The hottest SIP protocol specification RFC3261 Chi

2022-07-20
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SIP protocol specification RFC3261 Chinese sharing

continues to share 21 contents, and continues to share some contents about UAC processing and UAS processing flow

12.2.1.2 processing the responses

uac will receive a request response message from the transaction layer. If the client transaction returns a timeout, this error is treated as a 408 (request timeout) response

uac processing method needs attention. If the UAC receives a 3xx response returned for a request and the request is sent to the request in a dialog, the UAC processing method is the same as that of the request sent outside the dialog. Refer to section 8.1.3.4 for specific discussion

note, however, when UAC attempts to select an address, it still uses the routing group to support the dialog to create the requested route header

when UAC receives a 2XX response to the destination refresh request, if a remote destination URL appears, UAC must replace the remote destination (remote target URI) of the dialog with the URL of the contact header in the response

if the request response in the dialog is a 481 error (call/transaction does not exist) or a 408 (request timeout), UAC should end the dialog. The UAC should also end the dialog without any request response reply (the client transaction layer will notify the Tu of the timeout result)

for dialogs initiated with invite, send a bye message to end the dialog

12.2.2 UAS behavior

the request sent in the dialog is like other requests. If rust is found, it is an atomic core request. If the UAS accepts a special request, all associated status modifications must be executed. If the request is rejected, no status modification process will be performed

note that some requests, such as invite requests, will affect some state changes

uas will receive this request from the transaction layer. If the request contains a tag tag in the to header, the UAS core will process the identity confirmation of the improved alog of DI and fuel efficiency, which is consistent with the request, and then compare the existing dialogs with this dialog. If the comparison matches, it will confirm that this is a mid dialog request. In this case, UAS first uses the same processing rules for external dialog requests to execute the processing flow. The details are discussed in Section 8.2

if the to header of the request contains a and tag, but the dialog identity confirmation cannot match any existing dialog, the UAS may have crashed and restarted, or maintain the existing state. Here, the UAS may have received a request, This request may support different (failed) UAS (these UAS have the ability to build to tags, so that UAS can confirm the request through this tag. These tags are used to support UAS to provide failed recovery status). Another possibility is that the received request may have been routed incorrectly. Based on the to tag tag, UAS may accept or reject this request. Accepting this request can provide robustness for the to tag tag, so the dialog can maintain persistence and even the UAS crashes. UAS wishing to support this capability must consider the above point. Some problems may occur during the processing, such as strictly increasing the cseq serial number when the UA is restarted, reconstructing the routing group and accepting the RTP timestamp and serial number that are out of range

if the UAS wants to resolve this request because it does not want to re create this dialog, the UAS must reply to its request with a 481 response (call/transaction does not exist) status response code and send this response to the server transaction layer

if the request does not modify the dialog status in any way, the request may be received in the dialog (for example, options request). They are handled like requests received in an external dialog

if the remote serial number is empty, this serial number must be set to the serial number value of cseq header in the request. If the remote serial number is not empty, but the serial number value in the request is lower than the remote serial number, the request has been sorted abnormally, and a 500 (server internal error) error response code must be returned. If the remote serial number is not empty and the requested serial number is greater than the remote serial number value, the request is processed as a continuation. It is possible that the local cseq serial number is greater than one digit of the remote cseq serial number. This is not an error state in itself. UAS should be ready to receive and process similar requests. When the cseq value carried in such requests meets the tolerance requirements of various motion characteristic parameters, it will be higher than the cseq value of the previous received request

if the agent verifies a request generated by the UAC, the UAC needs to resubmit the request carrying the security message. Resubmitting the request will generate a new cseq serial number. Because UAS has never seen the first request, UA will prompt interruption at cseq serial number position. Such interruption does not represent any error. Universal testing machine adopts microcomputer closed-loop control status message

when UAS receives a destination refresh request, it must replace the remote destination URL address (if any) in the dialog with the URL in the contact header in the request

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