atm passive optical networks (pons)

8/14/2019 ATM Passive Optical Networks (PONs)

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Asynchronous Transfer Mode (ATM)Passive Optical Networks (PONs)

Definition

This tutorial discusses the economics, operator and customer benefits, andtechnological development of optical distribution networks with asynchronoustransfer mode passive optical networks (ATM PONs). ATMPON infrastructureis widely cited by telecommunications carriers and equipment vendors aspotentially the most effective broadband access platform for provisioningadvanced multimedia services as well as legacy services such as tier 1 (T1). Since

1995, an influential group of worldwide carriers and equipment vendors has beendeveloping requirement specifications for a full-service access network with ATMPON as the core technology.

Overview

The deployment of fiber-optic technology to homes and businesses is poised tochange the way telecommunications servicesprimarily voice, data, and videoserviceswill be delivered to the twenty-first century, information-basedeconomy. Interest is high among business and residential consumers for

advanced, broadband services such as fast Internet access, electronic commerce,video on demand, digital broadcasting, teleconferencing, and telemedicine,among others. However, the lack of available bandwidth to deliver these serviceseffectively to the last mile of homes and businesses has stifled development ofnew multimedia applications.

An optical distribution network with ATM PON as the core technology promisesbenefits to end users as well as carriers and service providers. When opticalnetwork access is achieved in scale, businesses and consumers will realizeopportunities for advanced services at relatively low costs. Because of costsavings inherent with the ATMPON platform, telecommunications carriers andservice providers will realize efficiencies in provisioning future applications and

upgrading bandwidth to satisfy customers' demands.

Topics1. The Case for Fiber-Optic Access

2. How ATM PONs Work


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3. Benefits of ATM PONs

4. Technology Comparison with xDSL

5. Full-Service Access Network Initiative

6. Major Players

7. The Future of ATM PONs

Self-Test

Correct Answers

Glossary

1. The Case for Fiber-Optic Access

Fiber-optic technology, offering virtually unlimited bandwidth potential, iswidely considered to be the ultimate solution to deliver broadband access to the

last mile. Today's narrowband telecommunications networks are characterized bylow speed, service-provisioning delays, and unreliable quality of service. Thislimits the ability of a consumer to enjoy the experience at home or the ability ofworkers to be efficient in their jobs. The last mile is the network space betweenthe carrier's central office (CO) and the subscriber location. This is wherebottlenecks occur to slow the delivery of services. The subscriber's increasingbandwidth demands are often unpredictable and challenging fortelecommunications carriers. Not only must carriers satisfy today's bandwidthdemands by leveraging the limits of existing infrastructure, they also must planfor future subscriber needs.

A new network infrastructure that allows more bandwidth, quick provisioning ofservices, and guaranteed quality of service (QoS) in a cost-effective and efficientmanner is now required. Today's access network, the portion of a public switchednetwork that connects CO equipment to individual subscribers, is characterizedby predominantly twisted-pair copper wiring.

Fiber-optic technology, through local access network architectures such as fiber-to-the-home/building (FTTH/B), fiber-to-the-cabinet (FTTCab), and fiber-to-the-curb (FTTC) offers a mechanism to enable sufficient network bandwidth forthe delivery of new services and applications. ATMPON technology can beincluded in all these architectures, as shown in Figure 1.


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Figure 1. ATMPON Architectures

In general, the optical section of a local access network can either be a point-to-point, ring, or passive point-to-multipoint architecture. This tutorial focuses onthe passive point-to-multipoint architecture (PON). The main component of thePON is an optical splitter device that, depending on which direction the light istraveling, splits the incoming light and distributes it to multiple fibers orcombines it onto one fiber.

The PON, when included in FTTH/B architecture, runs an optical fiber from a COto an optical splitter and on into the subscriber's home or building. The opticalsplitter may be located in the CO, outside plant, or in a building.

FTTCab architecture runs an optical fiber from the CO to an optical splitter andthen on to the neighborhood cabinet, where the signal is converted to feed the

subscriber over a twisted copper pair. Typically, the neighborhood cabinet isabout 3 kft from the subscriber's home or business.

FTTC architecture runs an optical fiber from the CO to an optical splitter andthen on to a small curb-located cabinet, which is near (typically within 500 ft) tothe subscriber. It is then converted to twisted copper pair.

The PON can be common to all of these architectures. However, it is only in theFTTH/B configurations that all active electronics are eliminated from the outsideplant. The FTTCab and FTTC architectures require active outside-plantelectronics in a neighborhood cabinet or curb. This tutorial will focus on FTTH/B

architectures.When fiber is used in a passive point-to-multipoint (PON) fashion, the ability toeliminate outside plant network electronics is realized, and the need for excessivesignal processing and coding is eliminated. The PON, when deployed in anFTTH/B architecture, eliminates outside plant components and relies instead onthe system endpoints for active electronics. These endpoints are comprised of the


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CObased optical line terminal (OLT) on one end and, on the other, the opticalnetwork termination (ONT) at the subscriber premises. Fiber-optic networks aresimple, more reliable, and less costly to maintain than copper-based systems. Asthese components are ordered in volume for potentially millions of fiber-basedaccess lines, the costs of deploying technologies such as FTTH, FTTB/C, and

FTT/Cab become economically viable.

One optical-fiber strand appears to have virtually limitless capacity.Transmission speeds in the terabit-per-second range have been demonstrated.The speeds are limited by the endpoint electronics, not by the fiber itself. For theATMPON system today, speeds of 155 Mbps symmetrical and 622 Mbps/155Mbps asymmetrical are currently being developed. As the fiber itself is not theconstraining factor, the future possibilities are endless. Furthermore, becausefiber-optic technology is not influenced by electrical interferers such as cross-talkbetween copper pairs or AM band radio, it ensures high-qualitytelecommunications services in the present and future. In addition, fiber does notexhibit radio frequency (RF) emissions that can interfere with other electronics

and is regulated by the Federal Communications Commission (FCC).

While copper-based transport technologies remain ubiquitous, the long-termindustry belief holds that it is inevitable that fiber will replace copper throughoutthe access infrastructure. Because copper infrastructure is embedded incommunications systems, this transformation to optical transport is expected tooccur over many years. Over time, new builds ("Greenfield") will be all fiberbased, and existing builds will be rehabilitated by replacing copper with fiber orby overlaying new fiber on the existing copper infrastructure. Electronicequipment, as well, must be replaced with optical equipment.

2. How ATM PONs Work

Recent technological advances and economies of scale have drawn increasinginterest to optical-distribution networks with ATM PON. A functional overview ofATMPON architecture is presented in Figure 2.


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Figure 2. Functional Overview of ATMPON Architecture

Figure 2 shows the ONT placed at the customer premises, which suggestsFTTH/B architecture. The carrier's demarcation point would be the subscriberside of the ONT, typically in the form of a T1, Ethernet, integrated services digitalnetwork (ISDN), plain old telephone service (POTS), etc.

For FTTCab and FTTC architecture, an optical network unit (ONU), rather thanan optical network termination (ONT), is used. It is placed in the outside plantand must be temperature-hardened and properly enclosed. The final drop to thenetwork termination (NT) at the customer premises may be copper or fiber. The

carrier demarcation point is the subscriber side of the NT in the form of a T1,Ethernet, ISDN, POTS, and etc.

Access to bandwidth on the PON may be obtained by several methods, includingtime division multiple access (TDMA), wave division multiple access (WDMA),code division multiple access (CDMA), and subcarrier multiple access (SCMA).TDMA in the upstream and TDM in the downstream were chosen by the Full-Service Access Network (FSAN) group and submitted to the InternationalTelecommunications Union (ITU) for standardization, based on their simplicityand cost-effectiveness.

As shown in Figure 2, the network components supporting ATM PON consist of

OLT, ONT, and a passive optical splitter. One fiber is passively split up to 64times between multiple ONTs that share the capacity of one fiber. Passivesplitting requires special actions for privacy and security, and a TDMA protocol isnecessary in the upstream direction. The use of the optical splitter in the PONarchitecture allows users to share bandwidth, thus dividing the attendant costs.Costs are further reduced by a decrease in the number of opto-electronic devicesneeded at the OLT; one interface may be shared among many ONTs.


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The ATMPON system uses a double-star architecture. The first star is at theOLT, where the wide-area network interface to services is logically split andswitched to the ATMPON interface. The second star occurs at the splitter whereinformation is passively split and delivered to each ONT. The OLT is typicallylocated in the carrier's CO. The OLT is the interface point between the access

system and service points within the carrier's network. When data content fromthe network reaches the OLT, it is actively switched to the passive splitter usingTDM in the downstream. The OLT behaves like an ATM edge switch with ATMPON interfaces on the subscriber side and ATMsynchronous optical network(SONET) interfaces on the network side.

The ONT will filter the incoming cells and recover only those that are addressedto it. Each ATM cell has a 28-bit addressing field associated with it called avirtual path identifier/virtual channel identifier (VPI/VCI). The OLT will firstsend a message to the ONT to provision it to accept cells with certain VPI/VCIvalues. The recovered ATM cells are then used to create the service interfacerequired at the subscriber side of the ONT (see Figure 2).

Because TDMA is used in the upstream direction, each ONT is synchronized intime with every other ONT. The process by which this happens is called rangingthe ONTs. Basically, the OLT must determine how far away in distance each ONTis so they can be assigned an optimal time slot in which to transmit withoutinterfering with other ONTs. The OLT will then send grant messages via thephysical layer operation, administration, and maintenance (PLOAM) cells toprovision the TDMA slots that are assigned to that ONT. The ONT will then adaptthe service interface to ATM and send it to the PON using the TDMA protocol.

Ethernet and T1s are two examples of what can be transported over the ATM

PON. As ATMPON is service-independent, all legacy services and futureservices can be readily transported.

The basic frame format between the OLT and ONT for the symmetrical 155 Mbpsrate is shown in Figure 3.


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Figure 3. ATMPON Frame Formats

The asymmetrical version of 622 Mbps/155 Mbps downstream/upstream issimilar but beyond the scope of this document.

As can be seen in Figure 3 the downstream payload capacity is reduced to 149.97Mbps because of the PLOAM cells. These cells are responsible for allocatingbandwidth (via Grant cells), synchronization, error control, security, ranging, andmaintenance.

In the upstream direction the capacity is reduced to 149.19 Mbps because there

are 3 overhead bytes per ATM cell. In addition to the three overhead bytes percell there are PLOAM cells in the upstream direction, the rate of which is definedby the OLT for each ONT, depending on the required functionality. Theminimum PLOAM rate in the upstream direction is one PLOAM every 100 ms.This equates to approximately one PLOAM every 655 frames, which is negligible.Although the maximum PLOAM rate is undefined, it is also expected to benegligible. The 3 overhead bytes contain a minimum of 4 bits of guard time toprovide enough distance in time to prevent collisions with cells from other ONTs.This field length is actually programmable by the OLT. The preamble field is usedto acquire bit synchronization and amplitude recovery. The Delimiter field is usedto indicate the start of an incoming cell.

Given that a single fiber is used for both the upstream and downstream paths,two wavelengths of light are used1550 nm for the downstream and 1310 nm forthe upstream. Although one wavelength can also be used, two provide betteroptical isolation between the laser transmitters and receivers and eliminate theneed for expensive beam-splitting devices. Instead, low-cost planar light circuits(PLCs) can be used, which enable low-cost manufacturing techniques to be


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employed, somewhat similar to the production of silicon chips. ATM cells aredirectly converted to light and sent to the PON. Because of the broadcast natureof the PON, encryption techniques are employed to prevent security breaches. Inthe upstream direction, the ONT uses the TDMA protocol and again directlyconverts ATM cells to light for transport over the PON (see Figure 2).

A typical ATMPON system can furnish up to 64 customer locations on a single,shared strand of fiber running at 155 Mbps. Most, however, will likely utilize 32locations in the distribution and drop portion of the network in the near term. Inthe future, the ATMPON specification does allow for up to 64 locations to beserved.

3. Benefits of ATMPONs

The ATMPON system offers a number of benefits for carriers and end users.

Because fiber is less costly to maintain than copper based systems, carriersbenefit by being able to reduce costs and thereby increase profit margins orsimply lower prices to end users to ward off competitive threats.

ATMPON transmission is conducted through a single strand and therebyconserves fiber. Using a single fiber strand for up to 64 end users provides greatcost savings over the current point-to-point architecture.

ATM PON conserves optical interfaces at the OLT because a single fiber is used toservice as many as 64 end-user locations. Thus, a 64 to 1 reduction in opticalinterfaces is achieved in comparison to point-to-point optical systems.

Another advantage of the ATMPON system is the aggregation andconcentration of ATM cells in the OLT. This concentration allows the carriers toserve many more customers than if only TDMbased techniques are used. At thesame time, QoS benefits of ATM allow the carriers to provide service-levelagreements (SLAs) and rest assured that service is guaranteed. It is estimatedthat ATMPON technology can achieve savings of 20 to 40 percent over circuit-based access systems. ATM PON realizes these savings through the use of ATMconcentration and statistical multiplexing in addition to sharing active opto-electronic components through the splitter elements.

Because the ONTs share the same fiber and optical splitter, the bandwidth can

also be shared. In the future, dynamic bandwidth-allocation protocols will allowthe carriers to serve more users by allocating bandwidth on an as-needed basis.These protocols are already part of the FSAN specification as an optionalrequirement. Therefore, more users can be served with a smaller number ofOLTs, leading to additional savings.


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Operational and maintenance savings will be derived from ATM PON. Becausethe system is based on ATM, a single management system can completelyprovision the bandwidth end to end. Also, if the service interface is a high-speedlocal-area network (LAN) such as 10/100BaseT, where the carrier's ATM circuitrather than the physical interface bit rate is the limiting factor to the bandwidth,

then bandwidth can be incrementally provisioned over time as needed, up to thelimitations of the physical interface. For example, if a small business needs only 1Mbps capacity at first but will require 2 Mbps a year from now, then the carriermust only provision greater ATM PVC rate, rather than having to do a truck rollto wire more T1 lines (as is currently done).

Because the PON system will be ATMbased, it can adapt to virtually any servicedesired. Telco operators, for instance, can deliver all of their legacy services, suchas T1 and T3 lines, or deliver new services, such as transparent LAN service (TLS)over the optical network (see Figure 4). This future-proofs the architecture. Newrevenue streams are derived by being able to provide transparent LAN services toend users quickly and easily.

Figure 4. Transparent LAN over the Optical Network

The ONT is proportioned for small- to medium-sized businesses and costs little.This low cost is achieved because there are more small businesses than largeones. Currently, service providers serve small businesses from synchronousoptical network (SONET) ring nodes, and these are costly elements whencompared to small ATMPON ONTs. ATM PONs will mean new business forcarriers and services providers, as they can eliminate the need to place small- andmedium-sized businesses on SONET rings that exist in most metropolitan areanetworks.


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Active components of the ATMPON system are located at the customerpremises or CO, rather than at remote outside plant terminals. Thus, costsassociated with outside plantbattery backup systems and active electronics thatmust incur severe temperature variations are eliminated. Battery backup systemscan be placed indoors at the customer premises and thus last much longer

between maintenance intervals. In addition, the option of having the end userprovide the battery backup from low-cost computer UPC systems can be offeredon a per-user basis. With typical outside-plant systems (such as DLC or FTTCab)that are shared between many users, this option is simply not available.

As ATMPON architecture and processes mature, end users will benefit by beingable to provision their own services, whenever they are needed, through anautomated process. This process will either link the carriers' service managementsystem (SMS) with the customers' network management system or allow thecustomer access to the SMS through a secured Web-browser interface. The COthen updates network elements and provisions the new bandwidth.

4. Technology Comparison w ith xDSL

This section will compare ATMPON systems with xDSL technologies anddescribe the issues associated with each.

ATM is an ultrahigh-speed, one-size-fits-all, cell-based data transmissionprotocol that may be run over many physical-layer technologies such as xDSLmodems. These are attached to twisted-pair copper wiring and transmit data atspeeds of 1.5 Mbps to 9 Mbps downstream to the subscriber and 64 Kbps to 1.5Mbps upstream, depending on the condition and distance of the copper line.

Asymmetric digital subscriber line (ADSL), for instance, offers users an always-on service, but its maximum downstream and upstream speeds are ultimatelylimited by distance and the aging copper infrastructure; typically, only speeds of1.5 Mbps over 12 kft are achieved. If the customer is not directly connected to aCObased digital subscriber line access multiplexer (DSLAM), then an expensiveupgrade to an existing outside-plant DLC system is usually the only solution.

Very-high-speed DSL (VDSL) extends ADSL downstream speed to a potential 52Mbps, with a proportionately lower upstream speed, but offers a shorter distancerange (1 kft to 3 kft) than ADSL. However, this too requires expensive outsideplant electronics installed in a cabinet that must survive severe temperature

variations.

In addition to the distance problem, xDSL technology has inherent interferenceproblems, a liability with copper-based technology. ATM PONs cannot beinterfered with by AM band radio and other radio frequency interference(RFI)/electromagnetic interference (EMI) sources. XDSL is largely considered tobe a short-term broadband solution; since it can be easily installed without an


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expensive outside-plant infrastructure build, the existing copper plant can beused. The PON system, however, is believed to offer an ultimate, end-to-endbroadband platform that is future-proofed.

5. Full-Service Access Network Initiative

Overseeing the development of passive optical networks as part of fiber-opticbackbones is the Full-Service Access Network (FSAN) Initiative. FSAN is a groupof 20 telecommunications companies working collaboratively with equipmentsuppliers to agree on a common broadband access system for provisioning bothbroadband and narrowband services.

Since June 1995, the FSAN group has been working on the international initiativeand recognizing that each member has differing needs, depending on regulatory,business, and structural environment in each country. FSAN is not a standardsbody, but rather submits specifications to standard bodies such as the

International Telecommunications Union (ITU). Existing standards areincorporated where applicable. In October of 1998, the ITU adopted the G.983.1broadband optical access system based on PON.

Members of the initiative throughout the process have intended to introduceelements of their results to appropriate standards bodies. On June 22, 1999, fourFSAN membersNTT, British Telecom, BellSouth, and France Telecomissueda common technical specification for ATM subscriber systems. Because eachinitiative member understood the need to develop future access networks, thegroup realized that industry-wide benefits could be achieved through adopting acommon set of specifications. The consortium determined that the per-line cost

of producing a full-service access network will decrease slowly with theproduction volume.

The group concluded that as volume increases, the development of newtechnologies will enable significant reductions in per-line equipment andinstallation costs. Fiber-based broadband networks could be cost-effective todeploy if their component part were built in bulk quantities for tens of millions ofaccess lines, rather than according to today's typical 300,000-line system order.

The group's work has occurred in two phases. First, its task was to identifytechnical and economic barriers to the introduction of a broadband accessnetwork. It was determined that an ATM PON was the most promising

technology to achieve large-scale, FSAN work deployment that could meet theevolving service needs of network users. The consortium felt that ATM PON wasthe best means of supporting a range of architectures such as FTTH, FTTB/C,and FTTH/CAB. Members have recognized that all operators require the sameelements in their access network. The major differences come from thepositioning of the optical network unit (ONT). All members see the need for a


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PON system. Second, the group's work was to devise a common set ofspecifications for full-service access networks. Six working teamssystemsengineering/architecture; optical access networks; home network/networktermination; operation, administration, and maintenance (OAM&P); VDSL; andcomponent technologyundertook the development process.

6. Major P layers

Japan's Nippon Telegraph and Telephone Corporation (NTT) is recognized as aleading telecommunications carrier in the creation of high-speed optical-networkaccess systems. Its leadership is demonstrated by its involvement in the FSANInitiative as well as by its own cutting-edge research and development andcollaboration with other carriers. NTT already has deployed narrowband andvideo-distribution FTTH and broadband ATMPON systems. In 1999, it willintroduce a fully FSANcompliant, FTTB/C ATMPON system.

According to a press release issued by NTT and BellSouth in June 1998, the twocompanies announced that they would work together. NTT and BellSouthannounced they would deliver a high-speed optical-network access platform,pooling their respective research and development resources to advance theavailability of affordable FTTH technology. In June 1999, BellSouth unveiledplans to install a FTTH system to the Atlanta area using FSANcompliant ATMPON technology.

In the news release about the Atlanta installation, BellSouth announced thatsuburban Atlanta residents will be the first in North America to experience thenearly unlimited speed and bandwidth of passive optical networking delivered

directly to their homes. BellSouth's vision for FTTH is for customers to buycommunications appliances for voice, video, data or imaging applications at retailstores and plug them into their home optical telecommunications network. TheBellSouth fiber network, by talking to the appliance, would deliver the necessaryprovisioning. Both BellSouth and NTT believe that customer orientation anddemand will drive down the cost of FTTH equipment and accelerate itsworldwide availability. Historically, both BellSouth and NTT have pioneeredfiber-optic technology. In the late 1980s, BellSouth launched an FTTH trial nearOrlando, Florida. Historically, NTT has actively promoted FTTH, particularly inthe area of interface specifications for high-speed optical access systems. NTT'sFTTB/C project, to be launched in 1999, will replace copper cable with fiber

throughout most of NTT's subscriber system.

7. The Future of ATM PONs

As a future-proof technology, ATM PON will serve as a framework forapplications yet to be developed or advanced. While commercial deployments of


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ATM PONwith the exception of examples in limited areas in Japan by NTThave yet to occur, trials have been increased in 1999 and are expected toaccelerate in 2000. Perhaps the biggest advantage for ATM PON is that interestin the technology exists on a global scale, a situation that may be attributed ingreat part to the collaboration of the FSAN Initiative. Carriers and equipment

makers believe that extensive collaboration on ATMPON physical-layerinteroperability will lead to an increase in the production volume of siliconchipsets that can be created to the global specification. Interoperability amongthe technology's management layers will depend on alliances among strategicvendors. Settling on the core framework, however, is what will propel thetechnology forward.

Carriers and service providers are expected to focus initially on business usesthrough FTTB, as real revenue streams typically originate in these areas. Asproduction accelerates, operators will increasingly look to the mass residentialmarket. Through the Internet age, small- and medium-sized businesses havebeen characterized as being on the down slope of technology. However, ATM

PON, with its cost savings and flexibility, is capable of bringing more of thesebusinesses on-line quickly.

Future applications aimed at FTTH scenarios include asymmetric broadbandservices (such as digital broadcast, video on demand, distance learning, and fastInternet), symmetric broadband services (such as telecommunications servicesand teleconferencing opportunities), and narrowband telephone services (such asthe public switched telephone network [PSTN] and integrated services digitalnetwork [ISDN]).

Self-Test1. The access network, which is the portion of a public switched network that

connects access nodes to individual subscribers, is predominantlycharacterized today by which of the following?

a. fiber-optic cable

b. hybrid-fiber coaxial cable

c. twisted-pair copper wiring

d. electrical wiring

2. Fiber to the home (FTTH), fiber to the building/curb (FTTB/C), and fiber tothe cabinet (FTTCab) are examples of which of the following?

a. local access network architectures


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b. digital loop carriers

c. transport protocols

d. fiber-optic components

3. A single optical-fiber strand's capacity lies in what range, according to recentdemonstrations?

a. Mbps

b. kbps

c. virtually limitless

d. Gbps

4. Asynchronous transfer mode (ATM) is ____________.

a. a cell-based data transmission protocol

b. an opto-electronic component

c. a circuit-switched access systems

5. ATM PON is attractive to telecommunications carriers because it contains__________.

a. active electronics

b. no active electronics in outside plant

c. SONET rings

d. copper-based wiring

6. A typical ATM PON system can furnish up to _____________.

a. 64 customer locations on a single, shared strand of fiber

b. 72 customer locations on a single, shared strand of fiber

c. 96 customer locations on a single, shared strand of fiber

d. 128 customer locations on a single, shared strand of fiber


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7. The use of the splitter in the PON architecture allows network users to___________.

a. share bandwidth

b. provision bandwidth

c. increase bandwidth

d. ensure privacy and security

8. The optical line termination (OLT) in the ATM PON system is typicallylocated _____________.

a. at the customer premises

b. in a curbside cabinet

c. in a residential gateway device

d. in the carrier's CO or POP

9. It is estimated that an ATMPON system can achieve savings of___________.

a. 20 percent to 40 percent over circuit-based access systems

b. 40 percent to 60 percent over circuit-based access systems

c. 60 percent to 80 percent over circuit-based access systems

d. 80 percent to 100 percent over circuit-based access systems

10. Full-service access network (FSAN) is ____________.

a. a standards body that regulates broadband networks

b. an access network for delivering broadband services

c. a group of 20 global telecommunications equipment manufacturerscollaborating on specification requirements for broadband access

systems

d. a group of 20 global telecommunications carriers collaborating onspecification requirements for broadband access systems


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11. The main advantages afforded to the carriers of ATM PON are_________________.

a. cost savings due to lower maintenance costs than copper

b. cost savings due to use of single fiber for up to 64 users

c. cost savings due to easy bandwidth upgrading with no truck rolls

d. cost savings due to aggregation and concentration in the OLT

e. all of the above

Correct Answers

1. The access network, which is the portion of a public switched network that

connects access nodes to individual subscribers, is predominantlycharacterized today by which of the following?

a. fiber-optic cable

b. hybrid-fiber coaxial cable

c. twisted-pair copper wiring

d. electrical wiring

See Topic 1.

2. Fiber to the home (FTTH), fiber to the building/curb (FTTB/C), and fiber tothe cabinet (FTTCab) are examples of which of the following?

a. local access networ k architectures

b. digital loop carriers

c. transport protocols

d. fiber-optic components

See Topic 1.

3. A single optical-fiber strand's capacity lies in what range, according to recentdemonstrations?

a. Mbps


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b. kbps

c. virtually limitless

d. Gbps

See Topic 1.

4. Asynchronous transfer mode (ATM) is ____________.

a. a cell-based data transm ission protocol

b. an opto-electronic component

c. a circuit-switched access systems

See Topic 2.

5. ATM PON is attractive to telecommunications carriers because it contains__________.

a. active electronics

b. no active electronics in outside plant

c. SONET rings

d. copper-based wiring

See Topic 2.

6. A typical ATM PON system can furnish up to _____________.

a. 64 custom er locations on a single, shared strand of fiber

b. 72 customer locations on a single, shared strand of fiber

c. 96 customer locations on a single, shared strand of fiber

d. 128 customer locations on a single, shared strand of fiber

See Topic 2.7. The use of the splitter in the PON architecture allows network users to

___________.

a. share bandw idth

b. provision bandwidth


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c. increase bandwidth

d. ensure privacy and security

See Topic 2.

8. The optical line termination (OLT) in the ATM PON system is typicallylocated _____________.

a. at the customer premises

b. in a curbside cabinet

c. in a residential gateway device

d. in the carrier's CO or POP

See Topic 2.

9. It is estimated that an ATMPON system can achieve savings of___________.

a. 20 percent to 40 percent over circuit-based access system s

b. 40 percent to 60 percent over circuit-based access systems

c. 60 percent to 80 percent over circuit-based access systems

d. 80 percent to 100 percent over circuit-based access systems

See Topic 3.

10. Full-service access network (FSAN) is ____________.

a. a standards body that regulates broadband networks

b. an access network for delivering broadband services

c. a group of 20 global telecommunications equipment manufacturerscollaborating on specification requirements for broadband accesssystems

d. a group of 20 global telecom mu nications carrierscollaborating on specification require ments for bro adbandaccess systems

See Topic 4.


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11. The main advantages afforded to the carriers of ATM PON are_________________.

a. cost savings due to lower maintenance costs than copper

b. cost savings due to use of single fiber for up to 64 users

c. cost savings due to easy bandwidth upgrading with no truck rolls

d. cost savings due to aggregation and concentration in the OLT

e. all of the above

See Topic 3.

Glossary

ADSLasymmetric digital subscriber line

ATMasynchronous transfer mode

CDMAcode division multiple access

COcentral office

DLCdigital loop carrier

DSLdigital subscriber line

FTTB/Cfiber-to-the-business/curb

FTTCabfiber-to-the-cabinet

FTTHfiber-to-the-home

FSANfull-service access network


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HDSLhigh bit-rate digital subscriber line

ISDNintegrated services digital network

LANlocal-area network

NTnetwork termination

OAM&Poperation, administration, and management protocol

OL Toptical line terminal

ONToptical network termination/terminator

ONUoptical network unit

PLCplanar light circuit

PONpassive optical network

POPpoint of presence

POTSplain old telephone service

QoSquality of service

SDMAsubcarrier division multiple access

SLAservice-level agreement

SMSservice management system


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SONETsynchronous optical network

TDMAtime division multiple access

VDSLvery high speed digital subscriber line

WDMAwave division multiple access

atm passive optical networks (pons)

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