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2004 Allied Telesyn, Inc.

Active vs. PON FTTx Technology Choices, 6/30/04, Rev Awww.alliedtelesyn.com PAGE 1of 10

Technical Brief

FTTx Technology Choices

When it comes to FTTx deployment, many carriers mistakenly assume that PON is thebest or only game in town. This paper addresses some of the myths surrounding Active

Ethernet and PON technologies and explains why Active Ethernet networks arebecoming the preferred choice among many leading service providers.

Two of the largestFTTP initiatives inNorth America havechosen activesolutions, citing lowerCapEx and OpEx askey drivers.

So which is the bettersolution? Thats whatthis white paper will

cover.

By now weve all heard of the Super RFP issued by the RBOCs in 2003for their plans to deploy fiber to the premises (FTTP). Their decision to

deploy BPON, a Passive Optical Network architecture based on ATMstandards, has thrust PON into the spotlight and has given some peoplethe idea that PON is the only viable option for FTTP networks.

Meanwhile, two of the largest FTTP initiatives in North America,SureWest Communications and UTOPIA, have both decided to deployActive Ethernet fiber solutions citing the lower CapEx (capitalexpenditure) and OpEx (operating expenditure) of Active Ethernet as keydecision drivers.

So which is the better solution? The answer depends on many factors,including legacy infrastructure, bandwidth requirements, and the servicesto be offered.

This paper will explore some of the myths about PON and Activenetworks and provide an in-depth look at why Active Ethernet is quietlybecoming the preferred choice among leading service providersworldwide for their fiber deployments.


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PON uses poweredequipment in thecentral office andcustomer premise. Inthe outside plant, ituses passive splittersand couplers to dividebandwidth among upto 32 users over adistance of 10-20km.

A Passive Optical Network (PON) consists of an optical line terminator (OLT)

located at the Central Office (CO) and a set of associated optical network

terminals (ONT) to terminate the fiber usually located at the customers

premise. Both of these devices require power. PON gets its name because

instead of using powered electronics in the outside plant, it instead uses passivesplitters and couplers to divide up the bandwidth among the end users typically

32 over a maximum distance of 10-20km. Because this is a shared network, it is

sometimes referred to as Point to Multipoint or P2MP.

Similar to PON, Active

networks usepowered, hardenedequipment in the field,enabling them toprovide a dedicatedpipe to eachsubscriber.

Active networks canserve a virtuallyunlimited number ofsubscribers over an80km distance.

An Active network looks very similar to a PON, however, there are three main

differences. First, instead of having passive, unmanageable splitters in the field, it

uses environmentally hardened Ethernet electronics to provide fiber access

aggregation. Second, instead of sharing bandwidth among multiple subscribers,

each end user is provided a dedicated pipe that provides full bi-directional

bandwidth. Because of its dedicated nature, this type of architecture is sometimesreferred to as Point to Point (P2P). The third architectural difference between PON

and Active is the distance limitation. In a PON network, the furthest subscriber must

be within 10-20km from the CO, depending on the total number of splits (more

splits = less distance). An Active network, on the other hand, has a distance

limitation of 80km, regardless of the number of subscribers being served. The

number of subscribers is limited only by the switches employed, and not by the

infrastructure itself, as in the case of PON.

Figure 1: PON Architecture

Figure 2: Active Architecture

//

//

//

//

//

//

//

//ONT

OLT

Optical splitter

1x16 (1x2, 1x8)

1x32 (1x4, 1x8)

Usually 10Usually 10--20 km20 km

//

//

//

//

////

//

//

//CPE

Switch

Up to 70 kmUp to 70 km Up to 10 kmUp to 10 km

Single Fiber (EFM)

Powered Device(Ethernet Switch)


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PON vs. Active FTTx Technology Choices, 6/30/04, Rev Awww.alliedtelesyn.com PAGE 3of 10

Years ago, ActiveEthernet required twofibers, and did nothave options foroutside plant, but newstandards and

products haveremoved thoseconcerns.

With the basics of these topologies understood, we can now explore the five most

common myths surrounding PON vs. Active networks:

1. PON Networks Make Better Use of Fiber

2. Active Electronics In the Field Are a Liability3. PON Systems Dont Require Set Top Boxes for Video

4. PON Systems Provide Plenty of Bandwidth

5. PON Has Dominant Market Share Over Active.

! "# $ % & The root of this misperception is one based in reality. However, it is no longer valid

because of two technological developments that have occurred in the past year. The first

of these developments is the completion of the IEEE 802.3ah Ethernet in the First Mile

(EFM) standard that defines, among other things, a method for delivering Ethernet over a

single strand of fiber. Before this standard emerged, Active Ethernet solutions required

two strands of fiber to every subscriber (one to send, the other to receive). Years ago,

when fiber was very expensive, one can understand what a costly proposition this was.

The second development has been the evolution of environmentally hardened Ethernet

devices that can be placed in the outside plant. Prior to the availability of this type of

gear, network operators would have to pull the fiber from every subscriber all the way

back to their CO or else rely on Controlled Environment Vaults (CEVs) or other types of

air conditioned/heated Remote Terminals (RTs).

The two of these developments, along with the fact that fiber costs have dropped to a

fraction of what they were just a few years ago, make the question of which network uses

less fiber virtually a non-issue.

' ! ( ) *To assess where it makes most sense to place powered devices, one should understand

the different theories of outside plant design. These designs, along with their pros andcons, are described below.

Traditional PONThe promise of PON has been that you can push a single strand of fiber far out into the

field and split it with a passive, unmanageable device close to the customer premises

(Figure 3). Unfortunately, this approach has a number of drawbacks. One of the biggest

disadvantages is that these splitters have no intelligence, and therefore cannot be

managed. You cannot communicate with them remotely, and with hundreds or thousands

of splitters scattered around in the field, driving to each one to check for problems when

a service outage occurs becomes a very slow and a very expensive proposition.

Another major disadvantage to PON is its inflexibility. If a 1x4 splitter is used to serve

four homes, hooking up a fifth customer requires pulling a new strand of fiber all the wayfrom the upstream splitter, or re-designing the network to accommodate a larger splitter

near the customer premises without violating the 32 split maximum allowed.

Unfortunately, changing any splitter in the network requires all downstream customers to

come offline while the work is done.

Figure 3: Traditional PON


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Traditional PONs 32-split maximum can bemitigated by under-

utilizing capacity, butthat can drive up per-subscriber costs.

Passive Star PON

provides morecentralizedtroubleshooting, but isstill limited by PONstree-based topologies.

Active Star networksrequire power in theoutside plant;however, those activeelectronics do bring

intelligence andmanagement to theaccess edge.

A logical alternative to alleviate this problem is to under-utilize the capacity in the outside

plant. In other words, instead of maxing out each PON port with 32 splits, only deploy 16

or 24 splits to allow room for growth. Important to remember, however, is that each PON

port in the OLT carries a very high price tag since it is intended to be amortized across

32 customers. By not fully loading up that PON port, you increase the per-subscriber

costs dramatically. The network operator, in this scenario, is forced to decide which is the

lesser of two evils low flexibility or inflated per-subscriber costs.

Finally, since PONs are shared networks, each subscriber becomes a homogonous

member of the PON port they are connected to. Each subscriber gets the same

bandwidth, each must receive software updates at the same time, and each must have

the same ONT at the customer prem. This introduces significant challenges when

businesses looking for higher bandwidth services are mixed in with these residential

subscribers, when updating a new load of code, or when migrating to new technology in

the future (eg. BPON to GPON).

Passive Star PON

A Passive Star architecture is designed to alleviate some of the flexibility challenges of atraditional PON topology. Instead of pushing the splitters all the way out to the customer

premises location, they are pulled back and aggregated in a more centralized location,

typically housed in a cabinet. This design helps drive more efficiency and lightens the

burden of troubleshooting since the splitters are now more centralized.

But Passive Star is still subject to the inherent drawbacks of a PON network. One of

these is the lack of diverse paths through the network. PONs, by their nature, subscribe

to tree-based topologies. Even if the splitters are pulled back to an aggregation cabinet,

there is still only one physical path upstream, and that introduces a dangerous

dependency on that link. Because these splitters have no intelligence, there is no ability

to provide emergency fail over to a diverse path in the event of a link failure.

Another drawback is high first subscriber costs. As mentioned earlier, each PON port

carries a high price because it is expected to be divided by 32 subscribers. Therefore, to

activate that first subscriber, a significant CapEx investment must be made to provide

them service.

Active StarAn Active Star architecture has one arguable drawback from a deployment perspective,

and thats the requirement for power in the outside plant. However, Active electronics in

the field are nothing new. Telcos have been deploying DLC networks for decades that

have powered electronics in the field. As the types of services evolve to include

advanced, bandwidth intensive content like video, having intelligent devices at the edge

of a network actually becomes an extremely significant advantage for the following

reasons.

For video applications, intelligence at the edge of a network allows multicast streams to

be replicated for downstream delivery using IGMP. This means regardless of how many

people downstream of the switch are watching the

Figure 4: Passive Star


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While PON systemsdo not require a set-top box for analogsignals and monosound, todays digitalapplications dorequire a set-top boxwhen run over bothActive and PONinfrastructure.

same channel, only one stream is pulled down from the head end. That multicast stream

is then replicated in the Access switch and sent to the subscribers. This not only speeds

up channel change times, but it also makes more efficient use of your network backbone.

Another benefit to having Active electronics in the field is resiliency. By ringing these

nodes together and choosing a vendor that supports Ethernet Protection Switching Rings

(EPSR), true carrier-class resiliency is introduced which provides sub-50ms failover in

the event of a link failure. For a video customer, it means a split second of picture tiling in

the worst case, and for a voice customer, it means the call is not dropped.

Other advantages, of course, include full management and troubleshooting capabilities,

high flexibility for deploying different services to residential and business customers, and

low first subscriber costs. When striving for Five Nines reliability and maximum flexibility

in a FTTP network, one can quickly see how venerable a PON network is to link failure,

and how deploying Active electronics in the field actually becomes an asset instead of a

liability.

+ ! "# , -. " / $0 & 1)PON systems are able to support a somewhat complex method for deploying video

services that most closely resembles what MSOs (ie. cable TV providers) do today. This

method utilizes EDFAs (Erbium-Doped Fiber Amplifiers) to send an RF signal over aseparate wavelength on the fiber to deliver a signal to the customer prem. This is

sometimes referred to as delivering video out of band since it is outside of the IP data

stream.

If this signal contains analog video when it reaches the customer premise, it can be

delivered straight to the television without the need for a set top box just like the basic

service many people receive from cable TV providers today. The experience is exactly

the same the same video quality and the same mono sound.

If the signal contains digital video when it reaches the customer premises, however, a

digital set top box must be introduced again just as in a digital cable service offered

today by the MSOs. This set top box descrambles the digital video signal and delivers it

to the TV.

Where it starts to get more complex is when advanced, interactive services are

introduced like video on demand (VoD). Since an RF signal is a one-way

Figure 5: Active Star

Figure 6: Video Deployment Options


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When providing on-demand services,PON systems musteventually use IP tocommunicate with theHead End andtherefore require

adapters to convertthe RF signal.

Active Ethernetsystems use IP fromend to end, using anIP set top box toconvert the signals.

Depending on the

type of PON

deployed,

downstream

bandwidth can range

from 19Mbps to

38Mpbs. Under-

utilized splits offer

more bandwidth, butspeeds become

steadily slower as

more subscribers join

the network.

communication, the IP stream must be utilized to send commands up to the head end. In

order to do this, an RF adaptor must be added at the customer premises to demodulate

the upstream set top box communications and translate them into IP packets. Once

converted to IP, they are sent up through the IP path (or in-band) to the head end to

make the specified request. The requested content is then sent back down over the RF

path (out of band) using DWDM to that specific subscriber location.

Obviously, this requires a good bit of effort to provide a service that many would consider

to be the same as what cable TV operators are already doing today. As with any me too

service, this approach leaves very little opportunity to differentiate based on anything

other than price.

The alternative, and what many consider to be the best way of delivering advanced video

services, is using IP to deliver the content. This is sometimes called IP Video or Switched

Digital Video. In this solution, instead of having a traditional digital set top box, an IP set

top box is used to receive the IP packets, decode them, and provide audio and video

output to the TV. The experience is a powerful, all-digital experience with full Dolby 5.1

sound, crisp, high quality video, and interactivity unmatched by any other service

available today. Think of the interactive power of the Internet combined with high quality

broadcast TV. The result is strong differentiation that allows service providers to compete

on things other than just price. While IP Set Top Boxes carry a slightly higher price tagtoday than traditional digital set top boxes, when you add in the cost of the RF adaptor

required at each customer premises, the CapEx costs for both solutions are quite

comparable.

From the network perspective, the most compelling advantage for deploying IP video is

having a fully converged IP network to manage and maintain. IP has long been the

protocol-of-choice for delivering data services, and in recent years we have seen the

rapid emergence of Voice over IP (VoIP) as the preferred method for delivering voice

services as well. Using IP for video as well allows a network operator to use the same

infrastructure for all three services and realize significant CapEx and OpEx savings by

standardizing on one network infrastructure instead of two as is required in an RF video

deployment.

2 ! "# ) & $))To determine how much bandwidth is enough, a service provider must evaluate what

services they intend to offer over the life of the network. Since the capacity and longevity

of a fiber infrastructure is virtually limitless, one must look out as far as possible to ensure

the equipment that is deployed will handle the bandwidth needs for the foreseeable

future.

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Figure 7: Bandwidth Comparison by Technology


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Active Ethernetprovides dedicatedbandwidth to eachsubscriber, regardlessof network population.

Speeds are mostcommonly 100Mbpsto 1Gbps.

As illustrated in Figure 7, different technologies will offer different levels of bandwidth in

the upstream and downstream directions. APON and BPON, for example, deliver

622Mbps in the downstream direction, so assuming it is split among 32 subscribers, it

provides 19Mbps to each customer. In the upstream direction, it provides 155Mbps split

32 ways, resulting in under 5Mbps. EPON is a technology that provides 1Gbps in both

the downstream and upstream directions, providing 30Mbps of bi-directional bandwidth

to each subscriber. Finally, GPON, the newest standard for PON technology, provides

1.2Gbps in the downstream direction resulting in 38Mbps per subscriber assuming 32

splits, and 622Mbps in the upstream direction allowing 19Mbps per subscriber.

Active Ethernet, in comparison, provides dedicated bandwidth to each subscriber, which

means there is no sharing of network traffic. Speeds most commonly found in the

marketplace today are 100Mbps bi-directional to residential customers and even 1Gbps

to business customers.

When you consider that Active Ethernet solutions, on average, cost less to deploy and

maintain than comparable PON systems, the opportunity to secure more bandwidth for

less investment is certainly a compelling proposition. But how much bandwidth is

enough? All of these speeds are compelling by todays DSL and Cable broadband

standards, but deploying advanced IP video and other next generation services takesthings to a completely new level.

Consider whats being offered today at SureWest Communications in Sacramento, CA.

Over their Active Ethernet FTTP network, they offer residential customers a service

bundle of 200 digital channels with interactive TV services such as video on demand,

voice service with a full package of features such as call waiting and various messaging

options, and 10Mbps of high-speed internet for one low monthly price. To deliver these

types of services, a network would require at least 22Mbps of bandwidth assuming 3

TVs per house at 4Mbps per video stream plus the 10Mbps for high speed Internet.

Based on the bandwidth capabilities of PON-based architectures, it is clear this network

would already be beyond the capabilities of BPON and pushing up against the

capabilities of even the newest PON standard, GPON.

Figure 8: FTTP Residential Services Today vs. Tomorrow

10MbpsHigh Speed Internet:

60Mbps

HDTV (IP):

20Mbps per stream x 3 TVs:


60Mbps

HDTV (IP):



12Mbps

Broadcast TV (IP):



12Mbps

Broadcast TV (IP):



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PON networks will beseverely challengedby emerging high-bandwidthapplications such asHDTV.

PON and ActiveEthernet technologiescurrently split theFTTP market nearlyequally

Now if we look at what is just over the horizon HDTV we can quickly see how a PON

network will not scale to meet the requirements. This is before we even begin to consider

how other applications will take off such as distance learning, video conferencing, smart

home services, personal video recorders (eg. TiVo), etc. Each of these will carry their

own bandwidth requirements that must be planned for.

89 : # " According to Render, Vanderslice & Associates, a noted research firm focused

exclusively on the FTTP market, the number of actual deployments of FTTP networks

shows a nearly equal split between PON and Active technologies at 48% and 46%

respectively (Figure 9). When the RBOCs proclaimed they would deploy BPON in the

Super RFP, many believed that PON would become the dominant technology choice

for all FTTP deployments. When you stop to consider that their legacy infrastructure is

ATM-based and that video is not a priority for them, however, it becomes clear that while

it makes perfect sense for their needs, it most definitely will not be the best choice for all

deployments.

For network operators interested in offering video as a key differentiator and are not

locked into a legacy ATM infrastructure, on the other hand, most are realizing the value

of deploying a fully converged IP network that is based on the most ubiquitoustechnology in the world Ethernet.

Homes Connected as of

October 2003

EPON

3%

Hybrid

Active/

PON

3%

Active

46%

APON/

BPON

48%

Source: Render, Vanderslice & Associates.

Figure 9: Deployments by Technology


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"##

;In the end, each network operator will make their decision of which

technology to deploy based on their own unique circumstances. The

purpose of this paper is not to suggest that one technology is the best for

every situation. On the contrary, the intention of this paper is simply to make

network operators aware that there is an attractive alternative to PON-based

FTTP architectures that leverages the benefits of IP and Ethernet to deliver

services that will provide compelling differentiation based on the unique

experience it delivers to customers and not just on price.

To learn more about Active Ethernet FTTP solutions and how Allied Telesyn

is helping some of the worlds largest FTTP network operators realize the

benefits of carrier grade IP/Ethernet, visit www.alliedtelesyn.com or call

1-800-424-6596.

)#


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