The VTAM® CTC function supports two protocols: blocking and nonblocking. If VTAM is communicating with another VTAM through the CTC adapter and both VTAMs support the blocking protocol, blocking is the chosen protocol. If one VTAM does not support blocking protocols, the nonblocking protocol is used.

You cannot specify the protocol choice during system definition. Because the blocking protocol is the preferred mode, it is used if both VTAMs support it.