Bug #3230
closed
best-route strategy: initial retx suppression is too low
100%
Description
best-route strategy has consumer retransmission suppression feature.
A consumer retransmission, from same or different downstream face, is suppressed (not forwarded) if it arrives within a suppression duration calcuated with an exponential back-off algorithm.
The initial suppression period is 1ms.
This setting is causing excessive retransmissions when multiple consumers are requesting the same contents.
One notable example is:
- Run one NDNRTC producer, connected on one NDN testbed router.
- Run two NDNRTC consumers fetching the same stream at same bitrate, connected on another NDN testbed router.
- Observe NDN testbed bandwidth map.
Expected: most traffic is forwarded on one path between the two routers.
Actual: about 10% traffic is also forwarded on a second path.
It's believed that this observation is caused by Interests from the second consumer being treated as a consumer retransmission.
When the two consumers are not perfectly synchronized, and the second Interest arrives more than 1ms later but less than RTT, it would be forwarded on a secondary path.
Setting a larger initial suppression period, such as 10ms, should prevent this behavior, but still allow consumer to retransmit the Interest if application detects a packet loss.
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