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What is Reflective QOS in 5g and how is it handled?

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What is Reflective QOS in 5g ? how is it handled. I am looking for detailed info on how the UE derives uplink QOS flow info from downlink?
Also another related doubt is : What happens if the UE needs to send the DL packet before any uplink packets arrived (to derive the mapping in UL as per Reflective QOS) ?

posted Aug 19 by Pdk

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1 Answer

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Best answer

I am new to 5G but would like to share my understanding on reflective QoS. In LTE, quality of service is implemented at the bearer level while in 5G, it is implemented at IP flow level. In 5G, an IP flow can be served with different QoS on dynamic basis. Just to avoid signalling between 5G devices and Network for the QoS change, reflective QoS comes into picture. Where Service Data Adaptation Layer (SDAP) plays a major role.
SDAP sits on top of PDCP layer to map different QoS Flows to data radio bearers. Whenever there is a change in QoS Flow at network side, it informs to gNB using the SDAP header and gNB forwards the information to 5G device at it is, based on received DL packet, 5G device derives the QoS rule with new QFI.
As per my understanding, QoS flows first changes at core network and then at UE side, that's why DL packet with the updated QFI will be received. There is no chance of QFI update first for UL packet.

answer Sep 15 by Harshita
Thankyou Harshita for the nice explanation. Helped me a lot.
But on the other hand, I have a doubt regarding the IP flow map to QOS Flow (which more of core functionality i.e UPF). Can two IP flows (SDFs)map to same QOS  flow ?
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+1 vote

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 ?

+1 vote

How the PDU session to QOS flow to DRB mapping handled and which IEs in the relevant protocol stacks facilitate the multiplexing and demultiplexing these sessions/flows?

Thanks for your help

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