TCP Timeout Algorithm

• TCP must determine when to timeout and retransmit a packet

• Reasonably accurate calculation of this value is critical

• • Timeout too low
  • • Unnecessary retransmissions
  • Timeout too high
  • • Unnecessary delays

• TCP originally used a strict low-pass filter to estimate RTT

• • Could not adjust quickly enough to rapidly varying delays
  • Internet delays exhibit infinite variance in the form of self-similarity (fractals)