?????? "5G SDAP Layer: Data Flow, QoS Mapping, and Protocol Headers" ???????

?? SDAP LAYER

Main Function: The SDAP layer is crucial when a Base Station is connected to the 5G core network. It's part of the user plane and sits at the top of the Radio Access Network protocol stack.

Data Flow: It receives downlink data from the User Plane Function (UPF) across the N-GU interface.

?? Downlink Data:

Connection to QoS Flows: Downlink user plane data is linked to specific Quality of Service (QoS) flows, which is identified using an identifier called 'PDU session container' within the GTP-U header.

?? SDAP's Role in QoS:

Mapping QoS Flows to DRBs: The primary task is to map QoS flows onto Data Radio Bearers (DRBs).

?? Reflective QoS:

Information Addition: The SDAP layer adds header information to downlink data packets when Reflective QoS is enabled, affecting either the Access Stratum or Non-Access Stratum layers.

Downlink Data Packets: Packets can be sent with or without an SDAP header, depending on the usage of reflective QoS.

?? Header Information:

Size: The header has a size of 1 byte.

RQI: Reflective QoS to DRB Mapping Indication (RQI) tells the device (UE) to apply reflective QoS at the Access Stratum.

QFI: QoS Flow Identity (QFI) is needed to map the data packet to the appropriate QoS flow.

?? SDAP-Config Structure:

Parameters:sdap-HeaderDL: Can be present or absent.

sdap-HeaderUL: Same, can be present or absent.

defaultDRB: Identifies the 'Default DRB' if no specific DRB is mapped.

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