8] CHAPTER 4 IEEE 802. 16m System Operation and State Diagrams Connected Mode Dormant State Active State Idle Mode FIGURE 4-27 State transitions in 3GPP LTE-Advanced UE [26] transitions from RRC_CONNECTED to RRC_IDLE, the eNBs delete the keys they store, such that state for idle mode UEs only has to be maintained in MME. It is also assumed that eNB no longer stores state information about the corresponding UE and deletes the current keys from its memory. In 3GPP LTE-Advanced, the requirement for UE transition from the Idle Mode, with allocated IP address, to the Connected Mode is less than 50 ms, including the establishment of the user-plane and excluding the S1 transfer delay. The transition requirement from Dormant State (Sleep Mode coun- terpart in IEEE 802.16m) to Active State (corresponding to Active Mode in IEEE 802.16m) in Connected Mode is less than 10 ms. These requirements are stricter than those for 3GPP LTE. In the Dormant State, the UE has an established RRC connection and radio bearers. The UE has already been identified at cell level, but it may be in DRX to save power during inactivity periods. The UE may be either synchronized or unsynchronized (see Figure 4-27). Although 3GPP LTE already fulfills the latency requirements of IMT-Advanced systems, several new techniques are being utilized in 3GPP LTE-Advanced to further reduce the user-plane and control- plane latencies as follows [26]: Combined RRC Connection Request and NAS Service Request allows those two messages to be processed in parallel at the eNB and MME, respectively, reducing overall transition latency from Idle Mode to Connected Mode by approximately 20 ms. Reduced processing delays in different nodes form the major part of the delay (about 75% for the transition from Idle Mode to Connected Mode assuming a combined request); thereby any improvement has a large impact on the overall latency Reduced Random Access Channel (RACH) scheduling period from 10 ms to 5 ms results in decreasing of the average waiting time for the UE to initiate t