Abstract ISO 10681-2:2010 specifies the requirements for a communication protocol tailored to meet the requirements of FlexRay-based vehicle network systems as specified in the FlexRay Communications Systems Protocol Specification. As the communication protocol combines the network-layer and transport-layer functionality (OSI layers 3 and 4), this document does not explicitly distinguish between these layer services. The technical features of this communication protocol are as follows: transmit messages with known data length; transmit messages with unknown but finite data length; additional acknowledgement with retry mechanism; routing data on the fly; support of dynamic frame length.