Hardware manual

80-001113 SysLINK Administrator’s Guide Page 73
Chapter 4: Modem Emulation
The gateway can be configured to allow legacy devices that interact with a Hayes
compatible modem to function over a TCP/IP network. When modem emulation is enabled
on a serial port, the gateway will respond to AT commands generated by the attached
device. After receiving the dial command, the gateway will make a TCP connection to the
specified host. The gateway will also accept incoming TCP/IP connections and generate the
appropriate response codes. As with incoming TCP connections, each Systech serial port
accepts incoming TCP connections on two TCP ports: an 8000-series port (for raw or SSL
data), and a 9000-series port (for telnet data).
Modes
A port with modem emulation enabled can be in one of two modes: command or data. The
port starts out in command mode. In command mode, the port is only interacting with the
host/device connected to the serial port. It accepts AT style command interaction and
responds appropriately. Successfully making an outgoing connection, ("dialing" with the
ATD command) or accepting an incoming connection ("answering" with the ATA command)
switches the port to data mode. In data mode, characters received on the serial port are
transmitted to the TCP connection and vice versa.
Escape Sequence
When in data mode, the gateway looks for an incoming escape sequence on the serial port.
The escape sequence consists of a pause, three break characters ('+'), and a final pause. Upon
receiving this sequence, the port switches to command mode. The default pause is one
second but can be changed in the S12 register. The escape character ("+")is not
programmable.
Types of TCP/IP connections
TCP/IP connections may be in raw TCP mode (with or without SSL security), telnet or telnet
binary mode. These are the same settings available for the Incoming/Outgoing network
connection services on the gateway. In raw mode, TCP data is passed to/from the TCP/IP
connection without any modification. In telnet and telnet binary mode, data coming in the
TCP/IP connection is scanned for telnet sequences that are handled appropriately. In telnet
binary mode, outgoing TCP/IP connections attempt to negotiate telnet binary mode. Telnet
and telnet binary connections may negotiate RFC 2217 mode.