chan_sip

${SIPCALLID}         * SIP Call-ID: header verbatim (for logging or CDR matching)
${SIPDOMAIN}         * SIP destination domain of an inbound call (if appropriate)
${SIPFROMDOMAIN}       Set SIP domain on outbound calls
${SIPUSERAGENT}      * SIP user agent (deprecated)
${SIPURI}            * SIP uri
${SIP_MAX_FORWARDS}    Set the value of the Max-Forwards header for outbound call
${SIP_CODEC}           Set the SIP codec for an inbound call
${SIP_CODEC_INBOUND}   Set the SIP codec for an inbound call
${SIP_CODEC_OUTBOUND}  Set the SIP codec for an outbound call
${SIP_URI_OPTIONS}   * additional options to add to the URI for an outgoing call
${RTPAUDIOQOS}         RTCP QoS report for the audio of this call
${RTPVIDEOQOS}         RTCP QoS report for the video of this call