What is SSAC Service Specific Access Control

SSAC: Service Specific Access Control Explained Technically

Within the realm of mobile communication networks, Service Specific Access Control (SSAC) is a mechanism implemented in the Evolved Packet System (EPS), specifically targeting Universal Mobile Telecommunications System (UMTS). It allows operators to control access to the network based on the type of service being requested. Here's a breakdown of its technical details:

Motivation for SSAC:

• In emergency situations like earthquakes or tsunamis, a surge in mobile originated voice calls can lead to network congestion, potentially hindering communication for critical services.
• SSAC addresses this challenge by providing a way to differentiate between bandwidth-intensive voice calls and data services.

Functionality:

• SSAC allows the network operator (Visited Public Land Mobile Network - VPLMN) to selectively restrict access to the network for specific service types (typically voice calls) during congestion scenarios.
• This control is achieved by utilizing Access Class Barring (AC Barring) parameters within the System Information Broadcast (SIB) messages.
• The UE (User Equipment) receives these SIB messages and interprets the AC Barring parameters to determine whether access for a particular service type (e.g., voice calls) is barred or allowed.

Implementation Details:

• SSAC operates within the EPS domain, which is packet-switched (PS) based.
• Traditional Domain Specific Access Control (DSAC) used in UMTS targeted circuit-switched (CS) services and wasn't applicable to EPS.
• SSAC defines specific features for controlling access to different service types within the EPS domain.
• The network operator configures the AC Barring parameters in the SIB messages to control access for:
  • Mobile Terminated (MT) voice calls (MMTEL voice)
  • Mobile Originated (MO) voice calls (MMTEL voice)
  • Video calls (MMTEL video)

Benefits of SSAC:

• Prioritization of Critical Services: During network congestion, SSAC allows operators to prioritize access for emergency voice calls or other critical services by barring access to less critical services like data.
• Improved Network Performance: By managing access based on service type, SSAC can help mitigate network congestion and maintain acceptable performance for essential services.
• Flexibility: Operators can configure SSAC parameters to suit their specific needs and network conditions.

Limitations of SSAC:

• Granularity: SSAC offers limited control compared to more sophisticated access control mechanisms. It primarily differentiates between voice and data services.
• Impact on User Experience: Barring access to certain services, even temporarily, can negatively impact user experience.
• Triggering and Deactivation: The mechanism for triggering and deactivating SSAC during congestion scenarios needs careful consideration to avoid unnecessary service disruptions.

Evolution of Access Control:

• SSAC served as an initial step towards service-specific access control within EPS.
• More advanced techniques like Dynamic Spectrum Access (DSA) are being explored for more efficient and dynamic spectrum utilization, potentially leading to more granular control over access for various service types.

Conclusion:

SSAC provides a valuable tool for mobile network operators to manage network congestion during emergencies by prioritizing critical services. Understanding its technical details and limitations is essential for appreciating its role in maintaining network performance and ensuring communication continuity in critical situations.