I've read through all ISO documents and can't figure out in which cases we need extended addressing in ISO-TP, though I've seen packets from BMW CAN traffic where UDS uses extended addressing.
Why does ISO-TP protocol need to specify target address if all nodes do the filtering by CAN ID? Is it possible that nodes will also filter packed by ISO-TP target address?
Any ideas?
On
ISO-TP protocol allows for the transport of messages that exceed the eight-byte maximum payload of CAN frames. ISO-TP segments longer messages into multiple frames, adding metadata that allows the interpretation of individual frames and reassembly into a complete message packet by the recipient. It can carry up to 4095 bytes of payload per message packet.
ISO 15765-2 (ISO-TP) is a transport protocol over CAN, so it needs to use its own address for specific purpose. When ISO 15765-2 need to refer to one single node, it uses CAN address as ISO-TP address. When it has to send information throught a gateway, it uses extended address, taking one CAN Payload Byte to specify gateway address (only have 7 bytes left for data).