Why SOME/IP-TP required?

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If the message size is larger than the MTU, I know that fragmentation occurs in the IP layer. Why still need SOME/IP-TP?

I couldn't find the reason why SOME/IP-TP is needed even in AUTOSAR Spec.

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Julio Angulo On

The Segmentation occurs in the TCP/UDP layer. TCP supports segmentation but UDP doesn't. According to SOME/IP spec, you should use SOME/IP over TCP if very large chunks of data need to be transported and no hard latency is required.

If you need hard latency required then there is SOME/IP-TP

4.2.1.4 Transporting large SOME/IP messages of UDP (SOME/IP-TP) The UDP binding of SOME/IP can only transport SOME/IP messages that fit directly into an IP packet. If larger SOME/IP messages need to be transported over UDP (e.g. of 32 KB) the SOME/IP Transport Protocol (SOME/IP-TP) shall be used. The SOME/IP message too big to be transported directly with the UDP binding shall be called "original" SOME/IP message. The "pieces" of the original SOME/IP message payload transported in SOME/IP-TP messages shall be called "segments". Use TCP only if very large chunks of data need to be transported (> 1400 Bytes) and no hard latency requirements in the case of errors exists