WO2011157218A1

WO2011157218A1 - Conference establishment method and system based on back to back user agent

Info

Publication number: WO2011157218A1
Application number: PCT/CN2011/075828
Authority: WO
Inventors: 高扬; 李世涛
Original assignee: 中兴通讯股份有限公司
Priority date: 2010-06-18
Filing date: 2011-06-16
Publication date: 2011-12-22
Also published as: CN102291379B; CN102291379A

Abstract

A conference establishment method based on a Back to Back User Agent (B2BUA) is provided in the present invention, and the method comprises: after receiving a session initial request, an Application Server (AS) performing the B2BUA behavior modifies an initial Filter Criteria (iFC) of the user initiating the initial request; when receiving a subsequent request message which meets the modified iFC, a Serving Call Session Control Function (S-CSCF) triggers the AS performing the B2BUA behavior. A conference establishment system based on a B2BUA is also provided in the present invention, and the system comprises an AS, a Home Subscriber Server (HSS) and an S-CSCF; the system comprises a modifying unit, configured in the AS performing the B2BUA behavior and the S-CSCF, for modifying the iFC of the user initiating the initial request; and a triggering unit, configured in the S-CSCF, for triggering the AS performing the B2BUA behavior. The present invention can still ensure the correct access of the user request after additionally configuring an AS performing the B2BUA behavior.

Description

Conference establishing method and system based on back-to-back user agent

The present invention relates to conference establishment technology, and in particular, to a conference establishment method and system based on a back-to-back user agent (B2BUA) for use in an IP Multimedia Subsystem (IMS, IP Multimedia Subsystem). Background technique

The 3rd Generation Partnership Project (3GPP) defines the application server (AS, Application Server). When processing Session Initiation Protocol (SIP) messages, the behavior mode can be proxy (proxy), route back to back. User Agent (Routeing B2BUA, Routeing Back to Back User Agent) or Initial Back-to-Back User Agent (Initiating B2BUA). When the AS uses the Routeing B2BUA or Initiating B2BUA behavior mode, the Dialog IDs on both sides of the AS are modified by AS, and the Dialog IDs on both sides of the AS will be different.

Figure 1 is a schematic diagram of the AS performing B2BUA behavior. As shown in Figure 1, for the request of the dialog 1, B2BUA-1 uses the new dialog 2 to forward the request due to the B2BUA behavior. The specific process is as follows:

Step 101: UE-A initiates a call request, where the call request carries a dialog information session 1;

Step 102: After receiving the call request, the Serving Call Session Control Function (S-CSCF) sends the call request to B2BUA-1 according to the subscription rule of the UE-A.

Step 103: Since the B2BUA-1 functions as a B2BUA, when it receives the call request, replace the dialog 1 information in the request, for example, replace it with the conversation 2, and forward it to S-CCSF;

Step 104: The S-CSCF may further send the call request to another AS according to the subscription rule of the user, and finally reach the called UE of the UE-B.

Step 105: The dialog information in the call request received by the called party at this time is the information of the dialog 2, and responds with a 200 OK response;

Step 106: After receiving the 200 OK response, the S-CSCF triggers the response message to B2BUA-1.

Step 107, B2BUA-1 converts the dialog information in the received 200 OK response into the information of the dialog 1 according to the relationship of the previous dialog transition, and forwards the information to the S-CSCF;

Step 108: The S-CSCF forwards the converted 200 OK response to the UE-A.

In the process, it can be seen that the dialogue faced by UE-A is conversation 1 and the conversation confronted by UE-B is conversation 2, and its association management is handled by B2BUA-1;

There are various ways to establish a conference in the prior art. One of the scenarios is to add a user to the conference service through the conference application server. Figure 2 is a flow chart of the establishment of the existing conference service. As shown in Figure 2, UE-A and UE-B establish a session first, then UE-A establishes another conference service, and hopes to add UE-B to the establishment. The multi-party call is implemented in the conference service. The standard process is as follows:

Step 201: UE-A initiates a call request.

Step 202: The call request control function entity (P-CSCF, Proxy Call Session Control Function) sends the call request to the S-CSCF serving the UE-A.

Step 203: The S-CSCF sends the call request to the called user UE-B.

Step 204 to step 206, the UE-B sends a 200 OK response to the UE-A, and the session established between the UE-A and the UE-B may be referred to as the conversation 1;

Step 207: UE-A desires to perform a multi-party call, and then initiates a conference establishment request to the conference AS. Steps 208 to 209, and send the conference establishment request to the S-CSCF through the P-CSCF. Meeting AS;

Step 210 to step 212, the conference AS receives the conference establishment of the UE-A, and returns a 200 OK response to the UE-A, and the dialog established between the UE-A and the conference AS 2;

Step 213 to step 215, at this time, UE-A wants to add UE-B to the newly established conference service, and replaces the conversation between the original UE-A and UE-B, and UE-A sends a handover to the conference AS (REFER). a request, which carries a Replaces header field or parameter whose value is the information of the dialog 1;

Step 216 to step 217, after receiving the transfer request, the conference AS sends a new call request to the called user UE-B, which also carries a Replaces header field or parameter whose value is the information of the conversation 1;

Step 218: After receiving the call request, the UE-B first finds the session 1 information on the UE-B, and determines that the new call is to replace the originally established session 1;

Step 219 to step 220, after the UE-B agrees to the request, sending a 200 OK response to the conference AS;

Step 221 to step 223, at the same time, UE-B sends a request to UE-A to end the original conversation 1; Step 224 to step 226, UE-A sends 200 OK, accepts the end of conversation 1.

At this point, the conversation 1 is replaced by the conference service, but in the above process, there is no B2BUA in the process of session establishment, because in the existing IMS network, there are many ASs participating in the user. Serving the user in the session, so during the session establishment process

The emergence of B2BUA is a very common situation.

Figure 3 is a flowchart of a B2BUA in the process of establishing a conference service. As shown in Figure 3, when a B2BUA occurs during the conference setup process shown in Figure 2, the process is as follows:

Step 301 to step 302, the user initiates a call request, which is the same as steps 201 to 202 shown in FIG. 2;

Step 303: The S-CSCF triggers the call request according to the subscription rule of the user. B2BUA-1;

Step 304, since the B2BUA-1 functions as a back-to-back user agent, the B2BUA-1 replaces the session 1 information of the call request with the conversation A and then forwards it to the UE-B;

Step 305, the UE-B replies with a 200 OK response, and the session information established on the UE-B is the conversation 2;

Step 306 to step 308, the B2BUA-1 forwards the 200 OK of the UE-B to the UE-A, and then converts the dialog A into the information of the conversation 1. At this time, the conversation 1 is established on the UE-A;

Steps 309 to 319 are the process of establishing a conference. The conference establishment process is the same as steps 207 to 217 shown in FIG. 2;

Step 320: After the UE-B receives the call request sent by the conference AS, it searches for the conversation 1. Since a B2BUA-1 has passed during the establishment of the previous conversation 1, there is no information of the conversation 1 on the UE-B. ;

Step 321 : Since the information of the conversation 1 is not found, the UE-B rejects the call request sent by the conference AS, so that the adding process fails.

Obviously, when there is B2BUA participation in the conference service establishment process, if the existing call process is still used, the call addition will fail. Summary of the invention

In view of the above, it is a primary object of the present invention to provide a method and system for establishing a conference based on back-to-back user agents, which can accurately resolve and initiate a call when a call request is initiated in a call flow with a back-to-back user agent.

In order to achieve the above object, the technical solution of the present invention is achieved as follows:

A method for establishing a conference based on back-to-back user agents, including:

After the AS that performs the B2BUA behavior receives the initial request of the conversation, the initial filtering rule of the initiator user of the initial request is modified;

The S-CSCF triggers the subsequent request message that meets the modified initial filtering rule. The AS that performs the B2BUA behavior.

Preferably, the modified initial filtering rule is:

For the S-CSCF of the initiator user, the receiving subsequent request message carries a replacement parameter or a replacement header field, and the value of the replacement parameter or the replacement header field is the established session, and the receiving in the subsequent request message The party user is the receiver user of the established session, and triggers the AS that performs the B2BUA behavior for the subsequent request message.

Preferably, the AS performing the B2BUA behavior and the S-CSCF are respectively an AS and an S-CSCF of the initiator user;

Modifying the initial filtering rule of the initiating user is specifically: modifying the initial filtering rule in the home user server HSS by the AS performing the B2BUA behavior;

The method further includes: after the HSS modifies the initial filtering rule, notifying the S-CSCF of the initiator user to modify an initial filtering rule of the initiator user.

Preferably, the subsequent request message is a subsequent request message of the initiator user or the receiver user; the subsequent request message is an invite INVITE request message or a transfer REFER request message.

Preferably, the method further includes:

The modified initial filtering rule is placed at the head of the initial filtering rule trigger sequence.

Preferably, the triggering the AS that performs the B2BUA behavior for the subsequent request message is:

After receiving the subsequent request message, the S-CSCF of the initiator user, when determining that the subsequent request message meets the modified initial filtering rule, sends the subsequent request message to the AS that performs the B2BUA behavior. And triggering, by the AS that performs the B2BUA behavior, to replace the replacement parameter or the replacement header field in the subsequent request message;

The method further includes:

Transmitting, by the AS performing the B2BUA behavior, the replaced subsequent request message to the The S-CSCF of the initiator user; the S-CSCF of the initiator user initiates a call request to the recipient user for the replaced subsequent request message.

After receiving the subsequent request message, the S-CSCF of the initiator user sends the subsequent request message to the conference AS, and the conference AS sends a call request to the S-CSCF of the initiator user; the call request carries a replacement parameter or a replacement header field of the subsequent request message;

When the S-CSCF of the initiator user determines that the received call request from the conference AS meets the modified initial filtering rule, the received call request is sent to the B2BUA, and the AS that performs the B2BUA behavior is triggered. Substituting a replacement parameter or a replacement header field in the subsequent request message;

The method further includes:

The AS performing the B2BUA action sends the replaced subsequent request message to the S-CSCF of the initiator user; the S-CSCF of the initiator user initiates the message to the replaced subsequent request message The recipient user initiates a call request.

A conference establishment system based on a back-to-back user agent, including an AS, an HSS, and an S-CSCF; the system includes a modification unit and a trigger unit;

a modifying unit, configured to be used in the AS and the S-CSCF that perform the B2BUA behavior, and configured to modify an initial filtering rule of the initiator user of the initial request after receiving the initial request of the dialog;

The triggering unit is configured in the S-CSCF, and is configured to trigger the AS that performs the B2BUA behavior when receiving the subsequent request message that meets the modified initial filtering rule.

Preferably, the modified initial filtering rule is:

The S-CSCF of the initiator user carries a replacement parameter or a replacement header field in the received subsequent request message, and the value of the replacement parameter or the replacement header field is the established session, and the subsequent The recipient user in the request message is the recipient user of the established session, and the AS that performs the B2BUA behavior is triggered for the subsequent request message.

The modifying unit is further configured to modify the initial filtering rule in the HSS;

After the HSS modifies the initial filtering rule, the S-CSCF of the initiator user is further notified to modify the initial filtering rule of the initiator user.

Preferably, the subsequent request message is a subsequent request message of the initiator user or the receiver user; the subsequent request message is an INVITE request message or a REFER request message.

Preferably, the system further comprises:

A placement unit that places the modified initial filter rule at the head of the initial filter rule trigger sequence.

Preferably, the S-CSCF of the initiator user, after receiving the subsequent request message, further determining that the subsequent request message meets the modified initial filtering rule, sending the subsequent request message to the The AS that performs the B2BUA behavior triggers the AS that performs the B2BUA behavior to replace the replacement parameter or the replacement header field in the subsequent request message;

The AS that performs the B2BUA action is further configured to send the replaced subsequent request message to the S-CSCF of the initiator user; the S-CSCF of the initiator user initiates the replaced subsequent request message. A call request is initiated to the recipient user.

Preferably, the S-CSCF of the initiator user further sends the subsequent request message to the conference AS after receiving the subsequent request message, and the conference AS is further configured to send a call to the S-CSCF of the initiator user. a request; the call request carries a replacement parameter or a replacement header field of the subsequent request message;

The S-CSCF of the initiator user further determines that the received call request from the conference AS meets the modified initial filtering rule, and sends the received call request to the The B2BUA triggers the AS that performs the B2BUA behavior to replace the replacement parameter or the replacement header field in the subsequent request message;

In the present invention, after receiving the initial dialog request, the AS performing the B2BUA behavior modifies the initial filtering rule of the initiator user of the initial request after receiving the initial request of the dialog; the S-CSCF receives the modified initial When the subsequent request message of the rule is filtered, the AS that performs the B2BUA behavior is triggered. In this way, when the S-CSCF of the receiving user receives the subsequent request message, it determines whether the modified initial filtering rule is met, and after performing the corresponding initial filtering rule on the received subsequent request message, the corresponding initial Call request. The invention can still ensure the correct establishment of the conference requested by the user after adding the AS that performs the B2BUA behavior. DRAWINGS

Figure 1 is a schematic diagram of the AS performing B2BUA behavior;

Figure 2 is a flow chart showing the establishment of an existing conference service;

Figure 3 is a flow chart of a B2BUA in the process of establishing a conference service;

4 is a flow chart showing an application example 1 of a conference establishing method based on back-to-back user agents according to the present invention;

FIG. 5 is a flow chart showing an application example 2 of a conference establishing method based on back-to-back user agents according to the present invention; FIG.

FIG. 6 is a schematic structural diagram of a conference establishing system based on a back-to-back user agent according to the present invention. detailed description

The basic idea of the present invention is that after the AS performing the B2BUA behavior receives the initial session request, after receiving the initial request of the session, the initial user of the initiator of the initial request is modified. Filtering rules, when the S-CSCF receives a subsequent request message that meets the modified initial filtering rule, triggers the AS that performs the B2BUA behavior.

The present invention will be further described in detail below with reference to the accompanying drawings.

FIG. 4 is a flowchart of a first embodiment of a method for establishing a conference based on a back-to-back user agent according to the present invention. As shown in FIG. 4, the conference establishing method based on the back-to-back user agent includes the following steps:

Step 401 to step 403, the session establishment process is the same as step 301 to step 303 in FIG. 3, that is, the UEA sends a call request to the S-CSCF via the P-CSCF, and the S-CSCF forwards the call request to the B2BUA-1 after receiving the call request. (AS that performs B2BUA behavior). The call request carries the dialog 1 identifier.

Step 404: After receiving the call request, the B2BUA-1 initiates modification of the initial filter rule (iFC, initial filter Criteria) to the HSS.

Step 405: The HSS modifies its own iFC. After the HSS modifies the iFC, the HSS notifies the S-CSCF of the latest modified iFC rule. The modified initial filtering rule is: for the S-CSCF of the initiator user, the receiving subsequent request message carries a replacement parameter or a replacement header field, and the value of the replacement parameter or the replacement header field is the established session. The recipient user in the subsequent request message is the recipient user of the established session, and the B2BUA-1 is triggered for the subsequent request message.

In the present invention, in order to ensure that the modified initial filtering rule is executed first, the modified iFC is placed in the head of the iFC trigger sequence.

Step 406: After receiving the notification, the S-CSCF correspondingly modifies the iFC. The modified iFC is the same as the modified iFC in the HSS. The S-CSCF sends a modified iFC completion response to the HSS.

Step 407: The HSS sends an acknowledgement response to the S-CSCF.

In the present invention, after receiving the initial request for the conversation, the B2BUA-1 is directed to the S-CSCF. Before the initial request is initiated to the recipient user of the initial request, the iFC in the HSS is modified, and the iFC modification in the S-CSCF is completed.

Step 408 to step 414, which are identical to steps 303 to 308, and are used to establish a session 1 between UE-A and UE-B;

At this time, the session information established on the UE-A is the conversation 1, and the session information established on the UE-B is the conversation A;

Steps 415 to 420, these steps are the process of the conference establishment, which is the same as the steps 309 to 318 in FIG. 3, at this time, the UE-A completes the establishment of the conference service, and requests the conference AS to add the UE-B to the conference service;

Step 421: Step 422: The UE-A sends a handover (REFER) request to the S-CSCF through the P-CSCF. The REFER request carries the replacement parameter or the replacement header field.

Step 423: The S-CSCF sends a REFER request to the conference AS. The REFER request carries a replacement parameter or a replacement header field.

Step 424: The conference AS sends a call request to the S-CSCF, where the call request carries a replacement parameter or a replacement header field.

Step 425 to step 426, after receiving the call request sent by the conference AS, the S-CSCF performs matching according to the new iFC rule. Since the call request includes a Replaces header field, and the called party of the call is UE-B, The S-CSCF triggers the call request to B2BUA-1 according to the new iFC rule;

Step 427, after receiving the call request, the B2BUA-1 searches for the information of the dialog 1, and finds the corresponding relationship;

Step 428, B2BUA-1 forwards the call request to the S-CSCF according to the B2BUA, and changes the value of the replaces header field to the dialog A;

Step 429, the S-CSCF sends the forwarded call request to the called user UE-B;

Step 430, at this time, UE-B can find conversation A in itself and replace the pair with a new call. Word A;

Step 431 to step 433, UE-B sends a 200 OK response to the conference AS. Step 434 to step 436, UE-B sends an end request to UE-A, ending session A, where B2BUA-1 converts the end dialog A into End dialog 1 is sent to UE-A; UE-A returns 200 OK.

FIG. 5 is a flowchart of a second embodiment of a method for establishing a conference based on a back-to-back user agent according to the present invention. As shown in FIG. 5, the conference establishing method based on the back-to-back user agent includes the following steps:

Steps 501 to 522 are identical to steps 401 to 422 shown in FIG. Step 523: After receiving the REFER request, the S-CSCF performs matching according to the new iFC rule. Since the REFER request includes a Replaces header field, and the called party of the call is UE-B, the S-CSCF follows the new iFC. Rule, trigger the REFER request to B2BUA-1;

Step 524: The S-CSCF triggers the REFER request to the B2BUA-1. After receiving the REFER request, the B2BUA-1 searches for the information of the dialog 1 and finds the corresponding relationship.

Step 525, B2BUA-1 forwards the REFER request to the S-CSCF according to the B2BUA, and changes the value of the replaces header field to the dialog A;

Step 526, the S-CSCF sends a REFER request to the conference AS.

Step 527: The conference AS sends a call request to the S-CSCF.

Step 528: The S-CSCF sends a call request to the called user UE-B, where the dialog A identifier is carried.

Step 529 to step 535 are identical to steps 430 to 436.

4 and FIG. 5 are descriptions of the REFER request message as an example. Those skilled in the art should understand that the foregoing REFER request message may also be replaced by an INVITE request message, and the present invention does not provide a flowchart for processing the INVITE request message. . The INVITE request message or the REFER request message in the present invention may be a request message initiated by the initiator user or the recipient user. The back-to-back user agent-based conference establishing system of the present invention is applied to an IMS, including an AS, an HSS, and an S-CSCF. FIG. 6 is a schematic structural diagram of a conference establishing system based on a back-to-back user agent according to the present invention. The conference establishing system based on the back-to-back user agent of the present invention further includes a modifying unit 60 and a triggering unit 61;

The modifying unit 60 is configured to be used in the AS and the S-CSCF that perform the B2BUA behavior, and after the initial request for receiving the session, modify an initial filtering rule of the initiator user of the initial request;

The triggering unit 61 is configured in the S-CSCF, and is configured to trigger the AS that performs the B2BUA behavior when receiving a subsequent request message that meets the modified initial filtering rule.

The AS and the S-CSCF that perform the B2BUA behavior are respectively the AS and the S-CSCF of the initiator user; after the HSS modifies the initial filtering rule, the S-CSCF of the initiator user is further notified to modify the initiation. The initial filtering rules of the party user;

The S-CSCF of the initiator user is further configured to modify an initial filtering rule of the initiator user, and then establish a dialogue for the initiator user and the recipient user.

The above modified initial filtering rules are:

For the S-CSCF of the initiator user, the receiving subsequent request message carries a replacement parameter or a replacement header field, and the value of the replacement parameter or the replacement header field is the established session, and the receiving in the subsequent request message The party user is the receiver user of the established session, and the AS that performs the B2BUA behavior is triggered for the subsequent request message.

The subsequent request message is a subsequent request message of the initiator user or the receiver user; the subsequent request message is an INVITE request message or a REFER request message.

As shown in FIG. 6, the conference establishing system based on the back-to-back user agent of the present invention further includes a placing unit 62 for placing the modified initial filtering rule in the initial filtering rule trigger sequence. First.

The AS performing the B2BUA behavior and the S-CSCF are respectively an AS and an S-CSCF of the initiator user;

The modifying unit 60 is further configured to modify the initial filtering rule in the HSS;

After receiving the subsequent request message, the S-CSCF of the initiating user further determines that the subsequent request message meets the modified initial filtering rule, and sends the subsequent request message to the performing B2BUA behavior. AS, triggering, by the AS that performs the B2BUA behavior, to replace the replacement parameter or the replacement header field in the subsequent request message;

After receiving the subsequent request message, the S-CSCF of the initiating user further sends the subsequent request message to the conference AS, and the conference AS is further configured to send a call request to the S-CSCF of the initiator user. The call request carries a replacement parameter or a replacement header field of the subsequent request message;

The S-CSCF of the initiator user further determines that the received call request from the conference AS meets the modified initial filtering rule, and sends the received call request to the B2BUA to trigger the B2BUA behavior. The AS replaces the replacement parameter or the replacement header field in the subsequent request message;

The AS performing the B2BUA behavior is further configured to send the replaced subsequent request message to the S-CSCF of the initiator user; the S-CSCF of the initiator user is used for the replaced The subsequent request message initiates a call request to the recipient user.

It should be understood by those skilled in the art that the back-to-back user agent-based conference establishing system shown in FIG. 6 is designed to implement the foregoing back-to-back user agent-based conference establishing method, and the implementation functions of the foregoing processing units may refer to the foregoing method. Understand the relevant description. The functions of the various processing units in the figure can be implemented by a program running on a processor, or by a specific logic circuit.

The above is only the preferred embodiment of the present invention and is not intended to limit the scope of the present invention.

Claims

Claim

A method for establishing a conference based on a back-to-back user agent, characterized in that the method comprises:

The application server AS performing the back-to-back user agent B2BUA behavior, after receiving the initial request of the session, modifying the initial filtering rule of the initiator user of the initial request;

The serving call session control function entity triggers the AS that performs the B2BUA behavior when receiving the subsequent request message conforming to the modified initial filtering rule.

2. The method according to claim 1, wherein the modified initial filtering rule is:

The method according to claim 1 or 2, wherein the AS performing the B2BUA action and the S-CSCF are respectively an AS and an S-CSCF of the initiator user;

The method according to claim 3, wherein the subsequent request message is a subsequent request message of the initiator user or the receiver user; the subsequent request message is an invite INVITE request message or a transfer REFER Request message.

The method according to claim 4, wherein the method further comprises: placing the modified initial filtering rule on the head of the initial filtering rule triggering sequence.

6. The method according to claim 5, wherein the request for the subsequent request The message triggers the AS that performs the B2BUA behavior as:

The method further includes:

The method according to claim 5, wherein the triggering the AS that performs the B2BUA behavior for the subsequent request message is:

The method further includes:

A conference establishing system based on a back-to-back user agent, comprising an AS, an HSS, and an S-CSCF; wherein the system includes a modifying unit and a triggering unit;

The modification unit is set in the AS and the S-CSCF as the B2BUA behavior, and is used in After receiving the initial request of the conversation, modifying an initial filtering rule of the initiator user of the initial request;

9. The system of claim 8 wherein the modified initial filtering rules are:

The system according to claim 8 or 9, wherein the AS performing the B2BUA action and the S-CSCF are respectively an AS and an S-CSCF of the initiator user;

The system according to claim 10, wherein the subsequent request message is a subsequent request message of the initiator user or the receiver user; the subsequent request message is an INVITE request message or a REFER request message. .

The system according to claim 11, wherein the system further comprises: a placing unit, configured to place the modified initial filtering rule on the head of the initial filtering rule triggering sequence.

The system according to claim 12, wherein the S-CSCF of the initiator user further determines that the subsequent request message meets the modified initial filtering rule after receiving the subsequent request message. Sending the subsequent request message to the AS performing the B2BUA behavior, triggering the AS performing the B2BUA behavior to the subsequent request message. Replacement parameters or replacement header fields in the replacement;

The system according to claim 12, wherein the S-CSCF of the initiator user further sends the subsequent request message to the conference AS after receiving the subsequent request message, and the conference AS is further used for Sending a call request to the S-CSCF of the initiator user; the call request carries a replacement parameter or a replacement header field of the subsequent request message;

The S-CSCF of the initiator user further determines that the received call request from the AS that is not the B2BUA meets the modified initial filtering rule, and sends the received call request to the B2BUA, triggering the execution. The AS of the B2BUA behavior replaces the replacement parameter or the replacement header field in the subsequent request message;