QoS introduction
5G QoS model is based on QoS flow in 5G.
5G QoS supports both GBR QoS traffic and non-GBR QoS traffic.
QoS flow is the finest granularity of QoS in a PDU session.
QoS Flow ID (QFI) is used to identify QoS flow in 5GS.
QFI can be dynamically allocated or equal to 5QI.
QFI is unique to a PDU session.
QoS profile will be provided by SMF to AMF to AN at the N2 interface.
QoS rules may be provided by SMF to UE via AMF on N1 interface.
QoS configuration file
QoS can be GBR or non-GBR depending on QoS profile.
QoS profile contains below QoS parameters below:
For each QoS flow, it will include:
1. 5G QoS identifier (5QI)
2. Assignment and Reservation Priority (ARP)
For each non-GBR QoS flow, the QoS profile includes:
1. Reflective QoS attribute (RQA)
2. Guaranteed Traffic Bit Rate (GFBR) for UL and DL
3. Maximum Streaming Bit Rate (MFBR) for UL and DL.
For each non-GBR QoS flow, the QoS profile includes:
1. Notification Control
2. Maximum Packet Loss Rate UL and DL
QoS Traffic Control
1. When a normalized 5QI or a pre-configured 5QI with a 5QI range is with-in QFI value, then the 5QI value can be used as a QFI flow for QoS in non-GBR QoS flow.
2. In other cases for both GBR and non-GBR dynamically allocated QFI should be used.
QoS Rules
QoS rules are used to perform classification and marking of UL user plane traffic.
QoS rules can be provided explicitly to UE during PDU session establishment/modification procedures.
QoS rules can be pre-configured in UE
Or it can be implicitly derived by the UE by applying reflective QoS.
A QoS rules will contains QFI, packet filter settings, priority values.
If QFI is allocated dynamically, QoS rules and other QoS flow parameters like 5QI, GFBR, MFBR are signaled to the UE per QoS flow basis.
There can be multiple QoS rules associated with the same QoS.
There will be a default QoS rules needs to be sent to the UE for each PDU session.
For unstructured PDU type, the default QoS rules does not contain packet filter set.
If the default QoS rule does not have a packet filter setting or of the packet filter set that allows UL packets, reflective QoS should not be applied.
QoS flow mapping
SMF binds the SDF to the QoS flow according to the QoS service requirements.
SMF will assign QFI to the new QoS flow and derives QoS profile, corresponding UPF directives and QoS rules from the PPC rules.
SMF will provide RAN with below details:
1. QFI
2. Transport level packet marking value for UL traffic.
3. DL PR containing DL packet filtering settings for SDF templates.
4. PDR priority value of the two PDR.
5. QoS related information
6. Unique QoS rule identifier
DL flow
Below are the characteristics applied to DL traffic:
UPF maps user plane traffic to QoS flow based on PDR.
UPF performs session-AMBR enforcement.
UPF will also perform packet counting for accounting.
UPF will then transmit the PDUs of a PDU session to 5GC and RAN, UPF includes the QFI.
UPF will perform transport level packet marking in DL.
UL flow
Below are the characteristics applied to UL traffic:
UE stores the QoS rules to determine the UL user plane traffic and QoS flow. UL behavior is specified in TS 38.300[27] clause 10.5.2.
RAN performs transport-level packet marking in UL.
RAN will send PDU to UPF over N3 channel.
UPF will verify the QFI in UL PDU is same as the QOS rules provided to the UE.
AMBR/MFBR enforcement
UL and DL session related AMBR will be in SMF.
DL session related AMBR will be implemented in each UPF.
If UE receives session-AMBR, UE shall use the session-AMBR to perform UL rate limiting.
In UPF, MFBR will be enforced downlink GBR QoS flows.
In RAN, MFBR will be enforced downlink and uplink GBR QoS flows.
Priority Value
5QI:
5QI is used to define 5G QoS characteristics.
ARP: Allocation and Retention Priority
ARP priority ranges from 1 to 15, 1 being the highest priority.
It sets the information about priority level, pre-emption capability and pre-emption vulnerability.
RQA
Reflective QoS Attribute (RQA) is used in UL.
Notification Control
Additional GBR QoS flow will have below additional parameters:
1. QoS Notification Control
2. GFBR
3. MFBR
Notification Control
Notification control is used to notify SMF when a GFBR cant be met.
Guaranteed Traffic Bit Rate (GFBR) :
Used in UL and DL. This is the lowest recommended bitrate that a UE is expected to get.
Maximum Straming Bit Rate (MFBR) :
This is applicable in UL and DL. This is the highest expected by ths QoS flow.
Aggregated Bit Rate
Each PDU session are associated with below QoS parameters:
1. Session AMBR
2. UE-AMBR
3. Default Values
4. Maximum Packet Loss Rate
1. Session AMBR
Session AMBR parameter is retrieved by SMF from UDM.
SMF can modify it based on local policy.
Session-AMBR does not apply o GBR QoS flows.
2. UE-AMBR Aggregated Maximum Bit Rate per UE.
UE-AMBR limits the aggregated bit rate that can be expected to be provided in non-GBR flows to a UE.
3. Default Values
SMF retrieves the users default 5QI and ARP values from UDM.
SMF can changes the default values based on local configuration.
4. Maximum Packet Loss Rate
This is applicable to voice media.
It indicates the maximum rate of lost packets for a QoS flow that can be tolerated in both uplink and downloink direction.
QoS features
1. Resource Type
2. Priority
3. Packet Delay Budget
4. Packet Error Rate.
5. Average Window
6. Maximum data burst.
Reflective QoS
Reflective QoS enables the UE to map UL user plane traffic to QoS flows, if the QoS rules provided by SMF.
UE-related QoS rules
A UE related QoS rules contain in the following parameters:
1. UL packet filter
2. QFI
3. Priority Value.
Packet Filter Settings
Packet filter settings are used in QoS rules to identify one or more packets.
IP Packet Filtering Settings are as follows:
Source/destination IP address or IPv6 prefix.
Source/destination port number.
The protocol ID of the protocol above the IP/Next header type.
Type of Service (TOS) (IPv4) / Traffic Class (IPv6) and Mask.
Flow label (IPv6).
Security parameter index.
Packet filtering direction.