What is SDON?

This article is reprinted from the WeChat public account "Xianzao Classroom", the author is Xiaozaojun. Please contact the WeChat public account of Xianzao Classroom to reprint this article.

Hello everyone, I am Xiaozaojun.

I have introduced SDN, or Software Defined Network, to you many times before.

We know that SDN is the future development trend of data networks. It separates the control and forwarding functions of traditional network nodes (switches, routers), centralizes the control function, realizes unified management and scheduling of the entire network, and improves the efficiency and flexibility of the network.

SDN Architecture

Well, we can't help but think that SDN is a reconstruction of the data communication network. We are now in the era of optical communication. Telecommunications networks, including 5G, and transmission networks are basically all-optical networks. So can optical networks also support SDN technology?

The answer is yes.

This technology, which introduces SDN into the optical transport network (OTN) and realizes the programmability of the optical network, is called SDON (Software Defined Optical Network).

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In terms of principle and architecture, SDON and SDN are very similar.

SDON also separates the control plane and forwarding plane of network nodes, and then introduces the concept of controller, integrating network management functions into the controller to achieve centralized control and unified scheduling of the entire optical network.

SDON Architecture Diagram

Although SDON and SDN look very similar, SDN is proposed for IP networks after all, and lacks support for underlying optical networks. The properties of the optical layer and the electrical layer are completely different, and there is no one-to-one correspondence between the two.

Therefore, SDON cannot directly copy the SDN technology, but must be expanded on the basis of SDN.

IP layer (electrical layer) and optical layer are independent of each other

Key technologies of SDON

Generally speaking, the three key technical links of SDON are: programmable optical layer technology, SDON controller and optical network virtualization technology.

Let’s look at them one by one, from the bottom up.

First, there is programmable optical layer technology.

To achieve software definition and programmability of the optical layer, the prerequisite is that the optical layer devices must be flexible enough. In other words, some performance parameters of the optical modules and optical devices at the bottom layer can be modified and cannot be "hard-coded".

In fact, with the rapid development of optical communication technology, our optical modules and devices now basically have programmable capabilities. The wavelength, input and output power, modulation format, signal rate, forward error correction code (FEC) type selection of the optical transceiver, and the gain adjustment range of the optical amplifier, etc., these parameters can be adjusted online.

In addition, the emergence of flexible grid technology breaks the limitation of fixed grid of traditional wavelength channels. ROADM technology breaks the interval division of traditional wavelength channels of 50GHz and 100GHz.

All these prerequisites finally make optical path switching programmable. The previously unchangeable optical path has evolved into a dynamic system with perceptible and adjustable physical properties. Only such an optical layer can be flexibly scheduled by the SDON controller.

Let's take a look at the SDON controller.

If optical layer programmability is the nerve endings of SDON, then the SDON controller is the brain of SDON.

In the SDON network architecture, the control of optical network performance parameters is handed over to the SDON controller, which implements global control and adjusts various parameters to achieve optimal network performance.

With the rapid development of 5G and data centers, the user demands and application scenarios faced by the transmission network are becoming more and more complex. In response to different demands and scenarios, the transmission network needs to have different QoS, latency, bandwidth and other indicators, and there are many matching modes.

If optical networks want to flexibly respond to these demands, they must introduce SDON controllers with service orchestration capabilities.

Finally, let’s take a look at optical network virtualization.

The core concept of the SDON architecture system is to virtualize the optical network.

To put it simply, optical network virtualization is to create multiple independent virtual optical networks based on a complete set of physical optical network underlying resources.

The physical layer becomes several virtual abstract layers, and users control the abstract layers through open programmable interfaces.

Users can control the network through apps. The complex operations of the underlying physical network are completely shielded, and users can easily call and deploy optical network resources like building blocks.

This is the secret of SDON - "application drives the network" and "software defines the network".

Advantages of SDON

Finally, let’s talk about the advantages that SDON will bring in practical applications.

In short, the advantages of SDON include three aspects:

1. Improve operation and maintenance efficiency and reduce operation and maintenance costs

2. Rapid service activation, support for appointment activation

3. Dynamic path protection, flexible channel reduction

Let’s look at them one by one.

First, improve operation and maintenance efficiency and reduce operation and maintenance costs.

This advantage is obvious. After SDON technology separates control and forwarding, it centralizes the underlying network management capabilities and realizes the evolution of optical networks from "manual static network management configuration" to "real-time dynamic intelligent control".

This is like traffic control. In the past, there had to be a traffic policeman at each intersection. Now, all intersections are under the unified control of the traffic police command center. Efficiency will inevitably increase and costs will inevitably decrease.

Second, the service is activated quickly and supports appointment activation.

In addition to operation and maintenance, SDON also improves the speed of service provisioning.

In fact, if it is only activated manually, it will not be much faster. The key is that the SDON controller can introduce AI to help.

The SDON controller with AI can provide available routes quickly through intelligent calculations after receiving a service activation request based on the current network topology (including parameters such as rate and bandwidth) and business needs, allowing services to be quickly activated.

SDON can also build a configuration library for similar services based on log analysis, and directly call or refer to these configurations when opening new services. This is of course much faster than manual decision-making.

Service packages are not static. During the use of services, SDON also supports "automatic adjustment" of bandwidth, which can also save resources and reduce costs.

The so-called scheduled activation is easier to understand. It means that all the configurations are done in advance, and the service is automatically launched during the specified time period.

The third one is dynamic path protection and flexible channel reduction.

After the introduction of SDON, the operation status of the optical network is fully monitored. When a node or path in the network has a problem, SDON can immediately plan a new route and implement path switching within 50ms to reduce the impact on the business.

Sometimes, the network is not completely interrupted, but performance has degraded (such as fiber aging). In this case, SDON does not need to reroute, but based on network programmability, it can modify optical network parameters, such as modulation mode, and achieve another form of dynamic path protection by reducing network performance (such as reducing the rate).

There are many benefits of SDON, the above are just some of them.

Under the SDON architecture, the entire optical network becomes more like a whole. Optical resources become a resource pool, which makes quantification and statistics more convenient, and commissioning and operation and maintenance more intelligent. Users are happy to use it, operators' investments are protected, CAPEX is further reduced, and everyone is happy.

Because SDON has obvious advantages, it is gradually becoming the mainstream development direction of the industry.

The SDN of optical transmission networks has gone through the concept verification in 2014 and the field test in 2015, and is currently in the early commercial stage. Operators at home and abroad have successively commercialized SDON. Not long ago, Tianjin Unicom and ZTE successfully deployed SDON services, which greatly improved the efficiency of core aggregation services in large cities. It is believed that more optical networks will realize the transformation to SDON in the future.