Binary-Synchronous (bisync) is IBM's version of polled
sync protocol. All of our products completely emulate the capabilities
of bisync devices. Furthermore, we support most of the features
available with the different bisync hosts and terminals.
Bisync Overview
IBM terminals are designed on a
controller principle. The controller performs all network interaction and passes the
data to the terminal. The terminal performs all device formatting and operator
interaction. Depending on the terminal, the controller is placed in a separate
unit and cable attached to the terminals. In other units, the controller is
incorporated into the terminal. In either case, the controller is assigned a unique
network address. Some bisync emulations also assign an address to the attached
terminals (for example: 3270).
The terminal only answers
polls with the correct controller address. If several terminals are attached to
a controller, the controller will determine the status of each terminal before
responding to the poll. The host can also directly poll a specific terminal.
Bisync Addressing
There are two methods of device addressing
supported by bisync devices. Both methods support switched (dial) and non-switched (leased)
connections. The two methods are:
Contention
- This method
is designed for switched lines and only allows one device on the
communications line. Addresses are not used. Once the connection
is established with the other device, the two devices bid for control
of the line. This is the normal mode used by RJE terminals.
Multipoint
- This method
uses addresses to identify the specific terminal. The host controls
all message flow on the communications line through poll and select
line-bid sequences. The individual terminals respond only when their
address is selected by the host. This is the normal mode used by
3270 terminals.
Bisync Terminal Support
There are many different terminal
implementations of bisync protocol. Each terminal supports different hardware and can
perform different functions. The terminal designer tailored the bisync support to optimize
the terminal's price and performance.
Bisync terminals are grouped into two major categories: Remote Job Entry (RJE)
and interactive (3270). The RJE terminals are characterized by large amounts of
data sent in long bursts. An interactive terminal is characterized by an exchange
of small messages with the network.
RJE and interactive terminals normally do not share the same communications line
because the RJE terminals monopolize the line during transmission.
Further information on the RJE terminals is available here.
Information on the 3270 terminals is available here.
Bisync Transparency
Some bisync terminals support
bisync transparency which allows Data Link Characters to be sent as text. Both
devices must support transparency. The Data Link Characters are (SOH, ACK, STX, DLE,
ETX, NAK, EOT, SYN, ENQ and ETB)
Data Formats
Bisync devices can support
either ASCII or EBCDIC data formats.
Error Reporting
Bisync terminals use error
reporting to indicate that a problem has occurred at the terminal (for example: printer out of paper).
The error condition is reported to the application program. 3270 terminals use Status
and Sense bytes to report error conditions. Most RJE terminals reject inbound Selects
when an error condition occurs.
To view the available options that can be specified for this protocol,
please review the worksheets.
If you need further information on bisync protocol or our implementation
and support for this protocol, please e-mail
us.
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