Time - Sensitive Networking (TSN) in IEC 61850 substation automation networks

Authors: Patrick Wetterwald, Cisco, France and Maik G. Seewald, Cisco, Germany

These main properties of a Deterministic Network could be summarize by the following:

  • Bounded Latency
  • Bounded Jitter (latency variation)
  • Extraordinary low packet loss

Deterministic traffic and normal IT traffic (best effort and QOS managed traffic) will cohabit on the same network without impacting the deterministic flows.

This level of determinism in a network can be reached by synchronizing all the nodes participating to the network, by reserving physical resources along the path and by defining path redundancy (duplication and elimination of packets in a 1+1 or 1+N scheme).

A typical network that appears to be a topology of end points, routers and bridges could be illustrated as in Figure 1.
Listeners are receiving the flow coming from the talker via different layer 2 islands interconnected by layer 3 routers.
In a deterministic network, the connectivity is not enough; we need to ensure that all the devices along a path have the necessary resources to handle the time sensitive streams to meet the deterministic requirements. The network now could be represented by a suite of time aware buffers and links as described in the Figure 2.

The management of Queues, Buffers and Transmission Medium (wires or wireless links) replaces the notion of router and bridge.

Existing Application Domains
Technologies based on deterministic networking already exist in several industries. The media industry has already adopted the merits of determinism in order to stream huge amounts of data in music and film productions, broadcast scenarios, cinemas, and live recordings.

Low latency and time synchronized nodes are especially important in these scenarios.
In the industrial environment including manufacturing, TSN (Time Sensitive Network) allows precise machine-to-machine coordination and communication including robots and other actors. Deterministic access to controls and IO devices from higher layers leads to a truly converged architecture. It enables full visibility of machine functions and diagnostics in real-time which leads to higher efficiency and utilization of the installed equipment. TSN is a key enabler for initiatives like Digital Factory or Industry 4.0.

In the automotive industry, Deterministic Ethernet enables the integration of safety and non-safety functions in a single network based on partitioning. This approach reduces the complexity and allows seamless sub-system integration. The entire design of a car including maintainability and flexibility will benefit from the adoption of TSN technologies. Other prominent areas for TSN are oil & gas, aerospace and defense as well as the transportation industry.

This brief collection of user domains depicts that TSN is already deployed in use case scenarios related to control systems with harsh safety requirements. And this makes perfect sense because critical parameters are guaranteed with TSN based technologies. Hard, real-time network performance for demanding control applications are addressed perfectly. Robustness and reliability of the control systems will benefit. Secondly, TSN supports the need for a converged architecture to increase efficiency, to allow a multi-service concept and to enable new applications. A single, switched network interconnecting various subsystems comes along with a list of benefits: fewer cables and control equipment, real-time coordination and optimization. This leads to cost reduction in development and operations because the convergence on a few standards based network lowers the operations and maintenance expenses, reduces need for specialized skills and components, and reduce dependency on purpose-built products. (Figure 3).

Power. Flexible. Easergy.
BeijingSifang June 2016