[ENet-discuss] Optimizing ENet Protocol ?

[Emmanuel Rivoire]

Hello,

I have been using DirectPlay from DirectX9 since 6 years in my games 
and have been pretty happy with it since then, except I cannot use it 
on Mac OSX.

So I've decided to give Enet a try and I just had a deep look at 
Protocol.c & .h .

DirectPlay gives a packet overhead of 4 bytes for unreliable & 
unsequenced messages.
ENet overhead is 10 bytes (without the optional stuff) for this kind 
of messages.

In a general way, ENet protocol header always contains : peerID (on 9 
bits) and dataLength on 16 bits.
As far as I know, dataLength is already in the UDP header ( 
http://en.wikipedia.org/wiki/User_Datagram_Protocol ) and incomplete 
packets are dropped, so there's no need to have it within ENet header.
peerID should be deducted from packet's sender IP & Port which are in 
ENetHost::receivedAddress .

That'd be already 3 bytes saved on each packet in all cases of use of ENet.

Moreover, I'm planning to remove 
ENetProtocolSendUnsequenced::unsequencedGroup which is not mandatory 
at ENet level (this is an arguable opinion ;) ), mainly because I 
already have the attached functionality in the high level part of my 
network code, but using less bits, so it's redundant and less 
effective at ENet level.
2 more bytes saved.

Lastly, if I understood the code correctly 
ENetProtocolSendUnsequenced::header::reliableSequenceNumber isn't 
needed (it's always set to 0), so that's 2 bytes wasted (only for 
unsequenced message case).

So we're now down to an overhead of 3 bytes = 1 byte for flag (in 
upper part of peerID, with 1 bit free) + 1 for command number (with 4 
bits free) + 1 byte for channel ID.
So I'm going to stuck the channel ID in the 4 free bits of the 
command bytes, and the overhead will be of only 2 bytes.

I'm not a network specialist, so maybe I got something wrong, so 
please let me know if I did something incorrect, especially if I 
overlooked something.

And globally, does it sound doable in a timely fashion ..? I hope to 
spend only a couple of days to do all of that.

But for now, I'm going to begin by converting my mid-level network 
code from DirectPlay to ENet, as it's the 1st step on the road..! ;-)