Version 1.0, 4/10/02
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degrade in these scenarios, and the design becomes subject to ATM overflows from running
“_VolgaGetChanCounters”.
Ethernet
Input
Ports
ATM
Transmit
Rate [%]
IXF6012
Transmit
Idle
ATM
Receive
Ports
IXF6012
Overflows Ethernet
Transmit
KFrame/s
Ethernet
Transmit
[MB/s]
8 84 N/A 1 0 138 - 147 8.8 – 9.4
7 73 N/A 1 0 142 - 148 9.0 – 9.5
6 63 N/A 1 0
144 – 148 9.2 – 9.5
0 0 N/A 1 0 148,808 9.5
Figure 6 – Single-cell/PDU Performance using 143MHz DRAM
Repeating the same measurements for 143 MHz DRAM results in the same ATM transmit
bandwidth in all cases (Figure 6). Interference from “_VolgaGetChanCounters” is gone however,
even in the 8 port configuration. Ethernet Transmit performance is slightly better, but still sub-
wire-rate in the 8 port configuration. When there is no Ethernet input at all, the ratio between
packets dropped by the IP Router versus full Ethernet transmit queues improved such that the
Ethernet Transmit queues drop 45% and the IP Router drops only 55% of the excess input.
Hardware 40-byte packet performance
Ethernet
Input
Ports
ATM
Transmit
Rate [%]
IXF6012
Transmit
Idle
ATM
Receive
Ports
IXF6012
Overflows Ethernet
Transmit
KFrame/s
Ethernet
Transmit
[MB/s]
8 97 30,000 1 700 88,300 5.6
7 100 1,500 1 69 88,300 5.6
6 100 700 1 0 88,300 5.6
5 100 0 1 0 88,300 5.6
4 84 N/A 1 0 88,300 5.6
Figure 7 – Two-cell PDU Performance on 133MHZ DRAM
For the 40-byte (2 cell/PDU) workload there are half as many IP lookups/second as are required
in the 29-byte (1 cell/PDU) workload. As expected, the IP Router was able to keep up with this
workload and didn’t drop any packets.
For five Ethernet input ports, the design performed perfectly, and “_VolgaGetChanCounters” did
not cause any dropped cells.
Reducing the Ethernet input to 4 ports did not allow enough input to saturate ATM Transmit.
Increasing the Ethernet input ports to 6, 7 and 8 allowed over-subscription in the Ethernet to
ATM forwarding direction, as evidenced by the ATM Transmit idle cells and ATM Receive
overflows. Indeed, even under nominal conditions, the 8 port input configuration was able to
drive only 97% of the ATM wire.
For this packet size, Ethernet is more efficient that ATM, and the Ethernet transmitter cannot be
expected to be driven at wire rate. Indeed, under nominal conditions the Ethernet transmitter
performed perfectly for all tested configurations.