With a growing need for Time-Sensitive Networking (TSN), primarily to meet new and developing industrial automation and in-vehicle networking applications, the IEEE 802.1 Working Group continues to expand the development of standards for the transport of synchronized time over Ethernet (IEEE 802.3) and Wi-Fi (IEEE 802.11) networks. This is essential as there is an increased demand from the automotive, industrial and manufacturing sectors to deploy TSN applications to help advance productivity, grow their businesses and provide end-users with improved products and services.
The IEEE 802.1 Working Group recently completed work on IEEE 802.1AS™-2020 – Standard for Local and Metropolitan Area Networks–Timing and Synchronization for Time-Sensitive Applications, which includes features of the also recently completed IEEE 1588™-2019 Precision Time Protocol (PTP). Prior to publication of the original IEEE 802.1AS standard, IEEE 1588 was used for transport of precise time in local area networks. That said, the specification of time transport in the original IEEE 802.1AS and the new features of IEEE 802.1AS-2020 will allow applications in the industrial automation and automotive sectors to use IEEE 802-based synchronization with convergence to a single standard.
The recent release of IEEE 802.1AS-2020 builds upon IEEE 802.1AS-2011, originally developed to support plug-and-play audio and video applications. In fact, IEEE 802.1AS-2020 represents a significant standard revision that also addresses 5G integration requirements, while maintaining backward capabilities with the original standard.
New Feature Benefits
Although IEEE 802.1AS is based on IEEE 1588, the requirements in IEEE 802.1AS-2011 focused on two aspects that are very important for local area network applications:
- Increased Cost Savings: Use of a free-running clock allows for use of low-cost oscillators that are common in networks for applications such as industrial automation and automotive in-vehicle.
- Improved Reliability: The IEEE 802.1AS protocol uses mechanisms to validate that all devices in a network operate the protocol. For example, if an Ethernet switch is detected and found to not operate IEEE 802.1AS, that switch is excluded from transporting time. This provides consistent performance, which is essential to many local area network applications.
IEEE 802.1AS-2020 builds upon IEEE 802.1AS-2011 by adding:
- Transport over IEEE 802.11 links that use the fine timing measurement (FTM) protocol, which allows for better time accuracy than the timing measurement (TM) protocol of IEEE 802.11 used in IEEE 802.1AS-2011
- Multiple domains that are needed:
- for professional audio/video and newer industrial and automotive applications to help facilitate fault tolerance and redundancy
- to allow both working clock and global time for industrial applications
- Improved facility to detect the presence of devices not compliant to IEEE 802.1AS-2020 and/or IEEE 802.1AS-2011, eliminating the use of these devices for timing transport
- Inclusion in the PTP profile of the new Common Mean Link Delay Service of IEEE 1588-2019, which allows a single PTP link delay measurement to be made for use by all PTP domains.
All of the above features were developed while satisfying the requirements for IEEE 1588 profiles. The collaboration on the development of IEEE 802.1AS-2020 and IEEE 1588-2019 helped to ensure consistency between the two newly revised standards. This included facilitating the inclusion in IEEE 1588-2019 of the measurement of frequency offset relative to the grandmaster by accumulation of neighbor frequency offsets and the media-independent/media-dependent layer architecture. It also led to the development of the Common Mean Link Delay Service feature of IEEE 1588-2019. This feature was initially identified as a requirement for IEEE 802.1AS-2020; however, it was felt other PTP profiles might benefit from it, as well.
New Feature Benefits
Due to the relevance of IEEE 802.1AS to many local area network applications, work is in progress to standardize use of IEEE 802.1AS in new markets:
- Industrial automation: IEEE 802.1AS is specified as a requirement for time synchronization in drafts of IEC/IEEE 60802, TSN Profile for Industrial Automation.
- Automotive in-vehicle: IEEE 802.1AS is specified as a requirement for time synchronization in drafts of IEEE P802.1DG, TSN Profile for Automotive In-vehicle Ethernet Communications.
- 5G: For integration of the 5G System into industrial automation applications, IEEE 802.1AS is specified as a requirement in specifications for 5G technology in 3GPP.
Initially driven by the industrial automation and in-vehicle network communication, and the deployment of 5G, TSN is growing in importance and demand and will continue to spark innovation in new markets. The IEEE 802.1 Working Group remains committed to supporting new beneficial applications through the development of new standards and revision to existing ones. Already, new work on an amendment to IEEE 802.1AS-2020 has begun to specify hot-standby as an option for improved fault tolerance and redundancy.
Authors:
- Glenn Parsons, IEEE 802.1 Working Group Chair
- Geoffrey Garner, IEEE 802.1AS Editor
