When the remote user is a hard phone there is generally no support for a VPN connection at the phone and use of an SBC (Session Border Controller) to allow connection to the Telephony Control Server is necessary.
Even when use of VPNs is possible it is advantageous to use the SBC solution for remote users so that the difficulties of supporting and managing large numbers of VPNs are avoided. The SBC in the main office data center is given a publicly accessible URL and IP address, and the home workers use this as the address of their SIP Registrar and SIP Server for their SIP phones or SIP soft clients. The SBC also has a second IP address, and a separate LAN connection, in the corporate LAN, to communicate with the server.
The following redundancy considerations apply for remote users:
Lotus Sametime Unified Telephony cluster nodes are co-located in one data center (or geo-separated but in the same sub-net).Parent topic: SBC (Session Border Controller)
If a High Availability SBC cluster is deployed, then failure of one SBC is transparent to the branch users.
If a non-redundant SBC is used then failure of the SBC results in loss of service until the SBC is repaired.
Lotus Sametime Unified Telephony cluster nodes are geo-separated in different data centers with different sub-nets.
A data center outage requires the users to register with the SBC in the other data center before they can originate or receive new calls. In this scenario the phones must be configured with the IP addresses of the SBC's in both data centers and must register with the secondary SBC when connectivity to the primary SBC is lost.