LTE: How does pre-emption process work for the bearers within lte ?

Question

In specification, I found two categories of QoS rules i.e., Signaled and Derived QoS rules. At a high level what I know that signaled QoS rules are the rules which are generated at core network and sent to UE as part of PDU SESSION ESTABLISHMENT. But I want to know what is derived QoS and where it is generated and used ?

Answer 1

In lte network, each E-RAB has QoS parameters i.e. priority level, pre-emption capability, pre-emption vulnerability. LTE core network provides all these parameters to E-UTRAN while establishing/modifying a bearer. Whenever there is a crunch of radio resource, E-UTRAN may decide to pre-empt existing bearer(s) based on their QoS parameter. E-UTRAN pre-empts sessions/bearers in the ascending order of priorities.