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Protocol Enveloping
In prptocol enveloping mode, the 3708 supports an ASCII end-user device as an LU
type 1 with a Network Terminal Option (NTO) appearance. The 3708 does not
provide any device-specific support other than that provided by NTO for devices
that are compatible with TWX 33/35. The application program must provide any
device-specific support. The 3708 supports the following functions in protocol
enveloping mode:
• It mayor may not modify the ASCII data, depending on how the port is
configured. The data can be modified by using a translate table, delay
characters, substitution characters, and other options that are defined during
configuration. If the data is translated from ASCII to EBCDIC, the 3708 can
use one of two standard translate tables or a user-defined translate table.
• It can provide a delay after a Carriage Return, Vertical Tab, Form Feed, or
Horizontal Tab.
• It can use either a default substitution character or a user-defined substitution
character when it detects a data error. When it detects a parity error in a
character, the 3708 can replace the character with the Parity Error Substitution
character configured in the 3708. When it detects a framing error, the 3708
always replaces the framing error with the Parity Error Substitution character.
• It can use up to five different turnaround characters, which are defined during
configuration, to control communication. When the 3708 receives a line
turnaround character from an end-user device, the 3708 sends data from the
device to the host.
Because the 3708 does not control the keyboard in protocol enveloping, users
must know when they can and cannot enter data. A character string that tells
the user when to enter data can be defined for each port. To define the
character string, see "Send Read Prompt" on page 13-40. In addition, a port
can be configured to enable the 3708 to echo characters that are entered at the
keyboard.
• It can provide for transparent data flow. The 3708 can support 256-character
sets and output-only devices, such as printers and plotters.
• It can allow the host to dial out to devices. For more information, refer to IBM
3708 Network Conversion Unit Description.
ASCII Pass-Through
In ASCII pass-through mode, the 3708 serves as a wire connection between an
ASCII end-user device and an ASCII host. The host and the end-user device are
responsible for data and protocol error checking.
N~te:
A programmable modem can be installed on a port configured as an ASCII
host. The 3708 allows the user to dial out through the programmable modem in
ASCII pass-through mode and gain access to an ASCII host, printer, or other
device.
2-4
3708 Planning and Installation
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