I am trying to understand when a user busy is returned.
I have come across the following (GSM 02.01):
NETWORK DEFINED USER BUSY NDUB: which is the VMSC saying that the either the traffic channels are conjested or that there is another call termination or origination attempt going for that sub i.e. not an active call going on
USER DEFINED USER BUSY UDUB: Which is the MS saying that the MS or the subscriber is busy.
Now what does UDUB mean?? does it mean that the MS is engagged in an exisiting call??
If not then what is the MS doing ??
Also, if the MS is engaged in an active call, can this not be indicated by the VMSC, rather than offering the call to the MS.
It means that the user trminal (MS) is engaged, sometimes for Data or Voice, either one the user can’t receive any request, however if there is a call waiting service activated for that MS, in the VLR it is noted, & still can page the MS.