings. PONs can also be used to backhaul traffic from remote DSLAMs, or for wireless backhaul between base station controllers and mobile switching centers of marketing at vendor Terawave.
During the deployment of the optical access network, market players are seriously taking into account OPEX (operational expenditure), which constitutes an integral part the lifecycle of the network. As a type of pure-medium network, the PON is nowadays considered by most operators as the “best technology that is currently available” and better oriented to synchronize with future optical access technology, although the CAPEX (capital expenditures) may be somewhat higher than that for peer-to-peer and copper wire access. In order to fulfill requirements imposed by both operators and users, PON technology may further develop according to the following alternatives:
1. Although hard in implementation due to the excessive requirements imposed on international industry, it is possible to expand the bandwidth of each single wavelength, to reach up to 10 Gbps.
2. The other option is to increase the number of wavelengths, that is from 16-wavelengths (CWDM) and 32-wavelengths (DWDM), to 64-wavelengths and 128-wavelengths, or more.
Nevertheless, crosstalk between channels brings several problems, especially when the number ofwavelengths reaches a certain threshold, which results in an exponential cost increase. Consequently, WDM-PON technology alone will not be able to fully satisfy the requirements of carriers/users in terms of the price performance ratio.
While PON has been discussed for decades, only today are network operators seriously deploying this exciting technology and increasing its penetration (Pesavento & Kelsey, 1999). Until very recently, PON deployment has been constrained by the pace of protocol standardization, equipment availability and cost, conservatism in moving to new technology, regulatory uncertainty, but most importantly by the cost of installing new fiber all the way to customer sites. However, a PON driver is the sharp decline of cost of fiber deployment in the access space over the last 10 years. In the mid-1990s, the capital cost for fiber access was around $7,500 per subscriber. This has fallen to less than $2,000 today and is expected to drop to less than $1,000 per subscriber in the near future. With this spectacular decrease in capital cost for fiber access, an enormous barrier for fiber-to-the-user (FTTU) has been virtually abolished.
Market researchers view PON as a rapidly growing market segment (Ernhofer, 2006). According to recent estimates (Rashid, 2004), the 2004 market volume amounted to approximately US$525 million, and this figure was expected to rise to 2.15 billion by 2008, corresponding to an average annual growth rate of 42%. Especially high growth is predicted for two regions: in particular North America, where high volumes of data must cross great distances; and Asia, where the next few years will see the emergence of modern urban areas with completely new infrastructures. Deployment is being driven primarily by established operators, offering a wider range of enhanced services to retain and increase their revenues. With the capability to support both today’s and tomorrow’s services, PON technology is an ideal solution for market players and consumers as well.
KEY TERMS
Asymmetric Digital Subscriber Line (ADSL): Transmission technology that consists of modems attached to twisted-pair copper wiring that transmit from 1.5 Mb/s to 8 Mb/s downstream (to the subscriber) and up to 1.5 Mb/s upstream, depending on line distance.
Broadband PON: A term used to refer to the entire system described by the G.983.x family of ITU-T Recommendations. This includes a wide range of broadband services and goes beyond ATM access.
Ethernet: A large, diverse family of frame-based computer networking technologies that operates at many speeds (typically at 10, 100, or 1000 Mb/s) for local area networks (LANs). The name comes from the physical concept of the ether. It defines a number of wiring and signaling standards for the physical layers, through means of network access at the media access control (MAC)/data link layer, and a common addressing format. (Ethernet has been standardized as IEEE802.3.)
Ethernet Passive Optical Network (EPON): A type of PON technology that runs on the Ethernet protocol. EPON is applicable for data-centric networks, as well as full-service voice, data, and video networks.
FTTH (Fiber To The Home): A form of fiber optic communication delivery in which the optical signal reaches the end user’s living or office space.
Optical Line Termination (OLT): The service provider endpoint of a passive optical network; placed at the central office or head end of a fiber-based system. Also called optical line terminal.
Passive Optical Network (PON): Network in which fiber optic cabling (instead of copper) brings signals all or most of the way to the end user. It is described as passive because no active equipment (electrically powered) is required between the central office (or hub) and the customer premises. Depending on where the PON terminates, the system can be described as an FTTx network, which typically allows a point-to-point or point-to-multipoint connection from the central office to the subscriber’s premises; in a point-to-multipoint architecture, a number of subscribers (for example, up to 32) can be connected to just one of the various feeder fibers located in a fiber distribution hub, dramatically reducing network installation, management, and maintenance costs.
Point-to-Multipoint (P2MP, PTMP, or PMP) Communication: Refers to communication that is accomplished via a specific and distinct type of multipoint connection, providing multiple paths from a single location to multiple locations.
SONET (Synchronous Optical NETwork): A protocol for backbone networks capable of transmitting at extremely high speeds and accommodating gigabit-level bandwidth. It has been standardized by the American National Standards Institute (ANSI).
Triple-Play Services: The ability of a telecommunications operator to supply voice, data, and video applications all at once. A typical example of a triple-play proposal would include one or multiple phone lines, a high-speed Internet connection, and television/video services (such as HDTV), all offered by the same provider. Also known as bundled services.
