Please see http://trac.pjsip.org/repos/ticket/950 for the spec. To enable socket QoS tagging with PJSUA-LIB, just set "qos_type" and/or "qos_params" in pjsua_transport_config [http://www.pjsip.org/pjsip/docs/html/structpjsua__transport__config.htm] Cheers Benny