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voice over wifi call flow

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Voice over Wi-Fi (VoWiFi) allows users to make voice calls using a Wi-Fi connection instead of a traditional cellular network. The call flow for VoWiFi involves several steps and protocols.

Below is a technical explanation of the call flow:

  1. Device Registration and Authentication:
    • The user's device connects to a Wi-Fi network and performs initial authentication.
    • The device may use protocols like EAP (Extensible Authentication Protocol) to authenticate itself with the Wi-Fi network.
  2. IMS Registration:
    • The device establishes a connection with the IP Multimedia Subsystem (IMS) network.
    • It uses the IPsec (Internet Protocol Security) protocol to create a secure tunnel to the IMS network.
  3. SIP Signaling:
    • The device initiates a Session Initiation Protocol (SIP) session by sending a REGISTER request to the IMS network.
    • This request includes the user's identity, capabilities, and location information.
    • The IMS network responds with a 200 OK message, indicating successful registration.
  4. User Location Retrieval:
    • The IMS network may retrieve the user's location information from the Home Subscriber Server (HSS) or another location repository.
    • This information is crucial for call routing and management.
  5. Call Establishment:
    • When a user initiates a voice call, the device sends an INVITE message to the IMS network.
    • The INVITE message contains details such as the called party's identity, codecs supported, and session description information.
    • The IMS network processes this request and determines the appropriate routing for the call.
  6. Media Negotiation and Setup:
    • Once the call is accepted, the IMS network sends a 200 OK response back to the device.
    • The devices negotiate codecs and other parameters for the media stream (audio in this case) through the SDP (Session Description Protocol) included in the SIP messages.
    • Secure Real-time Transport Protocol (SRTP) may be used to encrypt the voice data to ensure security.
  7. Voice Transmission:
    • The voice data is transmitted between devices over the established Wi-Fi connection.
    • RTP (Real-time Transport Protocol) is used to transmit the voice packets.
    • The devices continuously exchange RTP packets containing encoded voice data.
  8. Call Termination:
    • When the call ends, either party sends a BYE message to terminate the call.
    • The IMS network acknowledges this message with a 200 OK response, and resources allocated for the call are released.
  9. Session Termination:
    • The device sends a SIP message to the IMS network to deregister from the network when the user leaves the Wi-Fi coverage or switches off VoWiFi calling.