Which device is the initiator of a StationD message in a Cisco Unified Communications Manager SDI trace?

C.

All messages to and from a skinny device are preceded by either the words StationD or StationInit.

StationD messages are sent from call manager to IP phone.

Skinny message transmission such as this between the IP phone and CallManger occurs for every action undertaken by the IP phone, includinginitialization, registration, on-hook, off-hook, dialing of the digits, key press on the phone, and so much more.

In a Cisco Unified Communications Manager (CUCM) Session Description Protocol (SDP) Interface (SDI) trace, a StationD message refers to a message sent between the CUCM and an endpoint, typically an IP phone or a gateway, to set up or tear down a call.

The initiator of a StationD message depends on the type of endpoint involved in the call.

For SCCP (Skinny Client Control Protocol) IP phones, the initiator of a StationD message is the IP phone itself. SCCP is a proprietary protocol used by Cisco IP phones to communicate with the CUCM, and the IP phone sends StationD messages to the CUCM to request call setup, teardown, or other call control functions.

For SIP (Session Initiation Protocol) IP phones, the initiator of a StationD message is also the IP phone itself. SIP is an industry-standard protocol used by many different types of endpoints, and SIP IP phones send SIP INVITE messages to initiate calls, which are translated into StationD messages by the CUCM.

For MGCP (Media Gateway Control Protocol) analog gateways, the initiator of a StationD message is the CUCM. MGCP is a protocol used to control analog gateways, and the CUCM sends StationD messages to the gateway to request call setup or other call control functions.

For digital voice gateways, the initiator of a StationD message can be either the CUCM or the gateway itself, depending on the specific configuration. Digital voice gateways support a variety of protocols, including MGCP, SIP, and H.323, and the way in which they interact with the CUCM can vary depending on the protocol and the specific implementation.

Therefore, the correct answer to the question is C. Cisco Unified Communications Manager, as the initiator of a StationD message depends on the type of endpoint involved in the call, and can be the CUCM itself, the IP phone or the gateway.