Below are some test results with the latest CCID4 subtree; two tests were performed:
(a) iperf throughput tests
(b) audio streaming using paraslash.
Both tests were performed using DCCPv6 only, so DCCPv4 supposedly works also.
1. iperf throughput testing
---------------------------
To make iperf accept IPv6 addresses, the -V option had to be passed to
the program; below are the results of running between two hosts
connected via a 100Mbps (crossover) LAN:
+--------+-------------------+--------------------+
| `s' | iperf throughput | packets per second |
+--------+-------------------+--------------------+
| 16b | 12.6 kbps | 98.43 |
| 32b | 25.1 kbps | 98.05 |
| 64b | 50.3 kbps | 98.24 |
| 128b | 101.0 kbps | 98.63 |
| 256b | 201.0 kbps | 98.14 |
| 512b | 402.0 kbps | 98.14 |
| 1024b | 805.0 kbps | 98.27 |
| 1420b | 1.12 Mbps | 98.60 |
+--------+-------------------+--------------------+
The tests were run over DCCPv6 only which is why the highest MPS is 1420 bytes
(Ethernet; with minimum set of features the MPS is 1440 for v4 and 1420 for v6).
It is noticeable that CCID4 uses a built-in speed-limiter: the packets-per-second
speed is the same in each case (the value is only approximate, the column simply
shows throughput / (8 * s), one would want to take IPv6/DCCP header sizes into
the calculation as well; not done here).
So in this regard CCID4 behaves like CCID3: when there is no loss, it quickly
climbs up to link speed, or rather maximum the speed limit.
How the results were obtained: when iperf is used without the `-b' option, it
completely tries to overrun the socket with data,
so for all packet sizes less than 1420 bytes,
the -b switch was set to the default value (1 Mbps);
for 1420b it was set to `-5m' which corresponds to a
constant bitrate of 5Mbps.
2. Audio streaming using paraslash
----------------------------------
CCID4 was set as default CCID using the {rx,tx}_ccid sysctls and a longer (50 min) MP3
file was streamed from server to client. It is a less boring setup than iperf, since when
there is a problem, it will become audible very quickly.
When doing the MP3-streaming, I had on DCCPv6
* average packet size: 160 bytes
* and the X_recv observed in the DCCP-Acks was
frequently set to 6042 bytes/sec
* which corresponds to ~ 48kbps, which is in agreement with the above table
* and it also agrees perfectly with the encoding of the MP3 file -- its
header says that it was encoded for 48 kbps joint-stereo and I think
that means constant bitrate since VBR in MP3 is a bit more complex.
Gerrit
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