.. _knowledge-base-osi-model:

UDS OSI Model
=============
Overview of `OSI model <https://en.wikipedia.org/wiki/OSI_model>`_ for UDS protocol.


.. _knowledge-base-uds-standards:

UDS Standards
-------------
UDS is defined by multiple standards which are the main source of information and requirements about this protocol.
Full list of standards is included in the table below:

+--------------+-------------+-------------+-------------+-------------+----------------+-------------+
|   OSI Layer  |    Common   |     CAN     |   FlexRay   |   Ethernet  |     K-Line     |     LIN     |
+==============+=============+=============+=============+=============+================+=============+
| Layer 7      | ISO 14229-1 | ISO 14229-3 | ISO 14229-4 | ISO 14229-5 | ISO 14229-6    | ISO 14229-7 |
| Application  |             |             |             |             |                |             |
|              | ISO 27145-3 |             |             |             |                |             |
+--------------+-------------+-------------+-------------+-------------+----------------+-------------+
| Layer 6      | ISO 27145-2 |             |             |             |                |             |
| Presentation |             |             |             |             |                |             |
+--------------+-------------+-------------+-------------+-------------+----------------+-------------+
| Layer 5      | ISO 14229-2 |             |             |             |                |             |
| Session      |             |             |             |             |                |             |
+--------------+-------------+-------------+-------------+-------------+----------------+-------------+
| Layer 4      | ISO 27145-4 | ISO 15765-2 | ISO 10681-2 | ISO 13400-2 | Not applicable | ISO 17987-2 |
| Transport    |             |             |             |             |                |             |
+--------------+             |             |             |             |                |             |
| Layer 3      |             |             |             |             |                |             |
| Network      |             |             |             |             |                |             |
+--------------+             +-------------+-------------+-------------+----------------+-------------+
| Layer 2      |             | ISO 11898-1 | ISO 17458-2 | ISO 13400-3 | ISO 14230-2    | ISO 17987-3 |
| Data         |             |             |             |             |                |             |
+--------------+             +-------------+-------------+             +----------------+-------------+
| Layer 1      |             | ISO 11898-2 | ISO 17458-4 |             | ISO 14230-1    | ISO 17987-4 |
| Physical     |             |             |             |             |                |             |
|              |             | ISO 11898-3 |             |             |                |             |
+--------------+-------------+-------------+-------------+-------------+----------------+-------------+

where:

- OSI Layer - OSI Model Layer for which standards are relevant
- Common - standards mentioned in this column are always relevant for UDS communication regardless of bus used
- CAN - standards which are specific for UDS on CAN implementation
- FlexRay - standards which are specific for UDS on FlexRay implementation
- Ethernet - standards which are specific for UDS on IP implementation
- K-Line - standards which are specific for UDS on K-Line implementation
- LIN - standards which are specific for UDS on LIN implementation


.. _knowledge-base-pdu:

Protocol Data Units
-------------------
Each layer of OSI Model defines their own
`Protocol Data Unit (PDU) <https://en.wikipedia.org/wiki/Protocol_data_unit>`_.
To make things simpler for the users and our developers, in the implementation we distinguish following PDUs:

- Application Protocol Data Unit (A_PDU) - called `diagnostic message` or `UDS Message` in the implementation
  and documentation. More information about A_PDU can be found in:

  - :ref:`knowledge base section - diagnostic message <knowledge-base-diagnostic-message>`

  - :ref:`implementation - diagnostic message <implementation-diagnostic-message>`

- Network Protocol Data Unit (N_PDU) - called `packet` in the implementation and documentation.
  More information about N_PDU can be found in:

  - :ref:`knowledge base section - packet <knowledge-base-packet>`

  - implementation - :mod:`uds.packet`

- Data Protocol Data Unit (D_PDU) - called `frame` in the implementation and documentation.
  We do not have any internal `frames <https://en.wikipedia.org/wiki/Frame_(networking)>`_ documentation.
  Implementation of frames is usually provided by external packages.

.. figure:: ../../diagrams/KnowledgeBase-PDUs.png
  :alt: UDS PDUs
  :figclass: align-center
  :width: 100%

  UDS Protocol Data Units on different layers of OSI Model.