5G Quality of Service Terminology


Welcome to this episode of Apis TechTips, a series of short explainer excerpts from real Apis training courses.

This episode teaches you the relevant words when talking about quality of service in 5G, and it comes from the course “5G NG-RAN in an Hour”.


If you enjoyed this Apis Tech Tip, check out the full Apis course ”5G NG-RAN in an Hour” where this video came from. This course provides a quick overview of the fifth generation mobile technology, and its radio access network, NG-RAN in particular.

Here are some of the topics that are covered in “5G NG-RAN in an Hour”:


      • What Is 5G and Why

      • The 3GPP 5G System

      • Evolution from 4G to 5G

      • NG-RAN

      • The gNodeB

      • What Makes New Radio New

    To learn more about this course, go to https://apistraining.com/portfolio/5g-ng-ran-in-an-hour/

    This TechTip is also part of a whole eBook of tips, all focusing on 5G technology. We call it an eBook+ since all chapters are both text and video. If you want to read the text, you can do that, and if you want to watch a teacher tell the story, you can choose that.

    All the video chapters are excerpts taken directly from our recorded lessons, so if one of them piques your interest, you can easily go to the course and dive deeper into that particular subject.

    This particular eBook+ is called “5G Demystified: Use Cases, Architecture, and More”, and you only need to CLICK HERE to request it for immediate download.

    Below you can find the transcribed text for this particular TechTip.

    5G QoS Terminology

    A User Equipment (UE) that is connected to some data network, like the Internet or IMS or some intranet, has a so-called PDU session to that data network. The PDU session starts in the user equipment and goes via the radio network into the core network, where we have a so-called User Plane Function (UPF). This PDU session will carry uplink protocol data units and downlink protocol data units. That’s the purpose of the PDU session, and in order to do so, we have an N3 tunnel from the radio access network to the core network.

    This is because the interface between RAN and UPF happens to be called the N3 interface. In the radio network, we have so-called data radio bearers that will carry the user plane protocol data units from the user equipment to the radio access network like the gNodeB and vice versa. In the example in the illustration, there are two data radio bearers because I decided so. In reality, there can be one data radio bearer for a session. There can also be two, there can be three, there can be four, and there can be, in principle, any number of data radio bearers in a session.

    And in 5G, we have the QoS (Quality of Service) flows. All traffic in a PDU session will belong to a QoS flow. In the example in the image, we have three. But then again, this is just a made-up example. So, in a real situation, there can be any number of QoS flows in a session, and the idea is that each QoS flow has some QoS profile, for instance, a certain bitrate, a certain latency, or a certain packet loss tolerance and this is how we can differentiate traffic to and from one user equipment.

    If this PDU session goes to the public internet, maybe one QoS flow is for web browsing, another QoS flow is for video streaming, and the third QoS flow is for online gaming because these are services that have different QoS requirements.

    So again, when we talk about QoS parameters, we talk about things like bit rates. Sometimes, there is a guaranteed flow bitrate, and sometimes, there is no guaranteed flow bitrate. There can be a maximum flow bitrate. There can be some type of priority, how important a certain QoS flow is compared to other QoS flows, in case there’s a shortage of resources, for instance.

    We need to prioritize, and each QoS flow is also associated with a so-called 5QI value, a 5G QoS Identifier. This value is a pointer or a reference to things like priority delay and error tolerance, and obviously, all nodes, including the user equipment, which are involved in this session, will need to implement these QoS parameters on their respective interfaces.

    So, in order to make sure that the DRBs, the data radio bearers, have the right QoS profile for the QoS flows, well, that’s the responsibility of the radio access network like the gNodeB, for instance.


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