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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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OTN switching: Creating efficient and cost-effective optical transport networks4
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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5OTN switching: Creating efficient and cost-effective optical transport networks
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.
OTU2has a line rate of
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.
OTU3has a line rate of
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.
OTU4has a line rate of
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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OTN switching: Creating efficient and cost-effective optical transport networks6
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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7OTN switching: Creating efficient and cost-effective optical transport networks
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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OTN switching: Creating efficient and cost-effective optical transport networks8
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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9OTN switching: Creating efficient and cost-effective optical transport networks
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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OTN switching: Creating efficient and cost-effective optical transport networks10
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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11OTN switching: Creating efficient and cost-effective optical transport networks
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 switching: Creating efficient and cost-effective optical transport networks12
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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13OTN switching: Creating efficient and cost-effective optical transport networks
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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OTN switching: Creating efficient and cost-effective optical transport networks14
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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15OTN switching: Creating efficient and cost-effective optical transport networks
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.
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