What’s the Difference Between Ethernet and Time-Sensitive Networking?

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如今，从事工业通信工作的任何人必定会违反时间敏感网络（TSN）的主题。TSN肯定会来到这里。唯一必须澄清的是什么形式和形式。但是，即使在今天，它在工业通信方面的优势并不总是很清楚。

History

以太网在1980年代初期被介绍给办公室，由于（当时）轰动一时的10 mb/s，由于其高吞吐量而很快变得非常受欢迎。但是，对于实时应用，该以太网对于实时应用不实用，因为它使用了称为派对线的常见媒介。以高利用率发生的碰撞导致办公室设置问题。

1. In this Ethernet frame, data fields relevant to TSN data-flow identification are shown in green.

In the next step of its development, collisions were eliminated through the introduction of switched networks. In addition, with quality of service (QoS), Ethernet datagram prioritization was introduced(Fig. 1)。

对于工业应用，保证的延迟尤为重要。尽管QoS，办公室中使用的标准以太网只能保证潜伏期直至某个点，尤其是在高网络利用率的情况下。

造成这种情况的原因有很多，主要问题是商业多层开关中常用的商店和前景策略以及不可能保留带宽的事实。

存储和向前表示，转发之前，开关会接收完整的数据报。这在开关中的处理方面具有优势，但它也带来了可能对潜伏期和可靠性产生负面影响的潜在问题：

When going through a switch, a datagram is delayed by an amount depending on its length. If switches are cascaded, the effect is magnified.
由于开关没有无限的存储容量，因此如果网络经历过度利用（流量过多），则可以拒绝数据报；这意味着数据报（即使给予更高的优先级的数据”都可以丢失。
Long datagrams can block a port for relatively long times.

开关级联从一开始就在工业环境中提出了挑战。除了在IT领域，线，环和树拓扑中使用的星形拓扑外，经常用于自动化(Fig. 2)。These adapted topologies significantly reduce Ethernet installation wiring requirements and costs. Hence, in industry, two-port switches employing a cut-through strategy are integrated into field devices. Cut-through means that datagrams are forwarded before being completely received.

2. Among the frequently used topologies in automation are line and ring.

One Size Fits It All: Industrial Ethernet up to Now

由于经典以太网没有足够的带宽保留功能，因此自动化专家在2000年开始开发自己的以太网扩展。但是，他们所采取的道路差异很大。在以下方法之间进行了区分：

使用以太网作为现场总线的传输介质的协议。这些协议要求自己对以太网介质的完全控制。经典的TCP/IP通信只能通过FieldBus（EtherCat和PowerLink）或通过FieldBus（SERCOS）分配的频道以Piggyback样式进行。带宽控制牢固地掌握在田野总线手中。
通过以太网上的时间切片程序保证带宽保留的协议(Fig. 3)。Profinet Irt应该在此处提及。IRT可以在操作软的实时或背景流量的相同电缆上进行硬确定性实时数据传输。传输路径的精确计时模型是规划时间切片的必要条件。
基于以太网电缆共享的协议。这些协议使用QoS，并在工厂和过程自动化应用中在家中。Profinet RT和以太网/IP是值得注意的示例。这些协议仅限于软实时（周期时间≥1ms）的范围。

对于这些标准，需要特殊的硬件支持，因此需要特殊的ASIC。由于Profinet RT和以太网/IP也基于带切割的嵌入式两端口开关，因此它们在这里也不豁免。

3.物理，电缆和开关有助于数据传输的延迟。必须使用时间插槽方法（Profinet IRT和TSN Time Aware Shaper（TAS））来考虑这一点。

Enter TSN

With TSN, extensions for standard Ethernet in accordance with IEEE 802.1 that break free of past limitations have successfully been developed. Thus, there’s now a standardized layer 2 in the ISO 7-layer model with upward compatibility to the previous Ethernet and hard real-time capability. With 802.1AS-rev, TSN also defines an interoperable, uniform method for synchronizing distributed clocks in the network.

由于TSN总是进行最佳努力通信，因此对于硬实时应用程序以及所有其他应用程序（Web服务器，SSH等）来说，有可能使用电缆的常见用途。在这方面，TSN与Profinet Irt并不不同，并且提供了可比的性能。

TSN的新功能是需要更广泛的网络配置。可以进行集中或分散的配置。目前正在讨论和实施两种类型的配置。两种配置机制之间的互操作性是未来的发展目标。

实际优势

The most common answer is that with a larger market, less expensive network interfaces also appear on the market. After all, TSN will also be found in building automation and the automotive industry in the future. As a matter of fact, the market for embedded TSN solutions is expected to be significantly bigger than the current market for all industrial Ethernet solutions put together.

The greatest technical advantage of TSN over previous industrial Ethernet methods is its scalability. Unlike current industrial networks, TSN was not defined for a specific transmission rate. TSN can be used for 100 Mb/s just as for 1 Gb/s, 10 Mb/s, or 5 Gb/s.

It also enables topologies to be better optimized because now adapted data rates can be selected for various segments. Whether it’s Gb/s, 100 Mb/s, or 10 Mb/s, a unified layer 2—IEEE802.1/TSN—is used.

A uniform network infrastructure also helps personnel tasked with setting up and maintaining the network. That’s because, thanks to TSN, solutions can now be used in sectors other than automation: building, process, and factory automation, as well as energy distribution.

这提示了下一个优势 - 培训因素。TSN在许多大学中已经是一个主题，主要是在研究阶段。但是，技术和职业学院已经对此主题表现出兴趣。可以肯定地说，TSN将成为工程师，技术人员和熟练工人的基本知识。不再需要为不同的现场插头进行重新培训。

Brownfield, or What Will Happen to Today’s Protocols?

在几乎所有与TSN相关的工作组中，都有反复出现的主题：如何保护向TSN的过渡以及对现有安装的供应，例如Brownfield应用程序？

在各方面,重点是放在我t possible for customers to easily and smoothly transition to TSN. It can already be said today that the existing industrial Ethernet protocols aren’t just going to vanish overnight. On the contrary, anyone using PROFINET, EtherNet/IP, EtherCAT, or a similarly widespread industrial Ethernet protocol today can safely assume that he or she will also be able to operate networks with these protocols— and receive support and replacement parts—in 10 years’ time.

4.将TSN段与profinet和ethercat结合使用。

所有工业以太网组织都提供了描述现有工厂如何与新的基于TSN的设备合作的模型。现有工业网络的界面由网关（SERCO），耦合器（Ethercat）或没有任何特殊硬件（PROFINET RT）制作（图4）。In particular, PROFINET and EtherNet/IP plan to make their complete protocols available right on TSN as layer 2. This makes stepwise transition to TSN possible.

结论

TSN will be found everywhere in new installations, as well as in the form of islands or segments introduced incrementally into existing installations.

However, with TSN, there will be new players in the industrial Ethernet field. OPC UA with new transport protocol PUB/SUB, in conjunction with TSN, is already a competitor to classic protocols. For the manufacturers of field devices, this means that the classic industrial Ethernet solutions, as well as TSN and the new players, must be supported.