What is SSN Subsystem Number

SSN Subsystem Number Explained Technically

SSN (Subsystem Number) refers to a numbering scheme used within Signaling Connection Control Part (SCCP) communication protocols. SCCP is a core element for establishing and managing connections between network entities in telecommunication systems, particularly those employing Signaling System No. 7 (SS7). Here's a breakdown of the technical details of SSN:

Functionality:

• SCCP utilizes SSNs to identify and differentiate between various subsystems (applications) residing within a network element. It acts like a unique identifier for specific functionalities within a device.
• When establishing an SCCP connection, both parties specify the desired SSN in the message header. This allows the receiving entity to route the incoming message to the appropriate internal application or subsystem based on the designated SSN.

Numbering Scheme:

• SSNs are assigned integer values ranging from 1 to 255. However, there's a recommended allocation strategy:
  • Globally Standardized Range (1-31): These SSNs are pre-assigned for specific network functionalities like Mobile Switching Center (MSC) or Gateway MSC (GMSC) used in mobile communication networks. Standardizing these values simplifies interoperability between different network providers.
  • National Network Range (32-128 & 151-254): This broader range is allocated by national telecommunication authorities for specific national network applications.
  • Network Specific Range (129-150): This reserved range allows network operators to assign SSNs for internal, private applications within their own network infrastructure.

Benefits of using SSN:

• Efficient message routing: SSNs enable efficient routing of SCCP messages within a network element by directing them to the relevant subsystem based on the designated number.
• Simplified network management: Clear association of SSNs with specific applications simplifies network management tasks like monitoring, troubleshooting, and configuration.
• Interoperability: Globally standardized SSNs for core network functionalities promote seamless communication between networks from different providers.

Additional Considerations:

• The specific assignment of SSNs within the national network range (32-128 & 151-254) can vary depending on the national telecommunication standards and regulations.
• While SCCP is a core component of SS7, modern communication networks are increasingly transitioning to more secure protocols like Diameter. However, understanding SSNs remains valuable for those working with legacy SS7 networks or telecommunication protocols that utilize SCCP for message exchange.