580EX 'Master-to-Slave' Communication channel - what is it ?

While a Master 580EX communicates with a Slave 580EX, is it managed over an 'optical burst of flashes', or over an 'optical burst of IR (Infra Red) signals' ?

(I kinda understand that the communication channel between the ST-E2 to a 580EX Slave is in fact an IR channel)

The 580ex/550ex communicates with the slaves via pulses emitted by the flash itself.

Thanks.
To me it sounds a bad design.
Control data (from Master to Slave) consists of quite a bit of items, and conveying it via a burst of flash pulses seems a waist of energy and slow, compared to doing it via an IR channel.

BTW - the 580EX (as a Slave device) must already have an IR receiver to receive commands sent to it by an ST-E2. Why Canon didn't complement it with a IR Transmitter is beyond me to comprehend.

Why do you say that using the flash is a waist of energy and slow compared to using IR? IR is nothing more than light that's in the part of the light spectrum adjacent to the red light (and hence the term infra red). Even if you can't see IR, it's still light that's being emitted so I can't see where there would be a difference in the two methods. The advantage of using the flash over a dedicated IR LED is that the flash provides a greater range of wireless ETTL coverage only because if can put out more power than an IR LED.

I assume that a Flash energy in terms of charging up the Flash capacitor for a pulse duration of, say, 1/10 of a second is at least 10 folds greater than that dissipated by the IR LED transmitter.

I also assume that in terms the frequency that can be modulated by an IR LED device, it is at least 10 folds greater than the one that can be modulated by the Flash bulb.