This feature preserves stable bearer connections for TDM endpoints and IP stations during an upgrade of duplex servers. TDM and IP connection of branch gateways, with the duplex servers being the main call controller, are also preserved.

This feature is supported on all duplex servers and all port networks. It applies when upgrading to a newer release of Communication Manager.

This feature is not call preserving and only preserves connection on stable calls. Connection preservation does not apply to calls involving H.323 IP trunks; these are H.323 IP calls and SIP calls. Connection preservation does not apply to IP trunks and ISDN-BRI stations and trunks using branch gateway resources.