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Out-of-order delivery
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This article includes a list of references, related reading, or external links, but its sources remain unclear because it lacks inline citations. (February 2012) |
In computer networking, out-of-order delivery is the delivery of data packets in a different order from which they were sent. Out-of-order delivery can be caused by packets following multiple paths through a network, by lower-layer retransmission procedures (such as automatic repeat request), or via parallel processing paths within network equipment that are not designed to ensure that packet ordering is preserved. One of the functions of TCP is to prevent the out-of-order delivery of data, either by reassembling packets in order or requesting retransmission of out-of-order packets.
See also
[edit]External links
[edit]- RFC 4737, Packet Reordering Metrics, A. Morton, L. Ciavattone, G. Ramachandran, S. Shalunov, J. Perser, November 2006
- RFC 5236, Improved Packet Reordering Metrics, A. Jayasumana, N. Piratla, T. Banka, A. Bare, R. Whitner, June 2008
- https://web.archive.org/web/20171022053352/http://kb.pert.geant.net/PERTKB/PacketReordering
- https://www-iepm.slac.stanford.edu/monitoring/reorder/
- https://www.usenix.org/conference/nsdi12/minion-unordered-delivery-wire-compatible-tcp-and-tls
Out-of-order delivery
View on Grokipediafrom Grokipedia
Out-of-order delivery, in the context of computer networking, occurs when data packets arrive at their destination in a different sequence than the order in which they were originally sent, violating the expected monotonic increase in sequence numbers.[1] This phenomenon arises in IP-based networks, which provide best-effort delivery without guarantees of packet ordering, as packets may take multiple paths with varying delays or be processed in parallel.[2] Common causes include route changes leading to differing path lengths, load balancing across links, layer-2 retransmissions, or buffer management issues in routers.[1]
The effects of out-of-order delivery can degrade network performance, particularly for transport protocols like TCP, which interpret significant reordering as potential packet loss, triggering unnecessary retransmissions and reducing throughput.[1] For instance, TCP's default duplicate acknowledgment threshold of three can cause premature fast retransmit if packets are reordered beyond this limit, leading to congestion window reductions.[1] In contrast, UDP does not inherently reorder packets but delivers them as received, leaving reassembly to the application layer, which may result in errors for time-sensitive applications like voice or video streaming if buffering is insufficient.[2] Metrics such as the reordered packet ratio (total reordered packets divided by total received) and reordering extent (the maximum gap in sequence numbers) are used to quantify and evaluate the severity of reordering in network paths.[1]
To mitigate out-of-order delivery, receivers employ reordering buffers to hold early-arriving packets until their predecessors arrive, though buffer size and delay limits constrain effectiveness.[1] Extensions like TCP SACK (Selective Acknowledgment)[3] and D-SACK help distinguish reordering from loss, improving robustness,[4] while protocols such as Deterministic Networking (DetNet) incorporate packet ordering functions for applications requiring strict sequencing.[5] Overall, while minor reordering is common and often tolerable, excessive instances highlight underlying network inefficiencies that can impact reliability across diverse applications.[6]
