rtcp.c shows how to configure a connection for RTCP using a multi command.

/*=================================================================================
        This function shows how to set the RTCP options for a connection.
        It configures the RTCP report granularity, sname and 
        enable simple RTCP (no indications, extended indications, etc ...)
=================================================================================*/
#include <vapi.h>
#include <gtl.h>
#include <msp.h>
#include <vapi/comcerto-rtcp-types.h>

int set_rtcp(U32 conn_id, int granularity, int sname_len, char *sname)
{
        VSTATUS result;
        void *config_message;
        struct _SDES_CNAME sdes_cname_options;
        struct _RTCP_ENA rtcp_ena;

        U32 response_len = DEFAULT_FIFO_MAX_SIZE;
        U8 device_response [DEFAULT_FIFO_MAX_SIZE];

        /* allocate a message to query the current options */
        config_message = VAPI_AllocateMessage(DEFAULT_FIFO_MAX_SIZE);
        if (config_message == NULL)
                return -1;

        /* build the command to set the rtcp options*/
        result = VAPI_SetMessage(config_message, CMD_CLASS_CONF_CHANNEL, CMD_TYPE_CONF_CHANGE, 
                        FC_SET_RTCP_GENERATION_GRANULARITY, 2, granularity, 1);
        if(result != SUCCESS)
                goto err;

        sdes_cname_options.length = sname_len;
        UT_MemCopy(&sdes_cname_options.sdes_cname, sname, sdes_cname_options.length);

        /* build the command to set the rtcp cname options*/
        result = VAPI_SetMessageFromBuffer(config_message, CMD_CLASS_CONF_CHANNEL, CMD_TYPE_CONF_CHANGE, 
                        FC_SDES_CNAME, 1 + (sdes_cname_options.length/2), (U16 *)&sdes_cname_options);

        if(result != SUCCESS)
                goto err;

        /* enable simple RTCP (no indication, extended indication, etc ...)*/
        rtcp_ena.param_4.word = 0x0000;
        rtcp_ena.param_4.bits.rtcp = RTCP_ENA_RTCP_ENABLE;

        /* build the command to set the rtcp cname options*/
        result = VAPI_SetMessageFromBuffer(config_message, CMD_CLASS_CONF_CHANNEL, CMD_TYPE_CONF_CHANGE, 
                        FC_RTCP_ENA, sizeof(struct _RTCP_ENA)/2, (U16 *)&rtcp_ena);

        if(result != SUCCESS)
                goto err;

        /* send the query, the response is stored in device_response*/
        result = VAPI_SendConnectionMessage(conn_id, (SMsg *)config_message, NULL, device_response, &response_len);

err:
        VAPI_FreeMessage (config_message);

        return result;

}