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wifi calling call flow

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Wi-Fi calling, also known as Voice over Wi-Fi (VoWiFi), allows users to make and receive phone calls using a Wi-Fi network rather than a cellular network. This is particularly useful in areas with poor cellular coverage but a strong Wi-Fi signal. The call flow for Wi-Fi calling involves several steps to ensure a seamless user experience. Here's a technical breakdown:

1. Initial Network Attachment:

  • Device Initialization: When a user activates Wi-Fi calling on their device (smartphone), the device will initiate a Wi-Fi connection, either automatically or upon manual selection of a Wi-Fi network.
  • Authentication and Association: The device goes through the standard Wi-Fi authentication and association process with the Wi-Fi access point (AP). This involves exchanging Wi-Fi credentials, typically using WPA2-PSK or more advanced security protocols.

2. Access Point to Network Core:

  • Wi-Fi Gateway: The Wi-Fi access point forwards the VoWiFi traffic to the network's core infrastructure. This might involve tunneling mechanisms like IPsec or similar protocols to ensure security and quality of service.

3. Authentication and Authorization:

  • AAA Server Interaction: The core network interacts with Authentication, Authorization, and Accounting (AAA) servers. This is to authenticate the user and authorize their access to the voice service over Wi-Fi.

4. Establishing the Call:

  • SIP Signaling: Once authenticated, the device initiates a Session Initiation Protocol (SIP) call setup. SIP messages (like INVITE) are exchanged between the device and the VoWiFi server to establish the call.
  • Media Negotiation: After SIP signaling, the devices negotiate media parameters like codec selection (e.g., AMR-WB for HD voice) to determine how the voice data will be encoded and decoded.

5. NAT and Firewall Traversal:

  • Traversal Techniques: If the user's device is behind a Network Address Translation (NAT) or firewall, techniques like Session Traversal Utilities for NAT (STUN), Traversal Using Relays around NAT (TURN), or Interactive Connectivity Establishment (ICE) may be used to ensure that the voice packets can traverse these network barriers.

6. Call Termination:

  • End of Call: When either party decides to end the call, the SIP session is terminated, and any associated resources (like media streams) are released. A SIP BYE message is typically exchanged to signal the end of the call.

7. Quality of Service (QoS):

  • QoS Parameters: Throughout the call flow, Quality of Service mechanisms are applied to prioritize VoWiFi traffic over the Wi-Fi network. This ensures low latency, minimal jitter, and high voice quality.

8. Supplementary Services:

  • Additional Features: Wi-Fi calling may support supplementary services like call waiting, call forwarding, and multi-party conferencing. These are managed through additional SIP messages and backend server logic.

9. Billing and Logging:

  • CDR Creation: Call Detail Records (CDRs) are generated to log details of the Wi-Fi calls. This includes call start time, duration, involved parties, and other relevant information for billing and analytics purposes.

Conclusion:

The above steps provide a high-level technical overview of the Wi-Fi calling call flow. The actual implementation might vary based on the specific network architecture, equipment vendors, and service providers. The key is to ensure seamless integration between Wi-Fi networks and the traditional cellular infrastructure to deliver a consistent and reliable voice service over Wi-Fi.