A Real-Time Transport Protocol, RTP, packet transmission apparatus, characterized by comprising: a first obtaining unit of a group communication service application server, GCS AS, configured to obtain synchronization source information of a broadcast/multicast service center, BM-SC; the apparatus being characterized in that : a first sending unit of the GCS AS configured to provide, for user equipment, UE, the synchronization source information of the BM-SC or synchronization source reference information of the BM-SC, and an RTP packet that comprises synchronization source information of the GCS AS, so that the UE obtains and saves the synchronization source information of the BM-SC and the synchronization source information of the GSC AS in a trust list of the UE so that the UE can identify and trust the received RTP packet, and wherein the GCS AS is responsible for group member management and Multimedia Broadcast Multicast Service, MBMS, initiation functions, and wherein the synchronization source reference information of the BM-SC is information determined according to the synchronization source information of the BM-SC, wherein the first obtaining unit is configured to receive the synchronization source information of the BM-SC that is sent by the BM-SC. a first obtaining unit of a group communication service application server, GCS AS, configured to obtain synchronization source information of a broadcast/multicast service center, BM-SC; the apparatus being characterized in that : a first sending unit of the GCS AS configured to provide, for user equipment, UE, the synchronization source information of the BM-SC or synchronization source reference information of the BM-SC, and an RTP packet that comprises synchronization source information of the GCS AS, so that the UE obtains and saves the synchronization source information of the BM-SC and the synchronization source information of the GSC AS in a trust list of the UE so that the UE can identify and trust the received RTP packet, and wherein the GCS AS is responsible for group member management and Multimedia Broadcast Multicast Service, MBMS, initiation functions, and wherein the synchronization source reference information of the BM-SC is information determined according to the synchronization source information of the BM-SC, wherein the first obtaining unit is configured to receive the synchronization source information of the BM-SC that is sent by the BM-SC. a first sending unit of the GCS AS configured to provide, for user equipment, UE, the synchronization source information of the BM-SC or synchronization source reference information of the BM-SC, and an RTP packet that comprises synchronization source information of the GCS AS, so that the UE obtains and saves the synchronization source information of the BM-SC and the synchronization source information of the GSC AS in a trust list of the UE so that the UE can identify and trust the received RTP packet, and wherein the GCS AS is responsible for group member management and Multimedia Broadcast Multicast Service, MBMS, initiation functions, and wherein the synchronization source reference information of the BM-SC is information determined according to the synchronization source information of the BM-SC, wherein the first obtaining unit is configured to receive the synchronization source information of the BM-SC that is sent by the BM-SC. <EOS>