A method comprising: establishing (1102, 404-406) a first binding for a first session for a user equipment, UE, wherein the first binding includes, at least in part, policy charging and enforcement function, PCEF, connectivity information for a PCEF associated with a packet data network gateway hosting the first session for the UE, wherein the first binding is established by a first DIAMETER routing agent (144, 144.2, 194), DRA, serving the packet data network gateway in a first IP domain, wherein the first session for the UE is associated with a Gx session for the UE, wherein the PCEF connectivity information includes an origin-host identifier and an origin-realm identifier for the packet data network gateway hosting the first session for the UE and associated with the PCEF, and wherein the first binding further includes information identifying the UE; receiving (1104, 415) a request by a second DRA in a second IP domain associated with establishing a second session for the UE, wherein the request includes, at least, the PCEF connectivity information, and wherein the second session for the UE is associated with an Rx session for the UE; the first DRA determining (1106, 420, 810) a policy charging and rules function, PCRF, serving the first session for the UE based, at least in part, on the PCEF connectivity information; and the PCRF binding (1108, 424, 814) the second session for the UE with the first session for the UE based, at least in part, on the PCEF connectivity information. establishing (1102, 404-406) a first binding for a first session for a user equipment, UE, wherein the first binding includes, at least in part, policy charging and enforcement function, PCEF, connectivity information for a PCEF associated with a packet data network gateway hosting the first session for the UE, wherein the first binding is established by a first DIAMETER routing agent (144, 144.2, 194), DRA, serving the packet data network gateway in a first IP domain, wherein the first session for the UE is associated with a Gx session for the UE, wherein the PCEF connectivity information includes an origin-host identifier and an origin-realm identifier for the packet data network gateway hosting the first session for the UE and associated with the PCEF, and wherein the first binding further includes information identifying the UE; wherein the first binding includes, at least in part, policy charging and enforcement function, PCEF, connectivity information for a PCEF associated with a packet data network gateway hosting the first session for the UE, wherein the first binding is established by a first DIAMETER routing agent (144, 144.2, 194), DRA, serving the packet data network gateway in a first IP domain, wherein the first session for the UE is associated with a Gx session for the UE, wherein the PCEF connectivity information includes an origin-host identifier and an origin-realm identifier for the packet data network gateway hosting the first session for the UE and associated with the PCEF, and wherein the first binding further includes information identifying the UE; receiving (1104, 415) a request by a second DRA in a second IP domain associated with establishing a second session for the UE, wherein the request includes, at least, the PCEF connectivity information, and wherein the second session for the UE is associated with an Rx session for the UE; wherein the request includes, at least, the PCEF connectivity information, and wherein the second session for the UE is associated with an Rx session for the UE; the first DRA determining (1106, 420, 810) a policy charging and rules function, PCRF, serving the first session for the UE based, at least in part, on the PCEF connectivity information; and the PCRF binding (1108, 424, 814) the second session for the UE with the first session for the UE based, at least in part, on the PCEF connectivity information.