In general, this disclosure relates to the establishment of communication sessions between communication devices. In particular, this disclosure describes techniques that provide for quality of service (QoS) aware establishment of communication sessions. As an example, a communication device may attempt to reserve QoS for one or more codecs using a QoS reservation procedure corresponding to the access technology of an access network via which the communication device accesses a core network. The communication device selects one or more codecs to include in a call control message, such a Session Description Protocol (SDP) message, based on the QoS reservation and a QoS mode of the device.