When number of subscriber stations are increased the code gives a segmentation fault. 
In the function BsServiceFlowManager::ProcessDsaReq  , there is a statement :

      serviceFlow = GetServiceFlow (ssRecord->GetDsaRsp ().GetSfid ());

This returns NULL value. 
Which later gives a segfault when we try to access the element of serviceFlow in BsServiceFlowManager::ScheduleDsaRsp