{
  "slug": "tcp-receive-window",
  "term": "TCP receive window",
  "aliases": [
    "rwnd",
    "TCP advertised window"
  ],
  "definition": "The TCP receive window is the receiver-advertised byte count it is prepared to accept starting at the acknowledgment number.",
  "note": "Flow control: The advertised window is not the receiver's total socket buffer size; received data awaiting application consumption and space not yet advertised also matter. A zero window invokes probing and does not by itself mean the connection has failed [tcp-window].\n\nEncoding: Window scaling must be offered by both endpoints during the handshake. Its shift is fixed separately for each direction; window fields in SYN and SYN-ACK segments remain unscaled. The option enlarges the receive-window representation, not the sender's congestion window [tcp-scale].",
  "status": "shipping",
  "advantages": [],
  "limitations": [
    {
      "text": "A large advertised window does not prove that the application has consumed data or that a storage write is durable.",
      "citationIds": [
        "tcp-window",
        "tcp-scale"
      ]
    }
  ],
  "related": [
    "tcp-congestion-window",
    "bandwidth-delay-product",
    "nvme-tcp"
  ],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "citations": [
    {
      "id": "tcp-window",
      "title": "RFC 9293: Transmission Control Protocol, sections 3.1 and 3.8.6",
      "url": "https://www.rfc-editor.org/rfc/rfc9293.html#section-3.8.6",
      "accessed": "2026-10-26"
    },
    {
      "id": "tcp-scale",
      "title": "RFC 7323: TCP Extensions for High Performance, sections 2.2 and 2.3",
      "url": "https://www.rfc-editor.org/rfc/rfc7323.html#section-2.2",
      "accessed": "2026-10-26"
    }
  ],
  "provenance": [
    "Source review, not a measured network or storage result. TCP window budgets describe one sending direction of one connection."
  ],
  "updated": "2026-10-26"
}