So I'm having a discussion with a friend, and we're debating what seems like
an obvious point:

 

Is it actually any cheaper to send a 0-byte UDP packet than to send one that
is sized at the MTU?

 

I'd *hope* that it's cheaper, but I don't honestly know if this is the case.


 

Now of course the overhead of UDP, IP, Ethernet and so on is fixed
irrespective of the UDP payload size.  But I don't know enough about the
lower layers of the protocol stack to say with certainty that more 0-byte
UDP packets can be delivered per second over (say) a typical DSL connection
than a 1300 byte UDP packet.  Do you know?

 

For example, I'm kinda sketchy about the physical layer of Ethernet.  But if
two computers are on the same Ethernet, then they need to broadcast on the
same physical wire.  I don't know precisely what that entails, but I assume
that takes a nonzero amount of time, especially if there is a collision to
resolve.  Is it possible that the simple overhead of sending *any* packet
dwarfs the amount of time it takes to send the payload?

 

In other words, to what degree should a UDP protocol attempt to shave off
that extra few bytes per packet?

 

-david

 

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