This work is motivated by the need for the fundamental increase of spectral efficiency with the transmissions on the Transmission Control Protocol and the Internet Protocol (TCP/IP). To emphasize the work in physical layer, we define a bit-unit (BU) that is conceptually similar to an IP packet that contains sufficient information for its destination node to identify the address and interpret the contents in performing the message communication. Armed with these functions, we divide one BU into two parts, which are defined as opportunistic bit (OB) and conventional bit (CB), respectively. In addition, we design the sequential time-slots (TSs) in such a way that the OB can be mapped to the index of a TS, and the CB can be carried by the corresponding TS. To enable the communication, we pre-store a bit-to-TS mapping table at both of the transmitter and the receiver. As result, we can save time resource and gain spectral efficiency as shown in the theoretical analysis confirmed by the simulations.