SDN in Transport Networks - Challenges, Solutions & Benefits

According to a recent report from Market Research Future, the market size of transport networks is growing at a rate of 16% CAGR to reach $34 billion by 2023. The growth in the mobile towers, enterprise connectivity services and the rise of data centers are fueling the growth of transport networks. SDN-izing the transport network is not an easy task. This article provides some details on the challenges of managing the transport network, solutions available in the market and the benefits of SDN-izing transport networks. 

SDN had its roots in the data center - but, the technology has slowly crept into Enterprises, Campuses and even into the service provider networks. SDN is a powerful technology, if implemented right, can provide numerous operational benefits to the service providers.  SDN not only provides operational efficiencies, but also helps service providers to create newer revenue streams. SDN can potentially be deployed by the service providers at the Edge, Access and Transport segments of the network. Software Defined WAN (SD-WAN) solution is one of the popular WAN offerings from the service providers across the globe. According to IHS Markit, from just $444 million revenue in 2017, SD-WAN revenue has already surpassed $667 million as of 3Q'18. Now, service providers are exploring how SDN can be deployed in other segments of the WAN, especially to simplify the management of Transport Networks.

What is a Transport Network?

A transport network provides connectivity services for

• Mobile Towers - Connecting the mobile 3G/4G/5G towers to the core network
• Enterprises - Connecting the corporate and branch offices of an Enterprise, to provide a secure private IP network.
• Datacenters - By connecting the data centers together, using a secure link. 

A transport network includes multiple technologies such as packet, optical, microwave and satellite communications. Traditionally, the transport network had dedicated circuit switched technologies such as Synchronous Digital Hierarchy (SDH) and optical transport networks (OTNs). But, today packet/IP based technologies are deployed in the transport networks (in addition to the optical technologies), to share the same links across multiple customers. For example, Multi-Protocol Label Switching (MPLS) is a popular IP based protocol used in packet transport networks today.

Challenges faced by Service Providers in Transport Networks

Managing transport networks is always a nightmare for the service providers. Some of the challenges faced by service providers while managing transport networks are:

• The vendors who supply optical network equipment are different from the ones who supply packet network equipment. There is no standard way of managing these network equipment and hence, Service providers need to have specialists to manage these equipment. 
• Optical network equipment are managed by vendor specific proprietary Element Management Systems (EMS). This increases the number of "devices" that sit in the network, consuming additional power, cooling and space
• The packet layer and the optical layer equipment are managed separately. Hence, change management activities are complex, potentially taking several days or even weeks to implement.
• Any link failures in the optical layer doesn't immediately reflect in the packet layer (and vice versa). This negatively impacts the quality of service and the customer experience. 

How can SDN solve the Transport Network Challenges?

The need for SDN is today well understood and acknowledge by the industry. SDN can solve multiple problems faced by service providers while managing the Transport Networks.

1. SDN introduces standard APIs for managing multi-vendor network equipment. For example, the industry is looking at standardizing the management of ROADM (Reconfigurable Optical Add-Drop Multiplexer) devices. One such initiative is the Open ROADM initiative championed by AT&T. This group has recently reached a critical milestone where vendors such as Ciena and Fujitsu are able to demonstrate the interoperability of multi-vendor optical equipment, through standard APIs. Open Optical and Packet Transport group which is part of the Telecom Infra project, championed by Facebook is looking at standardizing the management of optical transponders, line systems, IP access devices, network simulation and planning tools
2. SDN supports multi-layer / multi-domain management capabilities. For example, Infinera and Sedona systems support capabilities to manage both optical layer and packet layer equipment through their SDN platforms such as Xceed and NetFusion, respectively. It is important to note that Xceed is based on open source OpenDaylight SDN controller platform. 
3. SDN allows programmatically creating and managing multiple virtual networks on top of a physical network. For example, a small cell in 5G network can automatically register with the network and establish a connectivity with the 5G core network. Or, an Enterprise customer can dynamically manage the bandwidth of their virtual pipe though a mobile application. 

What are some critical use cases of SDN in Transport Networks?

• Dynamically modify bandwidth based on the application requirements 
• Simplify operations through automation of multi-layer (packet/optical), multivendor & multi-domain orchestration 
• Improve the utilization of network resources by optimizing between the different layers and selecting an optimal network path 
• Improves the speed of rolling out new services by providing an API access to transport layer 

Benefits of SDN-izing the Transport Networks

SDN-izing transport networks provides both short-term and long-term business benefits such as the following:

• Lowers costs (CAPEX & OPEX) by standardizing the management of multi-layer, multi-vendor, multi-domain packet/optical network equipment
• Dramatically improves the speed of service provisioning and service activation, thereby improving customer experience 
• Makes transport resources dynamic and visible to applications for newer services