A method for communication includes receiving a packet at a first node for transmission over a link to a second node. The data in the packet is divided into a sequence of cells of a predetermined data size. The cells have respective sequence numbers. The cells are transmitted in sequence over the link, while storing the transmitted cells in a buffer at the first node. The first node receives acknowledgments indicating the respective sequence numbers of the transmitted cells that were received at the second node. Upon receiving an indication at the first node that a transmitted cell having a given sequence number was not properly received at the second node, the stored cells are retransmitted from the buffer starting from the cell with the given sequence number.