Bearer Management

Service networks

Some mobile platforms use the concept of grouped access points (also called SNAP or Service Network Access Point). In principle multiple configurations are grouped together and possibly even prioritized when compared to each other. This is useful for use cases where all configurations serve a similar purpose or context. A common context could be that they provide access to the public Internet or possibly only to the office Intranet. By providing a pool of configurations the system can make a decision based on given priorities which usually map to factors such as speed, availability and cost. Furthermore the system can automatically roam from one access point to the next one while ensuring minimal impact on the user experience.

The QNetworkConfiguration::Type flag specifies to what category a configuration belongs. The QNetworkConfiguration::InternetAccessPoint type is the most common example. It represents a configuration that can be used to create a session. The above mentioned grouping behavior is provided by QNetworkConfiguration::ServiceNetwork configurations. Service networks are place holders until such time when the user attempts to open() a new session. At that point in time the system determines which of the configurations QNetworkConfiguration::children() is best to use. The selection algorithm is provided by the platform and is usually managed by network settings applications. A service network can only have one level of indirection which implies children can only be of type QNetworkConfiguration::InternetAccessPoint.

Most systems allow the user to define the systems default configuration. Usually the default behavior is either a service network, a particular Internet access point or the user instructs the platform to ask the user once an application requests the network. User interaction is generally implemented by some sort of system dialog which shows up at the appropriate point in time. The application does not have to handle the user input. This API provides the QNetworkConfigurationManager::defaultConfiguration() call which serves a similar purpose. The subsequent code snippet provides a quick way how an application can quickly create a new network session without (or only minimal) user interaction:

 // Set Internet Access Point
 QNetworkConfigurationManager manager;
 const bool canStartIAP = (manager.capabilities()
                           & QNetworkConfigurationManager::CanStartAndStopInterfaces);
 // Is there default access point, use it
 QNetworkConfiguration cfg = manager.defaultConfiguration();
 if (!cfg.isValid() || (!canStartIAP && cfg.state() != QNetworkConfiguration::Active)) {
     QMessageBox::information(this, tr("Network"), tr(
                                  "No Access Point found."));
     return;
 }

 session = new QNetworkSession(cfg, this);
 session->open();
 session->waitForOpened(-1);

To accommodate the "Ask user" use case the default configuration can be of type QNetworkConfiguration::UserChoice. A user choice configuration is resolved as part of the QNetworkSession::open() call. Note that a UserChoice configuration is only ever returned via QNetworkConfigurationManager::defaultConfiguration() and not QNetworkConfigurationManager::allConfigurations().

On systems which do not maintain a list of defaultConfiguration() an invalid configuration is returned. A possible workaround could be to implement a custom dialog which is populated based on what QNetworkConfigurationManager::allConfigurations() returns.