An Investigation into Transport Protocols and Data Transport ...

A.2. Network Interface Cards 283
Throughput (Mbit/sec)
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1472 bytes
Throughput (Mbit/sec)
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Interpacket Wait-Time (usec)
(a) Syskonnect
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Interpacket Wait-Time (usec)
(b) Intel
Figure A.10: Throughput performance of 1Gb/sec NIC cards (66Mhz in 64-bit
PCI buses).
Figure A.10 shows the throughput achieved by flooding the NIC with
UDP packets with various packet sizes and inter-packet times. As with the
tests involving latency, identical computer systems were connected back-toback
via their NICs.
Figure A.10 shows the throughput achieved by the same two cards that
were used for the latency tests. They show the 1 t
relation as measured by
the UDPMon [HJ] program.
It was noticed that as small inter-packet wait times were used, a plateau
on the rate at which data is transferred was reached.
The length of the
plateau of each curve is defined by the amount of time required to put a
packet on the wire. More specifically, this is defined by packet size divided
by the line rate, i.e. ‘standard’ IP packets of size 1500B would require 1, 500×
8/1, 000, 000, 000 = 12µsec per packet. As the packet processing is First-In-
First-Out (FIFO), the packets are simply queued if a inter-packet wait time
that is less than the physical time required to put the packet on the wire.
Figure A.10 also shows that more stable performance was achieved for
low wait times between packets with the Intel card compared to that of
the Syskonnect. This was found to be due to high CPU utilisation of the