ICM version 4.1 onwards can support Expanded Call Context (ECC) Variables. After opening a session, and before using any ECC variables, the VRU must send a Register_Variables message to the ICM. The Register_Variables message contains a flag for each of the ten standard call variables and an optional list of ECC variable names.
The flags allow the VRU to select which call variables (CallVariable 1 through CallVariable 10) it wants to receive from the ICM. The VRU is initially assumed to have interest in all 10 standard call variables. The flags control only the sending of the call variable values from the ICM to the VRU.
Each ECC variable name has an associated tag value, chosen by the VRU, that is used to identify the variable in all later messages. Each ECC variable supplied contains a tag number and a string name. The tag number identifies the ECC variable in values to or from the VRU.