Appendix C. Protocol Details

This appendix covers call signaling protocols and application protocols included in Cisco CallManager. Call signaling protocols support communication with trunks and endpoints, and application protocols enable the development of additional applications that complement CallManager functionality.

CallManager uses the following signaling protocols to communicate with its devices:

• H.323
• QSIG
• SIP (Session Initiation Protocol)
• Skinny Client Control Protocol (SCCP)

Signaling protocols provide an agreed-upon set of rules that define the format of messages used to transmit information and commands between devices.

This chapter addresses each of the signaling protocols in detail in the following sections:

• "H.323 Signaling" presents message details for Registration, Admission, and Status (RAS) and H.225 signaling described in Chapter 4, "Trunk Devices."
• "QSIG" presents message details for the QSIG feature-to-feature messages that CallManager uses for feature transparency. Chapter 4 provides an overview of QSIG.
• "SIP Signaling" presents the message headers that CallManager sends and receives over its SIP trunk interface, which is described in Chapter 4.
• "SCCP Call Signaling" presents an example message flow that CallManager uses when establishing calls to a Cisco IP Phone. Chapter 3, "Station Devices," describes Cisco IP Phones in more detail.