AbstractThis paper discusses a signal transmission method based on the existing digital hierarchical transmission system that transmits signals as defined in the network node interface (NNI) of the new CCITT synchronous digital hierarchy (SDH). The method transmits the information corresponding to two virtual containers (VC‐3s) with the capacity of 28 of 1.5 Mbit/s over existing transmission systems using the fourth digital level, which is the basic unit of operation in the existing network. The fourth digital level signal in Japan has a bandwidth of 97.728 Mbit/s as specified in Rec. G.702. If two VC‐3s are to be contained according to the basic SDH philosophy of NNI, the required transmission capacity is 103.68 Mbit/s. The method that allows two VC‐3s to be transmitted at 97.728 Mbit/s should be considered.It is shown first that the use of the pointer introduced in SDH is adequate. A pointer scheme with a fourmultiframe structure is proposed, aiming at efficient information transmission. The characteristics of the fourmultiframe‐type pointer are then discussed, and the assignment of the overhead required in the transfer of maintenance/operation information is considered. Based on those discussions, the frame structure for the 97.728 Mbit/s signal is derived, which is the fourth level of the existing digital hierarchy.