This paper discusses the advantages of using MPLS as a Software Determined Network than deploying it directly on a complex network.

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Name:ChinmayUpasani
G-number:G00935325
MPLS as a Software-
Defined Network
1. ABSTRACT:
This paper discusses the advantages
of using MPLS as a Software Determined
Network than deploying it directly on a
complex network. Here, we focus on the
problems arising by directly deploying
MPLS on a complex network by the local
ISP’s and how introduction of MPLS-SDN
helps us in solving that problem. We
explain briefly about MPLS, MPLS-TE and
the objective of MPLS-TE. We also discuss
the advantages that MPLS-SDN has over
MPLS and why it is preferred; we’ll also
see the application of MPLS-SDN in carrier
networks and finally come to conclusion
weather application of MPLS-SDN over
regular MPLS is advantageous or just
increasing the difficulties for ISP’s by
increasing the complexity of the network.
2. INTRODUCTION:
MPLS has become critically
important for Internet Service Providers
(ISP) since it provides us IP over ATM
integration. The two key services that made
MPLS so important were:
(A) Traffic engineering in IP networks
(B) L2 or L3 enterprise VPNs
However, when this was used by the ISP’s
it was found that even though MPLS data
plane was meant to be simple, vendors
ended up deploying MPLS on a complex,
energy consuming core routers and control
plane had become more complex with
variety of protocols being used in the data
plane.
A new approach to MPLS has been
considered in which MPLS uses a standard
data plane with a simpler and extensible
control plane based on SDN. The
significant advantage using this approach is
the control plane is greatly simplified and is
dissociated from a simple data plane. The
ISP’s can still provide all the services
provided by the MPLS networks. More
importantly, the services can be globally
optimised since they become more
dynamic. Hence, to create a new service all
we have to do is to programme a new
networking application on the top of the
SDN controller.
3. MPLS
Since its introduction MPLS has
gained a lot of importance in the field of
networking mainly because it enables the
service providers to carry other protocols
than just IP i.e. it gives us a unified network
to carry all the kinds of traffic.
In MPLS, the data packets are
forwarded based on labels; these labels
usually corresponding to IP destination
networks. These labels can also be mapped

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Name:ChinmayUpasani
G-number:G00935325
to other parameters such as QoS or source
address.
Some of the main reasons why
MPLS was this successful are:
 MPLS embraced IP
 MPLS is quite flexible
 MPLS is very neutral protocol
 MPLS is pragmatic
 MPLS is adaptable
 MPLS supports metrics
 MPLS is quickly scalable
Using MPLS service providers were
able to provide better and a faster service
which was not possible by only IP routing
protocol. Apart from these MPLS was also
able to transport latency sensitive
applications like voice and video
effectively.
3.1 What are Control and
Data Planes?
The two major components in
MPLS are the control and the data planes:
Control Plane: Exchanges Layer 3 routing
information and labels; contains complex
mechanisms such as OSPF, EIGRP, IS-IS,
and BGP to exchange routing information
and LDP, RSVP and TDP to exchange
labels.
Data Plane: Forwards packets based on
labels; has a simple forwarding engine.
In laymen terms a control plane
learns about packet and decides what to do
while a data plane helps in actually moving
the packets that have been learned by the
data plane.
3.2 MPLS-TE
With the help of traffic
engineering in MPLS we can use the
network optimally i.e. all the links even the
ones which are under-utilized are also used.
With traffic engineering we can select a
path from point A to point B which is
different from least-cost path.
The result is that the traffic can
be spread more evenly over the available
links in the network and make more use of
the under-utilized links in the network. In
MPLS-TE networks, the same routing
protocols are used to advertise even more
information about links by extending them,
and it gives even more reasons to generate
control traffic as link-state changes with
bandwidth reservations. Again more
dampening mechanisms like timers and
thresholds are employed to keep things
stable, at the cost of having stale link-state
information in routers. The possibility of
having stale information when performing
a CSPF (constrained SPF) calculation for a
TE-LSP, in turn the use of distributed
signalling mechanisms like RSVP-TE
becomes necessary.
3.3 Problems with MPLS-
Traffic Engineering
In a typical traffic engineered
MPLS network, we need to run different
protocols like OSPF, LDP, RSVP-TE, I-
BGP, and MP- BGP. The distributed nature
of these protocols sometimes results in
congestion since there is excessive traffic of
update messages when there are frequent
changes in the network. This causes the
routers to spend a lot of CPU time
recalculating routing information. Hence,
CPU message queues may get filled leading
to incoming hello messages getting
dropped. This leads to false link-state
information being distributed throughout
the network.

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Name:ChinmayUpasani
G-number:G00935325
The described vicious cycle causes
large convergence times for the above
protocols, meaning excessive control traffic
on the network and stale information on the
routers. The figure below shows a normal
network running on MPLS-TE. From the
above scenario we notice that MPLS fails
when there are multiple protocols running
on the same network. Hence, a different
approach has been taken where MPLS is
run over a SDN to overcome these
congestion problems.
4. What is SDN?
SDN stands for Software Defined
Networking it is an approach that allows the
ISPs to manage the services by the
abstraction of lower level functionality.
This is achieved by separating the system
that makes decisions about where traffic is
to be sent i.e. the control plane form the
underlying system that forwards the traffic
to the selected destination i.e. data plane.
However, the SDN needs some method for
the control plane to communicate with the
data plane; one of the widely used
mechanisms for this is the open flow
mechanism.
Software defined networking
(SDN) is a network architecture which is
meant to be dynamic, manageable, cost-
effective, and adaptable, also needed to be
suitable for the high-bandwidth, dynamic
nature of today's applications. SDN
architectures decouple network control and
forwarding functions, enabling network
control to become directly programmable
and the underlying layers to be separated
from applications and network services.
4.1 Open Flow Protocol
Open flow allows the routers to
determine the route through which the
packets have to be forwarded in the
network. Ideally, two controllers are
recommended in which one is used as a
backup. This separation allows more
effective control network traffic and routing
protocols. Open flow allows us to use
switches from different manufacturers;
generally each has their own interfaces and
scripting languages using a single open
protocol.
Open flow allows remote
administration of a switch’s packet
forwarding table by adding, modifying and
removing packet matching rules and actions
This way, routing decisions are made
periodically by the controller and translated
into rules and actions with a lifespan which
can be configured, these decisions are then
deployed to a switch's flow table. Packets
that are left unmatched by the switch will
be forwarded to the controller. The

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Name:ChinmayUpasani
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controller can then decide whether to
modify existing flow table rules on one or
more switches or to deploy new rules, to
prevent a structural flow of traffic between
switch and controller. Provided that it has
told the switch to forward entire packets
instead of just their header, it could even
decide whether to forward the traffic itself
or not.
5. MPLS-SDN:
In SDN, the Network Operating
System (NOS) is responsible for
constructing and presenting a logically
centralized map of the network. Instead of
a set of distributed protocols implemented
on each router, we implement these
functionalities as simple software modules
that work on the network map in NOS.
Implementation of these functions on a
logical map of the network is very simple.
Hence, by pushing the control plane
functionality to NOS, we benefit from not
only simplicity of implementation, but also
the fact that maintaining and updating
applications is easy. This is because new
features will no longer need multiple
protocols that would have to be changed. In
fact, with the controller in charge of the
control plane, there is no need for any
distributed protocol running in the routers
as the NOS has complete knowledge of the
network. The Open Flow protocol allows
discovery of the network topology by the
Controller, and keeping the topology and
network-state updated via statistics, status
and error messages. Open Flow also
provides mechanisms to manipulate each
data-plane switch’s flow-table.
.
The following network shows MPLS
with SDN. Both the networks have same
topology but, one has MPLS-TE and the
other is MPLS-SDN. As we can see all the
network applications running on the control
plane are controlled by using software
programming
5.1 MPLS Control Plane VS
SDN Control Plane
In packet switched networks a
router can act both as a control element
which controls the flow of data and a
forwarding element which is used to
forward the data. Furthermore, in IP/MPLS
networks, another layer of complexity is
added with the need for distributed
signalling and label distribution
mechanisms like RSVP-TE and LDP.
Within a domain, an IP/MPLS network may
additionally support a host of other
protocols such as iBGP, RIP, LMP, SNMP
and MP-BGP together with many more

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Name:ChinmayUpasani
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protocols for multicast and IPv6. All of
these features contribute to the increase in
the control plane load, fragility and cost.
The distributed protocols are fragile if there
are frequent changes in the network; the
updates are sent regularly hence there is a
chance of occurrence of congestion.
The network OS based applications
can then make all network-control
decisions, when presented with the network
topology, state and the power to classify
traffic into ‘flows’ and control switch
forwarding. The controller and its
applications can decide how each flow is
forwarded (reactively as new flows start, or
proactively in advance), how it is routed,
which ones are admitted, where they are
replicated, the data-rate they receive and
more. They can then cache the decision in
each data plane’s flow table via various
types of actions that Open Flow allows on
flows. And so it is the control plane
network-applications that determine access
control, routing, multicast, load-balancing,
tunnelling and so on, eliminating the need
for fully distributed routing and signalling
protocols. Importantly the need for creating
a new protocol for every new
service/feature is also eliminated –all that is
needed is a new application. The logically-
centralized nature of the Controller implies
that while the decision making is performed
in a centralized manner, the Controller itself
is distributed over multiple-physical servers
for fault-tolerance and performance.
6. ADVANTAGES:
There are many advantages of using
MPLS as a software defined network some
of them are:
 Centralized Network: SDN’s provide
the entire view of the network
architecture making it easy for
enterprise management and
provisioning.
 Enterprise Management: To
accommodate the new requests the
enterprises have set up new
applications and virtual machines.
With the help of SDN ISP’s can
experiment with the network
configuration without impacting the
network.
 Security: Using MPLS over SDN
allows the ISP’s to have centralized
security this is one of its main
advantages. Virtualization has made
network security management more
complex with the help of SDN we can
provide central point of control to
distribute security information and
policy information equally throughout
the given network.
 Lower Costs: By using MPLS as a
SDN we should be able lower overall
operating costs and result in
administrative savings since many of
the routine network administration
issues can be centralized and
automated.
 Increased Efficiency: Since all the
operations and administrative
operations are centralized the overall
efficiency of the network is increased.
 BetterReliability: The ability to shape
and control data traffic is one of the
primary advantages of software
defined networking. Being able to
direct and automate data traffic makes
it easier to implement quality of
services.

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Name:ChinmayUpasani
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7. OTHER APPLICATIONS
OF SDN BASED MPLS
The map-abstraction brings the benefits of
a simpler, more-extensible control plane to
IP/MPLS networks, and provides network-
applications with a global-view of network
state. Together with the flow-abstraction in
the MPLS data-plane and MPLS networks
based on SDN could potentially solve
problems seen in networks. We know issues
that carriers face in MPLS networks and a
few examples are given on how the SDN
approach could help meet those challenges.
1) MPLS-VPN: In MPLS the VPN’s
are of two type’s layer 2 and layer 3.
While both use MPLS backbone, the LSP
in layer 3 carry IP packets and layer 2
carry Ethernet frames. Layer 3 VPNs
create unique address space by over
lapping the address space of the customer
the main problems in L3-VPNs is that the
service provider has to carry/propagate
millions of customer IP addresses using
protocols like MP-BGP. The SDN
approach can reduce the routing
burden by eliminating the need of
other protocols.
2) Eliminating Auto-Bandwidth:
With SDN, operators have the ability to
take an ‘offline’ optimization tool ‘online’.
Map-abstraction offers the full-visibility
required by optimization-tools. But more
importantly, the Controller can access the
results of the optimization tool and use
Open Flow to directly manipulate the
forwarding tables of all LSRs. In other
words, Open Flow acts as a switch-API that
dynamically updates flow-table state, and
therefore LSP state. And it can do so in
parallel, for multiple LSPs, originating
from multiple head-ends, while minimizing
network-churn.
Only two applications are mentioned
apart from those MPLS-SDN can be used in
improving the fast reroute application, the
problem arises when the network is large in
this using SDN we try to use fast reroute by
optimally routing back-up paths while
backing up everything in the network and
MPLS-TP (transport profile) in which the
basic idea is to have transport networks that
are packet switched, but should retain
capabilities of traditional circuit switched
based networking.
8. CONCLUSION:
MPLS can cause problems when
deployed in a complex energy consuming
networks. This is because all the routers in
a network are not from the same
manufacturer and because of this they may
different protocols this causes congestion in
the network which results in data loss since
the packets will be dropped when there is
congestion. Congestion not only causes
data loss but also results in the increase of
load on the core and also makes it energy
inefficient. Thus, MPLS is used as a SDN
in which the ISP’s had to write a new
program over a network operating system
for any changes in the network topology or
in protocol being used. This was a better
and efficient option since using MPLS-TE
many tunnels were created for load
balancing which would eventually cause
congestion. Hence, we can conclude that
deploying MPLS as SDN in a better option
since it avoids congestion and helps us to
manage the network more efficiently.

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Name:ChinmayUpasani
G-number:G00935325
9. REFERENCES:
1) http://archive.openflow.org/wk/index.php/MPLS_with_OpenFlow/SDN
2) http://www.networkworld.com/article/2266069/lan-wan/7-reasons-mpls-
has-been-wildly-successful.html
3) http://en.wikipedia.org/wiki/Software-defined_networking
4) http://en.wikipedia.org/wiki/OpenFlow
5) http://blog.ine.com/2011/06/15/control-plane-vs-data-plane/
6) http://www.ingrammicroadvisor.com/big-data/7-advantages-of-software-
defined-networking
7) http://yuba.stanford.edu/~sd2/Ch_5.pdf
8) http://yuba.stanford.edu/~nickm/papers/ofc11-saurav-mpls.pdf
9) http://archive.openflow.org/wk/images/d/d6/OFC11_symposia_MPLS_fi
nal.pdf