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Modems have a maximum of bearers allowed to be connected at a time, number which is given by the number of available ports that may be used for data connections. When Simple.Connect() tries to launch a connection, it will try to find first an existing bearer with the required parameters (e.g. APN, IP type). If such bearer is found, it will just use it. If no such bearer is found, it will try to create one. When trying to create one, if there is no more room for bearers in the modem, we will remove the first disconnected bearer that we find, if any, before trying to create the new one. This logic now makes sure that no connected bearer gets removed in order to create a new one, and also that only one existing gets removed if possible (not every bearer as we did previously). Further logic to connect multiple bearers at a time cannot be done using the Simple interface.
ModemManager. The problem ModemManager tries to solve is to provide a unified high level API for communicating with (mobile broadband) modems. While the basic commands are standardized, the more advanced operations (like signal quality monitoring while connected) varies a lot. Using. ModemManager is a system daemon and is not meant to be used directly from the command line. However, since it provides DBus API, it is possible to use 'dbus-send' command to control it from the terminal. There's an example program (tests/mm-test.py) that demonstrates the basic API usage. Implementation. ModemManager is a DBus system bus activated service (meaning it's started automatically when a request arrives). It is written in C. The devices are queried from udev and automatically updated based on hardware events. There's a GInterface (MMModem) that defines the modem interface and any device specific implementation must implement it. There are two generic MMModem implementations to support the basic operations (one for GSM, one for CDMA,) which are common for all cards. Plugins. Plugins are loaded on startup, and must implement the MMPlugin interface. It consists of a couple of methods which tell the daemon whether the plugin supports a port and to create custom MMModem implementations. It most likely makes sense to derive custom modem implementations from one of the generic classes and just add (or override) operations which are not standard. There's a fully working plugin in the plugins/ directory for Huawei cards that can be used as an example for writing new plugins. Writing new plugins is highly encouraged! API. The API is open for changes, so if you're writing a plugin and need to add or change some public method, feel free to suggest it!