Abstract:
The present invention relates to an AAL switch for multicast and a switching method for performing a flexible multicast connection. An AAL 2  switch for multicast and a switching method for performing a flexible multicast connection can be used in applications like video conference and video on demand. An AAL 2  switch can include a plurality of receiver circuits that convert an AAL 2  packet into a CPS packet by demultiplexing, a plurality of storing devices that store a CPS packet separated from the AAL 2  packet, and a plurality of transmitter circuits that periodically search the plurality of storing device and convert the searched CPS packet into an outgoing AAL 2  packet by multiplexing. The transmitter circuits can transmit the outgoing AAL 2  packet.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an ATM adaption layer (AAL) switch in a mobile communication system, and more particularly to a switching method and an AAL 2  type AAL switch for multicast. 
     2. Background of the Related Art 
     An AAL 2  switch is one of the core technologies of IMT-2000, which combines ATM signals for efficient use of broadband width in an ATM network that is used as a transmission path between stations using IMT-2000, i.e., a base station, base station controller and mobile switching center.  FIG. 1  is a block diagram of a related art ATM switch system. 
     Referring to  FIG. 1 , the related art ATM switch system includes an AAL 2  receiving end  11 , an ATM switch  12 , and an AAL 2  transmitting end  13 . An AAL 2  packet is demultiplexed by the AAL 2  receiving end  11 , and the AAL 2  packet is converted into an ATM cell of 53 bytes having an internal format. The converted ATM cell, i.e., the common part sublayer packet (CPS) is switched by the ATM switch  12 , and reverse-converted into the AAL 2  CPS packet from the internal format, and multiplexed by the AAL 2  transmitting end  13  to be transmitted to a destination. 
     As described above, the ATM switch  12  does not switch the AAL 2  packet immediately or directly, but first has to convert the AAL 2  packet into an ATM cell using the internal format. Further, when performing the switching at an ATM level, the related art ATM switching system cannot achieve the AAL 2  multicast switching due to the CPS packet in a multiplexed state. 
     As described above, the related art ATM switch system has various disadvantages. As shown in  FIG. 1 , in the related art ATM switching system, the AAL 2  packet has to be converted into CPS packet by the internal format. After the switching, the converted CPS packet has then to be re-converted into AAL 2  CPS packet. Such an overhead causes service quality deterioration and efficiency deterioration such as delayed transmission of cells. Further, many manufacturers develop proprietary or use their own internal formats such as AAL 2  and AAL 5 . Further, since the related ATM switch system cannot support the multicast function of multiplexed AAL 2 , it is impossible to apply the system to the 3-G mobile communication system like the IMT-2000. In the related art ATM switch system, since the ATM cell multiplexed into AAL 2  packet has a plurality of user information, the AAL 2  packet has to be divided into CPS packets to be copied into a plurality of cells. Accordingly, there have been increasing demands and a need exists for an AAL 2  switch for multicast, which will achieve a more efficient communication system and increase or maximize the traffic transmission efficiency. 
     The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to solve at least the above problems and/or disadvantages and to provide at least the advantages described hereinafter. 
     Another object of the present invention is to provide an ATM adaption layer (AAL) switch for multicast and a switching method thereof that improves an existing ATM switch for multicast. 
     Another object of the present invention is to provide an AAL switch for multicast and a switching method thereof that improves an existing AAL 2  switch for unicast. 
     Another object of the present invention is to provide an AAL switch for multicast and a switching method thereof in a mobile communication system that increases traffic efficiency rates. 
     Another object of the present invention is to provide an AAL 2  switch for multicast and a switching method thereof for performing a multicast connection in applications like video conference or video on demand (VOD) in an IMT-2000 system. 
     Another object of the present invention is to provide an AAL 2  switch for multicast and a switching method thereof in a 3-G mobile communication system that increases or maximizes traffic efficiency rates by improving an existing ATM switch for multicast or AAL 2  switch for unicast. 
     To achieve at least the above objects in a whole or in part, there is provided an AAL 2  switch for multicast in a mobile communication system, the switch includes a plurality of receiver circuits each receiving and demultiplexing an AAL 2  packet for converting into at least one CPS packet, a plurality of memories that store the at least one CPS packet, and a plurality of transmitter circuits each coupled to the plurality of memories that search the plurality of memories, convert the searched CPS packet into an AAL 2  packet by multiplexing, and transmit the AAL 2  packet. 
     To further achieve the above objects in a whole or in part, there is provided a switching method of an AAL 2  switch for multicast in a mobile communication system, the method including converting a received AAL 2  packet into a CPS packet by demultiplexing the received AAL 2  packet, generating a new VPVC and routing information based on VPVC and CID in the received AAL 2  packet, storing the CPS packet and the new VPVC according to the routing information in at least one of a plurality of storage areas in a memory, extracting the CPS packet by searching the plurality of storage areas, and transmitting an AAL 2  packet by converting the extracted CPS packet into an AAL 2  packet and transmitting the AAL 2  packet. 
     To further achieve the above objects in a whole or in part, there is provided a switching method of an AAL switch for multicast in a mobile communication system, the method including converting a received AAL 2  packet into a CPS packet by demultiplexing the received AAL packet, storing the CPS packet according to a routing information, converting the stored CPS packet into an AAL packet, and transmitting the AAL packet. 
     Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described in detail with reference to the following drawings in which like reference numerals refer to like elements wherein: 
         FIG. 1  is a block diagram of a related art ATM switching system; 
         FIG. 2  is a block diagram that shows a preferred embodiment of an AAL 2  switch for multicast according to the present invention; 
         FIG. 3  is a block diagram that shows an internal structure of a memory shown in  FIG. 2 ; 
         FIG. 4  is a diagram that shows a structure of an allocated memory shown in  FIG. 2 ; 
         FIGS. 5   a  and  5   b  are diagrams that show exemplary first and second tables shown in  FIG. 2 , respectively; and 
         FIG. 6  is a flowchart that shows a preferred embodiment of an AAL 2  switching method according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Preferred embodiments of ATM adaption layer (AAL) switches and Switching methods for multicast in a communication system according to the present invention will now be described with reference to the accompanying drawings. In the description, matters defined such as detailed constructions and elements of circuits are exemplary ones provided with respect to preferred embodiments to assist in a comprehensive understanding of the present invention. Thus, it is apparent that the present invention can be carried out without such defined matters. Further, well-known functions or constructions are not described in detail since they would be known to one of ordinary skill in the art. 
       FIG. 2  is a block diagram that shows a preferred embodiment of a AAL 2  switch for multicast according to the present invention. As shown in  FIG. 2 , the AAL 2  switch includes a plurality of AAL 2  receiving ends  21   a - 21   n , a plurality of memories  22   a - 22   n  and a plurality of AAL 2  transmitting ends  23   a - 23   n . Further, the AAL 2  switch can include a first table  24  and a second table  25 . 
     The AAL 2  receiving ends  21   a - 21   n  are coupled to respective input ports (e.g., input PORT 1 -PORTN), and preferably demultiplex an ATM cell of 53 bytes, which is a multiplexed form of an AAL 2  CPS packet. Thus, an AAL 2  receiving end (such as the AAL 2  receiving end  21   a ) of the AAL 2  receiving ends  21   a - 21   n  can separate a CPS packet from the AAL 2  packet inputted through each port of the input ports. The AAL 2  receiving end  21   a  transmits a CPS packet to the memory  22   a  according to a new virtual path virtual circuit (VPVC) and a routing tag preferably determined in the first table  24  (e.g., see  FIG. 5   a ) where the new VPVC and the routing tag are allocated responding to VPVC and channel identifier (CID) of the AAL 2  inputted through the input ports. The routing tag preferably means a start point of each storage area or location in memory. Based on the routing tag as shown in  FIG. 2 , the AAL 2  receiving end  21   a  stores the CPS packet into the memory  22   a  that is coupled to the AAL 2  receiving end  21   a . Storage areas (i.e., addresses), which preferably correspond to the output ports in number, can be allocated in the memory  22   a  in advance. Accordingly, based on the routing tag, the CPS packet determined in the AAL 2  receiving end  21 - 21   n  can be stored in one of the pre-allocated addresses of the corresponding memory  22   a - 22   n . Meanwhile, the new VPVC can also be stored in the corresponding memory  22   a - 22   n  (e.g., memory  22   a ) when the CPS packet is stored. 
     The plurality of memories  22   a - 22   n  are preferably coupled to the plurality of AAL 2  receiving ends  21   a - 21   n  in an one-to-one basis, and can store the CPS packet and the VPVC transmitted from the AAL 2  receiving ends  21   a - 21  n. The memories  22   a - 22   n  will now be described in additional detail. 
       FIG. 3  is a block diagram showing an exemplary internal structure of memory in the preferred embodiment of a AAL 2  switch for multicast. The memory as shown in  FIG. 3  means one of the memories preferably existing equal in number to a number of output ports. As shown in  FIG. 3 , a memory such as the memory  22   a  can be divided into a plurality of storage areas each preferably including a memory status field, a copy port field and a port area. The memory status field preferably indicates whether the CPS packet is stored in the memory (e.g., the memory  22   a ) or not. For example, if the CPS packet and VPVC are stored in the memory  22   a , a prescribed value such as “1” is set in the memory status field of the corresponding storage area. The copy port field preferably indicates the output port where the copied CPS packet is transmitted for multicast. For example, if the CPS packet for multicast is intended to be sent to the output ports  3 ,  8 ,  14  and  27 , a value such as “1” can be set in each bit of the copy port field that corresponds to the output ports  3 ,  8 ,  14  and  27 . Each bit of the copy field can correspond to an output port to indicate each of the output ports to which the CPS packet is transmitted. Also, the CPS packet and the new VPVC information can preferably be stored on the port area corresponding to the bit of ‘1’ set from the copy port field. 
       FIG. 4  is a diagram showing an exemplary construction for allotting addresses or storage areas in memory in the preferred embodiment of a AAL 2  switch for multicast. As shown in  FIG. 4 , the memory (e.g., memories  22   a - 22   n ) has storage areas corresponding to output ports (output PORT 1 -PORTN) in number. In each of storage areas, the memory status field, the copy port field and the port area can be separately included. To support one switch port, each of storage areas can be preferably allocated in total 73 bytes, which includes 68 bytes of port area, 1 byte of memory status field and 4 bytes of copy port field. As shown in  FIG. 3 , storage areas are allocated in number corresponding to the number of the output ports, because when the CPS packet is for multicast, the CPS packet has to be copied and stored in the respective ports through which the packet is intended to be transmitted, and the CPS packet has to be searched and transmitted by the AAL 2  transmitting end  23   a . The memory status field preferably includes 1 byte intended to indicate whether the CPS packet is stored or not. The copy port field indicates area to which the CPS packet for multicast should be copied and transmitted. The port area can include 3 bytes of a new VPVC, 1 byte of CPS packet length and an allocation or maximum 64 bytes for the CPS packet. A DPRAM (Dual Port RAM) or the like can be used as the memory  22   a - 22   n.    
     As shown in  FIG. 2 , the plurality of AAL 2  transmitting ends  23   a - 23   n  preferably search or search periodically based on the memory status field whether there are CPS packets stored for the respective memories  22   a - 22   n . As described above, the CPS packet transmitted from the AAL 2  receiving end  21   a  can be stored in the corresponding memory  22   a . For example, to indicate that the CPS packet is stored, ‘1’ is preferably set in the memory status field of the memory  22   a . Accordingly, the AAL 2  transmitting end  23   a  searches each of the plurality of memories  22   a - 22   n  to determine whether ‘1’ is set in the memory status fields. When there is ‘1’ set in the memory status field, the CPS packet stored in the corresponding memory  22   a  can be extracted. If the CPS packet is for multicast, in addition to the memory status field, the AAL 2  transmitting end  23   a  also searches the copy port field to determine whether the copy port field area is set at ‘1’ for its corresponding output port PORT 1 . When the copy port field is set at ‘1’, the AAL 2  transmitting end  23   a  confirms the output port to which it is coupled and extracts the CPS packet stored in a corresponding port area at this time. The AAL 2  transmitting end  23   a  can then transmit the AAL 2  packets preferably by multiplexing the extracted CPS packet based on the new VPVC and a new CID preferably allocated in the second table  25  or the like. 
       FIG. 6  is a flowchart that shows a preferred embodiment of an AAL switching method according to the present invention. For example, the preferred embodiment of an AAL switching method can be used in the preferred embodiment of a AAL 2  switch for multicast as shown in  FIG. 2 . As shown in  FIG. 6 , after a process starts, when an AAL 2  packet is inputted to one of a plurality of AAL 2  receiving ends (e.g., AAL 2  receiving end  21   a - 21   n ) such as the AAL 2  receiving end  21   a , the AAL 2  receiving end  21   a  separates the CPS packet from the AAL 2  packet in step S 51 . From step S 51 , control continues to step S 53 , where a new VPVC and a routing tag are allocated, for example in the first table  24 , based on the VPVC and CID of the AAL 2  packet. From step S 53 , control continues to step S 55 . 
     In step S 55 , the AAL 2  receiving end can store the CPS packet based on the VPVC and CID using Table  1  in the corresponding memory (i.e., storage areas). At this time, storage areas can preferably be pre-allocated in the memory (e.g., memory  22   a ) corresponding to the number of the output ports. Each of storage areas in the memories  22   a - 22   n  can include a memory status field, a copy port field, and a port area. However, the present invention is not intended to be so limited. Based on the routing information, it is determined in step S 55  whether the CPS packet is stored in any corresponding storage area in the storage areas of the memory  22   a , and accordingly, the CPS packet and the new VPVC can be stored in the corresponding storage area. 
     At this time, when the CPS packet is stored in a corresponding storage area of the memory  22   a  or the like, the memory status field of the corresponding storage area is set at ‘1’ or a prescribed value. Further, when the CPS packet is for multicast, not only the memory status field, but also the copy port field can be set at ‘1’ or a prescribed value. 
     From step S 55 , control continues to step S 57  where the AAL 2  transmitting end  23   a  periodically searches the plurality of memories  22   a - 22   n  and extracts the searched CPS packet. Thus, one AAL 2  transmitting end of the plurality of AAL 2  transmitting ends  22   a - 22   n  transmitting end preferably can search the plurality of memories  22   a - 22   n . While the AAL 2  transmitting end (e.g.,  23   a ) searches to discriminate whether the internal memory status fields are set at ‘1’ or not based on the plurality of memories  22   a - 22   n , the AAL 2  transmitting end  23   a  extracts the corresponding CPS packet when determining that a memory status field is set at the prescribed value such as ‘1’. If the CPS packet is for multicast, since the bit corresponding to the copy port field of the object port for transmitting is also set at ‘1’, the AAL 2  transmitting ends also have to search a corresponding bit of the copy port field. If the bit corresponding to the copy port field is set at ‘1’,it is determined whether the output port is coupled to the searching AAL 2  transmitting end (e.g., AAL 2  transmitting end  23   a ) itself. For example, if the bit corresponding to the copy port field set at ‘1’ is the port connected with the AAL 2  transmitting end  23   a , at this time the AAL 2  transmitting end  23   a  extracts the CPS packet stored in the port area corresponding to the bit set at ‘1’. Further, when the CPS packet is extracted, the new VPVC can also be extracted together with the CPS packet. 
     The CPS packet extracted through the above-described searching process performed in step S 57  is input to the AAL 2  transmitting end  23   a  and converted into the AAL 2  packet by multiplexing the CPS packet, and the AAL 2  packet can be transmitted through the output port in step S 59 . Here, the ‘multiplex’ means a combination of the plurality of CPS packets extracted from the respective memories  22   a - 22   n  by the AAL 2  transmitting end such as the AAL 2  transmitting end  23   a . The new VPVC, which is extracted together with the CPS packets, can be generated, and a new CID can be allocated based on the new VPVC, for example, using the second table  25 . Accordingly, the AAL 2  packet is transmitted based on the new VPVC and the new CID. 
     As described above, preferred embodiments of an AAL 2  switch and switching method according to the present invention have various advantages. In the preferred embodiments of an AAL 2  switch and switching method, the CPS packets separated from the ATM cell are stored in a predetermined position of the memory according to the routing tag, and the transmitting ends search the respective memories to discriminate whether there is the CPS packet to be transmitted to the output port. Accordingly, a higher rate switching can be performed by an AAL switch, and a multicast function can be extended to and performed at the AAL level. Further, the traffic efficiency rate can be greatly increased to a level that enables the provision of efficient multicast services in third generation (3-G) technology, such as video conference in the IMT-2000 system and video-on-demand (VOD), or the like. 
     The foregoing embodiments and advantages are merely exemplary and are not to be construed as limiting the present invention. The present teaching can be readily applied to other types of apparatuses. The description of the present invention is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures.