A Packet Data Network Gateway, a PDN-GW (105), arranged to receive and forward packet data of at least a first and a second service flow in both an uplink and a downlink direction, with a first access network (125) of a first kind being used for the first service flow and a second access network (130) of a second kind being used for the second service flow. The PDN-GW (105) is arranged to transmit to a PCRF (110), a Policy and Charging Rules Function, information regarding which kinds of access networks that the PDN-GW (105) can handle, and to receive, in reply from the PCRF, rules for which of said access networks (125, 130) that should be used for said service flows. The PDN-GW (105) is also arranged to use said rules to bind a service flow to an access network (125, 130) in the downlink direction and to perform access network binding verification in the uplink direction.