Deterministic, Time Sensitive Networking

Initial scope of IEEE 802.11be is being developed by Extremely High Throughput or EHT study group and it is a potential amendment to Wi-Fi technology standard in future. This spec aims to support a higher throughput in the range of 30gbps along with major focus on real-time latency support.

An emerging category of real-time applications can function correctly only when the underlying packet transport supports very low end-to-end latency and a strict upper bound on time taken to deliver packet from point A to point B.

In a standalone single node real-time system - request, response, scheduling, pre-emption, prioritization take place locally within the node’s operating system. What if we need to distribute such a system running across multiple real-time nodes?

Motivation behind the distributed design could be to scale up overall system capacity or due to the nature of the underlying application. Whatever be the reason, once we do distribution of processing, even though each individual node maintains their own real-time property, another important factor gets added – the network connecting these real-time nodes.

The message latency between node-A and node-B over the network will be higher compared to local communication internally, but that’s not a complete show-stopper. More importantly the latency must be predictable. A message or packet originated at time T must be delivered and processed by time T + t. This much strict latency requirement is not common in best-effort network. Underlying network needs to ensure this packet delivery time “contract” is not violated. All parts of the distributed system must be synchronized to the same clock and remain so for ever. T needs to represent the same moment of time on all entities for the entire scheme to work.

High precision time sensitive communication is not new. TSN or Time Sensitive Networking Task Group of the IEEE 802.1 Working Group has several standards to provide zero congestion loss and bounded latency in a standard Ethernet network. The scope of TSN capability is within a L2 segment. There are more optimistic proposals like Deterministic Networking (or DetNet) that aims to provide similar latency sensitive packet delivery service at L3 spanning across multiple TSN segments. Needless to say, time synchronization protocols like PTP are indispensable part of this.

Pre-standard 802.11be proposal also talks about native support and better integration with other TSN networks - a heterogeneous network consisting of wireless LAN and Ethernet. This and similar other technologies will enable us to support life changing real-time applications in the field of remote healthcare, industrial automations etc.