andersen duarte et ali ieee commag 1997

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ABSTRACT

There is a worldw ide ef fort to define a ful l-service access network. The Broadbandloop project was form ed by a European con sortium

funded by the European Union with th e objective o f defining a strategy for evolution from a narrowband voice and data network to a

broadband network The project is defining a system concept based on new innovative PON technology, which enables fiber to cost

effectively penetrate close to th e customer, and

VDSL

technology for transmission over twisted copper pairs. The system concept is vali-

dated i n field trials in Denmark, Portugal, and Poland. The article describes the d iffere nt requirements f or a full-service access network,

the system concept, and technologies developed. Results from modeling of broadband traffic and the corresponding bandw idth are

given The cost effectiveness of using new o ptical fiber vs. reusing existing telepho ne copper p lant has been evaluated, and results fro m

these studies are presented.

Niels Engell Andersen, DSC Comm unic at ions AIS

Paul0 M . N, Nordeste, Portu gal Telecom-CET

A. Man uel d e Ol ive i ra Duarte , Univers idade de Aveiro

Hans Erik Lassen, TeleDanmark

And ers Ekblad, Tel ia

Andrze j

R.

Pach, University

of

Krakow

Krzys zto Am bors ki, Telekom unik acja Polska TPSA)

Lars Di t tm ann, EM1

o support economica rlevelopment across Europe, there is

T

need to advance the availability and decrease the cost of

both basic and enhanced telecommunication services.To facili-

tate this, the European Union

(EU)

has initiated a process of

deregulation and a general opening up of the public telephony

network. While there are many network design options avail-

able, the EU’s program for Advanced Communications Tech-

nologies and Services (ACTS)

[

11 in cooperation with other

organizations has funded a project to evaluate and recommend

strategies for access network deployment, designs of a full-ser-

vice access network, and the economic balance between deploy-

ment of new fiber in the access network and reuse of the

existing copper infrastructure. This project started in Septem-

ber 1995 and is planned to conclude by the end of

1998.

The Broadbandloop (BBL) project1 will define and demon-

strate, in live field trials, a concept for

a

full-service access

network which migrates fiber gracefully into the local loop

when bandwidth demand increases. The services offered will

target two customer groups: small t o medium-sized businesses

and residential customers. BBL supports the needs of network

operators to provide both narrowband and broadband ser-

Partners

n

the Broadbandloop project are DSC Commun ications, Por-

tugal Telecom -CET , Universidade de Aveiro, TeleDanmark, Telia Uni-

versity o Mining and Metallurgy in Krakow, and Telekomunikacja P olska.

vices, such as high-speed Internet access and video on

demand , which ar e economically justified in a competitive

environment. The field trial sites, located in Denmark, Portu-

gal, and Poland, have been purposely selected to enable anal-

ysis of typical problems which may be e ncoun tere d when

legacy networks, such as those using existing copper andlor

coax for broadband access or those with little or old telephony

infrastructures, are expanded for new service.

BBL is a near-term project with the aim of developing and

testing technologies which will be ready for mass deployment

within the next three years. The system scheduled for deploy-

ment uses

a

hybrid fiber-copper concept based on a combina-

tion of

a

passive op tical network (PON)

and

very high-rate

digital subscriber line (VDSL) technology. The PON provides

the low-cost fiber acccss, while VDSL providcs the high-speed

transmission to t he custome r over a final short length of

unshielded twisted pair copper or coax. PONs have until now

not

been widely accepted for commercial deployment. BBL is

addressing som e of t he key issues to pr omote the use of

PONs

such

as

integration into the standardized synchronous

digital hierarchy (SDH) network, operational stability, upgrad-

ing of bandwidth, and flexibility to provide protected routing

and allow multiple services.

This article will present t he BBL system concept , traffic

modeling and bandwidth requirements, optical design, techni-

cal and economic evaluations, and plans for the field trials.

0163-6804/97/ 10.00 997 IEEE IEEE Communications Magazine December 1997

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..

....

_...

. -

I

i

i

i

i

OLT:

Optical l ine terminal

ONU: Optical network unit

SIM: Subscriber interface module

NT: Network terminat io n

ODN: Optical distr ibu t ion network

SDH

ring (STM-1 or STM-4)

Single business custome r

Voice1

2 Mb/s

I

ult ipl e residentiallsmall business customers

(reuse of existing copper in customer drop )

i

ultip le VDSL cards

~

Passive

split ter

Mu ltipl e residentiaVsmall business customers

OLT (new network)

E l

POTS,

ATM-25,

t Ether net cards

n x 5 1

Mbl;

--..

n

x 51 Mbls

. -...

W Figure 1. TheBBL system concept.

BBL CONCEPT

egacy network operators in western Europe will require a

L roadband system which provides services as an overlay to

the existing telephony or cable television (CATV) network. If

the existing copper resources need replacement or are insuffi-

cient, narrowband services should also be made available

through the new broadband system.

Network operators without a copper network or with a net-

work with low penetration will require a system for both nar -

rowband and broadband services from the outset. An example

of such a network with low penetrat ion is Poland. In general,

the existing copper access network plant in Poland has a low

penetration of about

20

percent with higher penetration found

only in large cities. The services required initially are plain old

telephony service (POTS), Internet access, and local area net-

work (LAN)-t o-LAN interconnect ions with evolution to

broadband services. Therefore, the new access network must

provide basic narrowband services at low cost and be upgrad-

able to provide full broadband services in the future. Since the

new infrastructure must be established for both narrowband

and broadband service, it favors deployment of fiber deeper

into the access network.

A

common requirement for both applications of the system

is that it must integrate synchronous and asynchronous ser-

vices. For economy the system must be designed for sharing

of resources in an environment where customer penetration is

low. Active electronics in the field must be kept at a mini-

mum. This favors the PON with long feeder length and wide

coverage. Some customers require protected routing which

the system must therefore be able to provide on an individual

basis according to demand.

The BBL network topology is shown in Fig. 1.This system is

based on a single fiber PON architecture [2] with a splitting

ratio of up to 16. The bandwidth capacity of the PON is 155

-..

.

Mbls bidirectionally in the basic version which can be gracefully

extended to provide 1Gb/s in the downstream direction and

576 Mb/s in the upstream direction. The PON consists of the

optical line terminal (OLT), a single fiber optical distribution

network (ODN), and up to 16 optical network units (ONUs) per

link. Multiple links are connected to a single subrack system. Cus-

tomers are connected directly to the ONUs or use a VDSL

modem in the final drop, depending on the application.

The BBL PON effectively integrates transport of syn-

chronous and asynchronous traffic in t he access network.

The switched network will continue to be a separate narrow-

band and asynchronous transfer mode (ATM) based broad-

band infrastructure for many years to come. Therefore,

separation and grooming of the synchronous and asyn-

chronous traffic is performed at the OLT at the access node.

In its simplest form, the OLT is a single module forming an

integrated part of the SDH network. Standard

S D H

virtual

contai ners with a 2

M bls

payload (VC12) are dropped

through the PON to the ONU. The ONU provides I nterna-

tional Telecommunication Union (1TU)-compliant

G.703/G.704 connections to a primary rate multiplexer with

narrowband service interfaces such

as

POTS or data line

cards. When cell-based broadband services arc requi red, an

ATM crossconnect module is installed in the OLT and ATM

service modules are installed in the ONUs.

n

important factor in addition to the requirements for low

initial installation and operational cost is the graceful migration

of the network as bandwidth demand increases. The BBL pro-

ject is pioneering subcarrier multiplexing technology applied

to PONs. This technology provides for a selective upgrade

path for customers requesting the upgrade and a robust, sim-

ple, bandwidth-efficient system which meets the requirements

for future commercial PONs. The subcarrier multiplexing con-

cept is explained in more detail in the fourth section.

The design and physical location of t he O NU is of key

IEEE

Communications Magazine December 1997

9




importance in obtaining a cost-

effective network. The different

ONU designs depicted in

Fig.

1

are all compact and versatile. The

ONUS illustrated are optimized for

the three scenarios of: new net-

works for business customer offices

where fiber is extended to the cus-

tomer premises; for broadband

upgrade of copper networks with

VDSL modems; and for new net-

works where installation in a

building is preferred. The ONU

provides a combination of inter-

faces and is shared by many cus-

tomers. The

ONU

design for

outdoor applications is made such

that expensive installation of new

street cabinets can be avoided if

buildings are not available. The

field trials have beeg designed to

demonstrate the features of these

scenarios.

VDSL modems are used to

connect the customers to the

Figure

2 . Bandwidth related tograde of service.

ON U via existing copper twisted pair s o r coax used for

CATV distribution. The bandwidth from t he O NU to the

customer varies between 12 Mbls and 51 Mb/s depending on

transmission distances, which range from

300

to 1500 m. In

the opposite direction of transmission; capacity varies

between 1.6 Mbls and 26 Mbls. Therefor e, cust omers

requesting high bandwidth have the ONU located close to or

at their premises, while customers requesting lower band-

width are connected through an ONU located more centrally

in the network where the cost of the ONU is shared by more

customers.

The frequency spectrum for VDSL [3] is designed such

that POTS or basic rate integrated services digital network

(BR-IS DN) may be provided on the same copper pair.

POTS or BR-ISDN users may be connected via passive fil-

ters between the O NU and customer. The initial version of

VDSL used in

BBL

is based on carrierless amplitude and

phase (CAP) modulation in the downstream direction and

quadrature phase shift keying (QPSK) modulation in the

upstream direction. This technology provides the lowest

cost and earliest commercial availability. The VDSL fre-

quency spectrum is limited to 30 MHz and permits VDSL

to

be combined with an analog CATV distribution system

on coax.

The selected broadband service interfaces for the customer

are ATM-25 and Ether net. ATM-25 provides transp arent

ATM transport to the customer premises equipment and is

recommended by the Full Service Access Network (FSAN)

group [4] Ethernet is widely available in personal computers

today and therefore allows for faster take-up of high-speed

Internet access.

he broa

video on demand (VOD) and high-speed Internet

access. To accurately estimate the correlation between

bandwidth demand on the system and the service quality

seen by the residential customers, the BBL project consor-

tium has developed a computer model and performed traf-

fic simulations to determine t he

project ed gra de of service

offered.

NETWORKODEL

A computer model based

on

the

ATM network depicted in Fig. 1

was used to est imate the band-

width demand to serve an area

with up to

500

residential cus-

tomers. The initial assumption

about services was that residen-

tial customers in the area would

receive VOD and high-speed

Interne t access. The VO D ser-

vice is assumed to be variable bit

rate and the Internet service to

be unspecified bit rate where no

service guarantee is given. Traf-

fic for residential customers will

mainly occur in the downstream

direction fro m network t o cus-

tomer. Upstream traffic consists

mainly of commands from t he

users

e . g . ,

to reauest a film or

download a file). Bandwidth requGementsL[5] of t he new

downstream services are expected to be megabits per sec-

ond. In the downstream direction the V OD peak bit rat e

and mean bit rate used are 6 and 4 Mbls. Internet access bit

rates used are 2 and 0.128 Mb/s. The VOD bandwidth val-

ues assume that Motion Picture Experts Gr oup type

2

(MPEG-2) coding is used. The allocation of upstream band-

width is assumed to be 128 kbls for the peak and mean rates

for both residential services.

NETWORK

IMENSIONING

The global bandwidth was est imated for the BBL network

with calculations based on varying values for service penetra-

tion (SP) (i.e., the population of users with access to the ser-

vices), as well as varying grade of service which quantifies the

probability that a given connection request finds all the net-

work resources occupied and therefore does not succeed. The

grade of service was calculated using the Erlang loss formula

[ 6] .The offered traffic for VOD and Internet access services

is (A

=

500*SP*BHCA*HT)based on the pair BHCA:

busy

hour call attempts, HT: holding time)

and is chosen to be

(0.03,

2 hr) and (0.2,

1

hr), respectively.

Figure 2 gives the estimated downstream bandwidth for the

VOD and Internet services for service penetrations of 5 and

50

percent (from a maximum Qf 500 potential users in the

area). Peak rate allocations only are shown for simplicity rea-

sons. The grade of service is varied and shown in a log scale.

As an example, the variable Internetjeak (5 percent penetra-

tion) gives the estimated bandwidth for the Internet service in

the downstream direction for a peak rate allocation and 5 per-

cent

SP.

Figure 2 indicates that even for reasonably high ser-

vice penetrations the bandwidth requirement remains

moderate. The bandwidth variation with varying grade of ser-

vice is demonstrated to be relatively small.

The results of the model have helped to determine the

estimated bandwidth requirements and grade of service for an

ONU having a number x

=

1,

...,

32) of users. An ON U

providing the VOD service would require, for a grade of ser-

vice = 10 percent, between

6

Mbls and 24 Mbls in the down-

stream direction. The bandwidth estimation for the ONU is

based on the different number of users given above and a

peak rate allocation.

9

IEEE

Communications

Magazine *

December 1997




OPTICAL RANSPORT

YSTEM

\

I

/

he optical transport system between the OL T and the

TONUs must

be

designed to accommodate both narrow-

band and broadband services, and circuit-based and packet

traffic over a point-to-multipoint PON. Infrastructure cost

must be kept low and closely connected to th e service

requirements. New network deployments will ofte n be

based on narrowband POTS with initial low penetration.

The networ k must be cost-effective in this scenario but

upgradable as the demand for services increases. The

upgrade must be accomplished with a minimum of, prefer-

ably no, disruption to customer service. The bandwidth effi-

ciency, which is the ratio between the bandwidth required

for transportation of the payload (including overheads) and

the available bandwidth, must be high. To keep the installa-

tion and maintenance costs low, the system must be simple

and insensitive to the performance of the optical network

in the outside plant.

MULTIPLEXING

In BBL, subcarrier multiple access (SCMA) technology

[7]

has been chosen as the method to transmit from individual

ONUs to the OLT (multipoint-to-point) direction. With

SCMA one or more electrical subcarriers are assigned to each

ONU. In t he OLT th e traffic from the individual ONU s is

selected via electrical filters. SCMA has been proven to be

robust and simple in operational field trials [7,

81.

It allows

optimization of the ONU, with respect to processing power

and operational speed, in line with the capacity of the individ-

ual subcarrier, not the entire PON bandwidth. Additionally,

SCMA eliminates the ranging issues commonly found in time-

division-multiple-access-based PON systems. This issue is par-

ticularly important when protected redundant routing must be

provided. SCMA allows for fast resynchronization in case of

switchover to an alternative route.

The basic optical system provides a total of 9.72 Mb/s of

upstream capacity on a narrowband subcarrier for each ONU.

In addition, a subcarrier-based bandwidth upgrade will be

demonstrated providing extra upstream capacity of

51

Mb/s

on a broadband subcarrier per ONU. In th e direction from

the OLT t o the ONU , broadcast baseband transmission is

chosen for the basic system with a transmission speed of 155

Mb/s. Upgrade to higher bandwidths will also

be

possible

through the addition of extra subcarriers, each with a capacity

of 51 Mb/s. This will allow capacity upgrade on a selective

basis without widening the operating window of all ONUs.

Figure 3 illustrates the principle of carriers with different

capacity terminat ed in ei ther narrowband or broadband

ONUs. Broadband subcarriers can be added on an individual

basis without interrupting service from other ONUs. The

SCMA technology also allows ONUs to be connected and dis-

I

OLT

I

Year

OLT I-&-

Customers

f t b

SDH>

Customers

I

-. .

~. i

W

Figure 3

Illustration of broadband upgrade

of

an

ONU

and

insertion o

a

new ONU

in

an operating

PON

connected from the optical distribution network without dis-

turbing other ONUs.

ATM has been selected as the key multiplexing technique

for broadband service transmission in the time domain trans-

ported within different subcarriers. The use of ATM provides

the flexibility required for full-service integrat ion. It enables

both static time-division multiplexing (TDM), via an emula-

tion protocol, and sta tistical multiplexing, which will make

low-cost data communication possible for applications such as

residential user connectivity over the Internet.

OPTICAL ESIGN ONSIDERATIONS

The BBL PON benefits from single-fiber working. This is

fast becoming a network operato r preference, since it saves

on optica l fiber outlay and hence simplifies fiber handling.

Loo p length s below 20

km

are considered, and optical

amplifiers will not be us ed in t he system. Optical wave-

length-division multiplexing (WDM) provides a clear sepa-

ration of downstream and upst ream transmissions, which

are carried on 1550 and 1310 nm, respectively. This enables

reuse of electrical frequency bands in bot h transmission

directions. The required laser modulation bandwidth is

therefore reduced, which enables low-cost laser technology

to be used.

In BBL the key optical component is an integra ted optical

transceiver containing a Fabry-Perot laser diode, a PIN photodi-

ode, and an optical WDM to separate 1550 and 1310 nm chan-

nels. Furthermore, an additional optical filter is incorporated to

keep optical crosstalk as low as

-50

dB. The O NU opto-

transceiver is a commercially available

component developed for digital appli-

cations, enabling the BBL system to

benefit from its low mice.

~

i

- - -

As indicated in Fig. 4 the BBL sys-

. .

6

'

tem is based on SCMA. Downstream

every ONU accesses an STM-1 base-

band signal on a TDM basis and may

furthermore have access

to

a broad-

band subcarrier channel. Upstream a

Optics based on Optics based on narrowband or broadband subcarrier

is allocated to each ONU . All chan-

nels are designed, with regard to

i

.

power budgets, to meet a bit error

Figure 4.

BBL PON based

on

subcarrier upgrade both up- and downstream

by tak-

ONU I

:

t

optotransceiver

iscrete elements

rate which is better than

IEEE Communications Magazine

December

1997

91




ing into account link losses in the interval

10-25 dB and at the same time obtaining

sufficient signal-to-noise ratios, when con-

sidering the relative intensity noise (RIN),

shot noise, thermal noise, and optical

beat noise (see below). In addition, a 3

dB implementation margin is incorporat-

ed. In order to limit the t otal bandwidth

capacity in the system an efficient

1

Hz/l

b/s modulation scheme is used for all

sub-

carrier channels.

In a multicarrier system, with a total

frequency plan covering more than one

octave, ONU laser nonlinearity must be

kept below a certain level because inter-

modulation products within information

bands cannot be avoided. To ensure low

intermodulation distortion arising from

laser modulation, the lasers are not mod-

ulated near their threshold currents. This

complicates the equalization of the sub-

carriers at the OLT, but is necessary to

obtain a dense subcarrier frequency plan,

limit the total bandwidth, and avoid chan-

nel interference. The

ONU

transmitter is

Cusl;mer

ccess

point Flcxiblity po int

1

Flexibility point 2

2. PON 1:16)+

VDSL

(Downstrmm26 M ~ / s

:FON 1:16)+

VDil

(Dowrstieam SI Mb/s

I:?st:?xn

1.6

MWs)

4: ?ON 1: 6

i

I

5: PON (~5 4

Access point Typidy ?

OC0 to

i O i j 0 0 hotrie5

pzss.-tl

1 3CO i r i fr:m i:icLo*:irr

Flexibility point

l : - p ~ ~ ~ ~ ~ ~

00 to 200 huinrs pi,ved:

500 in

froi:i r.u>.oin?r

Flexibility point 2:

Tyypice

~v

io

60

homes p e , s d I n n

71

iorri CUST071211

STM: STMI interfacc to core

SDH

inemul-k

A- M: ATM ciosrco me3

ADSL: Asymmetric diyit al s ubsci ilrr line

VDSL Veiy high-rat? digiidl 5ubscrii-;dr L i?

OLM: Optical line nodde

ONM: Optical network inodul?

ATM25:

ATM

UN1 with

25

Mbs trdiistrii>sirin 6 I e

-

-. ..

W

Figure

5 . ife cycle cost scenarios.

able to automatically adapt to a differential link loss of 15

dB in the PON. This is achieved through a number of mech-

anisms, one of which involves keeping the mean laser optical

output power inversely adjusted

to

the mean received optical

power. However, the 15 dB dynamic range cannot be cov-

ered solely in the DC domain without modulating the laser

close to threshold. Consequently, regulation of the modula-

tion index is included in the equalization process to obtain

the required dynamic range.

When designing a laser driver, cost and power consump-

tion can be reduced by avoiding the use of Peltier coolers to

maintain constant laser temperature. Consequently, the design

of the BBL ONU has allowed for lasers with fluctuating tem-

perature and hence varying light current characteristics. The

driver automatically adapts

to

temperature changes by use of

an onboard temperature sensor.

In subcarrier multiple access systems the headend receiver

is simultaneously illuminated by n optical signals. The noise

level experienced by an individual channel is affected by the

RIN from all the ONU lasers. This is due to the fact that the

RIN level in the OLT receiver depends on the total incoming

light level, and high RIN levels could potentially limit the sys-

tem performance. The laser in the transceiver has been char-

acterized with respect to RIN to verify that the bit error rate

can be kept below the design level even at worst-case combi-

nation of the link losses.

Subcarrier multiple access PONS potentially suffer from

optical beat noise that may degrade the optical transmission

performance. Opt ica l

bea t

noise arises when the optical

spectra of two or more lasers, illuminating the OLT optical

receiver, overlap. The level of optical beat noise depends on

the distribution of the optical wavelengths of the ONU

lasers; consequently, the optical beat noise level fluctuates

with time and temperature. This can lead to a momentary

increase of bit error rate. The PON system is designed to be

resilient

to

this phenomenon. The optical beat noise level is

supervised at the OLT, and in case of an increased level the

wavelengths of a number of ONU lasers will be fractionally

adjusted under the control of embedded software, until an

acceptable noise level is reestablished. By this control

method the bit error rate is kept below the design level

given above.

TECHNICALCONOMIC COMPARISON

OF

DEPLOY

ENT SCHEMES

ife-cycle cost studies in the BBL project have compared the

6 ost for deployment of five different access networks over a

span of 10 years assuming a certain development in service

demand and number of customers connected to the system.

Customers are predominantly residential. The life-cycle cost

includes accumulated investment and operation, maintenance,

and administration costs.

The assumption behind the study was that a telephone net-

work with a penetration

of 95

percent would be available. It was

also assumed that the number of customers connected to broad-

band services would increase linearly from none at the beginning

of year

0

to a penetration of either

20

or 40 percent connected

after 10 years. The five scenarios (Fig. 5) compared were:

1 Asynchronous DSL (ADSL) from the access point to the

customer.

2) PON with split ratio 1:16 from the access point

to

flexibility

point 1and VDSL from flexibility point 1 o the customer

3)

PON with split ratio 1:16 from the access point to flexibility

point 2 and VDSL from flexibility point 2 to the customer

4)PO N with split ratio 1:16 from the access point to the

customer

5)PON with split ratio 1: 64 from the access point to the

customer

The ADSL technology has the advantage that existing cop-

per can be used from the access point to the customer; there-

fore, for initial broadband service deployment fiber is n o t

required. However, the bandwidth may not be sufficient for

future demand.

With the assumptions made about relatively

low

bandwidth

requirements and customer penetration evolving to 20 per-

cent, the most cost-effective method is scenario

1.

For this

application, ADSL will require very little new investment in

infrastructure. If the number of customers connected

to

the

network increases to 40 percent, the difference between sce-

nario 1 and scenario 2 is .relatively small when viewed over 10

years. Scenario 5 showed a marginally lower cost than sce-

nario 4. However, a splitting ratio of 1:64 would limit the flex-

ibility of the network design.

92

IEEE Communicat ions

Magazine December

1997




The choice of scenario will depend on expectations for devel-

opment in services. Providing severalT V channels simultaneous-

ly, for instance, may require the bandwidth

VDSL

can provide.

An operator may also,

for

strategic reasons, want to penetrate

fiber deeper into the access network for future growth.

Civil engineering work and installation of cabinets and

powering contributes the most significant portion of first

installed cost in all cases. It was found that the cost for churn

(connection and disconnection

of

customers) also contributed

significantly to the cost over 10 years. Centralized manage-

ment is expected to reduce life-cycle cost in favor of scenario

4 and scenario 5.

A similar study was performed for a residential ar ea in

Poland where li ttle existing telephony infrast ructure exists.

The results from this study show that the fiber-intensive sce-

narios 3 and 4 provide the lowest costs when considering the

increasing broadband service demand assumed for the west-

ern European partners.

FIELD

TRIALS

nstalling and evaluating trials in three different countries

IPoland, Denmark, and Portugal -will give important infor-

mation about actual availability of existing network resources

for broadband transmission and design of access networks for

implementation as an overlay to legacy networks and for

installation in green field areas. A field trial installed in

Aveiro, Portugal, in

1995

by the RACE project FIRST

[7 81

demonstrated the design of a simple, low-cost, robust P O N

system. This was based on subcarrier multiplexing technology

for upstream transmission between the ONUSand the OLT.

This trial is still in operation, providing

50

users with narrow-

band services.

The new trials under ACTS will evaluate the trade-off

between the use of optical technologies and of VDSL over coax

or twisted pairs. The objective is to demonstrate that PONs can

provide

a

low-cost entry solution which evolves as bandwidth

demand increases by evaluating the cost of fiber deployment

versus that of upgrading the existing copper network. Opera-

tional issues to be studied are the number of cable pairs that

can be used for broadban d transmission, range of

VDSL,

influence of cable age, influence of external noise, and t he

electromagnetic emission problems

VDSL

may cause.

Results expected from the trials will generate dimensioning

rules for the access network, informat ion about optimal

design of hybrid access networks, and improved definition and

understanding of usage profiles for broadband services.

CONCLUSION

n this article we discuss what we consider t o be t he most

l

mportant issues for evolution to a broadband access network

and how the Broadbandloop project is supporting the evolution.

The preliminary conclusions are that upgrade of the old copper

network to provide broadband transmission is a viable strategy

in the near term. The PON is cost effective in greenfield areas

and must provide low-cost telephony and evolution capability

to broadband services. The Broadbandloop project is develop-

ing and demonstrating new optical technologies which are

improving reliability and cost effectiveness of PONs.

ACKNOWLEDGMENTS

We would like to acknowledge the ACTS program and th e

parent organizations involved in the project for their support

in terms of funding, technologies, infrastructure, network

users, and logistics, which all together make it possible

to

carry out the Broadbandloop project.

RE ERENCES

[

]

Europe an Com mission, ”ACTS ’96, Advanced Communications Technolo-

gies and Services, Project Summaries,” Sept. 1996.

[2] N. E. Andersen, “Optimising Access Network Architectures, Comparing

PONS w it h Alternat ive Techno logies,” I IR Conf. , Londo n, U.K., July

[3]G. T. Hawley, ”System Co nsiderations fo r the Use of xDSL Technolog y for

Data Access,”

/€E€

Commun., vol.

35,

no.

3,

Mar.

1997,

pp.

56-60.

[41 ”Full

Service Access Network-GX, Network Termination-Home Network,

Functional requirements,“ 8th Int‘l. Wksp. OpticaVHybrid Access Net-

works, Atlanta, CA, Mar.

1997.

[5] E. Jaunart a nd P. Crahay, “ATM Super PON Dimensioning for Future

Resident ial and Business Demand,” Broa dba nd Superhighwa y, D. W.

Faulkner and A. L. Harmer, Eds., EFOVLAN

1996.

[61

H. Saito, Teletraffic Technologies

in A T M

Networks, Artech House, 1994.

[7] D. E. A. Clarke,

R.

Mudhar, and A. Purser,” A European Initiative Lead-

in g towa rds a Practical Customer Access Link Using Fibre,” BT Tech.

J.

vol. 11, no. 1 Jan. 1993.

[8]

P. Woolnough BTetal. , RACE

R2014

FIRST, del.

1011,

”Final Studies,

Evaluat ion and Recom mendations (contact Niels Engell Andersen a t e-

mail address below for a copy).

15-1 6, 1996.

BIOGRAPHIES

NIELS NGELL [email protected]) received an M.Sc. degree from

Georgia Inst itute of Technology in

1978. He

has worked for dif ferent pri-

vate companies ondevelopment and implementat ion o f advanced cont ro l

and comm unications systems. Since

1989

he has been wit h DSC Communi-

cat ions

A S

(formerly NKT Elektronik), whe re he

is

manager for develop-

me nt of access technologies and field trials.

PAULO

M. N. [email protected]) received an M.

Sc.

degree from Essex

University in electrical engineering in 1980 and CEPAC from Universite‘ Libre

de Bruxelles in

1989.

He has been head o f th e Traffic Engineering Department

at CET in Aveiro and m embe r of scientific sta ff in DGXIII-F in the European

Union. He

is

a m ember of the board o f MEGASIS, president of the General

Assembly of th e Portug uese Electrotechnical Institu te (IEP), representative of

Portugal Telecom in the General Assembly of Eurescom, and membe r o f the

board of INESCTEL.

A. MANUELE OLIVEIRA [email protected]) received a “Licen-

ciatura” degree in electrical engineering fro m th e University o f Coimbra in

1976, and M.Sc. and Ph.D. degrees in telecomm unica t ions systems and

electrical engine ering sciences, respect ively, in 1981 and 1984 f r o m t h e

University

of

Essex, U.K. He joine d t he University o f Aveiro

in 1978

were he

i s

n o w a n a s s o ci a te p r o f e s s o r i n t h e D e p a r t m e n t of Elec t ron i cs and

Telecommunications.

HANS

RIK

LASSEN eceived ([email protected]) M.Sc. and Ph.D. degrees from the

Electromagnetics Inst itute at the Technical University of Denmark in 1984

and 1991, respectively. From 1986 t o 1988 he was assistant professor with

the Electromagnetics Institute. From

1988

he has been with Tele Danma rk

Research

ANOERS

KBLAO

(anders.l .ekblad@tel ia.se) received his Master’s degree in

electrical engineering fr om Chalmers University of Technology, Gothen burg,

Sweden,

in 1988.

He has been employed at the Networks Division of Telia

AB since

1988.He

is no w engaged in Telia’s strategic dev elopme nt of the

broadband access netwo rk . In former pos i t ions he was engaged in the

development o f opt ical f iber cables and ou ts ide plant in which he holds

several pa tents.

ANDRZEJ. PACH ([email protected]) received an M.S. degree in electrical

engineering and a Ph.D. degree in telecommunications fro m the University

of

Mini ng and M etallurgy, Cracow, Poland, in 1976 and 1979, respectively, and

a Ph.D. Hab. in telecommunicat ions and compu ter networks from the War-

saw University of Technology in

1989.

In

1979,

he joined the Telecommuni-

cations Department at the University of Mining and Metallurgy, where he

is

currently a professor.

[email protected]. tpsa.pl) received an M.Sc.degree from

Warsaw Technical Univers i ty in te lecommun icat ion in

1964,

an M. A. i n

1971 f rom the Univers ity of Warsaw in mathematics, and a Ph.D. in 1972

fro m Warsaw Technical University. Since 1965 he has been assistant profes-

sor at W arsaw Technical University. In

1994 he

was appointed

expert for

Telekomunikacja Polska S.A.

[email protected]) (MSc. 1988, Ph.D. 1995) s assistant profes-

sor at th e Cen ter for B roadband Telecommunications (CBT/EMI) at th e Tech-

nical Univers i ty of Denmark wi th respons ib i l i t y for ATM swi tching and

netw orkin g activities. His current interest is resource management, and the

implications for network design and requirements for network elements.

IEEE

Communications Magazine Decem ber 1997

9

andersen duarte et ali ieee commag 1997

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