SDAP Protocols

Overview of SDAP

SDAP is a protocol layer introduced in 5G networks that resides at the top most layer of the Radio Protocol stack, above the Packet Data Convergence Protocol (PDCP) layer. It is specifically designed for the 5G network to ensure QoS flow in Non-Access Stratum (NAS) signaling. Its main function is to map QoS flows to data radio bearers (DRBs) and to handle QoS at the Packet Data Unit (PDU) session level.

Key Functions of SDAP

1. QoS Flow to DRB Mapping:
2. Marking QoS Identities:

Key Functions of SDAP:

1. QoS Flow to DRB Mapping: SDAP maps QoS flows (which are characterized by specific performance requirements) to appropriate DRBs. This is crucial because each DRB can have distinct capabilities in handling different types of data traffic based on latency, data rate, reliability, etc.
2. Marking QoS Identities: It handles the marking of packets with QoS Flow Identifiers (QFI), which are essential for the network to apply the correct QoS rules to different flows.

SDAP Architecture

• SDAP Layer Structure: The SDAP layer can be configured for multiple DRBs, with each DRB capable of supporting one or more QoS flows. It is designed to be flexible and scalable to support various services demanded by 5G applications.
• SDAP Entities: Each SDAP layer within a UE (User Equipment) has multiple SDAP entities, each corresponding to a PDU session. Each entity is responsible for handling the SDAP operations related to its respective session.

SDAP Procedures

The document outlines several procedures associated with the operation of SDAP:

1. SDAP Entity Handling:
2. Data Transfer:
3. Reflective QoS Mapping:

SDAP Procedures:

1. Entity Handling: This involves the setup and release of SDAP entities that correspond to each PDU session in a UE (User Equipment).
2. Data Transfer:
3. Reflective QoS Mapping: Allows the UE to adapt the QoS flow mappings from downlink to uplink, ensuring consistency in QoS treatment across both directions.

SDAP Entity

• Function: Handles SDAP-specific processing for each PDU session.
• Responsibility: Ensures data packets are correctly associated with QoS flows and treated accordingly during network transmission.

SDAP-SAP (Service Access Point)

• Definition: Interface between the SDAP sublayer and the QoS flows.
• Functionality: Provides an entry point for SDAP entities to receive QoS requirements from the application layer to manage data packets effectively.

QoS Flows

• Description: Streams of data sharing the same QoS characteristics.
• Treatment: Each flow is treated based on specific requirements such as latency, jitter, packet loss, and bandwidth to meet service quality needs.

Mapping QoS Flows to DRBs

• Role of SDAP: Maps QoS flows to appropriate Data Radio Bearers (DRBs).
• DRBs: Transmission channels on the radio interface that handle data between the UE and the network, configured to meet the QoS needs of the data they carry.

SDAP-PDU (Protocol Data Unit)

• Definition: Format of data encapsulated by the SDAP layer for transmission.
• Contents: Includes headers or identifiers like the QoS Flow Identifier (QFI), aiding in packet processing and prioritization.

PDCP Entity

• Location: Resides in the PDCP sublayer.
• Functions: Manages tasks like header compression/decompression, encryption/decryption of user data, and integrity protection of control plane data.

PDCP-SAP (Service Access Point)

• Definition: Interface between the PDCP sublayer and the SDAP sublayer.
• Purpose: Facilitates the delivery of SDAP-PDUs to the PDCP layer for further processing.

PDCP-SDU (Service Data Unit)

• Definition: Data units managed by the PDCP layer.
• Process: Receives SDAP-PDUs from SDAP, processes them (compression, encryption), and forwards them as PDCP-PDUs to the radio interface.

Radio Bearers

• Definition: Channels through which data is transmitted between the UE and the network.
• Connection: Serve as the physical manifestations of DRBs on the radio link, transmitting data across the network.

Mapping QoS Flows to PDCP to Radio Bearers

Input: List of QoS Flows each with specified QoS requirements

Output: Data packets transmitted on appropriate DRBs

Steps:

1. Initialization:
2. SDAP Processing:
3. SDAP to PDCP Handover:
4. PDCP Processing:
5. Radio Bearer Assignment:
6. Transmission:

Use of SDAP in Special Scenarios

• Sidelink Communication: SDAP also finds application in sidelink communications, particularly for services such as V2X (Vehicle to Everything), where direct communication between UEs (such as vehicles) occurs without traversing the network infrastructure.

Test Your Knowledge about SDAP protocols.

• What distinguishes SDAP from PDCP in the 5G protocol stack?

A) SDAP provides end-to-end encryption

B) SDAP focuses exclusively on QoS mapping to DRBs

C) SDAP is responsible for compression

D) SDAP operates at the network layer

• Which QoS identifier is essential for SDAP operations?

A) QCI (QoS Class Identifier)

B) ARP (Allocation and Retention Priority)

C) 5QI (5G QoS Identifier)

D) QFI (QoS Flow Identifier)

SDAP's role in QoS mapping is critical because:

A) It supports RRC signaling.

B) It enables network slicing.

C) It prevents congestion.

D) It facilitates differentiated treatment of flows.

Which statement best describes the Reflective QoS Mapping feature in SDAP?

A) It allows SDAP to adjust QoS based on real-time network conditions.

B) It enables SDAP to use the same QoS mapping for uplink as observed in downlink.

C) It ensures that all DRBs maintain consistent QoS parameters.

D) It reflects the network's QoS policies back to the user equipment.

How does SDAP interface with other network functions for its operations?

A) Directly communicates with the AUSF for authentication.

B) Coordinates with the AMF for session management.

C) Relies on the SMF for policy application.

D) Collaborates with the RRC for bearer management.

What does the term 'SDAP header' imply in the context of data transfer?

A) A header used for routing and forwarding at the network layer.

B) A header encapsulating metadata for security purposes.

C) A header that includes QoS markings like QFI.

D) A header containing timestamp information for latency calculations.

In which scenario is SDAP's QoS flow to DRB mapping most crucial?

A) Low-latency applications such as VR.

B) High-throughput scenarios like video streaming.

C) Basic web browsing sessions.

D) Background data transfers like software updates.

SDAP mapping rules are primarily influenced by which type of network information?

A) The physical location of the user equipment.

B) The type of application being used.

C) The historical data usage patterns.

D) The current network traffic conditions.

Which of the following is NOT a direct function of SDAP?

A) Encrypting data packets.

B) Mapping QoS flows to DRBs.

C) Marking packets with QFI.

D) Ensuring in-order delivery of packets.

What impact does improper configuration of SDAP have on 5G services?

A) It can lead to decreased battery life of UE.

B) It may cause improper QoS handling, affecting service quality.

C) It could disable the entire 5G network.

D) It results in overutilization of network resources.

During which phase is the SDAP configuration primarily established?

A) During initial network design.

B) At the start of each new session.

C) Periodically, as determined by the network operator.

D) Whenever there is a handover event.

SDAP's effectiveness is critical in which type of 5G deployment?

A) Rural areas with sparse user density.

B) Enterprise environments with heavy machine-type communications.

C) Urban areas with high user mobility.

D) Scenarios involving broadcast services.

Reflective QoS mapping in SDAP is utilized to:

A) Mirror the downlink QoS settings in the uplink path.

B) Reflect changes in user behavior in real-time.

C) Ensure symmetric QoS provisioning on both ends of the network.

D) Provide feedback to the network about QoS effectiveness.

The QoS flow identifier (QFI) in SDAP is critical because:

A) It helps in the routing of packets within the core network.

B) It indicates the priority of packets at the radio interface.

C) It dictates the encryption standards for each flow.

D) It manages the session persistence across different network nodes.

Which of the following best describes the function of SDAP in relation to network slicing?

A) It ensures that each slice receives appropriate bandwidth allocation.

B) It manages the creation and deletion of slices.

C) It maps QoS flows to DRBs within specific slices.

D) It encrypts data differently based on the slice.