SIP Registration Cache Limiting

Using SIP registration cache limiting for SIP endpoint access deployments, you can restrict the size of the SIP registration cache for the global SIP configuration.

You can implement this feature if you have been seeing issues where, either due to network failure scenarios or incorrect sizing of system capabilities, the Oracle® Enterprise Session Border Controller and/or the SIP registrar cannot support the number of registering endpoints. Although the Oracle® Enterprise Session Border Controller protects itself and the registrar against SIP REGISTER floods, conditions can still occur where too many legitimate endpoints attempt to register with the registrar via the Oracle® Enterprise Session Border Controller.

By enabling SIP registration cache limiting, you restrict the number of legitimate endpoints that can register. The Oracle® Enterprise Session Border Controller rejects any endpoints beyond the limit you set. If you do not want to use this feature, simply leave the reg-cache-limit parameter set to its default of 0, meaning there is no limit to the entries in the SIP registration cache.

When you limit the number of registered endpoints allowed in the Oracle® Enterprise Session Border Controller’s registration cache, the Oracle® Enterprise Session Border Controller analyzes each registration before starting to process it. First, the Oracle® Enterprise Session Border Controller checks the contact header to determine if it is already in the list of contacts for the user. If it finds the contact in its cache list, the Oracle® Enterprise Session Border Controller treats the registration as a refresh; it treats any other headers as new. Note that the Oracle® Enterprise Session Border Controller checks the message prior to making any changes to the cache because it must either accept or reject the message as a whole.

The Oracle® Enterprise Session Border Controller adds the number of new contacts to the number already present in the cache, and rejects any registration with a contact that would cause it to exceed its limit. Rejection causes the Oracle® Enterprise Session Border Controller to send a response communicating that its registration cache is full. The default response is the 503 Registration DB-Full message, but you can use the SIP response mapping feature to use another message if required.

You can set an option in the global SIP configuration that defines the value in the Retry-After header. The Oracle® Enterprise Session Border Controller sends this header as part of its rejection response when the registration cache is full. Another option sets the percentage of the registration cache size which, if exceeded, causes the Oracle® Enterprise Session Border Controller to send an alarm.