When a branch office is isolated, the Lotus Sametime Unified Telephony cannot provide feature service anymore, because it has no connectivity to the branch. In order to give the Lotus Sametime Unified Telephony still access to the branch office, the branch office can set up a backup data connection through the PSTN.
The data center router is configured to set up the IPSec/GRE VPN tunnels to the branch offices. Each tunnel gets a unique name that is recorded in the CAC group for the branch office that is served with the tunnel.Parent topic: Survivability Overview
The data center router must be configured to be highly available through the Hot Standby Router Protocol (HSRP). This means that each data center must have a redundant pair of Cisco™ 2800 or 3800 series routers.
The routing tables for a route to the branch office must be set up to try the IPSec/GRE VPN tunnel through the WAN to the branch office with highest priority (lowest metric) and use the dialer watch to check for establishment of the ISDN backup tunnel through the PSTN.
The link status manager process must listen for messages on virtual IP addresses assigned at configuration time with the NCPE tool. These IP addresses must be addresses from the administration subnet. In case of geographic node separation an IP address in each separated subnet must be assigned.
The Lotus Sametime Unified Telephony must implement a new process (Link Status Manager) that acts as a SNMP (v2c/v3) Manager for the data center router. The purpose of the link status manager will be to receive status-link up/down traps from the data center router delivered via the Inform Request message or as a trap. It must implement a white list of IP addresses that may send these SNMP messages to it.
The data center router must be set up to send reliable link status notifications for the IPSec/GRE VPN tunnel connections to the Link Status Manager of the Lotus Sametime Unified Telephony.
DID pool for correlation service. This can be created only if the branch office is a survivable branch office (indicated via the 'Survivable' attribute on the branch office's representative endpoint).
General Characteristics of the SBC Branch Office Solution