WHITEPAPER –
Accelerate time-to-market with Ethernet TSN solutions
Accelerate time-to-market with reliable Ethernet TSN solutions using Comcores IP.
Ever since its introduction in 1973, the Ethernet protocol has expanded and evolved to support every conceivable connectivity application. Ethernet is designed to be a non-deterministic packet-based network, but this also means that Ethernet cannot satisfy the needs of applications that require time-critical, fail-safe operation. These short-comings are targeted by the Ethernet Time-Sensitive Networking (TSN) group of standards.
Time-sensitive applications require strict control of latency and jitter, which is not possible with conventional Ethernet. Ethernet TSN provides additional features and mechanism that address time synchronization, latency and reliability, which enables applications with time-sensitive, fail-safe requirements to use the same infrastructure as other Ethernet-based services.
Comcores is a pioneer in Ethernet TSN, offering a comprehensive portfolio of Intellectual Property (IP) components that can be used by equipment manufacturers to accelerate development of Ethernet TSN end-points, switches and gateways (Ethernet TSN MAC, Manticore Ethernet TSN Switch IP and Generalized PTP IP). With a dedicated program for continuous development of Ethernet TSN IP solutions, Comcores ensures supports for the latest Ethernet TSN standards, profiles and feature extensions.
What is Ethernet TSN?
Ethernet TSN is not a single standard, but a group of extensions to the existing Ethernet IEEE 802.3 standard that address time-sensitive and fail-safe applications. The work was started in 2012 with the formation of the IEEE 802.1 TSN task force, who were previously engaged in adapting Ethernet for audio/video bridging applications. The task force is focused on extending existing IEEE 802.1Q standards to accommodate the needs of time-sensitive networking as well as defining TSN profiles for mobile fronthaul, service provider network sharing, industrial automation and in-vehicle communication.
Figure 1: Ethernet TSN Components
Each of the extensions to the existing standards is designed to address a specific issue with conventional Ethernet. Figure 1 shows the four main components of Ethernet TSN addressing Ethernet challenges with respect to time synchronization, reliability, latency and resource management. In combination, they enable Ethernet TSN to be a viable solution for applications that previously could not be addressed with Ethernet.
The following sections will take a look at the major Ethernet performance issues and how the extensions address those shortcomings. This will be followed by an overview of the applications of TSN for 5G, industrial automation, automotive in-vehicle communications and avionics. The paper will conclude with a description of Ethernet TSN solutions offered by Comcores.
Figure 2: Generalized Precision Time Protocol
Time Synchronization
The first challenge to be addressed is that Ethernet is not a time synchronized network. The answer to this is Precision Time Protocol (PTP) defined in IEEE 1588-2008 as PTP version 2.0 and recently updated with a backward compatible version 2.1 in IEEE 1588-2019. In Ethernet TSN, an adaptation of PTP called Generalized PTP (gPTP) is used, which is defined in standard IEEE 802.1AS. Both use a hierarchical master-slave architecture to distribute clock synchronization and correction information in the physical network.
PTP is based on a network whose devices synchronize their time references using synchronization messages sent over the Ethernet Local Area Network (LAN). The connected clocks communicate and elect a grandmaster clock to be the ultimate reference and synchronize their time using messages from the grandmaster.
Figure 2 shows an Ethernet network supporting gPTP. PTP v2 introduced the concept of a “transparent clock”, which enables devices relaying PTP messages to support their own clock and send follow-up messages that adjust for the delay through the device. This is called two-step synchronization. gPTP has taken this concept further and required all network nodes to support transparent clocks. In gPTP, the grandmaster first sends a synchronization message and then a follow-up message indicating the precise time the synchronization message was sent. While PTP v2 supports one-step synchronization where a follow-up message is not required, gPTP requires two-step synchronization.
On each device, the receiving port is considered a clock slave port while all other egress ports then act as clock masters to other nodes in the network. Each master port propagates the synchronization message and also sends a follow-up message indicating the path delay from the grandmaster to the node plus the delay through the bridge. With the sync message and the delay information, each node can compensate and correct their clocks ensuring reliable time synchronization.
Latency
One of the main challenges when using conventional Ethernet for time-sensitive applications is latency. The absolute latency is an issue, but the variability and unpredictability of latency is of much more concern. If the latency and jitter in a network could be held within limits, or bounded, then it could be possible to support time-sensitive applications.
In Ethernet TSN, a number of extensions to existing standards have been proposed to address the latency challenge. The goal is not to eliminate latency or jitter, but to reduce the latency as much as possible and, above all, guarantee maximum limits for latency and jitter performance. Two solutions, in particular, go a long way towards meeting this goal; time-aware scheduling and preemptive forwarding.