Guaranteeing Hard Real-Time Requirements of In-Vehicle Multi-hop Communication Over Ethernet

 (12AE-0076/2012-01-0193)

Standard Ethernet for time dependant and time critical applications

Lars BrohneCEO

April 2012

Presentation content

• One minute TCN• Background • Challenges in-vehicle communications• Challenges in guaranteed analysis• Desired features and functionalities of a tool• Conclusion and future Work

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One minute TCN

• Time Critical Networks (TCN) produces softwareo Modeling – TCN TimeAnalyzer™o Verification – TCN StreamAnalyzer™

• Worst Case Holistic Response Time Analysiso Predict worst-case end-to-end reaction and age timeo Create cost-effective & robust hybrid CAN/switched

Ethernet systems Latency, jitter and no packet-drop guarantees

• Start-up under Chalmers Innovation – 2008o Unique patent-pending technology from years of research

Real-time systems and schedulability analysis

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Background

• Switched Ethernet starts to be considered for automotive architectureso Today used for fast batch transfers for sw updateo Planned for real-time traffic as wello More bandwitdh is the main driver

Camera systems and streaming video

• Design efficient and secure automotive Ethernet systemso Communication response time analysis will be importanto But how can we make a guaranteed analysis?

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Challenges in-vehicle communications

• Several tens of computers (ECUs)o In-vehicle electronic architecture will be

more complex, distributed, interconnected and interdependent

• Precise timing and prioritization of functions are essentialo For both safety and comforto Functions will depend on timing and

reliability constraints

• Make a design that is cost-effectiveo Right level with regard to performance,

energy consumption and cost

55 ECUs & 7 Buses of 4 types with Gateways

© Daimler Mercedes –Benz & Chrysler

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Challenges in-vehicle communications

• Switched Ethernet starts to be considered for automotive architectureso Guaranteed deliveryo Latency guaranteedo Time synchronizationo Redundancy 

55 ECUs & 7 Buses of 4 types with Gateways

© Daimler Mercedes –Benz & Chrysler

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Challenges in guaranteed analysis

• Traffic model and critical instanceso Proper models need to

be identified Representing real

traffic– Such as GMF

Eg. Periodic and sporadic data flows

o Critical instances may vary according to different models

Worst case scenarios

P

C

D

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Challenges in guaranteed analysis

• Serialization Phenomenon o In a multi-hop network, two related flows may

share several links, but they may not interfere each other over every link

o The extra queuing delay needs to be removed, otherwise we may get pessimistic results

E1

E2

E3

E4

Flow1: E1->E3

Flow2: E2->E4

S1 S2 S3

E5

Flow3: E5->E4

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Challenges in guaranteed analysis

• Indirect Interferenceo Sometimes two flows do not share any link, it seems that they are not related

But actually, they can still cause interference to each other– Flow2 may have a jitter (traffic model changed in S3)

Because of the contention with Flow1

o This behavior is common in a large multi-hop networko Must be taken into account, otherwise the result may be optimistic

Challenges in guaranteed analysis

• Further issues may cause challenges into the analysis which increases of the complexity of network topologies and traffic modelso Support for arbitrary deadlines

The deadline assumptions can be any value– less, equal or greater then the periods

o Support for non-fragmentation as well as fragmentations Max size per Ethernet frame is 1500 bytes

o May require different formulas for different situations

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• Network system modeling o Switch modeling o Host modelingo Link modeling

• Traffic modelingo Flow modeling

Single and multi frame support

Tasks– Executables in hosts

Desired features and functionalities of a tool

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Desired features and functionalities of a tool

• Computation analysis engine o The engine should generate guaranteed

results without optimism and with limited pessimism

• Network optimization engineo An optimization engine can help the

automotive system designers to optimize the system based on the analysis results

Consider given requirements and constraints– Reaction constraints, age constraints,

synchronization constraints, etc.

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Summary

• The paper discusses the challenges and important considerations for a guaranteed response time analysis over Etherneto But due to the unpredictability of the multi-hop

network behavior it is really difficult to achieve a precise analysis without

doing an exhaustive search for all appropriate traffic scenarios

• A tool designer should consider the balance between the accuracy and the computation timeo Find a proper algorithm that requires a limited

computing resource and still produce accepted results

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• Thank you!

www.timecriticalnetworks.com