What is SSC (Session and Service Continuity)

Session and Service Continuity (SSC) Explained Technically

In 5G New Radio (NR) cellular networks, Session and Service Continuity (SSC) plays a vital role in maintaining ongoing communication sessions and services when a user equipment (UE) moves between different cells or experiences network changes. Here's a breakdown of the technical details and functionalities:

Challenges of Network Mobility:

• As a UE moves around, it might connect to different base stations (gNBs) within the network. This process, called handover, can potentially disrupt ongoing communication sessions if not managed effectively.
• Maintaining seamless service continuity during handovers is crucial for applications like voice calls, video conferencing, or ongoing data transfers.

Functionality of SSC:

• SSC is a set of mechanisms within 5G NR that aim to ensure minimal interruption or service degradation when a UE experiences a network change.
• It focuses on two primary aspects:
  • Session Continuity: This refers to maintaining the established data path between the UE and the core network during a handover. This ensures that ongoing data transfers or communication sessions are not abruptly terminated.
  • Service Continuity: This focuses on preserving the user experience of the specific service being used. For example, a voice call should remain uninterrupted during a handover.

Types of SSC Modes:

• 5G NR defines three different SSC modes, each offering varying levels of continuity based on the specific service requirements and network conditions:
  • SSC Mode 1 (Preserves Connectivity): This mode aims to maintain the existing data path and IP address allocation during a handover. This is the most seamless option but might not be feasible in all scenarios.
  • SSC Mode 2 (May Release and Re-establish): In this mode, the network may release the existing data path and IP address upon handover. The UE then needs to re-establish a new connection with the target gNB. This can introduce a short service interruption.
  • SSC Mode 3 (Changes User Plane Anchor Point): This mode prioritizes maintaining service continuity but might change the IP address or data path anchor point during handover. This can be suitable for delay-sensitive services like voice calls.

Decision on SSC Mode:

• The decision on which SSC mode to utilize is made dynamically based on several factors:
  • Type of service being used: For real-time services like voice calls, higher continuity (Mode 1 or 3) might be preferred.
  • Network conditions: Factors like handover complexity or congestion might influence the feasibility of maintaining the same data path.
  • UE capabilities: The specific SSC modes supported by the UE's chipset also play a role.

Benefits of SSC:

• Improved user experience: Minimizes service interruptions and maintains ongoing communication sessions during handovers.
• Increased network efficiency: By avoiding unnecessary session terminations and re-establishments, network resources are utilized more efficiently.
• Enhanced support for mobile applications: Enables seamless operation of various applications that rely on uninterrupted data connections.

Challenges of SSC:

• Maintaining session continuity, especially Mode 1, can be complex in some network scenarios.
• Balancing service continuity with network efficiency requires careful design and implementation.
• Interoperability between UEs and gNBs from different vendors is crucial for seamless SSC operation.

Future Directions:

• Ongoing research and development efforts focus on:
  • Enhancing the robustness and reliability of SSC mechanisms.
  • Supporting even more granular service continuity requirements for future applications.
  • Optimizing network signaling and procedures for efficient handover management with SSC.

Conclusion:

SSC is a critical technology in 5G NR networks, ensuring a smooth and uninterrupted user experience during network changes. Understanding its functionalities, different modes, and trade-offs is essential for appreciating the challenges and advancements in maintaining seamless communication in mobile environments.