Optical Transport Network Switching

8/13/2019 Optical Transport Network Switching

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Optical Transport Network Switching:Creating efficient and cost-effective

optical transport networks

White Paper


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OTN switching: Creating efficient and cost-effective optical transport networks2

1.0 Executive summary:

Building for the future with optical transport networks

2.0 Trends in optical networking

Almost every day, headlines in the

communications media highlight the

phenomenal growth in data traffic

that networks across the world are

experiencing. The vast majority of this

growth is being driven by bandwidth-

hungry IP/Ethernet applications in both

private and corporate users. These

applications include VPN services,SAN networks, Internet browsing,

peer-to-peer video distribution, IPTV

and video on demand. As opposed to

the Internet and data applications of

the past which required only best effort

traffic, these new real-time services

require not only high bandwidth, but

also high availability, low latency, no

jitter and high Quality of Service (QoS).

While fixed lines will continue to carry

the majority of this traffic, mobile traffic

is set for a period of massive growth,

far exceeding anything that has gonebefore. This represents a major

opportunity for communications service

providers (CSP). The convergence of

fixed and mobile networks means that

this growth will drive traffic in every

network, placing new demands on the

2.1 Network evolution

Forecasters predict that consumer

Internet traffic will grow from over 10

Petabytes per month in 2010 to more

than 40 PB/month in 2014. Whats

more, this estimate could be blown out

transport core networks serving both

fixed and mobile customers.

These requirements will dramatically

change the structure of tomorrows

networks as their architecture shifts

from being PDH/SDH-based, originally

designed to support only voice, to

being packet based. Core networkswill have to cope with added traffic

demand, while metro and access

networks will need enhanced capacity

and changed interfaces to cope with

the new mix of data and legacy traffic.

The most effective solution for meeting

these challenges is implementing a

Packet Optical Transport Network

(POTN) with DWDM technology for

transport and cross connects for traffic

switching at the level of ODUs (Optical

Data Units). This OTN switching

concept forms a vital part of convergedoptical networks of the future.

OTN switches provide efficient

grooming of the optical signal on a

sub-wavelength level. This increases

the network efficiency by enabling

of the water by disruptive changes in

services or customer behavior, such

as the rapid rise of 3DTV. Meanwhile,

enterprise customers are pushing up

traffic volumes by relying increasingly

on cloud services to deliver their

business support systems.

more effective use of bandwidth.

In a mixed network that carries TDM

and Ethernet traffic.

OTN switches can switch data of any

format. OTN switches also provide

the most cost-effective way to offload

traffic from the IP network layer, thus

minimizing the amount of traffic handledby routers and enabling smaller and

less costly routers to be used.

There are many other benefits

available from deploying OTN

technology. These include support

of Operations, Administration and

Maintenance (OAM) features such as

fast end-to-end service provisioning

and rapid restoration. Furthermore,

a converged optical network is open

to being operated under a single

management system to achieve the

lowest overall costs. Together withthe adoption of mesh network topology

for the highest network availability,

extreme scalability and easy

implementation of new traffic types, it

effectively makes network investments

future proof.

The nature of traffic is changing too,

from merely browsing web pages

to real-time, high-bandwidth and

interactive applications that require

minimum loading and response times.

IP services are increasingly dominant.

Consumers and business users

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3OTN switching: Creating efficient and cost-effective optical transport networks

demand fast access to services, with

high QoS. Yet intense competitive

market pressures mean that they needpay little extra, or even nothing extra,

for ever-greater performance and

enhanced service capabilities.

It all adds up to a challenge for CSPs,

who face growing demand for network

capacity and quality at the same time

that the price they can typically charge

for each bit is flat or dropping. Driving

down the cost per bit is, in the majority

of cases, the most critical issue,

encouraging many CSPs to seek out

new ways to maximize the flexibility

and efficiency of their networks.Another key priority is to deliver a

great customer experience, and that

demands the network functionality to

provide end-to-end QoS and high

network availability.

Over recent years, many CSPs

have addressed the need for greater

network efficiency, for example,with the introduction of multi-service

provisioning platform (MSPP)

technology around a decade ago and

the convergence of IP and DWDM

roughly five years later. More recent

network evolution has removed

complexity and has broadly taken

place in two distinct steps.

First, the reduction and removal of

ATM and SDH traffic was achieved by

transporting traffic directly over the

DWDM layer. Then, these DWDM

networks were upgraded with theintroduction of multi-degree ROADM

nodes for switching optical traffic,

together with more transmission line

capacity and colored OTN interfaces

for traffic from the IP layer.

However, this process creates some

issues. For instance, theres the

question of multi-vendor compatibilityduring interworking, as well as the

complexity and time required to provide

network resilience in the optical layer

and the increased complexity and cost

when scaling the IP layer. The focus for

the most recent step in this evolution is

therefore a shift to promote greater

efficiency, scalability and functionality.

This can be achieved by introducing the

OTN concept as an intermediate layer

between the IP and the DWDM layers.

The key benefits arise from

implementing OTN switching at thecross-connects. This adds new value

to the network and promotes significant

CAPEX and OPEX savings. OTN

switching enables traffic in transit to

bypass many of the networks IP layer

main volume expectedin 2012 and further

IP

OTN

10G/40G/100G

DWDM (PXC)

Addressing IP over DWDM approach challenges

Multi-vendor compatibility at DWDM layer (transponder

interworking, optical performance)

High optical restoration switching time IP layer scalability (complexity and cost grows exponentially)

Addressing IP over DWDM approach challenges

Sub-lambda grooming for efficient pipe filling

IP traffic offload / optical bypassing

End-to-end networking (high-capacity & multi-service switch,

with simple OAM)

Intelligent management and carrier class network protection

Reduced power consumption and space requirement

Figure 1: Enhancing the network by introducing the OTN layer

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routers and thus reduces the amount

of expensive router capacity required.

It also provides efficient grooming ofthe optical signal on a sub-wavelength

level, which enables traffic to fill the

available DWDM bandwidth more

efficiently. This effectively minimizes

the capacity needed to carry a given

volume of traffic.

2.2 What is OTN switching?

OTN provides service-agnostic

switching that maps different client

services into ODU frames and then

switches them at that level. The actual

process of OTN switching handlesone or more ODU frames by bundling

them together in a new ODU packet.

This digital wrapper approach

encapsulates diverse data frames

from different sources together in asingle entity, regardless of their native

protocol, so they can be managed

more easily. The concept was first

described in ITU-T G.709.

The ODU concept has frames with fixed

size and uses bit rates ranging from 1G

to 100G to match interfaces for a range

of standards, including Ethernet, SDH/

SONET and others. The OTN switches

are also simple to manage, with SDH-

like operations and maintenance.

OTN delivers the key network functionsneeded to support high-quality end-

user services as flexibly and efficiently

as possible throughout the different

network domains. In the core networkit offers high-capacity networking

and rapid restoration, while the metro

network benefits from service-agnostic

aggregation and grooming. Users can

enjoy cost-efficient delivery of multiple

services in the access network, as well

as benefiting from the service quality

that can only be provided with end-to-

end networking and provisioning.

The following chapters discuss the

technology and architecture that

underpins OTN switching. Well also

consider what potential benefits OTNswitching promises to deliver to CSPs.

3.0 OTN technology overview

3.1 The principles of OTN

switching

OTN was developed by the ITUs

Telecommunication Standardization

Sector (ITU-T) as a way of optimizing

traffic efficiently while simultaneously

coping with a new traffic mix. The

ITU-T defines OTN as follows.

An Optical Transport Network (OTN) is composed of a set of Optical

Network Elements connected by optical fiber links, able to provide

functionality of transport, multiplexing, routing, management,

supervision and survivability of optical channels carrying client

signals. (http://www.networkworld.com/details/4521.html?def)

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OTN provides digital wrappers that

contain multiple data frames from

different client services together ina common ODU. This enables the

network to switch high volumes of

any type of traffic efficiently, including

Ethernet and legacy SDH traffic. OTN

ensures that all 40 Gbps and 100 Gbps

digital wrappers are fully packed to

make maximum use of the networks

available bandwidth.

A simple analogy of the principle behind

OTN is filling buses with passengers.

A bus may leave the bus station only

partly full. As more passengers arrive at

the bus station, more half-empty busesleave on their journeys in different

directions, which is clearly inefficient.

OTN switching is akin to ensuring that

every bus is filled to capacity before

it leaves and before passengers are

allowed to start boarding the next bus,

even if some will later change or get off

at intermediate stops.

This increased fill rate also applies to

optical channels, which are now using

their large available transport capacity

better. This limits the need to deploy

new and costly DWDM channels.According to a study in February

2009, using this kind of intermediate

traffic grooming with an ODU switch

can reduce wavelength usage by 40%

(Thomas Engel, AchimAutenrieth,

Jean-Claude Bishoff, Packet Layer

Topologies of Cost Optimized

Transport Networks, ONDM,

Braunschweig, Germany).

The OTN concept is simple yet

powerful, because a diverse range

of client signals can be managed

together. Its also more flexible than

the previously dominant architecture

(SONET/SDH).

OTN is currently offered in the following

line rates:

OTU1has a line rate of

approximately 2.66 Gbit/s and was

designed to transport a SONET OC-

48 or synchronous digital hierarchy

(SDH) STM-16 signal.


approximately 10.70 Gbit/s and

was designed to transport an

OC-192, STM-64 or WAN PHY

(10GBASE-W). OTU2ehas a line rate of

approximately 11.09 Gbit/s and

was designed to transport a 10 Gbit

Ethernet LAN PHY coming from

IP/Ethernet switches and routers

at full line rate (10.3 Gbit/s). This is

specied in G.Sup43.


approximately 43.01 Gbit/s and was

designed to transport an OC-768

or STM-256 signal or a 40 Gbit

Ethernet signal.

OTU3e2has a line rate of

approximately 44.58 Gbit/s and wasdesigned to transport up to four

OTU2e signals.


approximately 112 Gbit/s and was

designed to transport a 100 Gbit

Ethernet signal.

The OTUk (k=1/2/2e/3/3e2/4) is a

signal format into which another

information structure called ODUk

(k=1/2/2e/3/3e2/4) is mapped. ODUk is

the server layer signal for client data

signals. The main difference between

ODU and OTU signals is the forward

error correction (FEC) header

contained in the OTU format.

ODUk data generally follows the

same approach as OTUk, but some

new service formats cant fit into

any existing ODUk without wasting

bandwidth. Also, defining a new ODU

container each time a new client is

added would require upgrading ODUk

switch fabrics. ODUflex was therefore

introduced as a flexible lower order

container that can be right sized to

fit any client rate and overcome the

problem.

ODU data packets form the basis for

flexible mapping and multiplexing

within the OTN switching process.

Different services are converted into

ODU packets and these are directed to

their destination ports and converted

into OTU for optical transmission.

Its useful to distinguish between

single-stage and double-stage ODU

multiplexing, which is typically used for

mapping several small ODUs into one

large ODU. The flexible multiplexing

scheme also allows mapping, in oneor more steps, of small ODU data

packets into a larger ODU container,

maintaining a small data granularity

while using a large transport capacity.

Note that lots of services and service

types can be processed by a single

OTN switch simultaneously. All thats

required is the right mix of interface

cards to support the appropriate client

formats, for example GbE, and sufficient

port capacity. Figure 2 illustrates which

service types can be mapped into an

ODU packet and finally into the requiredtransport (OTU) format.

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Figure 3 highlights a scenario with

vast mapping options in an ODU4,

combining single ODUk and dual-stage

multiplexed ODUk, as well as different

ODUflex pipes.

3.2 The architecture of OTN

switches

The substantial cost saving benefit of

OTN switching is complemented by

increased network resilience and

greater flexibility. The way in which

OTN is implemented by the design of

the hardware has a significant impact

on the scale of these benefits. The

architecture of an OTN switch should

maximise flexibility and availability.

OTN switches are protocol-independent

and operate transparently both on

TDM and packet-based traffic. They

break traffic down into ODU packets in

a suitable interface card, then perform

the switching and grooming function in

a centralized switch fabric and forwardthe ODU packets to the switchs

relevant output port via the respective

interface card. This switch fabric is the

heart of the OTN switch, connecting

the interface cards via an electrical

backplane. The ODU packets are

processed in the electrical switch

matrix with agnostic cell switching.

The total traffic load from all the

interfaces in the switch can be shared

among several switching cards that

operate simultaneously. This approach

should provide CSPs with excellent

scalability in their switching capacity,thanks to multiple switch fabric

modules (SFMs) in a single chassis.

It opens up an opportunity to benefit

from a pay-as-you-grow approach to

investment.

To achieve maximum redundancy and

protection in the system, all the SFMs

in the OTN switch should be able to

share the traffic load. As well as

achieving effective load balancing, this

architecture ensures that, should one

card fail, the remaining cards can

redistribute the extra traffic betweenthem to avoid service interruptions.

This structure also enables CSPs to

carry out upgrades while the OTN

switch remains in service.

Similarly, redundancy should be

provided in the power supply cooling

fans and system controllers. Combined

with service protection, this results in

the highest, carrier-grade, availability.

Figure 5 summarizes the switch

architecture from the perspective of

the signal format. It illustrates ODUswitching functionality, which is used

for all different formats. Alternative

approaches might include packet

switching for MPLS/Ethernet signals

using an MPLS interface card,

or SONET interfaces for ODU or

VC4-based switching, all handled by

the same switch fabric. Therefore,

the OTN switch becomes the only

switching element for all the formats

present in the network.

ODU0 (L)GbE/DVB/FEFC 1G

STM-1/OC-3STM 4/OC-12

STM-16/OC-48FC 2G

STM-64/OC-19210 GBASE-W

STM-256/OC-76840 GBASE_R

FC 4GFC 8G

10 GBASE-R

FC 10G

100 GBASE_R

ODU1 (H)

ODU1 (L) OTU 1

ODU2 (H)

ODU2 (L) OTU 2

ODU2e (L) OTU 2e

ODU3 (H)

ODU3 (L) OTU 3

ODU flex (L) ODU4 (H)

ODU4 (L) OTU 4

Not specified in G.709, but in G.sup43

Figure 2: Flexible mapping and multiplexing scheme highlighting the ODU concept

Figure 3: Network capacity optimization example of ODU mapping and multiplexing forlarge capacity 100G channels

n x MPLS-TPtunnel

n x ODU flex(various size)

dual stage multiplexing(ODUflex via ODU2 / ODU3)

dual stage multiplexing(all ODUk)

ODU0 / ODU1 / ODU2(e) / ODU3

ODU4 (L)(100G)

Efficient bandwidth utilization

Built on flexible client service mapping andODU frame multiplexing acc. to ITU-T G.709

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OTN switches can be deployed in a

network in several ways.

In an existing DWDM network with

mesh topology, OTN switches can be

deployed as a standalone network

element (NE) operating as a cross-

connect at a network node. This is thetypical way in which OTN functionality

is introduced where only optical

switching at the wavelength level

has existed previously, for example,

using multi-degree ROADMs. The

wavelengths of the DWDM system

are optically de-multiplexed and

individually connected to the OTN

switch interface cards. The standalone

NE could also be connected toother equipment such as IP routers.

This kind of deployment is typical in

multi-vendor networks where the OTN

standard ensures interoperability

between many different platforms.

If the network is newly deployed and

the DWDM transport system and the

switch are both from a single vendor,

a single NE can be defined at the

network nodes of the mesh network,

incorporating the OTN switch and the

optical transport equipment logically

into one NE. The advantage of this

approach is that the composite

element is managed by the network

management system (NMS) as one

NE featuring OTN switching, MPLS-TP

switching, SONET switching, WDMswitching and WDM transmission.

In yet another scenario, the OTN switch

can be deployed as a standalone NE

together with extension shelves. This

enhances the capabilities of MSPP

platforms with additional OTN switching

functionality.

The next issue is where in the network

to deploy OTN switches. Typically,

most switching and aggregation takes

place in the metro and core parts of the

network, which define the capacity andconfiguration requirements for OTN

switches.

Figure 4: Example for the architecture of an OTN switch showing interface cards, the switch fabric andadditional controller cards

Figure 5: OTN traffic model based on ODU switched client formats

OTN interface card System controller card (w)

System controller card (p)

Peripheral controller card (w)

Peripheral controller card (p)

Flow Sensor Card (CFSU)

Switch FabricModule

2x / 3x (1+1)Power Supply Unit

8 / 12Fan Trays

Switch FabricModule

MPLS-TP interface card

Ethernet L2 interface card

SDH/SONET Bridge card

OTN interface card

SDH/SONET interface card

#1

#1

#6

#2

#3

#4

#5

#15 / #30

OTN interface card

OTN interface card

Client signal

Multiplexing

OTUi

-> ODUk -> ODUk

Ethernet-> ODUj

SDH/SONET

Other (FC, etc.)

Mapping

Line signal

Switching FabricModule

Client signal Line signal

ODU switching

packet switching

VC-4/STS-1switching

local node traffic

OTU signal

Ethernet signal

SDH / SONET signal

other signals

ODU frames

Ethernet / MPLS signal

virtual switching domain

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4.0 The major benefits of OTN switching

Generally, all OTN switches should

support the same overall functionality.

However, in metro networks the focus

is on the aggregation of different

services to fill the wavelengths

efficiently with various traffic formats

while ensuring service transparency

across the network.

The introduction of OTN switching will

bring major benefits for CSPs in terms

of lower costs, higher efficiency and

greater functionality in their transport

networks. As networks grow and need

to accommodate new types of traffic

alongside existing traffic, it becomes

vitally important to fill the available

transmission bandwidth efficiently. This

calls for techniques such as grooming

and aggregation. Beyond the task of

transporting and switching traffic, a

unified management system can add

value to the network by providing

simplified operations and functions

such as the end-to-end provisioning

of services and resilience schemes

For the core network, the focus is on

achieving switching capacity in the

Terabit range, practically distributed

over several chassis by capacity

expansion. Core-based switches

handle enormous traffic loads and

can switch any service from one

wavelength to another. They must also

throughout all the network layers and

segments. Its ultimately about aiming

for the most efficient and cost-effective

end-to-end networking. Such a

converged optical network shall fulfil

the following requirements.

Optimize and simplify the network

structure with new OTN switches.

Simplify network operations.

Migrate any installed base.

OTN switches are embedded in the

converged packet optical transport

system (P-OTS) and hence play a vital

role in the metro and core of such a

network. The choice of interface cards

support networking functions such as

protection and restoration.

Across the network domains, OTN

switches perform other advanced

networking functions such as end-to

end provisioning and different

resilience schemes.

enables these switches to handle the

dominant packet traffic as well as any

existing legacy formats, from MSPP or

Carrier Ethernet Transport (CET), for

example. Typical packet based

services are FE/GE/10GbE/40GbE

and 100GbE, which are mapped into

ODU0,2,2e,3,4,flex as already shown.

Moreover, advanced OAM capabilities

provide CSPs with a unified platform

to manage the network and services

effectively end-to-end, with common

service, fault and performance

management. This helps deliver a

high-quality end-user experience.

Services Access Metro Core NMS

Figure 6: OTN switches are typically placed in the metro and core networks

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Figure 7: The functional view of OTN switching in the P-OTS architecture

Figure 8: Sub-lambda grooming packs more streams into each wavelength and therefore effectively reducesthe number of required distinct wavelengths

Figure 7 illustrates how OTN switches

fit into this overall network architecture.

In the core network they connect the IP

layer and the DWDM-based optical

layer. They also provide traffic grooming

and aggregation throughout the rings

that make up the metro networks.

From there they direct the traffic to the

correct carrier in the access network,

whether thats Ethernet, DSL or a radio

cell, for example.

The following sections highlight what

OTN switching can deliver in terms

of capacity improvements, reduced

investment, increased availability and

reliability and improved support for

service management. This white paper

presents a broad network view, while

specific OTN topics are discussed in

more detail in complementary white

papers.

4.1 Filling the pipe with

sub-lambda grooming

In DWDM transport systems, line rates

are approaching 100 Gb/s with 80 or

more optical channels transmitted

simultaneously. This enormous

capacity can be handled purely on the

optical layer when using multi-degree

ROADMs for switching at network

nodes. However, with this technology

the smallest unit for switching is a

single optical wavelength. Given the

trend to high line rates, this translates

into an equally high granularity. On

the other hand, services demand

comparatively low data rates in the

Mb/s or low Gb/s range, which results

in inefficient fill rates in the optical

channels. The ideal solution for

CSPs would therefore be to create a

high-capacity network over DWDM

combined with low switching

granularity for efficiency.

Sub-lambda switching and grooming is

the answer. In this process, multiple

data streams carrying different services

are electrically multiplexed into larger

units that can be processed and

transmitted as single entities. In the

same way, such streams can also be

de-multiplexed at a switching node to

access and extract specific data. The

primary aim is to lower the cost of

handling traffic in the network by

making better use of the available

capacity. In this set-up, a DWDM

wavelength can be used as a pipe for

lots of different traffic. In particular,

adopting the ODU-based approach

in OTN switching can reduce the

wavelength used to carry a given

volume of traffic by 40% by enabling

CSPs to pack more streams into each

wavelength.

OTN

Up to 40% less

wavelengths in real

life networks reducesnumber of deployed

transponders

Channel 1

Channel 2

Channel 3

Sub-lambda grooming

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MSPP platforms carrying traditional

SDH/PDH services also support this

concept of switching. However, with

the ODU layer, the switching concept is

expanded into a fully service-agnostic

platform, incorporating new, IP/

Ethernet services in addition to legacy

services and combining impressive

scalability with a unified network

management system. This provides

a future-proof networking architecture

for CSPs to manage and evolve their

service portfolio easily.

4.2 Traffic offloading reduces

CAPEX

Routers are closely integrated into the

overall network where they provide

switching and routing capability. But,

in general, router capacity remains

expensive, with costs increasing as

more and more IP traffic is generated.

This increasing IP traffic can be divided

into multipoint-to-multipoint traffic, like

classical L3 VPN and VPLS and point-

to-point traffic like Internet, which is

directed from a PE router like a BNG or

GGSN/SAE-GW to the Internet peering

points. This point-to point traffic does

not necessarily need to be switched

by the large core routers, so the IP

core router can be saved for VPN

traffic. Alternatively, upgrades from

single-chassis routers to more costly

multichassis routing systems can be

avoided.

Put simply, routers alone will not be

able to keep up with the increasing

bandwidth demand in a techno-

economical environment and only a

combination of routers and optical

transport will be economically viable for

a traffic mix dominated by IP/MPLS.

MPLS is a technology for labeling IP

packets so they can be directed

around the network. The particular

MPLS Transport Profile (MPLS-TP)

supports carrier-grade OAM, as well as

performance and fault management.

There are some additional benefits that

the combination of MPLS-TP and ODU

brings over and above those offered by

the ODU concept alone. Generally, this

combination allows CSPs to optimize

the transport layer to handle the

dynamic behavior of IP/MPLS.

All IP/MPLS traffic and label-switched

paths (LSPs) can share the full

10G/40G/100G line interface capacity

between nodes that are acting as

MPLS-TP switches. This delivers

a statistical multiplexing gain and

increases efficiency in the network even

further. Since no fixed bandwidth is

assigned, this is a close approximation

of the dynamic nature of the IP/MPLS

traffic. In the metro network, MPLS-TP

helps provide more efficient packet

aggregation from MSPP/CET andDWDM sources.

MPLS-TP supports OAM functions so

the network operator can configure

traffic profiles, QoS, protection and

restoration to optimize the transport

layer and meet the quality requirements

of IP/MPLS.

A key advantage of combining MPLS-

TP functionality and OTN switching is

the ability to offload traffic from the IP

layer. This enables transit traffic to

bypass intermediate routers entirely,significantly reducing the required

router capacity and saving capital

expenditure (CAPEX) and operational

expenditure (OPEX).

In the traditional set-up, the IP and

transport networks are separated

entities. DWDM transport networks

offer plain connectivity to the IP core

network. Features such as resilience

are based in the IP layer. Such

networks are relatively slow scaling,

with increased capacity creating extra

cost, space and power challenges,even though the IP routers only

perform simple tasks such as label

switching for the majority of traffic.

2005

5 Tbps

10 Tbps

2010 2015 2020

Core router capacity [Tbps ]

Max single shelf

router capacity

Required core router

capacity

Figure 9: The evolution of core router capacity over time due to increasing IP traffic

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Incorporating MPLS-TP in the OTN

switches and transport layer - with theDWDM transport and OTN switching -

provides the following enhancements.

IP ofoad: Shifting trafc to the ODU

layer frees up core router interfaces

and saves CAPEX by requiring less

router hardware and lowers OPEX

by reducing power, footprint and

cooling

Transit trafc: Label-switched

routing can be carried out in the

transport domain, so transit trafc

can bypass the IP layer as it

traverses the OTN platform.

Resilience: MPLS-TP and ODU-

level mechanisms also offer fastservice recovery

DWDM-layer optimization:

Combined with the benet of sub-

lambda trafc grooming, it yields a

dramatic improvement in wavelength

utilization and network efciency.

For example, to assess the scale of

the potential savings, consider the

case of a European greenfield CSP

experiencing a 50% annual traffic

growth rate and using MPLS-TP to

offload IP traffic in order to limit the

need for large capital investment in

router capacity. Using OTN switches

to carry all peering traffic resultsin offloading 70% of all traffic from

routers, leaving the remaining 30%

of traffic within the router layer.

Comparing the cost of investing in

router capacity only with investing

in a combination of OTN switches

and routers reveals that the cost of

introducing the MPLS-TP layer would

be recouped within one year. The

cumulative CAPEX saving over a

five-year period amounts to about 60%

In addition, significant OPEX savingswould amount to a 60% saving, while

reduced power consumption would

equal CO2savings of up to 590 tonnes

over five years.

OTN switches that support MPLS-TP

also help to future-proof the architecture

by enabling the migration of legacy

circuit-switched transport networks to

next-generation packet-optimized

optical transport networks.

Last but not least, little investment

is required to implement MPLS-TPcapabilities, since it is merely a

software feature running on the OTN

switch.

Figure 10: Combining MPLS-TP functionality and OTN switching gives IP traffic the ability to remain in the transport layer,thus effectively offloading it from the IP layer

Figure 11: Incorporating MPLS-TP in the transport layer means that intermediate sites havereduced or no router traffic

IP service layer

Electrical switching layer

DWDM layer

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OTN switches equipped with MPLS-TP

can also carry out many of the traffic

management functions that wouldotherwise be handled exclusively by

IP-layer routers. Furthermore, by

incorporating them directly onto the

transport layer, these advanced

features become part of the transport

network, regardless of the IP router

actually used. This approach also

helps CSPs to generate significant

savings by reducing the router capacity

needed in the network.

4.3 Robust protection

promotes carrier-gradeavailability

As we have seen, combining OTN

switches in a mesh topology provides

an extremely robust network. The OTN

switches typically have redundant

hardware installed for maximum

reliability, but in the event of a major

failure or an incident on the DWDM

transport layer, such as a severed fiber,

traffic may need to be rerouted. The

right topology can even protect against

multiple failures.

Its possible to provide protection in the

IP layer, although it can be relatively

slow to recover. There are also

different techniques for protection that

can be applied directly on the DWDM

layer, based on GMPLS or simple 1+1

optical switching. The best solution for

a particular network depends to its

specific topology, but OTN switches

offer a new degree of sophistication for

traffic protection. Protection occurs on

the service level, making it possible to

apply different measures to traffic withdifferent QoS.

OTN technology supports the full range

of protection techniques to prevent

failures and speed up recovery times.

The first step to increase resilience

is to build alternative paths into the

network using ring topology, dual

nodes and high connectivity, for

example. The next consideration is

the functionality of the nodes where

the switching occurs in the event of a

failure.

OTN switches enable protection to be

configured at the level of the individual

ODUs, which provides much finer

granularity than protection provided

by the line interface alone. Features

include sub-network connection

protection (SNCP), which works on

different ports of the interface cards and

can protect particular ODUs. There are

also the same protection architectures

familiar in other layers of the network,

such as multilayer GMPLS (Och, ODUk

and VC4). OTN switching also supportstechniques such as hold-off timers

to prevent the triggering of multiple

protection measures and wait-to-

restore timers combined with revertive

protection, which automatically

restores the original traffic configuration

when possible.

The deployment of MPLS-TP with

OTN provides additional protection

at all levels from the end-to-end

transport path to individual links. The

above options are complemented by

packet-oriented protection schemesspecifically for LSP and pseudo wire

(PW) connections.

4.4 OAM capabilities support

a great customer

experience

Effective OAM comprises a set of

network-oriented mechanisms for

monitoring and managing the network

Capex Opex Weight-80*% -60% -60%IP CORE

ROUTER

OTN switch +

MPLS-TP

OTN switch +

MPLS-TP

OTN switch +

MPLS-TP

IP CORE

ROUTER

IP CORE

ROUTER

* Depending on final configuration. Example 50% OTU-2 and 50% Client 10G MPLS interfaces

Figure 12: Benefits deriving from OTN switching for the discussed network scenario

Figure 13: OTN switches within a mesh network topology supports protection switchingand creates a robust network

A

B E

FC

D G

Initial route

1st alternative route

2nd alternative route

3rd alternative route

Failure NN

3

1

2

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Figure 14: OAM capabilities shown for a performance management throughput test

infrastructure. Since the OTN switch

offers a lot of functionality within the

network environment, OAM support

optimizes the integration of OTN

switches into the overall network

management. In particular, the

deployment of MPLS-TP within the

OTN switch provides carrier-gradeOAM capabilities.

Common functions are performance

management (PM) and fault

management (FM). Together with

MPLS-TP, PM comprises packet loss,

packet delay and throughput, end-to-

end across the entire network. For FM,

features such as trace routing and LSP

pings are available, as well as a set ofproactive functions.

Figure 14 shows a throughput test for

PM. This is the typical approach for

verifying the bandwidth of an MPLS-TPtransport path before it is brought into

service. This is the configuration

typically used in the traffic offloading

scenario.

In the architecture shown here, we

consider a transport network domain

with OTN switches, comprising PE

switches at the edge and P switches

in between.

The throughput tests are performed

on the transport layer between the

two end points. The OAM systemscontrol the end points and a test-traffic

sequence is sent between them,

complete with a byte count.

The benefits of effective OAM include

fast end-to-end service provisioning,

maintenance and the fast restoration

of services. Improved performance

and the ability to trace network faults

in case of failures translate into less

downtime, which in turn helps to drive

down OPEX for CSPs.

MPLS-TP

MPLS-TP

NNI

MPLS-TP

NNI

P

LH-OTPLH-OTP LH-OTPLH-OTP

P PEPE

MEP MEP

Throughput test

5.0 Packet Optical Transport from Nokia Siemens Networks

Nokia Siemens Networks offers a

P-OTS solution with advanced

transport and optical and electrical

switching capabilities. The P-OTS

solution also supports the end-to-end

provisioning of services across a

network and provides restoration

functions for greater network resilience.

Nokia Siemens Networks P-OTS

can be tightly integrated with existing

DWDM platforms and features

advanced network architecture that

places no restrictions on services or

applications. DWDM transport capacity

is upgradable up to 96 channels with

40 Gbit/s or 100 Gbit/s, while switching

is scalable from a capacity of 0.2

Terabytes per second (Tbps) up to

more than 24 Tbps, complete with 40

Gbit/s and 100 Gbit/s optimized line

interfaces from a single platform.

Seamlessly integrating with the P-OTS

solution is the hiT 7100 OTN switch

that offers multilayer switching including

ODU -0/1/2/3/4/flex, MPLS-TP, L2

Ethernet and VC-4/STS-1. Using

intelligent multi-service interfaces, the

switch is future-proofed, because any

service can be processed transparently

by adding the relevant interface card.

This protocol-independent switch

features 3 Tbps switching capacity per

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chassis that can be flexibly scaled up to

48 Tbps in a multi-chassis configuration.

Carrier-class network resiliency is

provided by the hiT 7100s built-in

switch fabric module and controller

card redundancy offering N+1

protection, combined with several

protection options offered on ODU

layer. The hiT 7100 can be provided in

different configurations to suit any

network need, whether for a stand-

alone network element, or on top of

existing DWDM infrastructure.

OTN capacity planning is supported by

the Nokia Siemens Networks NPS10planning tool and optical network

planning is supported by TransNet.

Combined, this offers a complete

process of planning, configuration and

installation of packet optical networks

including configuration, upgrade,optimization, ordering, commissioning,

and network maintenance.

P-OTS network management is

performed via the carrier grade Nokia

Siemens Networks Transport Network

Management System (TNMS) solution

that provides automated or manual

provisioning of ODU connections and

interface connections. The system also

provides monitoring and performance

management at the element and

transport service levels.

Nokia Siemens Networks also

provides a full set of professional

services, including assessment, design,

database creation and adaptation, and

replacement preparations for upgrading

networks. Highly trained expertsthroughout the world can save CSP

time and effort by offloading lengthy

design and database management

activities, helping to lower the total

cost of ownership by allowing CSPs

to focus on their primary business,

providing customers the new, high

quality services they demand. The use

of Nokia Siemens Networks services

not only ensures the highest network

efficiency and integration of upgrades,

but also paves the way for future

upgrades.

6.0 Conclusion: OTN switches at the heart of efficient and

flexible packet transport

Deploying OTN switching technology

in metro and core networks is one of

the most cost effective opportunities

for CSPs to meet the booming

capacity demand and manage the

increasingly complex and dynamic

mix of traffic generated by advanced

IP-based services. While the concept

of introducing an optical switching

network layer may seem contrary

to the trend over the last decade of

simplifying networks by removing

layers, the technology does promise

substantial cost savings and

performance gains.

OTN switching can be combined more

efficiently with an IP core network,

saving significant CAPEX at the

network level. OTN switching enables

traffic in transit to bypass many of the

networks IP routers and thus reduces

the amount of expensive router

capacity required. It also provides

efficient grooming of the optical signal

on a sub-wavelength level. This uses

existing bandwidth more efficiently,

thereby minimizing the capacity

needed to carry a given volume of

traffic.

These benefits are compelling reasons

for CSPs to adopt OTN switching.

Using the Nokia Siemens Networks

converged optical packet portfolio,

CSPs can support a multitude of

applications in metro and backbone

optical transport networks. As these

networks are typically multiservice in

nature and contain complex mesh

topologies carrying many different bit

rates, an electrical grooming layer is

required, achieved when the P-OTS is

combined with the Nokia Siemens

Networks hiT 7300 DWDM platform.

These factors shape the Nokia

Siemens Networks converged

transport network vision, with IP

optimized optics enabling the

exponential growth of the Internet at

the lowest possible cost per bit. With

the P-OTS combination of the hiT

7100 OTN switch and hiT 7300

DWDM platform, CSPs can plan and

deploy their entire optical transport

network in the most cost effective way,

seamlessly migrating towards next-

generation packet optical networks.

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Summary of benefits of OTN switching

Capital and operationalcost reduction

Maximum utilization of wavelengths by sub-lambda grooming

IP traffic offloading reduces investment in IP network layer routers and reduces running costs

Multi-vendor interoperability simplifies procurement and operation

Common management system for OTN and DWDM layers reduces system complexity and simplifies

network operations

Carrier-class protection and migration to mesh network topology improves network availability and

reduces maintenance

Rapid return on investment Rapid service provisioning enables fast time to market and early revenue

Future-proofed network Extreme scalability and flexibility to adopt new service types protects investments

Migrate to IP/Ethernet services while supporting traditional SDH/PDH services

Abbreviations

ATM Asynchronous Transfer Mode

BNG Border Network Gateway

CAPEX Capital Expenditure

CET Carrier Ethernet Transport

CSP Communications service provider

DSL Digital Subscriber Line

DWDM Dense Wavelength Division Multiplexing

FEC Forward Error Correction

FM Fault Management

GMPLS Generalized Multi-Protocol Label Switching

GW Gateway

IP Internet Protocol

ITU-T International Telecommunication Unions

Telecommunication Standardization Sector

LAN Local Area Network

LSP Label-Switched Path

MPLS MultiProtocol Label Switching

MPLS-TP MPLS Transport Profile

MSPP Multi-Service Provisioning Platform

NMS Network Management System

OAM Operations, Administration and Maintenance

ODU Optical Data Units

OPEX Operational Expenditure

OTN Optical Transport Network

POTN Packet Optical Transport Network

PDH Plesiochronous Digital Hierarchy

PM Performance Management

P-OTS Packet Optical Transport System

PW Pseudo Wire

QoS Quality of Service

ROADM Reconfigurable Optical Add-Drop Multiplexer

SAN Storage Area Network

SDH Synchronous Digital Hierarchy

SFM Switch Fabric Module

SNCP Sub-Network Connection Protection

SONET Synchronous Optical Network

TDM Time Division Multiplexing

TNMS Transport Network Management System

VPN Virtual Private Network

WAN Wide Area Network

WDM Wavelength Division Multiplexing

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www.nokiasiemensnetworks.com

Nokia Siemens Networks

P.O. Box 1

FI-02022 NOKIA SIEMENS NETWORKS

Finland

Visiting address:

Karaportti 3, ESPOO, Finland

Switchboard +358 71 400 4000 (Finland)

Switchboard +49 89 5159 01 (Germany)

Order-No. C401-00725-WP-201107-1-EN

Copyright 2011 Nokia Siemens Networks.

All rights reserved.

Nokia is a registered trademark of Nokia Corporation,

Siemens is a registered trademark of Siemens AG.

The wave logo is a trademark of Nokia Siemens Networks Oy.

Other company and product names mentioned in this document

may be trademarks of their respective owners, and they are

mentioned for identification purposes only.

This publication is issued to provide information only and is notto form part of any order or contract. The products and services

described herein are subject to availability and change

without notice.

Optical Transport Network Switching

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