WhitePaper014 RevA RFPON

Aurora Networks, Inc.Aurora Networks, Inc.

June 2009

WHITE PAPER 14

©2009 Aurora Networks, Inc. All rights reserved.

©2009 Aurora Networks, Inc. All rights reserved.2

RFPON - The Next-generation RFoG Solution

Aurora Networks, Inc.

5400 Betsy Ross Drive

Santa Clara, CA 95054

Tel 408.235.7000

Fax 408.845.9045

www.aurora.com

Copyright © 2009 Aurora Networks, Inc. All rights reserved.

All rights reserved. No part of this document may be reproduced, stored in a retrieval

system, or transmitted in any form by any means, electronic, mechanical, photographic,

magnetic, or otherwise without the prior written permission of Aurora Networks.


White Paper 14

Abstract

Aurora’s RFPON system architecture enables

the migration of traditional RFoG (RF over

Glass) architecture into a system that supports

RFoG plus PON (GEPON / GPON / future

10GEPON) services simultaneously over the

same fiber (or fibers) to the home or premises.

This RFPON architecture builds upon and

utilizes the installed HFC fiber infrastructure

to feed RFPON fiber services to all areas of

the HFC plant, located anywhere between the

headend/hub and at distances in excess of 60

kilometers from the headend/hub.

.

BACKGROUND

Do cable operators need to deploy Fiber to the

Premises (FTTP) networks to provide all the

services demanded by subscribers, both today

and tomorrow? Resolutely no! The hybrid fiber/

coaxial (HFC) network, and Fiber Deep in

particular, can provide all the needed network

capacity and more. However, there are scenarios

where it makes sense for cable operators to deploy

fiber all the way to the home. In particular, FTTP

networks may stop cables’ competition from

securing new footholds and help displace the

competition. In rural areas with new builds or

extensive upgrades and with low population

density, FTTP may prove more cost effective while

providing additional operational benefits.

Moreover, FTTP may provide new revenue

streams more cost-effectively. Specifically, areas

of interest could be:

• New housing developments

• Rural, low-density areas

• Multi-Dwelling Units (MDUs)

• Commercial areas (co-located with

residential areas)

For a new housing development, the builder can

often raise the sale price of the house if it can be

claimed that the house is “fiber ready”. Indeed, in

many instances the extra cost of deploying the

fiber all the way to the home will be met or heavily

subsidized by the builder. FTTP keeps the

competition out.

For rural, low-density areas (<30 HP/mile) it is

always very difficult to deploy an HFC network

cost effectively, with many line extenders or

similar devices typically required to overcome the

loss in coaxial cables to reach remote households.

In this case, deploying FTTP brings many

advantages: limitless bandwidth potential with very

little loss of signal level, reduced operating costs

(maintenance and powering) and as system design

studies and cost analyses have shown, all for

approximately the same or even lower cost than

HFC or Fiber Deep deployments. With today’s

revenue generating unit (RGU) monthly payment

potentially in excess of $100, providing service

to these low-density homes now becomes viable.

MDUs offer another unique market segment

(assuming they are an existing development—new

MDU developments would be categorized as

“new housing developments”). Depending on the

locale, they may attract a commercial, high-band-

width demand or people who expect and would

RFPON – The Next-generation RFoG Solution



be happy to pay for a superior triple play service.

For this application, the fiber can be distributed

from the basement of the building and fed to the

actual dwelling unit, providing true FTTP.

However, there are other MDUs where this is

not feasible; for example, in a building already

cabled with coax, trying to replace that with fiber

may be prohibitively expensive. In these situations,

the fiber can be run into the basement of the

building and either distributed via coax from there

or further split and the fiber fed via elevator shafts

(or similar) to wiring closets on each floor, with

coax running from those closets to the unit.

For business areas, it may be optimum to start

with FTTP to provide commercial services via

PON, supporting high speed data and telephony.

However, many businesses require video as well

and this can be provided via traditional RFoG, all

on a single fiber.

In all these scenarios, the optimal application is

an architecture that operates from the same

headend equipment as the traditional HFC plant,

supports all the same services as HFC with

potential for new and innovative services,

interfaces with all the same back-office equipment

(in the same way) but is actually fiber to the

premises rather than the more traditional coax.

This solution runs fiber all the way to the premises

to serve a single-output “mini node” customer

premises equipment (CPE) so that traditional RF

output is maintained, enabling continued use of

set-top boxes, DOCSIS® cable modems and

eMTAs. This RFoG architecture, first deployed

by Aurora Networks in 2006, has been taken to

the next level with our next-generation RFoG

solution, RFPON. RFPON supports a traditional

RFoG architecture but with seamless support for

PON services, when needed. Alternatively, Aurora

Networks’ solution is so flexible that one can start

with PON and then add RFoG services.

This white paper introduces Aurora’s RFoG and

RFPON solutions, emphasizing how Aurora, with

the benefit of numerous field deployments, has

developed tools to both solve the inherent issues

with RFoG implementations and then provide a

smooth migration path to an all-IP access network

in the future, or vice-versa.

RFoG BUILDING BLOCKS

The reference architecture for a “tradi-

tional” RFoG system, from headend/hub,

is shown in Figure 1. The reference

architecture at the headend/hub site comprises a

downstream optical transmitter operating

nominally at 1550 nm, optical amplification as

required by the topology being served and a wave

division multiplexer (WDM) filter for combining

downstream and upstream optical signals on a

single fiber. It also comprises an upstream optical

receiver which receives the 1310 nm upstream

optical signals and converts them to RF. In the

field, conveniently located between the headend

and the end customers, there would be various

optical splitters, supporting distances up to 20

kilometers from the headend with each fiber

supporting up to 32 customers.

At the customer site, an RFoG CPE is required,

designed for either indoor or outdoor installation,

and which comprises a WDM filter to separate

the downstream optical signal (at 1550 nm) from

the selected upstream wavelength. The down-

stream optical receiver converts the RF down-

stream signals from the downstream optical

carrier, and the RF signal is then fed via coax into


White Paper 14

the home. In the upstream, the RF signal is

supplied to an upstream transmitter (with an output

at 1310 nm) for onward transmission to the

headend. Another emerging upstream wavelength

is 1610 nm; the wavelength of choice set by the

SCTE standards committee. This wavelength

provides compatibility on the same fiber with

existing PON and the emerging 10G-PON standard

wavelengths.

The associated RFoG reference diagram

frequency/wavelength spectrum for a typical North

America system is shown in Figure 2.

This is exactly the same suite of products offered

to any subscriber in any area of the existing HFC

cable plant, not just areas which are fed via fiber.

This results in a completely unified headend,

significantly simplifying operation for the cable

operator.

Figure 1. RFoG Reference Architecture, Highlighting Distance Limitations

Figure 2. RFoG Spectrum



LIMITATIONS OF HEADEND/HUB-BASED RFoG

While the system does meet many of

the objectives of the cable operator

to deploy an HFC-compatible

FTTP network, technically this solution has

limitations, namely:

• Limited downstream reach

• Limited upstream reach

• Fiber-intensive

While the downstream reach is important, and

limited by the power which can be launched into

the downstream fiber, the system limitation will

be driven by the upstream. The major cost

element in the system is the RFoG CPE and its

associated laser diode for return transport, hence

minimizing the cost of this component is important.

To overcome the upstream loss budget of 24–26

dB, a 20 km 32-split system with a fully loaded

return band (i.e., four DOCSIS channels to

support DOCSIS 3.0, plus an additional VoIP

DOCSIS channel), and a high power upstream

laser would be required (on the order of 10 dBm),

which is costly; this is clearly not the direction to

go for any type of CPE. Alternatively, an upstream

receiver technology breakthrough would be

required to achieve the very low input levels

required by a CPE using a cost-effective low power

laser, assuming acceptable carrier-to-noise

performance. A 1610 nm laser does provide PON

compatibility, and technically can provide the

higher optical power; however, this is a more

expensive unit. Aurora’s upstream receiver

solution supports a 24 dB loss budget at 1610

nm and 25.6 MHz load with just 3 dBm RFoG

CPE transmitters without special provisions or

modulation techniques and is compatible with any

directly-modulated laser RFoG CPE. There are

other solutions being proposed, namely FM and

digital links from the CPE, but they do not offer

the same compatibility and flexibility to the

operator.

Aurora can provide a traditional headend/hub-

based RFoG solution. However, depending upon

actual equipment and network configuration, the

reach will only be in the 10–20 kilometer range.

Unfortunately, this greatly impacts the area which

can be served directly from the cable systems’

headends/hubs.

In a typical RFoG deployment, each fiber would

serve up to 32 subscribers. For example, in a

256 home service area, a cable operator would

need to dedicate eight fibers from the headend/

hub to that area to ensure service to each

subscriber. Similarly, with these direct fiber runs

from the headend, there is no practical method to

provide any redundancy in the system. With the

growing importance of high-demand, high-

revenue services, lack of redundancy is not an

ideal solution.

AURORA NETWORKS’ VHUB-BASEDRFoG SOLUTION

Aurora has pioneered technology which

efficiently overcomes all the limitations

of an RFoG system: the VHub™. The

VHub houses a fully operational hub in a standard

node housing. In this application it is designed to

serve 256 subscribers. Effectively, it moves the

functionality of an indoor hub to a weather-proof

node enclosure that can be deployed closer to

subscribers in the network. The same can be

achieved with the OTN configuration so prevalent


White Paper 14

in xPON deployments, but the VHub solution

avoids requirements for permits and rights of way

access as well as land acquisition costs while, at

the same time, providing higher granularity,

scalability and security. VHubs can be strand or

pedestal mounted. The key VHub features for

this application are:

• Support for up to 12 plug-in modules

(forward path EDFAs, return path receivers,

integrated forward/return wavelength

management modules with or without return

path receiver functionality, digital transceiv-

ers and transponders, optical switches,

monitoring transceivers and optical

multiplexers)

• Monitoring and control of the VHub via our

Opti-Trace™ EMS software

• Redundancy and route diversity with switch-

ing times less than 10 milliseconds (typically

<5 milliseconds).

The Aurora VHub-based RFoG architecture is

shown in Figure 3.

The VHub system has been successfully deployed

world-wide for over five years in many different

applications and configurations. In addition to its

flexibility in placement—it can be located very

deep into the network—it overcomes the limita-

tions of the RFoG headend/hub-based reference

design by:

• Downstream reach. With forward path

EDFAs packaged for installation in this

housing, the downstream reach is no longer

limited.

• Upstream reach. At the VHub, the return

signals are processed from an analog to

digital signal format. With Aurora’s standard

digital return technology, the upstream reach

is no longer limited. With the VHub

configured with upstream analog return path

receivers, the subscriber CPEs only need to

transport back to the VHub, a very short

distance of typically no more than about 5

kilometers. With analog receivers in the

VHub, effectively 64 subscribers can share

Figure 3. VHub: Overcoming the Limitations of RFoG



the upstream bandwidth. Once received, the

upstream signals are then fed into two “2-

fer” digital return transmitters, each

transmitting on one of 15 CWDM wave-

lengths. Use of the digital return overcomes

the distance limitation (now with a reach >60

kilometers) while use of WDM technology

provides a very fiber-efficient solution.

(Aurora’s white paper titled “Digital Return

Technology” provides more detailed

information.)

• Fiber-intensive. With the traditional RFoG

approach, one dedicated transport fiber is

needed for 32 subscribers. With the VHub,

this is reduced to one transport fiber for 256

subscribers, with the forward and reverse

wavelengths sharing the same fiber. The

traditional approach needs eight times more

fiber. In addition, with the VHub, the existing

HFC fiber can be shared with the RFoG

wavelengths. With Aurora’s various “O”-

band and “C”-band multi-wavelength

technologies, a previously used fiber can be

freed up for this application.

• Route-redundancy option. Aurora’s

hardened VHub-based optical switch

provides route diversity with switching times

less than 10 milliseconds (typically <5 milli-

seconds). The only way to provide route

redundancy with traditional RFoG is to build

two separate systems.

In addition, Aurora has developed integrated

passive wavelength management modules,

simplifying input/output connections to the network

that are housed in the VHub. In particular, one

module provides a combined optical splitter for

the 1550 nm broadcast signals together with 1310/

1550 diplex filters. This compact design, with

MPO connectors, eliminates most fiber jumpers

and minimizes associated losses that are normally

created by broadcast splitting and/or 1310/1550

(or 1610/1550 as-needed) mux/demux functions.

This integrated module not only saves precious

VHub real estate but the removal of many of the

jumpers improves reliability and also greatly

simplifies the installation and maintenance of the

unit. Taking this to the next-level of integration,

Aurora has consolidated the return path receivers

into the integrated passive module while

maintaining the same module form factor. This

further simplifies operation and opens VHub slots

which can be populated with other modules.

Today there are eight fibers from the VHub, with

each fiber able to serve up to 32 subscribers.

(These subscribers can, of course, be either

residential or commercial.)

RFPON: EVOLVING RFoG WITH THEADDITION OF PON

When making the investment to de-

ploy FTTP, it has already been

stated by some that it is critical that

there exist an established path to take the network

from its current cable TV form of today to an

“all-IP world” that will be needed for future

generations. Aurora’s RFPON solution provides

that evolutionary path, enabling a step-by-step,

area-by-area upgrade with its award-winning

Node PON™ technology.

The choice of an upstream wavelength is not

arbitrary; the 1310 nm solution of today is more

cost-effective given the wide availability of

components (both active and passive) at this

wavelength. However, 1610 nm is potentially more


White Paper 14

future-proof; it permits an optional overlay with either

an IEEE 802.3ah (EPON, or GEPON) or an ITU

G.984 (GPON) system, given that both these systems

use 1310 nm for upstream data communications. An

additional factor in selection of the 1610 nm wave-

length is its compatibility with the emerging IEEE

802.3av (10GEPON) system which is heading towards

standardizing on 1577 nm downstream/1270 nm

upstream, but this currently remains a work-in-

progress. Meanwhile, other options can be made

available upon request, such as a 1590 nm up-

stream path already in use by several cable op-

erators worldwide.

The new wavelength frequency/content plan is

shown in Figure 4.

Figure 4. RFPON Supports the Best of Both Worlds

GEPON SOLUTION

Aurora Network’s Gigabit Ethernet

Node GEPON Module, the GE4132M,

is an OLT module designed to work in

all our VHubs and nodes, making PON delivery

from an outdoor platform a reality.

Using this OLT module, cable operators can cost-

effectively add all-IP services to their networks

on a service area by service area basis, operating

in parallel with traditional cable TV services that

are transported over the 1550 nm and 1610 nm

wavelengths. Ultimately, but only if and when

justified by revenue growth, Node PON equipment

can enable full migration of an installed HFC

network to a standards-based GEPON FTTP

network. With a VHub which can support one,

two or three Node PON modules, the dedicated

IP-bandwidth to a group of 256 subscribers can

be as high as 3 Gbps full duplex. (This is in addition

to all the traditional cable TV services that are

received from the traditional RFoG deployment.)

Of course, the CPE device at the home will also

need to be upgraded to support the new PON

services. However, by adhering to the widely-

deployed GEPON standard, the expectation is

that the additional CPE device would be cost-

effective, with costs driven down by wide-scale

deployment. Going one step further and eliminating

the RF overlay would allow five Node PON

modules to be supported—up to 5 Gbps

dedicated bi-directional bandwidth to 256

subscribers. With future generation support for

the evolving 10GEPON standard, bandwidth

potential is almost limitless. This is truly a future-

proof solution.

Today Aurora Networks is the only company to

provide this seamless evolution from an HFC

architecture to a full IP-based network on a



service area by service area implementation. In

addition, there are notable key features for our

Node PON solution:

• Fully-compliant with the GEPON standard—

compatible with off-the-shelf GEPON CPE

devices

• Today’s bandwidth is 1000 Mbps bi-

directional

• Each module can support up to 64

subscribers

• Designed to fully interoperate with existing

DOCSIS cable modem back-office

provisioning systems.

PRACTICAL EXAMPLE

The following example, shown in Figure

5, examines how a cable operator could

use Aurora’s RFoG and RFPON

solutions to serve a rural area.

Initially this deployment is viewed as an extension

of the installed HFC network. The VHub would

be located at a convenient place, being served

from the same headend equipment and

Figure 5. Serving a Rural Area


White Paper 14

provisioning system. If no route diversity is

required, the VHub would be served by just one

fiber from the nearest fiber node. If the broadcast

and narrowcast services are not available on the

1550 nm wavelength, then the appropriate trans-

mitter would need to be installed at the headend/

hub and a dark fiber to the node commissioned

(or a wavelength added to an existing fiber). From

the VHub, today there would be eight fibers, each

connected to the appropriate splitter, to service

the widely-distributed homes in the area. If the

cable operator is looking for a future-proof

solution, it is recommended that 1610 nm rather

than 1310 nm be adopted for the upstream signal.

The downstream services (broadcast TV,

downstream data and VoD traffic, etc.) are carried

on 1550 nm with all the associated upstream traffic

on 1610 nm. (The CPE device would also need

to mirror these wavelength selections.)

Once network capacity demand exceeds that

available, as a next-step a Node PON module

can be installed in the VHub, introducing dedicated

IP services. The corresponding CPE would need

to be upgraded to service the PON infrastruc-

ture. (Typically, GEPON-ready CPEs will not be

deployed until a subscriber has signed-up for those

services; this considerably reduces the upfront

capital cost.) The frequency/channel plan for both

the traditional and the IP services is shown in Figure

4. With the Node PON seamlessly integrating with

DOCSIS provisioning systems, the introduction

of this new technology does not cause disruption

to back-office processes and procedures.

Additionally, with each Node PON supporting

symmetrical bandwidth of up to 1 Gbps, this

solution is also compelling for providing service

to businesses which are co-located in the same

rural serving area. This could result in the cable

operator having a unified network for both

residential and business consumers with minimal

capital expenditure and no additional operating

expenses—and while gaining additional revenue

streams!

SUMMARY

Providing services to a new area is very

expensive for cable operators; however,

if it makes good business sense, then fiber

is the optimum way to provide connectivity. Aurora

has been pioneering in this space, developing and

optimizing solutions specifically for cable, and fiber

to the premises in particular. With our VHub

technology, the cable operator has an optimal

solution to deploy FTTP today: a solution which

cost-effectively overcomes the limitations

associated with other approaches. Importantly,

with the introduction of our Node PON GEPON

module and careful wavelength selection, our

RFPON solution provides the cable operator with

an evolutionary upgrade path capable of

supporting all-IP full-duplex services—once

justified by the potential revenue opportunity.

Aurora Networks—working with cable operators

to break access barriers.



Aurora Networks, Inc.

5400 Betsy Ross Drive

Santa Clara, CA 95054

Tel 408.235.7000

Fax 408.845.9043

www.aurora.com

Documents

WhitePaper014 RevA RFPON