Kaustav,

RAN is the radio network which is the carrier for the wimax technology. and ASN GW is more about the intelligent work in WiMAX... ASN GW will take care of your all mobile user mobility, authentication, radio resources management etc... now talking about ASN you will have different types of ASN from various vendor like Samsung, Nokia and Motorola and many more... so each ASN GW will support the appropriate WiMAX network profile...

I just tried to explain what it is so if you have any question please feel free to ask further...

regards

Devang