User:IveGoneAway/sandbox/Time-Triggered Communication Protocol
Time-Triggered Protocol (Disambiguation)
this article oa about the general TDMA method, for the commercial product, see TTP
Time-Triggered Protocol (Disambiguation)
A time-triggered communication protocol is a method of communication wherein a sequence of scheduled communication actions, distributed amungst multiple transmitters sharing a common channel, is repeated in a periodic cycle. [shorten]
- TTP is a registered trademark of TTTech
Time-Triggered Communication Protocol, Time-Triggered Protocol, or Time Triggered Protocol, or refer to a class of communication protocols that employ cyclic, isochronous scheduling of bus access by multiple transmitters, generally in the form of time division multiple access (TDMA).[1]
Time-triggered communication protocols generally provision for a fixed and repeating schedule of isochronous transmissions where channel access is distributed among multiple transmitters. The schedule (or cycle) may be divided into a fixed schedule of sub-cycles, each having a different but fixed schedule of transmissions. Portions of such cycles may be given over to other forms of non-isochronous channel access controls; for example, a cyclic time window or slot may be given over for a fixed period of asynchronous bus access, such as a limited period of CDMA arbitration as in the case of TTCAN.
Distinctions from other classes of communication protocols
Schedule
| Protocol | Access | Schedule | ||
|---|---|---|---|---|
| time-triggered | multiple | cyclic | distributed | a priori |
| MIL-STD-1553 | multiple | cyclic | central | a priori |
| ARINC 429 | single | cyclic | distributed | a priori |
| USB | multiple | cyclic | distributed | ad hoc |
distributed vs. central schedule
Time-triggered protocols rely on a distributed channel access schedule; that is, each transmitter node must have (1) a means of synchronization with the network schedule and (2) knowledge of when it is scheduled to have channel access within that schedule. More simply put, every node must be able to schedule itself such that it transmits it signals only within in its allotted time slots. Thus, these protocols are distinct from Bus Controller/Bus Master systems wherein only a single node is responsible for controlling multiple-transmitter bus access, even if that access may be within a cyclical schedule (an example being MIL-STD-1553).
multiple vs single access
Periodic multiple-transmitter time-triggered protocols are naturally distinct from periodic single-transmitter messaging protocols, ARINC 429 being an example of the latter. In the ARINC 429 protocol, exactly one transmitter is connected to the bus, thus avoiding requirements for multiple access techniques. Also, even though individual ARINC 429 messages are transmitted on periodic static schedules (within the maximum and minimum transmit intervals for each label), multiple labels on a bus are not necessarily collectively scheduled into a larger logical cyclic frame or major cycle. The specification of a single ARINC 429 label message includes its periodic timing, but not its timing relative to other labels that may be in the same channel[2] (although such cyclic effects may be a natural consequence of the implementation of the particular labels for a given channel).
static vs dynamic schedule
The safety-critical isochronous time-triggered protocol schedules are static (a priori) schedules as opposed to dynamic or auto-negotiated (ad hoc) schedules. That is, the a priori time-triggered schedule is typically predefined and qualified before operation, whereas ad hoc time-triggered schedules can be made up "on the fly" cases as of USB networks, which include auto-negotiated, plug-and-play, isochronous mode.
Implementations
Examples of time-triggered communication protocols include:[3]
- ISO 11898-4, CAN Time-Triggered Communication (TTCAN)
- SAE AS6802, Time-Triggered Ethernet (TTEthernet); effectively, time-switched ARINC 429 channels over Ethernet
- SAE AS6803, TTP Communication Protocol (TTP), SAE standardization of TTech's proprietary time
- FlexRay
- AUTOSAR Virtual Function Bus employs logical time-triggered Flexray frames, which are virtually or physically transported as Flexray frames or as shorter segments over other low-level protocols; e.g., CAN, LIN
- ARINC 825, General Standardization of CAN Protocol for Airborne Use[4]
See also
References
- ^ Cite error: The named reference
ObermaisserParawas invoked but never defined (see the help page). - ^ Cite error: The named reference
ARINC429was invoked but never defined (see the help page). - ^ Cite error: The named reference
ObermaisserCommwas invoked but never defined (see the help page). - ^ Knueppel,, Ralph (2012), "Standardization of CAN networks for airborne use through ARINC 825" (PDF), CAN in Automation, CAN in Automation
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External
Time-triggered CAN, CAN in Action (CiA)
- ^ Obermaisser, Roman (2005). Event-Triggered and Time-Triggered Control Paradigms. Springer Science+Business Media. pp. 21–23. ISBN 0-378-23043-2.
{{cite book}}: Check|isbn=value: checksum (help) - ^ Obermaisser, Roman (2011). Time-Triggered Communication. CRC Press. ISBN 978-1-4398-4661-2.
- ^ ARINC Specification 429, Part 1-17. Annapolis, Maryland: Aeronautical Radio, Inc. 2004-05-17.
- ^ FlexRay Communications System Protocol Specification