84
Data transmission may accidentally involve various types of errors. The BHT-protocol
is designed to recover from those errors as frequently as possible. What follows is the
BHT-protocol for phases 1 through 3.
Phase 1: Establishment of Data Link
■
Normal phase 1
The sending station transmits an ENQ to the receiving station. Upon receipt of an
ACK from the receiving station, the sending station shifts to phase 2.
ENQ
ACK
To phase 2.
■
Phase 1 with no response or invalid response
If the sending station receives no response or any invalid response from the
receiving station in response to an ENQ sent, it iterates sending of an ENQ at three-
second intervals up to 10 times.
If the sending station receives an ACK before sending an ENQ ten times, it shifts to
phase 2.
ACK
ENQ
3 seconds
3 seconds
ENQ
ENQ
Receiving station
Sending station
Sending
station
Receiving
station
To phase 2.
