Re: Surely someone knows this ?! Jens knew
Re: Surely someone knows this ?! Jens knew
- Subject: Re: Surely someone knows this ?! Jens knew
- From: Jens Alfke <email@hidden>
- Date: Tue, 30 Mar 2010 15:07:37 -0700
On Mar 30, 2010, at 2:51 PM, J P May wrote:
> I've gotten emails from people who were trying to figure out the same thing and felt from testing it's at least "a good few bytes", so that's the answer really. there's no point (seems to be the consensus) worrying about shaving off the last byte if you're only sending a couple bytes.
I don’t know the data rate of Bluetooth, but it’s probably around a megabit. At that rate, it sends a byte about every 10 microseconds. Chances are you are that’s not a significant amount of time for your application.
Where bytes do become significant is when the data payload overflows the size of a packet and has to be split across two. If you’re using an unreliable packet-based transport (like UDP), messages that have to be split across physical packets are inefficient because, if either of the packets gets lost, the entire message is considered lost and has to be resent. This can cause delays and wasted bandwidth on lossy wireless networks. (Again, I don’t know the size of a Bluetooth packet; on Ethernet it’s ~1500 bytes.)
> (It would be interesting to talk to a bluetooth mouse engineer, how do they do it, so smooth!)
I would guess they’re using the Bluetooth equivalent of UDP, and sending a packet every time the mouse coords change. They might throttle the update rate down to something like 100/sec.
> on another topic, it's funny about gamekit ... it is just so reliable and simple in a business sense, clients and so on will inevitably demand it even in situations not ideal, you know. it's the beginning of the end of He-man networking! :)
Easy network APIs are great (“Simple things should be simple” —Alan Kay) but they don’t work for every situation. He-man networking still applies when you run into more complex scenarios or have to push the limits of throughput. I found this out when I implemented audio streaming a few years ago. :-P
—Jens _______________________________________________
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