An Introduction to 5G

15Session Management, Policy and Charging

In this chapter, we will investigate how the 5G user plane delivers data packets between the mobile and an external data network. We will begin by elaborating on the concepts of protocol data unit (PDU) sessions and quality of service (QoS) flows, and by discussing how those concepts are actually implemented by means of data radio bearers and tunnels. We will then introduce some additional network functions into the 5G core, which mediate its interactions with external application servers, and which determine the quality of service that the user will receive and the amount that the user will be charged. The chapter closes with some examples of the relevant signalling procedures, including the establishment of a PDU session, and traffic steering under the influence of an application server.

The main sources of information for this chapter are the stage 2 specifications for the architecture of the 5G core network and the resulting signalling procedures [1,2]. Those are supplemented by the corresponding specifications for policy and charging control (PCC), namely TS 23.503 [3] and TS 29.513 [4].

15.1 Types of PDU Session

15.1.1 IP PDU Sessions

A PDU session is a bidirectional connection between the mobile and an external data network, in which the packets travel through one or more user plane functions (UPFs) that are themselves controlled by a session management function (SMF). Every PDU session has a PDU session type, which depends ...