After developing SDLC, IBM submitted it to various standards committees. Each of these protocols has become important in its own domain. Technology Basics SDLC supports a variety of link types and topologies. The primary polls the secondaries in a predetermined order.
Secondaries can then transmit if they have outgoing data.
The primary also sets up and tears down links and manages the link while it is operational. Secondaries can only send information to the primary, but cannot do this unless the primary gives permission. Intermediate secondaries pass messages through one another as they respond to the requests of the primary. The primary uses the outbound channel to communicate with the secondaries. The secondaries use the inbound channel to communicate with the primary.