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WCDMA Packet Switched (PS) Data Call Flow Explained

wcdma packet switch data call mobile communication protocol stack

This article provides an overview of the packet switched call flow (PS call/Data call) between a Mobile device (UE) and the network, compliant with the WCDMA standard.

​A WCDMA Packet Switched (PS) data call refers to the process by which UE (i.e. Mobile) establishes data session with WCDMA base station (NodeB). This mechanism offers internet browsing, email etc. It transmits data in packets rather than through continuous circuit switched connection.

WCDMA message flow

The figure depicts messages exchanged between UE and network during data call in WCDMA.It details the messages exchanged between Layer 3 entities on both sides. It also includes the channels used at Layer 1 to carry these messages over the air.

WCDMA packet switched data call flow

WCDMA Channels used

  • Logical Channels:

    • DCCH (Dedicated Control Channel): Carries control information.
    • DTCH (Dedicated Traffic Channel): Carries user data.​

  • Transport Channels:

    • DCH (Dedicated Channel): Used for dedicated data transmission.
    • HS-DSCH (High-Speed Downlink Shared Channel): Used for high-speed downlink data in HSDPA.​

  • Physical Channels:

    • DPDCH (Dedicated Physical Data Channel): Carries user data.
    • DPCCH (Dedicated Physical Control Channel): Carries control information.

WCDMA Packet Switched data call flow

Following steps describe WCDMA data flow.

  1. RRC Connection Establishment: The UE initiates RRC connection to network to begin communication.​
  2. Authentication and Security: The network authenticates UE and establishes security parameters.
  3. PDP Context Activation: The UE requests activation of PDP context, which includes assigning an IP address and defining QoS parameters.​
  4. Radio Bearer Setup: The network establishes radio bearers, which are logical channels configured to carry the user data with specified QoS.​
  5. Data Transfer: Once the setup is complete, data packets are transmitted between the UE and external network through the established bearers.​
  6. Session Termination: When the data session ends, the PDP context is deactivated, and the radio bearers are released.

Conclusion

Understanding the WCDMA PS data call process is crucial to optimize network performance and to ensure efficient delivery of data services to users.