Abstract:
In a method and an apparatus for multi-destination communication processing in a packet storage/exchange node, a line control module controls transmission and reception of a message that contains either a single destination message or a multi-destination message to and from a telephone subscriber line. A file storage stores the message in accordance with delivery destination addresses, and a file control module controls writing the message received from the line control module into the file storage and reading the message from the file storage to supply the message to the line control module. At least one multi-destination message tempeorary storage area of a multi-destination message temporary storage included in a multi-destination message storing/processing module temporarily stores a multi-destination message and at least one single destination message storage area of the multi-destination message temporary storage stores individual single destination messages expanded from the multi-destination message.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to packet storage/exchange nodes and more particularly to a multi-destination communication processing system in a packet storage/exchange node. The invention is suitable for excluding an abrupt increase in load on multi-destination message expansion processing and avoids mutual interference at message input and output of a subscriber circuit due to a bottleneck in node performance. 
     The term &#34;terminal&#34; is a general term indicative of packet exchange terminals such as computers, facsimile terminals and the like. The term &#34;node&#34; is a general term indicative of network elements having a packet exchange function. 
     A prior art packet storage/exchange node is generally constructed as shown in FIG. 1. Referring to FIG. 1, a line control module 1 controls transmission and reception of a message in the form of a packet to and from a telephone line such as a telephone subscriber line or telephone trunk line 10. A file control module 2 stores a message from the line control module 1 into a predetermined area of a file storage 3 and reads a message from the file storage 3 to supply the read message to the line control module 1. The file storage 3 stores messages in correspondence to individual single destination deliveries. 
     In designing such a packet storage/exchange node with a view of meeting an increase in load on the file control module, it has hitherto been practice to increase the number of file control modules involved correspondingly to thereby promote the capability of the node in total. This expedient is exemplified in FIG. 2 wherein a plurality of file control modules 2-1, 2-2 and 2-3 are provided. 
     With multi-destination message services introduced into the packet storage/exchange node, however, the load on the file control module is theoretically increased in proportion to (n-1) when the number of subscriber terminals associated with the node is n and the prior art system faces difficulties in complying with the increasing load. Consequently, there arises a problem that a multi-destination message from one of the subscribers interferes with communications in progress between the node and an other subscriber, causing a bottleneck in the file control module processing. 
     This will be detailed with reference to FIGS. 3A-3C. As illustrated in FIG. 3A the preformance of the file control module 2 is set to be such that the load factor typically measures 100% when n subscribers access the node at a time. Under multi-destination message services, multi-destination message expansion is required to be undertaken at the entrance to the file control module 2. As will be seen from FIG. 3B one multi-destination message for the total (n) deliveries issued from one subscriber occupies (n-1)/1×100% of the load factor of the file control module. Likewise, as illustrated in FIG. 3C, multi-destination messages for the total deliveries issued from n subscribers will load n×(n-1)/n×100=(n-1)×100% of the file control module&#39;s load factor upon the file control module 2. As a result, the node experiences, in its file control module, such a bottleneck as is liable to force the file control module to continue occupying the CPU at an activity ratio of about 100%, followed by stoppage of processings of lower priority grade or to fill up the input/output buffer to make the same inoperable. This means that the node becomes overloaded instantaneously. 
     Reference may be made to JP-A-58-204660, for example, as a relevant reference to multi-destination communications. 
     SUMMARY OF THE INVENTION 
     This invention contemplates avoidance of a bottleneck that can occur in the file control module of known systems when a plurality of multi-destination messages develop at a time in a packet storage/exchange. Such a bottleneck might otherwise adversely affect the CPU or the input/output buffer associated with the file control module to seriously degrade the performance of the node or to render the node inoperable. It is an object of this invention to provide a method and an apparatus for multi-destination communication processing capable of excluding inter-circuit interference which occurs between every available circuit and the node, the interference being, for example, disconnection of subscriber lines due to time-out. 
     To accomplish the above object, according to this invention, a multi-destination message storing/processing module has a multi-destination message temporary storage. A header in a message received from a telephone subscriber line is read and analyzed at a line control module. When the input message is detected to be a multi-destination message, this multi-destination message is transferred to the multi-destination message temporary storage at which it is temporarily stored and expanded into individual single destination delivery messages which in turn are transferred sequentially in units of one message to a file control module, thereby releasing the file control module from being loaded for multi-destination message expansion. During the multi-destination message expansion, the line control module deals with a transmission request from that telephone subscriber line by holding the request (keeping it pending) or making no response to the request. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1 and 2 are schematic diagrams showing prior art packet storage/exchange nodes. 
     FIGS. 3A to 3C illustrates problems encountered in the prior art systems. 
     FIG. 4 is a block diagram schematically showing a packet storage/exchange node according to an embodiment of the invention. 
     FIG. 5 is a block diagram schematically showing a multi-destination message storing/processing module used in the node of FIG. 4. 
     FIG. 6 illustrates a format of single destination message and multi-destination message. 
     FIGS. 7 to 12 illustrate, with the aid of diagrammatic representation and table, operational states and operational events in multi-destination message branching circuit, multi-destination message temporary storage, file control module and subscriber circuit. 
     FIG. 13 is a schematic diagram showing another embodiment of a multi-destination message temporary storage shown in FIG. 5. 
    
    
     DETAILED DESCRIPTION 
     The invention will now be described by way of example with reference to the accompanying drawings. 
     Referring to FIG. 4, there is illustrated a package storage/exchange node according to an embodiment of this invention. The node comprises a line control module 1, a file control module 2, a file storage 3 and a multi-destination message storing/processing module 4. The line control module 1 includes multi-destination message branching circuits 11, 12 and 13 respectively connected with telephone lines 101, 102 and 103 of a subscriber circuit 10. 
     A message, containing either a single destination message or a multi-destination message and received in a transmission unit from, for example, the line 101 is supplied to the multi-destination message branching circuit 11 included in the line control module 1. The multi-destination message branching circuit 11 reads and detects a header in the input message. When the input message is detected to be a single destination message, the multi-destination message branching circuit 11 transfers this single destination message directly to the file control module 2. On the other hand, when the input message is a multi-destination message, the multi-destination message branching circuit 11 transfers this multi-destination message to the multi-destination message storing/processing module 4 and at the same time informs the line 101 that it is temporarily disabled for reception. Concurrently with initiation of the multi-destination message reception, the multi-destination message storing/processing module 4 sets a multi-destination message reception inhibiting level signal into each of the multi-destination message branching circuits 11 to 13. These circuits 11 to 13 are thus held in multi-destination message reception inhibiting conditions, except for the circuit 11 which has already started receiving the multi-destination message. In response to another multi-destination message the reception inhibited circuits transmit, to the associated lines, a disconnection instruction or an affirmation waiting response. The &#34;disconnection instruction&#34; is issued from the line control module to the associated line to inform the line that the line control module refuses to acknowledge the receipt of multi-destination messages. The &#34;affirmation waiting response&#34; is also issued from the line control module to the associated line to instruct the line to wait until an affirmative signal indicates that the line control module is now ready for acknowledging the receipt of multi-destination messages. 
     After completion of the transfer of the multi-destination message to the multi-destination message storing/processing module 4, the multi-destination message branching circuit 11 to transmits a disconnection instruction or an affirmation waiting response to the line 101. 
     Under this condition, the multi-destination storing/processing module 4 temporarily stores a message in the multi-destination message and temporarily transfers delivery destination addresses from a header in the multi-destination message to a memory area. Thereafter it expands the multi-destination message into individual single destination delivery messages by preparing individual message headers, the number of which is equal to that of individual delivery destination addresses, and adding the stored message to the individual message headers. The thus expanded individual single destination delivery messages for all deliveries are sequentially transferred in units of one message to the file control module 2 through the multi-destination message branching circuit 11. Upon completion of the expansion and transmission of the temporarily stored messages for all the addresses, the multi-destination message storing/processing module 4 releases the multi-destination message branching circuits 11 to 13 from the multi-destination message reception inhibiting signal previously set therein. 
     The multi-destination message storing/processing module 4 may be materialized readily by using, for example, microcomputer architecture. FIG. 5 illustrates a structural example of multi-destination message storing/processing module 4 comprising an interface 41 coupled to the multi-destination branching circuits, a central processing unit (CPU) 42, a program memory (ROM) 43 and a data memory (RAM) 44 serving as the multi-destination message temporary storage. In the RAM 44, the multi-destination message is stored in a multi-destination message temporary storage area 441 and the stored message is divided into individual single destination messages (1), (2), (3), . . . (n) which in turn are stored in a single destination message storage area 442, under the control of the CPU 42. 
     More particularly, when receiving a multi-destination message from one of the multi-destination message branching circuits 11 to 13 through the interface 41, the CPU 42 operates to temporarily store the multi-destination message in the multi-destination message temporary storage area 441 of the RAM 44 and subsequently, to expand the stored multi-destination message into individual single destination delivery messages (1), (2), (3), . . . (n) the number of which is equal to that of individual delivery addresses designated by a header in the multi-destination message and set the expanded messages (1), (2), (3), . . . (n) in the single destination message storage area 442. Thereafter, the CPU 42 operates to sequentially read the expanded individual single destination delivery messages in units of one message and return them to that multi-destination message branching circuit through the interface 41. The CPU 42 also operates to transmit a multi-destination message reception inhibiting level signal to each of the multi-destination message branching circuits 11 to 13 when it receives the multi-destination message and to release the multi-destination message branching circuits 11 to 13 from the multi-destination message reception inhibiting level signal when the transmission of all of the individual single destination delivery messages in the single destination message storage area 442 has been completed. The CPU 42 executes a series of processings pursuant to a program stored in the ROM 43. 
     An example of a message format is illustrated in FIG. 6. The message format has a header of n bytes and a message of i bytes, the header being detailed in FIG. 6. The header includes an ID of two bytes for indentification of the type of message such as a transmission message, a response message or a control message; a MODE of two bytes indicative of the mode of communications; a CLS of two bytes for identification of the grade of communication class such as an express communication or an ordinary communication; a receiving terminal number of two bytes for identification of either a single destination delivery or a multi-destination delivery; a message field length of eight bytes for prescribing the length of a multi-destination address field; and a multi-destination address field of 256 bytes. 
     FIG. 7 shows a diagram useful to explain the operational state of the multi-destination message branching circuit as viewed from the subscriber. Table I describes the events in the operation. 
     FIG. 8 shows a diagram useful to explain the operational state of the multi-destination message temporary storage as viewed from the multi-destination message branching circuit. Table II describes events in the operation according to FIG. 8. 
     FIG. 9 shows a diagram for explaining the operational state of the multi-destination message branching circuit as viewed from the multi-destination message temporary storage. Table III is an event table which corresponds to FIG. 9. 
     FIG. 10 shows a diagram for explaining the operational state of the file control module as viewed from the multi-destination message branching circuit. Table IV is an event table which corresponds to FIG. 10. 
     FIG. 11 shows a diagram for explaining the operational state of the multi-destination message branching circuit as viewed from the file control module. Table V is an event table corresponding to FIG. 11. 
     FIG. 12 shows a diagram for explaining the operational state of the subscriber circuit as viewed from the multi-destination message branching circuit. Table VI is an event table corresponding to FIG. 12. 
     Table I describes state transition events in the muilti-destination message branching circuit as viewed from the subscriber circuit as shown in FIG. 7 and is as follows. 
     
         ______________________________________                Event OriginatorEvent                      Sub-    Other thannumber Events              scriber subscriber______________________________________7-1    Setting of a multi-destination                              O  message acknowledgement rejec-  tion (disconnection) directed  from the multi-destination  message storing/processing  module to the multi-destina-  tion message branching  circuit is released.7-2    A multi-destination message O  acknowledgement rejection  (disconnection) directed from  the multi-destination message  storing/processing module to  the multi-destination message  branching circuit is set.7-3    A single destination message                      O  is received from the sub-  scriber circuit.7-4    A multi-destination message                      O  is received from the sub-  scriber circuit.7-5    Setting of a multi-destina- O  tion message acknowledgement  rejection (disconnection)  directed from the multi-  destination message storing/  processing module to the  multi-destination message  branching circuit is  released.______________________________________ 
    
     Table II describes state transition events in the multi-destination message temporary storage as viewed from the multi-destination message branching circuit as shown in FIG. 8 and is as follows. 
     
         ______________________________________               Event OriginatorEvent                     Branch-  Other thannum-                      ing      branchingber   Events              circuit  circuit______________________________________8-1   The multi-destination message                     O temporary storage starts receiving a multi-destination message from the multi-desti- nation message branching circuit.8-2   Temporary storage of the     O multi-destination message is completed.8-3   Setting of a multi-destination                              O message acknowledgement rejec- tion (disconnection) directed from the multi-destination message storing/processing module to the multi-destina- tion message branching circuit is released.______________________________________ 
    
     Table III describes state transition events in the multi-destination message branching circuit as viewed from the multi-destination message temporary storage as shown in FIG. 9 and is as follows. 
     
         ______________________________________              Event OriginatorEvent                              Other thanNum-                     Temporary temporaryber   Events             storage   storage______________________________________9-1   The multi-destination message                              O branching circuit receives a multi-destination message from the subscriber circuit.9-2   A multi-destination message                    O acknowledgement rejection (disconnection) directed from the multi-destination message storing/processing module to the multi-destination message branching circuit is set.9-3   Setting of a multi-destina- tion message acknowledgement rejection (disconnection) directed from the multi- destination message storing/ processing module to the multi-destination message branching circuit is released.______________________________________ 
    
     Table IV describes state transition events in the file control module as viewed from the multi-destination message branching circuit as shown in FIG. 10 and is as follows. 
     
         ______________________________________              Event Originator                              Other thanEvent                    Branching branchingNumber Events            circuit   circuit______________________________________10-1   Completion of message trans-                    O  fer from multi-destination  message branching circuit  to file control module.10-2   Start of message transfer                    O  from multi-destination  message branching circuit  to file control module.10-3   Start of message transfer   O  from file control module  to multi-destination  message branching circuit.10-4   Completion of message trans-                              O  fer from file control module  to multi-destination message  branching circuit.10-5   Completion of message trans-                    O  fer from multi-destination  message branching circuit  to file control module.10-6   Start of message transfer                    O  from multi-destination  message branching circuit  to file control module.10-7   Completion of message trans-                              O  fer from file control module  to multi-destination message  branching circuit.10-8   Start of message transfer   O  from file control module to  multi-destination message  branching circuit.10-9   Simultaneous completion of                    O         O  mutual transfer of messages  between multi-destination  message branching circuit  and file control module. 10-10 Simultaneous start of mutual                    O         O  transfer of messages between  multi-destination message  branching circuit and file  control module.______________________________________ 
    
     Table V describes state transition events in the multi-destination message branching circuit as viewed from the file control module as shown in FIG. 11 and is as follows. 
     
         ______________________________________               Event Originator                             Other thanEvent                     File    fileNumber Events             control control______________________________________11-1   Completion of message transfer                             O  from multi-destination message  branching circuit to file  control module.11-2   Start of message transfer from                             O  multi-destination message  branching circuit to file  control module.11-3   Start of message transfer from                     O  file control to multi-destina-  tion message branching circuit.11-4   Completion of message transfer                     O  from file control to multi-  destination message branching  circuit.11-5   Completion of message transfer                     O  from file control to multi-  destination message branching  circuit.11-6   Start of message transfer from                     O  file control module to multi-  destination message branching  circuit.11-7   Simultaneous completion of                     O       O  mutual transfer of messages  between multi-destination  message branching circuit and  file control module.11-8   Simultaneous start of mutual                     O       O  transfer of messages between  multi-destination message  branching circuit and file  control module.11-9   Completion of message tranfer                             O  from multi-destination message  branching circuit to file  control module. 11-10 Start of message transfer from                             O  multi-destination message  branching circuit to file  control module.______________________________________ 
    
     Table VI describes state transition events in the subscriber circuit as viewed from the multi-destination message branching circuit as shown in FIG. 12 and is as follows. 
     
         ______________________________________              Event OriginatorEvent                              Other thanNum-                     Branching branchingber   Events             circuit   circuit______________________________________12-1  Troubles in subscriber system                              O or power turn-off.12-2  Recovery of subscriber system                              O from troubles or power turn-on.______________________________________ 
    
     FIG. 13 illustrates another embodiment of the multi-destination message temporary storage 44 shown in FIG. 5. A multi-destination message temporary storage 44A in FIG. 13 is a RAM and has a multi-destination message temporary storage area 441 comprised of a plurality of areas 441A, 441B, 441C, . . . 441i and a plurality of single destination delivery message storage areas 442A, 442B, . . . 442i provided in correspondence to the multi-destination message temporary storage areas 441A, 441B, . . . 441i. The RAM 44A operates similarly to the RAM 44 explained with reference to FIGS. 5 and 8. 
     The capacity of multi-destination message reception can be increased using the RAM 44A as shown in FIG. 13 and hence the occurrence of the reception inhibition is less frequent to promote services offered to the subscriber. 
     As has been described, according to the present invention, a multi-destination message from the telephone subscriber line or trunk line can be once absorbed by the multi-destination message temporary storage and after expansion of the multi-destination message, expanded individual single destination delivery messages can be processed message by message at the file control module, thereby preventing the file control module from being applied with an excessive load in the form of expanded individual single destination delivery messages whose number exceeds the upper limit of the number of messages that can be processed by the file control module. This makes it possible to eliminate operational congestion in the file control module otherwise caused by the load of the expanded individual single destination delivery messages at any time in course of processing of messages from a plurality of packet terminals and to exclude the disconnection instruction from being produced to the subscriber lines by the occurrence of operational congestion. Accordingly, interference between packet terminals due to a bottleneck in node performance during expansion of multi-destination messages can be eliminated completely.