Test Description:
This test shows two TCP connections with slightly different propagation delays on the two incoming links. The with a shorter delay receives a disproportionate share of packet drops due to phase effects. The phase effects usually remain with Reno TCP sources and with delayed-ACK sinks. From this test we find phase effects also exist with Tahoe TCP sources and delayed-ACK sinks.
Expected output:
  • The top connection with shorter delay receives a disproportionate share of packet drops due to phase effects.
Test Topology: 
 Server ................Router..................Client

        8Mbs 3ms
 5(0)------------------0(1)        800kbs 100ms
                            0(0)-----------------7(0)
 6(0)------------------0(2)
        8Mbs 5ms
SSF Test Configuration File: f7.dml
send window = receive window = 32 packets
SSF Tcpdump File:
f7_1.tcpdump

f7_2.tcpdump

Zoom in on SSF trace

NS Test with the same parameters

NS tcpdump trace file:f7.tr

Zoom in on NS trace

Trace Analysis:

The output is consistent with expected output.

The slight difference between the NS trace and SSF trace is due to the fact that the NS TCP contains an improved algorithm for fast retransmission under multiple losses, which disables fast retransmission in some situations.

The phase effect is evident in both the SSF and NS traces.