Exploring 5G Quality of Service (QoS): Unlocking the Potential of Next-Generation Networks
ABSTRACT:
One of the key features of 5G architecture is its ability to differentiate and manage traffic flows with different QoS requirements. This article aims to help readers understand how 5G architecture accomplishes this by employing distinct QoS measures for different types of traffic.
This article provides an overview of the essential elements of the 5G architecture that enable the implementation of Quality of Service (QoS) flows. It explains the concept of QoS flows and their creation process. Additionally, the article presents an overview of the various QoS parameters used in 5G networks.
By delving into the intricacies of 5G architecture, this article elucidates the mechanisms and techniques utilized to establish QoS flows.
INTRODUCION:
Quality of Service refers to the performance characteristics of a network or service experienced by its users. In the context of 5G, QoS encompasses a range of factors, including reliability, availability, latency, throughput, and prioritization of traffic. These aspects play a vital role in delivering an optimal user experience and catering to diverse application requirements.
I. Key Features of 5G QoS:
o Network Slicing:
One of the most notable advancements enabled by 5G QoS is network slicing. Network slicing allows service providers to create multiple virtual networks within a single physical infrastructure. Each network slice can be customized with specific QoS parameters, addressing the unique demands of various applications or user groups. This flexibility paves the way for improved resource allocation and tailored network experiences.
o Enhanced Mobile Broadband (eMBB):
eMBB is a primary use case of 5G, offering exponentially faster download and upload speeds compared to its predecessors. With 5G QoS, eMBB ensures consistent high data rates for bandwidth-hungry applications, such as 4K video streaming, virtual reality (VR), augmented reality (AR), and cloud gaming. The improved QoS parameters translate into seamless, uninterrupted multimedia experiences.
o Ultra-Reliable Low-Latency Communication (URLLC):
URLLC is another critical aspect of 5G QoS, catering to applications that require extremely low latency and high reliability. Industries such as autonomous driving, remote surgery, industrial automation, and smart grids depend on URLLC to enable real-time, mission-critical operations. By leveraging 5G’s capabilities, URLLC ensures minimal delay, ultra-reliable connections, and stringent QoS guarantees.
o Massive Machine-Type Communication (mMTC):
The Internet of Things (IoT) ecosystem thrives on mMTC, enabling the interconnectivity of billions of devices. 5G QoS accommodates mMTC by optimizing resource allocation for a massive number of low-power, low-data-rate devices. With efficient handling of mMTC traffic, 5G networks can support smart cities, smart homes, and industrial IoT applications seamlessly.
II. QoS Framework in 5G:
To facilitate efficient QoS management, 5G networks employ a comprehensive framework that encompasses both the control plane and user plane aspects.
When a UE powers on within a 5G cell or tracking area, it initiates the registration procedure with the 5G Core Network (5GS). During this procedure, the 5GS authenticates the UE’s SIM card with the assistance of the Authentication Server Function (AUSF) and the User Data Management (UDM) function to ensure that the UE has a valid subscription within the 5GS. The registration process involves multiple message exchanges among the UE, the Access and Mobility Management Function (AMF), and the UDM, including the utilization of predefined encryption keys by the UDM.
o Control Plane:
The control plane in 5G QoS involves policy control and enforcement functions. Policy control allows operators to define QoS policies based on application requirements and user preferences. It enables dynamic allocation of network resources and governs traffic prioritization and admission control.
1. UE Registration:
The UE performs cell acquisition, network selection, and cell selection to establish a radio connection. The AMF, which is responsible for access and mobility management, manages the registration of the UE. It initiates authentication and performs mobility management functions.
2. AUSF — Authentication Server Function:
The AUSF retrieves an Authentication vector from the UDM (Unified Data Management) and transfers it to the AMF. The AMF utilizes the Authentication vector to challenge the UE and verify the validity of the authentication response.
The Session Management Function (SMF) plays a crucial role in the establishment and management of PDU sessions. It is responsible for selecting the UPF that the UE desires to utilize for Data Network (DN) connectivity. Additionally, the SMF handles the allocation of IP addresses and interacts with the Policy Control Function (PCF) to make policy decisions regarding Quality of Service (QoS).
o User Plane:
The user plane focuses on data transmission and traffic handling. Here, packet scheduling, traffic shaping, and queuing mechanisms play a crucial role in ensuring QoS compliance. Dynamic packet prioritization and traffic classification techniques optimize the utilization of network resources while meeting the defined QoS objectives.
The User Plane Function (UPF) is responsible for data routing, enforcing Quality of Service (QoS), and managing Protocol Data Unit (PDU) flows. The UPF is connected through four distinct reference points:
o N3: This interface links the Radio Access Network (RAN), specifically the gNB (next-generation base station), with the initial UPF.
o N9: This interface facilitates communication between two UPFs, specifically between the intermediate UPF (I-UPF) and the session anchor UPF.
o N6: This interface connects the Data Network (DN) with the UPF, enabling data transfer between the two entities.
o N4: This interface establishes a connection between the Session Management Function (SMF) and the UPF, allowing for coordinated control and management.
A. PDU Session Establishment
The Policy Control Function (PCF) is responsible for determining the Quality of Service (QoS) parameters for a PDU session and making decisions regarding the charging mechanism for a flow.
To establish a connection with the external network (DN), the UE initiates a PDU session Establishment request to the Access and Mobility Management Function (AMF) through the gNB over the N1 interface. The PDU session is then established between the UE and the UPF.
The purpose of the UE’s PDU session establishment is to establish a default QoS between the UE and the Data Network (DN) via the gNB. Within the established PDU session, the UE can utilize the default QoS Flow to exchange traffic with the DN. In 5G, the QoS Flow represents the lowest level of granularity for a traffic flow, enabling the application of QoS policies and charging mechanisms. Each PDU session can have a maximum of two QoS flows.
B. QoS Flows
QoS in the 5G Core Network is determined by QoS flows, which include Guaranteed Bit Rate (GBR), Non-guaranteed Bit Rate (Non-GBR), and Reflective flows for dynamic configuration purposes. These QoS flows define the specific quality parameters that can be applied to user plane traffic.
Each QoS flow within the 5G Core Network is identified by a QoS Flow ID (QFI). The QFI serves as a unique identifier for a particular QoS flow and allows for the precise management and control of traffic based on its specific quality requirements.
When it comes to transmitting QoS flow information, the QFI is carried in an encapsulated header on the N3 (and N9) interfaces. This means that the original end-to-end packet header remains unaltered, ensuring efficient and seamless communication between network elements.
In a PDU Session, user plane traffic that shares the same QFI receives consistent treatment in terms of traffic forwarding. This includes factors such as scheduling and admission thresholds. By assigning the same QFI to related traffic flows, the network ensures that these flows are handled similarly, maintaining the desired QoS guarantees and consistency within the PDU Session.
The control and establishment of QoS flows are managed by the Session Management Function (SMF) within the 5G Core Network. The SMF has the authority to preconfigure QoS flows or dynamically establish them through procedures like the PDU Session Establishment or PDU Session Modification. This flexibility allows for efficient allocation and adaptation of QoS resources based on the specific requirements of the user plane traffic and network conditions.
C. QoS Flow Characterization:
A crucial aspect of Quality of Service (QoS) in the 5G Core Network is the characterization of QoS parameters. These parameters define the specific requirements and guarantees for a given QoS profile. The Session Management Function (SMF) provides the QoS profile either to the Radio Access Network (RAN) through the Access and Mobility Management Function (AMF) over the N2 reference point or preconfigures it directly in the RAN.
Within the QoS profile, one or more QoS rules are defined, along with the option to associate QoS flow level QoS parameters with these rules. QoS rules are responsible for specifying the specific behavior and treatment of user plane traffic based on their respective QoS requirements. By associating QoS flow level QoS parameters with these rules, further granularity and customization can be achieved, ensuring optimal quality and performance for each flow within the network.
In order to implement and enforce the defined QoS rules and parameters, the SMF provides one or more UL (Uplink) and DL (Downlink) Packet Detection Rules (PDRs) to the User Plane Function (UPF). These PDRs serve as guidelines for the UPF to properly handle and process user plane traffic, ensuring the desired QoS guarantees are met. The UL and DL PDRs play a crucial role in ensuring efficient and effective traffic management throughout the network.
D. QoS Profile:
The QoS profile in the 5G Core Network incorporates specific QoS parameters for each QoS flow. These parameters ensure that the network can provide the necessary level of service and meet the QoS requirements of different flows.
Two essential QoS parameters included in the QoS profile for each QoS flow are the Allocation and Retention Priority (ARP) and the 5G QoS Identifier (5QI). The ARP determines the priority level assigned to the QoS flow, enabling the network to allocate resources accordingly. The 5QI represents the specific QoS class assigned to the flow, defining the quality characteristics and service level agreement associated with it.
For Non-GBR (Non-Guaranteed Bit Rate) QoS flows, an additional QoS parameter called the Reflective QoS Attribute (RQA) may be included in the QoS profile. The RQA provides further information about the dynamic configuration requirements for the Non-GBR flow, allowing the network to adapt and adjust its behavior accordingly.
In the case of GBR (Guaranteed Bit Rate) QoS flows, the QoS profile must include specific QoS parameters. These parameters encompass the Guaranteed Flow Bit rate (GFBR) for both the Uplink (UL) and Downlink (DL), ensuring a minimum guaranteed bit rate for the flow. Additionally, the Maximum Flow Bit rate (MFBR) for both UL and DL defines the upper limit on the flow’s bit rate. Optional parameters such as {Notification control, Maximum Packet Loss Rate (UL and DL)} can be included, providing additional control and defining acceptable levels of packet loss for the GBR flow.
· QoS Profile: ARP
The inclusion of the Allocation and Retention Priority (ARP) parameter in the QoS profile serves various purposes within the 5G Core Network. Firstly, it allows the network to make decisions regarding the acceptance or rejection of QoS Flow establishment, modification, or handover requests, particularly in cases where resource limitations are present. By considering the ARP level of the requested flow, the network can determine if it can accommodate the flow’s resource requirements or if it needs to be rejected due to resource constraints. Moreover, ARP can also be utilized to prioritize which QoS Flow to release and free up resources during resource limitations, effectively managing resource allocation in a dynamic manner.
The ARP priority level assigned to a QoS Flow defines its relative importance within the network. The range of ARP priority levels spans from 1 to 15, with 1 being the highest level of priority. This allows for granular prioritization, enabling the network to distinguish between different flows and allocate resources accordingly based on their designated priority levels. By assigning specific ARP priority levels to QoS Flows, the network can ensure that flows with higher priority levels receive preferential treatment and resource allocation.
The ARP pre-emption capability is another aspect determined by the ARP parameter. It defines whether a QoS Flow can obtain resources that were previously assigned to another QoS Flow with a lower ARP priority level. In situations where resources become scarce, a QoS Flow with higher priority may need to pre-empt the resources of a lower-priority flow to meet its requirements. The ARP pre-emption capability allows the network to make informed decisions regarding resource reallocation and ensure that flows with higher priority levels can obtain the necessary resources even if they were initially allocated to lower-priority flows.
On the other hand, the ARP pre-emption vulnerability refers to the potential of a QoS Flow to lose its assigned resources in favor of admitting a QoS Flow with a higher ARP priority level. If a QoS Flow has a higher vulnerability to pre-emption, it means that it may be more susceptible to losing its allocated resources when a higher-priority flow needs to be accommodated. This vulnerability ensures that the network can adapt and allocate resources efficiently based on changing priorities and resource availability.
· QoS Profile: 5QI
The 5QI (5G QoS Identifier) is a scalar value that serves as a reference to a standardized combination of 5G QoS characteristics. It represents a set of access node-specific parameters that govern the QoS forwarding treatment for a specific QoS Flow. These parameters encompass various aspects such as scheduling weights, admission thresholds, queue management thresholds, and link layer protocol configuration, among others.
The standardized nature of the 5QI allows for interoperability and consistency across different access nodes within the network. It ensures that QoS flows with the same 5QI value receive similar treatment and are subjected to the same set of QoS characteristics. This standardization simplifies the management and configuration of QoS within the 5G Core Network, promoting efficiency and seamless integration between network elements.
E. QoS Profile 5QI — Parameters
· Resource Type: A GBR (Guaranteed Bit Rate) QoS Flow can utilize either the GBR resource type or the delay-critical GBR resource type. These resource types have distinct definitions for parameters such as Packet Delay Budget (PDB) and Packet Error Rate (PER). Additionally, the MDBV (Maximum Data Burst Volume) parameter is applicable only to the delay-critical GBR resource type. The choice of resource type determines the specific characteristics and requirements associated with the QoS Flow.
· Priority Level: The priority level assigned to a QoS Flow indicates its relative importance in the scheduling of network resources. The priority levels are defined in such a way that the lowest level corresponds to the highest priority. This parameter is used to differentiate between QoS Flows from the same UE (User Equipment) and also between QoS Flows originating from different UEs. By assigning priority levels, the network can effectively manage and prioritize the allocation of resources based on the specific needs and requirements of each flow.
· Packet Delay Budget: The Packet Delay Budget specifies the upper limit for the delay that a packet can experience between the UE and the termination point at the UPF (User Plane Function) over the N6 interface. This parameter ensures that the delay in packet transmission remains within acceptable bounds. The same value of the Packet Delay Budget is applicable for both the Uplink (UL) and Downlink (DL) directions, ensuring consistency in delay performance.
· Maximum Data Burst Volume (MDBV): The MDBV parameter represents the maximum amount of data that the 5G Access Network (5G-AN) is obligated to handle within a given period, which aligns with the PDB for the 5G-AN. It denotes the burst size of data that can be served by the 5G-AN without exceeding the specified limits. The MDBV parameter applies in the context of the QoS Flow’s resource allocation and ensures efficient resource management and allocation in accordance with the defined burst volume requirements.
· Packet Error Rate (PER): The Packet Error Rate parameter defines an upper limit for the rate of IP packets that have been processed by the sender of a link layer protocol, such as RLC (Radio Link Control), but were not successfully delivered by the corresponding receiver to the upper layer, such as PDCP (Packet Data Convergence Protocol). It sets a threshold for the acceptable level of packet loss in the transmission process, ensuring reliable delivery of data between network entities.
· Averaging Window: Each GBR (Guaranteed Bit Rate) QoS Flow is associated with an Averaging Window. The Averaging Window represents the duration over which the GBR (Guaranteed Bit Rate) and MBR (Maximum Bit Rate) parameters are calculated. This calculation occurs in various network elements, including the (R)AN (Access Network), UPR (User Plane Function at the RAN), and UE (User Equipment). The Averaging Window determines the time period over which the GBR and MBR values are measured and provides a basis for accurate resource allocation and management.
F. QoS Profile — GFBR and MFBR
GBR (Guaranteed Bit Rate) QoS Flows in 5G networks come with additional QoS parameters that include the Guaranteed Flow Bit Rate (GFBR) and the Maximum Flow Bit Rate (MFBR) for both the Uplink (UL) and Downlink (DL) directions.
The GFBR represents the minimum bit rate that the network guarantees to provide for the particular QoS Flow over the specified averaging time window. This parameter ensures that the QoS Flow receives a consistent and reliable bit rate, meeting the specific requirements and expectations of the application or service. It assures a certain level of service quality by ensuring a minimum bit rate is maintained.
On the other hand, the MFBR places an upper limit on the bit rate expected from the QoS Flow. It sets a maximum threshold for the bit rate, allowing the network to control and manage traffic that exceeds this limit. Excess traffic, beyond the maximum expected bit rate, may undergo shaping or policing mechanisms at various network elements such as the UE, UPF (User Plane Function), or RAN (Radio Access Network).
Both the GFBR and MFBR parameters are signaled to the RAN through the QoS Profile. Additionally, the UE receives the GFBR and MFBR values as QoS Flow-level QoS parameters for each individual QoS Flow.
G. QoS Profile — Notification Control
• The QoS parameter “Notification Control” indicates whether notifications should be requested from the NG-RAN (Next Generation Radio Access Network) when the Guaranteed Flow Bit Rate (GFBR) for a QoS Flow can no longer be guaranteed or can be guaranteed again during the lifetime of the flow. This parameter is particularly useful for GBR (Guaranteed Bit Rate) QoS Flows where the application traffic has the ability to adapt to changes in QoS, such as triggering rate adaptation at the application function (AF).
• The SMF (Session Management Function) will enable Notification Control only when the QoS Notification Control parameter is set in the PCC (Policy and Charging Control) rule received from the PCF (Policy Control Function), which is bound to the QoS Flow. This parameter is then signaled to the NG-RAN as part of the QoS profile.
• If Notification Control is enabled for a GBR QoS Flow and the NG-RAN determines that the GFBR can no longer be guaranteed, the NG-RAN will send a notification to the SMF while keeping the QoS Flow active. The NG-RAN will continue to keep the QoS Flow even if it is unable to deliver the requested GFBR, unless specific conditions at the NG-RAN, such as radio link failure or RAN internal congestion, require the release of resources for this particular QoS Flow. However, the NG-RAN will make further attempts to guarantee the GFBR again.
• Upon receiving a notification from the NG-RAN indicating that the GFBR can no longer be guaranteed, the SMF may forward this notification to the PCF. In response, the 5GC (Fifth Generation Core Network) may initiate N2 signaling to modify or remove the affected QoS Flow.
• When the NG-RAN determines that the GFBR can be guaranteed again for a QoS Flow, it will send a subsequent notification to inform the SMF that the GFBR can be guaranteed again. This notification enables the SMF to forward the information to the PCF. The NG-RAN will continue to send notifications whenever necessary to update the SMF about the status of the GFBR for the QoS Flow.
H. QoS Rules
The association of uplink (UL) traffic to QoS Flows in the UE is facilitated by the QoS Rules defined in the NAS (Non-Access Stratum) protocol. When establishing or modifying a PDU (Packet Data Unit) session, the network provides the UE with one or more QoS rules that are explicitly signaled.
Each signaled QoS rule encompasses the following components:
a) An indication specifying whether the QoS rule serves as the default rule for the UE.
b) A QoS rule identifier (QRI) that uniquely identifies the QoS rule within the context of the session.
c) A QoS flow identifier (QFI) that identifies the associated QoS Flow.
d) Optionally, a set of packet filters that define the criteria for selecting specific IP packets to be associated with the QoS rule.
e) A precedence value that determines the relative importance or priority of the QoS rule among other rules.
I. PACKET DETECTION RULE (PDR)
During the provisioning of a Packet Detection Rule (PDR) in the User Plane Function (UPF), the Session Management Function (SMF) provides a Packet Detection Information (PDI) that contains specific instructions for packet matching. The PDI includes the following parameters:
· Source Interface: This parameter identifies the interface from which the incoming packets originate. It specifies the network interface through which the packets are received by the UPF.
· Matching Parameters: The PDI includes a combination of parameters that the incoming packets must match. These parameters can include:
· Local F-TEID: The PDI may specify a particular Local F-TEID (Fully Qualified Tunnel Endpoint Identifier) that the incoming packets should have.
· Network Instance: The PDI may define a specific network instance that the packets should belong to.
· UE IP address(s): The PDI can include one or more UE IP addresses that the packets are expected to have.
· SDF Filter(s): The PDI may include specific Service Data Flow (SDF) filters that the packets must satisfy.
· Application ID: The PDI can specify an Application ID that the packets are associated with.
For 5G Core, the PDI may additionally contain one or more QFI(s) to detect traffic pertaining to specific QoS Flows
J. SDAP
The SDAP layer plays a crucial role in mapping QoS flows from a PDU session onto data Radio Bearers (DRBs). In this context, a data radio bearer (DRB) can be understood as a logical channel that determines the packet treatment on the radio interface. Each DRB is responsible for handling packets with the same packet forwarding treatment, ensuring consistency and uniformity.
To facilitate the mapping process, the QoS Flow Identifier (QFI) is carried in an encapsulated header over the N3 interface. The QFI serves as a reference or pointer to the corresponding QoS Profile associated with the QoS flow. This allows the SDAP layer to accurately identify and apply the appropriate QoS parameters and policies for each flow.
To manage and control the QoS flows within a PDU session, the SDAP sublayer is configured with an SDAP entity. In cases of single connectivity, where only one gNB (Next Generation Node B) is used, there will be as many SDAP entities as there are PDU sessions established by the 5G Core Network (5GC). Each SDAP entity is responsible for handling and managing the QoS flows associated with its respective PDU session, ensuring proper QoS enforcement and adherence to the specified policies.
K. PDCP and RLC
The PDCP (Packet Data Convergence Protocol) layer plays a vital role in the 5G network by handling Data Radio Bearers (DRBs). It ensures the delivery of packets to upper layers in the correct order without any duplicates. Additionally, the PDCP layer performs header compression whenever necessary and enforces security measures in the Radio Access Network (RAN) through ciphering and integrity protection mechanisms.
To effectively manage the DRBs, the PDCP layer is configured with PDCP entities. Each PDCP entity is responsible for handling the configuration and operations of a specific radio bearer. Therefore, the number of PDCP entities corresponds to the number of radio bearers that need to be managed within the network. Each PDCP entity ensures proper in-order delivery, eliminates duplicate packets, performs header compression, and ensures the integrity and confidentiality of data transmissions in the RAN.
The RLC (Radio Link Control) layer is another important component of the 5G network architecture. It is responsible for segmenting data packets and providing error correction capabilities. In the transmitter, segmentation involves dividing PDCP Protocol Data Units (PDUs) into smaller segments that can fit within the payload allocated for transmission by the lower layers. This segmentation process ensures efficient transmission of data over the radio interface and allows for error correction and retransmission if needed.
Challenges and Future Directions:
Despite its tremendous potential, 5G QoS presents several challenges. Ensuring end-to-end QoS across diverse network architectures, integrating with legacy systems, and managing network slices efficiently require careful planning and collaboration. Additionally, as 5G continues to evolve, new QoS enhancements may be introduced to cater to emerging use cases, such as holographic communication and tactile internet.
Conclusion:
5G QoS acts as a cornerstone for unlocking the full potential of next-generation networks. With its ability to tailor network resources, prioritize traffic, and support diverse applications, 5G QoS empowers industries, revolutionizes user experiences, and drives innovation. As the 5G ecosystem evolves, continued focus on QoS improvements will be vital to harness the true power of this transformative technology.
References:
[1] 3GPP 23.501–5G System Architecture
[2] 3GPP 38.300 — NR and NG-RAN overall
[3] 3GPP 23.502 — Procedures for the 5G System
[4] 3GPP 38.415 — PDU Session User Plane Protocol
[5] 3GPP 29.244 — Interface between UP and CP
[6] 3GPP 37.324 — SDAP
[7] 3GPP 38.321 — MAC
[8] 3GPP 38.322 — RLC
[9] 3GPP 38.323 — PDCP
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