KR930006034B1 - Message transfer part system by common channelling method - Google Patents

Abstract

The method gives level 3 function to the common channel signalling number 7 message transfer part so that a TDX-1 has ISDN function. The method comprises the steps: (A) initializing parameters and data; (B) executing signalling link handling (SLH) routine for supervising states of signalling link; (C) executing signalling message handling (SMH) function for processing signalling message and for supervising routine table; (D) executing signalling point handling routine for supervising signalling points and states of routes and executing link set handling routine for supervising link set.

Description

Implementation Method of Level 3 Function of Common Line Signaling (No.7) Message Transmitter

1 is a hardware configuration diagram of a common line signaling system (No. 7) to which the present invention is applied.

2 is a block diagram of a level 3 software inter-block functional module to which the present invention is applied.

3 is a flow diagram of a method for implementing a level 3 function according to the present invention.

4 is a flow chart of a SLH in a level 3 software block in accordance with the present invention.

5 is a flowchart of an SMH in a level 3 software block according to the present invention.

6 is a flowchart of the LSH in a level 3 software block according to the present invention;

7 is a flowchart of an SPH in a level 3 software block according to the present invention.

* Explanation of symbols for main parts of the drawings

1: IOIP 2: SAIP

3: MTIP 4: DKIP

5: SAP 6: DTLP

7: SMP 8: SPB

9: CSIOB 10: STB

11: MGMT 12: ISUP

13: OMH 14: SMH

15: LSH 16: SPH

17: SLH 18: STH

The present invention relates to a message transfer part (MTP) function of common line signaling (No. 7), and more particularly, to a method for implementing a level 3 function of a message transfer part.

As the information society develops, the expectation for communication is increasing and diversifying internationally. In addition, ISDN services were needed to meet the various needs of users, and as part of these services, specific protocol No.7 common line signaling (CCS No.7) recommended by the International Telegraph and Telephone Advisory Committee (CCITT). The message delivery unit function is implemented.

The present invention provides a method for implementing a level 3 function of a common line signaling (No. 7) message transfer unit that maximizes reliability and efficiency of message delivery in order to add an ISDN function to a TDX-1 electronic switch currently being distributed in Korea. Has its purpose.

In order to achieve the above object, the present invention performs IOIP for displaying a message to the operator of the processing result to the operating terminal, SAIP for receiving and processing an alarm signal, MTIP for controlling the magnetic tape, DKIP for controlling the disk, and performing statistical processing functions. SAP, SPLP that manages operation, maintenance, maintenance, and management functions in the exchange as a whole, DTLP having common line signaling user part function, SMP that performs processor startup, initialization, and function recovery, and SPB that is responsible for level 3 functions. In a method of implementing a level 3 function of a message transfer unit of a common line signaling system (No. 7) system including a signal terminal, and a CSIOB responsible for communication between the signal terminal and DTLP, various parameters and data values may be obtained. The first step of initializing, the second step of handling Signaling Link Handling (SLH) to manage the signal link state, the SMH (S signal processing and managing routing table) performed by a third step of processing ignalling message handling, a fourth step of processing SPH (Signalling Point Handling) to manage signal points and a route state, and a fifth step of link set handling (LSH) to manage a link set. It is characterized by.

Hereinafter, with reference to the accompanying drawings will be described an embodiment of the present invention;

1 is a configuration diagram of a common line signaling system to which the present invention is applied, 1 is IOIP, 2 is SAIP, 3 is MTIP, 4 is DKIP, 5 is SAP, 6 is DTLP, 7 is SMP, 8 is SPB, 9 Is CSIOB and 10 is STB, respectively.

1 is a hardware configuration diagram of the No.7 common line signaling system, showing the connection of the functional blocks of the electronic switchboard and the level 3 and level 2 functions of the message transfer unit. The IOIP 1 has a function of displaying a message on the operation terminal informing the operator of the processing result. The SAIP 2 receives the information signal and processes it. The MTIP 3 controls the magnetic tape. The DKIP 4 controls the disc. The SAP 5 performs a statistical processing function. The DTLP 6 manages the operation, maintenance, maintenance, and management functions in the exchange as a whole, and has a common line signaling user part function.

The SMP 7 performs startup, initialization, function recovery and the like of the processor. The CSIOB 9 is responsible for communication between the signal terminal (STB) 10 and the DTLP 6 which is in charge of the user processor part of the SPB (System Processor Board) 8 which is responsible for the level 3 function. The STB 10 is in charge of the level 2 function.

Level 3 function and operation, maintenance, and maintenance function according to the present invention is located in the SPB (8) to perform its function.

FIG. 2 is a block diagram of the level 3 software block function module to which the present invention is applied. 11 is MGMT, 12 is ISUP, 13 is OMH, 14 is SMH, 15 is LSH, 16 is SPH, 17 is SLH, and 18 is STH.

As shown in FIG. 2, the overall structure of the software to which the present invention is applied is divided into four blocks and the function of each block is as follows.

As shown in FIG. 2, the software to which the present invention is applied includes a message processing function block SMH (Signalling Message Handling) 14, a signal link state management block SLH (Signalling Link Handling) 17, and a link set management block. Link Set Handling (LSH) 15, and Signaling Point Handling (SPH) 16, which is a signaling point and root state management block.

The exchange of information between functional blocks uses defined internal primitives, and each block manages its own data. Looking at the primitive attributes between blocks, the SMH 14 receives the user part message from the local user unit (ISUP) 12 and sends it to the Signaling Terminal Handling (STH) 18, which is a level 2 functional block. Receive the message from the STH (18) through the user part message and transmits it to the user part of the local station, and in the case of the network management message to the LSH (15) or SPH (16) according to the message type.

The SLH 17 receives the activation, deactivation, and recovery request of the link from the LSH 15 and transmits a service start or stop command to the STH 18. When the state change in the signaling terminal occurs, the SLH 17 receives the request from the STH 18. The LSH 15 is informed of the status change of the signaling link for reporting and reconfiguration of traffic in the link set. In addition, the SLH 17 initiates simultaneous activation of the signal link or collects information on the unavailable signal link at a certain point in time according to the request of the SPH 16 in connection with the signal point resumption and reports it to the LSH 15. .

The link set management block, LSH (IS), reports a signal link state change from the SLH 17 and informs the SPH 16 when this requires traffic reconfiguration at the destination level. The LSH 15 also receives a network management message related to the linkset level from the SMH 14 and requests the SMH 14 to change the routing table upon traffic reconfiguration at the linkset level.

The SPH 16 notifies the LSH 15 and the SLH 17 of the start and end of signal point resumption, receives a change in the state of the link set from the LSH 15, and receives a network management message related to the signal point and the root level. It receives from the SMH 14. In addition, the SPH 16 transmits an MTP status signal (reception point access function, impossibility, congestion status, etc.) to the user unit (ISUP) 12, and receives the user unit available and unavailable state from the ISUP (12). The traffic reconfiguration at the level requires the SMH 14 to change the routing table.

Each block also provides an interface with the Operation Maintenance Handling (OMH) 13, which is an MTP operation, maintenance, and maintenance block.

The outline function of each block is as follows.

SLH (17) has signal link status management, non-signal activation and deactivation, and signal link recovery procedure. LSH (15) performs link set status management, link set activation and deactivation, and link set signal link. Status management, traffic switching and return procedures within the link set, and signaling link prohibition and prohibition.

In addition, the SMH 14 has a signal message processing function for transmitting a message to a sending signal terminal, a local station or a local network management related block by discrimination and distribution routing when receiving a message from a local station or a message point of a local station. In addition, it has a routing table management function that updates a corresponding routing table when a routing update request for a specific signal link (LSH) or destination point route (SPH) from a network management related block is requested. The routing update request is routing initiation, routing stop, routing initiation and routing initiation and routing termination for each route (link set) by destination and destination point in a link set.

In addition, the SPH 16 performs the procedure of restarting the local station signal point (Restart) and the neighboring signal point restart, management of the state of the called point (available state, congestion state), network management timer management by the destination, route status management by the destination (available) Status, traffic status, congestion status, physical status, route priority, etc.) Manage network management timer for each route, perform traffic switching and return procedures to alternate routes (between link sets), and link set status management connected to adjacent signaling points. Have

3 is an overall flowchart of a method for implementing a level 3 function according to the present invention.

Level 3 starts to perform the initialization of various parameters and data values (20). Then, when one of the SLH, SMH, or SPH blocks receives the message ((21) or (26) or (31)), it is interpreted from which block and the signal is transmitted (22, 27, 32). When the signal is interpreted, the corresponding protocol processing is performed for each signal (23, 28, 33), and if there is a message to be transmitted to another block (25, 29, 34), the message is transmitted (25, 30, 35). ). When the LSH block receives a message (36), it distinguishes whether the signal link state is available or unavailable (37), interprets which block the message was sent from, and interprets the signal (38, 39). When the signal is interpreted, the corresponding protocol processing is performed for each signal (40, 41), and if there is a message to be transmitted to another block (42), the message is transmitted (43).

4 is a flowchart of the SLH in the level 3 software block according to the present invention.

When SLH, the signal link status management block, receives a signal link activation request from LSH and SPH (44), one signal link in LSH and one signal link deactivated for all registered inactive signal links in SPH. It is determined whether the link is recognized (45). If the signal link activation request is made with Signaling Terminal Handling (STH) for the deactivated signal link (46), and the signal link state is serviceable from level 2 (47), the SLH sends a test message for each signal link at regular intervals ( 48) If the test message received matches the condition (49), the LSH reports that the activation of the signal link is successful (50).

Upon receiving a signal link deactivation request from the LSH for the signal link in service (51), it requests to deactivate to level 2 (52).

If it is received from the level 2 that the signal link that was in service (53) immediately informs that the signal link is broken by LSH (54) and analyzes and identifies the cause of the failure and maintains the signal link in the broken state (55).

Receiving a signal link recovery request from the LSH for a failed signal link (56), recovers a message previously not transmitted by the signal terminal (57), and processes to activate the failed signal link when message recovery of that signal link is completed. After performing (58), upon receipt of an emerging link from the level 2 that the emerging link becomes available (59), the SLH immediately sends a signallink test message (60), just like an activation request. If the message test succeeds (61), it reports that the recovery succeeded (62).

When the SLH receives operator maintenance requests related to statistical data processing and signal terminal status inquiries on the signal link (63), it requests the signal terminal status test and various statistical data at level 2 (64) and reports the results to the operator. (65).

5 is a flowchart of the SMH among the level 3 software blocks according to the present invention.

When SMH, a message processing block, receives a message received from the other station from level 2 (66), it interprets the table of messages (67), and if it is a number of local users, it sends it to the user part (71). Transfer to the processing module (70).

Upon receipt of a message from the user (72), the message transmission route is selected according to the called point code and the signal link selection code (73). If the selected path is buffered (74), it is buffered (76) otherwise the message is sent to level 2. Transmit (75).

Receiving messages about traffic and route table modifications from the local user unit or other blocks within level 3 (77) cleans up the relevant data and tables (78) and in particular in the case of messages about the initiation of routing Transmit to level 2 (80). If a message failed to be transmitted from level 2 is received (81), it is stored in the reverse buffer (82).

6 is a flowchart of the LSH in the level 3 software block according to the present invention. When the signal link receives link availability from the SLH in the unavailable state (83), it checks for the presence of another available link in the link set (84) and, if present, a request for a return declaration to the alternate link with a buffering initiation request (85). And (86) if there is no alternate link, it reports to the SPH that the link set is available (87) and is in an available state.

When the signal link receives the time control switching procedure end from the SPH in the unavailable state (88), it requests the link recovery start request to the SLH and then remains in the unavailable state (89). Receiving the switch response from the SMH (90), it is searched (91) if a switch between link sets has occurred. If so, report the completion of the switching message exchange to the SPH (92) and decide whether to switch normally or urgently (93). If it is urgent, request for link recovery initiation (95). After 94, the signal link state becomes unavailable. In order to perform normal switching without switching between link sets, a signal terminal buffer update request (96,97) is requested, otherwise a routing start request to an alternate link (98) is required, and then a link recovery start request is requested to SLH ( 99). When the signal link receives the return message exchange request from the SPH in an available state (100), it sends a return declaration request to the SMH (101).

Upon receipt of the completion of the time control return procedure (102), it searches (103) for completion of the return to all alternate link sets, notifies return completion (104), and requests the routing initiation request to SMH (105). If the return is not completed, it indicates 106 that the return message has been exchanged on the corresponding link set.

Receiving the start of the time control return procedure (107) indicates that the time control procedure is in progress on the link set (108).

Upon receiving the return confirmation from the SMH (109), if the return is not completed between all the link sets and not the completion of the return to all the alternate links (110, 111), the return message exchange completion is indicated on the corresponding alternate link (113). If a return occurs between the link sets, the same procedure as when the time control return procedure is terminated is performed (110 and 103). In addition, if the return between the link sets has not occurred and the return to all the alternate links is completed (110, 111), the routing initiation request is requested to the SMH (112).

When the signal link receives a return declaration in an available state (114), a request to send a return response is sent to the SMH (115). When the network management message transmission request is received from the SPH (116), the signal link to be transmitted is selected (117), and the message transmission request is made to the SMH (118). If a link is received from the SLH as unavailable (119), once buffering is requested to the SMH (120), it is checked if there is an alternate link available in the link set (121). After the request 122 is switched to the unavailable state and if there is no alternate link, the link set is notified to the SPH that it is unavailable (123) and then converted to the unavailable state. When receiving the switch command from the SMH (124), the signal terminal service stop request is sent (125).

When the signal link receives the completion of the buffer update in an unavailable state (126), it checks whether a switch between link sets occurs (127), and if a switch between link sets occurs (128), requests the completion of the switch procedure (128). After requesting the routing start request of the SMH (129), the link recovery start request to the SLH (130).

When receiving the switching message transmission request from the SPH (131), the transmission link is selected (132) and the message transmission request is requested to the SMH (133), and if the message is not a switching command but a message switching response (134, 135), whether it is a normal switching or an emergency switching. In step 136, if it is normal, it performs a signal terminal buffer update request (137). If it is urgent, it requests a link recovery start request to SLH (138).

When the signal link receives the prohibition request from the OMH in an unavailable state (138), it displays the prohibition of the home country (139) and searches for the existence of an alternative link in the link set (140). If not, it requests data accessible to an adjacent signal point (142). If it receives a signal point from the SPH that it is accessible (143), it checks whether it is prohibited (144). If it is prohibited, it requests to send a prohibited message (145). If the prohibition is released, a request for sending a prohibition release message is requested (147).

If a signal point is received from the SPH that it is not accessible (148), it is searched for banning (149), if it is banned, and the ban is sent to OMH (150). 152) Report ban release impossible (153) and if the link is not broken, perform ban message sending request (154).

When the signaling link receives the prohibition message from the SMH in the unavailable state (155), the prohibition confirmation message is sent (156). In addition, when receiving the prohibition acknowledgment message (157), it reports the signal link prohibition to the OMH (158).

Upon receipt of the release request from the OMH (159), the management release indication is displayed (160), and if there is an available link in the link set (161), the request is sent to the SMH (162) if the available link is sent. If not, the data accessible to the adjacent signal point is queried (163).

If the signal link is received in the unused state and receives the link release message (164), it requests the release of the release acknowledgment message (165) and detects whether the link is broken (166). Is converted to an available state.

When receiving the release request (signal routing function) from the SPH (168), it detects whether the link is broken (169). If it is not a failure and is prohibited from home (170), it sends out a release message (171). (173) A request is made to send a forced release message.

Receiving a release confirmation message from the SMH (174), the release is reported to the OMH (175), and if the link is broken (176), if the failure is not initiated (177) and then switched to the signal link available state.

When a signal link is received and a link prohibition request is received from the OMH (178), it displays the prohibition of the host (179), searches for the existence of an alternative link in the link set (180), and sends a prohibition message if the prohibition is present and prohibits it (181). If a request is made (182) and a relative prohibition is requested, SMH is requested to send a prohibition acknowledgment message (184), then a link prohibition is reported to the OMH (185). If there is no alternate link (180), it is inquired whether or not it is prohibited (183). When the prohibition message is received from the SMH (192), the relative prohibition is displayed (193), and the process proceeds to the alternative link presence search step 180 of the link set and performs the procedure.

If it is received from the SPH as prohibitable (187), the process proceeds to step 181 of searching for whether the local or relative is prohibited.

In the case of receiving a prohibition (188), if it is prohibited from homeland, the rejection of the prohibition is reported to the OMH (189, 190).

When the signal link receives the prohibition confirmation message in the available state (194), if the home country is prohibited, the link is notified to the OMH (196) and the switch is started (197). When the rejection message is received from the SMH (198), the link rejection is reported to the OMH (199).

7 is a flowchart of the SPH in the level 3 software block according to the present invention.

When the signaling point and root state management block SPH receives from the LSH that the link set is available (200), it selects the affected destination point (201), and if the destination point is accessible (202), it requests the unlocking of the destination point (202). 203) Report to the user part that the called point is accessible (204). It then sends a Permission to Send message (205) and if the destination is the last (208) and needs to be returned (209), the alternate route collected is selected (210) and accessible to the adjacent signaling point (211). If it is requested (212) and if it is not accessible (211), it sends out the time control return start (214) and continues until it becomes the last alternate loop (215). In addition, when the last destination point (208) and the return is unnecessary (209), the return termination is sent to the LSH (213). After the affected callpoint is selected (201), if the called point is not accessible (202), a routing stop request is sent to the SMH (206) and then alternate loop data collection (207).

When the SPH receives the end of the return procedure from the LSH (216), it requests a routing initiation (217). When the SPH receives from the LSH that the link set is unavailable (218), it selects the affected called point (219) and then sends a stop routing request (220) and if it is the last called point (221), whether there is an alternate link set as an adjacent signaling point. If it is present (222), if there is a switch message transmission request (223), if not present, time control switching is started (224).

When the SPH receives the completion of the switching message exchange from the LSH (225), if the normal switching and the signal terminal buffer update are completed (226,227), the affected destination is selected (228), and if the alternative route exists (229) Requests to start routing of 230 and continues until the last incoming point (231). If there is no alternate route (229), the destination is notified of the inaccessibility to the user unit (232) and the destination is closed to send to the SMH (233). When the SPH receives the completion of the update of the signaling terminal buffer from the LSH (234), it is determined whether the switching message exchange is complete (235), and if the completion state is selected (236), the affected destination point is detected (236) and if there is an alternative route (237) If present, a routing initiation request to the alternate route is sent to the SMH (238), and it continues until the last destination (241). If the alternate route does not exist, it informs that the destination is not accessible (239) and the destination is closed (240).

If the SPH receives a route test message from the SMH (242) If the destination status does not match (243) If the called point is accessible (244) Requests to send a forwarding permit message (245) If the called point is not accessible (244) A request to send a prohibition of delivery message is made (246).

When the SPH receives the delivery control message (247), it notifies the user unit that a call destination congestion has occurred (248). When the SPH receives the signal point access data request (249), it searches for whether the signal point is accessible (250) and reports the signal point access if it is accessible (252), and reports the signal point inaccessible if the signal point is inaccessible (251). .

When the SPH receives an Inquiry Prohibition from the LSH (253), it selects the affected called point (254), if there is an alternate loop (255) and if it is the last incoming point (256), it reports the prohibition to the LSH (257) and replaces it. If the route does not exist (255), it reports a non-prohibitable (258). When the SPH receives the delivery permission message from the SMH (259), it determines whether the called party is accessible (260), requests to stop routing to the alternate route if possible (265), and starts the timer (266). Go to standby (267). If the timer expires (268) in the idle state, it requests to start routing (269). If the called point is inaccessible, it notifies that the called point is unlocked (261), requests to start routing (262), notifies the user part that the called point is accessible (263), and sends a transmission permission message (broadcasting method) (264). .

If the SPH receives a prohibition message (270), it requests to stop routing (271), and if an alternate route exists (272), it requests to start routing to the alternate route (277) and then sends a routeset test message. It is required to send (276). If the alternate route does not exist (272), the caller is closed (273), the user is notified that the caller is inaccessible (274), and after sending the prohibition message (broadcast method) (275), the routeset test message is sent Is required as LSH (276).

The present invention configured and operated as described above accumulates the technology underlying the common line signaling method (No. 7), and delivers data with reliable message delivery and multiple recovery functions, including the prevention of the error of the user's information message. Therefore, there is an effect that can be the cornerstone of the comprehensive information communication network infrastructure construction technology.

Claims (5)

IOIP (1) to display the operation result message to the operator, SAIP (2) to receive and process the alarm signal, MTIP (3) to control the magnetic tape, DKIP (4) to control the disk, statistical processing SAP (5) to perform functions, DTLP (6) having the common line signaling method user part function to manage the overall operation, maintenance, maintenance, management functions in the exchange, and perform the startup, initialization, recovery of functions, etc. SMP (7), SPB (8) for level 3 functions, signal terminal (STB) 10, and CSIOB (9) for communication between the signal terminal 10 and DTLP (6) A method for implementing a level 3 function of a message transfer unit of a common line signaling system (No. 7) configured; The first step 20 of initializing various parameters and data values, the second step 21, 22, 23, 24, 25 of signaling link handling (SLH) processing to manage the signal link state, and processing and routing signal messages. The third step (26, 27, 28, 29, 30) processing the signaling message handling (SMH) to manage the table, the fourth step (31, 32) processing the SPH (Signalling Point Handling) managing the signaling point and route status Message performed by the fifth step (36,37,38,39,40,41,42,43) for managing the link set handling (LSH) for managing the link set How to implement Level 3 functionality of the delivery unit. 2. The method of claim 1, wherein the second step includes a first process (44, 45, 46, 47, 48, 49, 50) of receiving and processing a signal link activation request signal, and receiving and processing a signal link deactivation request signal. The second process (51, 52), the third process (53, 54, 55) for receiving and processing the signal link failure signal, the fourth process (56, for receiving and processing the signal link recovery request signal for the failed signal link) 57, 58, 59, 60, 61, 62, and the fifth process (63, 64, 65) of receiving and processing the operator maintenance request signal, the method of implementing a level 3 function of the message delivery unit . The method of claim 1, wherein the third step includes a first process (66, 67, 68, 69, 70, 71) of receiving and processing a message from level 2, and a second process of receiving and processing a message from a user part ( 72, 73, 74, 75, 76, third process (77, 78, 79, 80) for receiving and processing a message about modification of traffic and route table from the local user unit or other block in level 3, and And a fourth process (81, 82) of receiving and processing a retrieval message from level 2. 2. The method of claim 1, wherein the fourth step includes a first process (200 to 215) for receiving and processing a link set available state, a second process (216, 217) for receiving and processing a return procedure end signal, and a link set unavailable state. The third process (218 to 224) of receiving and processing the, The fourth process (225 to 233) of receiving and processing the switch message exchange completion signal, the fifth process of receiving and processing the update completion signal of the signal terminal buffer (234) 240), a sixth process (242 to 246) of receiving and processing a route test message, a seventh process (247, 248) of receiving and processing a delivery control message, and an eighth process of receiving and processing a signal point access data request signal (249 to 252), the ninth process (253 to 258) for receiving and processing the inquiry whether or not prohibited, the tenth process (259 to 269) for receiving and processing the delivery permission message, and receiving and processing the prohibition message It is performed by the eleventh process (270 to 277) Method of implementing a level 3 function of the message delivery unit, characterized in that. The method of claim 1, wherein the fifth step includes the first steps (83 to 87) of processing the signal link state from the unavailable state to the link available state, and receiving the end of the time control switching procedure when the signal link state is not available. The second process (88,89) of processing the third process (90 to 99) of receiving and receiving the switch response signal when the signal link state is not available, receiving the completion of the buffer update in the signal link state is not available The fourth process (126 to 130) for processing, the fifth process (131 to 137) for receiving and processing the switch message sending request signal when the signal link state is not available, the signal link state to the prohibition request signal in the unavailable state Sixth processes (138 to 142) for receiving and processing, signal point accessible signal in the state that the signal link state is not available Seventh processes (143 to 147) for receiving and processing the signal point access signal, the signal point when the signal link state is unavailable Be inaccessible signal Process (148 to 154) to process and receive the prohibition message in the signal link state is not available, processing (9,155, 156) receiving and processing the prohibition acknowledgment message in the signal link state is not available. Steps 157 and 158, an eleventh step 159 to 163 for receiving and processing a prohibition release request signal when the signal link state is not available and receiving and processing a link prohibition release message when the signal link state is not available. Twelfth processes 164 to 167, thirteenth processes 168 to 173 for receiving and processing the prohibition release request signal when the signal link state is not available, and receiving a prohibition release confirmation message when the signal link state is not available. Fourteenth process (174 to 177) of processing, the fifteenth process (100, 101) of receiving and processing a return message exchange request signal when the signal link state is not available, time control return clause when the signal link state is available Sixteenth process (102 to 106) of receiving and processing the difference termination signal, the seventeenth process (107 to 108) of receiving and processing the time control return procedure start signal when the signal link state is available, the signal link state is available 18th processes (109 to 113) of receiving and processing a return confirmation signal in step 19, 19th processes (114, 115) of receiving and processing a return line when the signal link state is available, and a network management message when the signal link state is available Twentieth processes (116 and 118) for receiving and processing a transmission request signal, and twenty-first processes (119 and 123) for receiving and processing a link unavailable signal when the signal link state is available, and receiving a switch command when the signal link state is available. The twenty-second process (124, 125) of processing, the twenty-third process (178, 186) of receiving and processing a link inhibit signal when the signal link state is available, receiving and processing a prohibition message when the signal link state is available Twenty-fourth process (192, 193, 180, 181, 182, 183, 184, 185, 186), twenty-fifth process (187, 181, 182, 184, 185, 186) in which the signal link state is available for receiving and processing; 191), the twenty-seventh process (194 to 197) of receiving and processing a prohibition acknowledgment message when the signal link state is available; and the twenty-eighth process (198, 199) of receiving and processing a prohibition rejection message when the signal link state is available. Method of implementing a level 3 function of the message delivery unit, characterized in that performed by.