What is SGsAP SGs application part

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SGsAP (SGs Application Part) Explained Technically

SGsAP, or SGs Application Part, is a protocol used in telecommunication networks, specifically within the context of GSM (Global System for Mobile Communications) and UMTS (Universal Mobile Telecommunications System) networks. It operates on the SGs interface, which connects the Mobility Management Entity (MME) in the Evolved Packet System (EPS) with the Visitor Location Register (VLR).

Here's a detailed breakdown of SGsAP and its functionalities:

Understanding the Need for SGsAP:

• Traditional circuit-switched services like voice calls rely on dedicated signalling channels in GSM and UMTS networks.
• With the introduction of LTE (Long-Term Evolution), which utilizes an all-IP (Internet Protocol) core network, the need arose to maintain functionality for these circuit-switched services while leveraging the new packet-switched architecture.
• SGsAP facilitates this interworking by enabling the MME in the EPS to communicate with the VLR, which resides in the legacy circuit-switched core network (typically the MSC/VLR or MSC Server/VLR).

Functionalities of SGsAP:

• Paging for Non-EPS Services: SGsAP allows the MME to send paging messages to the VLR to locate UEs (User Equipments) that are not actively connected to the EPS (e.g., UEs only using SMS). These paging messages trigger the VLR to notify the UE about an incoming call or message.
• Location Updates for Non-EPS Services: When a UE with CS fallback capability (ability to switch between circuit-switched and packet-switched services) changes its location, SGsAP facilitates the exchange of location update information between the MME and VLR. This ensures the network can continue to reach the UE for non-EPS services.
• Alerting Procedures: SGsAP enables the MME to alert the UE about events like incoming calls or messages even when the UE is not actively using the EPS. This allows for seamless notification and service continuity.
• IMSI Detach from EPS Services: When a UE detaches from the EPS (e.g., powers off), SGsAP allows the MME to inform the VLR so the UE's location information remains updated within the circuit-switched core network.
• Mobility Management procedures (limited): SGsAP might also support basic mobility management functionalities like handover information exchange for UEs with CS fallback capability, but to a lesser extent compared to protocols used within the EPS itself.

Benefits of SGsAP:

• Maintains Circuit-Switched Services: SGsAP allows operators to continue supporting legacy circuit-switched services like voice calls and SMS over LTE networks, ensuring a smooth transition and continued service availability for users.
• Optimizes Network Resources: By offloading circuit-switched service signaling to the legacy core network, SGsAP frees up resources in the EPS for packet-switched data services, leading to improved overall network efficiency.
• Facilitates Interworking: SGsAP acts as a bridge between the new EPS and the existing circuit-switched core network, enabling seamless communication and service delivery for UEs utilizing both technologies.

Future of SGsAP:

• As LTE networks mature and voice over LTE (VoLTE) becomes more widely adopted, the reliance on traditional circuit-switched services is expected to diminish. This could potentially lead to a decrease in the significance of SGsAP in the long run.
• However, during the transition period and for networks supporting a mix of legacy and modern services, SGsAP remains a crucial protocol for ensuring service continuity and interworking.

Conclusion:

SGsAP plays a vital role in enabling the coexistence of circuit-switched and packet-switched services within LTE networks. It facilitates communication between the EPS and the legacy core network, allowing functionalities like paging, location updates, and alerting procedures for UEs using non-EPS services. While its importance might diminish in the future as networks evolve, SGsAP is currently a critical protocol for smooth operation and maintaining service availability for users.