[Nel] Ok, some food for your toughts

[Sal]

> You can take the long, hard route:
> use UDP (and code redundancy for the elements you need to guarantee
> transmission of, putting some badly made subset of TCP in it).

    I find it easier to put some simple checking into UDP than to manage two
sets of sockets for each client, one TCP and one UDP.  Also the important
data that needs reliable transmission is usually rare.... like you said,
when someone casts a spell... and maybe chat text.  Most data in a networked
game is usually skippable.   I think this is why most games use simple UDP,
because of simplicity of implementation, and because there is so little data
that needs to be sent reliable, a less-than-efficient reliable stream is
o.k.   The strength in TCP/IP comes mostly when sending large amounts of
data, since it makes compromises with packet acknowledgement over a period
of time to gain its efficiency. But for short bursts of data typical for a
MMOG it wouldn't perform significantly better.

> Or you can take the smart route: use two protocol paths, one which carries
> the correctable elements over UDP (since you don't care if you lose a % of
> them), and one which carries the critical ones over TCP (which provides
you
> the service guarantee you need).

    This is one possible route... not a bad one either.  There would not be
any sort of performance loss in comparison to a pure-UDP implementation,
since the operating system's TCP/IP implementation is probably more
efficient than the custom UDP one.

    I guess its a matter of preference, of the developers are willing to
code something that manages two sets of sockets int the clients and servers,
then go for it :-)

> One of the minor advantages of the dual-protocol path is that it allows
you to
> bypass firewalls that refuse to forward UDP: you fold back the UDP
protocol
> path into TCP. You start losing performance, but at least, you do have a
> way of passing thru (don't forget to make your UDP packet protocols
> compatible with TCP streaming).

    This is true.  Then again, a most of today's networked games use UDP so,
the genre of people who would play a MMOG would probably have dealt with the
firewall issues before, and would expect to fix their config to accomodate a
new game.  Of course thats a slight generalization...

Just adding some more food to the bowl ;-)
-Sal