1. Mobile services
   1. Bearer services
      1. Transparent bearer services
         1. physical layer(layer 1)
         2. constant delay
         3. forward error correction(FEC)
      2. Non-transparent bearer services
         1. layer 2 and 3
   2. Tele services
      1. telephony
      2. emergency
         1. highest priority
      3. short message service(SMS)
   3. Supplementary services
      1. identification
      2. call redirection
      3. forwarding of ongoing calls
      4. closed user groups
2. System architecture
   1. radio subsystem(RSS)
      1. Base station subsystem(BSS)
      2. Base transceiver station (BTS)
      3. Base station controller(BSC)
      4. Mobile station(MS)
   2. network and switching subsystem(NSS)
      1. Mobile services switching center (MSC)
      2. Home location register (HLR)
      3. Visitor location register (VLR)
   3. operation subsystem(OSS)
      1. Operation and maintenance center (OMC)
      2. Authentication centre (AuC)
      3. Equipment identity register (EIR)