When Will 5G Enter Industrial TSN?
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By Jeff Shepard for Mouser Electronics
Published March 7, 2022
Time-sensitive networking (TSN) is being deployed across a growing number of applications. But for 5G-based wireless TSN (WTSN), it’s still early. WTSN will open new applications, such as mobile robots, electric power grids, chemical plants, smart cities, and other geographically dispersed applications, plus automotive and transportation systems that can’t be connected to wired TSN networks (Figure 1). WTSN will bring revolutionary new capabilities to TSN. It will also increase the deployment flexibility and reduce the installation costs of TSN. 5G-based WTSN is tantalizingly close, but it’s not quite ready for deployment; the needed standards are still evolving and emerging, and the hardware and software are under development.
Figure 1: 5G-WTSN will expand the use of time-sensitive networking to new applications not possible with wired TSN implementations. (Source: wladimir1804/Stock.Adobe.com)
Many industrial applications require fast, deterministic communication for real-time control. In IEEE 802, definitions have been added to make Ethernet deterministic. 3GPP Release 16 adds support for integration of TSN protocols to guarantee latencies in 5G communications. The pending Release 17 will take 5G further toward supporting WTSN. The upcoming IEC/IEEE 60802 profile specifies the application of TSN for industrial automation and gives guidelines regarding the TSN support needed from 5G.
In addition to the 3GPP, IEC, and IEEE, several efforts are underway to integrate 5G with TSN to create combined WTSN/TSN industrial networks. The EU-funded 5G-SMART is a consortium of industry partners and research institutes exploring 5G-enabled smart manufacturing concepts, including WTSN. The 5G Alliance for Connected Industries and Automation (5G-ACIA), has identified how 5G has all the essential capabilities required to interwork with TSN for industrial automation.
Four main areas are included in IEEE 802.1 TSN standards: Time synchronization, bounded latency, reliability, and resource or network management. This article looks at how each of those four areas maps into 5G and explores how 5G will move WTSN forward to the next generation of industrial automation devices and the industrial internet of things (IIoT). It reviews existing and emerging standards in Release 16, Release 17, and IEC/IEEE 60802, looking at how 5G ultra-reliable low latency communication (URLLC) will be enhanced with direct device-to-device communication enabled by sidelink, which doesn’t require relaying data through the network for communication to take place. It also considers radio spectrum options and deployment choices such as architectures for hybrid public/private networks and network slicing.
5G Time Synchronization
The move to basic 5G services didn’t result in any fundamental change in radio network time synchronization needs, but WTSN will require more stringent local synchronization accuracy for 5G nodes. The telecom industry has standardized the IEEE 1588 precision time protocol (PTP) to support synchronization requirements in the millisecond range. The 3GPP TS 23.501 specification addresses the integration of a 5G network into a TSN synchronization network and supports WTSN. IEEE 1588 includes the development of application-specific profiles. One result is the IEEE 802.1AS general PTP (gPTP) profile within the TSN standards and implementations defined in the TSN profile for industrial automation.
Industrial automation networks benefit from fast initialization and time synchronization in a few seconds. It’s also desirable to use off-the-shelf network interconnect cards with lower cost and less accurate oscillators. Compared with the physical syntonization (frequency alignment) technique used in other PTP implementations, gPTP uses a logical syntonization technique together with real-time measurements of path and device delays to achieve fast and accurate time alignments.
The exchange of time-stamped messages is used to communicate time from a master clock to the various bridge and end-point devices. Unlike other PTP implementations, gPTP also uses time-stamped messages to calculate frequency offsets and adjusts for these during operation.
5G Bounded Latency
URLLC and sidelink are key features in Release 17 that support bounded (ultra-low and deterministic) latency in WTSNs. URLLC is designed to ensure data delivery within specific latency bounds from tens of milliseconds to 1 millisecond and desired reliability levels from 99% to 99.999%, as defined by application requirements.
As noted above, sidelink is a new communication paradigm enabling 5G devices to communicate directly without relaying their data via the network. In conventional uplinks and downlinks, the network centrally controls resources and link adaptations. In sidelinks, each device performs both functions locally, gaining more control of how to use network resources. The upcoming Release 17 is expected to add support for sidelink-based relaying and possibly even multi-link relaying. As sidelink capabilities expand, the combination of sidelink and URLLC will increasingly support the use of 5G-based WTSN in the IIoT (Figure 2).
Figure 2: Sidelink enables network devices to communicate directly without relaying their data via the network and is expected to expand WTSN 5G deeper into the IIoT. (Source: metamorworks/Stock.Adobe.com)
Sidelink supports expanded use cases for 5G. For example, restricting the communication link to one hop in mission-critical industrial applications greatly reduces latency. Public safety networks could also benefit from sidelink’s ability to provide direct communication between devices. In applications where milliseconds matter, sidelink is expected to be a significant development given the capacity and latency improvements associated with the move from two-hop communication through a 5G base station to one-hop, device-to-device connections.
Future iterations of sidelink multi-hop relaying are expected to support lower power consumption when used in an IIoT network. Another potential use case is multi-hop relaying, where multiple sidelink connections are used to leap from device to device, overcoming link budget constraints and eventually even replacing some of the Bluetooth and Wi-Fi links that currently connect IIoT devices.
WTSN In Converged Networks
The anticipated IEC/IEEE 60802 standard will provide a basis for interoperability in industrial automation converged networks. These converged networks will include industrial Ethernet and wireless, including 5G and/or Wi-Fi communications. IEC/IEEE 60802 is a joint effort between IEC SC65C/MT9 and IEEE 802, with the first official release expected in 2022. The standard will include details for the application of TSN in industrial automation, including guidelines for integrating 5G-based WTSN. Once released, all the components for building a TSN/WTSN network will be standardized using IEC/IEEE 60802.
Two device types, bridges and end stations, are included in IEC/IEEE 60802. Initially, the standard will include two classes of devices for both device types. Feature-rich devices will be called Class A. Class B devices will support a smaller set of features. Devices belonging to the same class will have the same mandatory and optional TSN/WTSN capabilities.
All device types and classes require the Link Layer Discovery Protocol (LLDP) (802.1AB) and time synchronization. LLDP supports the discovery of the network topology and neighbor information. In the case of time synchronization, Class A devices are expected to support a minimum of three-time domains, and Class B devices will support at least two-time domains. Class A devices will be required to support a range of TSN functions (including Scheduled Traffic, Frame Preemption, Per-Stream Filtering and Policing, Frame Replication and Elimination for Reliability (FRER), and TSN configuration), but that will be optional for Class B devices.
The ultimate goal of IEC/IEEE 60802 is to provide a sufficiently structured TSN/WTSN profile for industrial automation that is also flexible and offers a wide range of options to support the deployment of convergent networks that efficiently blend different protocols into a single network.
Private 5G Networks for WTSN
Converged deployments may find their first implementations on private 5G networks, also called non-public networks (NPNs). In addition to supporting converged networks, 5G is offering a unified architecture that supports the needs of various industrial applications, including three primary categories of service: Massive machine type communication (mMTC) with connection density of up to 100 nodes per square meter, enhanced mobile broadband (eMBB) with peak data rate of up to 10Gbps, and URLLC, providing as little as one-millisecond latency with > 99.999% reliability. With these various choices, users can optimize the quality-of-service (QoS) for specific applications. Unlike other wireless technologies such as 4G or Wi-Fi, 5G provides guaranteed QoS for critical industrial applications.
Deployment of 5G NPNs is not limited to the licensed spectrum bands; it can take advantage of unlicensed spectrum such as the 2.4GHz, 5GHz, and 6GHz bands already used by Wi-Fi, Bluetooth, ZigBee, and other protocols. Unlicensed spectrum is implicitly open for shared use and has already been included in some 4G-LTE networks. 5G in unlicensed spectrum can be implemented in two ways.
Standalone unlicensed NPNs operate entirely in the unlicensed spectrum. Unlicensed operation of 5G is expected to be led by private organizations that do not offer public mobile networking services and are focused on non-critical use cases. One of its main attractions is that it can be deployed with no need for expensive licensed spectrum. The Multefire protocol is the corresponding 4G implementation on unlicensed spectrum. It uses a listen-before-talk (LBT) protocol to co-exist with other spectrum users in the same band efficiently. Without sidelink, ultra-low latency may not be possible in standalone unlicensed 5G deployments.
NPNs using a combination of licensed and unlicensed spectrum are called licensed anchor operations. The corresponding capability in LTE is licensed-assisted access (LAA), where the unlicensed band is used to supplement the available licensed band. Licensed anchor operation is expected to be used by operator-deployed private networks that need extra capacity.
5G Network Slicing
Network slicing is another tool network engineers have for getting the maximum benefit from 5G in focused industrial applications. The concept of network slicing is new with 5G and enables the creation of multiple logical networks over a single physical infrastructure. Each of the logical networks can be tailored to the specific requirements of an application (Figure 3). Various functions such as business processes, logistics operations, and time-critical processes and manufacturing can be operated on dedicated, isolated networks. Creating networks within a network is expected to be especially useful in converged networks and NPNs.
Figure 3: Network slicing can create multiple logical networks over a common physical infrastructure, with each logical network optimized for specific application requirements. (Source: metamorworks/Stock.Adobe.com)
Network slicing can be a powerful tool for resource and network management. For example, a public 5G network can be sliced to include a private 5G network isolated and dedicated to specific activities. 5G NPNs can serve a range of heterogeneous industrial communication requirements with different QoS demands. Some slices can be dedicated to non-time-sensitive communications, while other slices can support moderate QoS levels required for closed-loop-control of industrial processes, and dedicated slices can be created to provide the higher QoS required for real-time communications with mobile robots.
Management of computing, storage, and general networking resources can be improved using network slicing to maximize the efficiency of resource utilization across an organization. It also enables the development of slice-specific policies for security, privacy, access levels, and more.
Summary
5G-based WTSN will bring revolutionary new capabilities to TSN, but it’s not ready for deployment. Once it arrives, capabilities such as time synchronization, bounded latency, sidelink, and interoperability across various device classes will help speed the deployment of 5G-based WTSNs. Support for converged networks, private networks, and network slicing will provide improved resource allocation and network management. And 5G-based WTSN will increase the deployment flexibility and reduce the installation costs in existing TSN installations.