I found that a flat-out upload with my VMG 1312-10As while a long download was in progress could really hurt the downstream transfer rate; that is not good, but maybe things are just set up wrong so that the required number of ACKs are not getting through on time. I don’t really understand this though with TCP, because if one ACK cannot get through for ages then surely a later ACK will be sent upstream and it will have a later sequence number by then, so its effect will be to allow more stuff to be sent downstream by the remote end, and the later ACK will qualify as an ACK for all the non-received earlier ACKs.