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GPON MigrationEnsuring my Network is Ready toMigrate to GPON

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The demand for higher bandwidth by residential customers has led carriers to one

simple conclusion optical fiber with its almost limitless bandwidth capability will

be a network necessity. The driver for such high consumer bandwidth usage is the

need for carriers to deliver video, along with voice and data services, to complete

the triple play package.

As traditional carriers experience declining revenue from voice services, they must

find ways to increase the revenue from data and video services. Since video is the

highest revenue generator, the ability to compete with cable companies is critical.

Delivering the same high-quality video customers have received from their cable

provider can only be accomplished using video-over-IP technologies.

Passive optical network (PON) architecture is the key element for allowing carriers to

support the demand for advanced broadband services today, while also providing the

flexibility to scale outside plane infrastructures to meet next generation broadband

requirements. But deploying PON technology requires one particularly careful

consideration how easily will the network migrate from one PON flavor to the next

as bandwidth demand continues to rise.

GPON MigrationEnsuring my Network is Ready to Migrate to GPON

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Ensuring my Network is Ready to Migrate to GPON

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Standardizing PON

As with many telecom technologies, standards have playedan important role in the development of PON protocols.These standards drive the underlying protocols and thebasic specifications for specific telecom and data systems.Ultimately, standards define the specifications to makeinteroperability a reality and ensure product performance.

PON standards and recommendations were establishedby the Full Service Access Network (FSAN) and theInternational Telecommunications Union (ITU). ATM PON(APON) was the first iteration of the technology for fiber-to-the-premise (FTTP) solutions. However, APON lacked thebandwidth required for more robust applications and itspopularity was short-lived.

Broadband PON (BPON) was standardized in 2001 asthe first viable PON flavor for general use in early FTTPapplications. It provided 622 Mbits/sec downstream and155 Mbits/sec upstream. More importantly, it providedcarriers with the capability to overlay RF video. Still, asbandwidth demand increases in the FTTP market with

newer services, BPON will struggle to meet the grade inmany deployments.

Ethernet PON (EPON), also referred to as Ethernet inthe First Mile (EFM), is an ongoing standard that usesEthernet protocol for packet data transport. Even with itshigher level protocols, offering 1.2 Gbits/sec symmetricalbandwidth, it may not be enough to handle therequirements of higher bandwidth applications.

It is the view of ADC that Gigabit PON (GPON),standardized in 2003, will be the target for the majorityof PON migration paths while transitioning from onePON to another for meeting higher bandwidth demand.

GPON combines the quality of service capabilities of BPONwith EPONs ability to transport and interface on an allIP network. It can address higher application bandwidthrequirements by offering 2.4 Gbits/sec downstream and1.2 Gbits/sec upstream.

The promise of 1x64 split capabilities adds to theattractiveness of GPON solutions in FTTP networks. Thisenables carriers to double the number of customers servedfrom a single splitter in a fiber distribution hub (FDH).

PON architectures

Architectural decisions regarding any FTTP network buildout

are driven by initial and targeted take rates and a focuseddesign. This applies equally to overbuilds, Greenfieldapplications, or even a migration network. To be profitable,its imperative to understand the impact of the decisionsmade early in the planning stages of the process.

The best example of how an early decision can affectfuture operational costs can be found in the particularpoint-to-multipoint PON architecture selected for the initialFTTP outside plant. There are three possible scenarios andeach has advantages in certain situations. But network

architects should also be concerned with the aspects offuture-proofing the PON portion of the system to makemigrations to next-generation architectures as bandwidthdemands reach new levels.

The first PON architecture is the central switched, or homerun, whereby splitters are placed within the central office(CO), headend, or remote terminal. A key advantage of thisdesign is that all changes, either in the electronics or split

ratios, can be done at one centralized location.

Next, there is the distributed or cascaded splitterconfiguration which uses some combination of multiplesplitters (usually 1x4 and 1x8) at multiple locations. Thisdesign is particularly effective in rural or widely spacednetworks where the number of customers per mile isrelatively sparse. Transitioning to a GPON in a distributedarchitecture presents significant challenges since carriersare forced to migrate every subscriber or make costlymodifications to the OSP portion of the network.

Finally, there is the centralized splitter design where asingle coupler is placed within the central hub or cabinet.

From there, the distribution fiber interfaces with the entiresplitting scheme with drop cables extending directly toeach customer. This scheme offers great flexibility for futuremigration to GPON and typically involves an upgrade ofelectronics at each end of the PON.

Additional considerations

There are several additional considerations when designinga PON for ease of migration to GPON. These include thefiber optic cable characteristics, optics classes, and split ratioimplications. Well briefly address each of these topics.

Fiber optic cable

Different fiber cable from various manufacturers may havesimilar loss characteristics but they may also be quitedifferent. The spectral attenuation refers to the loss ofa signal as a direct correlation between the wavelengthand the distance traveled. The lower the wavelength, thehigher its spectral attenuation will be.

When applied to distances and calculating the linkloss budget for a given architecture, fiber optic cablemanufacturers must specify the spectral attenuation for theirproducts. When designing the FTTP network, the networkengineer typically designs for the wavelength with the highestloss characteristics. For BPON and GPON, this will always be

1310 nm, but the loss will differ between manufacturers.When increasing split ratios from 1x32 to 1x64 or evenhigher, for example, spectral attenuation will becomean important factor to consider. Additionally, due to thephenomena of hydrogen aging, attenuation increasesin fiber optic cables as they get older. The molecules ofhydrogen atoms in the silica or glass tend to break downover time, making the fiber less clear for transporting lightpulses. This may be an additional consideration when re-using fiber in an overlay scenario.

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