CMS and Communication Manager connect using a data link that implements a proprietary binary protocol called the Switch Processor Interface (SPI). Access is controlled by IP address. Communication Manager sends ACD configuration information and ACD-related events to CMS using this proprietary protocol over the communication channel.

Beginning with CMS Release 19.1, the SPI data link is encrypted using TLS 1.3 when the CMS is connected to a Communication Manager Release 8.1.2.0 or newer system. Before these specific versions of CMS and Communication Manager, SPI link encryption was not available.