V.27 Signon by the Secondary Node

This scenario assumes that the node attempting signon has been identified as the secondary node.

Figure 1. V.27 Modem Protocols: Secondary Node Signon

START:
      Allow operator intervention to stop this
      process, otherwise continue until 'SOH ENQ' is received.

      Issue  PREPARE (cc)
             READ
      If ANY SERIOUS ERROR (e.g. device not available)
            -Terminate immediately

CKREAD: (Successful I/O completion)
      See if data read is 'SOH ENQ'
      If so, SEND 'DLE ACK0'
             READ
       ... normal protocols follow
      If not 'SOH ENQ', go back to START