Introduction

• slow internet problems is the result of congestion control
• loss-based congestion control keeps buffers full and causes memory bloat.
• slowest link in a route determines data delivery rate
• queue shrinks only when departure rate exceed arrival rate

• TCP views arbitrarily complex routes as a single link

• Characterizing bottlenecks
  • TCP runs at peak performance when bottleneck packet arrival is the bottleneck bandwidth and the total data in flight is equal to the BW-D product
  • bottleneck bandwidth and round trip propagation are constantly changing - so they must constantly be estimated
  • RTT = RT_prop + n_t
    • n_t is noise introduced by queues along path
  • estimate of bottleneck bandwidth is the delivery rate of packets.
  • bottleneck bandwidth calculated by max delivery rate in a sliding window (6-10 RTTs)
  • impossible to know both bottleneck bandwidth and RTprop at the same time
• sometimes acks are grouped together, causing delays in updates to bottleneck bandwidth

  • set cwnd_gain to a alrger value (2) to account for additional RTT time.