Through analyzing the security of SIP

combining PKI technology

digital time authentication

digital certifi-cate and the characteristic of SIP network

the safe communicated model of SIP network based on improved SIP protocol was put forward.New call established protocol was constituted used the primary flow for reference

new register protocol and roam register protocol were constituted

time synchronization protocol and negotiating key protocol was added for this model

and test the safe communicated model in real circumstance.The result of the experiment proved that this model improved the confidentiality

integrality

usability

non-repudiation and novelty of the SIP network with the millisecond delay which can be accepted.