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OpenFlow is a widely adopted dataplane protocol insoftware-defined networking (SDN). However, the expansion ofsupported match fields in OpenFlow brings additional pressure tothe storage space of ternary content addressable memory (TCAM)in physical device, since the arbitrary wildcard support in thematch field of OpenFlow relies heavily on TCAM for looking-upspeed. In this paper, a mathematical model aiming at the storagespace reduction of the flow table in TCAM is presented, which isnamed as RETCAM. RETCAM analyzes the relationships amongall the match fields and then categorize the redundancy amongdifferent fields into three types. Based on the three redundancytypes, three compression algorithms named as inter-field merge,field mapping and intra-field compression are presented. The outcomes of each compression algorithm are flow entries with smallerbit-width which is sent to TCAM for flow matching. In this way, theflexibility of OpenFlow is not harmed, thus maintaining the function integrity of the original flow table. Simulation at the end showsthat RETCAM saves almost about 60% of TCAM space for a givenflow table with no damage to the function integrity of OpenFlow,and the compression performance stands stable with the increaseof flow table size.