Channel-associated signaling (CAS) carries control signals in the same channels as voice and data signals. This arrangement differs from common channel signaling (CCS). With CCS, several voice-and-data channels share a separate channel used only for control signals.
CAS is also known as per-trunk signaling (PTS). It directs the payload of voice or data to its destination. The routing information encodes and transmits in the same channel as the payload. This information can transmit in the same band or a separate band to the payload. Call setup faces congestion since signaling channels share. CAS potentially lowers available bandwidth for the payload.
The CAS server handles client communication for Exchange. It provides mailbox access for multiple Exchange clients, except Outlook clients. The CAS routes mail between Exchange Server and external email systems. It also enables offline address book, autodiscover, and availability services. In Exchange 2013, CAS is one of three server roles along with Mailbox and Edge Transport. The CAS stores no data.
The robbed bit signaling technique makes each channel responsible for its own operation, called channel associated signaling (CAS) or in-band signaling. A channel bank converts 24 phone lines to one T1 line. It handles interfacing and conversion between analog and digital protocols.