Data message sending method, device and communication system

The present invention relates to communication technologies, discloses a packet data transmission method, apparatus and a communication system, wherein the data packet transmission method is applied to a user terminal handover between networks, comprising: when the data channel is not available, the transmission protocol context request; receiving a response protocol context request to the context response protocol, the protocol context response message including the available data channel; and sending the data packet by using the available data channel. The present invention is the use of the technical solutions provided in the embodiments, the context can be correctly transmitted when the uplink data packet saved protocol unavailable.