Methods in OMA SEC_CF for providing security services to traffic over UDP between a client and a server and the relevant entities are provided. A pre-shared key is pre-shared between the client and the server. A pair of IPSec ESP SAs between the client and the server is established without shared key negotiation, wherein traffic data cryptographic algorithms are determined. Traffic data security keys are derived from the pre-shared key via the determined traffic data cryptographic algorithms. Then, data of the traffic can be provided with security services with the traffic data security keys through use of IPSec ESP.