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Torna a TCP over Hsdpa.

GoodputRTTPLR/TimeoutsGoodput/RTT
Back downlink/ uplink downlink/ uplink downlink / uplink downlink / uplink

TCP Congestion Control over live HSDPA Network[edit]

We report results obtained by an extensive measurement campaign over a live HSDPA network involving more than 3000 flows resulting in around 60 hours of active measurements. The considered TCP variants are the following:


The experimental evaluation has been carried out by accessing the public Internet using a commercial HSDPA card (see figure below) and by employing the linux Kernel 2.6.24.

HsdpaTestbed.png

The following instantaneous variable measurements have been collected by using the libnetmeas library:

The main findings of the investigation can be summarized as follows:

  1. TCP variants provides similar goodputs
  2. TCP Bic/Cubic exhibit inflated values for average RTT due to the aggressive nature of their probing phase. TCP NewReno and TCP Westwood+ provide lower values of RTT, TCP Westwood+ exhibiting the lowest.
  3. TCP Bic/Cubic provoke two times packet retransmission values with respect to TCP Westwood+ and TCP NewReno.
  4. TCP Bic/Cubic provoke roughly three times the number of timeouts wrt TCP Westwood+ and TCP NewReno, TCP Cubic exhibiting the highest number.

Results of the experiments and Conclusions[edit]

We report cumulative distribution function plots:

Conclusions Reasons not to deploy TCP Bic/Cubic are rooted in its more aggressive probing phase. In particular, in common network conditions, TCP BIC/CUBIC exhibits: 1. a larger RTT average wrt to TCP NewReno or TCP Westwood+; 2. a larger number of retransmission wrt to TCP NewReno or TCP Westwood+; 3 larger throughput but same goodput wrt toTCP NewReno or Westwood+. In other terms, its more aggressive probing increases both throughput and retransmission but leaving unchanged the goodput that is neutral for the users but negative for the network.

Congestion window and RTT evolutions[edit]

Typical congestion window and RTT evolutions of the considered TCPs in the case of a single flow over the HSDPA downlink

Hsdpa cwnd 1 flow downlink westwood.png Hsdpa cwnd 1 flow downlink newreno.png Hsdpa cwnd 1 flow downlink bic.png Hsdpa cwnd 1 flow downlink cubic.png