WHITE PGPON Migration Ensuring my Network is Ready to Migrate to GPON... The demand for higher bandwidth by residential customers has led carriers to one simple conclusion – optical fib
Trang 1WHITE P
GPON Migration
Ensuring my Network is Ready to
Migrate to GPON
Trang 2The 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 Migration
Ensuring my Network is Ready to Migrate to GPON
Trang 3Standardizing PON
As with many telecom technologies, standards have played
an important role in the development of PON protocols
These standards drive the underlying protocols and the
basic specifications for specific telecom and data systems
Ultimately, standards define the specifications to make
interoperability a reality and ensure product performance
PON standards and recommendations were established
by the Full Service Access Network (FSAN) and the
International Telecommunications Union (ITU) ATM PON
(APON) was the first iteration of the technology for
fiber-to-the-premise (FTTP) solutions However, APON lacked the
bandwidth required for more robust applications and its
popularity was short-lived
Broadband PON (BPON) was standardized in 2001 as
the first viable PON flavor for general use in early FTTP
applications It provided 622 Mbits/sec downstream and
155 Mbits/sec upstream More importantly, it provided
carriers with the capability to overlay RF video Still, as
bandwidth demand increases in the FTTP market with
newer services, BPON will struggle to meet the grade in
many deployments
Ethernet PON (EPON), also referred to as Ethernet in
the First Mile (EFM), is an ongoing standard that uses
Ethernet protocol for packet data transport Even with its
higher level protocols, offering 1.2 Gbits/sec symmetrical
bandwidth, it may not be enough to handle the
requirements of higher bandwidth applications
It is the view of ADC that Gigabit PON (GPON),
standardized in 2003, will be the target for the majority
of PON migration paths while transitioning from one
PON to another for meeting higher bandwidth demand
GPON combines the quality of service capabilities of BPON
with EPON’s ability to transport and interface on an all
IP network It can address higher application bandwidth
requirements by offering 2.4 Gbits/sec downstream and
1.2 Gbits/sec upstream
The promise of 1x64 split capabilities adds to the
attractiveness of GPON solutions in FTTP networks This
enables carriers to double the number of customers served
from 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 focused
design This applies equally to overbuilds, Greenfield
applications, or even a migration network To be profitable,
it’s imperative to understand the impact of the decisions
made early in the planning stages of the process
The best example of how an early decision can affect
future operational costs can be found in the particular
point-to-multipoint PON architecture selected for the initial
FTTP outside plant There are three possible scenarios and
each has advantages in certain situations But network
architects should also be concerned with the aspects of future-proofing the PON portion of the system to make migrations to next-generation architectures as bandwidth demands reach new levels
The first PON architecture is the central switched, or home run, whereby splitters are placed within the central office (CO), headend, or remote terminal A key advantage of this design 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 splitter configuration which uses some combination of multiple splitters (usually 1x4 and 1x8) at multiple locations This design is particularly effective in rural or widely spaced networks where the number of customers per mile is relatively sparse Transitioning to a GPON in a distributed architecture presents significant challenges since carriers are forced to migrate every subscriber or make costly modifications to the OSP portion of the network
Finally, there is the centralized splitter design where a single coupler is placed within the central hub or cabinet From there, the distribution fiber interfaces with the entire splitting scheme with drop cables extending directly to each customer This scheme offers great flexibility for future migration to GPON and typically involves an upgrade of electronics at each end of the PON
Additional considerations
There are several additional considerations when designing
a PON for ease of migration to GPON These include the fiber optic cable characteristics, optics classes, and split ratio implications We’ll briefly address each of these topics
Fiber optic cable
Different fiber cable from various manufacturers may have similar loss characteristics – but they may also be quite different The spectral attenuation refers to the loss of
a signal as a direct correlation between the wavelength and the distance traveled The lower the wavelength, the higher its spectral attenuation will be
When applied to distances and calculating the link loss budget for a given architecture, fiber optic cable manufacturers must specify the spectral attenuation for their products When designing the FTTP network, the network engineer typically designs for the wavelength with the highest loss 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 even higher, for example, spectral attenuation will become
an important factor to consider Additionally, due to the phenomena of hydrogen aging, attenuation increases
in fiber optic cables as they get older The molecules of hydrogen atoms in the silica or glass tend to break down over time, making the fiber less clear for transporting light pulses This may be an additional consideration when re-using fiber in an overlay scenario
Trang 4PON optics classes
Optical link budgets are determined by individual vendors’ active components – PON chips within the electronics, lasers, and receivers The loss range for each class is as follows:
Class A – Min 5 dB to max 20 dB Class B – Min 10 dB to max 25 dB
Class B+ Min 10 dB to max 28 dB Class C – Min 15 dB to max 30 dB
Traditional BPON equipment has typically used Class B optics, but it was determined that some of the PON network of 20 km were actually stretching the budget to the limits, forcing active equipment
manufacturers to increase budgets to 26.5 dB These increased budgets, coupled with a possible
requirement to increase the split ratios of GPON, resulted in an increase in the Class B receiver photo detectors to allow for a 28 dB loss budget – thus, establishing the Class B+ optics category
However, despite the increase, these Class B+ optics have not escalated to the higher Class C pricing while maintaining better PON loss characteristics In the future, however, the need to transport greater distances (30 km or 40 km) and even higher split ratios (1:128) could eventually force equipment manufacturers to use the Class C optics
With Class A optics typically associated with fiber-to-the-curb (FTTC) applications, Class B and Class B+ optics provide today’s FTTP PONs with the best reach and split ratios However, the need to reach longer distances could make Class C optics tomorrow’s choice – with significant cost implications
Split ratio implications
Splitter loss depends mainly on the number of output ports on the splitter and, contrary to some
expectations, adds about the same loss whether traveling in the downstream or upstream direction Each splitter configuration is assigned a particular maximum split ratio loss, including connectors, defined by the ITU G.671 standard and Telcordia GR-1209
Since the GPON standards have not yet defined the current split ratio maximum for 1x64 splitters, network designers must use a single 1x2 splitter interfacing two 1x32 splitters to make up the 1x64 configuration Although this is allowable with today’s packaging, using Class B optics only leaves 5.35 dB of “head room.” Therefore, even with the best fiber manufactured, where the spectral attenuation is 0.31 dB per kilometer, only a 17.25 km PON network is achievable without including any of the connectors within the
CO or the splices in the OSP
However, the design engineer does have some options In designing the network, premium splitters and low loss connectors can be deployed, and fusion splices must be kept well below 0.05 dB of loss per splice There are other techniques ADC will be using until the standards line up with the technology for 1x64 and higher split ratios
ADC is working closely with customers to ensure their networks can easily and cost-effectively migrate as higher bandwidth demand dictates At the end of the day, making the correct initial decisions regarding PON implementation techniques, carriers will maximize the flexibility of their networks to enable smooth and rapid migration to the next PON level – and provide customers with many years of reliable cutting edge services and applications
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