- RATFallBack for Voice in 5G SA - September 3, 2020
- 5GS-WiFi(ePDG) Calling/Offloading Aspects - July 11, 2020
- Emergency Services(E911) FallBack procedures in 5G - May 16, 2020
The concept of QoS in 5G is flow based. Packets are classified and marked using QFI (QoS Flow Identifier). The 5G QoS flows are mapped in the AN (Access Network) to DRBs (Data Radio Bearers) unlike 4G LTE where mapping is one to one between EPC and radio bearers. It supports following QoS flow types.
- GBR QoS flow, requires guaranteed flow bit rate.
- Non-GBR QoS flow, does not require guaranteed flow bit rate.
- Delay Critical QoS flow, For Mission Critical guaranteed flow bit rate.
The 5G QoS flows are mapped in the AN (Access Network) to DRBs (Data Radio Bearers) unlike 4G LTE where mapping is one to one between EPC and radio bearers.
5G NR QoS Architecture
New Quality Of Experience (QoE) in 5G
How 5G QoS is differ from 4G
General
The concept of QoS in 4G LTE is based on Bearers. The Concept of QoS in 5G is based on Flow Based.
In 4G, EPS Bearer ID (EBI) is used to distinguish between different Quality Of Services (QoS).
5G uses QoS Flows, each identified by a QoS Flow ID (QFI). As with 4G LTE both non-GBR flows and GBR flows are supported in 5G, along with a new delay-critical GBR. 5G also introduces a new concept – Reflective QoS.
The 5G QoS flows are mapped in the AN (Access Network) to DRBs (Data Radio Bearers) unlike 4G LTE where mapping is one to one between EPC and radio bearers.
4G vs 5G QoS flow parameters
5G – 5GC QoS Packet Filtering
In 5G, QoS Flow mapping happen two times. In the 5GC, there is only a single user plane network function – the UPF – for transport of data between the gNB and the core. In 5G, there is a one-to-many relationship between the GTP-U tunnel on N3 and the DRBs on the air interface. Each QoS flow on N3 is mapped to a single GTP-U tunnel. The gNB may map individual QoS flows to one more DRBs. Therefore, a PDU session may contain multiple QoS flows and several DRBs but only a single N3 GTP-U tunnel. A DRB may transport one or more QoS flows.
5G QoS Parameters / Attributes
QoS flow is
identified by QFI within PDU session. This QFI is carried in an encapsulation
header over NG-U.
• For each UE, 5GC establishes one or more PDU sessions and NG-RAN
establishes at least one DRB together with PDU session. Additional DRBs are
configured for QoS flows of that PDU session consecutively.
• NG-RAN maps packets which belong to the different PDU sessions to different
DRBs.
NAS level packet filters in UE and in 5GC associate UL/DL packets with QoS flows. At NAS level, QoS flow is characterised by QoS profile provided by 5GC to NG-RAN and QoS rules provided by 5GC to UE.
AS-level mapping rules in UE and in NG-RAN associate UL/DL QoS flows with DRBs. At AS (Access Stratum) level, DRB defines packet treatment on radio interface (Uu).
5G QoS Flow Descriptions
The network can also provide the UE with one or more QoS flow descriptions associated with a PDU session at the PDU session establishment or at the PDU session modification.
Each QoS flow description contains:
a) a QoS flow identifier (QFI);
b) if the flow is a GBR QoS flow:
1) Guaranteed flow bit rate (GFBR) for UL;
2) Guaranteed flow bit rate (GFBR) for DL;
3) Maximum flow bit rate (MFBR) for UL;
4) Maximum flow bit rate (MFBR) for DL; and
5) optionally averaging window, applicable for both UL and DL;
OR
If the flow is aNon-GBR QoS flow:
- Reflective QoS Attribute (RQA) in DL
- Additional QoS Flow Information
c) 5QI, if the QFI is not the same as the 5QI of the QoS flow identified by the QFI; and
d) ARP
e) optionally, an EPS bearer identity (EBI) if the QoS flow can be mapped to an EPS bearer .
5G QoS Rules
5G Signaled QoS Rule
The NAS protocol enables the network to provide the UE with signalled QoS rules associated with a PDU session.The network can provide the UE with one or more signalled QoS rules associated with a PDU session at the PDU session establishment or at the PDU session modification.
Each signalled QoS rule contains:
a ) an indication of whether the QoS rule is the default QoS rule;
b) a QoS rule identifier (QRI);
c) a QoS flow identifier (QFI);
d) optionally, a set of packet filters; and
e) a precedence value.
5G Derived QoS Rule
The reflective QoS in the UE creates derived QoS rules associated with a PDU session based on DL user data packets received via the PDU session.
Each derived QoS rule contains:
a) a QoS flow identifier (QFI);
b) a packet filter for UL direction; and
c) a precedence value of 80 (decimal)
5G QoS Flow Characteristics
- Resource Type (GBR, Delay critical GBR or Non-GBR);
- Priority Level;
- Packet Delay Budget (including Core Network Packet Delay Budget);
- Packet Error Rate;
- Averaging window (for GBR and Delay-critical GBR resource type only);
- Maximum Data Burst Volume (for Delay-critical GBR resource type only).
5G QoS Flow Table
Hi
I look your article well.
In 5G QOS , while processing packets What kind action of QoS have to be applied by UPF?
Session AMBR
QFI marking
..?
thanks.
Session AMBR is a subscription parameter in UDM. However, it can be modified by PCF and same is conveyed to SMF over N7. UPF will enforce the session AMBR received from SMF.
Actually, all the QFI marking is done by UPF only. I have not covered that topic and tried to cover aspect in terms of Layer 3 and RN side. I wll post new article for that
What is the difference between 5G QoS and 5G end-to-end slicing? Do they have the similar criteria or parameters to monitor/track?
Hi,
Sorry for late reply. 5G QoS is attributes to define end to end Slicing. For Slicing, there should be some attributes that distinguish between different slices like Bitrate, criticality, priorities. So those things are cover by QoS between UE and 5GC.
Hello,
Thanks for a very interesting article.
One question/clarification.
QoS flows are marked by QFI. This defines characteristics of the flow as you have described. What is not clear to me is how the 5QI fits in with this? Thanks for clarifying this.
Thanks for the question. Actually, QFI is part of QoS FLow Description and and QoS Rule. 5QI is just like QCI value defined in 4G. this is generally defined once we need to assign different QoS profile liek Voice, Video etc .
Nice informative article. Can you please explain Reflective QoS in much detail
Reflective QoS is another separate topic to cover . i will share a new article for that.
Hi, Can you please also provide some information on what basis a UE IP packet is mapped to a QFI and how the required information is configured/provisioned in the 5GS?
Thanks
UPF knows about QFI and during IP-data flow port, IP, and QFI, 5QI used for packet routing on UPF.
like for VOice , 5QI 1 , IP, port use to routing
Hi
Thanks for nice article.Could you please share info with end-to-end flow of like how UE/AN requesting Qos profile,5QI and QFI mapping and how no of PDR’s defined based on that.This will give more clarity on end-to-end flow (wrt QoS contribution towards each NF’s and decision making)
Actually, I had covered information from NAS – Radio Interfscae mainly. Please see 5QI and QFI details in blog. it is UPF responsibility to assign/forward respective FLow to DN
Please add some 3GPP spec references for further reading. Thank you.
23.501
23.502
38.300
37.340
Very well summarized article on 5G QoS. Know you from Aricent time.
Can you give more info on: Do NAS have to give the QoS info received in PDU session estbn accept or mod to upper layers? Who does the actual packet filtering in UE for PDU sessions, is it upper layer(flow cache?) of NAS?
Hi,
Yes, I remember you 🙂
NAS layer provide QFI, PDU Session info to SDAP . and SDAP use this infor for packet filtering in User plane.
THere is QFI+ PDUSession unique Flow mapping on user plane
How to configure the DRB in 5G.. i.e How many DRB can be configured in 5G
DRBs are configured on gNB in RRCReconfiguration. mapping of DRBs -QFI/PDUSession are done by SDAP and check in sdap-config. MaxDRBs can be value 30 as per 38.331
Hi, does the bounded delay per service cover the end to end transmission wholly?
Hi..many thanks for this excellent article. Very well explained.
One question please :How UE is assigned to QoS policy when a PDU session established? Is it PCF that assigns QoS policies to UE through NAS..is the interface through PCF-SMF-AMF-UE or PCF-AMF-UE?
If no SDAP header is present in the packet , is the packet mapped to the default bearer ?
If no SDAP header is present in the packet , is the packet mapped to the default flow ?
Hi,
I need your explanation regarding QFI and 5QI value.
QFI is 6 bits so the value are in the range 0-63
5QI value could be bigger than 63
Now if the flow needs to use 5QI = 70 could you help me to understand what could be the QFI value?
Hi,
Nice article. Clearly explains the relationships between DRBs, QoS flows and PDU sessions.
I understand that there is 1:1 relationship between PDU Session and GTP-U tunnels on N3 (Between CU-UP and UPF). As you said, QFI is part of one of the GTP-U Extension headers.
In case of disaggregated RAN, you have GTP-U tunnels between DU ad CU-UP too. As I understand CU-UP is the one that understands DRBs and PDU sessions and hence that is the one that does the mapping. Set of questions:
What is granularity of GTP-U tunnels at F1-u (Between DU and CU-UP)?
A. Is it per DRB?
B. Is it per UE?
C. Or is it independent of DRBs and global between a given pair of DU and CU-UP.
I am guessing that answer is (A). It is per DRB. Appreciate if you confirm or send the correction.