When Lotus Sametime Unified Telephony nodes are geographically separated between two data centers for redundancy purposes then an SBC (Session Border Controller) is required at both data centers.
In order for SIP registration data to be synchronized in real-time between the SBC's in the two data centers a layer 2 connection is required between the SBC's.
The AcmePacket SBC can use a layer 3 IP connection but maximum packet delay that can be tolerated is 50 ms.
If a connection between the SBC's that meets the above requirements is not possible, or if the two data centers are not within the same sub-net, then failover from the primary data center to the secondary data center involves a loss of VoIP connectivity for the users until the users re-register with the secondary data center.
In this scenario the remote user phones must be configured with the IP address of both the primary SBC and the secondary SBC (or use DNS to obtain both IP addresses) and must be able to register with the secondary SBC after detecting failure to communicate with the primary SBC. For this failure scenario remote users will not be able to receive incoming calls until the registration refresh time expires, or until they attempt an outgoing call (which will initiate a re-registration with the other SBC).
The SBC should be configured with a short registration refresh interval on the access side to minimize the outage interval. It is recommended that the short registration interval be 60 seconds, or if in the case of NAT, 30 seconds. Network planning must take account of remote users sending SIP REGISTER requests at such short intervals.
For TLS (Transport Layer Security) transport the Lotus Sametime Unified Telephony "connectivity-check" mechanism is not supported. SIP clients may be configured to support the "connectivity-check" but will not receive any support indications for remote users, and are required to provide alternative TLS connectivity checking based on a shortened SIP registration interval controlled by the SBC. The lack of a registration response allows a new TLS connection to the secondary SBC and/or Telephony Control Server to be quickly established and a new registration request sent to the Telephony Control Server to minimize the time that a user is unreachable following a failover.
System Specific Information
The following figures show the principles of geographic separation when central SBCs are involved as well as some examples of SBC deployments with Geographically Separated Lotus Sametime Unified Telephony nodes:
Parent topic: Additional SBC (Session Border Controller) Capabilities
The following figure illustrates the redundancy capabilities when both Lotus Sametime Unified Telephony nodes and the central SBCs are in the same subnet with full layer 2 connectivity between the network elements:
The following figure illustrates the redundancy capabilities when the Lotus Sametime Unified Telephony nodes and the central SBCs are in the different data centers with different subnets and only layer 3 connectivity between the data centers:
The following figure illustrates the typical physical interconnections in a geographically separated scenario where both data centers are in the same subnet with layer 2 connectivity between the data centers:
The following figure illustrates the typical physical interconnections in a geographically separated scenario where the data centers are in different subnets with only layer 3 connectivity between the data centers:
The following figure illustrates the physical connections at the Acme Packet SBC when two SBCs are used in a high availability configuration with both Lotus Sametime Unified Telephony nodes and SBC nodes in the same subnet: