SIN 498, modems and routers must support retransmission in the downstream, but it is not a mandatory requirement in the upstream. Taking this into account and to maintain a high level of service, when we first rolled out retransmission to our Huawei estate we introduced interleaving on all lines where the modem/routers did not support retransmission in the upstream.
SIN498 Requires devices be G.INP capable on Downstream, it was only when upstream was enabled with G.INP that everything went wrong.
I've witnessed my neighbours HH5a see an increase of 9Mb/s* since G.INP Phase 2 was rolled out on our DSLAM.
* note this is 9Mb/s faster than when the modem was connected in fast path mode and before any G.INP was rolled out on our DSLAM.