In a communication between a mobile unit (UE) and a gateway general packet radio system (GGRS) support node (GGSN) wherein resource reservations setup protocol (RSVP) capabilities are shared there between by a session setup mechanism, preferably session initiation protocol (SIP) in which RSVP capabilities of the UE and GGSN are defined and exchanged. In addition, the SIP is utilized to identify the preferred RSVP mode of operation by negotiations. The SIP is utilized to indicate that : the UE is RSVP capable ; those media flows which are based on RSVP ; the preferred mode of operation i.e. either UE based RSVP signaling or GGSN proxy based RSVP signaling and to communication a final setup mode for RSVP signaling to the UE from policy control function (PCF). The SIP may also be employed to enable the UE and network to indicate intended quality of service (QoS) protocol during a call setup procedure. The SIP is further utilized to enable the terminating UE and/or network to indicate in their response the capability of supporting a particular QoS protocol, the call being rejected with a clear indication of the cause when the terminating network is not capable of supporting the proposed QoS protocol.