In its simplest form, this is the graceful shutdown procedure. Details and exceptions to this procedure when there are active calls or registrations are discussed in later paragraphs. The first six actions are performed whether or not the OCSBC is part of an Oracle Communications Subscriber-Aware Load Balancer (SLB) Cluster

• The OCSBC receives the set-system-state offline command.
• The OCSBC transitions to becoming offline mode.
• The OCSBC accepts calls and subscribes from registered endpoints.
• The OCSBC rejects calls from non-registered endpoints.
• The OCSBC rejects new registrations with a 503 Service Unavailable error message.
• The OCSBC checks the number SIP INVITE based sessions and number of SIP registrations. When both counts are 0, the OCSBC transitions to the offline state.

If the OCSBC is part of an SLB Cluster:

• The SLB client on the OCSBC changes its cluster status to shutdown state.
• The OCSBC informs the SLB that it is offline.
• The SLB ceases to forward new end-points to the OCSBC and puts the OCSBC in a shutdown state.
• SLB continues to forward all messages for existing registered endpoints to the offline OCSBC.
• The OCSBC continues to send heartbeat updates the SLB as before.