Communication Protocol for Providing Video Customized Alerting Tones Based on Early Session Model

Abstract

A communication protocol for providing video CAT (Customized Alerting Tones) based on an early session model is disclosed. The present disclosure provides an optimal method for transmitting a video set by the recipient during a voice call connection to the caller as a video CAT (Customized Alerting Tones). More specifically, to generate a video call that transmits the video CAT in the form of early media from a voice call, the present disclosure provides a communication protocol that negotiates and establishes a session for early media using an early session model presented in the 3GPP standard. In addition, the present disclosure provides a method for handling exceptions in a communication protocol for video CAT transmission to ensure stable communication in the event of errors occurring during the codec negotiation process for video CAT in a network, server failure situations, and malfunctions between a terminal and a server.

Description

Technology Field

[0001] The present disclosure relates to a communication protocol for providing video CAT (Customized Alerting Tones) based on an early session model. More specifically, it relates to a communication protocol for negotiating and establishing a session for early media using an early session model in order to transmit a video set by the recipient to the caller as a video CAT during a voice call connection. Background Technology

[0002] The following description merely provides background information related to the present invention and does not constitute prior art.

[0003] Customized Alerting Tones (CAT) are connection tones pre-set by the recipient to be delivered to the caller, and voice, audio, or video data may be used. When applying video CAT, it may be difficult to modify the voice outgoing signal to include video information depending on whether the recipient is subscribed to a service. Therefore, it is necessary to convert the voice outgoing signal into a video outgoing signal; however, since video cannot be transmitted over the voice session established upon a voice call request, the method presented in the 3GPP standard may be utilized. The 3GPP TS 24.182 specification describes a method for delivering CAT from the recipient to the caller using the forking model and the early session model (see Non-Patent Literature 1).

[0004] The forking model separates dialogue for early media from the dialogue of the final voice session, but instead does not generate separate Session Description Protocol (SDP) information for the originating terminal used in the early media dialogue. Meanwhile, the early session model does not separate dialogue for early media from the dialogue of the final voice session, but uses a separate SDP when establishing an early media session in the middle.

[0005] Therefore, in order to use video as an alerting tone during a voice call, the early media session must be changed to a new video session, so it is advantageous to operate based on an early session model. The operation method for the early session model follows the 3GPP standard (see Non-Patent Literature 1). The 3GPP standard describes situations where the early media is voice, but it does not consider changes in session information when switching between voice and video. Therefore, the 3GPP standard does not specify methods for how to transmit the content server's SDP to the terminal, or methods for changing the session.

[0006] As a solution to this, the most common approach is for the Telephony Application Server (TAS) of the receiving network to establish a separate session with the content server and include the SDP received during the session establishment process in the call control message. However, the codec information of the content server can only be obtained after the TAS has established a session with the content server at least once. Therefore, since a session update with the content server must be performed to switch to video content, there is a problem of call delays caused by the establishment of additional sessions and performance degradation due to additional transactions.

[0007] In addition, in addition to the method of establishing a SIP session according to the standard, there is also a method in which a call application directly plays a video corresponding to CAT using a 3G / LTE / 5G data network and stops playing the video when a call between the caller and the recipient begins. However, if the video is not played because data communication is not possible, the IMS call network, which cannot recognize this situation, controls the call by assuming that the video is playing, so silence may occur.

[0008] Therefore, an effective call flow is required to provide a highly effective service by resolving issues arising from session setup between the TAS and the content server. Prior art literature

[0009] Non-patent Document 1: TS 24.182, 3rd Generation Partnership Project; Technical Specification Group Core Network and Terminals; IP Multimedia Subsystem (IMS) Customized Alerting Tones (CAT); Protocol specification (Release 16). The problem to be solved

[0010] The present disclosure provides an optimal method for transmitting a video set by the recipient to the caller as a video CAT (Customized Alerting Tones) during a voice call connection. More specifically, the main purpose is to provide a communication protocol that negotiates and establishes a session for early media using an early session model presented in the 3GPP standard in order to generate a video call that transmits the video CAT in the form of early media from a voice call.

[0011] In addition, regarding a method for establishing a session for early media delivery using an early session model presented in 3GPP standards, the present disclosure appropriately omits a part of the process to reduce the burden on the network caused by additional transactions and the time and cost required for said transactions during the process of updating the content server's session one more time. There is an additional purpose in providing a communication protocol.

[0012] In addition, the present disclosure has an additional objective of providing a method for handling exceptions in a communication protocol for video CAT transmission to ensure stable communication in the event of errors occurring during the codec negotiation process for video CAT in a network, server failure situations, and malfunctions between a terminal and a server. means of solving the problem

[0013] According to an embodiment of the present disclosure, a method for providing early media by an application server during a Session Initiation Protocol (SIP)-based call connection between a sending terminal and a receiving terminal comprises: receiving a first INVITE message containing SDP information of the sending terminal; performing a procedure to establish an early session for negotiating capabilities with the sending terminal to provide a video as the early media; and, if the establishment of the early session is successful, providing the early media to the sending terminal based on capabilities negotiated using the early session, wherein the procedure to establish the early session comprises: transmitting an early session offer message to the sending terminal containing first SDP information specifying one or more video codecs available for the early media; and receiving an early session answer message containing second SDP information specifying one or more codecs supported by the sending terminal and to be used for the early media.

[0014] According to another embodiment of the present disclosure, a method for providing early media is provided, characterized by further including the step of terminating the provision of the early media when a 200 OK message containing SDP information of the receiving terminal is received as a response to the first INVITE message.

[0015] According to an embodiment of the present disclosure, a computer capable of reading a recording medium storing a computer program, wherein by executing the computer program, the computer provides a method for providing early media during a Session Initiation Protocol (SIP)-based call connection between a sending terminal and a receiving terminal, comprising: receiving a first INVITE message containing SDP information of the sending terminal; performing a procedure for establishing an early session for negotiating capabilities with the sending terminal to provide a video as the early media; providing the early media to the sending terminal based on capabilities negotiated using the early session when the establishment of the early session is successful; and terminating the provision of the early media when a 200 OK message containing SDP information of the receiving terminal is received as a response to the first INVITE message, wherein the procedure for establishing the early session comprises: transmitting an early session offer message to the sending terminal containing first SDP information specifying one or more video codecs available for the early media; The present invention provides a computer capable of reading a recording medium storing a computer program, characterized by including the step of receiving an early session answer message comprising second SDP information that specifies one or more codecs supported by the sending terminal and to be used for the early media.

[0016] According to another embodiment of the present disclosure, a method for providing early media is provided, wherein, when a Session Initiation Protocol (SIP)-based call connection is established between a sending terminal and a receiving terminal, the sending terminal performs a method for receiving early media, comprising: transmitting an INVITE message including SDP information of the sending terminal and header information indicating that an early session is supported; receiving an early session offer message from an application server including first SDP information specifying one or more video codecs available for the early media; and transmitting an early session answer message to the application server including second SDP information regarding one or more codecs supported by the sending terminal and to be used for the early media.

[0017] According to another embodiment of the present disclosure, a Session Initiation Protocol (SIP) based call processing method performed by a network call processing device comprises: receiving a first INVITE message from a sending terminal that includes SDP information of the sending terminal and header information indicating whether the sending terminal supports the early session; if the header information indicates that the sending terminal supports the early session, transmitting a second INVITE message that includes SDP information of the sending terminal to an application server and a receiving terminal; receiving an early session offer message from an application server that includes first SDP information specifying one or more video codecs available for early media, transmitting the early session offer message to the sending terminal; and receiving an early session answer message from the sending terminal that includes second SDP information specifying one or more codecs supported by the sending terminal and to be used for the early media, transmitting the early session answer message to the application server. The present invention provides a call processing method characterized by including the step of transmitting the 200 OK message, which includes SDP information of the receiving terminal, to the application server and the sending terminal when the receiving terminal receives the 200 OK message in response to the second INVITE message.

[0018] According to an embodiment of the present disclosure, a computer capable of reading a recording medium storing a computer program, by executing the computer program, comprises the steps of: receiving a first INVITE message from a sending terminal including SDP information of the sending terminal and header information indicating whether early session is supported; transmitting a second INVITE message including SDP information of the sending terminal to an application server and a receiving terminal when the header information indicates that the sending terminal supports the early session; transmitting the early session offer message to the sending terminal when the application server receives an early session offer message including first SDP information specifying one or more video codecs available for early media; and transmitting the early session answer message to the application server when the application server receives an early session answer message including second SDP information specifying one or more codecs supported by the sending terminal and to be used for the early media. The present invention provides a computer capable of reading a recording medium storing a computer program, characterized by including the step of transmitting the 200 OK message, which includes SDP information of the receiving terminal, to the application server and the sending terminal when the receiving terminal receives the 200 OK message in response to the second INVITE message.

[0019] According to another embodiment of the present disclosure, a computer program stored on a computer-readable recording medium is provided to execute each step comprising a method for an application server to provide early media.

[0020] According to another embodiment of the present disclosure, a computer program stored on a computer-readable recording medium is provided to execute each step included in a method performed by a transmitting terminal.

[0021] According to another embodiment of the present disclosure, a computer program stored on a computer-readable recording medium is provided to execute each step included in a method performed by a network call processing device. Effects of the invention

[0022] As explained above, according to the present embodiment, by providing a communication protocol that negotiates and establishes a session for early media using the early session model presented in the 3GPP standard, it is possible to change a voice call into a video call for early media delivery and deliver a video set by the recipient to the sender side as a video CAT.

[0023] In addition, according to the present embodiment, in a method for establishing a session for early media delivery using an early session model presented in the 3GPP standard, a part of the process of updating the content server's session one more time is appropriately omitted. By providing a communication protocol, it is possible to reduce the burden on the network caused by additional transactions in the process and the time and cost involved.

[0024] In addition, according to the present embodiment, by providing a method for handling exceptions such as errors occurring during the codec negotiation process for video CAT in the network, server failure situations, and malfunctions between the terminal and the server in the communication protocol for video CAT transmission, it is possible to ensure stable communication in the aforementioned exception situations. Brief explanation of the drawing

[0025] FIG. 1 is a configuration diagram of a service system for providing early media according to one embodiment of the present disclosure. FIG. 2 is a flowchart sequentially illustrating a method for providing early media according to one embodiment of the present disclosure. FIG. 3 is a flowchart of a method for exception handling when an application server fails to establish a session with a content server according to one embodiment of the present disclosure. FIG. 4 is a flowchart of a method for exception handling when a video playback error occurs at a transmitting terminal according to one embodiment of the present disclosure. FIG. 5 is a flowchart of a method for exception handling when a session processing error occurs at a sending terminal according to one embodiment of the present disclosure. Specific details for implementing the invention

[0026] Hereinafter, embodiments of the present invention will be described in detail with reference to the exemplary drawings. It should be noted that in assigning reference numerals to the components of each drawing, the same components are given the same reference numeral whenever possible, even if they are shown in different drawings. Furthermore, in describing these embodiments, if it is determined that a detailed description of related known components or functions could obscure the essence of these embodiments, such detailed description is omitted.

[0027] In addition, terms such as first, second, A, B, (a), (b), etc. may be used when describing the components of the embodiments. These terms are intended only to distinguish the components from other components, and the essence, order, or sequence of the components is not limited by these terms. Throughout the specification, when a part is described as 'comprising' or 'equipped' with a certain component, unless specifically stated otherwise, this means that it may include additional components rather than excluding other components. Furthermore, terms such as '…part' or 'module' described in the specification refer to a unit that processes at least one function or operation, and this may be implemented in hardware, software, or a combination of hardware and software.

[0028] The detailed description disclosed below, together with the attached drawings, is intended to describe exemplary embodiments of the present invention and is not intended to represent the only embodiment in which the present invention can be practiced.

[0029] The present embodiment discloses a communication protocol for transmitting a video set by the recipient to the caller as a video CAT (Customized Alerting Tones) during a voice call connection. More specifically, to generate a video call that transmits the video CAT in the form of early media from a voice call, the present embodiment provides a communication protocol that negotiates and establishes a session for early media using an early session model presented in the 3GPP standard.

[0030] Hereinafter, the service means providing video CAT in an early media format.

[0031] FIG. 1 is a configuration diagram of a service system for providing early media according to one embodiment of the present disclosure.

[0032] A service system (100, hereinafter referred to as the "service system") for providing early media according to the present disclosure performs a communication protocol for providing video CAT in the form of early media based on SIP (Session Initiation Protocol). The service system (100) includes all or part of a SIP server (104), an application server (106, hereinafter referred to as "AS"), and a content server (108). Additionally, the service system (100) may additionally include a sending terminal (102, hereinafter referred to as "UE (User Equipment) A") and a receiving terminal (110, hereinafter referred to as "UE B") to provide early media. Meanwhile, the SIP server (104) and the application server (106) involved in the call flow with terminals based on SIP are collectively referred to as a SIP core (107).

[0033] The sending terminal (102) is a terminal that receives early media according to the present disclosure and may be equipped with performance sufficient to receive and play early media in the form of a video CAT. The sending terminal (102) may notify the subscriber of the sending terminal (102) that a call connection request to the receiving terminal (110) is in progress by receiving and playing video data provided as early media. Here, the video data may include images, videos, and flash animations that can be played on the screen of the sending terminal (102).

[0034] The receiving terminal (110) is a terminal of a subscriber who has pre-subscribed to a service for providing early media. When the sending terminal (102) requests a call connection, the service setting information of the receiving terminal (110) for providing early media to the sending terminal (102) is used until the call connection is established.

[0035] A SIP server (104) is a device for routing messages that perform a Call Session Control Function (CSCF) between a sending terminal (102), a receiving terminal (110), and an application server (106), and includes a P-CSCF (Proxy-CSCF, not shown) that acts as a proxy for a subscriber and controls the Quality of Service (QoS), and an S / I-CSCF (Interrogating / Serving-CSCF, not shown) that performs the main functions for call processing.

[0036] The main methods of SIP used in the present disclosure include an invite (hereinafter 'INVITE') to invite a service or user to join a session, an ACK to confirm that a final response (200 OK) has been received to the INVITE request, an INFO to transmit additional information within an established session or conversation, a PRACK for the sending terminal to temporarily accept a response, and a BYE to terminate an established session.

[0037] Meanwhile, the main responses of SIP used in the present disclosure include a 180 message transmitted by the receiving terminal to the sending terminal to indicate that the receiving terminal is ringing to the user, a 183 message which is a provisional response to transmit other call progress information, a 200 OK message to notify that the request has been processed successfully, a 4XX message to notify of an error situation, and a 5XX message to notify that the service is not implemented.

[0038] For example, the SIP server (104) transmits an INVITE message received from the sending terminal (102) to the application server (106) and transmits an INVITE message from the application server (106) to the receiving terminal.

[0039] Additionally, when the SIP server (104) receives an INVITE message from the sending terminal (102), it can check whether the subscriber of the receiving terminal (110) to receive the message is subscribed to a service for providing early media. If the subscriber of the receiving terminal (110) is not subscribed to a service for providing video CAT according to the present disclosure, the SIP server (104) can perform a procedure for providing conventional early media, such as voice and audio data, to the sending terminal (102). Hereinafter, the explanation will focus on the case where the subscriber of the receiving terminal (110) is subscribed to a service according to the present disclosure.

[0040] The application server (106) performs individual processing and management of the operation of the sending terminal (102) and the receiving terminal (110) based on SIP. In order for early media according to the service setting information of the subscriber of the receiving terminal (110) to be provided to the sending terminal using an early / regular session, the application server (106) performs the procedure for sending and receiving messages with the content server (108) and establishing a session with the sending terminal (102).

[0041] In the present disclosure, a session for providing a call between a sending terminal (102) and a receiving terminal (110) may be divided into an early session and a regular session. Here, an early session refers to a separate session for providing early media, and a regular session refers to a session for a regular call (a voice call in the present disclosure) between the two terminals. In the case of a terminal that does not support an early session, early media may be provided using a regular session without a separate early session distinction (forking mode), and in the case of a terminal that supports an early session, early media may be provided using an early session established according to a separate session negotiation procedure (early session model). As described above, the present disclosure assumes the use of a terminal that supports an early session model.

[0042] The application server (106) can determine whether to provide a service using an early session by analyzing the header information of an INVITE message received from the sending terminal (102) to check whether the sending terminal (102) supports an early session model.

[0043] The content server (108) is a device that exchanges messages with the application server (106) and provides early media to the sending terminal (102). That is, the content server (108) provides media information for service provision using message communication with the application server (106), and can provide early media to the sending terminal (102) in accordance with the media provision instructions from the application server.

[0044] FIG. 2 is a flowchart sequentially illustrating a method for providing early media according to one embodiment of the present disclosure.

[0045] The sending terminal (102) transmits an INVITE message containing SDP information of the sending terminal (102) to the SIP server (104) for call connection (step 1).

[0046] The INVITE message transmitted by the sending terminal (102) may include, for example, the IP address of the sending terminal, information of the receiving terminal, a service processing identifier, and information of the sending terminal's SDP (Session Description Protocol). Here, the IP address of the sending terminal refers to an address value for identifying the sending terminal when performing TCP / IP (Transmission Control Protocol / Internet Protocol)-based communication, and the receiving terminal information may be the phone number of the receiving terminal. Meanwhile, the service processing identifier is information about a service supported by the sending terminal, and an example of the service may be support for an early session for providing early media.

[0047] A sending terminal (102) capable of video CAT service must specify that reception of early media is possible using an early session model by including a 'Supported: early-session' header as a service processing identifier in an INVITE message. Additionally, the sending terminal (102) may specify that reception of early media is possible by inserting a separate private header into the INVITE message if necessary. For example, 'P-XXX-VoLTE-Info: vrbt' included in the INVITE message of the sending terminal (102) in the illustration of FIG. 2 (step 1) is a private header indicating that vrbt (video ringback tone) is supported in relation to VoLTE (Voice over LTE). Generally, 'XXX' may indicate an organization, company, etc. that introduced this private header. Meanwhile, the 'Supported: 100rel' header is an option tag indicating that PRACK, which is a reliable provisional ACK, is supported.

[0048] The SIP server (104) receives an INVITE message from the sending terminal (102) (step 1), and if the subscriber of the receiving terminal (110) is subscribed to a service for providing early media, it transmits the INVITE message to the application server (106) (steps 2 and 3), receives an INVITE message from the application server (106) (step 6), and delivers it to the receiving terminal (110) (step 7).

[0049] The application server (106) receives an INVITE message containing SDP information of the sending terminal (102) (step 3), and if the subscriber of the receiving terminal (110) is subscribed to the video CAT service, it performs a procedure to analyze the INVITE message to determine whether the terminal is capable of supporting early sessions and capable of receiving video as early media.

[0050] For a service-enabled sending terminal (102), if the application server (106) is a service subscriber for providing video CAT to the receiving terminal (110), the application server (106) transmits a receiving INVITE message to the receiving terminal (110) via the SIP server (104) (steps 6 and 7).

[0051] A receiving terminal (110) that has received an incoming INVITE message transmits a 180 message to the SIP server (104) to indicate that it is ringing. Meanwhile, in order to establish a regular session for a voice call, a call flow for incoming connection following the transmission of the 180 message is required. For incoming connection, the SIP server (104) requires steps such as transmitting the 180 message to the application server (106), and the sending terminal, which has received a 200 OK message corresponding to call acceptance from the receiving terminal, transmitting an ACK message to the receiving terminal. However, the call flow for incoming connection is outside the scope of the present disclosure and is not illustrated in FIG. 2, and further detailed explanation thereof is omitted.

[0052] The application server (106) sends an INVITE message to the content server (108) to establish a video session for early media (step 9). At this time, the application server (106) may announce that the video content must be provided as early media by including a separate private header in the INVITE message sent to the content server (108).

[0053] For example, 'P-XXX-MRF-SVC: play', 'P-XXX-MRF-CRBT: 08 or 09', etc. included in the INVITE message transmitted to the content server (108) in the city of FIG. 2 (step 9) are private headers. Here, MRF is another notation for the content server (108).

[0054] Based on the contents of the private header, the content server (108) returns a 200 OK message containing a Session Description Protocol (SDP) for available video codec information to the application server (106) (step 10).

[0055] Before sending an ACK message for the received 200 OK message to the content server (108), the application server (106) performs a procedure for establishing an early session with the sending terminal (102). First, the application server (106) transmits a 183 message to the sending terminal (102) via the SIP server (104) (steps 11 to 13). At this time, the application server (106) can execute a function to offer the establishment of an early session by including 'Require: 100rel', 'Require: early-session', the private header if there is a private header received from the sending terminal (102), and the video-related SDP included in the 200 OK message received from the content server (108) in the 183 message. However, if the network does not support an early session model, general voice / audio CAT operations based on a forking model can be performed by not including 'Require: early-session'.

[0056] In response to this, the sending terminal (102) can respond to the proposal to establish an early session by setting a negotiable codec among the codecs received in the 183 message, and then sending a PRACK message containing SDP information specifying the corresponding codec to the application server (106) via the SIP server (104) (steps 14 to 16).

[0057] After receiving the PRACK message, the application server (106) transmits an ACK message containing SDP information specified by the PRACK message to the content server (108) (step 17). The content server (108) can establish an early session based on the ACK message. The content server (108) provides a video CAT if there is a video codec in the codec information of the ACK message, but provides a voice / audio CAT service if there is no video codec.

[0058] The application server (106) completes the procedure for establishing an early session by transmitting a 200 OK message for the PRACK message to the sending terminal (102) via the SIP server (104) after transmitting the ACK message (steps 18 to 20). Meanwhile, regarding the 200 OK message for the PRACK message, the P-CSCF in the SIP server (104) can set the QoS for the video CAT using a PCRF (Policy and Charging Rule Function, not shown) and an AAR (Authorize / Authenticate Request) message based on the negotiated codec information.

[0059] The application server (106) requests the content server (108) to transmit a video corresponding to early media using an INFO message (step 21). The content server (108) transmits a 200 OK message for the INFO message to the application server (106) (step 22), and then transmits the video requested in the INFO message to the address of the SDP received in the ACK message, which can generally be transmitted to the IP / PORT side of the P-CSCF within the sending terminal (102) or SIP server (104).

[0060] After the subscriber accepts the call (e.g., off-hook, touch on the call button, etc.), the receiving terminal (110) sends a 200 OK message to the SIP (104) server side as a response to the incoming INVITE message (step 23). At this time, the 200 OK message corresponding to the call acceptance is the voice of the receiving terminal (110). Includes SDP information.

[0061] The SIP server (104) receives a 200 OK message from the receiving terminal (110) (step 23) and transmits it to the application server (106) (step 24). The application server (106) receives the voice of the receiving terminal (110). A 200 OK message containing SDP information is received and transmitted to the sending terminal (102) (steps 25 to 27).

[0062] After the P-CSCF in the SIP server (104) receives a 200 OK message regarding the acceptance of the call from the receiving terminal, it can set the voice QoS for the call again using the PCRF and AAR (Authorize / Authenticate Request) message.

[0063] The application server (106) sends a 200 OK message to the sending terminal (102) and then sends a BYE message to the content server (108) to end the early session (step 28), thereby inducing the establishment of a regular session for voice calls.

[0064] As explained above, according to the present embodiment, by providing a communication protocol that negotiates and establishes a session for early media using the early session model presented in the 3GPP standard, it is possible to change a voice call into a video call for early media delivery and deliver a video set by the recipient to the sender side as a video CAT.

[0065] In addition, according to the present embodiment, in a method for establishing a session for early media delivery using an early session model presented in the 3GPP standard, a part of the process of updating the content server's session one more time is appropriately omitted. By providing a communication protocol, it is possible to reduce the burden on the network caused by additional transactions in the process and the time and cost involved.

[0066] Hereinafter, using the flowcharts of FIGS. 3 to 5, a method for handling exceptions to ensure stable communication in error situations that may occur during the execution process of a service for providing early media is explained.

[0067] FIG. 3 is a flowchart of a method for exception handling when an application server fails to establish a session with a content server according to one embodiment of the present disclosure.

[0068] After the application server (106) transmits an INVITE message to the content server (108) to establish a video session for early media (step 9), it expects a 200 OK message from the content server (108), but the session establishment may fail due to an error in the establishment process (reception of a 4XX or 5XX message) or a timeout (step 10). In this case, the application server (106) can send a 180 message to the sending terminal (102) (steps 11 to 13) to induce playback of a local ringback tone.

[0069] Meanwhile, if the sending terminal (102) that receives the 183 message proposing an early session does not have a video codec capable of negotiation or cannot properly accept the early media due to an operational error, the sending terminal (102) may execute one of two methods as shown in the flowchart of FIG. 4 or FIG. 5.

[0070] FIG. 4 is a flowchart of a method for exception handling when a video playback error occurs at a transmitting terminal according to one embodiment of the present disclosure.

[0071] If the sending terminal (102) does not possess a negotiable video codec, it may respond to the application server (106) by specifying only available voice codecs in the PRACK message (steps 14 to 16). Since the provision of early media using video is impossible, if the sending terminal (102) possesses an available voice codec, it may induce the provision of early media using voice.

[0072] After receiving the PRACK message, the application server (106) transmits an ACK message containing an SDP containing a voice codec specified by the PRACK message to the content server (108) (step 17).

[0073] A content server (108) that receives an ACK message containing only a voice codec can confirm that the sending terminal (102) is unable to receive video, and if voice CAT service is possible, establish an early session to provide voice CAT service.

[0074] After the application server (106) transmits the ACK message, it transmits a 200 OK message for the PRACK message to the sending terminal (102) (steps 18 to 20). At this time, for the 200 OK message for early media, the P-CSCF in the SIP server (104) can set the QoS for the voice CAT using the PCRF and AAR message based on the negotiated voice codec information.

[0075] If there is no available voice codec, the content server (108) can send a BYE message to the application server (106) and, when the video CAT session ends, send a 180 message to the sending terminal (102) to induce playback of the local ringback tone.

[0076] FIG. 5 is a flowchart of a method for exception handling when a session processing error occurs at a sending terminal according to one embodiment of the present disclosure.

[0077] If a session processing error occurs due to malfunction, etc., the sending terminal (102) does not send a PRACK message, thereby allowing the application server (106) to recognize the timeout and send a 180 message to the sending terminal (102) (steps 14 to 16). Upon receiving the 180 message, the sending terminal (102) plays a local ringback tone.

[0078] The application server (106), having detected the passage of time, sends an ACK message that does not contain any SDP information to the content server (108) to notify this (step 17). The content server (108) can terminate the process related to the early session by sending a BYE message to the application server (106) (step 18).

[0079] As explained above, according to the present embodiment, by providing a method to handle exceptions such as errors occurring during the codec negotiation process for video CAT in the network, server failure situations, and malfunctions between the terminal and the server in the communication protocol for video CAT transmission, it is possible to ensure stable communication in the aforementioned exception situations.

[0080] Although each flowchart according to the present embodiment describes the execution of each process sequentially, it is not necessarily limited thereto. In other words, since it may be applicable to modify the processes described in the flowchart or to execute one or more processes in parallel, the flowchart is not limited to a chronological order.

[0081] Various embodiments of the systems and techniques described herein may be realized as digital electronic circuits, integrated circuits, field programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), computer hardware, firmware, software, and / or combinations thereof. These various embodiments may include being implemented as one or more computer programs executable on a programmable system. A programmable system comprises a storage system, at least one input device, and at least one programmable processor (which may be a special-purpose processor or a general-purpose processor) coupled to receive data and instructions from at least one output device and to transmit data and instructions to them. Computer programs (which are also known as programs, software, software applications, or code) include instructions for the programmable processor and are stored on a "computer-readable recording medium."

[0082] Computer-readable recording media include all types of recording devices in which data that can be read by a computer system is stored. Such computer-readable recording media may be non-volatile or non-transitory media such as ROM, CD-ROM, magnetic tape, floppy disk, memory card, hard disk, magneto-optical disk, and storage device. Additionally, computer-readable recording media may be distributed across networked computer systems, and computer-readable code may be stored and executed in a distributed manner.

[0083] Various embodiments of the systems and techniques described herein may be implemented by a programmable computer. Here, the computer includes a programmable processor, a data storage system (including volatile memory, non-volatile memory, or other types of storage systems, or a combination thereof), and at least one communication interface. For example, the programmable computer may be one of a server, a network device, a set-top box, an embedded device, a computer expansion module, a personal computer, a laptop, a PDA (Personal Data Assistant), a cloud computing system, or a mobile device.

[0084] The above description is merely an illustrative explanation of the technical concept of the present embodiment, and a person skilled in the art to which the present embodiment belongs would be able to make various modifications and variations within the scope of the essential characteristics of the present embodiment. Accordingly, the present embodiments are intended to explain, not limit, the technical concept of the present embodiment, and the scope of the technical concept of the present embodiment is not limited by these embodiments. The scope of protection of the present embodiment shall be interpreted by the claims below, and all technical concepts within an equivalent scope shall be interpreted as being included within the scope of rights of the present embodiment. Explanation of the symbols

[0085] 100: Service system for providing early media 102: Calling Terminal (UE A) 104: SIP Server 106: Application Server 107: SIP Core 108: Content Server 110: Receiving Terminal (UE B)

Claims

Claim 1 A method for an application server to provide early media when establishing a Session Initiation Protocol (SIP)-based voice call connection between a sending terminal and a receiving terminal comprises: receiving a first INVITE message, wherein the first INVITE message includes SDP information of the sending terminal, a header specifying that an early session is required, and a private header specifying that a video is to be provided as early media; performing a procedure to establish an early session for negotiating capabilities with the sending terminal to provide the video as early media; and, if the establishment of the early session is successful, providing the early media to the sending terminal based on capabilities negotiated using the early session, wherein the procedure to establish the early session includes the step of transmitting an early session offer message to the sending terminal that includes first SDP information specifying one or more video codecs available for the early media. A method for providing early media, characterized by including the step of receiving an early session answer message comprising second SDP information that specifies one or more codecs supported by the sending terminal and to be used for the early media. Claim 2 A method for providing early media according to claim 1, further comprising the step of terminating the provision of the early media when a 200 OK message containing SDP information of the receiving terminal is received as a response to the first INVITE message. Claim 3 A method for providing early media according to claim 1, characterized in that the early session proposal message is a provisional response message and the early session response message is a PRACK message. Claim 4 A method for providing early media according to claim 1, wherein the early session proposal message comprises a header specifying that the early session is required, a private header specifying that the video is provided as early media, and the first SDP information. Claim 5 A method for providing early media according to claim 1, characterized by including the step of, when the establishment of the early session fails, transmitting a ringing message to the sending terminal to induce playback of a local ringback tone. Claim 6 A method for providing early media according to claim 1, wherein the procedure for establishing the early session further comprises: a step of transmitting a second INVITE message to a content server that includes a private header specifying that the video is provided as early media in order to obtain the first SDP information; and a step of receiving a 200 OK message containing the first SDP information from the content server as a response to the second INVITE message. Claim 7 A method for providing early media according to claim 6, wherein the step of providing the early media comprises the step of transmitting an ACK message containing the second SDP information to the content server as a response to the 200 OK message, so that the content server transmits the early media using a codec supported by the sending terminal. Claim 8 A method for providing early media according to claim 6, wherein if the establishment of the early session fails due to the early session response message not being received within a predetermined time, the method comprises the steps of: transmitting a ringing message to the sending terminal to induce playback of a local ringback tone; and transmitting an ACK message not containing any SDP information to the content server as a response to the 200 OK message. Claim 9 A method for providing early media according to claim 1, wherein the step of providing the early media comprises, if the second SDP information includes at least one video codec, providing a video encoded with the at least one video codec as the early media, and if the second SDP information includes only a voice codec, providing a voice encoded using the voice codec as the early media. Claim 10 A method for providing early media performed by a sending terminal to receive early media when establishing a Session Initiation Protocol (SIP)-based voice call connection between a sending terminal and a receiving terminal, comprising the step of transmitting a first INVITE message, wherein the first INVITE message includes SDP information of the sending terminal, a header specifying that an early session is required, and a private header specifying that video is provided as early media; the step of receiving an early session offer message from an application server that includes first SDP information specifying one or more video codecs available for the early media; and the step of transmitting an early session answer message to the application server that includes second SDP information regarding one or more codecs supported by the sending terminal and to be used for the early media. Claim 11 A Session Initiation Protocol (SIP)-based voice call processing method performed by a network call processing device comprises: receiving a first INVITE message from a calling terminal, wherein the first INVITE message includes SDP information of the calling terminal, a header specifying that an early session is required, and a private header specifying that a video is provided as early media; if the information of the header specifying that an early session is required indicates that the calling terminal supports the early session, transmitting a second INVITE message including the SDP information of the calling terminal to an application server and a receiving terminal; and if an early session offer message including the first SDP information specifying one or more video codecs available for early media is received from an application server, transmitting the early session offer message to the calling terminal. A voice call processing method characterized by comprising: a step of transmitting an early session answer message to an application server upon receiving from the sending terminal an early session answer message containing second SDP information that specifies one or more codecs supported by the sending terminal and to be used for the early media; and a step of transmitting the 200 OK message to the application server and the sending terminal upon receiving from the receiving terminal a 200 OK message containing SDP information of the receiving terminal as a response to the second INVITE message. Claim 12 A voice call processing method according to claim 11, further comprising the step of setting a Quality of Service (QoS) for video early media and maintaining the set QoS until the 200 OK message is received, when the second SDP information received from the transmitting terminal includes a video codec. Claim 13 A computer program stored on a computer-readable recording medium to execute each step included in the method of an application server providing early media according to any one of paragraphs 1 through 9. Claim 14 A computer program stored on a computer-readable recording medium to execute each step included in the method performed by the sending terminal according to paragraph 10. Claim 15 A computer program stored on a computer-readable recording medium to execute each step included in the method performed by a network call processing device according to either paragraph 11 or 12.

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