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SSR Cluster Overview


A standalone SBR Carrier server runs the entire AAA process using a local session database process on a single machine.

The SSR module helps you implement a highly reliable and highly available session database. The SSR module enables the AAA functions that are running on two or more RADIUS servers in a clustered environment to use a common session database, making the RADIUS servers stateless.

The RADIUS server and session database collaborate to create a single virtual AAA server that provides:

  • High availability

  • State preserved during failover between front-end SBR Carrier nodes

  • Application session awareness

  • Centralized IP address management

  • Centralized concurrency management (if the optional Concurrency and Wholesale Module is installed on all SBR Carrier servers)

To work efficiently and to provide redundancy, a production SSR cluster must be built on a fast, isolated, and redundant network infrastructure. It must include multiple hosts and nodes so a single node failure cannot prevent the cluster from operating.

Because the SSR database contains detailed attributes for each session it serves, it is a logical source for applications that query the AAA environment for correlative and verification purposes. The default SSR database schema addresses standard requirements for most wireless and wireline service providers. It can also be customized to address unique requirements or to support other applications. For example, a video portal or streaming server would know the IP address of a session but needs to discover the user identity attached to the session for billing or personalization. The video gateway can query the SSR database in real time to correlate information about any active session.

RADIUS Class Attributes are part of the RADIUS standard, but not all network access servers (NAS) fully support them. In order for the SSR to reliably track sessions throughout each session’s lifetime, the network NASs must support the Radius Class Attribute.


During a multinode failure of the cluster, the stability of SBR Carrier may be affected. You can use the auto-restart module (radiusd script) to mitigate such events.