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Most simple configuration, consisting of a single SM and CM. SM and CM may be integrated in the same device. Provides real time capabilites but not Fault Tolerance!

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Priority-base mechanism to realize system-of-systems architectures. Synchronization Priority stored in every device and the Sync Priority field of every PCF. A device may be configured to synchronize to the highest priority PCFs it received or to the priority level specified manually. Supports full operation of parts of the network, i.e. it‘s possible to power down both parts idividually.

Once it is powered on again, both sub-networks synchronize either automatically or upon host acknowledgment.

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Fault tolerance is the only possible solution to achive highly dependable systems. High dependablity is required e.g. in safety critical applications like the aerospace industry. The dual-fault tolerant configuration tolerates two faulty devices without degradation of the TTEthernet services.

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A channel is any connection between two end systems.

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Scheduler will take care of arranging the TT frames in such a way that they will never be ready for transmission on the same outgoing port of a switch or end system at the same point in time. Slots, not used by TT or RC traffic are used to transmit BE traffic, even if a TT message is scheduled but not used (e.g. because there is no new data to be transmitted) The Schedule Plan is cyclic and the period is called Message Period. Sometimes, the term “Communication Cycle” is used synonymously to Message Period. The Schedule Plan is loaded into each device offline, i.e. before the networks operation starts.

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On Online-Scheduling scheduling decisions are made during runtime. A scheduling algorithm is used to decide which packet is forwarded next. On Offline-Scheduling the schedule plan is generated in advance and thus the worst case delays are known and the plan can be proven to be free of conflicts. To be applicable, all traffic has to be kown in advance.

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In Scenario A, a TT frame is currently transmitted when a BE frame becomes ready for transmission. The solution for this conflict is obvious: the lower priority BE traffic is delayed.

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In Scenario B it‘s vice versa: a BE frame is currently transmitted when a TT frame becomes ready for transmission. In the early academic version of TTE the BE frame was preemted, to be able to transmit the TT frame in time. This results in a waste of bandwith, as the BE frame has to be transmitted again after the transmission of the TT frame has finished. Timely Block takes advantage of the time triggered nature of TT traffic, i.e. a BE packet is not transmitted in the first place, if a conflict with the next TT packet would occour. It might be possible to schedule a shorter BE packet, if ready for transmission. When Shuffeling is used, the TT packet may be delayed. However, an upper bound for the delay is known in advance because the maximum size of an Ethernet frame is restricted to ~1526 Byte (for Ethernet II framing) Timely Block and Shuffeling are implemented in current TTE versions.

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In the most basic configuration one integration cycle equals one cluster_cycle. Then the global time is determined by the position within the cluster cycle. If a cluster cycle contains more than one inegration cycle (thus new devices can integrate more often and the clock sync algorithm is executed more often), then the local_integration_cycle counter is needed to completely determine the position within the cluster cycle. For debug purposes and runtime analysis it might be useful to know the current cluster_cycle and thus the time elapsed since the network started its operation.

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In Step 1, the SMs send PCFs to the CMs. The CMs then calculate an averaging falue from the realtive arrival times of these PCFs. In Step 2, the CMs send out a new PCF to all SMs and SCs.

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Entries of the Protocol Control Frame

Integration Cycle: The integration cycle in which the Protocol Control Frame was sent. A cluster may consist of >= 1 integration cycles to allow devices to integrate faster. Membership New: A bit-vector with an static configured one-to-one relation from a bit to a Synchronization Master in the system. Sync Priority & Sync Domain: Used with System-of-Systems configuration. Static value for each SM, CM, SC. Type: Coldstart frame, coldstart acknowledgement frame or integration frame Transparent clock: Accumulate the relay latencies of the frame through the network.

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Dynamic delays are not predictable, e.g. delays due to Shuffling Static delays and wire delays are known in advance

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PIT = Point In Time The intermediate value max_transmission_delay – pcf_transparent_clock is often called permanence_delay.

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The max_transmission_delay is a global constant stored in all nodes of the network, whereas the pcf_transparent_clock is stored individually in each PCF. Important events (from left to right): 1. Sender 1 starts transmitting PCF1 2. Sender 2 starts transmitting PCF2 3. The transmission of PCF2 may be faster than the transmission of PCF1. Think

of longer wires or multiple hops between Sender 1 and the Switch. Thus PCF2 is sent to the Receiver earlier than PCF1.

4. The receiver receives PCF2 and calculates its permanence PIT. 5. The receiver receives PCF1 and calculates its permanence PIT. 6. Because of the permanence algorithm PCF1 becomes permanent before PCF2.

Thus the correct ordering of PCF1 and PCF2 is known. Furthermore, the time between the two permanence PITs equals the time between the two PITs, when the PCFs were transmitted by Sender 1 and Sender 2. This fact will be important when it comes to the Clock Synchronization Algorithm.

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The CM starts a compression function, when a PCF becomes permanent and no other compression function is running at the moment. The CM continues collecting PCFs for a configurable interval called Observation Window (OW).

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cm_permanence_i is the PIT, when the i-th PCF (i > 1) becomes permanent at the CM. cm_permanence_1 is the PIT, when the first PCF becomes permanent at the CM. max_obervation_window and calculation_overhead are constants calculated offline compression_function_delay is just an intermediate value cm_compressed_pit is the PIT, when the compression function has be computed and the new PCFs are ready. It‘s again just an intermediate value dispatch_delay is a configurable offset between the time, when the PCFs are ready for transmission and actually transmitted (dispatched) Note that in TTE the global time is never transmitted explicitly (as content in a packet), but the schedule is known by all End Points and Switches. Thus from permanence PIT of the cm_dispatch_pit each device can conclude the offset of its own local clock.

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The smc_scheduled_pit is calculated offline and part of the schedule. smc_permanence_pit is the PIT, when the PCF received by the CM becomes permanent.

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As stated on slide „Compression Function (2)“ each CM will correct the dispatch_pit for its PCF by the compression_correction. Thus the scheduled and the actual receive PIT will differ.

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Main purpose of Orion: Cargo and crewed missions to the International Space Station ISS. Futher use for crewed missions to the Moon, astroids and the Mars.

TTE is used in mixed criticality integrated control systems for a variety of distributed applications like avionics. TTE is used in some evaluation projects not yet public.

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Acceptance means, a message is considered “in schedule” if it is received within a reception window around the scheduled receive PIT and “out of schedule” otherwise. A clique detection service detects clique scenarios. These are unintended scenarios where disjoint subsets of devices within a synchronization domain are synchronized within the subset but not over subset boundaries.

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