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8.8 Simulated 20fps Uncompressed Video Data Under Severe Network Loading, Relieved Near End

This test is similar to the previous test, except the network congestion is relieved manually about three-fourths of the way through the transfer.

XUDP

XUDP received approximately half of the parcels generated by the sending side (table 8.11, with the majority lost during the period of 13 seconds to 28 seconds. The transfer was able to recover nicely once the network congestion was relieved, evidenced by the increased slope and point density in the upper right of the graph in Figure 8.29.

 

Measurement Result
Total Data Acknowledged 4033.607 KBytes
Total Transmission Time 33.206 seconds
Network Bandwidth Utilization 121.472 KBytes/second
Average Round Trip Time 50.1 milliseconds
Average Window Size 16.3 packets
Total Parcels Received 265 parcels
Total Transmission Time 32.219 seconds
Total Parcels Skipped 316 parcels
Network Bandwidth Utilization (14.4 KBytes/parcel) 118.439 KBytes/second
Average Parcel Reception Frequency 8.225 parcels/second
Table 8.11: XUDP Test 18:54, March 17, 1997

 

  
Figure 8.29: Parcels Received (XUDP Test 18:54 3/17/97)

Figure 8.30 shows the plateau in bytes received during the period of time the network was congested.

  
Figure 8.30: Bytes Acknowledged (XUDP Test 18:54 3/17/97)

  
Figure 8.31: Round Trip Times (XUDP Test 18:54 3/17/97)

  
Figure 8.32: Packets In Network (XUDP Test 18:54 3/17/97)

The congestion window (figure 8.32), interestingly did not adjust itself once network congestion had been relieved. The activity from 31 seconds until 35 seconds is due to residual acknowledgments remaining in XUDP's queues (acknowledgments of XUDP command parcels, primarily).

TCP

TCP held close to a 200KBytes/second bandwidth for the duration of the transmission (table 8.12). Note that the slope of the parcel received curve (figure 8.33 rises towards the end of the connection, indicating TCP's response to the increase in available bandwidth.

 

Measurement Result
Total Parcels Received 581 parcels
Total Transmission Time 42.571 seconds
Total Parcels Skipped 0 parcels
Network Bandwidth Utilization (14.4 KBytes/parcel) 196.528 KBytes/second
Average Parcel Reception Frequency 13.648 parcels/second
Table 8.12: TCP Test 18:44, March 17, 1997

 

  
Figure 8.33: Parcels Received (TCP Test 18:44 3/17/97)

Comparison

This example is by far the best in this suite at illustrating the functionality of XUDP's timed-obsolescence algorithm. XUDP's stream is finished in just over 32 seconds, while TCP's stream isn't finished until the 42 second mark - a ten second difference. A XUDP application could have presented the XUDP stream unbuffered with satisfactory results, while the TCP's unbuffered stream would, on average, get presented 25% slower!

  
Figure 8.34: Comparison of TCP vs. XUDP Parcels Received (Tests 18:44 and 18:54 3/17/97)


next up previous contents
Next: 9 Conclusions and Directions Up: 8 Results and Analysis Previous: 8.7 Simulated 20fps Uncompressed

Mike Andrews
Wed Mar 19 16:07:58 EST 1997