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TX (out) |
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RX (in) |
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GND |
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DSR and DTR on the serial device side are connected to the DSR signal of the Digi device.
Scenarios for Modem Emulation
Outgoing Modem Emulation Connection
Serial device sends ATDx.x.x.x:y command, which triggers the device server to establish a telnet connection to destination IP=x.x.x.x, port=y.
Incoming Modem Emulation Connection
A device on the network telnets to port 50001 (50000+1 = 1st serial port). This incoming connection triggers the device server to generate a RING on the serial port. The device attached to the serial port will answer the RING and the connection is established.
Modem Emulation Pooling
This is a combination of Incoming Modem Emulation Connection and a hunt group. A device on the network telnets to port 50000. The device server checks if a serial port configured for modem emulation is available. If so, it connects to the port, otherwise returns an error.
Modem Emulation Bridge
A combination of Outgoing and Incoming Modem Emulation Connections, in which both serial devices require to talk to a modem. The first serial device telnets to the second device using ATDx.x.x.x:y, the second device gets a RING and accepts the incoming telnet connection.
Originating, Answering, and Disconnecting Calls
In the following table, an application requests a TCP session with the Digi device. The table displays the responses of the Digi device and application as they negotiate a TCP connection.
Application AT Com- | Digi Device Server Response | Notes | |
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AT&F | OK. | AT command request to restore defaults to factory set- | |
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| Receives request to start a | Request to start TCP session with IP address and TCP | |
ATDT ipaddress:TCPport# | TCP session. CONNECT | port number of the Digi device | |
| 115200. | starts a TCP session | |
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<P>+++<P> | OK | “+++” being the escape sequence in ASCII characters - | |
Digi device server switches from AT command to data | |||
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Chapter 7 Special Features: Modem Emulation | 45 |