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# ZTE MF 823 (Megafon M100-3) 4G Modem

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## Installation

As described below, usb_modeswitch will likely comes out handy. Install it.

## Device identification

When the device is switched to an `1405` product code you will get:

    $ lsusb

    Bus 002 Device 018: ID 19d2:1405 ZTE WCDMA Technologies MSM

Here are the USB product codes for this device:

1225
  Default mode in which the device looks like a USB Mass Storage Device with CD-ROM interface, and a card reader. Corresponds to AT+ZCDRUN=9+AT+ZCDRUN=F

1403
  A Communication mode in which the device has an wikipedia:RNDIS like interface in addition to the card reader interface. The non recommended kernel module rndis_host might handle such an interface. Corresponds to AT+ZCDRUN=8+AT+ZCDRUN=F.

1405
  A communication mode in which the device has a wikipedia:USB communications device class interface in addition to the card reader interface. Communications Device Class (CDC) should work in Linux. The cdc_ether kernel module is required. This mode will be the one `usb_modeswitch` will switch the device into.

0016
  Download Mode. Under the name of ZTE., but simply a mode where available diagnostic port and two command (analog modem port and PC UI devices Huawei). Corresponds to AT+ZCDRUN=E

0076
  "real" Download Mode. Includes a standard for devices running QC methods.

If your modem does not appear as `19d2:1405` (or `1403`), check the USB 3G Modem#Mode switching article.

## Ethernet connection established

When the device has an Ethernet interface the usual Network configuration programs should handle it. When they are, you will see that the LED (Blue - 2G/3G or Green - 4G) on modem is not blinking. To establish a connection, the following link (CGI command) should be entered in a browser:

http://192.168.0.1/goform/goform_set_cmd_process?goformId=CONNECT_NETWORK

To avoid entering this link every time, switch the device to auto-connection mode:

http://192.168.0.1/goform/goform_set_cmd_process?goformId=SET_CONNECTION_MODE&ConnectionMode=auto_dial

If you are setting up internet using a command-line shell you should make request with referrer, as in:

    curl --header "Referer: http://192.168.0.1/index.html" http://192.168.0.1/goform/goform_set_cmd_process?goformId=CONNECT_NETWORK

otherwise you will get response {"result":"faulure"}

## Commands

CGI command for 2G/3G/4G mode selection:

    http://192.168.0.1/goform/goform_set_cmd_process?goformId=SET_BEARER_PREFERENCE&BearerPreference=

following options available after "=" sign (case-sensetive)

    NETWORK_auto
    WCDMA_preferred
    GSM_preferred
    Only_GSM
    Only_WCDMA
    Only_LTE
    WCDMA_AND_GSM
    WCDMA_AND_LTE
    GSM_AND_LTE

This should be followed by the NETWORK CONNECT CGI command given before.

To switch the modem to FACTORY mode (WARNING! Unable to recieve further CGI commands, connection will be lost!), issue this link:

    http://192.168.0.1/goform/goform_process?goformId=MODE_SWITCH&switchCmd=FACTORY

You may then need to run the following command (as root) in order to access the AT command serial port:

    # echo 0x19d2 0x16 > /sys/module/usbserial/drivers/usb-serial:generic/new_id

The port should appear as `/dev/ttyUSBn`, e.g. `/dev/ttyUSB1`. When you discover the command port, you can use your favourite serial terminal emulation program to control the device. The commands below may be especially useful (here shown with modem-cmd):

    # modem-cmd /dev/ttyUSB1 AT+ZCDRUN=8     # switch to 1403 mode (RNDIS)
    # modem-cmd /dev/ttyUSB1 AT+ZCDRUN=9     # switch to 1225 mode (default)
    # modem-cmd /dev/ttyUSB1 AT+ZCDRUN=F     # exit DOWNLOAD mode and switch to selected mode (RNDIS or default)

## Telnet connection

The modem is available for telnet connection:

    telnet 192.168.0.1
    login: root
    password: zte9x15

As you can see, the modem has an embeded Linux system inside. You can even install some ARM-base packages (mc, nano...) or change something in Web-menu. Explore it carefully!

## Possible usage with product code 1403

For some reason this device can get stuck in mode 0016 and fails to switch to any other mode. I was unsuccessful in trying to switch modes using `usb_modeswitch` or sending AT commands to /dev/ttyUSB0 on various Linux systems. I successfully managed to change modes from 0016 to 1403 using Mac OSX. I was then able to use the dongle on Linux.

In mode 0016 on OSX you will see the follow interfaces:

    /dev/tty.ZTEUSBATPort_
    /dev/tty.ZTEUSBModem_
    /dev/tty.ZTEUSBDIAGPort_

You can switch modes to 1403 by sending AT commands to the USBModem_ port by doing:

    screen /dev/tty.ZTEUSBModem_ 9600

    >>ATI
    Manufacturer: ZTE CORPORATION
    Model: MF823
    Revision: MF823_T03
    IMEI: 866948013728723
    +GCAP: +CGSM

    >>AT+CREG?
    +CREG: 0,1
    OK

    >>AT+COPS?
    +COPS: 0,0,"Telstra Mobile",7
    OK

    >>AT+ZCDRUN=8+AT+ZCDRUN=F
    exit download mode result(0:FAIL 1:SUCCESS):1
    OK

Now the device should act as a ethernet interface no matter which system you plug it into.

## See also

whirlpool.net.au - Linux & Serial Diags

gsmforum.ru - ZTE MF823 thread (partially paywalled, in Russian)

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