In 5G New Radio (NR), Quality of Service (QoS) configuration is an evolution of the principles established in LTE, designed to support a wider range of services, more diverse network conditions, and higher levels of service requirements. The 5G system introduces new QoS frameworks and mechanisms to address these needs, reflecting the network's capabilities to handle everything from ultra-reliable low-latency communications (URLLC) to massive machine type communications (mMTC), in addition to enhanced mobile broadband (eMBB).
Here’s how QoS is configured in 5G/NR signaling:
High-Level Overview
- QoS Flow: The fundamental building block of QoS in 5G is the QoS Flow. A QoS Flow is a bearer type that provides a specific QoS level for data delivery. It is the finest granularity of QoS differentiation in the 5G network, ensuring that data packets are treated according to the QoS requirements of the application or service.
- 5QI (5G QoS Identifier): Each QoS Flow is characterized by a 5QI, which defines the QoS characteristics such as priority level, packet delay budget, and packet error rate. The 5QI is similar in concept to the QCI in LTE but is designed to support a broader range of services and more granular QoS levels.
Detailed Configuration Steps
- Session Establishment: When a UE (User Equipment) initiates a session, the network establishes a PDU (Protocol Data Unit) Session, which can carry multiple QoS Flows. Each PDU Session corresponds to a single IP address allocation for the UE but can support multiple services or applications each requiring different QoS levels.
- QoS Flow Setup: For each service or application, a specific QoS Flow is set up within the PDU Session. This setup involves signaling between the UE and the network to agree on the 5QI and other QoS parameters such as GBR (Guaranteed Bit Rate) and MBR (Maximum Bit Rate), similar to the dedicated bearers in LTE.
- QoS Rules and QoS Profiles: The network configures QoS Rules that determine how packets are classified into QoS Flows based on factors like destination IP address, port number, or application identifier. Each QoS Flow is associated with a QoS Profile that specifies its 5QI and any GBR or MBR requirements.
- Dynamic QoS Adjustments: The network can dynamically adjust QoS settings in response to changing network conditions or application requirements. This includes modifying existing QoS Flows or establishing new ones as needed.
- Integration with Network Slicing: 5G's network slicing capabilities allow for the creation of multiple virtual networks (slices) over the same physical infrastructure. Each slice can have its own set of QoS Flows, enabling differentiated treatment of traffic not just within the slice but also at the granularity of individual applications or services.
Key Signaling Messages Involved
- NAS (Non-Access Stratum) Messages: The UE and the 5G Core (AMF/SMF) exchange NAS messages to establish and modify PDU Sessions and their associated QoS Flows. Examples include
NAS: PDU Session Establishment Request and NAS: PDU Session Modification Request.
- NGAP (Next Generation Application Protocol): Between the gNB (5G base station) and the 5G Core, NGAP messages such as
NGAP: PDU Session Resource Setup Request and NGAP: PDU Session Resource Modify Request are used to set up and manage QoS Flows at the radio access network level.
- RRC (Radio Resource Control) Messages: The gNB and UE use RRC messages to configure radio bearers that map to QoS Flows, such as
RRC: RRC Reconfiguration.
QoS Flow Example
QoS Flow ID |
5QI |
GBR |
MBR |
Application |
1 |
1 (Conversational Voice) |
Yes |
Yes |
Voice Call |
2 |
6 (Video Streaming) |
No |
No |
Video App |
3 |
9 (Default Data) |
No |
No |
Web Browsing |
Summary
- 5G QoS is highly flexible and granular, supporting a wide range of applications and services.
- QoS Flows, 5QI, and network slicing are key concepts enabling differentiated service levels.
- QoS configuration is achieved through coordinated signaling between the UE, gNB, and 5G Core using NAS, NGAP, and RRC protocols.