CN101026815A - Multimedia communication session establishing method - Google Patents

Abstract

The present invention provides a method for establishing a multimedia communication session. The method mainly includes: according to a session establishment request sent by a user, one or more pre-established sessions are pre-established between the user and a session server, and the negotiated The session capability attribute is inactive; when the session server receives the service establishment request sent by the session participating user, it establishes the actual session according to the selection information carried in the service establishment request and the pre-established session, and establishes the actual session During the process, modify the negotiated session capability attribute to active. By using the method of the invention, it is possible to select a required session from pre-established composite sessions or multiple sessions to establish an actual session, and to modify the pre-established session.

Description

Multimedia communication session establishment method

technical field

The invention relates to the field of network communication, in particular to a method for establishing a multimedia communication session.

Background technique

With the development of broadband networks, mobile communications will not be limited to traditional voice communications, but multimedia services that combine audio, video, pictures, text and other media types will gradually develop. The multimedia service can be combined with data services such as presence (presentation service), short message, WEB (web page) browsing, positioning information, PUSH (push service) and file sharing, to provide users with various service services. The various business services include:

Message service: instant message and chat room, multimedia short message, etc.

Video business: entertainment, multimedia information, daily communication, etc.

E-commerce: product catalog, search engine, shopping cart, order management, payment, etc.

Games: single player games, group games, etc.

Positioning business: tracing, guide, alarm, etc.

Personal assistant: address book, calendar, bookmark management, file storage, event reminder, e-mail, etc.

Driven by the above-mentioned multiple business service applications, the 3GPP (Third Generation Partnership Project) standard organization has launched the IP-based IMS (Internet Multimedia Subsystem) architecture, with the purpose of using a standardized open structure in the communication network To achieve a variety of multimedia applications, to provide users with more choices and richer experience.

With the development of network technology, multi-party communication has become a common business. In order to realize multi-party communication, it is necessary to have a unified control point to manage the system, and it is necessary to ensure the consistency and real-time performance of management. For example, when a user applies for sending audio data, the system needs to have one and only one control point to process the application. Current multi-party multimedia communication systems include PoC (Push-to-talk over Cellular) systems, Conference (multimedia conference) systems, and the like. Among them, the PoC system is a centralized control multi-party multimedia communication system.

In order to increase the speed of establishing a session, the prior art provides a method for pre-establishing a session, that is, establishing a session in advance and negotiating session parameters. Subsequent use of the negotiated session parameters directly establishes an actual session, which can speed up session establishment.

The actual session establishment method after the session is pre-established in the multimedia communication system in the prior art is: after the session is pre-established and the session parameters are pre-negotiated, when the actual session is established, the session server and the user can only session parameters to execute, no other selections can be made. A schematic diagram of the actual session establishment method after the session is pre-established is shown in FIG. 1 .

The disadvantage of the actual session establishment method after the session pre-establishment in the above prior art is: in practical applications, there may be a relatively large time interval between the pre-establishment session and the actual session establishment, and the user has reserved resources during the pre-establishment stage , this will waste more resources, and in the case of supporting multimedia sessions, the user needs to have multiple types of session establishment options, and the actual session that the user subsequently establishes can only be the same as the pre-established session. It cannot meet the needs of users to establish sessions flexibly.

Contents of the invention

In view of the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a method for establishing a multimedia communication session, so as to realize the establishment of an actual session by selecting a required session from among pre-established compound sessions or sessions such as multiple sessions. Pre-established sessions are modified.

The purpose of the present invention is achieved through the following technical solutions:

A method for establishing a multimedia communication session, comprising the steps of:

A. According to the session establishment request sent by the user, one or more pre-established sessions are pre-established between the user and the session server, and the negotiated session capability attribute of the pre-established session is inactive;

B. When the session server receives the service establishment request sent by the session participating user, it establishes the actual session according to the selection information carried in the service establishment request and the pre-established session, and in the process of establishing the actual session, the The above-mentioned negotiated session capability attribute is changed to active.

Described step A specifically comprises:

A1. The user sends to the session server one or more session pre-establishment requests carrying session capability requirements or sends a session pre-establishment request carrying multiple session capabilities, wherein the requested session capability attribute is inactive;

A2. After the session server receives the session pre-establishment request, it assigns a session identifier to the session pre-establishment request, and at the same time judges the session description protocol SDP parameter carried in the session pre-establishment request according to the subscription data, and assigns the session pre-establishment request to the session pre-establishment request. SDP parameters for requesting selection of system licenses;

A3. The session server sends a session pre-establishment response carrying the assigned session identifier to the user who sent the session pre-establishment request, and saves the pre-established session, negotiated SDP parameters, and session identifier.

Described step A3 also includes:

The user of the pre-established session establishes a bearer according to the negotiated SDP parameters;

In the IP Multimedia Subsystem IMS system that supports policy control, when an entity in the IMS receives the session establishment response sent by the session server, it requests the policy selection function PDF for the bearer establishment identification Token, and adds the acquired Token in the session establishment response. After the Token is issued, the session establishment response is sent to the user who sent the session pre-establishment request.

Described step A3 also includes:

The user who sends the session pre-establishment request uses the obtained Token to establish a bearer after receiving the session establishment response carrying the Token.

Described step A3 also includes:

In the wideband code division multiple access WCDMA system, the user who sends the session pre-establishment request establishes a packet data protocol PDP connection of the bearer service; in the CDMA system, the user who sends the session pre-establishment request establishes a point-to-point bearer service PPP connection or instance.

The session parameters in the SDP parameters include session-level description, timing description, and media type and format description.

Described step A also includes:

A4. The user who has pre-established the session sends a session update request carrying session identification information and SDP information to the session server. After receiving the session update request, the session server obtains the session update request in the pre-established session stored in the session The session corresponding to the session identifier carried in ;

A5. The session server negotiates the SDP information carried in the session update request with the SDP information and subscription data of the corresponding session, modifies the corresponding session, and then sends a session update request to the The user sends a session update response.

Described step B specifically comprises:

B1. A user who has pre-established a session sends a service establishment request carrying a session identifier and/or an SDP identifier to invite other users to the session server where the session server is located. Select the corresponding session and SDP information in the pre-established session;

B2. The session server uses the selected SDP information to form a session establishment message, sends the session establishment message to the invited user, and simultaneously sends a confirmation message to the calling user of the pre-established session;

B3. After the session server receives the response returned by the invited user, the session server sends a connection request message carrying a session identifier to the calling user of the pre-established session.

Described step B1 also includes:

The session server initiates an update process to change the inactive state of the selected SDP information to an active state.

Described step B1 also includes:

If the user of the pre-established session has not established a bearer, the user may establish a bearer;

In the IMS system supporting policy control, if the user of the pre-established session has not established a bearer, the user can use the obtained Token to establish a bearer.

Described step B2 also includes:

If the user of the pre-established session has not established a bearer, the user may establish a bearer;

In the IMS system supporting policy control, if the user of the pre-established session has not established a bearer, the user can use the obtained Token to establish a bearer.

Described step B2 also includes:

The session server or the calling user of the pre-established session initiates an update process to change the inactive state of the selected SDP information to an active state.

Described step B3 also includes:

In the IMS system supporting policy control, when the entity in the IMS system receives the response message sent by the session server, it requests the resource usage permission from the PDF, and after obtaining the resource usage permission of the PDF, the The calling user of the pre-established session can use the allocated resources.

Described step B specifically comprises:

B4, after the session server where the user who has pre-established the session receives the session establishment request sent by other users, the SDP information carried in the session establishment request is compared with the SDP information of the pre-established session of the user who has pre-established the session match;

B5. The session server acquires, from the SDP information of the pre-established session, SDP information that is equal to or equivalent to the media type and/or media capability information of the SDP information carried in the session establishment request, and according to the equality or Select the corresponding session according to the SDP information of the price, and send a response message to the user who sends the session establishment request;

B6. The session server sends an update request to the user who has pre-established the session, and the session server or the user who has pre-established the session initiates an update process, and the inactive state of the equal or equivalent SDP information Modified to active status.

Described step B5 also includes:

If the user of the pre-established session has not established a bearer, the user may establish a bearer;

In the IMS system supporting policy control, if the user of the pre-established session has not established a bearer, the user can use the obtained Token to establish a bearer.

Described step B6 specifically comprises:

In the IMS system that supports policy control, the session server applies to the PDF for resource usage authorization for the selected session, and after obtaining the authorization of the PDF, sends a connection request carrying a session identifier to the user who has pre-established the session .

Described step B5 also includes:

When the media type and/or media capability information of the SDP information of a pre-established session is equal to or equivalent to the media type and/or media capability information of the SDP information of the session establishment request, the session server Respond to the SDP information, and send a notification message carrying the session identifier to the user who sent the session establishment request;

or,

When the media type and/or media capability information in the SDP information in the SDP information group of the pre-established session is equal to or equivalent to the media type and/or media capability information in the SDP information of the session establishment request, then The session server responds according to the SDP information of the pre-established session, and sends a notification message carrying the session identifier and the SDP information identifier to the user who sent the session establishment request.

The session server may be an access server or a centralized control server. In the cellular-based push-to-talk PoC system, the session server is a PoC server performing a control function or a PoC server performing a participation function.

As can be seen from the technical solution provided by the present invention above, the present invention pre-establishes sessions such as composite sessions or multiple sessions between the calling user and the session server, and the calling user sends a session update request or a session re-application request to the session server, Modifications to pre-established sessions can be implemented. When establishing an actual session, according to the request of the calling user or the called user, the required session can be flexibly selected from the pre-established composite session or multiple sessions to establish the actual session. The multimedia conversation can be better supported, and the problems in the prior art are effectively solved.

Description of drawings

FIG. 1 is a schematic diagram of an actual session establishment method after session pre-establishment in the prior art;

Fig. 2 is the specific processing flowchart of the embodiment of the method of the present invention;

Fig. 3 is a schematic diagram of pre-establishing a session between a calling user and a server and modifying the pre-established session;

4 is a schematic diagram of pre-establishing a compound session including multiple parameter levels between the session server and the calling user;

Figure 5 is a schematic diagram of pre-establishing multiple sessions between the session server and the calling user;

Fig. 6 is the schematic diagram of establishing an actual session by the session server according to the actual session establishment request carrying the session id sent by the calling user;

Figure 7 is a schematic diagram of establishing an actual session according to the called user's request when a compound session is pre-established between the calling user and the session server;

Figure 8 is a schematic diagram of establishing an actual session according to the called user's request when one or more non-composite sessions are pre-established between the calling user and the session server;

FIG. 9 is a flow chart in a policy-controlled resource management mode;

FIG. 10 is a flow chart in another policy-controlled resource management mode;

Fig. 11 is a flow chart in a resource management mode without policy control;

FIG. 12 is a flow chart in another resource management mode without policy control;

Fig. 13 is a schematic diagram of the whole process of pre-establishing both the calling party and the called party under the policy-controlled resource management mode;

Fig. 14 is a schematic diagram of the whole process of pre-establishing both the calling party and the called party in the resource management mode without policy control.

Detailed ways

The present invention provides a method for establishing a multimedia communication session. The core of the present invention is: to pre-establish a compound session or multiple sessions between a calling user and a session server, and to modify the pre-established session as required. When establishing an actual session, a required session is selected from pre-established composite sessions or multiple sessions to establish an actual session.

The method of the present invention is described in detail below in conjunction with the accompanying drawings. The specific processing flow of the embodiment of the method of the present invention is shown in Figure 2, including the following steps:

Step 2-1. The calling user pre-establishes a composite session or multiple sessions with the session server, and modifies the pre-established session by exchanging messages with the session server.

The calling user first sends a session pre-establishment request to the session server. The session pre-establishment request may be one or more session pre-establishment requests carrying session capability requirements, or one session pre-establishment request carrying multiple session capabilities, wherein The requested session capability attribute is Inactive (inactive), that is, the inactive state.

After the session server receives the session pre-establishment request, it distributes the corresponding session id (session identification) to the session pre-establishment request, and judges the SDP (Session Description Protocol) parameter carried in the session pre-establishment request according to the subscription data , select the SDP parameters permitted by the system for the session pre-establishment request. The session parameters in the SDP parameters include session-level description, timing description, and media type and format description.

The session server may allocate multiple SDP parameter levels to the session pre-establishment request carrying multiple session capabilities, for example, allocate SDP1 parameter level, SDP2 parameter level and SDP3 parameter level. That is, compound sessions are pre-established. FIG. 3 is a schematic diagram of pre-establishing a compound session including multiple parameter levels between the session server and the calling user.

The session server may allocate corresponding SDP parameter levels to the one or more session pre-establishment requests carrying session capability requirements, so multiple sessions are pre-established between the session server and the calling user. A schematic diagram of establishing multiple sessions in advance between the session server and the calling user is shown in FIG. 4 .

Then, the session server sends a session pre-establishment response carrying the assigned session identifier to the user who sent the session pre-establishment request, and saves the pre-established session, negotiated SDP parameters, and session identifier.

In an IMS (IP Multimedia Subsystem) system that supports policy control, when an entity in the IMS receives the session establishment response sent by the session server, it requests a Token (bearer establishment identifier) from the PDF (policy selection function), and in the session After the obtained Token is added to the establishment response, the session establishment response is sent to the user who sent the session pre-establishment request. After receiving the session establishment response carrying the Token, the user can immediately use the obtained Token to establish a bearer; or, the user can establish a bearer when the service needs to be used later.

In the WCDMA (Wideband Code Division Multiple Access) system, the above-mentioned bearer is the PDP (Packet Data Protocol) connection of the bearer service; in the CDMA (Code Division Multiple Access) system, the above-mentioned bearer is the PPP (Point-to-Point Protocol) connection of the bearer service or instance.

Before establishing an actual session, the calling user can send an update (session update request) or reinvite (session re-application request) carrying sessionid and SDP information to the session server. After the session server receives the update or reinvite, it modifies the session corresponding to the session id carried in it, and the modified content includes the media capability parameters and address information in the above session parameters. Then, the session server returns a session update response or a session reapplication response to the calling user.

A schematic diagram of pre-establishing a session between the calling user and the server and modifying the pre-established session is shown in FIG. 5 .

When the SIP (Session Initiation Protocol) protocol is running between the calling user and the session server, the above-mentioned session pre-establishment response, session update response, and session re-application response can be implemented through the No. 200 message of the SIP protocol.

Step 2-2. When establishing an actual session, the calling user or the called user sends an actual session establishment request carrying session id and SDP parameter level information to the session server, and the session server selects the corresponding session based on the session id and SDP parameter level information. Pre-established session information and process accordingly.

When establishing an actual session, according to the service establishment request sent by the user who has pre-established the session, the process of establishing the actual session includes the following steps:

Step 1. The user who has pre-established a session sends a service establishment request carrying a session ID and an SDP ID to the session server where the session server is located to invite other users. Select the corresponding session and SDP information.

In this step, the session server may initiate an update process to change the inactive state of the selected SDP information to an active state. If the user of the pre-established session has not established a bearer, the user may establish a bearer. In the IMS system supporting policy control, if the user of the pre-established session has not established a bearer, the user can use the obtained Token to establish a bearer.

Step 2: The session server uses the selected SDP information to form a session establishment message, sends the session establishment message to the invited user, and simultaneously sends a confirmation message to the calling user of the pre-established session.

In this step, the session server or the calling user of the pre-established session may initiate an update process to change the inactive state of the selected SDP information to an active state. If the user of the pre-established session has not established a bearer, the user may establish a bearer. In the IMS system supporting policy control, if the user of the pre-established session has not established a bearer, the user can use the obtained Token to establish a bearer.

Step 3. After the session server receives the response returned by the invited user, the session server sends a connection request message carrying a session identifier to the calling user of the pre-established session.

In this step, in the IMS system that supports policy control, when the entity in the IMS system receives the response message sent by the session server, it requests the resource usage permission from the PDF. After permission, the calling user of the pre-established session is notified that the resource that has been allocated can be used.

The schematic diagram of establishing an actual session by the session server according to the actual session establishment request carrying the session id sent by the calling user is shown in FIG. 6 .

When establishing an actual session, according to the service establishment request sent by other users, the process of establishing an actual session includes the following steps:

Step 1. When establishing an actual session, when the session server where the user who has pre-established the session is located receives the service establishment request sent by other users, it will share the SDP information carried in the service establishment request with the user who has pre-established the session. Match the SDP information of the pre-established session.

Step 2. The session server obtains, from the SDP information of the pre-established session, SDP information that is equal to or equivalent to the media type and media capability information of the SDP information carried in the session establishment request, and according to the equality or equivalent The SDP information of the corresponding session is selected, and a response message is sent to the user who sent the session establishment request.

In this step, if the user of the pre-established session has not established a bearer, the user can establish a bearer. In the IMS system supporting policy control, if the user of the pre-established session has not established a bearer, the user can use the obtained Token to establish a bearer.

In this step, when the media type and media capability information of the SDP information of the pre-established session are equal or equivalent to the media type and media capability information of the SDP information of the session establishment request, the session server The SDP information of the session responds, and sends a notification message carrying the session identifier to the user who sends the session establishment request;

or,

When the media type and media capability information in the SDP information in the SDP information group of the pre-established session is equal to or equivalent to the media type and media capability information in the SDP information of the session establishment request, the session server according to the The SDP information of the pre-established session responds, and sends a notification message carrying the session identifier and the SDP information identifier to the user who sent the session establishment request.

Step 3, the session server sends an update request to the user who has pre-established the session, and the session server or the user who has pre-established the session initiates an update process, and the inactivity of the equal or equivalent SDP information Status changed to Active.

When the compound session is pre-established between the calling user and the session server, the schematic diagram of establishing an actual session according to the called user's request is shown in FIG. 7 . When one or more non-compound sessions are pre-established between the calling user and the session server, a schematic diagram of establishing an actual session according to the called user's request is shown in FIG. 8 .

In this step, in the IMS system supporting policy control, the session server applies to the PDF for resource usage authorization for the selected session, and after obtaining the authorization of the PDF, sends a connection request carrying a session identifier to the already selected session. Users with pre-established sessions.

The flow charts in the above resource management mode based on policy control are shown in FIG. 9 and FIG. 10 . Figure 13 shows a schematic diagram of the entire process of pre-establishing both the calling party and the called party in the resource management mode based on policy control.

When there is no policy control, the resources requested by the user can be used directly by the user, and do not need to be controlled through PDF. The time for bearer establishment is also optional. The time for changing the inactive state of the SDP information to the active state is also optional, and can also be initiated by the user or the server.

Figure 11 and Figure 12 show the flow charts of the above resource management mode based on policy-free control. A schematic diagram of the whole process of pre-establishing both the calling party and the called party in the resource management mode based on no policy control is shown in FIG. 14 .

The above-mentioned method of the present invention is applicable to systems such as a multi-party multimedia communication system.

The above-mentioned session server in the present invention may be an access server or a centralized control server. In a cellular-based push-to-talk PoC system, the session server is a PoC server performing a control function or a PoC server performing a participation function.

The above is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed in the present invention can easily think of changes or Replacement should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be determined by the protection scope of the claims.

Claims (18)

1. A method for establishing a multimedia communication session, comprising the steps of:

A. according to a session establishment request sent by a user, one or more pre-established sessions are pre-established between the user and a session server, and the negotiated session capability attribute of the pre-established session is inactive;

B. after receiving a service establishment request sent by a session participation user, the session server establishes an actual session according to the selection information carried in the service establishment request and the pre-established session, and modifies the negotiated session capability attribute into activity in the process of establishing the actual session.

2. The method according to claim 1, wherein the step a specifically comprises:

a1, user sends one or more session pre-establishment requests carrying session capability requirements or sends one session pre-establishment request carrying multiple session capabilities to the session server, wherein the requested session capability attribute is inactive;

a2, after receiving the session pre-establishment request, the session server allocates a session identifier to the session pre-establishment request, and at the same time, according to the subscription data, determines a Session Description Protocol (SDP) parameter carried in the session pre-establishment request, and selects a system-permitted SDP parameter for the session pre-establishment request;

a3, the session server sends the session pre-establishment response carrying the allocated session identifier to the user sending the session pre-establishment request, and saves the pre-established session, the negotiated SDP parameter and the session identifier.

3. The method according to claim 2, wherein said step a3 further comprises:

the user of the pre-established session establishes a bearer according to the negotiated SDP parameter;

in an IP multimedia subsystem IMS system supporting policy control, when an entity in the IMS receives a session establishment response sent by a session server, the entity requests a bearer establishment identifier (Token) from a policy selection function (PDF), and after the obtained Token is added in the session establishment response, the session establishment response is sent to a user sending a session pre-establishment request.

4. The method according to claim 3, wherein said step A3 further comprises:

and after receiving the session establishment response carrying the Token, the user sending the session pre-establishment request establishes a bearer by using the obtained Token.

5. The method according to claim 2, wherein said step a3 further comprises:

in a Wideband Code Division Multiple Access (WCDMA) system, the user sending the session pre-establishment request establishes a Packet Data Protocol (PDP) connection of a bearer service; in a CDMA system, the user sending the session pre-establishment request establishes a point-to-point PPP connection or instance of the bearer service.

6. The method of claim 2 wherein the session parameters in the SDP parameters comprise a session level description, a timing description, and a media type and format description.

7. The method of claim 1, wherein step a further comprises:

a4, the user with pre-established conversation sends a conversation update request carrying conversation identification information and SDP information to a conversation server, and after receiving the conversation update request, the conversation server obtains the conversation corresponding to the conversation identification carried in the conversation update request from the saved pre-established conversation;

a5, the session server negotiates the SDP information carried in the session update request with the SDP information of the corresponding session and subscription data, modifies the corresponding session, and then sends a session update response to the user sending the session update request.

8. The method according to claim 1, 2, 3, 4, 5, 6 or 7, wherein the step B specifically comprises:

b1, the user who has pre-established conversation sends the business establishment request carrying the conversation mark and/or SDP mark to the conversation server, the conversation server selects the corresponding conversation and SDP information from the pre-established conversation of the user according to the carried conversation mark and/or SDP mark;

b2, the session server uses the selected SDP information to form a session establishment message, sends the session establishment message to the invited user, and sends a confirmation message to the calling user of the pre-established session;

and B3, after the session server receives the response returned by the invited user, the session server sends a connection request message carrying a session identifier to the calling user of the pre-established session.

9. The method according to claim 8, wherein said step B1 further comprises:

and the session server initiates an updating process to modify the inactive state of the selected SDP information into an active state.

10. The method according to claim 8, wherein said step B1 further comprises:

if the user of the pre-established session does not establish the bearer, the user can establish the bearer;

in the IMS system supporting policy control, if a user of the pre-established session does not establish a bearer, the user may establish a bearer using the obtained Token.

11. The method according to claim 8, wherein said step B2 further comprises:

if the user of the pre-established session does not establish the bearer, the user can establish the bearer;

in the IMS system supporting policy control, if a user of the pre-established session does not establish a bearer, the user may establish a bearer using the obtained Token.

12. The method according to claim 8, wherein said step B2 further comprises:

and the session server or the calling party of the pre-established session initiates an updating process to modify the inactive state of the selected SDP information into an active state.

13. The method according to claim 9, wherein said step B3 further comprises:

in the IMS system supporting policy control, after receiving a response message sent by the session server, an entity in the IMS system requests PDF for authorization of resource use permission, and after obtaining the resource use permission of PDF, the calling user of the pre-established session can use the allocated resources.

14. The method according to claim 1, 2, 3, 4, 5, 6 or 7, wherein the step B specifically comprises:

b4, after the session server of the user who has pre-established the session receives the session establishment request sent by other users, matching the SDP information carried in the session establishment request with the SDP information of the pre-established session of the user who has pre-established the session;

b5, the session server obtains the SDP information in the SDP information of the pre-established session, which is equal or equivalent to the media type and/or media capability information of the SDP information carried in the session establishing request, selects the corresponding session according to the equal or equivalent SDP information, and sends a response message to the user sending the session establishing request;

b6, the session server sends an update request to the user of the pre-established session, and the session server or the user of the pre-established session initiates an update process to modify the inactive state of the equal or equivalent SDP information to the active state.

15. The method according to claim 14, wherein said step B5 further comprises:

if the user of the pre-established session does not establish the bearer, the user can establish the bearer;

in the IMS system supporting policy control, if a user of the pre-established session does not establish a bearer, the user may establish a bearer using the obtained Token.

16. The method according to claim 15, wherein the step B6 specifically comprises:

in the IMS system supporting policy control, the session server applies resource use authorization to the selected session to the PDF, and sends a connection request carrying a session identifier to the user who has pre-established the session after obtaining the authorization of the PDF.

17. The method according to claim 14, wherein said step B5 further comprises:

when the media type and/or media capability information of the SDP information of the pre-established session is equal or equivalent to the media type and/or media capability information of the SDP information of the session establishment request, the session server responds according to the SDP information of the pre-established session and sends a notification message carrying a session identifier to the user sending the session establishment request;

or,

when the media type and/or media capability information in one SDP information in the SDP information group of one pre-established session is equal or equivalent to the media type and/or media capability information of the SDP information of the session establishment request, the session server responds according to the SDP information of the pre-established session and sends a notification message carrying a session identifier and the SDP information identifier to the user sending the session establishment request.

18. The method of claim 1, wherein the session server is an access server or a centralized control server, and in a push-to-talk over cellular (PoC) system, the session server is a PoC server performing a control function or a PoC server performing a participation function.

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