1

A media negotiation method for an IP multimedia link, applicable to a process of establishing an IP multimedia link between a first entity and a second entity through an application server (AS) of an IP multimedia subsystem (IMS), the media negotiation method comprising:said AS sending said second entity an invite message, which includes media resource information of said first entity;

said AS, after receiving a message with media resource information from said second entity before an answer message is received or receiving a response message with media resource information from said second entity, sending said first entity an IMS re-invite message without media source information; and

said AS, after receiving an IMS signaling message with media resource information from said first entity, sending said first entity the media resource information returned by said second entity.

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2

The media negotiation method according to Claim 1, wherein said media negotiation method is triggered under the following conditions:a first terminal serviced by said first entity firstly establishes a call link with other terminal via said AS, the call link comprising an IP multimedia link S2 between said first entity and said other terminal, afterwards, said first terminal further calls the second entity via said AS so as to establish a three-party conference, or said other terminal initiates an IMS transfer service or a transfer service in an IMS centralized service to said second entity via said AS, to replace said IP multimedia link S2 with an IP multimedia link between said first entity and said second entity, thereby triggering said AS to perform said media negotiation process.

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3

The media negotiation method according to Claim 2, whereinsaid second entity is a second terminal, and the invite message sent to the second terminal from said AS is a call message, which includes media resource information of said first entity, and said AS obtains the media resource information of said second terminal from the response message sent from the second terminal; the media resource information of said first entity as included in said call message is media resource information of said first entity used for an IP multimedia link S2 as recorded by said AS during the call establishment between said first terminal and said other terminal.

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4

The media negotiation method according to Claim 3, whereinsaid AS makes an identification of said IP multimedia link S2 included in the re-invite message sent to said first entity;

said first entity, after receiving said re-invite message, sends said AS a re-invite response message, including the media resource information of said first entity being used by the IP multimedia link S2; and

said AS, after receiving said re-invite response message, sends said first entity a response acknowledgement message, including media resource information of said second terminal.

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5

The media negotiation method according to Claim 1, whereinsaid first entity is an entity having a gateway and a gateway control function, where the gateway control function part for performing message interaction with said AS is implemented by a mobile switch center enhanced (MSCe) or a media gateway control function (MGCF), and the media resource information of said first entity is media resource information of the gateway part.

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6

A media negotiation method for an IP multimedia link, applicable to a process of establishing an IP multimedia link between a first entity and a second entity through an application server (AS) of an IP multimedia subsystem (IMS), the media negotiation method comprising:said AS sending the second entity an invite message, which includes media resource information of said first entity, and sending said first entity an IMS re-invite message without media source information;

said AS, after receiving an IMS signaling message with media resource information from said first entity, and if either a message with media resource information before an answer message is received or a response message with media resource information from said second entity is not received within a specific time or within a specific retransmitted number of said IMS signaling messages with media resource information returned by said first entity,

sending an IMS signaling message with media resource information to said first entity, and then further sending a re-invite message without media resource information to said first entity; and

said AS, after receiving a message with media resource information from said second entity before an answer message is received or receiving a response message with media resource information from said second entity, sending said first entity an IMS signaling message with the media source information returned by said second entity.

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7

The media negotiation method according to Claim 6, whereinWhen, within a specific time or within a specific retransmitted number of said IMS signaling messages with media resource information returned by said first entity, said AS receives the message with media resource information from said second entity before an answer message is received or receives the response message with media resource information from said second entity, then said AS directly sends said first entity an IMS signaling message with the media resource information returned by said second entity; otherwise, said AS, after receiving the IMS signaling message with media resource information sent again by said first entity, sends said first entity the media resource information returned by said second entity;

wherein said specific time is shorter than the overtime of said first entity waiting for said AS to send an IMS signaling message with media resource information, and the retransmitted number is smaller than or equal to the number of IMS signaling messages with media resource information retransmitted before said first entity waits overtime.

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8

The media negotiation method according to Claim 6, wherein said media negotiation method is triggered under the following conditions:a first terminal serviced by said first entity firstly establishes a call link with other terminal via said AS, the call link comprising an IP multimedia link S2 between said first entity and said other terminal, afterwards, said first terminal further calls said second entity via said AS so as to establish a three-party conference, or said other terminal initiates an IMS transfer service or a transfer service in an IMS centralized service to said second entity via said AS, and replaces said IP multimedia link S2 with an IP multimedia link between said first entity and said second entity, thereby triggering said AS to perform said media negotiation.

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9

The media negotiation method according to Claim 8, whereinthe re-invite message without media resource information each time sent by said AS to said first entity includes a session identification of the IP multimedia link S2; and

before said AS receives a message with media resource information from said second entity before an answer message is received or receives a response message with media resource information from said second entity, in an IMS signaling message with media resource information each time sent to said first entity, the available media type in said media resource information is identical to the available media type in media resource information used for the IP multimedia link S2.

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10

The media negotiation method according to Claim 8, whereinsaid first entity is an entity having a gateway and a gateway control function, where the gateway control function part for performing message interaction with said AS is implemented by a mobile switch center enhanced (MSCe) or a media gateway control function (MGCF), and the media resource information of said first entity is media resource information of the gateway part; and

said second entity is a second terminal, and said AS makes media resource information of said first entity included in a call message sent to said second terminal, and obtains the media resource information of said second terminal from a response message sent by said second terminal; media resource information of said first entity as included in said call message is media resource information of said first entity used for the IP multimedia link S2 as recorded by said AS during the call establishment between said first terminal and said other terminal.

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