A communication network operable to provide online charging for a session of a dual mode device that is transferred from a first network domain to a second network domain, the communication network comprising: at least one network element in the second network domain that is operable to receive a handover charging identifier for the session that was handed over from the first network domain to the second network domain, wherein the handover charging identifier is assigned to said session and distributed to network elements (112, 113) in the first network domain and the second network domain, the at least one network element is further operable to store the handover charging identifier, to identify a triggering event for charging during the session over the second network domain, to generate an online charging request for the session and insert the handover charging identifier in the online charging request, and to transmit the online charging request to an online charging system, so that said online charging system can correlate said online charging request with other online charging requests for the session based on the handover charging identifier to determine a charging rate, and further comprising a handover application server operable to: receive a session initiation request from the at least one network element in the second network domain; identify the handover charging identifier for the session; and distribute the handover charging identifier to the at least one network element in the second network domain indicating the handover charging identifier to be used in online charging requests to the online charging system. at least one network element in the second network domain that is operable to receive a handover charging identifier for the session that was handed over from the first network domain to the second network domain, wherein the handover charging identifier is assigned to said session and distributed to network elements (112, 113) in the first network domain and the second network domain, the at least one network element is further operable to store the handover charging identifier, to identify a triggering event for charging during the session over the second network domain, to generate an online charging request for the session and insert the handover charging identifier in the online charging request, and to transmit the online charging request to an online charging system, so that said online charging system can correlate said online charging request with other online charging requests for the session based on the handover charging identifier to determine a charging rate, and further comprising a handover application server operable to: receive a session initiation request from the at least one network element in the second network domain; identify the handover charging identifier for the session; and distribute the handover charging identifier to the at least one network element in the second network domain indicating the handover charging identifier to be used in online charging requests to the online charging system. receive a session initiation request from the at least one network element in the second network domain; identify the handover charging identifier for the session; and distribute the handover charging identifier to the at least one network element in the second network domain indicating the handover charging identifier to be used in online charging requests to the online charging system.