Abstract:
An ATM multicast communication system for identifying and multiplexing ATM cells at a receiving node by using AAL5 cell. This system has an insertion means for inserting ATM cell having RC (Routing Cell) with past record information or route information, when ATM cell of AAL5 is multiplexed. As multiplexing may occur several times on the communication line, RC acts not only as the identifier between the multiplexed cells, but also as the carrier of the past record of multiplexing. More specifically, the ATM cells transported from plural different input ports are multiplexed in the multiplexing equipment. Every time the destined input port is exchanged, the RC is inserted in front of said ATM cell. At receiving node, the RC is monitored, and the following ATM cells are distributed for each RC.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a multiplexing method and equipment for the multicast communication (selectively simultaneous communication) in ATM(Asynchronous Transfer Mode) communication. 
     2. Description of the Prior Art 
     There is known a multicast connection as one of the techniques supporting the multicast communication in ATM communication. In the point to multi point connection, among them, ATM cells from different transmitting nodes toward one receiving node are multiplexed into one UNI (User Network Interface) when transmitted. In this case, it is necessary that, at the receiving node, the ATM cells with the same VPI/JVCI (Virtual Pass Identity/Virtual Channel Identity) addresses be identified for each receiving node and be re-combined into a packet of (ATM Adaptation Layer). 
     Hitherto, the above mentioned identification was implemented by by using MID (Multiplexing Identification) field of AAL 3 / 4 , as shown in ITU-T 1.363. 
     The ATM cell format of AAL 3 / 4  is shown in FIG.  7 . As shown in (a) of FIG. 7, the ATM cell of AAL 3 / 4  has  10  bit MID field  71  for multiplexing. When the value of this field is set so as to be different for each receiving node, multiplexed ATM cells can be identified at the receiving node. 
     As shown in FIG. 7, comparing the ATM cell of AAL 3 / 4  with the ATM cell of AAL 5  as recommended by ITU-T, the payload  73  of ATM cell of AAL 5  is 48 octet payload, while that of AAL 3 / 4  is 44 octet and therefore, has greater overhead than AAL 5 . Accordingly, the communication by using the ATM cell of AAL 3 / 4  is less efficient than AAL 5 . Furthermore, the ATM cell of AAL 3 / 4  is costly and complex in management, because AAL 3 / 4  has 5 functional fields including MID field  71  in addition to the cell header. 
     On the other hand, when more efficient AAL 5 , instead of AAL 3 / 4 , is employed for multiplexing, there is the disadvantage that the multiplexed cells per se can not be distinguished at receiving node, because AAL 5  has not any identification field corresponding to the MID field of AAL 3 / 4  for multiplexing. 
     SUMMARY OF THE INVENTION 
     Therefore, an object of the present invention is to identify cells at receiving node, by using AAL 5  in cell multiplexing for multicast communication, by using AAL 5 . 
     Another object of the present invention is to improve efficiency and performance of ATM multicast communication, by constructing a multiplexing system, wherein the received cells can be identified at receiving port by using AAL 5  which is more efficient than AAL 3 / 4 . 
     In accordance with the present invention, there is provided an ATM cell multiplexing system, which comprises ATM cell multiplexing means for inserting the ATM cells that have past record information or route information, as routing cell, when multiplexing said ATM cells inputted at different plural ports, and separation means for receiving said ATM cells, detecting routing cells from said ATM cells, separating said ATM cells on the basis of the information of said routing cells. 
     Further, in accordance with the present invention, there is provided a method of ATM communication wherein packets are transmitted as cells, which comprises the step of inserting routing cell to identify multiplexed ATM cells in receiving node, when multiplexing said ATM cells inputted at different plural ports. 
     As a result of inserting RC (Routing Cell), the present invention can improve the efficiency and the performance of ATM multicast communication, by implementing a multiplexing system such that the received cells can be identified at receiving node, by using AAL 5  which is more efficient than usual AAL 3 / 4 . 
    
    
     BRIEF EXPLANATION OF THE DRAWINGS 
     FIG. 1 is a block diagram of the mode of embodiment of the present invention. 
     FIG. 2 is a block diagram explaining the whole system construction of the present invention. 
     FIG. 3 is an illustration explaining the operation of the present invention. 
     FIG. 4 is a figure showing the RC (Routing Cell) format used in the present invention. 
     FIG. 5 is a flow chart explaining the operation of the present invention. 
     FIG. 6 is a figure showing an example of the structure of the receiving node in the present invention. 
     FIG. 7 ( a ) and FIG. 7 ( b ) show the ATM format of AAL 3 / 4  and AAL 5 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the accompanying drawings, the preferred embodiments of the present invention is explained. At first, an example of the construction of the whole system is shown in FIG.  2 . The ATM cells of AAL 5  transmitted to receiving node  27  from transmitting node  21 ,  22  and  23  are multiplexed at multiplexing connection point  24  and  25 , and received at receiving node  27  through ATM switchboard  26 . 
     At multiplexing connection points  24  and  25 , in FIG. 2, RC(Routing Cell)  34  is inserted by multiplexing equipment  30  as shown in FIG.  3 . As shown in FIG. 3, ATM cells  31 , 32  and  33  transported from different input ports are multiplexed, and outputted at single output port. RC  34  is inserted just in front of the ATM cell at each transporting input port. 
     The example of the construction of the multiplexing equipment shown in FIG. 3 is shown in FIG.  1 . The inputted cell is once buffered at input ports  11 ˜ 13 . Then, by using, as a trigger, the control signal from control function block  15  to input ports  11 ˜ 13 , the inputted cells are transported from input ports  11 ˜ 13  to multiplexing function block  16 , and buffered here again. 
     The cell which is transported from input ports  11 ˜ 13  to multiplexing function block  16 , is transported simultaneously to control function block  15 , and is analyzed there. As a result of the analysis, if RC be inserted, the control signal is sent from control function block  15  to RC generating function block  14 , and RC generating function block  14 , after detecting the control signal, generates RC (Routing Cell)  34  and transfer it to multiplexing function block  16 . 
     Multiplexing function block  16  outputs immediately the transported RC. Control function block  15  sends uninterruptedly the control signal to multiplexing function block  16 , and multiplexing function block  16  manages the buffered cell, detecting the control signal. After all, multiplexing function block  16  outputs the control signal, if the cell is a user cell. On the other hand, it discards the control signal , if the cell is RC. As a result of the analysis, if RC needs not to be inserted, the control signal is sent immediately from control function block  15  to multiplexing function block  16 , and the cell buffered at multiplexing function block  16  is managed likewise. 
     Next, the self format of RC in the present invention is explained, referring to FIG.  4 . RC is based on OAM (Operation Administration and Maintenance) of end-end F 5  flow. 5 octet cell header region  40  is header of ATM cell, and PTI (Payload Type identifier) has the value  101  showing the OAM cell of end-end F 5  flow of OAM cell. 4 bit OAM cell class region  41  uses the unused value (for example 00011) to indicate that it is RC(Routing Cell). 
     PADDING region  42  holds padding information. 10 bit error detection code region  44  is used for error detection by CRC  10 .  45  octet route information  43  consists of the 8 bit Hop region for counting the number of multiplexing and RI region  46  for indicating past record of multiplexing. 
     For example, if the payload of RC received at receiving node is such that Hop=3, RI[ 1 ]=2, RI[ 2 ]=1, RI[ 3 ]=3, it is understood that this specific packet passes three multiplexing connection points and that its transmitting node is identified by the value 3-1-2 seen from the receiving node. 
     FIG. 5 shows a flow chart of the insertion of RC, corresponding to the actions of control function block  15  and RC generating block  14  in FIG.  1 . The function block which manages the flow of FIG. 5 has Routing table  10 , and the registers S and H, where routing table  10  of Hop ( 45  in FIG. 4 ) and RI ( 46  in FIG. 4 ) exists for every input port. In Routing table  10 , the port number n of Port [n] is shown actually. 
     First, in the step  1 , the contents of the above mentioned registers S and H and Routing table  10  are initialized to 0. 
     Next, in the step  2 , ATM cell transported from input port is analyzed, and header information (VPIIVCI) is stored in the register H. 
     Continuously, in the step  3 , cell header and OAM function class field are inspected to identify whether the ATM cell is RC or not. In the step  3 , if the ATM cell is found to be RC, the input port number [S] is memorized in the step  4 , and the Routing table  10  is renewed according to the information of RC in the step  4 . 
     Exactly, the value of Hop field of RC is copied into the Hop field of Port[S] in Routing table  10 , and the corresponding value of RI of RC is copied into each RC field in the step  4 . This RC is once terminated in the step  4 . 
     After the step  4 , RC is generated again immediately in the step 5 , and inserted in the step  6 . 
     In the step  5 , the value such that the value of Hop field of Port[S] is incremented by 1 is buried into the Hop field of the generated RC, and the value of the corresponding RI of Port[S] is copied into all the RI field, and, furthermore, the value of the register S indicating the port number is written in RI[Hop] of RC where Hop is the value after the increment. 
     Also, while the memorized value of H is written in the header of RC, PTI field is put to be  101 , and the OAM cell class field is put to be 0011. Afterwards, Padding and CRC  10  are added. 
     Further, when ATM cell is not found to be RC in the step  3 , then the step  7  is executed. 
     If the number of the input port where cell is transported is the same number as the value of the register S , the cell is outputted immediately without inserting RC in the step  9 . 
     On the other hand, If they are not identical, the value of the number of the input port is set in the register S in the step  8 , and then the step  5 , the step 6 , the step  9  are followed. 
     Namely, concerning the cell transported continuously from the same port, when the cell is RC, the multiplexing means of the present invention once terminates the RC, increments its value of Hop by 1, inserts new RC by writing the port number in the RI[Hop], transports the following user cell as it is into output line. When cell is transported from different port, if the first cell is a user cell, then “1” is written in Hop, generates new RC[ 1 ], and insert it in front of the said user cell. Thereby, the payload information of RC can uniquely correspond to each physically different transmitting node, multiplexed cell can be distinguished at receiving node. 
     FIG. 6 shows an example of the construction to restore AAL 5  packet at receiving node, where block  60  is the characteristic portion of the present invention. Cell sequence including RC is inputted in separation function block  61 . In RC analysis function block  65 , cell inputted into separation function block  61  is monitored, and RC is analyzed, and control signal is sent to separation function block  61 . 
     Based on the above mentioned control signal, separation function block  61  distributes input cell sequences for buffer function blocks  62 ,  63  and  64  for each transmitting node. Then, the cell sequences are transported under packet unit to SAR (Segmentation And Re-assembly) function block  67  through multiplexing function block  66 . Thereby, AAL 5  packet is assembled normally in SAR function block  67 . 
     As a result of inserting RC(Routing Cell), the present invention can improve the efficiency and performance of ATM multicast communication by implementing a multiplexing system, wherein ATM cells can be identified at receiving node by using AAL 5  which is more efficient than usual AAL 3 / 4 . 
     Although the present invention has been shown and described with respect to the best mode embodiment thereof, it should be understood by those skilled in the art that the foregoing and various other changes, omissions, and additions in the form and detail thereof may be made therein without departing from the spirit and scope of the present invention.