Voice service in 5G

Article by Abhijeet Kumar

Voice Services in 5G:

1. Overview

5G introduces a complex but highly efficient framework for handling voice services, leveraging advancements in network technology to support seamless voice communications. The diagram represents the integration of various network elements including 5G New Radio (NR), VoNR, Enhanced Voice Services (EVS), and fallback mechanisms such as EPS (Evolved Packet System) fallback to ensure comprehensive coverage and service continuity.

5G Devices and Network Configurations

• Devices: All voice services in 5G are handled by devices specifically designed to support 5G NR capabilities. These devices are equipped to handle high-speed data and voice services directly through the 5G network.
• 5G NR (New Radio): This is the standard for the wireless air interface that delivers significantly faster data speeds and more reliable connectivity compared to 4G LTE.

VoNR (Voice over New Radio)

• 5G Network Core: At the core of the 5G network, VoNR is the primary technology for handling voice calls over the 5G infrastructure. It utilizes the 5G Core (5GC) to manage voice services without relying on older network technologies, thereby providing higher quality and more reliable voice communications.

EN-DC Network (E-UTRAN New Radio - Dual Connectivity)

• VoLTE in EN-DC: Within the dual connectivity setup, where devices are connected to both LTE and NR, VoLTE can still be utilized. In this setup, the device uses the LTE network as an anchor for connectivity while accessing NR for additional bandwidth and services.
• 5G NR: This part of the network supports data services and can also support voice in tandem with LTE under EN-DC, providing flexibility and enhanced capacity.

EPS Fallback

• EPS Fallback for IMS Voice: In areas or scenarios where 5G NR or VoNR is not available, devices can fallback to the EPS network to ensure voice service continuity using IMS (IP Multimedia Subsystem) over LTE.
• LTE Network and VoLTE: This traditional technology continues to play a crucial role in the ecosystem, ensuring that voice services can be maintained even when the 5G network is not available. LTE and its Core are used for voice (VoLTE) as well as data services during fallback scenarios.

In the transition to 5G, ensuring service continuity for all users is paramount, particularly when it comes to voice services. EPS Fallback (EPS-FB) is a critical mechanism in this process, providing a reliable bridge between existing 4G networks and new 5G infrastructures. Here’s an in-depth look at EPS Fallback, its importance, and how it functions within the broader network ecosystem.

What is EPS Fallback?

EPS (Evolved Packet System) Fallback is a technology that allows devices to switch to the 4G LTE network when voice services are not available through the 5G network. This ensures that users can still make and receive calls seamlessly, even if the 5G network does not support voice services or if the coverage is insufficient.

How EPS Fallback Works

The diagram shared illustrates the flow of voice and data services across different network technologies—4G LTE and 5G NR (New Radio), utilizing various network elements such as eNB (LTE base station), gNB (5G base station), 5G EPC (Evolved Packet Core), and 5GC (5G Core).

1. Voice and Data Handling in 5G: In regions where 5G is available and supports voice services, devices primarily use the 5G network (gNB) for both voice and data. The 5GC handles network functions, routing calls through the IP Multimedia Subsystem (IMS) for voice over IP services.
2. Switching to 4G LTE: When a device is in an area where the 5G network cannot support voice, or if it is not available, the device 'falls back' to the 4G network. This involves switching from the 5G base station (gNB) to the 4G base station (eNB) to access voice services.
3. Seamless Transition: This fallback does not affect data services significantly, as modern devices can maintain data connection over 5G while handling voice over the LTE network. This simultaneous connectivity ensures there is minimal disruption to the user experience.

The Role of Network Interfaces and Elements

• eNB (LTE Base Station): Connects devices to the LTE network, handling voice and data services through the EPS fallback mechanism.
• gNB (5G Base Station): Provides connectivity to the 5G network for both voice (where available) and high-speed data.
• 5G EPC and 5GC: These core networks handle data routing and network management for LTE and 5G networks, respectively. The EPC and 5GC are crucial for integrating network services and ensuring users receive uninterrupted service.
• IMS (IP Multimedia Subsystem): A key component in delivering voice over IP services across both 4G and 5G networks, facilitating high-quality voice calls.

Benefits of EPS Fallback

• Service Continuity: EPS Fallback ensures that users do not experience service interruptions, particularly for voice calls, as they move between areas with varying levels of 5G coverage.
• Network Flexibility: Provides operators with the flexibility to deploy 5G at different paces across regions without compromising voice service availability.
• User Experience: Maintains high-quality voice services and seamless connectivity, enhancing the overall user experience.

As 5G technology reshapes the telecommunications landscape, understanding its core components and their functions becomes essential. The integration of gNB (5G NodeB), 5GC (5G Core), and IMS (IP Multimedia Subsystem) demonstrates how modern networks handle voice and data seamlessly. Here’s an in-depth look at this configuration and its significance in the 5G network.

1. Introduction to 5G Components

The 5G network architecture is designed to offer not just faster data speeds but also higher efficiency and reliability for both voice and data transmission. This is achieved through a sophisticated network structure comprising the gNB, 5GC, and IMS, each playing a pivotal role in ensuring optimal service delivery.

2. gNB (5G NodeB)

• Functionality: The gNB serves as the primary base station in 5G networks, responsible for all radio-related functions. It facilitates the connection between user devices and the network, handling radio wave transmissions and receptions.
• Technology: Utilizing advanced beamforming techniques, gNB supports massive MIMO (Multiple Input Multiple Output) that significantly increases the capacity and efficiency of network communications.
• Role in Voice and Data: gNB is crucial for managing data throughput and ensuring robust connectivity for voice calls made over the network, leveraging the enhanced capabilities of 5G technology.

3. 5GC (5G Core)

• Overview: The 5G Core is the backbone of the network, responsible for overall control, management, and orchestration of network functions.
• Functionality: It processes data and voice packets, managing network slicing, which allows operators to provide customized network capabilities tailored to specific needs or applications.
• Seamless Integration: 5GC supports both standalone and non-standalone deployments, enabling it to operate independently or in conjunction with existing LTE networks.

4. IMS (IP Multimedia Subsystem)

• Purpose: IMS is a standardized architectural framework for delivering multimedia and voice services over IP networks.
• Voice Services: In 5G, IMS is critical for handling voice communications, allowing voice services to be delivered as data flows over the network, which simplifies and enhances the service quality.
• Advantages: With IMS, voice, and multimedia services can be delivered with lower latency and higher reliability, enhancing the user experience in 5G networks.

5. Operational Flow: From Voice/Data to Service Delivery

The interaction between these components can be visualized as follows:

• Voice and Data Request: The user’s device initiates a voice call or data session.
• gNB Interaction: The signal is first processed by the gNB, where it is prepared for transmission over the network.
• 5GC Processing: The 5GC receives the data from gNB and manages its routing, ensuring efficient handling of network resources.
• IMS Delivery: For voice calls, the IMS processes the voice data, converting it into a format suitable for transmission over IP, ensuring that the voice service is maintained with high quality and minimal delay.

Call Flow VONR.

User->>5G Device: Initiate Call
  5G Device->>gNB: Send INVITE
  gNB->>5GC: Forward INVITE
  5GC->>IMS: INVITE
  IMS-->>5GC: 183 Session Progress
  5GC-->>gNB: 183 Session Progress
  gNB-->>5G Device: 183 Session Progress
  5G Device-->>User: Ringing
  User->>5G Device: Answer Call
  5G Device->>gNB: 200 OK
  gNB->>5GC: 200 OK
  5GC->>IMS: 200 OK
  IMS-->>5GC: ACK
  5GC-->>gNB: ACK
  gNB-->>5G Device: ACK
  5G Device-->>User: Call Connected
  5G Device->>gNB: QoS Flow Setup
  gNB->>5GC: QoS Flow Setup
  5GC->>IMS: QoS Flow Setup
  IMS-->>5GC: QoS Flow Modification
  5GC-->>gNB: QoS Flow Modification
  gNB-->>5G Device: QoS Flow Modification
  5G Device-->>User: Voice Media Exchange
  User->>5G Device: Terminate Call
  5G Device->>gNB: Send BYE
  gNB->>5GC: Forward BYE
  5GC->>IMS: BYE
  IMS-->>5GC: 200 OK
  5GC-->>gNB: 200 OK
  gNB-->>5G Device: 200 OK
  5G Device-->>User: Call Terminated        

#include <iostream>
#include <string>

// Enum to represent the current state of the VoNR call
enum class VoNRState {
    IDLE,
    INITIATED,
    RINGING,
    CONNECTED,
    DISCONNECTED
};

// Function to simulate sending an INVITE message
void sendInvite() {
    std::cout << "Sending INVITE message to the network.\n";
}

// Function to simulate receiving a response
void receiveResponse(const std::string& response) {
    std::cout << "Received " << response << " response from the network.\n";
}

// Function to simulate setting up QoS flow
void setupQoSFlow() {
    std::cout << "Setting up 5GS QoS flow.\n";
}

// Function to modify QoS flow
void modifyQoSFlow() {
    std::cout << "Modifying 5GS QoS flow.\n";
}

// Main function to handle the VoNR call flow logic
int main() {
    VoNRState callState = VoNRState::IDLE;

    // Simulate user initiating a call
    std::cout << "User initiates the call.\n";
    sendInvite();
    setupQoSFlow();
    callState = VoNRState::INITIATED;

    // Simulate network responses
    receiveResponse("180 Ringing");
    callState = VoNRState::RINGING;

    receiveResponse("183 Session Progress");
    modifyQoSFlow();

    receiveResponse("200 OK");
    std::cout << "User answers the call.\n";
    modifyQoSFlow();
    callState = VoNRState::CONNECTED;

    // Simulate voice media exchange
    std::cout << "Voice media exchange starts.\n";

    // Simulate call termination
    std::cout << "Call terminated by user.\n";
    callState = VoNRState::DISCONNECTED;

    return 0;
}
        

C++ Code to perform a VONR Testing, output of the Code

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