Protocol Enveloping - IBM 3708 Description

Protocol Enveloping
In protocol enveloping mode, the 3708 supports an ASCII end-user device as an LV
type I 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. To support an ASCII end-user device in
protocol enveloping mode, the 3708 can do the following:
• 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.
• It
can tell the user when to enter data. Because the 3708 does not control the
keyboard in protocol enveloping, users must be notified when they can and
cannot enter data. A character string (Read Prompt) that tells the user when to
enter data can be defined for each port.
• It can indicate keyboard data that is to be sent up on the SNA SSCP-SLU flow.
Because the 3708 does not support keyboard mapping in protocol enveloping
mode, an optional sequence (System Request Simulation String) is provided to
indicate keyboard data that is to be sent up on the SNA SSCP-SLU flow.
The user can configure the 3708 for the following operations:
• Transparent data flow. In this mode, the 3708 supports 256 character sets and
output-only devices, such as printers and plotters. See "Transparency" on
page 5-14.
• Host dial out. The 3708 and an attached modem can also be configured to
allow the host to dial out to devices. See "Host Autodial" on page 5-14.
Chapter 1. Introduction
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