 basic CID (for 2nd access station selection) Wait for RNG-RSP with MAC address Obtained RNG-RSP with MAC address / T18 expired and have more retries/ Process RNG-RSP (Send SBC-REQ) Send SBC-REQ Obtained RS_AccessRS-REQ/ Process RS_AccessRS-REQ (T18 expired and retries exhausted) or Wait for (received RNG-RSP (abort) from BS) SBC-RSP Authenticated Obtained SBC-RSP/ Process SBC-RSP Not Authenticated Obtained SBC-RSP/ Authentication (T17 expires and retries exhausted) or Process SBC-RSP and Key Received RNG-RSP (abort) from BS Exchange Authenticated by PKM/ Send REG-REQ, T6 expired and more retries/ Start T6 Send REG-REQ Wait for (T6 expires and retries exhausted) REG-RSP or RNG-RSP (abort) or RES-CMD from BS Obtained REG-RSP T67 expired and more retries/ Process REG-RSP Send RS_NBR_MEAS-REP Wait for RS AccessRS REQ or RS Config- Obtained RS_Config-CMD/ Obtained RS Config-CMD/ Process RS_Config-CMD Process RS Config-CMD re-transmission (Send MR_Generic-ACK) Wait for Action Frame Number Action Frame Number Relay Operational FIGURE 4-21 Network entry state machine of the relay station [10] CHAPTER 4 IEEE 802. 16m System Operation and State Diagrams Failed Operation Path Normal Operation Path Power ON/OFF Initialization State Operational State Power Down FIGURE 4-22 State transition diagram of a femto base station scenario. A femto BS may obtain time and frequency synchronization by using schemes such as GPS, IEEE1588, xii etc. Femto base stations are plug-and-play devices that, once connected to the operator's core network, are automatically configured and are self-optimized and self-organized while in operation. Since femto BS has limited coverage, it is typically used as an overlay with the macro BS (Although it may operate in remote and non-overlay cases, as well). The femto BS and macro BS may operate on the same or different frequency assignment (FA) or frequency band. Femto BS may belong to an open (accessible to all subscribers) or closed (accessible to authorized subscribers) group. Since the femto base stati