R2 signaling is a Channel Associated Signaling (CAS) system developed in the 1960s that is still in use today in Europe, Latin America, Australia, and Asia.
R2 signaling exists in several country versions or variants in an international version called Consultative Committee for International Telegraph and Telephone (CCITT-R2). The R2 signaling specifications are contained in ITU-T Recommendations Q.400 through Q.490.
E1 R2 signaling is an international signaling standard that is common to channelized E1 networks. E1 R2 signaling has been supported on the Cisco AS5200, 5300, and 5800 series access routers. E1 R2 signaling was introduced to the Cisco 2600/3600 series routers in Cisco IOS Software Release 12.1.2XH and 12.1(3)T. E1 R2 is also supported on the E1 voice WAN interface cards (VWICs), which can be inserted into the WIC slot on the IAD2430s. Furthermore, Cisco AS5350, 5400, and 5850 also support this application.
Note: R2 signaling is not supported on the Cisco MC3810 router.