Synchronization Supercharged with DornerWorks TSN & AVB Ethernet IP

Posted on September 21, 2022 by Matthew Russell

Networked products need data to be synchronized to function properly. Depending on the environment in which those products function, that can be a challenge.

For example, sending and receiving messages has traditionally become more difficult when more devices begin using the network, or when more hops are required in a message’s path.

Ethernet provides one way to link products together on a single, reliable network. Today, Audio Video Bridging (AVB) and Time-Sensitive Networking (TSN) systems are enhancing the capabilities of Ethernet, making it possible to synchronize devices in some of the harshest environments on Earth or in space.

Traffic scheduling

One of the simplest set of rules in time synchronization fall under Strict Priority scheduling, in which the highest priority Quality of Service (QoS) transmits first. There is no guarantee those messages will get the bandwidth or time they need, however, which is where AVB and TSN prove useful.

AVB and TSN are both sets of networking standards that utilize the Precision Time Protocol (PTP) which defines how devices on a network should be synchronized to each other.

On top of that, AVB adds bandwidth shaping so that data stream bandwidth can be prioritized. This is useful in applications which require a constant stream of data.

“AVB has two benefits,” explains DornerWorks FPGA engineer Andrew DeZeeuw. “The ability for there always to be bandwidth allocated for that stream, as well as taming the burstiness which can help downstream devices handle that data more easily.”

TSN adds even more standards to enable time partitioning, an important aspect of networking for tightly synchronized measurements. Having a time slice allocated for a stream across the entire network allows synchronous traffic sources to communicate across the network with low latency.

AVB and TSN can further be combined and applied to network traffic at the same time, which allows for a wide variety of applications to schedule network traffic.

AVB and TSN in practice

Strict Priority scheduling only.

DornerWorks TSN Multi-port EndPoint Demo features 8 QoS queues, each of which can be scheduled using Strict Priority, AVB bandwidth partitioning or TSN time partitioning.

AVB scheduling only.

With strict priority scheduling, multiple data queues attempt to transmit at once. Any available bandwidth is assigned to the highest priority queue.

TSN scheduling only.

In AVB scheduling, different amounts of bandwidth are allocated to multiple queues, which are able to utilize the full bandwidth of that configured limit for each QoS.

The Credit Based Shaper (IEEE 802.1Q-2018, formerly IEEE 802.1Qav) provides a method for bandwidth partitioning for each QoS using a “leaky bucket” shaper,” DeZeeuw explains.

“For each QoS, credit is spent when transmitting a packet and earned when unable to transmit,” he says. “Credit must return to zero after transmission to send again, so the slopes at which credit is incremented and decremented is used to specify a percentage of total bandwidth in the system. This allows high priority asynchronous traffic to have reserved bandwidth in the system, while allowing lower priorities to transmit when not being used.”

TSN scheduling relies on a timed approach, with QoS streaming at regular intervals.

The Time Aware Shaper (IEEE 802.1Q-2018, formerly IEEE 802.1Qbv) enables time partitioning of packets, determining when different QoS queues are allowed to transmit.

“Any number of QoS queues can be configured to transmit within each schedule entry, allowing for flexible configuration over a wide variety of traffic types,” DeZeeuw says. “This schedule can be configured and synchronized throughout the entire network, allowing synchronous messages to have a reserved time band to transmit throughout the entire network.”

The demo also tests combinations of Strict Priority, credit shaping (AVB) and time-sensitive networking (TSN), enabling a range of possible applications.

Strict Priority, AVB and TSN scheduling combined.

DornerWorks TSN Multi-port EndPoint Demo runs through 15 tests, applying the pictured modes of determinism in three groups:

Best Effort & AVB (Tests 1-5)

  • Bandwidth approach
  • Determinism based on maintaining bandwidth

TSN Only (Tests 6-10)

  • Timed approach
  • Determinism based on prioritized QoS streaming at a regular interval

AVB & TSN (Tests 11-15)

  • Mixed approach
  • Determinism based on prioritized QoS that are assigned bandwidth and scheduled in available time increments

Other standards on DornerWorks AVB/TSN IP roadmap that will further enhance deterministic Ethernet networking solutions. For example:

  • IEEE standard 802.1CB Frame Replication and Elimination for Reliability in Time-Sensitive Networks, uses redundant paths on a network to transmit duplicate frames to enable the reliability required for high fault tolerance applications in aviation or other industries that work with high levels of criticality.
  • IEEE 802.1Qcc describes a Centralized Network Configuration (CNC) that can configure AVB and TSN functionality across devices on the network.
  • IEEE 802.1Qca describes path control and reservation, which defines paths through the network for individual streams and reserves bandwidth along that path. This can work in tandem with the CNC to provide administration for the entire network.

DornerWorks AVB and TSN IP is currently available for purchase. Order the IP today and supercharge your networked products.

Matthew Russell
by Matthew Russell