A transmission system and a transmission method are provided. The transmission system comprises a compressor, an intermediate terminal, and a decompressor. The compressor transmits an initial Internet Protocol package (IP package). The initial IP package comprised an initial forwarding table. The initial forwarding table records at least one candidate context identification (CID). The intermediate terminal receives the IP package and selects the at least one candidate CID different from an intermediate CID recorded in the intermediate terminal, so as to create an intermediate forwarding table. And, the intermediate terminal transmits an intermediate IP package. The decompressor receives the intermediate IP package. The decompressor selects the at least one candidate CID different from a decompressor CID recorded in the decompressor to be a target CID.