# SIGTRAN The [[IETF - Internet Engineering Task Force]] has defined the SIGTRAN protocol suite that implements levels 2, 3, and 4 protocols compatible with [[SS7 - Signaling System No. 7|SS7]]. Legacy, was [[SS7 - Signaling System No. 7]] over [[CS - Circuit Switched]] Now [[SS7 - Signaling System No. 7]] over [[IP - Internet Protocol]]