s not support HARQ feedback; uses radio link control (RLC) unacknowledged mode (UM) and the receiving UE must maintain at least one RLC UM entity per transmitting UE; a receiving RLC UM entity used for sidelink communication does not need to be configured before reception of the first RLC UM protocol data unit (PDU); and robust header compression (RoHC) unidirectional mode is used for header compression in PDCP for sidelink communi- cation. A UE may establish multiple logical channels. In that case, the logical channel ID (LCID) included in the MAC subheader uniquely identifies a logical channel with one source layer-2 ID and destination layer-2 ID combination [7]. The parameters for logical channel prioritization are not configured. The access stratum is provided by ProSe per- packet priority (PPPP)6 of the PDU transmitted over PC5 interface by higher layers. Note that there is one PPPP associated with each logical channel [6]. The user-plane protocol stack and functions are further used for V2X sidelink communication. In addition, for V2X sidelink communication, the sidelink traffic channel (STCH) is used. Non-V2X data (e.g., public safety) is not multiplexed with V2X data transmitted over the resources configured for V2X sidelink communication. The access stratum is provided by the PPPP of a PDU transmitted over PC5 interface by upper layers. The packet delay budget (PDB), which refers to the permissible latency of data packets transported between UE and P-GW, of the PDU can be determined from the PPPP. The low PDB is mapped to the high priority PPPP value. The existing logical channel prioritization based on PPPP is used for V2X sidelink communication [6]. The control-plane protocol stack for the sidelink broadcast channel (SL-BCH) is also used for V2X sidelink communication (see Fig. 7.12). A UE that supports V2X sidelink commu- nication can operate in two modes for resource allocation: (1) scheduled resource allocation, In 3GPP Rel-13, ProSe per-packet priority (PPPP) was introduced to enable QoS differenti