My home router (Linux box) is configured to shape upstream traffic to just below the link rate to avoid Bufferbloat – this greatly improves interactive performance under load. Recently I’ve experimented with various packet sizes. The charts below show the effect of small packets.
- Between 0-6 seconds the link is idle.
- From 6-14 seconds the upstream link is flooded with 1,400 byte packets (10Mb/sec of traffic trying to get through a 6.2Mb link)
- At 17 seconds the upstream link is flooded with 64 byte packets (10Mb/sec as well)
Notice how much higher the latency and jitter are with small packets.
Confusingly, these results were gathered with the bandwidth shaper configured for 53 bytes of overhead  which is my current understanding of the per-packet overhead on VDSL2 [53 is a coincidence with the ATM cell size].
Per-packet overhead for VDSL2 (without ATM) and PPPoE:
- 5 Bytes for PTM
- 40 bytes for 802.3
- 8 bytes for PPPoE
Either the above overhead numbers or wrong or there is something else going on.
 – overhead argument to tc.