Session State Registrar Overview
The Session State Registrar (SSR) solution implements a stateless, highly reliable and highly available cluster. It separates front end processes from back-end data functions that take place on two or four data servers. Multiple C Series Controllers collaborate and perform different aspects of operation within the cluster to provide a common sessions database in a highly-available, redundant environment. The common shared resources of the cluster can be accessed simultaneously by up to twenty-four C Series Controllers acting as SSR clients.
The front-end SSR client hosts and SSR back-end data servers collaborate to provide:
Session state preservation during failover of front-end client nodes
Application session awareness
When used in conjunction with an MX Series router running the packet-triggered subscribers and policy control (PTSP) solution, the SSR stores the IP edge attachment sessions learned from IP edge devices in the centralized SSR database. The IP edge session stored in the SSR database can be used by the SAE to map the sessions received from the MX Series router. An IP edge session is uniquely identified by IP address and VPN ID, and includes subscriber identity information, which is used to locate the subscriber profile for MX sessions that have the same subscriber IP address.
To work efficiently and to provide redundancy, a production SSR cluster must be built on a fast, isolated, redundant network infrastructure. It must include multiple hosts so a single point of failure does not prevent the cluster from operating.