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1

Hierarchy and dynamics of optical networks.

F.-Joachim Westphal(1), Andreas Gladisch(1), Matthias Gunkel(2)

(1) Deutsche Telekom AG, Laboratories(2) Deutsche Telekom Netzproduktion GmbH

2Deutsche Telekom Laboratories

Source: Odlyzko et al: http://www.dtc.umn.edu/mints/2002-2008/analysis-2002-2008.html

1E+00

1E+01

1E+02

1E+03

1E+04

1E+05

1E+06

1E+07

1E+08

1980 1990 2000 2010 2020year

Dat

a Tr

affic

(PBy

te/m

onth

)

Extrapolation

MINTS low WW

MINTS high WW

Cisco WW

MINTS low US

MINTS high US

Cisco US

2 dB/year

Introduction.The Internet traffic growth.

Worldwide annual Internet traffic growth rate: 50-60%


Outline.

IntroductionBasics of OTN evolution and effects on networksOTN functionsOptical network elementsGeneric hierarchical optical transport architectureTraffic demand forecast and types of servicesWhere to locate configurable optical network elementsConclusions

IntroductionBasics of OTN evolution and effects on networksOTN functionsOptical network elementsGeneric hierarchical optical transport architectureTraffic demand forecast and types of servicesWhere to locate configurable optical network elementsConclusions

Deutsche Telekom Laboratories

Set of WDM / OTN point to point Remote configurable on L-ODU & H-ODU

Introduction.Evolution of optical networks.

OTNOTNEvolutionEvolution

Auto. bandwidth dedication OTN NE:DWDM OTN system; ROADMelectronic XC; L2 integration

Concentrate on optics only in this presentation.


Some effects of optics, WDM and OTN on network architecture.

Distance and bandwidth is key, optics relaxed restrictions on transmission distances and has a reasonable cost pointStructural change

Regenerator less transmissionAllows to expand access Allows to reduce number of sites

Costs of transmission has declined for yearsRethinking about functional and topology split of aggregation - backbone


Cost improvement of optical transport.

Backbone DWDM per-bit, per-km cost improvements over time

Ovum

Beside technical advantages optical transport has well improved in cost over the years.


Optics in access / aggregation.

Reductions of number of sites by a order of magnitude.

Examples of planed reduction of number of sites: BT in UK & DT in Germany


Multiplex. / switching levels of OTN Flexible switching of OTN

OTN: Transparent, flexible structure of λ and sub-wavelength.Sub-wavelength: L-ODU; wavelength: H-ODU.

L1 clients(CBR)

sub-wavelengthLower Order ODU

OTU2(e)

OTU1

ODU2(e)

1x

OTU4ODU4

OTU3(e)ODU3(e)

100 Gbit/s

40 Gbit/s

1x

10 Gbit/s

1x

2.5 Gbit/s

ODU1

1x

ODUflexnx1.25G

1x

1x

1x

1x

wavelength / OTU / higher order ODU

1 GE

10 GE

L1 any bitrate

100 GE

ODU01.25 Gbit/s

ODU2e

L-ODU

L-ODUOADM

1 GE

1 GE

H-ODU

L-ODU (n x 1,25 Gbit/s)

λ

OADM

H-ODU

λ

L-ODUH-ODU

λ

Multiplexing

Switching

OTN: Two flexible and independent level of switching and multiplexing.


Types of optical add/drop multiplex. Principle of multi-degree ROADM

Key for switching on wavelength level: Different types of OADMs.

FOADMs & ROADMs come with quite different price tags.

FOADM

WSS

WSS

WSSWSS

Line Line

Line

Line

Local

Local Local

LocalAdd/drop of fixed configured λ

Fibers in 2 directions

Add/drop of remotely configurable λ

Fibers in up to 8 directions

ROADM

Multi-degreeROADM


Generic architecture.

Generic hierarchical optical transport architecture

OTN Core

OTN RegioAccess

Access

OTN Regio

Two architecture/hierarchy variations:1. Two levels of hierarchy: Partly meshed

core interconnects metro/regiodomains based on ring topology

2. Flat architecture without hierarchies. Maybe subdivided in different optical domains

Study based on first variation: Maybe more suitable for large national footprint and dominance of IP broadband services.


Traffic demand.

0%

100%

200%

300%

400%

500%

2010 2011 2012 2013 2014 2015 2016 2017

Traffic demand forecast on national infrastructure

Generic traffic demand forecast, has to be detailed concerning mix of services.


Types of services / service-bundles.

Classical set of service / service-bundles of incumbent operator

Types of services grouped in IP/xDSL/FTTX and leased line / VPN based services.

IP/xDSL/FTTx based services:Double/Triple Play(incl. video; video on demand)Internet accessL3-VPNIP-TransitIP-Wholesale

Ethernet based services:Bitstream AccessEthernet Link p2p (leased lines)L2 VPN p2mp

SubstitutionLayer-1:

Leased Lines (SDH based)Leased Lines (OTN/ WDM based)

Any-to-any geographic distribution

Any-to-any geographic distribution

IP backhauling, centrallized service creation,

fixed, tree-like logical topology to IP/MPLS edge

IP backhauling, centrallized service creation,

fixed, tree-like logical topology to IP/MPLS edge


Split of different types of traffic.

0%

100%

200%

300%

400%

500%

2010 2011 2012 2013 2014 2015 2016 2017

Traffic demand forecast on national infrastructure

Majority of traffic has to follow fixed configured aggregation path to IP/MPLS edge devises.

Leased lines and L2 VPN are 20-30% of the traffic volume only.

Majority of traffic is residential IP, it will not benefit from flexible configuration

of optical layer in the aggregation.

Leased lines and L2 VPN are 20-30% of the traffic volume only.

Majority of traffic is residential IP, it will not benefit from flexible configuration

of optical layer in the aggregation.


Geographical distribution of leased line traffic (I).

Statistics of traffic distribution based on deployed Ethernet services

Only 20-30% of all leased lines are inter-regional.⇒ Traffic which benefits from configuration in the core of the network is further reduced.

OTN Core

OTN Regio

100%within access zone: 30%

within region:40-50%

inter-regional: 20-30%

Non-linear distribution of LL distance: Mainly very short and very long distances.⇒ Variation of core or regional diameter

has minor influence on distribution only.


Geographical distribution of leased line traffic (II).

Distribution of source/sink-sites based on deployed Ethernet services

5% of all sites (mostly inter-regional sites) are responsible for 50% of all leased lines.Concentrate flexible configuration on these sites might help to minimize investment.

0%

20%

40%

60%

80%

100%

0% 20% 40% 60% 80%Number of Locations

Leas

ed L

ines

Dem

and


Potential locations of flexible optical switching node. (MD-)ROADM.

Two-2 or multi-degree optical switching node at various locations?

OTN Core

OTN RegioAccess

Access

OTN Regio

(MD-)ROADMs allow to (re-)configure network from a centralized management center.

1

2

2

23

4

4


OTN in metro / regio.

Comparison of one fiber per demand, OTN p-t-p system and OTN ring

In many cases OTN rings will make sense for national networks in Europe and traffic demands of the next years.

OTN-systems are great in saving fiber-resources OTN p-t-p may save CapEx compared to OTN-ring in case of very high demandsCash-out tradeoff in-between OTN p-t-p and OTN-ring influenced by:

OTN-systems are great in saving fiber-resources OTN p-t-p may save CapEx compared to OTN-ring in case of very high demandsCash-out tradeoff in-between OTN p-t-p and OTN-ring influenced by:

longer distance aggregation site - hub

higher number of optical channels per OTN-systemOTN-ring

OTN p-t-psystem

Higher bitrate per channel

Increasing demand per site


OTN in metro / regio.Example of CapEx comparison

Comparison of OTN p-t-p system, FOADM based OTN ring, ROADM based OTN ring

Taking today’s price tags into account, ROADM based rings are more expensive as FOADM based rings, but will outperform OTN p-t-p solutions.

Calculation based on simplified ring model using parameters of DT national infrastructure and commercial available OTN systems.Calculation based on simplified ring model using parameters of DT national infrastructure and commercial available OTN systems.

900 sites aggregated towards 24 core PoPs

protected 10G demands per site

kum

mul

ativ

eC

apEx

2 4 6 8 10 12 14

OTN p-t-p system

ROADM based ring

FOADM based ring


OTN in metro/ regio.OpEx parameters

Comparison of FOADM based OTN ring, ROADM based OTN ring

Separate work in central network management center and work in the field, traveling cost have major impact.

Central network management center

Work in the field

Central network management center

Work in the field

network management & planingBasic

InstallationPort

InstallationBasic

InstallationPort

Installationplaning & installation OTN-equipment X Xproduktinstallation OTN X Xproduktinstallation THS X Xautom. Configuration Xverification NE and ports X X X

manual work in the fieldtraveling basic installation X Xtraveling port installation Xtravelling fiber patch X XInstallation ET, OLA, FOADM XInstallation ROADM XInstallation transponder Xinstallation transponder Xpatching fiber X X X

Ring FOADM Ring ROADM


OTN in metro/ regio.OpEx


ROADM based rings will save OpEx compared to FOADM based ones. Savings will increase with increasing churn rate.

Churnrate: 50% of ports 10x reconfigured

protected 10G demands per site0 2 4 6 8 10 12 14

Ope

x

FOADM

ROADM

Δ without churn

Δ With churn


OTN in metro/ regio.Kumulative CapEx and OpEx


To reduce OpEx, a lot of additional CapEx has to be spend for ROADMs.

protected 10G demands per site

Δ

Δ

2 4 6 8 10 12 14

kum

ulat

ive

Cap

Ex

/ OpE

x

FOADM

ROADM

Capex

Opex


Where to place (MD-)ROADMs?

Placement of (MD-)ROADMs in regio and core

(MD-)ROADMs are more suitable within the (core) network, but less at the edge.

1. Within coreAll partial meshed nodes

2. Regio - coreAll regio – core nodes

3. Multi-ring aggregation in regioDepending on demandDepending on individual regio-topology

4. Access – regioOnly if high density of leased line demands, but individual manual configuration needed in most casesNot needed for residential IP backhauling

OTN Core

OTN RegioAccess

Access

OTN Regio

1

2

2

23

4

4?

?


Conclusion

OTN allows flexible implementation of multiplexing and switching functions on wavelength and sub-wavelength level (and integration of L2 functions).Optical OTN functions and network elements allow reasonable priced transport of growing demands.OTN relaxed restrictions on transmission distances and enables concepts to reduce number of sites.Traffic demand forecast indicates continues growth of traffic volume, mainly drive by residential IP services.Only leased line and L2 VPN types of services can really benefit from flexible reconfigurable wavelengths, but those services are the minority of overall traffic demand.Today’s price difference in-between ROADMs and FOADMs can’t be overcompensated by OPEX reduction.Placement of (MD-)ROADMs within the (core-)network more suitable, as at the edge of the aggregation.

OTN allows flexible implementation of multiplexing and switching functions on wavelength and sub-wavelength level (and integration of L2 functions).Optical OTN functions and network elements allow reasonable priced transport of growing demands.OTN relaxed restrictions on transmission distances and enables concepts to reduce number of sites.Traffic demand forecast indicates continues growth of traffic volume, mainly drive by residential IP services.Only leased line and L2 VPN types of services can really benefit from flexible reconfigurable wavelengths, but those services are the minority of overall traffic demand.Today’s price difference in-between ROADMs and FOADMs can’t be overcompensated by OPEX reduction.Placement of (MD-)ROADMs within the (core-)network more suitable, as at the edge of the aggregation.

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Thank you for your attention!F.-J. Westphal (1), A. Gladisch (1), M. Gunkel (2)

(1) Deutsche Telekom AG, LaboratoriesGoslarer Ufer 35, 10589 Berlin, Germany

(2) Deutsche Telekom Netzproduktion [email protected]

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