Some analyzing when MS termination call is not successful

Some analyzing when MS termination call is not successful
Typical case:
Originated MS signal is normal;
Originated MS finally can here voice record: “the number you dialed is not reachable”.

Analyzing:
Commonly the reason may be the following:
The terminated MS is not in service area or the signal coverage is poor;
The terminated MS just crosses LAC and does not start location update registration;
The terminated MS is just in idle handoff state.
In order to confirm which reason causes the problem, need analyze the condition and locate the problem.
Acquire if the terminated MS is in coverage area and judge if the reason is MS has moved over coverage area or signal is too bad;
Acquire if the terminated MS is in the border of two LACs, judge if the reason is MS does not make registration in time (Signal tracing can be used to analyze), usually one city should be assigned only one LAC area, except for very big city;
If the above two cases can be excluded, it is very possible that MS is just in idle handoff and can not be terminated successfully.
In IS-95A 6.6.2.1.4.2 protocol:
In idle handoff, MS will go into non-slot mode. After idle handoff, MS will throw away all the messages from the old BTS, which has not been processed. This means: when BTS sends paging message to MS, MS is just in idle handoff and MS can not receive the message correctly; furthermore, even if MS has received the message, it can still not send paging response. These two cases will lead that MS can not be terminated successfully.

This is why we often meets the case: the first dialing to other MS, we will hear voice record: “the number you are dialing is not reachable” (because MS is just in idle handoff); but the second dialing will be successful (because MS has finished idle
handoff).

Note:
System not support access handoff also can cause terminated call failure. When MS is paged successfully and MS is just moving from the current cell to another cell, MS will access failure because the system does not support access handoff and the current cell pilot fades too fast.
In this case, MSC side often sends voice record to origination MS like: “The network is busy now, please redial later”. Certainly different operators may send different voice records.

Optimization method:
If the reason is coverage, it is normal;
If the reason is crossing LAC, check LAC planning. Usually the border of LAC should be set in the low traffic area;
If the reason is idle handoff, it is normal phenomenon. If the problem is very heavy,
consider adjusting the network topology structure and changing idle handoff area.