Abstract: A novel system and apparatus for transmitting data between the two nodes of a network is provided. The transmission is effected by using an error recovery protocol featuring a positive group acknowledgement. A sender unit on one node receives the user data and groups the data into consecutive cells, the cells being clustered into groups, each cell in a group being assigned a unique sequence number. The groups of cells are transmitted over a physical channel to a receiver unit on a different node. The receiver unit examines the cell stream and issues an acknowledgment message to the sender unit only when all of the cells in a group have been received. Once the sender unit has completed the transmission of a group of cells, it starts observing the physical channel for an acknowledgement message from the receiver unit. If after a predetermined time period the acknowledgement message has not been received, the sender unit transmits the group of cells again.