Labels:black | darkness OCR: BSC HLR VLR PSTN SIM MSC ISDN, PSPDN - BTS CSPDN ME BSC BTS EIR AuC Um Abis Mobile Station Base Station Subsystem Network Subsystem SIM Subscriber Identity Module BSC Base Station Controller MSC Mobile services Switching Center ME Mobile Equipment HLR Home Location Register EIR Equipment Identity Register BTS Base Transceiver Station VLR Visitor Location Register AuC Authentication Center