During Traffic analysis, I found that SDCCH congestions were extremely high but voice traffic were low. When I checked radio command, the sites were down. This had happened in urban areas where we had a lot of cells. Even one cell was down, the neighbor cells used to serve that area without latching in external network.
I do not understand why MS performs LU. But my MSC’s colleague told me that once site was down , MS performed LU when the BTS was UP again.
We are using Siemens network.