Embodiments of a method in a network node configured to transmit data using an automatic retransmission process are disclosed. The method comprises: receiving data to be transmitted to a remote endpoint; and when all process identifiers in a predetermined set of process identifiers are currently in use: selecting one process identifier from the predetermined set of process identifiers; storing information pertaining to a previously transmitted transport block in a temporary buffer, the previously transmitted transport block including the selected process identifier; and transmitting the received data in a second transport block including the selected process identifier.