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Double Socket Transpond of Cellular Modems USR-G781

Double Socket Transpond of Cellular Modems USR-G781


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Double socket transpond of cellular modem USR-G781



1. Connection diagram 3

2. Before your test 4

3. hardware connection 5

4. Utility configurations 6

4.1 Set parameters 7

4.2 Enable double socket 8

4.3 Restart the device 9

4.4 Data transmissions 10


1. Connection diagram 

Your control devices(LOCATIONB)->(LAN)G781->(4G)->PC(LOCATIONB)

 Connection diagram


In this project , we need establish two socket to realize your requirement.

Note: there is a special function in G781 which name is DOUBLE SOCKET TRANSPOND



Your device(TCP Server)->(LAN port)G781(TCP client)                            (location A )



   G781(TCP client)->PC(TCP server )                                  (location B )


At last:     

You device-> G781->PC


2. Before your test 

1. Please log on this link:

And download the Utility:


2.Make sure your location B ‘s PC’S IP address is public network ip address .


3.Your device controller can  built TCP connection with G781


4.The PC in location B has software that can built TCP connection with G781.



3. hardware connection

 hardware connection of cellular modem USR-G781

Note: RS 232 converter USB

 RS232 converter USB


4. Utility configurations

Open this software after download in your PC

picture of setup software - cellular modem USR-G781


G781 factory default serial port parameter: baud rate 115200, check/data/stop: NONE/8/1. Open the serial port as shown in the figure below

 Utility configurations of cellular modem USR-G781


Click to enter the configuration state. If you print +++ a a OK as shown in the figure below, then you enter the configuration state correctly. If the print information as shown in the figure below is not displayed, possible reasons:

1.The serial port number selected is not consistent with the serial port number of the computer connected to the device

2. No serial driver

3. The baud rate is not consistent with the actual baud rate of the device (if you have set the baud rate before and forget what the modified baud rate is, you can restore the factory setting and use the factory default parameters)

4. Hardware problems. Try replacing a serial cable



4.1 Set parameters

Working mode: transparent transmissions mode, server A address and destination port are set to A remote server, such as, 7118. 
The address of server B is the device IP and port. Such as and 2317

 Set parameters of cellular modem USR-G781


4.2 Enable double socket

Serial port sending instructions:



Turn on the double-socket transmissions function (AT instruction should end with carriage return newline)

 Enable double socket of cellular modem USR-G781


4.3 Restart the device

After enabled the double socket function  please save parameter and restart

 Restart the cellular modem USR-G781

NOTICE :AT  command is followed by a carriage return and newline


Set and save all parameters, and restart, wait for the serial port to print the start information usr-g781, indicating that the start is complete, then open the computer port monitoring,G781's link A and link B indicator lights will light up, indicating that the two socket successfully established and connected

 cellular modem USR-G781's link A and link B indicator lights will light up


4.4 Data transmissions

After the setup is complete, you can see the device connection on the server as follows. You can test the two-way data communication to indicate that the test is OK

 Data transmissions of cellular modem USR-G781