A useful test that we can perform from the VTY is to send a text message to a subscriber:
OpenBSC# subscriber id 1 sms send Hello, H Open Readers!
With a second handset provisioned – this subscriber has been given the extension 1004 and a friendly name of Ben – we can make calls.
GSM uses time-division multiplexing (TDM) to divide a radio channel into 8 timeslots and the OpenBSC default is for 6 of these to be configured to carry voice calls. These are timeslots 2-7 and, while the call is in progress, we can use the monitor firmware to confirm that timeslot 2 is in use by one handset and timeslot 3 by the other.
With the call in progress we can also use the VTY to view resource usage at the level of the network and the BTS.