Stream Control Transmission Protocol (SCTP) Data Acknowledgement with Non-Renegable Selective Acknowledgements (NR-SACKs).
University of Delaware
University of Delaware
University of Delaware
Cisco Systems
Connecticut College
Stream Control Transmission Protocol (SCTP) [RFC4960] specifies Selective Acknowledgements (SACKs) to allow a transport layer data receiver to acknowledge DATA chunks which arrive out-of-order. In SCTP, SACK information is advisory because the data receiver is permitted to renege; that is, later discard a DATA chunk which previously has been SACKed. Since delivery of a SACKed out-of-order DATA chunk is not guaranteed, a copy of this DATA chunk MUST be kept in the data sender's retransmission queue until this DATA chunk is cumulatively acked. This document specifies Non-Renegable Selective Acknowledgements (NR- SACKs), an extension to SCTP's acknowledgment mechanism. NR-SACKs enable a data receiver to explicitly acknowledge out-of-order DATA chunks that have been delivered to the receiving application. (Recall that, in SCTP, out-of-order data sometimes can be delivered.) NR-SACKs also enable a data receiver to indicate any out-of-order DATA chunks on which the receiver guarantees never to renege. As opposed to SACKed DATA chunks, a sender can consider NR-SACKed DATA chunks as never requiring retransmission, thus freeing space in the data sender's retransmission queue sooner.