What will be the resolution for Images and Icon set which will support iOS 7+ and iPhone 4s above.?

Hi,
I have gone through some documentation which tells me how naming convention for Icons and images should be, in order to render it on retina and non retina devices.
My question is do I need to have separate PNG images/Icons for all sort of screen sizes and all sort of retina and non retina devices? or is there any better solution for this. also I need to know what should be the resolution of PNG images if there is any unique way.
SVG is not supported by xamarin. I hope some one will answer.