Hawking is different from either singing, talking or shouting, but combines elements of all three. Try it for 8 to 12 hours...*grin*seriously, a hawker's cry DOES combine elements of singing, shouting and talking. Breath control is important and so are pitch, volume and projection.
I have spent my summer weekends hawking for about 8 years now. When I am not hawking, I am probably doing a "patter" judging games. Oddly enough, the "patter" is more wearing on the voice.