Abstract:
A label switching router having an internal channel share function over an asynchronous transfer mode that sets up an internal channel in advance of the external channel and shares it when an external channel needs to be set up, and a method for sharing an internal channel using the same. The label switching router includes a forwarding engine for setting up a label switched path by using a signaling protocol, extracting an egress forwarding engine number and a channel identifier, allocating an extension tag, searching a previously-set internal channel, forming a forwarding information base/label information base including the previously-set internal channel identifier and the extension tag, adding a header having the internal channel identifier and extension tag to a received internet protocol packet by referring to the forwarding information base/label information base, and forwarding the internet protocol packet, and a merging unit for receiving label switched path set information from a peer forwarding engine, forming an extension information base/merging table where an internal channel identifier is mapped to an extension tag, performing merging when receiving an internet protocol packet having the extension tag, extracting the extension tag, mapping the extension tag to the internal channel identifier, and forwarding the internet protocol packet to an internal channel having the mapped internal channel identifier.

Description:
CLAIM OF PRIORITY  
         [0001]    This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from an application entitled “LABEL SWITCHING ROUTER HAVING INTERNAL CHANNEL SHARE FUNCTION OVER ATM, AND METHOD FOR SHARING INTERNAL CHANNEL USING THE SAME” earlier filed in the Korean Intellectual Property Office on 15 Feb.  2003  and there duly assigned Serial No. 2003-9644.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a label switching router (LSR) having an internal channel share function over an ATM which sets up internal channels in advance and shares internal channels when an external channel needs to be set up, and a method for sharing an internal channel using the same.  
           [0004]    2. Description of the Related Art  
           [0005]    In general, an Multiprotocol Label Switching network (or MPLS network) improves transmission of layer  3  (L 3 ) packet by an internet protocol (or IP) header used in an existing local area network/wide area network (LAN/WAN), and thus efficiently and rapidly transmits the L 3  packets by using a new label stack having a short length, namely an MPLS header. The connection structure of the MPLS network includes an end system for performing a router function, and LSRs classified into label edge routers (LER) positioned on contact points to the existing network, and core LSRs positioned in the MPLS network according to their functions.  
           [0006]    An MPLS control protocol stack for supporting MPLS functions includes a label distribution protocol (LDP) layer for transmitting/receiving label values between the LSRs. An MPLS, also called a label switch path or LSP, is set up to transmit the L 3  packets by the corresponding LDP layer according to the MPLS. In the ATM MPLS network, when the L 3  packet is transmitted from the existing network such as the LAN through ATM (or Asynchronous Transfer Mode) access such as an IP over ATM (or IPOA) of the end system, an MPLS layer of an ingress or incoming ATM-LER positioned on the boundary of the ATM MPLS network transforms the L 3  packet into ATM cells, and transmits the ATM cells to a core ATM-LSR through an ATM LSP determined by an LDP layer. Identically to general ATM cell transmission, the core ATM-LSR transmits the ATM cells to an egress or exiting ATM-LER by VPI/VCI (or virtual path identifier/virtual channel identifier) switching of the ATM cells in an ATM layer. The egress ATM-LER assembles the ATM cells into L 3  packet and transmits the ATM cells to the existing network through the end system.  
           [0007]    In order to set up an external channel such as the LSP or IPOA PVC (or permanent virtual circuit), the virtual path (or VP) tunnels are set up in the form of a VP full mesh in the ATM MPLS network. That is, the ATM MPLS network sets up the VP tunnels by using the internal channel set process due to the external channel. When one external channel LSP or IPOA is set up, the internal channels must then be connected as many as the value obtained by subtracting the set Forwarding Engines (or FEs)  200  from the whole FEs  200 . Accordingly, when N LSPs are set up, a number of channels required in the ATM MPLS network is represented by following formula 1:  
           Network channel number=external channel number ( N )+ N *( FE  number−1)  &lt;Formula 1&gt; 
           [0008]    Considering the mapping relations between the internal and external channels, the general internal channel allocation restricts capacity of the ATM MPLS network. For example, when 16 K of LSP and 16 K of IPOA PVC are needed per 622 Mbps of FE in 10 G of MPLS network, 512 K of channel capacity is required to set up channels. However, channel capacity per 622 Mbps is restricted to 64 K, which influences the ATM MPLS network.  
         SUMMARY OF THE INVENTION  
         [0009]    It is therefore an object of the present invention to provide an improved LSR.  
           [0010]    It is also an object of the present invention to provide an improved method for switching ATM data through a network having LSR&#39;s.  
           [0011]    It is also an object of the present invention to eliminate the consumption of unnecessary resources in a switch when possible.  
           [0012]    It is further an object to provide a network and an method for switching data through the network that is faster, more efficient and has a broader bandwidth.  
           [0013]    It is also an object of the present invention to share an internal channel to transfer data between an internal switch and a destination when the data originates in more than one source.  
           [0014]    These and other objects may be achieved by having the internal channels in an MPLS network already set up before any data needs to be transferred and before an external channel arrives at the network. In addition, this invention allows for the sharing of the internal channels of the network thereby enhancing speed. By sharing channels instead of using many channels, resources are conserved in that unnecessary channels do not have to be set up.  
           [0015]    Provided is a label switching router having an internal channel share function over an ATM which sets up an internal channel in advance in an ATM MPLS network and shares the internal channel when an external channel needs to be set up. Provided also is a method for sharing an internal channel using the same.  
           [0016]    There is provided a label switching router having an internal channel share function over an ATM, the label switching router having a forwarding engine for setting up a label switched path by using a signaling protocol, extracting an egress forwarding engine number and a channel ID, allocating an extension tag, searching a previously-set internal channel, forming a forwarding information base/label information base (FIB/LIB) including the previously-set internal channel ID and the extension tag, adding a header having the internal channel ID and extension tag to a received IP packet by referring to the forwarding information base/label information base, and forwarding the IP packet. The label switching router further having a merging unit for receiving label switched path set information from a peer forwarding engine, forming an extension information base/merging table (EIB/MT) where an internal channel ID is mapped to an extension tag, performing merging when receiving an IP packet having the extension tag, extracting the extension tag, mapping the extension tag to the internal channel ID, and forwarding the IP packet to an internal channel having the mapped internal channel ID. A single channel is shared and used to transmit data originating from more than one source and going to a single destination instead of having a separate channel for each originating source.  
           [0017]    There is also provided a method for sharing an internal channel by using a label switching router over an ATM, the method starting out with a first step where a forwarding engine sets up a label switched path by using a signaling protocol, extracts an egress forwarding engine number and a channel ID, allocates an extension tag, and forms a forwarding information base/label information base table by using a previously-set internal channel. The second step being where the forwarding engine adds a header having the internal channel ID and extension tag to a received IP packet by referring to the forwarding information base/label information base, and forwards the IP packet. The third step being where a merging unit receives label switched path set information from a peer (or ingress) forwarding engine, forms an extension information base/merging table where an internal channel ID is mapped in an extension tag. The method concludes with a fourth step where the merging unit forwards a received IP packet having the extension tag to an internal channel having the internal channel ID mapped to the extension tag by referring to the extension information base/merging table. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    A more complete appreciation of the invention, and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference symbols indicate the same or similar components, wherein:  
         [0019]    [0019]FIG. 1 is a structure diagram illustrating an ATM MPLS network;  
         [0020]    [0020]FIG. 2 is a concept diagram illustrating a general process for setting up an LSP;  
         [0021]    [0021]FIG. 3 is a structure diagram illustrating an ATM MPLS system having an internal channel share function according to the principles of the present invention;  
         [0022]    [0022]FIG. 4 is a block diagram illustrating an internal structure of a line interface card of FIG. 3;  
         [0023]    [0023]FIG. 5 is a block diagram illustrating an internal structure of an ICB interface of FIG. 4;  
         [0024]    [0024]FIG. 6 is a block diagram illustrating an internal structure of a forwarding engine of FIG. 3;  
         [0025]    [0025]FIG. 7 is a block diagram illustrating an internal structure of a merging unit of FIG. 3;  
         [0026]    [0026]FIG. 8 is a concept diagram illustrating a process for setting up an LSP according to the principles of the present invention;  
         [0027]    [0027]FIG. 9 is a flowchart illustrating the process for setting up the LSP in according to the principles of the present invention; and  
         [0028]    [0028]FIG. 10 is a flowchart illustrating a process for sharing an internal channel in according to the principles of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0029]    Turning now to the figures, FIG. 1 is a structure diagram illustrating an ATM MPLS network  10 . Referring to FIG. 1, an IP packet  20  entering the MPLS network  10  is transformed into ATM cells  21  in a first LER  11  which is an ingress LER. The transformed ATM cells  21  are then switched by ATM switches along an LSP path. The IP packet  20  is reassembled from the ATM cells  21  in a third LER  13  which is an egress LER, and the IP packet is outputted from the MPLS network  10 .  
         [0030]    In FIG. 1, IP routing functions of a router such as IP packet assembling/segmentation, IP header analysis and processing, and routing table lookup are performed once in each LER  11  and  13 , and the ATM cells  21  are rapidly ATM switched in the MPLS network  10 . In addition, a data transmission path is identical to a connectionless IP network path. A transmission side of two adjacent routers on one path is upstream Ru and a reception side is a downstream Rd. A path calculated by a routing protocol operated in each network element is an LSP path. Here, a protocol used between the network elements is an LDP. That is, when the LSP is set up by the LDP, the first LER  11 , which is an ingress LER, analyzes a header of the IP packet  20 , and determines an LSP according to the destination IP address. Thereafter, the first LER  11  segments the IP packet  20  into the ATM cells  21 , and transmits the ATM cells  21  to a first LSR  110  which is a peer LSR by using a selected label as a VPI/VCI value. The first through fourth LSRs  110  through  140  transmit the IP packet to the third LER  13 , which is an egress LER, by cell switching without assembling/segmenting the IP packet. The third LER  13  reassembles the input cells, analyzes an IP header, and performs L 3  forwarding.  
         [0031]    The LER&#39;s includes a plurality of line interface cards (LIC) for connecting the LER to an external environment (such as terminals or other systems). The LER&#39;s also include a plurality of forwarding engines (FE) for forwarding packets. Each of the LICs may include a variety of interfaces such as an ATM interface, Ethernet and frame relay. The external terminals or other systems can be connected to the LERs through the plurality of LICs in the form of various services. Such connections are connected to the FEs so that they can process the input packets and transmit them to destinations.  
         [0032]    On the other hand, when the MPLS LER/LSR over the ATM sets up the LSP through the MPLS network, a VP full mesh type internal channel must be determined between the FEs. Each FE must set up VPI channels of the whole FEs composing the ATM MPLS network. For example, as illustrated in FIG. 2, FE-1  200   b  must set up three LSPs (34, 35 and 36) for one channel (CH), the three paths being FE-0&gt;FE-1&gt;FE-2&gt;FE-1 and FE-3&gt;FE-1. In addition, four open channels 1, 2 3 and CH are opened in consideration of one IPOA PVC. As will be discussed later, this is unnecessary.  
         [0033]    The process for setting up channels will now be explained. In initialization of the ATM MPLS network, virtual path (VP) tunnels are set up between the whole FEs in the ATM MPLS network by a general switch management protocol (GSMP). The VP tunnel information is registered in a VP mapping table of the MPLS LER. For example, as illustrated in FIG. 2, entry information such as FE-0, FE-1, VPI(i), FE-2, FE-1, VIP(2), FE-3, FE-1 and VPI(3) is registered in the VP mapping table of the FE-1  200   b . After this registration, when receiving an LSP or IPOA PVC connection request, the MPLS LER then allocates channels, and searches VPI information connected to the FE-1  200   b  in the VP mapping table. The MPLS LER searches VPI values of FE-1, FE-0, VPI(1), VCI(4), FE-1, FE-2, VPI(2), VCI(5), FE-1, FE-3, VPI(3) and VCI(6), and receives VCI values thereof from a VCI pool.  
         [0034]    Turning to FIG. 3, FIG. 3 is a structure diagram illustrating an ATM MPLS system  300  having an internal channel share function in according to the principles of the present invention. As illustrated in FIG. 3, the ATM MPLS system  300  having the internal channel share function includes a switch  301 , a main control unit  302 , an IP/MPLS control unit  303 , LICs  304 , MUX/DMUXes  305 , FEs  306 , and VC or virtual channel merging units (VM)  340 .  
         [0035]    The switch  301  switches ATM cells. The main control unit  302  controls software parts, namely call processing, maintenance/repair, charging and statistics. The LICs  304  match with external links, distinguish ATM data flows through a VPI/VCI, control traffic types and properties by ATM data flows, and transmit the ATM data flows to the switch  301 .  
         [0036]    Turning now to FIG. 4, FIG. 4 illustrates, in detail, an LIC  304  of FIG. 3. LIC  304  is made up of a line physical interface  308 , a port control unit  310  and an Interface Control Block or ICB interface  311 . Each of these devices are controlled by a main control unit  302 . LIC  304  is further made up of LINE MUX/DMUX  309 .  
         [0037]    Turning now to FIG. 5, FIG. 5 illustrates, in detail, internal control block or ICB interface  311  of FIG. 4. As depicted in FIG. 5, the ICB interface  311  of the LIC  304  includes a cell transmitting/receiving unit  312 , a cell format transforming unit  313  and an internal cell transmitting/receiving unit  314 . Each device  312 ,  313  and  314  is controlled by the main control unit  302 .  
         [0038]    The cell transmitting/receiving unit  312  transmits/receives cells to/from the port control unit  310 . When the port control unit  310  and the ICB interface  311  have different cell formats, the cell format transforming unit  313  equalizes the cell formats. The internal cell transmitting/receiving unit  314  transmits/receives cells format-transformed into internal cells. The cell format transforming unit  313  is required because most of the ATM exchanges transform standard ATM cells into internal cells and switch them. In addition to the fields of the standard ATM cell, the internal cell further includes a field for storing extra information such as an internal channel ID for switching in the exchange.  
         [0039]    The line physical interface  308  of the LIC  304  of an ingress LER extracts the standard ATM cells from a transmission frame, and a line physical interface of an egress LER adds the standard ATM cells to the transmission frame, and transmits it. The cell format transforming unit  313  of the ICB interface  311  of the LIC  304  of the ingress LER processes the standard ATM cells according to a corresponding protocol, and transforms the ATM cells into internal cells. The cell format transforming unit  313  stores the internal channel ID mapped to the VPI/VCI value in the field of the ATM standard cell by referring to an input end table mapping the VPV/VCI value to the internal channel ID.  
         [0040]    When the internal channel ID mapped to the VPI/VCI value of the standard ATM cells is stored in the fields of the internal cells, a cell format transforming unit of the egress LER processes the internal cells according to a corresponding protocol, and transforms them into the standard ATM cells. Here, the cell format transforming unit stores the VPI/VCI value mapped to the internal channel ID in the fields of the standard ATM cells by referring to an output end table mapping the internal channel ID to the VPI/VCI value. On the other hand, the IP/MPLS control unit  303  performs software functions such as an IP, routing protocol or RP, GSMP and LDP.  
         [0041]    The FEs  306  assemble the IP packets and analyze the IP header of the IP packets. In addition, the FEs  306  generate labels according to the analyzed IP headers, add the labels to the IP packets, segment the IP packets into the ATM cells, and transmit the ATM cells to a succeeding node (for example, exchange or router). The FEs  306  are hardware boards for rapidly processing various traffic such as IP packets, point-to-point protocol or PPP packets and MPLS packets inputted to the ATM MPLS exchange, and transmitting them to corresponding output interfaces.  
         [0042]    Turning now to FIG. 6, FIG. 6 illustrates in detail forwarding engine (FE)  306  of FIG. 3. As illustrated in FIG. 6, the FE  306  includes an input end ICB interface  315 , an SAR (or segmentation and reassembly or just segmentation) receiving unit  316 , a lookup control unit  317 , an FIB/LIB  323 , an SAR transmitting unit  318 , a control memory  320 , a packet memory  321  of the SAR receiving unit  316 , a control memory  324 , a packet memory  325  of the SAR transmitting unit  318 , and an output end ICB interface  319 . The control memories  320  and  324  store SAR control information, and the packet memories  321  and  325  store received packets. The input end ICB interface  315  transforms the internal cell into the standard ATM cells to perform SAR, and copies and stores an internal channel access ID stored in the fields of the internal cells in specific fields of the standard ATM cells. The SAR receiving unit  316  reassembles the standard ATM cells having the same internal access ID to generate the IP packet, and transmits the IP packet to the lookup control unit  317 .  
         [0043]    In addition to the internal channel ID information for routing between the FEs  306 , an extension tag must be set up in the FIB/LIB  323  of the FE  306  of the ingress LER to share the internal channel. The internal channel ID serves to distinguish internal channels set up between the FE  306  of the ingress LER and the FEs of the egress LER. In the related art, different internal channel IDs are allocated according to an external VPI/VCI, and thus a plurality of internal channel IDs are set up between the FEs of the ingress LER and the FEs of the egress LER. However, according to the principles of the present invention, the internal channel ID is not newly set up when the external VPI/VCI is set up. Instead, in the present invention, a previously established internal channel ID is used, and the external VPI/VCI is distinguished by using the extension tag (which will later be explained with reference to FIG. 8). Accordingly, when the external VPI/VCI is set up, the internal channel is not newly set up but routed to the same path by using the previously-set internal channel ID, which extends an available bandwidth. The extension tag is mapped to the newly-set external VPI/VCI, and the VPI/VCI mapped to the extension tag is designated in an extension information base/merging table (EIB/MT)  335  of the VC merging unit or VM  340  of the egress LER.  
         [0044]    The lookup control unit  317  reads the IP address, the mapped internal channel ID and extension tag, and the label from the FIB/LIB  323 , performs IP lookup for L 3  switching for adding them to the header of the IP packet, and transmits the IP packet to the SAR transmitting unit  318 . The SAR transmitting unit  318  segments the IP packet to reproduce the standard ATM cells storing the internal channel ID in their specific fields. The output end ICB interface  319  transforms the standard ATM cells into the internal cells, and copies the internal access ID stored in the fields of the standard ATM cells to the fields of the internal cells. In the MPLS system using the ATM exchange, when a data rate of one port which is a basic unit of the switch  301  is greater than a data rate of one LIC, the MUX  305  combines a plurality of LIC data streams to form one switch port-sized data stream. The VMs  340  receive the IP packet having the capsulated extension tag from the FEs  306 , extract the extension tag, confirm the internal channel according to the extension tag, and transmit the IP packet to the internal channel. The external channel information corresponding to the extension tag must be managed in a connection extension information base/merging table (EIB/MT)  335  of the VM  340 .  
         [0045]    Turning now to FIG. 7, FIG. 7 illustrates in detail VM  340  of FIG. 3. The VM  340  includes an input end ICB interface  326 , an SAR receiving unit  327 , a lookup control unit  328 , an EIB/MT  335 , an SAR transmitting unit  329 , a control memory  331  and a packet memory  332  of the SAR receiving unit  327 , a control memory  333  and a packet memory  334  of the SAR transmitting unit  329 , and an output end ICB interface  330 . The control memories  331  and  333  store SAR control information, and the packet memories  332  and  334  store received packets. The input end ICB interface  326  transforms the internal cells into the standard ATM cells to perform SAR, and copies and stores the internal channel access ID stored in the fields of the internal cells in specific fields of the standard ATM cells. The SAR receiving unit  327  reassembles the standard ATM cells having the same internal access ID to generate the IP packet, and transmits the IP packet to the lookup control unit  328 . The lookup control unit  328  confirms the extension tag of the IP packet, reads the mapped internal channel ID, stores it in a corresponding field of the IP packet, and transmits the IP packet to the SAR transmitting unit  329 . The SAR transmitting unit  329  segments the IP packet to reproduce the standard ATM cells storing the internal channel ID in their specific fields. The output ICB interface  330  transforms the standard ATM cells into the internal cells, and copies the internal access ID stored in the fields of the standard ATM cells to the fields of the internal cells.  
         [0046]    A cell format transforming unit (not illustrated) which is a succeeding unit of the VM  340  X of the egress LER processes the internal cells according to a corresponding protocol, and transforms the internal cells into the standard ATM cells. Here, the cell format transforming unit stores the VPI/VCI value mapped to the internal channel ID in the fields of the ATM standard cells by referring to an output end table mapping the internal channel ID to the VPI/VCI value. Thereafter, a line physical interface (not illustrated) of the egress LER adds the standard ATM cells to a transmission frame, and transmits it.  
         [0047]    [0047]FIG. 8 is a concept diagram illustrating the method for sharing the internal channel in the ATM MPLS network according to the principles of the present invention. The main control unit  302  registers the LSP having a destination address (for example, IP-A, IP-B) by the GSMP. The main control unit  302  searches the FE number of the egress LER from the registered LSP information, and also searches the internal channel ID (used by the FE of egress LER to externally transmit the ATM cells) corresponding to the destination IP address to which the FE of the egress LER intends to transmit cells. In addition to the FE number of the egress LER and the internal channel ID, the main control unit  302  extracts and manages the VPI/VCI.  
         [0048]    Thereafter, the main control unit  302  receives the extension tag for the internal channel ID used by the egress FE to transmit the ATM cells. Here, the main control unit  302  receives an extension tag that has not been allocated to the other channel IDs. For example, in the case of the IP packet having the destination IP address of IP-A, when the FE number of the output channel is ‘1’ and the channel ID is ‘1’ in the LSP information, if ‘e’ has not been allocated to the other channel IDs having the FE number of ‘1’, the main control unit  302  of the ingress LER receives ‘e’ for the extension tag indicating the destination IP-A. Similarly, in the case of the IP packet having the destination IP address of IP-B, when the FE number is ‘1’ and the channel ID is ‘a’, if ‘f’ has not been allocated to the other channel IDs having the FE number of ‘1’, the main control unit  302  receives ‘f’ for an extension tag indicating the destination IP-B.  
         [0049]    Here, the FEs of the ingress LER have the same egress FE, and use the same extension tag for the destination IP address from the egress FE to the same internal channel. Therefore, when the egress FE is ‘1’ and the channel ID is ‘1’, the FE-2 control unit receives the same extension tag ‘e’. Also, when the egress FE is ‘1’ and the channel ID is ‘a’, the FE-2 control unit receives the same extension tag ‘f’.  
         [0050]    The main control unit  302  of the router searches the previously-set internal channel to the corresponding egress FE in the VP mapping table. For example, when the channel ID of the 11 previously-set internal channel from FE-0 to FE-1 is ‘2’, the main control unit  302  sets up the channel ID to be ‘2’, designates the allocated extension tag, and generates a forwarding information base/label information base (FIB/LIB)  323  for a newly-set LSP path.  
         [0051]    In addition, when the channel ID of the previously-set internal channel from FE-2 to FE-1 is ‘3’, the main control unit  302  sets up the channel ID to be ‘3’, designates the extension tag, and generates a forwarding information base/label information base FIB/LIB  323  for a newly-set LSP path.  
         [0052]    Thereafter, the egress main control unit  302  receives the LSP set information from the main control unit  302 , and generates and stores an extension information base/merging table EIT/MT  335 . In the extension information base/merging table EIT/MT  335 , the internal channel ID is mapped to the extension tag. For example, when the extension tag is ‘e’, the channel ID is mapped to ‘1’, and when the extension tag is ‘f’, the channel ID is mapped to ‘a’.  
         [0053]    The main control unit  302  generates a merging table for the internal channel ID, and stores it in the mapping table. For example, the internal channel having the internal channel ID of ‘2’ is mapped to the internal channel having the internal channel ID of ‘1’, and the internal channel having the internal channel ID of ‘3’ is mapped to the internal channel having the internal channel ID of ‘a’.  
         [0054]    On the other hand, when the procedure of setting up the LSP is finished, the FE of the ingress LER receiving the IP packet looks up the forwarding information base/label information base FIB/LIB  323 , adds the allocated internal channel ID, the extension tag and the label to the IP packet, and transmits it to the channel having the internal channel ID. The IP packet is segmented to ATM cells, and transmitted to the internal channel. The switch performs switching according to the internal channel ID. For example, when FE-0 receives the IP packet having the destination IP address of IP-A, it looks up the forwarding information base/label information base FIB/LIB  323 , adds the internal channel ID of ‘2’, the extension tag of ‘e’ and the label to the IP packet, segments the IP packet to generate a plurality of ATM cells having the internal channel ID of ‘2’ and the extension tag of ‘e’, and transmits them to the internal channel having the internal channel ID of ‘2’. Likewise, when FE-2 receives the IP packet having the destination IP address of IP-B, it looks up the forwarding information base/label information base FIB/LIB  323 , adds the internal channel ID of ‘3’, the extension tag of ‘f’ and the label to the IP packet, segments the IP packet to generate a plurality of ATM cells having the internal channel ID of ‘3’ and the extension tag of ‘f’ and transmits them to the internal channel having the internal channel ID of ‘3’.  
         [0055]    The FE of the egress LER merges the ATM cells from the same internal channel ID, and searches the internal channel ID to which the ATM cells mapped to the extension tag will be transmitted by referring to the extension information base/merging table EIB/MT  335 . Thereafter, the FE of the egress LER transmits the ATM cells having the same extension tag to the internal channel having the internal channel ID. For example, when FE-I receives the ATM cells having the internal channel ID of ‘2’, the extension tag of ‘e’ and the destination IP address of ‘IP-A’ from FE-0, it confirms that the internal channel ID is ‘1’ through the extension information base/merging table EIB/MT  335  by referring to the extension tag of ‘e’, and transmits the ATM cells to the channel  8  having the internal channel ID of ‘1’. In the case that FE-1 receives the ATM cells having the internal channel ID of ‘3’, the extension tag of ‘f’ and the destination IP address of ‘IP-B’ from FE-2, it confirms that the internal channel ID is ‘a’ through the extension information base/merging table EIB/MT  335  by referring to the extension tag of ‘f’, and transmits the ATM cells to the channel having the internal channel ID of ‘a’.  
         [0056]    Each FE forwards data to be transferred to a corresponding switch, and switch block  301  transfers received packets to a VM of a corresponding block. The receiving VM reallocates received data to corresponding CHIDs.  
         [0057]    Referring to FIG. 8, the packet forwarded to the switch in FE-0 and FE-2 is transferred via an internal channel to VM-1. VM-1 then allocates the packet to the CHIDs.  
         [0058]    The novel channel sharing will now be described in conjunction with FIG. 8. In FIG. 8, FIB/LIBs connected to the (FE-0, VM-0) and (FE-2, VM-2) is allocated with different internal channel IDs mapped with IP addresses. So, when packets of equal VPI and VCI and different CHIDs are introduced into switch  301  as illustrated in FIG. 8, the packets are transferred to VM-1 via a single channel  400  instead of using multiple channels, one for each source. This is different from the scenario of FIG. 2 where when each of (FE-0, VM-0), (FE-2, VM-2) and (FE-3, VM-3) forwards packets to (FE-1, VM-1), different channels (1, 2, 3) are used to deliver the packets from switch  210  to (FE-1, VM-1). By using different channels  1 ,  2 ,  3  in FIG. 2, the number of channels is disadvantageously large. Also, unnecessary resources are consumed to set up each of these channels between switch  210  and (FE-1, VM-1).  
         [0059]    The present invention solves the problem of FIG. 2 by transferring the packets of equal VPI and VCI having different CHIDs using only a single channel  400 . Therefore, the packets the packets from (FE-0, VM-0) and (FE-2, VM-2) are transferred in a package by sharing internal channel  400  from switch  301  to VM-1, the destination of transmission. By using a single channel  400  in FIG. 8 instead of many channels in FIG. 2, unnecessary channel setting is eliminated.  
         [0060]    Turning to FIG. 9, FIG. 9 is a flowchart illustrating the process for setting up the LSP in accordance with the preferred embodiment of the present invention. As illustrated in FIG. 9, the main control unit  302  of the ingress LER registers the LSP having the destination address by the GSMP (S 110 ). The main control unit  302  of the ingress LER searches the FE number of the egress LER from the registered LSP information, and also searches the internal channel ID corresponding to the destination IP address to which the FE of the egress LER transmits cells (S 112 ). In addition to the FE number and the internal channel ID, the FE of the egress LER extracts and manages the VPI/VCI. Thereafter, the main control unit  302  of the ingress LER receives the extension tag for the internal channel ID used by the egress FE to transmit the ATM cells. Here, the main control unit  302  of the ingress LER receives the extension tag which has not been allocated to the other channel IDs (S 114 ). The main control unit  302  of the ingress LER searches the previously-set internal channel to the corresponding egress FE in the VP mapping table (S 116 ). Then, the main control unit  302  of the ingress LER generates the forwarding information base/label information base FIB/LIB table  323  having the searched internal channel ID and extension tag (S 118 ). The main control unit  302  of the egress LER receives the LSP set information from the ingress main control unit  302 , and generates and stores this information in an extension information base/merging table EIB/MT  335 . Here, the internal channel ID is mapped to the extension tag in the extension information base/merging table EIB/MT  335  (S 122 ).  
         [0061]    Turning now to FIG. 10, FIG. 10 is a flowchart illustrating a process for sharing the internal channel in accordance with the preferred embodiment of the present invention. Referring to FIG. 10, when the procedure of setting up the LSP is finished, the FE of the ingress LER receiving the IP packet (S 210 ) looks up the forwarding information base/label information base FIB/LIB  323 , adds the allocated internal channel ID, the extension tag and the label to the IP packet (S 212 ), and transmits it to the channel having the internal channel ID (S 214 ). Here, the IP packet is segmented to ATM cells, and transmitted to the internal channel, and the switch performs switching according to the internal channel ID.  
         [0062]    The FE of the egress LER merges the ATM cells from the same internal channel ID (S 216 ), and searches the internal channel ID to which the ATM cells mapped to the extension tag will be transmitted by referring to the extension information base/merging table EIB/MT  335  (S 218 ). Thereafter, the FE of the egress LER transmits the ATM cells having the same extension tag to the internal channel having the internal channel ID (S 220 ).  
         [0063]    On the other hand, the procedure of setting up the LSP has been described in this embodiment, but the procedure of setting up the IPOA PVC is performed in the same manner.  
         [0064]    As discussed earlier, in the related art, when the external channel such as the LSP and the IPOA PVC is set up, resources of the MPLS network are consumed to set up the internal channel, thereby reducing the whole capacity of the MPLS network. In accordance with the present invention, the resources of the MPLS network can be efficiently used by sharing the internal channel.  
         [0065]    While the invention has been illustrated and described with reference to a certain preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.