This object indicates the type of GPRS service that will be
enabled on the device:
undefined - the GPRS service functionality is turned off.
ggsn - the device will function as a GGSN.
sgsn - the device will function as SGSN.
gtpdirector - the device will function as GDM.
When the device is configured to function as GDM, all the other
objects in this MIB will not be accessible and the
CISCO-GTP-DIRECTOR-MIB should be used for managing the device.