i think "NORMALLY" the reciever is aware when he doesnt get a packet, so doesnt just take the next one, but waits for the missing one, then times out, so it can be resumed ok, but the sender had no idea, as he was just tossing packets out saying "catch , catch , catch, catch" "what you missed one?",
To cavets here, i said "I think" and I also said "normally" since i have heard of somepeople missing a packet and getting a shortened file with one bity missiing in the middle.
Seems pretty unlikely to me tho. altho I think the ack sends back how much you have recieved so far, so a missed packet could slide by if /fastsends were on i guess.
I have never seen a speed difference if its on or off, then again i dont use a 56k modem LOL