This part of ISO 15765 specifies a transport protocol and network layer services tailored to meet the requirements of CAN-based vehicle network systems on controller area networks as specified in ISO 11898-1. It has been defined in accordance with the diagnostic services established in ISO 14229-1 and ISO 15031-5 but is not limited to use with them and is also compatible with most other communication needs for in-vehicle networks.ISO 11898-1 specifies variable length CAN frames with a maximum payload size dependent on the protocol device used. A CLASSICAL CAN protocol device can transmit/receive frames with payload sizes ranging from 0 bytes to 8 bytes per frame. A CAN FD (flexible data rate) protocol device can transmit/receive frames with payload sizes from 0 bytes to 64 bytes. A CAN FD protocol device is also capable of transmitting/receiving CLASSICAL CAN frames.The diagnostic communication over controller area network (DoCAN) protocol supports the standardized service primitive interface as specified in ISO 14229-2 (UDS).This part of ISO 15765 provides the transport protocol and network layer services to support different application-layer implementations such as— enhanced vehicle diagnostics (emissions-related system diagnostics beyond legislated functionality, non-emissions-related system diagnostics),— emissions-related on-board diagnostics (OBD) as specified in ISO 15031,— world-wide harmonized on-board diagnostics (WWH-OBD) as specified in ISO 27145, and— end of life activation on on-board pyrotechnic devices (ISO 26021).The transport protocol specifies an unconfirmed communication.NOTE This part of ISO 15765 does not determine whether CLASSICAL CAN, CAN FD or both are recommended or required to be implemented by other standards referencing this part of ISO 15765.