Future<Reply> linger({int timeoutSeconds: 10})

Tells FreeSWITCH not to close the socket connect when a channel hangs up. Instead, it keeps the socket connection open until the last event related to the channel has been received by the socket client.

Source

Future<Reply> linger({int timeoutSeconds: 10}) =>
    _subscribeAndSendCommand('linger', new Duration(seconds: timeoutSeconds));