Hacker News new | past | comments | ask | show | jobs | submit login

Indeed! Thanks for confirming :)

Yes, it's me. I did my networking work at Ford Aerospace in the early 1980s. But I left in 1986. It still bothers me that the Nagle algorithm (which I called tinygram prevention) and delayed ACKs interact so badly.

That fixed 200ms ACK delay timer was a horrible mistake. Why 200ms? Human reaction time. That idea was borrowed from X.25 interface devices, where it was called an "accumulation timer". The Berkeley guys were trying to reduce Telnet overhead, because they had thousands of students using time-sharing systems from remote dumb terminals run through Telnet gateways. So they put in a quick fix specific to that problem. That's the only short fixed timer in TCP; everything else is geared to some computed measure such as round trip time.

Today, I'd just turn off ACK delay. ACKs are tiny and don't use much bandwidth, nobody uses Telnet any more, and most traffic is much heavier in one direction than the other. The case in which ACK delay helps is rare today. An RPC system making many short query/response calls might benefit from it; that's about it. A smarter algorithm in TCP might turn on ACK delay if it notices it's sending a lot of ACKs which could have been piggybacked on the next packet, but having it on all the time is no longer a good thing.

If you turn off the Nagle algorithm and then rapidly send single bytes to a socket, each byte will go out as a separate packet. This can increase traffic by an order of magnitude or two, with throughput declining accordingly. If you turn off delayed ACKs, traffic in the less-busy direction may go up slightly. That's why it's better to turn off delayed ACKs, if that's available.

One of the few legit cases for turning off the Nagle algorithm is for a FPS game running over the net. There, one-way latency matters; getting your shots and moves to the server before the other players affects gameplay. For almost everything else, it's round-trip time that matters, not one-way.

Guidelines | FAQ | Support | API | Security | Lists | Bookmarklet | Legal | Apply to YC | Contact