What is STN-SR Session transfer number single radio

STN-SR (Session Transfer Number for Single Radio Voice Call Continuity) Explained Technically

Within mobile communication networks, STN-SR plays a crucial role in enabling Single Radio Voice Call Continuity (SRVCC). Here's a breakdown of the key technical details:

Understanding SRVCC:

• Single Radio Voice Call Continuity (SRVCC): This technology allows a mobile call to seamlessly transition between a Voice over LTE (VoLTE) call on the LTE network and a traditional circuit-switched voice call (CS call) on the UMTS (3G) network, all while using a single radio interface on the user equipment (UE).
• Benefits of SRVCC: It ensures uninterrupted voice calls when moving between areas with strong LTE coverage and areas with limited LTE but good UMTS coverage.

Role of STN-SR:

• Session Transfer: During SRVCC, the voice call session needs to be transferred from the LTE network (evolved Packet Switched Domain - EPS) to the UMTS network (Circuit Switched Domain - CS).
• Signaling and Routing: STN-SR acts as a routing number used by the network to facilitate this session transfer process. It carries information about the ongoing voice call session and helps establish the connection on the UMTS network.
• MSC Server Involvement: The Mobile Switching Center (MSC) server within the UMTS network plays a vital role. Upon receiving the STN-SR along with relevant call information, the MSC server initiates the handover process and sets up the CS call connection.

Technical Specifications:

• Standardization: STN-SR is defined in 3GPP technical specifications, particularly 3GPP TS 23.003 (Identifiers for ISC and SRVCC) and related documents.
• Format: STN-SR typically follows the ITU-T Recommendation E.164 format, which is the same format used for international telephone numbers. However, in the context of SRVCC, it doesn't represent a publicly dialable phone number.

Benefits of Utilizing STN-SR:

• Seamless Call Transitions: STN-SR facilitates smooth handover of voice calls between LTE and UMTS networks, minimizing call drops and ensuring continuity of the conversation.
• Efficient Network Management: The use of STN-SR enables the network to efficiently manage call sessions and resources during SRVCC handovers.

Additional Considerations:

• Security: While STN-SR itself is not directly related to voice call security, the overall SRVCC process should adhere to established security protocols for voice calls on both LTE and UMTS networks.
• Alternative Approaches: Newer cellular standards like LTE-Advanced (LTE-A) might utilize different signaling mechanisms for SRVCC handovers, potentially reducing reliance on STN-SR. However, STN-SR remains relevant for legacy SRVCC implementations.

Understanding STN-SR is valuable for engineers working on:

• Cellular network core network functionalities and call management procedures.
• Mobile network handoff mechanisms and Single Radio Voice Call Continuity (SRVCC).
• Optimizing voice call service continuity and handover performance in mobile networks.

By facilitating efficient session transfer between networks, STN-SR plays a key role in ensuring seamless voice call continuity during SRVCC handovers, enhancing user experience in mobile communication networks.