What is SS-7 Signaling System Number 7

SS-7 (Signaling System Number 7) Explained Technically

SS-7, also known as Signaling System Number 7 or Common Channel Interoffice Signaling (CCIS-7) in North America, is a set of telephony signaling protocols used in public switched telephone networks (PSTNs) worldwide. It plays a critical role in establishing, managing, and tearing down telephone calls, as well as enabling various network services beyond basic voice communication.

Here's a breakdown of the key aspects of SS-7:

Functionality:

SS-7 operates on a separate channel dedicated to signaling information (control plane) distinct from the voice channels carrying the actual conversation (user plane). This separation allows for efficient call setup, management, and network control without interfering with the voice communication itself.

Key Features:

• Call Setup and Tear Down: SS-7 facilitates the exchange of information between network elements (switches) to establish a call connection, including routing, number translation, and call progress information.
• Network Management: SS-7 enables functionalities like overload control, congestion routing, and alternate routing to optimize network performance.
• Supplementary Services: SS-7 supports various supplementary services like call forwarding, call waiting, caller ID, and call conferencing by exchanging control information between network elements.
• Mobile Network Integration: SS-7 plays a crucial role in integrating mobile networks with the PSTN, enabling seamless call handoff and mobility management.
• Short Message Service (SMS): SS-7 serves as the underlying signaling protocol for SMS, facilitating the exchange of control information for message routing and delivery.

Network Architecture:

SS-7 utilizes a layered network architecture with different entities performing specific functions:

• Signaling Point (SP): Represents a network element (switch) equipped with SS-7 capabilities and connected to other SPs through signaling links.
• Service Switching Point (SSP): An SP responsible for originating and terminating calls, interacting with user equipment (phones) and other network elements.
• Signal Transfer Point (STP): An SP specifically designed for routing signaling messages between other SPs within the network.
• Service Control Point (SCP): An optional database containing information for specific services like subscriber data, routing tables, and supplementary service configurations.

Benefits of SS-7:

• Improved Efficiency: Dedicated signaling channels enable faster call setup and network management compared to traditional in-band signaling.
• Enhanced Features: Supports a wide range of supplementary services and facilitates integration with mobile networks.
• Scalability: The layered architecture allows for network expansion and integration of new services.

Security Considerations:

• SS-7 was not originally designed with robust security features. Vulnerabilities have been identified, potentially allowing unauthorized access or manipulation of call routing.
• Implementing strong authentication and encryption mechanisms is crucial for securing SS-7 networks.

Evolution and Future:

• Newer signaling protocols like Diameter are being adopted for specific functionalities, but SS-7 remains a critical component of global telecommunication infrastructure.
• Ongoing efforts focus on improving SS-7 security and exploring integration with next-generation network architectures.

Conclusion:

SS-7, despite its limitations and security concerns, remains a vital technology in modern telephony networks. Its efficient signaling capabilities enable a vast array of communication services we rely on daily. Understanding SS-7 provides insight into the complex infrastructure that powers our phone calls and messaging services.