ncements defined in Release-15 5G NR, which could be useful in addressing this issue. Another promising method to reduce the overall delay of most of the procedures is the reduction of the RACH procedure from four steps to two steps. The random access pro- cedure specified in LTE and NR has four messages and is illustrated on the left side of Figure 5.3.7: 1. The UE starts the procedure by transmitting the Random Access Preamble (Msgl). 2. The gNB responds with a Random Access Response (RAR) providing a temporary UE identity, a TA, and an uplink grant (Msg2). 3. The following Layer 3 Message, originated at the UE, depending on the RRC procedure may include for instance an RRC Connection Request message (Msg3). Random Access Preamble & Random Access Preamble UE ID and data transmission Random Access Response Contention Resolution Scheduled Transmission Contention Resolution Figure 5.3.7 Four-step RACH versus two-step RACH procedure. (Source: Reproduced by permission of © 3GPP). 5 NG-RAN Evolution 4. The NR gNB resolves any possible collision by including a UE contention resolution identity (Msg4). A two-step RACH procedure is currently being studied in 3GPP in Release-16. In this two-step RACH procedure, a new combined MsgA consists of both a preamble as well as uplink data, while a new combined MsgB includes the RAR as well as some downlink data (including contention resolution). While this new procedure can help enable low-rate, low-latency uplink services, it also provides significant benefits for the RRC procedures in NTNs (3GPP R2-1818510). The two-step RACH procedure (when standardized) will essentially halve the required latency for most of the RRC procedures, if the first RRC message can already be sent together with the Random Access Preamble. 5.3.4.4 NR Mobility within NTN Connected mode mobility is another critical area due to the additional delay in the avail- ability of UE measurement reports in uplink and the reception of handover commands in downlink. Several enhancements are under consideration in 