gents,
purpose of media gateway in 3g is to carry payload and to bridge between different transport technologies.it can be considered as a switch between two transport modes.for example suppose a caller from PSTN network call a 3g subs.the payload from PSTN may be TDM is converted at media gateway into IP/ATM payload for its further propagation upto MS.
NODE B TO RNC payload over ATM as VCIs.
ARSHAD M