In 5G, the QoS (quality of service) flow has the finest granularity for differentiating and prioritizing data traffic (in terms of scheduling, queue management, rate shaping and so on). In other words, the 5G system treats all data traffic within the same QoS Flow in the same way, while applications with different QoS requirements require separate QoS flows. Figure 1 shows a high-level overview.
A device such as a UE can establish one or more PDU (packet data unit) sessions. A PDU session can consist of one or more QoS flows, and a QoS flow can comprise one or more traffic flows (such as IP packets or Ethernet frames).
Each QoS flow has a QoS profile consisting of a set of QoS parameters such as 5QI (5G QoS identifier), UL (uplink) / DL (downlink), GFBR (guaranteed flow bit rate), and UL/DL MFBR (maximum flow bit rate). The 5QI in turn comprises the packet delay budget (PDB), packet error rate (PER), and resource type.
An Industrial Internet of Things (IIoT) application can define the QoS that it needs for its connections by specifying 5QI and other QoS parameters such as GFBR, MFBR, etc.
A PDU session is a (logical) connection within the 5G system that carries IP packets or Ethernet frames between a user equipment (UE) and the 5G network (more specifically, the user plane function (UPF) in the 5G network).
Once a connection (a PDU session) has been successfully established, the 5G system is responsible for providing the required QoS. Whether or not it can do so depends on the UE subscription options, implemented and deployed 5G system capabilities, and network conditions (radio and system load).
How PDU sessions and QoS flows are set up in 5G is invisible to the IIoT application. It doesn’t matter whether the IIoT application connects to 5G via a UE (where the application client runs) or an application function (where the application server runs).
When multiple IIoT applications connect via the same UE and all of them need to send or receive data packets over the same data network, there is no need to initiate any additional PDU sessions. A single PDU session between the UE and the data network is enough to support the traffic of all of the IIoT applications. This lets multiple applications share the same PDU session if their traffic passes through the same data network. However, the 5G system also makes it possible to separate the connections of different IIoT applications into distinct PDU sessions when required, for example if some of them use IP connectivity while others use Ethernet. For an overview of the ways in which an IIoT application’s QoS can be established, see “Ways to Establish an Application’s QoS”.
The information in this topic is based on the white paper “5G QoS for Industrial Automation”. A more in-depth description of 5G QoS is available there.
