Circuit switching system for interconnecting logical links between packet switching networks

Description: TECHNICAL FIELD [Detailed description of the invention]

Technical field The present invention establishes a large number of logical links between a packet switching network, a voice concentrator, and a data multiplexer according to circuit switching of packets, particularly a switching protocol, and performs compressed voice calls and subrate data calls on one logical channel. Regarding circuit switching methods that can be handled. Background technology Communication between packet-switched networks sets up a logical channel between two packet-switched networks, and the logical links in this logical channel are used to communicate between digital terminals connected to both packet-switched networks. It is realized by setting. One logical link is assigned to each pair of digital terminal communication through the packet switching network. This logical link shares the same logical channel with other logical links. The ISDN standard Q.931 specifies the packet protocol used by packet-switched networks to configure multiple links through the same logical channel. As a result, there will be a large number of packet calls between pairs of digital terminals that share the same logical channel. Circuit switching sets up one logical channel for each voice or data call it is currently dealing with. The reason is that the bandwidth required for a voice call is large, so a voice call with a general bandwidth cannot share a logical channel with other voice calls. The ISDN standard Q.931 specifies the protocol used by circuit-switched schemes to configure logical channels through networks formed by a large number of circuit-switched systems. Problems arise when trying to interconnect two packet-switched networks with a circuit-switched system. The problem is that circuit-switched schemes allow only one call per channel according to ISDN standards and do not recognize requests for logical links on logical channels. When a packet-switched network needs a logical link, the circuit-switched system assigns this logical link to a logical channel. If a second request comes in through the same logical channel and requests another logical link, the switchboard rejects the second request. This second request for the logical channel requires a second call. As a result, using a line switch to interconnect packet switches is a great waste. Although it is possible to form a system as a whole by a packet switching method, there are many circuit-switched networks in both self-employed communication systems and public telephone networks, and this problem becomes important. The same problem exists for subrate data calls. For subrate data, two data multiplexers multiplex the logical channel into a time slot and then put the data call into the time slot. The data call is set by a single data multiplexer that requires the setting of the data call. The voice concentrator works in the same way, giving a compressed voice call to the time slot of the logical channel. A line switch inserted between a data multiplexer or a voice concentrator sets the logical channel according to each request. As a result, each compressed voice or sublator data call uses an individual logical channel. Abstract of the invention The above problem is solved by a method and device for creating a circuit switching method such as setting multiple logical links in the same logical channel between endpoints having two packet functions such as two packet switching networks. New progress will be realized. Advantageously, this circuit-switched scheme sets up multiple compressed voice calls in the same logical channel between voice concentrators and multiple subrate data in the same logical channel between data multiplexers. Calls can be set. Furthermore, the line switch sets the logical link and channel in response to the packet protocol, and determines the destination of the logical link. In addition, the line switch uses the same packet protocol to signal the packet switch. The line switch also sets compressed voice and subrate data calls in response to the compressed voice and subrate data protocol. Advantageously, the line switch is connected by trunk equipment to terminals with packet capabilities, voice concentrators and data multiplexers. Each trunk facility has a large number of logical channels and at least one signal chinnel. Requests to set calls and links are given through the signal chinnel. Advantageously, a circuit-switched system has multiple circuit-switched networks interconnected, each within a logical channel in response to requests for setting multiple logical links, compressed voice calls or subrate data calls. It is like handling such a request and transferring the request to the next circuit-switched network or other circuit-switched system when leaving the circuit-switched system. The method of connecting a terminal system having a plurality of packet functions connected by a trunk facility to a line switching system is a method of connecting a terminal system having a first packet function to a second terminal system through a logical channel. In response to the logical link setting request from the first terminal system; the second setting request for the second terminal system to request the second logical link from the first terminal system to the second terminal system. In response to, the second logical link is set via the chinnel, and when there is a request for a logical link from the first terminal system to the third terminal system through the same chinnel, this is done. Acts to reject. Detailed explanation The block diagram of FIG. 1 shows a circuit-switched customer exchange 104 for performing exchange of packet data, compressed voice data, or subrate data (these are referred to as logical calls), which is the subject of the present invention. For purposes of illustration, only one packet switch is shown in Figure 1. However, the system 104 can be connected to any combination of packet switch, voice concentrator or data multiplexer. These systems process requests from packet switches, voice concentrators or data in a similar manner. The type of terminal system required is indicated in the bearer capability field of Level 3 messages of the ISDN protocol. The customer switch 104 responds to requests from the packet switches 102, 101, and 103, and sets a large number of logical links in each logical channel of the customer switch 104 that is inheritably connected to these packet switches. Although packet exchanges are illustrated in FIG. 1, it is clear to those skilled in the art that one or more of these exchanges may be replaced by terminals with packet functionality, such as computers and ISDN terminals. The customer switch 104 and the packet switch are physically connected by an ISDN primary group interface (RRI) trunk, each with 23 logical channels (B channels) and one control channel (D tinnel). Each channel has a transmission capacity of 64 kbps. The terminal and the packet switch are connected by an ISDN basic interface (BRI) line, which has two 64 kbps channels and one 8 kbps control channel. Each logical channel can have a plurality of logical links, and each logical link makes an individual data call and data communication. In addition, the system 104 can directly terminate the BRI line and establish a logical link to either of the two logical channels of each BRI line. In order for a packet switch to set up communication with a terminal connected to another packet switch, the packet switch sends a request to the customer switch 104 through the first logical channel and of the logical link of the first logical channel. Requests to be used to set up communication. Customer exchange 104 handles the first logical channel in one of three ways. The first logical channel is already connected to the second logical channel, which may be connected to another packet switch. Second, the first logical channel may be free. Third, the first logical channel is connected to the third logical channel, which may be connected to the third packet switch. If the first logical channel is then connected to another packet switch through the second logical channel, customer switch 104 sets up communication via the second logical channel. If the first logical channel is free, the customer switch 104 sets up a connection to another packet switch via the second logical channel that was previously free, and puts the two logical channels inside. Connect to. After connecting the two logical channels, the customer exchange 104 sets up communication. In the third case, the customer switch 104 rejects the request to set the logical link via the first channel and negotiates a different channel with the first packet switch. For example, suppose terminal 118 requests to set up communication with terminal 105. The packet switch 101 sends a request to set a logical link to the terminal 105 through the customer switch 104. The customer switch 104 sets up a logical link on the logical channel 108 and sends a message to the packet switch 102 via the D channel associated with the logical channel 110, a second between the packet switch 102 and the customer switch 104. Set up a logical link. The latter packet switch then sets up a third logical link to terminal 105. Further, if the terminal 117 requests a connection to the terminal 106, the packet switch 101 sets up communication via the customer switch 104 via the fourth logical channel in the logical channel 108. To request. Next, the customer switch 104 requests the packet switch 102 for a fifth logical channel via the logical channel 110, and sets communication to the terminal 106 through the packet switch 102. However, if the terminal 117 requests to set up communication with the terminal 107, the customer switch 104 rejects the request for communication settings from the packet switch 101 via a logical link through the logical channel 108. The customer exchange then returns a message suggesting that it uses another logical channel, such as logical channel 109. If the packet switch 101 accepts the suggested logical channel, the customer switch requests a logical link on the logical channel 111 to set up communication with terminal 107. If the packet switch 103 accepts this request, the customer switch 104 internally connects the logical channels 109 and 111. By connecting the two logical channels, the customer exchange 104 sets up communication. The data calls handled by the customer exchange 104 consist of half each. Each half of the data call takes one of the four states shown in Figure 14. All of the numerous logical links are considered to be in free state 1401 if it is not in any of the other states in Figure 14. When the packet switch 101 sends an initial request to the customer switch 104, a logical link is formed and combined with other logical links currently existing on the logical channel 108. In addition, a logical link for the second half of the call is generated for packet switch 102 via logical channel 110. Further, a setting request is sent to the packet switch. Here both halves of the call enter the call-up state 1402 of FIG. 14 through path 1407. In this state, the customer switch waits for a response indicating acceptance of the setting request to be received from the packet switch 102. When the packet switch 102 begins to call the terminal 105, it sends a call instruction message to the customer switch, which the customer switch 104 returns to the packet switch. Further, in the call-up state, a different call state instruction may be returned from the packet switch 102 to the packet switch 101 via the customer switch 104. Such a call state instruction may indicate that the packet switch 102 must leave the ISDN network (eg, via a modem) in order to communicate with the terminal 105. Once the packet switch 102 sets up a connection to the terminal 105, it returns a connection instruction via the customer switch 104. This message activates the customer exchange 104 to bring the second half of the call into active state 1403 through path 1412. Customer Switch 104 also retransmits the connection message to Packet Switch 101 via the D channel associated with logical channel 108, activating the first half of the call through path 1412. In the call-up state, when the ISDN protocol fails between the packet switch 101 and the customer switch 104, or the packet switch 101 abandons the call because the terminal 108 or the like disconnects, half of the call goes through route 1409. And return to the free state 1401. The other half of the call goes into a calldown state through path 1413. In this state, the other half of the call sends an appropriate disconnect message to packet switch 102, and when the response to this disconnect message is returned to packet switch 102, the other half of the call goes to free 1401 through route 1410. Return. While in active state 1403, the first half of the call responds to a disconnect message from packet switch 101, enters free state 1401 through path 1408, and while doing this, the second half of the call. Goes into calldown state 1404 through route 1414. If packet switch 102 sends a disconnect message, the second half of the call immediately goes free and the first half of the call goes down. The customer exchange 104 is shown in detail in FIG. Customer exchange 104 includes switch modules 203-204, time matrix switch (TMS) 202, and control processor 201. Each switch module is shown terminating multiple ISDN PRI trunks or BRI lines. Each switch module handles calls within all modules within it, whereas calls between modules are handled through TMS202. The data received from the PRI trunk in switch module 203 is interconnected via the Timed Multiplex (TDM) bus 210, and each channel sends a time slot and data to receive the data on the bus 210. All time slots are switched through the Time Slot Interchange (TSI) 205. In this example, the data on logical channel 108 is received by port 207 and transmitted through TDM bus 210 TSI205 to port 207, where it is transmitted as logical channel 110. Data on logical channel 109 is communicated via trunk 114 and is transmitted to logical channel 111, which is communicated to trunk 116. Data communication between channel 109 and channel 111 is communicated through port 208, TDM bus 210, TSI205, TMS202, TSI211, TDM bus 215 and port 213. The functions performed by the TDM buses TSI205 and TMS202 are well known to those skilled in the art. The switch module 204 operates differently from the switch module 203. The channels communicated within the switch module 204 do not need to be exchanged through TSI211 but are exchanged directly on the TDM bus 215. TSI211 is used only for inter-module calls. ISDN messages are transmitted over the PRI trunk through the D channel of channel 24. Within switch module 203, messages associated with logical channel 108 are received through channel 24 of trunk 113 and terminated at ISDN level 2 by PRI port 207. Communication messages between levels, called L2-L3 primitives, are then given to module processor 206 through interprocessor bus 217. ISDN messages associated with logical channel 111 are communicated on channel 24 of trunk 116. These messages are forwarded to the module processor 212 via LAN bus 216. LAN bus 216 is not used for packet switching. The module processor terminates level 2 before transferring the L2-L3 primitive to control processor 210 over data link 221. Customer exchange 104 also connects terminals with digital telephones using the AT & T DCP protocol, as well as various standard analog telephones and trunks. Such telephones and terminals are not shown in FIG. FIG. 3 illustrates the software structure of ISDN implemented by control processor 201. The non-ISDN functions performed by the control processor 210 and the low-level functions performed by the module processor are not shown, but the line call processing block 305 and maintenance block 312 are performed by the control processor 201, because of the non-ISDN functions. Includes call processing and maintenance. In general, blocks 304-306 are related to voice and data call management, and blocks 309-313 are tentatively related to maintenance and resource management tasks. Blocks 307 and 308 are used for high level applications. The software structure in Figure 3 receives messages sent from Level 2 through I / O paths 338 and 339. The format of these messages is illustrated in Figure 11, see AT & T Technical Document No. 41449 and Appendix 41459 for further details on Level 2 and Level 3 messages. L2-L3 message I / O block 301 receives information from route 311. Primitives on routes 338 and 331 are defined in field 1103 in Figure 11. After handling these messages, block 301 forwards and processes the received L2-L3 primitive that indicates the DL_DATA_INDICATION Q.931 message. Q.931 Message handling block 302 transfers and processes it. All other L2-L3-primitives received by block 3011 are transferred to block 309 for processing. Q.931 Message handling block 302 is responsible for checking and generating Q.931 messages. Block 302 interfaces with the L2-L3 message I / O 301 to receive or receive all DL_DATA_INDICATION primitives, including incoming and outgoing Q.931 messages. Q.931 Message handling module Q.931 Receives a request to pass a confirmed Q.931 message or create a Q.931 message by communicating with message processing 303. Q.931 Message processing 303 controls the operation of Q.931 and shows the state of each Q.931 channel Q.931 message protocol set or being set in any module of system 200 in Figure 2. Do this by maintaining the specified state table. Q.931 Message Processing 303 negotiates the settings for the Q.931 channel, monitors its activity, and finally releases it. Block 303 communicates with call handler 304, resource management handler 311 and timing block 310. The call handler 304 interfaces with the Q.931 message communicated between block 303 and line call processing 305, multilink 306, application manager 307 and maintenance 312. The line call processing 305 performs the entire call processing function in response to stimuli such as analog telephones and trunks. The call handler 304 responds to Q.931 message processing 303 and converts the message of Q.931 into an analog telephone or trunk-like stimulus that should be given to the line call processing block 305. Timing block 310 implements all the software timers required for block 303. Resource management handler 311 is responsible for controlling the level 2 link state and line service state. Maintenance 312 performs normal maintenance type work on the ISDN portion of system 104. The traffic block 313 performs standard traffic measurement type functions. The L2-L3 message I / O block 301 in Fig. 4 is illustrated in detail in Fig. 4. The ISD NI / O controller block 403 is a task that runs on the control processor 201 every 10 milliseconds and is responsible for transmitting all ISDN information to and from the control processor 201. The controller 403 operates by calling the microcode routines 401 and 402 to convey information to the input message buffer and to retrieve the information from the output message buffer, respectively. The input to controller 403 is DL_DATA_REQUEST Primitive, an L2-L3 primitive received by message handling block 302 through path 312. All messages received from level 2 by block 301 are given by controller 403 to primitive handling task 404. The primitive handling task 404 also runs every 10 milliseconds and behaves to process all L2-L3 primitives. The Primitive Handling task 404 handles these primitives in one of two ways. The first gives control to the routine specified by the primitive in block 302 or 309, which is done for the primitive that requires immediate execution. The second is to create information about the primitive and give it to the queue, which is then given to block 309. Remembering the primitive and its associated information is taken for the task, which may be performed later. When the primitive handling task 404 gives direct control to a routine, such as a message handling block, to process a primitive, it is giving control to control processor 201 and the execution of that routine has finished. When the routine received returns control for the primitive handling task 404. Q.931 Message Handling Block 302 is responsible for checking and generating all Q.931 messages. Block 302 interfaces with message I / O block 301 via routes 312 and 313 to receive DL_DATA_INDICATION primitives containing incoming or outgoing Q.931 messages and to send DL_DATA_REQUEST primitives. Block 302 communicates with the Q.931 message processing block via routes 314 and 315 to give a confirmed Q.931 message or to generate a Q.931 message upon request. Message confirmation block 503 receives control from message I / O block 301 when a Q.931 message is received and requires confirmation. Block 503 parses the message, inspects the message for formatting errors, and AT & Make sure that the required information is included according to the specifications given in T's technical documentation. All the information needed to inspect the received message is in message confirmation table 504. Message parsing is done by storing pointers in a buffer containing the message to enclose different types of information in the message. The correctly parsed message is given to message processing block 303 through route 315. Message confirmation block 503 handles two different types of errors in the received message. Certain errors are simply recorded in the general area of error recording, which will be analyzed later if necessary. Such an error occurs when the incoming message is simply incomplete. Another type of message error is when the message itself is complete, but specifies a logical entity that does not exist. It is necessary to respond immediately to such an error, and the message confirmation block 503 requested the message generation block 502 to send the erroneous message, and what kind of error was received by the sender. Send a message containing a code indicating. The message generation block 502 receives a request to create a message from the message confirmation block 503 or the Q.931 message processing block 303. Block 502 controls to generate messages correctly. All of the information elements contained in the message are created by the individual routines contained in the message generation routine block 505. Information for producing each type of message is contained in Message Generation Table 501. The message generation block 502 uses the routine in the message generation routine block 505 to generate the correct message information and assemble the requested message. Each of these routines is called for a particular information element (IE), and each IE routine has all the rules on whether IE should be generated for each situation and what information can be put into IE. Includes. Q.931 Message processing block 303 is illustrated in detail in Figure 6. Block 303 allows the system 104 to communicate with other data devices at the peer level of Q.931 by configuring peer-type communication of Q.931 and maintaining this communication and this when needed. Responsible for restoring communication. Message processing block 303 also maintains a set of tables that specify the status, call type, and facilities used, and handles all Level 3 links for both line and data calls. The processing executed by the block 303 is classified into maintenance, trunk side processing, and line side processing. Trunk-side and line-side processing are used to translate the call stimulus received in the Q.931 message into the call control message used in call processing block 305. Maintenance is used to handle all messages about lines and trunks that use "null" or "global" call references. A "null" reference value indicates that the message is not associated with any call, whereas a "global" reference value indicates that it is associated with all calls on the receiving BRI or PRI interface. .. The message queue server task 605 runs every 10 milliseconds on each module processor to see if block 303 has work to do in the form of incoming messages from block 304, 311 or 310. .. Incoming messages are placed in the message queue by these blocks. This also looks at the messages coming in from Q.931 Message Handling Block 302. Matrix server task 605 responds to these messages by interpreting the work to be performed, converting the work into state-stimulus information, and determining the state table to which the work applies and the specific call record. After doing this, the message queue server task 605 activates the message state sequence controller 604 and processes the state stimulus information using routines 606, 607, 608 along with the state sequence information coming from Tables 601, 602, 603. To do. The processed information is transferred to block 302, 304, 310 or 311 in the message queue. The call handler 304 is illustrated in detail in FIG. Call handler queue Server task 701 finds out if there is work in one of the two queues. One queue is the message from layer Q.931 received from block 303, and the second matrix is for the higher layers of blocks 305, 306, 307, 308 and 312. When work is found in any of these matrices, block 701 passes that information along with the stimulus to the call handler state controller 702. Controller 702 classifies stimuli and information in relation to maintenance or call type. Controller 702 sends a restart request and response maintenance type to maintenance block 312 for processing. Calls are categorized into four types: trunk, line, multilink and non-exchange. Calls are placed in one of these categories according to the contents of the call code table maintained by message processing block 303. If it is related to a call or only one channel, it is said to be a regular telephone call or a standard circuit-switched call. If a call is one of multiple calls on a channel, it is said to be a multilink call. If a call is not given a channel, it is considered a non-exchange call. Controller 702 processes each of these calls using another set of state tables. A standard circuit-switched call is processed by converting the stimulus into the analog telephone trunk format used by the circuit-switched block 305, and the processed stimulus is transferred to block 305. The multilink stimulus is processed and sent to the multilink block 306. Non-exchange stimuli are processed and transferred to application manager 307 via route 325. Circuit-switched block 305 is a well-known circuit-switched call process performed by a customer communication exchange system, also known as a PBX or PABX. An example of such a system is AT & T's System 85. The other L2-L3 primitive processing block 309 is illustrated in detail in FIG. Primitives received from block 301 to block 309 come in as processed directly by processing routine 801 or information is simply put into buffers 802 and 803. If the information is related to link setup or recovery, then block 301 will run routine 801 to process this information immediately, through route 332 to timing block 310 and through route 333 as a resource management handler. Give 311 the necessary stimulus. The need for such a quick response is that the resource management handler 311 and the timing 310 need to handle this information immediately so as not to disturb the system operation. If the primitive goes to maintenance 312 or traffic 313, this information is simply put into maintenance primitive matrix 802, traffic primitive matrix 803 until it is accessed and used by the appropriate block or this information, respectively. All L2-L3 primitives coming in from maintenance 312, resource management handler 311 or traffic 313 are forwarded to block 301 through paths 336 and 330 and directly through block 309. The resource management handler 311 is illustrated in detail in Figure 9. Management queue server task 901 receives all the information sent to block 311. Block 901 accepts the management request from Q.931 message processing 303 via route 327 and cancels the instruction from L2-L3 primitive processing, or accepts the visit-out request from maintenance 312. Management server task 901 takes these requests and forwards them to management request preprocessing 902. This block determines the specific request to be performed and translates the request into the stimulus given in the state table 904 to determine the required action in the form of a stimulus. After completing these functions, the management request preprocessing 902 transfers the requested stimulus to the resource management state controller 903. In response to the stimulus, controller 903 processes the stimulus using the resource management state sequence table 904 and the resource management routine 905. The output from controller 903 is a management primitive request that requires the busy-out request / response or information given for maintenance to be sent to the other side of the Q.931 interface. These management primitives are forwarded to Q.931 message processing 303 if it references call information, otherwise it is forwarded to L2-L3 processing 309 through route 33. The tenth illustrates the timing 310 in detail. Timing 310 provides all the timing for Q.931 level messages and responds to two different types of requests. First, Q.931 message processing 303 uses timing 310 to force the various time intervals required for the Q.931 message state via routes 328 and 329. Second, the timing 310 responds to the setting / recovery primitive detected by the L2-L3 primitive processing 309 and starts a timer for determining whether the link is restored or set in an appropriate time. If the required action is not performed at the correct time interval, the timing 310 then notifies block 303 of this and this block takes the necessary action. All requests for block 310 are received by timing manager 1002 through routes 329 and 332. The timing manager 1002 sets the necessary timing information in the status memory by reflecting which timer is running. Timing task 1001 runs every 100 milliseconds to determine when the timer has expired. When the timer expires, timing task 1001 creates a timer expired primitive and puts it in the primitive queue of Q.931 message processing 303. Q.931 Message processing 303 responds to the timer time-out primitive and forwards the message to the resource management handler 311 via route 327. Figure 11 illustrates the format of L2-L3 primitive packets. Field 1101 is used to communicate field 1102, which contains the scanner port number and the number of bytes in the packet. Field 1106 contains the required data. Fields 1104 and 1105 are the service access point identifier and the terminal endpoint identifier, respectively. The terminal endpoint identifier allows you to specify one or more endpoints in a message. Service access point identifiers allow one or more logical entities to correspond to terminal endpoint identifiers. Further information on these fields can be found in the AT & T technical documentation referenced earlier. Figure 12 illustrates the table maintained by message processing block 303 to show the level 3 links currently connected to a given module. Table 1201 has two contents for each B channel in the system. The first content in Table 1201 points to the linked list of ISDN call records, and the second content points to the second connected B channel if the B channel is active. For example, entry 1202 points to an ISDN call record list consisting of records 1205, 1206, 1207. The second content, entry 1203, refers to entries 1204 and 1210 associated with the connected B channel. When channel B is used for only one exchange call, the content in Table 1201 refers to only one ISDN call record. As illustrated by entry 1202, there are three ISDN call records associated with them, indicating the multilink usage associated with entries 1202 and 1203 in Table 1201. The structure of the ISDN call record is illustrated in detail in FIG. The call reference value 1301 is used to identify the data call between the customer exchange system 104 and other packet exchanges. D-channel number 1302 refers to the physical record of the D-channel that signals for the logical link assigned to the call record. Section 1303 of the call record specifies Level 3 state, stimulus, and sequence information used by message processing block 303 to implement the Level 3 protocol. Section 1304 contains the timer used at level 3 and the stimulus given when the timer expires. Section 1305 points to a pointer to Table 1201 from the call record in Figure 12. Sections 1306 and 1307 are used to link call records to other call records on the same logical channel. Section 1308 contains high levels of state, stimulus and sequence information used by blocks 304 and 306 for call processing. FIG. 14 is a state diagram of the multi-link call realized by the multi-link block 306 of FIG. Figures 15 to 20 illustrate the functions performed by the multilink block 306 to implement this phase diagram in the form of a flow chart. The data call consists of two halves. Block 306 realizes half of both. Messages between two halves of the same call are communicated within block 306. The call handler 304 in FIG. 3 determines whether the call is a circuit-switched call or a packet call. When a call request is received on that logical channel, call handler 304 determines if a call record already exists on that logical channel. If one call code already exists, block 304 considers it a multilink call and gives it to block 306. If no other call record exists, block 304 gives it to block 305. This causes block 305 to set the first link for the multilink call. Block 304 also verifies that the outbound logical link requested is the logical channel connected to the logical channel on which the second call request that sets the logical link thereby is received. Figure 15 illustrates the message that causes the call to escape from free 1401. Figure 15 shows four ways to make a call not free. The first method is handled by block 1501 and is by request to set a logical link message. This message comes from block 303 through call handler 304. In response to this request, block 1502 is executed, which adds an ISDN call record to the linked list of a particular logical channel, also as the B channel associated with the configuration message received in block 1501. Generally referred to. In this example, this action creates call record 1207 in FIG. 12 associated with logical channel 108 linked to call record 1206. Recall that the first link configured on that channel is actually configured by line call processing block 305. This happens because the call handler does not know that the first link is part of the multilink call. After call record 1207 is linked to call record 1206, block 1503 is used to send a message to processing block 33 via block 304, telling that the request is valid and the request is being processed. .. This message is returned to Packet Switch 101. Block 1504 is then executed, which takes the B-channel index 1204 of logical channel 110. Identification of the logical channel to connect to is performed by entry 1203, which points to the B channel index 1204. Entries 1203 and 1210 are initialized by block 305 in Figure 3 when the first logical link is set up. When block 1504 indicates a B-channel index, call record 1209 is generated and linked to call record 1208. This returns the second half of the call to the vacant state 1401 in Figure 14. Block 1505 sends a call request message to the second half of the call. The first half of the call represented by call record 1207 is advanced to the call-up state by exit block 1402. The second half of the call represented by call record block 1209 is in free state 1401, and execution of blocks 1506 and 1507 advances from free state to callup state 1402. Block 1506 is the stimulus response of the call request message from block 1505. In response to this stimulus, block 1507 sends a message to block 303 via block 304, resulting in a message to packet switch 102 to set up a link for the second half of the call. Be done. Then, through exit block 1402, the second half of the call, the second half of the call, enters call-up state 1402. Entrance blocks 1508 and 1509 respond to global messages. For each logical channel, there is a global call record that is always considered free 1401. When the packet switch removes all links from the logical channel, a message is sent, which is received through blocks 301-303, and a restart instruction message is received by block 306 through block 304 as represented by 1508. In response to this message, block 1509 removes all call records, such as call records 1205 to 1207, associated with logical channel 108 in this example. Similarly, blocks 1510 and 1511 respond to the stimulus indicated by block 1510, which is a restart request from a high level. For example, this request comes from the maintenance block when maintenance block 312 determines that a particular logical channel needs to be restarted. When a high-level restart request is received, block 1511 behaves like block 1509, removing call records from a particular logical channel. 16 to 18 show the call-up state 1402 of FIG. 14 in detail. The call-up state 1402 is entered from the free state 1401. The entry block 1601 of FIG. 16 shows the response sent from the packet switch 102 to the message sent from the block 1507 of FIG. Customer exchange 104 is waiting for the response. After sending the message, the customer exchange 104 remembers the instruction that the message was sent, and if no response is returned within a predetermined time, the message will be resent to the packet switch 102. Become. When a response is returned from the packet switch 102 as indicated by ingress block 1601, block 1602 dismisses the previous instruction that a response is needed and the call remains in the call-up state. Note that block 1601 deals with the second half of the call. When the packet switch 102 notifies the terminal 105 that a data call is coming, the packet switch 102 notifies the customer switch 104 by sending a call instruction message. The message is received by the second half of the call at entrance block 1602. At block 1604, a call request is made and sent to packet switch 101 through the first half of the calls interconnected by logical channel 108. The message generated by block 1604 is handled by the first half of the call by entry block 1801 in Figure 18. In response to this signal, block 1802 generates a call request primitive, which flows through call handler block 304, message processing block 303, message handling block 302 and message I / O block 301 (level 3 processing), and as a result. The message is sent to the packet switch 101 via the D channel associated with the logical channel 108 to inform the terminal 105 that a call is being made. During the call-up state 1402, the packet switch and the customer switch 104 exchange different messages indicating different types of call states. In this example, one type of call state indication is whether the packet switch 102 leaves the ISDN network to complete the packet call, eg, via a modem. If this happens, the packet switch 102 will notify this fact by sending a message, which will eventually arrive at terminal 118 through the customer switch 104 and the packet switch 101. The packet switch 102 sends this call state indication via the D channel associated with the logical channel 110, which is processed by block 303 via block 304 and then the customer switch call by ingress block 1605. Received by the second half of. In response to this message, block 1606 is executed, which transfers instructions to the first half of the call by transmitting a state request message. The entry point for the first half of the call for the state request message is entry block 1803 in Figure 18. In response to this message, block 1804 sends a status request message through block 304 to message processing block 303, which sends a status indication message to packet switch 101, from which it goes to terminal 118. When the packet switch 102 determines that the terminal 105 has answered the data call, it sends a connection instruction message to the customer switch 104 via the D channel associated with channel 110, thereby at level 3. A primitive is generated, which is received at entry block 1607 in Figure 16. In response to this connection instruction message, block 1608 sends a connection request message to the first half of the call, which is handled by block 1805 in FIG. Block 1609 sends a connection confirmation request to level 3, which receives the connection confirmation request to packet switch 102. The second half of the call then goes into active 1403. The message generated by block 1608 of FIG. 16 is internally forwarded within block 306 of FIG. 3 and then notified to entry block 1805 of FIG. Block 1806 responds to this connection request by sending a connection instruction message to level 3, which sends a connection instruction message to packet switch 101. In this regard, the first half of the call is waiting for a connection confirmation instruction to be received from packet switch 101. This connection confirmation instruction is handled by the entrance block 1610, and as a result, the connection confirmation instruction received at level 3 is restored. After executing block 1611, the first half of the call goes into active state 1403. During call-up state 1402, either packet switch can initiate a disconnect. There are two exits from call-up state 1402 in response to disconnection. It is either in free state 1401 or in calldown state 1404. Which exit to take depends on whether the first half of the call receives the first disconnect from the packet switch, but the second half receives it. If, for example, the packet switch 101 is the initiator of the disconnect procedure, the customer switch 104 gives an instruction to the second half of the call that the disconnect is occurring in response to this disconnect, and then the call number. Simply enter free 1401 for half of one. However, the second half of the call must notify the packet switch 102 and go to calldown state 1402 because it must wait for the response to this disconnect instruction to be returned from the packet switch 102. For example, the disconnect message from the packet switch 101 will be received via the D channel corresponding to the logical channel 108, resulting in a primitive received from level 3 at the inlet block 1701 of FIG. Block 1702 relinks the call records associated with this logical channel and removes the first half of the call. In addition, a primitive is generated in block 1703 to communicate with block 306, and the second half of the call is handled by block 1807 in Figure 18. In addition, block 1704 raises a primitive, which goes to level 3 via call handler 304, which returns a disconnect request to packet switch 101 via D channel associated with logical channel 108. The primitives generated by block 1703 are handled by the second half of the call by block 1807 in Figure 18. Block 1808 relinks its call record at the same time as block 1702 and cancels the call at block 1808. In addition, block 1809 is executed to send a disconnect request to level 3, which sends a disconnect request message to packet switch 102. Finally via block 1809 Go to calldown state 1404. When packet switch 102 receives the disconnect request message, it sends a message, which causes a disconnect request at level 3, which is received at entry block 2001 in Figure 20 in calldown state 1404. Become. Blocks 2002 and 2003 free the memory used in connection with the call, and the call returns to free 1401. In addition to sending a disconnect instruction during call state 1402, another way to interrupt the process of setting a call is to send a disconnect request. This request is made when an error occurs and it is determined that the Level 3 processing of Customer Switch 104 and the Level 3 processing of Packet Switch 101 or 102 are no longer synchronized for the correct state of Level 3. For example, if this determination is made by the packet converter 102, it sends a disconnect request to the customer exchange 104. This disconnection request is handled by the entrance block 1705 of FIG. Block 1706 relinks the call record to remove the logical link associated with the call. Block 1707 sends a disconnect request primitive, which is communicated internally within block 306 and notified to the second half of the call, thereby disconnecting the call in a normal manner. This primitive is handled by block 1807 in Figure 18, but its state has already been described . Blocks 1708 and 1709 free all memory associated with the call. Block 1709 also makes the call free 1401. Figure 19 shows the operation performed in the active state 1403. The functions executed in blocks 1901 to 1904 are the same as the functions executed in blocks 1701 to 1704 in FIG. The functions executed in blocks 1908 to 1912 are the same as the functions executed in blocks 1705 to 1709 in FIG. The functions executed in blocks 1905 to 1907 are the same as those executed in blocks 1807 to 1809 in FIG. FIG. 21 illustrates packet switches 2101 and 2104 to 2106 interconnected by customer switches 2102 and 2103. As shown, the logical channel 2121 is connected to the logical channel 2117 through the customer converter 2102, and the logical channel 2113 is connected to the logical channel 2117 through the customer exchange 2103. Logical channel 2123 is connected to logical channel 2119 through customer exchange 2102, and logical channel 2119 is connected to logical channel 2115 through customer exchange 2103. Packet Switch 2101 can communicate packets through a logical link that goes to Packet Switch 2105 through logical channels 2121, 2117 and 2113, and also via a logical link that goes to Packet Switch 2104 via logical channels 2123, 2119 and 2115. Can communicate packets. Customer exchanges 2102 and 2103 function similarly to the customer exchanges of FIG.

[Simple explanation of drawings]

FIG. 1 is a block diagram showing the concept of the present invention; FIG. 2 is a block diagram of a business communication system that realizes the present invention; Figure 3 shows the ISDN software structure used to control the system in Figure 2; Figure 4 is a block diagram showing the L2-L3 message IO301 in Figure 3; Fig. 5 is a block diagram showing the handling 302 of Q.931 message in Fig. 3; FIG. 6 is a block diagram showing the message processing 303 of FIG. 3; Figure 7 is a block diagram of the call handler 304 in Figure 3; Fig. 8 is a block diagram of L2-L3 primitive processing 309 in Fig. 3; Figure 9 is a block diagram of resource management 311 in Figure 3; Fig. 10 is a block diagram of timing 310 in Fig. 3; Figure 11 shows the format of L2-L3 primitive packets; Figure 12 is a block diagram of linked ISDN call records; Figure 13 shows the placement of ISDN call records; Fig. 14 is a phase diagram of multi-link calls; Fig. 15 is a flowchart of the free state 1401 in Fig. 14; 16th, 17th, and 18th are flowcharts of the call-up state 1402 in FIG. 14; FIG. 19 is a flowchart of the active state 1403 in FIG. 14; FIG. 20 is a flowchart of the calldown state 1404 of FIG. 14; FIG. 21 is a block diagram of a plurality of line exchanges that interconnect logical links between packet switching methods.

[Explanation of the sign of the main part] Name in the claims Code Name in the specification Terminal system 102 Packet switch Circuit switching method 104 Circuit switching machine