Wednesday, February 1, 2012

Zen In The Art Of Ethernet: Time-Critical / Time-Triggered / Scheduled Traffic

The masters of Zen archery can hit the target from different positions, unaffected by events or body position. When archers shoot correctly, beautiful shooting is realized naturally.

Imagine Ethernet networks delivering messages from A to B with fixed latency and µs-jitter, unaffected by other time-sensitive and best-effort Ethernet traffic. With this capability in every desktop, enterprise and every embedded network switch/bridge/network interface - the point can be reached where Ethernet becomes the Zen artist of deterministic networking.

Expanding Ethernet Capabilities: Low-Jitter Traffic in IEEE802.1
Interesting outcome of discussion on requirements for real-time applications in IEEE802.1 meeting in München, 16-19th January 2012, was the idea of adding time-critical communication capabilities to Ethernet standard. The implementation and design of mechanisms for scheduled time-critical communication, will be discussed in future meetings.
There is a little doubt that future development of IEEE802 will lead to Ethernet networks capable of handling time-sensitive (rate-limited), time-critical (scheduled) and best effort traffic.
Ethernet standard will be able cover all system integration requirements at high-bandwidth, using a shared Ethernet network infrastructure - a deterministic unified Ethernet.
IEEE802 Standards in Critical Applications
In the past, IEEE802 committees were focusing more on audio/video, home and commercial networks, where determinism and robustness were not the primary requirement.
In parallel new QoS Layer 2 services or Ethernet profiles for real-time and safety-critical applications have been developed in other standard organizations such as ARINC or SAE.
Available standards allow handling of time-critical traffic (SAE AS6802), time-sensitive traffic (ARINC664-P7) and best effort traffic in TTEthernet switches designed for deterministic unified Ethernet networking.
With functional integration of real-time functions in different applications, and increasing number of embedded devices and higher robustness requirements,  the direction of IEEE802  can abruptly change and provide a standard which would enable convergence of IT and embedded networks, and convergence of standard LAN, low-latency and low-jitter applications.
With pending approval of new Project Authorization Request (PAR) - P802.1Qbv and potential completion of standardization by IEEE in 2015-2016 timeframe, IEEE802 Ethernet could integrate all essential capabilities for design of time-aware queue-draining procedures, managed objects and extensions to existing protocols that enable bridges and end stations to schedule the transmission of frames based on system time. This can further extend the use of Ethernet as a unified network in deterministic systems.

Similar to SAE AS6802 this amendment will provide performance guarantees of latency and delivery variation (jitter!) to enable these applications in an engineered LAN, and also maintain the existing guarantees for the credit-based shaper and best-effort traffic described in IEEE802.1Q.

There is a great opportunity to see mechanisms implemented in SAE AS6802 as a part of IEEE802.1Q, and integrated with time-sensitive and best effort traffic. The key here will be to bring know-how in design of critical networks, communication protocols and robust synchronization. It is about adding a bunch of small things which can make or break the integrated system, in other words support or prevent the spreading of Ethernet in new applications.

Well before this part of Ethernet history is completed, we can only applaud and say "Never Bet Against Ethernet!"

See the presentation on Deterministic Ethernet & Unified Networking!
See the presentation on Robust Clock Synchronization!

IEEE802.1Qbv PAR(Project Authorization Request) References SAE AS6802

7.1 Are there other standards or projects with a similar scope:
Yes, SAE AS6802 (2011-11), Time-Triggered Ethernet
Explain: Time-Triggered Ethernet is a vertical aerospace standard
incorporating material that overlaps parts of 802.1Q, 802.1AS and
this amendment. Unlike AS6802, this amendment integrates scheduled
traffic with the existing credit based shaper and best effort traffic.
We will coordinate our work with the SAE through common membership and