Embodiments herein provide methods and systems for performing paging operation in 5G communication networks. The 5G core network can transmit a NAS message to a UE through a N3GPP access network, if the UE is reachable through the N3GPP access network. The NAS message can be sent by the 5G core network to the N3IWF. The N3IWF can send the NAS message to the UE, through the N3GPP access network. The UE can send a service request over 3GPP access, in response to the NAS message, to the 5G core network, through a 5G RAN. If the UE is not having access to the 5G RAN, then the UE can transmit a notification response message to the 5G core network, indicating the inability to transmit a service request. The transmission of NAS message through the N3IWF can lead to a significant saving of radio resources.