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Sathish Kumar M

SDN-based Hybrid Telco Backbone Networks
Sathish Kumar M General Manager | February 3, 2017

Software Defined Networking has emerged as a real game changer for Telecom Service Providers (TSPs) to transform their network, improve service efficiency, and monetize the network assets better at a reduced operational cost.

When we look at SDN deployments, the ideal scenario is to build a greenfield network with SDN-compliant network devices, preferably from a single OEM. This scenario still can be considered and achieved in a small scale enterprise WAN. However, in a large TSP environment, such a scenario is not practical owing to the existing large and complex heterogeneous network built over a period of time with heavy investments. On the other hand, the operation & maintenance cost of these legacy networks are high and it does not offer the much-needed flexibility and scalability.

Let us consider and discuss the Telco backbone network which plays a critical and vital role for TSPs service management. Today, most of the TSPs have invested in IP MPLS-based backbone networks. These IP MPLS networks offer Traffic Engineering (TE) capability to control the flow of the traffic, bandwidth, and priority of service. The MPLS Fast Reroute (FRR) enables network resiliency. While these address some of the problems faced by TSPs, there are still challenges and limitations with IP-MPLS based backbone networks.

Given this scenario, the TSP may plan to deploy SDN-based backbone network. However, it will not be possible and practical to replace the entire existing infrastructure and build a greenfield SDN-based backbone.

One of the best approaches would be to retain the existing IP-MPLS network elements and build a SDN controller that has backward compatibility to the existing network elements and protocols – A Hybrid model.

The network elements that do not support standard protocols (Open Flow, BGP-LS, PCEP, NETCONF) cannot interwork with the SDN controller. For such legacy network elements, a mediation layer with suitable plug-ins to map the legacy control model to the SDN control model can be developed.

#Hybrid models provide TSPs the best of both worlds with MPLS & SDN complementing each other

Let’s discuss how this could be achieved.

Traffic Engineering (TE):

Traffic Engineering ensures an effective and optimal use of network resources, route the traffic and meet SLAs. If the SDN controller has to manage the entire TE function centrally for a large TSP network, it would affect scalability and such a central control may not be necessary at all times.

In the hybrid model SDN implementation, MPLS-TE using CSPF protocol would be responsible for the primary and default TE function. The head end router of a Label Switched Path (LSP) would obtain the details on network topology, available bandwidth, shortest path, and make necessary adjustments in the event of any normal traffic congestion. While MPLS –TE is the default controller of the LSPs, the SDN controller would be monitoring in real time the overall network topology and traffic adjustments by MPLS-TE. If the SDN controller senses extreme traffic situation which MPLS –TE cannot manage, the SDN controller which has a global view of the network topology could take over the control and push PCEP commands to head end LSP to adjust the flow. Once the head end router receives PCEP commands from SDN controller, it would use the traditional RSVP to notify other routers.

This Hybrid approach would protect the current investments and offer the much-needed flexibility and service management capability to TSPs at an affordable cost.


  1. SDN Use cases for Service Provider Networks – Evolving to an SDN Enabled ISP backbone: Key Technologies and Applications - IEEE Communication Magazine Oct 2016
  2. IEEE Communication magazine Oct 2016.
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