An Investigation into Transport Protocols and Data Transport ...

A.2. Network Interface Cards 280
Model Processor Front Side PCI Word PCI Bus NIC Speed Inverse Data
Bus (Mhz) Length (bits) Speed (Mhz) (Mbit/sec) Rate (µsec/byte)
Supermicro 32-bit 400 64 133 1,000 0.011130
Supermicro 32-bit 400 64 133 10,000 0.003930
HP RX2600 64-bit 800 64 133 10,000 0.002992
Table A.11: Theoretical combined data rates of PCs
250
200
Minimum
Least Squares Fit: y=0.0177x+46.298 (R^2=0.9672)
250
200
Latency (usec)
150
100
Latency (usec)
150
100
50
50
0
0 200 400 600 800 1000 1200 1400 1600
UDP Packet size (bytes)
Minimum
Least Squares Fit: y=0.0146x+183.11 (R^2=0.7777)
0
0 200 400 600 800 1000 1200 1400 1600
UDP Packet size (bytes)
(a) Syskonnect
(b) Intel
Figure A.8: Ping-pong latency of 1Gb/sec NIC Cards (66Mhz in 64-bit PCI buses).
sum of the hardware components can be calculated by the y-intercept of a
latency/packet-size graph [HJS00]. Table A.11 shows the expected/theoretical
data transfer rates of various hardware combinations.
For each packet size, the request-response was initiated 1,000 times in
a serial fashion and the minimum values are reported. The spread of the
latencies experienced by the 1,000 packets for all packet sizes and testbed
configurations were not found to be significant and therefore is not presented.
Figure A.8 shows the performance of two popular 1Gb/sec Ethernet cards.
The smooth function of the Syskonnect indicates that the driver-NIC management
works well with a low latency suggesting that the driver interrupts
once for every packet received. The recorded slope of 0.177µsec/byte is also
within reasonable agreement with the theoretical value of 0.0111µsec/byte.
The Intel NIC, however, has much higher latency, suggesting that some