The Nagle Algorithm

• The goal of the Nagle algorithm is to eliminate packets with one byte of TCP data

• • 40 bytes of header,1 byte of data = 4000% overhead!
  • This is usually ok on a LAN, but will rapidly congest a WAN

• The Nagle algorithm forces TCP to refrain from transmitting a “small” packet until it receives an ACK for at least some of the data transmitted in the previous packet

• • E.g.: Telnet characters accumulate for an RTT
  • Self-clocking: very efficient!
  • In many implementations “small” means anything less than the MSS

• Not as important today as it was in 1984

• • WAN links are much faster, most RTT’s are under 500 ms
  • • People type about 1 character per 200 ms
  • Still manages to save bandwidth, but turned off in many performance critical applications (e.g., web servers)
  • Also turned off in traffic generators that need to create TCP packets of a particular size