Nagle Algorithm

• Early TCPs sent every application write in a separate packet

• This was death for character-at-a-time logins over slow links

  • link header + 40 bytes TCP/IP header + 1 byte data

• Nagle algorithm (RFC896, Jan 1984) applies simple heuristic:

  • If data avail for a max packet, send it
  • Else, send only if no unacked data in flight
  • I.e., stop-and-wait until requested throughput > 1 packet/round trip time

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