the following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention as defined by the claims and their equivalents . it includes various specific details to assist in that understanding but these are to be regarded as merely exemplary . accordingly , those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention . in addition , descriptions of well - known functions and constructions may be omitted for clarity and conciseness . the terms and words used in the following description and claims are not limited to the bibliographical meanings , but , are merely used by the inventor to enable a clear and consistent understanding of the invention . accordingly , it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention is provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents . it is to be understood that the singular forms “ a ,” “ an ,” and “ the ” include plural referents unless the context clearly dictates otherwise . thus , for example , reference to “ a component surface ” includes reference to one or more of such surfaces . the term ‘ terminal ’ as used herein may refer to a phone that a user can carry with him or her , and on which a voice service is possible over the packet network . the terminal may include , for example , a smart phone , a cellular phone , a tablet computer , and the like , and can access the network using , for example , wi - fi communications , 3rd generation ( 3g ) communications , long term evolution ( lte ) communications , and the like . in accordance with an exemplary embodiment of the present invention , while processing a volte call , a terminal prevents , if possible , an ap from waking up ( e . g ., transitioning to an active state ) to handle a message ( e . g ., an sip update request message ) which is received from the network and used to determine whether the terminal normally accesses the network . as a result , the power consumption of the terminal may be reduced . fig3 illustrates a structure of a terminal according to an exemplary embodiment of the present invention . referring to fig3 , the terminal includes an application processor ( ap ) 300 , a session inter - process communication ( sipc ) 320 and a communication processor ( cp ) 330 . the ap 300 includes an ip multimedia core network subsystem ( ims ) stack 315 in an ims library 310 . the ap 300 may also include a transfer control protocol / internet protocol ( tcp / ip ) 305 . in accordance with an exemplary embodiment of the present invention , the ims stack 315 does not handle sip update messages . the ims stack 315 is in charge of signaling related to network elements , and bearer setup . the ims stack 315 may exchange multimedia - type content such as photos , video clips , sound clips , and the like with the network using session - based messages , because the ims stack 315 processes various types of packet data services based on the ip transport protocol . in addition , during initial voice over lte ( volte ) call setup , the ims stack 315 in the ap 300 transfers a parameter for handling an sip update request message to an sip processor 338 in the cp 330 by session refresh inter process communication ( ipc ). the parameter for handling an sip update request message may include ‘ timer value ’, ‘ ip address info .’, ‘ destination port info .’ and the like , which are defined in table 1 below . the sipc 320 is a protocol for handling message exchange between the ap 300 and the cp 330 . the cp 330 may also include an sipc that is responsible for the communication ( or message exchange ). data exchanged between the ap 300 and the cp 330 may include circuit switched video telephony ( cs vt ), packet switched video telephony ( ps vt ), pulse code modulation ( pcm ) data , ps data , and the like that use a raw channel , such as the sipc message . the data exchanged between the ap 300 and the cp 330 may also include a formatted packet channel and an rfs packet channel . each channel is sent to a related processing block in a driver . if control and data delivery between the ap 300 and the cp 330 is needed , the sipc 320 may be used . if the ap 300 sends a message via the sipc 320 , an sipc block of the cp 330 receives the message . thereafter , the sipc block analyzes the message and delivers the analysis results to a related block in the form of a message . each of the parameters included in the message is stored in the form defined in advance with the processing block , and thereafter delivered ( e . g ., later on ). referring to table 1 , an ims refresh session message is defined . the ims refresh session message is determined based on 0x07 in a sub cmd field that the message corresponds to an ims refresh session message . the sipc block calls a relevant function depending on 0x1 ( start ), 0x2 ( stop ), and 0x3 ( init ) in an operation field . the cp 330 includes a voice engine 332 , a pdcp filter 334 , a tcp / ip 336 , and the sip processor 338 . the pdcp filter 334 performs filtering on the received voice packet and / or sip message . upon receiving an sip message from the network , the pdcp filter 134 according to the related art ( e . g ., as illustrated in fig1 ) sends the received sip message from the cp 130 of the terminal to the sip stack 115 in the ap 100 . however , according to exemplary embodiments of the present invention , the pdcp filter 334 operates as follows . an exemplary embodiment of the present invention in which there is no terminal user input will is described below . according to exemplary embodiments of the present invention , upon receiving a voice packet from the network , the pdcp filter 334 transfers the received voice packet to the voice engine 332 via the tcp / ip 336 . the voice engine 332 processes the received voice packet and transmits the received voice packet via the tcp / ip 336 . processing the voice packet received from the network may be formed in a similar or same way as the procedure according to the related art . in contrast , upon receiving an sip message , the pdcp filter 334 determines whether the received sip message corresponds to an sip update request message . in other words , the pdcp filter 334 extracts an sip update request message . if the received sip message corresponds to an sip update request message , the pdcp filter 334 sends the sip update request message to the sip processor 338 in the cp 330 via the tcp / ip 336 , instead of sending the sip update request message to the ap 300 . upon receiving the sip update request message , the sip processor 338 generates a response message ( e . g ., an sip update response message ) to the sip update request message , and sends the response message to the network via the tcp / ip 336 . fig4 is a flowchart illustrating an operation of a terminal according an exemplary embodiment of the present invention . referring to fig4 , an operation of a terminal that consumes relatively low power ( e . g ., to process an sip protocol ) according an exemplary embodiment of the present invention is illustrated . it will be assumed that before step 401 , during initial volte call setup , the ims stack 315 in the ap 300 transfers a parameter for handling an sip update request message to the sip processor 338 in the cp 330 by session refresh ipc . in step 401 , in a situation in which there is no terminal user input , the pdcp filter 334 receives an sip message / voice packet from the network . in step 403 , the pdcp filter 334 determines whether the received sip message corresponds to an sip update request message based on an sip protocol . if the pdcp determines that the sip message corresponds to an sip update request message in step 403 , then the pdcp proceeds to step 405 in which the pdcp filter 334 sends the sip update request message to the sip processor 338 in the cp 330 via the tcp / ip 336 , instead of sending the sip update request message to the ap 300 . in step 407 , upon receiving the sip update request message , the sip processor 338 generates an sip update response message in response to the sip update request message . in step 409 , the sip processor 338 sends the generated sip update response message to the network via the tcp / ip 336 . conversely , if the pdcp filter 334 determines that the received message does not correspond to an sip update request message in step 403 ( e . g ., if the received message corresponds to a voice packet ), then the terminal proceeds to step 411 in which the terminal allows the voice engine 332 to process the voice packet . according to exemplary embodiments of the present invention , through this process , the ap is not required to wake up to handle an sip update request message based on the sip protocol during a volte call , thereby contributing to a reduction in power consumption of the terminal . exemplary embodiments of the present invention may be implemented as computer - readable codes in non - transient computer - readable recording media . the non - transient computer - readable recoding media may include all kinds of recording devices storing computer - readable data . examples of the recording media may include read only memory ( rom ), random access memory ( ram ), compact disk ( cd )- rom , magnetic tape , floppy disk , optical data storage device , and the like . as is apparent from the foregoing description , according to exemplary embodiments of the present invention , the ap is not required to wake up to handle an sip update request message upon receiving a volte voice call , thereby contributing to a reduction in power consumption of the terminal during a volte call . if there is a need to process an sip protocol in a situation in which there is no user input , the terminal processes the sip protocol not in the ap but in the cp , thereby reducing the power consumption of the terminal . for example , the terminal enables the ap only in the situation in which there is a user input ( e . g ., only when the user takes an action of making or receiving a voice call ), thereby reducing the power consumption of the terminal . while the invention has been shown and described with reference to certain exemplary embodiments thereof , it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims and their equivalents .