This article discusses the best in class in
traffic engineering for SDN with attention to four cores including flow
management, fault tolerance, topology update, and traffic analysis. The
challenging issues for SDN traffic engineering solutions are talked about in
detail. SDN is a developing networking administration that isolates the network
control plane from the data sending plane with the guarantee to significantly
enhance organize asset usage, streamline network management, reduce working
expenses, and promote development and advancement. For network performance
optimization by dynamically analyzing, predicting, and regulating the behavior
of the transmitted data, traffic engineering is an important subject. Over the
last two decades traffic engineering has been exploited in asynchronous
transfer mode(ATM) and IP/multiprotocol label switching(MPLS). The existing
traffic engineering technologies rely on closed and firm architectural design,
where the control and data planes are firmly coupled and coordinated. The
inflexibility and the closed nature of the architecture prevents the existing
traffic engineering technologies to provide differentiated services that would
adapt to increasingly growing uneven and highly variable traffic patterns.
Coming back to the four cores flow management, fault tolerance, topology
update, and traffic analysis: Starting of with the flow management, in SDN the
significant overhead at both control and data planes caused when an OF switch
receives a new flow that doesn’t match any rule in its flow entry. To overcome
the bottle neck in SDN solution are discussed in the paper, by considering the
balance between latency and load balancing at the data plane and control plane.
In load balancing for the data plane, two methods are followed: Hash-Based ECMP
Flow Forwarding and Wildcard Rule Flow Forwarding. The hash-based Equal-Cost
Multi-Path(ECMP) is a load balancing scheme to distribute flows across
available paths using flow hashing methods. This solution can improve the band
width and processing overhead at the switches. In wildcard rule flow forwarding
to aggregate traffic flows, OF switches use flow match wild cards. In load
balancing for the control plane SDN may cause the network controller to become
a potential performance bottleneck, to overcome this controller load balancing
schemes have been used. They are logically centralized and physically
distributed controller, physically distributed controller, hierarchical
controller, hybrid controller, multithread controllers and generalized
controllers. The multithread controllers are developed to improve the request
processing throughput. The parallelism architecture of servers is used to
provide high throughput with scalability at the controllers in multithread multicore
SDN controllers. The research challenges in flow management are dynamic load
balancing scheme for the data plane and dynamic load balancing scheme for the
control plane. Now coming to the second core i.e. fault tolerance: for ensuring
the reliability of the network, SDN must be able to perform the failure
recovery straight forwardly and effortlessly when a failure occurs in the
network. Even though a switch could be used in such a failure, it has neither
the insight nor the information to make new route. For this it has to depend on
the controller. In this manner, we discuss the research efforts on fast failure
recovery in SDN networks. For fault tolerance in the data plane we have two
failure recovery mechanisms, which are restoration and protection. In restoration,
the recovery path can be pre-planned or dynamically designated. Whereas in
protection the recovery path must be pre-planned and reserved before the
failure occurs. Taking the bandwidth and latency factors into consideration,
for larger SDN systems the protection solution is used for faster failure

In the control plane the fault tolerance is an important
factor to maintain the efficiency of the network. A single point failure can
cause an entire network to degrade. The primary-backup replication method is
the most fundamental method used in the recovery process of the control plane.
The OF protocol do not have any coordination mechanisms for the primary and
backup controllers to use. For this reason, the coordination protocols are
wanted. In the deployment of the backup controller, properly placing the backup
controllers in the SDN we can increase the network reliability. There are mainly two research challenges in the fault
tolerance, they are cost-efficient and fast failure recovery for the data plane
and primary-backup replication with the traffic adaptivity for the control
plane. Now coming to the third core i.e. topology update. In the topology
update pre-planned changes like network policy rules change. When these changes
occur, each flow is identified and then it is guaranteed to be managed by
either the old or the new policy. There are two types of consistency:
per-packet consistency and per-flow consistency, which have a common update
operation that is the switches process the packet by following the old or new
policies until the old configuration rules are deleted by the controller. For
the problem which is caused by the duplicate policy scheme we require more
efficient update algorithm for implementing consistent update. The research
challenges that arises during the topology update are a single controller in a
large scale SDN network and multiple controllers in multi-domain SDN networks.
Now talking about the fourth or the last core i.e. traffic analysis. In traffic
analysis monitoring the network is significant for the network
management. When it comes to SDN networks, the existing monitoring solutions become
less efficient due to the large-scale nature of the network which effects the
central controller. Query-base and Push-based monitoring are the current
solutions available. The Query-based solution is based on the request or response
paradigm, whereas the Push-based solution is based on publish or subscribe or distribute
paradigm. The research challenges that come up during
the traffic analysis are traffic analysis, traffic monitoring and network
checking and programming debugging methods. In this paper, the investigation is
done on the SDN traffic engineering solutions form the various aspects of flow
management, load balancing, fault tolerance, topology update and traffic
analysis. The current state and research difficulties of SDN traffic engineering
are exhibited by the addressing the key SDN execution measurements as far as
scalability, availability, reliability, consistency and accuracy.

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