Understanding Transport SDN

Transport SDN is a network architecture that brings software-defined principles to the transport layer. Transport SDN enables centralized network management, programmability, and dynamic resource allocation by decoupling the control plane from the data plane. This empowers network operators to adapt to changing demands and optimize network performance swiftly.

Understanding its key components is essential to comprehend the inner workings of Transport SDN. These include the Transport SDN Controller, which acts as the brain of the network, orchestrating and managing network resources. Additionally, the Transport SDN Switches play a crucial role in forwarding traffic based on the instructions received from the controller. Lastly, the OpenFlow protocol is the communication interface between the controller and the switches, facilitating seamless data flow.

Real-World Applications of Transport SDN

1 = Transport SDN has found wide-ranging applications across various industries. In the telecommunications sector, it enables service providers to efficiently provision bandwidth, optimize traffic routing, and enhance network resilience.

2 = Within data centers, Transport SDN simplifies network management, allowing for dynamic resource allocation and improved scalability. Moreover, Transport SDN facilitates intelligent traffic management in smart transportation and enables seamless vehicle connectivity.

3 = While Transport SDN offers immense potential, it also has its fair share of challenges. Organizations must address some hurdles to ensure interoperability between different vendor solutions, security concerns, and the need for skilled personnel.

4 = Looking ahead, the future of Transport SDN holds promise. Advancements in technologies like artificial intelligence and machine learning are anticipated to enhance the capabilities of Transport SDN further, unlocking new possibilities for intelligent network management.

Critical Benefits of Transport SDN:

1. Improved Network Efficiency: Transport SDN allows for intelligent traffic engineering, enabling network operators to optimize network resources and minimize congestion. Transport SDN maximizes network efficiency and improves overall performance by dynamically adjusting routes and bandwidth allocation based on real-time traffic conditions.

2. Enhanced Network Agility: With Transport SDN, network operators can rapidly deploy new services and applications. Leveraging programmable interfaces and APIs can automate network provisioning, eliminating manual configurations and reducing deployment times from days to minutes. This level of agility enables organizations to respond quickly to changing business needs and market demands.

3. Increased Network Scalability: Transport SDN provides a scalable and flexible solution for network growth. Network operators can scale their networks independently by separating the control and data planes and adding or removing network elements. This scalability ensures that the network can keep pace with the ever-increasing demands for bandwidth without compromising performance or reliability.

SDN data plane

Forwarding network elements (mainly switches) are distributed around the data plane and are responsible for forwarding packets. An open, vendor-agnostic southbound interface is required for software-based control of the data plane in SDN.

OpenFlow is a well-known candidate protocol for the southbound interface (McKeown et al. 2008; Costa et al. 2021). Each follows the basic principle of splitting the control and forwarding plane into network elements, and both standardize communication between the two planes. However, the network architecture design of these two solutions differs in many ways.

SDN control plane

The control plane, an essential part of SDN architecture, consists of a centralized software controller that handles communications between network applications and devices. As a result, SDN controllers translate the requirements of the application layer down to the underlying data plane elements and provide relevant information to the SDN applications.

As the SDN control layer supports the network control logic and provides the application layer with an abstracted view of the global network, the network operating system (NOS) is commonly called the network operating system (NOS). In addition to providing enough information to specify policies, all implementation details are hidden from view.

The control plane is typically logically centralized but is physically distributed for scalability and reliability reasons, as discussed in sections 1.3 and 1.4. The network information exchange between distributed SDN controllers is enabled through east-westbound application programming interfaces (APIs) (Lin et al. 2015; Almadani et al. 2021).

Despite numerous attempts to standardize SDN protocols, there has been no standard for the east-west API, which remains proprietary for each controller vendor. It is becoming increasingly advisable to standardize that communication interface to provide greater interoperability between different controller technologies in different autonomous SDN networks, even though most east-westbound communications occur only at the data store level and don’t require additional protocol specifics.

However, API east-westbound standards require advanced data distribution mechanisms and other special considerations.

Applications of Transport SDN:

1. Data Center Interconnect: Transport SDN enables seamless connectivity between data centers, allowing for efficient data replication, backup, and disaster recovery. Organizations can optimize resource utilization and ensure reliable and secure data transfer by dynamically provisioning and managing connections between data centers.

2. 5G Networks: Transport SDN plays a crucial role in deploying 5G networks. With the massive increase in traffic volume and diverse service requirements, Transport SDN enables network slicing, network automation, and dynamic resource allocation, ensuring efficient and high-performance delivery of 5G services.

3. Multi-domain Networks: Transport SDN facilitates the management and orchestration of complex multi-domain networks. A unified control plane enables seamless end-to-end service provisioning across different network domains, such as optical, IP, and microwave. This capability simplifies network operations and improves service delivery across diverse network environments.

SDN in the application plane

SDN applications are control programs that implement network control logic and strategies. In this higher-level plane, a northbound API communicates with the control plane. SDN controllers translate the network requirements of SDN applications into southbound commands and forwarding rules that dictate the behavior of data plane devices. In addition to existing controller platforms, SDN applications include routing, traffic engineering, firewalls, and load balancing.

In the context of SDN, applications benefit from the decoupling of the application logic from the network hardware along with the logical centralization of the network control to directly express the desired goals and policies in a centralized, high-level manner without being tied to the implementation and state-distribution details of the underlying networking infrastructure. Similarly, SDN applications consume network services and functions provided by the control plane by utilizing the abstracted network view exposed to them through the northbound interface.

SDN controllers implement northbound APIs as network abstraction interfaces that ease network programmability, simplify control and management tasks, and enable innovation. Northbound APIs are not supported by an accepted standard, contrary to southbound APIs

**Data and Control Planes**

The traditional ways to build routing networks are where the SDN revolution is happening. Networks started with tight coupling between data and control planes. The control plane was distributed, meaning each node had a control element and performed its control plane activities. SDN changed this architecture, centralized the control plane with a controller, and used OpenFlow or another protocol to communicate with the data plane. However, all control functions are handled by a central controller, which has many scaling drawbacks.

**Distribution and Centralized**

Therefore, we seem to be moving to a scalable hybrid control plane architecture. The hybrid control plane is a mixture of distributed and centralized controls. Centralization offers global visibility, better network operations, and optimizations. However, distributed control remains best for specific use cases, such as IGP convergence. More importantly, a centralized element introduces additional value to the Wide Area Network (WAN) network, such as network traffic engineering (TE) placement optimization, aka Transport SDN.

For additional pre-information, you may find the following posts helpful:

1. WAN Virtualization
2. SDN Protocols
3. SDN Data Center