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ESP-4 MI Serial Hub Installer/User Guide
Modem emulation
ESP serial hubs may be used to replace costly POTS-line calls with cost-effective raw TCP
sessions. To accomplish this, the ESP hub provides a connection method called modem emulation.
Two ESP hubs work in conjunction to emulate the connection. One ESP hub will establish the
connection in response to AT commands. The other ESP hub will emulate a modem that has
received an incoming call.
The modem emulation connection method enables an ESP hub serial port to emulate modem dial
and answer functionality. The hub presents a Hayes-compatible modem interface to the attached
serial device by accepting AT modem commands and performing the required functions.
This connection method is valid only on RS-232 ports.
Table 3.5 describes this method’s configurable items for each serial port.
Table 3.5: Modem Emulation Connection Method Configurable Items
Item
Description
Enable/
Disable
Enables or disables the modem emulation connection method on the port. The default value
is disabled. This method cannot be enabled if any other connection method is already
enabled on the port.
Allow
Incoming
Calls
Enables or disables incoming calls (that is, raw TCP sessions originating remotely). When
enabled, the ESP hub will listen for inbound raw TCP connection requests. See
on page 22 for more information.
The default value is enabled.
Auto Answer
(Used only when Allow Incoming Calls is enabled.) Enables or disables auto answer. When
enabled, a connection will be accepted without interaction with the serial port. When disabled,
the ESP hub will send the appropriate string (RING or 2, depending on the ATV command or
configured Verbose Response value). Upon receipt of an ATA modem command, the call will
be accepted.
The default value is enabled.
Local IP Port
(Used only when Allow Incoming Calls is enabled.) Specifies the port where the ESP hub will
listen for incoming connection requests. Valid values are 1024-65535.
The default value is 5001 for port 1, 5002 for port 2, 5003 for port 3 and 5004 for port 4.
Allow
Outgoing
Calls
Enables or disables outgoing calls (that is, establishing a raw TCP connection in response to
AT commands received on the serial port). When this option is enabled, you may also set the
Default IP Address and Default IP Port options, which will be used if an ATDT modem
command is issued without parameters. When this option is disabled, valid ATDT strings will
be ignored. See
on page 20 for more information.
The default value is enabled.
Destination IP
Address
(Used only when Allow Outgoing Calls is enabled.) Specifies the IP address to be used when
an ATDT modem command is entered without an IP address. The address cannot be 0.0.x.x,
127.x.x.x, 248-255.x.x.x or the IP address of the ESP-4 MI hub.