This document specifies technical requirements related to the MOST data link layer functionality.A MOST network is comprised of two or more nodes connected through a physical layer. The data link layer functionality is provided by each node. On each network, all nodes are synchronised and one node provides the system clock. This node is the TimingMaster, while all other nodes are TimingSlaves. The timing configuration of the node (TimingMaster or TimingSlave) determines the tasks that need to be performed on the data link layer.The data link layer specifies the following subjects:— the service interface to the network layer;— the network frame, its areas and indicators;— the different network channels;— the different flow control mechanisms;— the load-adaptive arbitration and the round-robin arbitration;— the different addressing options;— the different cyclic redundancy checks, their usage and the CRC acknowledge;— the frame indicators.