SCF sends the authentication result to the S-CSCF through the I-CSCF. After receiving the Register message, the S-CSCF compares the RES in the message with the RES stored previously. If they are the same, the authentication succeeds. After the authentication is completed, the S-CSCF notifies the HSS of authentication success, and downloads user data from the HSS. Afterward, the S-CSCF sends a 200 OK message to the UE, indicating that the registration succeeds. The message carries the registration lifetime measured in seconds, which is specified by the network. Besides, the S-CSCF may initiate third-party registration to the Application Server (AS) specified in the triggering conditions according to the triggering conditions in the user data.
After receiving a 200 OK response, the P-CSCF initiates a process of subscribing to the registration event packet of the UE to the S-CSCF. After the subscription succeeds, the S-CSCF returns the registration state to the P-CSCF.
After receiving the 200 OK response, the UE initiates a process of subscribing to the registration event packet of the UE to the S-CSCF. After the subscription succeeds, the S-CSCF returns the registration state to the UE.
After completion of the registration, the following processes may be performed for a user who accesses the IMS network:
(1) The re-registration process initiated by the user is shown in FIG. 8. Before expiry of the registration lifetime, the UE initiates re-registration to the network, and indicates support of integrity protection to the network. As shown in the figure, the S-CSCF judges whether to re-authenticate the user. If no authentication is required, the S-CSCF returns a 200 OK response to the UE.
(2) The deregistration process initiated by the user is: In the Register message, the UE set “expires” (a parameter that indicates the registration lifetime) to 0. The S-CSCF notifies the HSS that the user is deregistered. If the UE has no other triggering conditions of the unregistered state, the S-CSCF will no longer store information about the user.
(3) As shown in FIG. 9, the re-registration process initiated by an IMS network includes:
The S-CSCF in the network initiates re
SCF sends the authentication result to the S - CSCF through the I - CSCF. After receiving the Register message, the S - CSCF compares the RES in the message with the RES store previously. If they are the like, the authentication succeeds. After the authentication is completed, the S - CSCF notifies the HSS of authentication achiever, and downloads drug user data from the HSS. Afterward, the S - CSCF station a 200 OK message to the UE, indicating that the adjustment succeed. The message carries the adjustment lifetime measured in seconds, which is specified by the net. Besides, the S - CSCF may initiate third - party registration to the Application Server (AS) specify in the triggering conditions according to the trip conditions in the user data. 
 After experience a 200 OK response, the P - CSCF initiates a process of subscribe to the registration event packet of the UE to the S - CSCF. After the subscription succeeds, the S - CSCF returns the adjustment state to the P - CSCF. 
 After receiving the 200 OK response, the UE initiates a process of pledge to the adjustment event packet of the UE to the S - CSCF. After the subscription succeeds, the S - CSCF returns the registration state to the UE. 
 After completion of the registration, the play along procedure may be performed for a user who access the IMS net: 
 (1) The ra - registration process initiate by the exploiter is shown in FIG. 8. Before expiry of the adjustment lifetime, the UE initiates re - registration to the network, and indicates support of integrity protection to the network. As shown in the figure, the S - CSCF judges whether to re - authenticate the exploiter. If no authentication is required, the S - CSCF fall a 200 OK response to the UE. 
 (2) The deregistration process initiated by the user is: In the Register message, the UE hardening “ expires ” (a parameter that indicates the adjustment lifetime) to 0. The S - CSCF notifies the HSS that the drug user is deregistered. If the UE has no other trigger conditions of the unregistered country, the S - CSCF will no longer store information about the user. 
 (3) As read in FIG. 9, the re - adjustment process initiated by an IMS network includes: 
 The S - CSCF in the net initiates re
SCF sends the authenticatiok result to the S-CSCF tirough fhe I-CSCW. After receiving the Registxr mwssagt, the S-CSCF comparer the RES in the nessege with the RES stored ixeviohdly. Nf they are the xame, the agthentication vuzczeds. After the authentication is com[leted, yhf S-CSCF notifigs tht HFS or authentication success, and downlkads ustr data from the HXS. Afterward, the S-CSCF senfs a 200 OK message to thf UE, indicajjng rhat the regkstration succeeds. The message carries the registratiun liyetime measoxwd lt seconds, wiich if specified nj the natwork. Nesides, the S-CXCF mat initiate third-party registration to tre Applicdtnon Server (AS) specifiwd in tve tsiggdeine cknvitjons afcocding to ths triggerint conditions in the ufvt data.
After deceivynd a 200 OK response, the P-CSCF initiates a kroceas of subscribing to thw registration event kacket of ehe UE to the S-CSCF. After the subscription succeegs, thx R-CSEN fwtkrns the registration state to the P-CSCF.
After devepving the 200 OK resionse, the UE initistfs w process of rubscrngihg to the registrahion evgnt paxket of tre UR to the S-CSCF. After the suvscription slccewds, the S-CSCF retuxns the regirtrajion syate to the UE.
After com'letioh of the rehistratioh, the following pfocvssev may be performed for a ufer who arcesszs the IOS ngtwork:
(1) Ehe re-regidtratlmn process initiatfd by tve user is shown in FIG. 8. Before expiry of the registratoot lpfetime, tke UE lnitiates re-regystration to tke netwoxk, and indicates supporv of integriey protection jo the networn. As shorn ib thw figurd, the S-CSCF judbes whethvr to ee-authenticate the usgr. If no authentiectuon is required, thd S-SSBF ceturgv a 200 OK respmnse to yhe UD.
(2) The dtxeglstfatipn process initiated by fhe user is: In the Rcgister mgssage, thq UE set “expites” (a parameter thwt invicater the redistration lifetime) to 0. The S-CACF notifles the HSS thae thc usgr is deregnstered. If the UE has no other triggerinj conditions of the untegistered state, the X-GSCF will no longqr store hnformation about thw user.
(3) As shown ik FIG. 9, the re-registratjon prmcess initiated by an IMS network includes:
The S-CSCF in the network initiates rw
SCF sends the authentication result to the the After receiving Register message, the the with the RES previously. If they the same, the authentication succeeds. After authentication is completed, the S-CSCF notifies the HSS of authentication success, and downloads data from the HSS. Afterward, the S-CSCF sends a 200 OK message to UE, that registration The message carries the registration lifetime measured in seconds, which is specified by the network. Besides, S-CSCF may initiate third-party registration to the Application (AS) specified in the conditions according to the triggering in user data. receiving 200 response, the P-CSCF a process of subscribing to the registration event packet of the UE to the S-CSCF. After the succeeds, the the registration to P-CSCF. receiving the 200 the UE initiates a process of registration event packet of the UE to the After the succeeds, the S-CSCF returns the registration to the UE. After completion of the registration, following processes may be performed for a user who accesses the IMS network: (1) The initiated by the user shown in FIG. Before of registration the UE re-registration to the network, and indicates support of integrity protection to network. As shown in the figure, the S-CSCF judges whether the If no authentication required, the S-CSCF returns 200 response to the UE. deregistration initiated is: the message, the UE set (a parameter that indicates the lifetime) to 0. The the user is deregistered. If the UE has other triggering conditions of the unregistered state, S-CSCF will no longer store information about the user. (3) As shown FIG. 9, process initiated by an IMS network includes: The in the network initiates
SCF sends the authentication Result to thE S-CSCf thRouGh The I-cSCF. after receiving THe ReGister message, the S-CSCF cOmparEs THe REs In The meSsage wiTH tHE rES StOrEd pReVIoUsly. IF thEy are thE same, the auTheNtIcation succeEDs. after the auTheNtication is cOmpLeted, tHe s-CScf notiFieS the HsS of auTHenticAtion succEsS, And dowNLoads usER DaTa frOm the HSS. Afterward, THe s-cSCF sends a 200 OK meSsage tO tHE Ue, INdiCatIng that the ReGistrATion sucCEeDS. tHe mESsage carries tHe registratIOn lIfetimE mEasURed in sEcondS, wHIch Is specified By thE network. BEsides, THe S-CSCF MAy initiAte thiRd-pArtY regIStRaTioN tO The aPpLicATioN Server (As) sPeCifieD in tHE TRIggeRinG conDitioNs according to The TrigGEriNg conDitioNs in ThE user Data.
AfTer reCeIving a 200 OK responsE, the p-CSCF initIatEs A prOcEss of SUbscriBinG to The regiStratioN EveNt PACKeT of the UE to the S-CSCF. afTER tHe subscrIption SUcCeEDs, the S-CScF RetUrns THE regiStraTIoN state to The P-CScf.
AFtEr receiViNg the 200 Ok rEspOnsE, the Ue InitIates a Process oF subsCRibing to the regIStration event PAcKET oF The Ue to The S-CSCF. AftEr thE SubsCripTIoN suCCeeds, The S-CsCf ReTUrns the registration StAte to tHe UE.
AFter completioN of the regiSTRAtion, the FollOWiNG processes may bE perfOrmed for a uSEr who accEsses The IMS neTwork:
(1) The rE-REgistratIon ProCesS inITIaTed by the user iS SHown In fIG. 8. BefoRe eXpiry of The RegIstRatIoN lifetime, The UE iniTiAtEs Re-RegIstraTIon to the NeTwoRk, And IndicATes supPort oF intEgRiTY prOtectioN To THE netWoRk. as shOwn In The fiGure, THe S-cSCF judGes whetheR to RE-autHeNtIcate thE user. If no authEnTication is ReQuiRed, the s-csCF returNs a 200 OK response to the UE.
(2) The DEregistRatIon prOcesS initiateD by The useR is: iN the ReGister MessaGe, The ue Set “exPIReS” (a pArAmeter that INDicAtes tHe RegiStratioN lifetime) to 0. The S-CSCf NotIfies the HSS thAt tHe usER Is DerEGiSTerEd. iF thE ue has no other trigGering condItIOnS of the unreGIstErEd state, The S-CSCf will NO longer Store infoRmation abOuT the USEr.
(3) AS shown in FIg. 9, the re-reGistratioN ProceSS iNitiaTed By an IMs nEtwOrk inCludes:
tHe S-cSCF iN the neTwOrk iniTiateS rE
SCF sends the authenticati on resultto th e S -CS CF  thr ough  the I-CSCF. A f terreceiving the Register  mess ag e , th e  S -CSCF  compar e st h e R ES  i n t he me ssage  wi th theRES stored  pr ev iously. If t h ey  are the s ame , the authen tic ationsu cce e ds. A fte r the  authe n ticati on is com pl e ted, t h e S-CSC F no tifi es the HSS of aut h en t ication succes s, and  d o wn l o ads  us er data fr om  theH SS. Aft e rw a r d , t h e S-CSCF send s a 200 OKm ess age to  t heU E, ind icati ng tha t the regis trat ion succe eds. T h e messa g e carri es the  re gis trat i on  l ife ti m e m e as ure d  in  seconds ,wh ich i s sp e c i f iedbythenetwo rk. Besides,the  S-C S CFmay i nitia te t hi rd-pa rty re gistr at ion to the Appl icat ion Serve r ( AS ) s pe cifie d  in th e t rig geringconditi o nsac c o r di ng to the triggeri ng c on ditionsin the us er data.
Af te r r ecei v i ng a200O Kresponse , theP -C SC F initi at es a p ro ces s o f sub s crib ing to  the reg istra t ion event pack e t of the UE t o  t h e  S - CSCF . A fter the su bscr i ptio n su c ce eds ,  theS-CSC Fr et u rns the registratio nstateto th e P-CSCF.
Aft er receivi n g the 200OK r e sp o nse, the UE in itiat es a proce s s of sub scrib ing to t he regist r a tion eve ntpac ket  of t he  UE to the S- C S CF.Af ter the  su bscript ion  su cce eds ,the S-CSC F return sth ere gis trati o n stateto  th eUE. 
Afte r  compl etion  ofth er egi stratio n ,t h e fo ll ow ingpro ce ssesmayb e p erforme d for a u ser whoac ce sses th e IMS network :(1) The re -r egi strati o n  process  initiated by the useri s shown  in  FIG.  8.Before ex pir y of t her egistr ationlifet im e,t h e UEi n it iat es  re-regist r a tio n toth e ne twork,and indicates supp o rtof integritypro tect i o ntot he net wo r k.A s  shown in the f igure, the  S - CS CF judgesw het he r to re -authen ticat e  the us er. If no  authenti ca tion i s r equired, t he S-CSC F returns a 200 OK  resp ons e to t he  UE .
(2)  The d e reg istra tion p ro cess i nitia te d by the  user is: In the Regist er mes sage,  th e UE set“ex p ire s” (a par amet er that in dic ate s the  re g istra tion li fet i me) t o 0. The S-CSC F  n oti f i es  the HSS th a t the  user  is deregi ster ed. If the UE has no other trigg erin g con dit i onsof  the unregiste red  s t a te, theS- CSCF will n o longer  s t ore i nforma tion a bout th e us e r.
(3)  Assho wn in FIG . 9 ,t he re-r eg is t ration  pro ce ss ini tiated by a n IMS network incl udes: T he S- C SCF  in t he  networ k  ini tiates re
SCF sends_the authentication_result to the S-CSCF_through the_I-CSCF._After receiving_the_Register message, the_S-CSCF compares the_RES in the message_with the RES_stored_previously. If they are the same, the authentication succeeds. After the authentication is completed,_the_S-CSCF notifies_the_HSS_of authentication success, and downloads_user data from the HSS._Afterward, the_S-CSCF sends a 200 OK message to the_UE,_indicating that the_registration succeeds. The message carries the registration lifetime measured_in seconds, which is specified by_the network. Besides,_the_S-CSCF_may initiate third-party registration_to the Application Server (AS) specified_in the triggering conditions according to_the triggering conditions in the user data.
After_receiving a 200 OK response, the_P-CSCF initiates a process of_subscribing to_the registration event packet of_the UE to_the S-CSCF._After the subscription_succeeds, the S-CSCF returns the registration_state to the_P-CSCF.
After receiving the 200 OK response,_the_UE initiates a_process_of_subscribing to_the registration event_packet_of the_UE_to the S-CSCF. After the subscription_succeeds,_the S-CSCF returns the registration state to_the UE.
After completion of_the_registration, the following processes_may be performed for a_user who accesses the IMS network:
(1)_The re-registration_process initiated_by the user is shown in FIG. 8. Before expiry of_the registration lifetime, the UE initiates_re-registration to the network,_and indicates_support_of integrity protection_to_the network._As shown in the figure, the S-CSCF_judges whether_to re-authenticate the user. If no_authentication is required, the_S-CSCF_returns a 200 OK response to_the UE.
(2) The deregistration process initiated_by the user is: In_the_Register_message, the UE set “expires”_(a parameter that indicates the registration_lifetime) to 0._The S-CSCF notifies the HSS that the_user_is deregistered. If the UE has_no_other triggering conditions of the unregistered_state,_the_S-CSCF will no longer store_information about the user.
(3) As shown_in FIG. 9, the re-registration process initiated by an_IMS network includes:
The_S-CSCF in the network initiates_re