nodes.
From this information, the scheduler defined:
1 – the frequency radio resources to be allocated for each mobile;
2 – the number of spatial layers that can be used, depending on the category of the mobile;
3 – the transmission TTI (Time Transmission Interval) instants.
The mobile listens to the information transmitted over the PDCCH (Physical Downlink Control Channel) logical control channel and decodes the information channel when it detects its radio identifier C-RNTI.
The scheduler makes its decisions at each slot. The duration of the TTI slot depends on the spacing between SCS (SubCarrier Spacing). While the scheduler decision is 1 ms in 4G, it is variable from 1 ms, 500 μs or 250 μs for 5G on the FR1 (Frequency Range 1) band, and can go down to 125 μs or 62.5 μs for the FR2 band.
Transmission on the downlink direction can be pre-empted for critical communication (low latency). The NG-RAN node informs the mobiles by transmitting the INT-RNTI identifier over the PDCCH control channel.
Semi-persistent scheduling allows us to periodically allocate radio resources for a mobile. The periodicity of the messages is transmitted over the RRC layer and the resource allocation is transmitted to the mobile via the CS-RNTI identifier.
1.4.2. Support for quality of service on radio link
The QoS (Quality Of Service) control consists of implementing the maximum quality of service applicable to a data flow.
Like the 4G mobile network, only the core network is aware of the service requirements: QoS management is under the control of the core network (AMF). The NG-RAN has no knowledge of the service to be managed. Thus, when establishing a PDU session, the AMF entity establishes QoS rules between the radio node and one or more UPF entities.
The PDU session carries IP flows with one or more different qualities of service for all flows. Each flow is associated with a QFI flow profile identifier. The flow profile corresponds to a QoS indicator (5QI: 5G QoS Identifier) and an allocation and retention priority (ARP). The QFI flag is unique within a PDU session. The flag is either configured during the PDU session establishment procedure or during the PDU session modification procedure.
The value of a QFI is configured by the AMF during the procedure of session establishment; the AMF querying the unified UDR database to know the user’s authorized QoS. For the establishment of dedicated services, the SMF chooses the QoS characteristics (5QI/ARP) according to the values stored at the SMF or by querying the PCF entity. The 5QI/ARP combination defined by the PCF link in a PDU session is a QoS flow binding.
The 5QI indicator is a parameter standardized by the 3GPP standard, allowing us to define:
1 – the type of resource (Guaranteed Bit Rate or not): GBR or non-GBR;
2 – priority;
3 – the maximum transmission delay within the 5GS mobile network;
4 – the residual error rate.
5 The standardization of the 5QI value makes it possible to indicate how the flow is processed on each element of the user’s plan, in order that processing is consistent between the entities of the 5G core network and of the NG-RAN access.
The 5QI indicator is identical to the QCI (QoS Class Identifier) indicator for the 4G network for non-critical services (indicator from 1 to 80). New QCI values (81–85) have been defined in the case of URLLC services to guarantee speed and critical delay (delay critical GBR).
Table 1.2. 5G QoS characteristics
| 5QI | Type | Priority | Packet Delay Budget | PLER | Services |
|---|---|---|---|---|---|
| 1 | GBR | 2 | 100 ms | 10−2 | Conversational Voice |
| 2 | 4 | 150 ms | 10−3 | Conversational Video (Live Streaming) | |
| 3 | 3 | 50 ms | 10−3 | Real Time Gaming, V2X messages | |
| 4 | 5 | 300 ms | 10−6 | Non-Conversational Video (Buffered Streaming) | |
| 65 | 0.7 | 75 ms | 10−2 | Mission Critical user plane Push To Talk voice (e.g. MC-PTT) | |
| 66 | 2 | 100 ms | 10−2 | Non-Mission-Critical user plane Push To Talk voice | |
| 75 | 2.5 | 50 ms | 10−2 | V2X messages | |
| 5 | Non-GBR | 1 | 100 ms | 10−6 | IMS Signaling |
| 6 | 6 | 300 ms | 10−6 | Video (Buffered Streaming) TCP-Based (e.g. www, email, chat, ftp, p2p, etc.) | |
| 7 | 7 | 100 ms | 10−3 | Voice, Video (Live Streaming), Interactive Gaming | |
| 8 | 8 | 300 ms | 10−6 | Video (Buffered Streaming) TCP-Based (e.g. www, email, chat, ftp, p2p, etc.) | |
| 9 | 9 | 300 ms | 10−6 | Video (Buffered Streaming) TCP-Based (e.g. www, email, chat, ftp, p2p, etc.). Typically used as default bearer | |
| 69 |
0.5
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