HP 3000 Manuals HP 3000 Manuals
Handshaking
With binary synchronous communications (BSC) and other line protocols of
this type, handshaking is the term commonly used to describe the
interaction between stations. Typically the following information is
exchanged:
* Message available for transmission
* Start of text transmission
* Acknowledgment or rejection of text
* Detection of errors
* Retransmission after error detection
* End of transmission
A simplified handshaking sequence is summarized in Figure C-1. This
shows handshaking between a terminal and computer, but it could also be
between two terminals or two computers. In this sequence, a terminal
tells a computer it has a message to transmit. The computer recognizes
the terminal and tells it to proceed with the message. When the computer
receives the message, it detects an error in the text and requests a
retransmission. The retransmission is error free and the computer asks
the terminal for another message. The terminal does not have anything
more to transmit and so informs the computer. If the computer had a
message to transmit to the terminal it may do so at this point. Since it
does not, it disconnects from the terminal.
__________________________________________________________
| |
| TERMINAL COMPUTER |
| |
| I HAVE A MESSAGE----> |
| <----GO AHEAD |
| SENDS DATA----> |
| <----ERROR - SEND AGAIN|
| RETRANSMITS DATA----> |
| <----OK - SEND NEXT ONE|
| SENDS END MESSAGE----> |
| <----OK - DISCONNECT |
__________________________________________________________
Figure C-1. Simplified Handshaking Sequence