Mobile phone call Process

 

After the user enters the called Number and presses the launch button, the mobile phone (which is replaced by Ms below) will perform a series of actions,

First, Ms will send a channel request message to BSS through the random access channel (Rach) to apply for a dedicated channel (sdcch). After the BSC successfully assigns the corresponding channel to the BSS, in the access permitted channel (AGCH), the dedicated channel assigned to the notification Ms by immediately allocating messages,

Then MS sends a layer-3 message-CM service request message on the allocated sdcch. In the message, the CM service type is mobile, this message is transparently transmitted to MSC by BSS. After MSC receives the CM service request message, it processes the access request message and notifies vlr to process the MS Access Service request. (At the same time, the SCCP Connection Service is used between the BSC and MSC. To establish a SCCP Connection, the MSC will return the connection confirmation message to the BSC)

After receiving the service access request, vlr first checks whether the MS has three authentication groups in the database. If yes, it will directly issue an authentication command to MSC. Otherwise, request the authentication parameter from HLR/AUC, obtain the three groups from HLR/AUC, and then issue the authentication command to MSC. After receiving the authorization Command sent by vlr, MSC sends an authentication request to Ms through BSS. The command contains the authentication parameters. After Ms receives the authentication request, it uses imsi and authentication in the SIM card.AlgorithmThe authentication result is obtained and delivered to MSC through the authentication response message. msc sends the authentication result back to vlr. vlr checks the authentication result reported by MS and the results in the authentication parameter obtained from HLR, if the two are inconsistent, the access request is rejected and the call fails. If the two are consistent, the authentication is passed. After the authentication is passed, vlr will first issue an encryption command to MSC, then, notify MSC that the MS Access request has been passed. msc notifies Ms that the MS service request has been passed through BSS, and then MSC sends an encryption command to MS, which contains the encryption mode, after Ms receives the command and completes the encryption, it sends back the encrypted message, which completes the entire access phase.

 

After the access phase and Authentication Encryption process, the caller's legal identity has been confirmed and has been connected to the network. In order to continue the call, more detailed information is required, in accordance with the specifications, in this case, Ms will send a set up message, which carries more detailed information such as the called number and the caller ID. After MSC receives the message, it first uses S. i. f. o The message queries the user's business information from vlr. vlr determines whether the call can continue based on the business category and the business information applied by Ms at the time of account opening.

If you can continue, send the user data back to MSC by completing the call message. After MSC receives the message, it continues the message through the call and notifies Ms that the call is being processed by the BSS. Then, based on the interface circuit, send a request to the BSC. In the message, select an ainterface circuit. After the BSC receives the command, it specifies wireless resources to the BTS and Ms, after Ms receives the instruction, it takes up the message of successful delivery allocation. By now, the TCH configuration phase has been completed, and our wireless resources and a interface circuit have been allocated successfully.

After receiving the request Completion message reported by MS, MSC performs the call analysis, addressing the request to HLR Based on the called number, and sending the route information request message. After HLR receives the message, query the called imsi to obtain the vlr where the called is located and request a roaming number from the vlr where the called is located. After receiving the request roaming number message, the vlr where the called is located allocates msrn to the corresponding MS, then, send the message back to HLR in the Response Message of the Request roaming number. After HLR obtains the msrn, it wants the MSC to send the route information response message, and MSC obtains the called msrn from the message, based on msrn, inter-board relay routing is selected and IAI messages are sent to the MSC where the called is located. So far, the main call signaling process has basically ended.

 

When an end server MSC receives the IAI message sent by the local ca, to determine whether the called user can accept the call, the MSC first uses the S. f. i. the C message queries the user information of the called user from the corresponding vlr. If vlr queries the user information, it finds that the user can accept the call (not shut down and can accept the call ), A paging command message is sent to MSC, which contains the user's location information (LAI). After MSC receives this information, it queries the data, obtain the signaling point code of the BSC controlling the location, and issue a paging command to the corresponding BSc. The BSC notifies the controlled BTs to send a paging message through the paging channel (PCH. The mobile phone has been listening on this channel. After receiving the paging message, it reports the paging response message in the random access channel (Rach). (because SCCP has been used in the interface, therefore, the paging response is also regarded as a connection to SCCP to establish a request message. The SCCP layer of MSC should return a connection confirmation message)

At the same time, MSC sends access request processing messages to vlr. vlr first starts the authentication process to view the user's authentication parameter groups. If the vlr does not have the user's authentication three groups, vlr initiates the process of obtaining authentication parameters from HLR (For details, refer to the authentication process in the access process of the caller). Otherwise, vlr will directly send a start authentication message to MSC, the START authentication message contains the user's authentication three groups (RAND, KC, SERS). After receiving the message, MSC will continue to notify the corresponding BSC and BTs to issue the authentication command, after Ms receives the authentication request, it calculates the corresponding SERS Based on the ki in the SIM card. Then, the SERS reports MSc in the authentication response message, and the MSC sends it back to vlr, after receiving the authentication response message, vlr checks whether the reported SERS is consistent with the SERS in the three groups obtained from HLR. If they are consistent, it sends an access request to MSC to accept the message, notify MSC that the user's access request is accepted. The called user information is sent back to MSC by completing the call message. If the user information is inconsistent, the call will be rejected.

after receiving the call completion message, MSC sends the setup message to the BSS side, prompting that a call will be established. After Ms receives the message, it returns the call confirmation message, MSC selects the corresponding A interface circuit and sends a request message indicating the configuration to the corresponding BSC. The BSC allocates the corresponding wireless resources based on the resource situation and notifies Ms, after MS is used successfully, the delivery refers to the completion message. At the same time, the MS is called to start the ring and return the ring message to its MSC. The MSC sends a full message to the MSC address where the main caller is located, the MSC where the caller is located sends the called ring message to ms. At this time, the host user can hear the return ring message. If the called user decides to accept the call, press the response button, and the call is translated as a connect message by the mobile phone, send to MSC. After MSC receives the message, it sends a Response Message (ANC) to the master MSC. After receiving the message, the master MSC sends a connection establishment request message to the master Ms, the caller MS sends a connection request to the caller's MSC to confirm the message. The message is sent to the called Ms by the MSC. Therefore, the call starts and both parties make a call.