This is suggestion to new Simple Terminal Client protocol. The protocol is based on Simple External Application protocol.
C header of the protocol definition is available here -

Link establishment

REWIND_SERVICE_SIMPLE_TERMINAL should be used as a service type.

Specific messages

Switch to IDLE mode

REWIND_TYPE_TERMINAL_IDLE, data should contain ASCII string of device token.
Server will respond with REWIND_TYPE_TERMINAL_IDLE having no content.

Switch to ACTIVE mode

REWIND_TYPE_TERMINAL_WAKE, data should contain ASCII string of device token.
Server will respond with REWIND_TYPE_TERMINAL_WAKE without any content data as well.

Text message data

REWIND_TYPE_MESSAGE_TEXT, data should contain struct RewindTextMessageData, where data has normal text in UTF-16LE format.
Server will respond to this message as REWIND_TYPE_MESSAGE_STATUS when message will processed.

Text message status

REWIND_TYPE_MESSAGE_STATUS, data should contain struct RewindTextMessageStatus, where status has same enumeration as normal DMR response data header.
Server will not respond to this message.

Location report

Server will not respond to this message.

Cloud Messaging extension (push notifications)

One of the targets of the Simple Terminal Client is mobile devices such as mobile phones. This kind of devices have very strong requirements for power saving (Power Management for Mobile Devices). To make access for these devices more comfortable we added support of a native activation mechanism to Simple Terminal Client. Now we can activate devices via Google's Firebase Cloud Messaging which is a native mechanism for Android devices.

Managing connection state

Please read sections switch to IDLE mode and switch to ACTIVE mode of this document.

Downstream message

In the connection's idle state the server will send any data such as the headers of any voice calls, data calls, and CSBK (but not voice frames) via Cloud Messaging. Client applications should then go back and switch the connection to an active state to get a stream over UDP.

  "data" :
     "type" : "Simpel Terminal Client",
     "data" : "010203040506070809..."
   "to" : "bk3RNwTe3H0:CI2k_HHwgIpoDKCIZvvDMExUdFQ3P1..."

data/data field contains normal DMRD message of Homebrew Protocol in hexadecimal representation.

Application IDs and keys

We strongly recommended to use your own application token ID. In that case please provide us your application token ID and authorisation key. Both will be hardcoded in the source code. Default application token ID is 393838907279