Abstract:
A system for transporting traffic is provided. The system transports traffic from a first network access path over a transport network path having multiple channels and transports traffic from a second network access path over the same transport network path. The system transports the traffic using transport network path channels wherein the bandwidth of the first network access path is higher than the capacity of any of the transport network path channels and wherein the bandwidth of the second network access path is higher than the capacity of any of the transport network path channels. The system allocates a first quantity of the transport network path channels for transporting traffic from the first network access path. The system allocates a second quantity of the transport network path channels for transporting traffic from the second network access path. And, the sum of the first quantity plus the second quantity is less than or equal to the total number of channels in the transport network path.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims priority from and is related to U.S. Provisional Application No. 60/296,432 entitled “System and Method for Transporting Channelized Ethernet Over SONET/SDH” which was filed on Jun. 6, 2001. The entire disclosure of U.S. Provisional Application No. 60/296,432 is hereby incorporated into the present application by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Technical Field  
           [0003]    The present invention is generally directed to the field of data communication networks. More specifically, the invention is directed to bandwidth efficient mapping of traffic from one network type into another.  
           [0004]    2. Description of the Related Art  
           [0005]    The SONET/SDH standards provide for a granularity of an STS-xC pipe (˜150 Mbits/s, x=1,2,3 . . . ). The SONET/SDH equipment on the market, however, support only STS-3c, STS-12c, STS-48c, etc. with their maximum data rates of 155.52 Mbits/s, 622.08 Mbits/s, and 2488.32 Mbits/s, respectively. Depending on the payload size required, it is inefficient to map a payload size of y into x when y&lt;&lt;x. For example, mapping a Gigabit Ethernet port into a SONET/SDH pipe using standard equipment would require the use of an STS-48c channel. STS-3c and STS-12c channels do not have sufficient data rates for Gigabit Ethernet. Consequently, an STS-48c channel would have to be used, and the use of an STS-48c channel would result in ˜40% bandwidth utilization, which is very inefficient.  
           [0006]    Virtual Concatenation as specified in ANSI T1.x1.5 has been proposed.  
         SUMMARY OF THE INVENTION  
         [0007]    A system for transporting traffic is provided. The system transports traffic from a first network access path over a transport network path having multiple channels and transports traffic from a second network access path over the same transport network path. The system transports the traffic using transport network path channels wherein the bandwidth of the first network access path is higher than the capacity of any of the transport network path channels and wherein the bandwidth of the second network access path is higher than the capacity of any of the transport network path channels. The system allocates a first quantity of the transport network path channels for transporting traffic from the first network access path. The system allocates a second quantity of the transport network path channels for transporting traffic from the second network access path. And, the sum of the first quantity plus the second quantity is less than or equal to the total number of channels in the transport network path. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    In order that the invention identified in the claims may be more clearly understood, preferred embodiments of structures, systems and methods having elements corresponding to elements of the invention recited in the claims will be described in detail by way of example, with reference to the accompanying drawings, in which:  
         [0009]    [0009]FIG. 1 is a schematic representation of an exemplary communication system that utilizes channelized transport;  
         [0010]    [0010]FIG. 2 is another schematic representation of an exemplary communication system that utilizes channelized transport;  
         [0011]    [0011]FIG. 3 is a block diagram of a preferred network element that facilitates channelized transport;  
         [0012]    [0012]FIG. 4 is a schematic diagram that illustrates channelized transport;  
         [0013]    [0013]FIG. 5 is a schematic representation of a SONET network that provides channelized transport; and  
         [0014]    [0014]FIG. 6 is an illustration of an exemplary SONET frame structure when SONET is used for channelized transport. 
     
    
     DETAILED DESCRIPTION  
       [0015]    [0015]FIG. 1 sets forth a schematic drawing of an exemplary communication system  2  wherein a plurality of network systems are provided with communication paths to other network systems via a transport network. In the embodiment shown, a transport network  4  is provided that includes a plurality of network elements  6 , labeled N 1 -N 4 , coupled in a ring structures by one or more communication paths  8 A,  8 B. The transport network  4  is preferably a SONET/SDH network, although other types of transport networks could be used. As shown in FIG. 1, the two paths  8 A,  8 B transport a plurality of SONET STS-N data streams in opposite directions about the SONET ring  4 . The communication paths  8 A,  8 B are preferably fiber optic connections (in SONET and SDH), but could, alternatively be electrical paths or even wireless connections (in other types of networks). In the case of a fiber optic connection, paths  8 A,  8 B could be implemented on a single fiber  8 , on dual fibers  8 A,  8 B, or some other combination of connections. In the dual fiber implementation, one of the fibers could be the working ring, and the other fiber could be the protection ring.  
         [0016]    The communication paths  8 A,  8 B comprise one or more transport network paths for transporting data from one node  6  to another node  6  in the network. The transport network  4  in this example is only capable of providing STS-1 transport paths, STS-3c transport paths, STS-12c transport paths, or STS-48c transport paths.  
         [0017]    In the ring  4 , each network element  6  is preferably coupled to two other network elements  6  in the ring structure. For example, network element N 2  is coupled to network elements N 1  and N 3 . The coupling between the elements is two-way, meaning that each element transmits and receives signals to and from each of the two other elements  6  to which it is connected. Each network element  6  includes at least two transmitter/receiver interfaces, one for each connection to another element  6 . The network elements  6  could be many types of well-known network devices, such as an add/drop multiplex (“ADM”), switch, router, a SMA, a Marconi MCN-7000 network element, an Access hub, an ATM/IP switch, or other types of devices.  
         [0018]    The network devices  6  are preferably ADMs. An ADM is a device having an upstream network element interface, a downstream network element interface, and an add/drop interface. These ADMs  6  are coupled to local elements  10  via network access paths L 1 -L 4 , and are used to add signals to the network data traffic from the local elements  10  and, conversely, to drop data signals from the network data traffic to the local elements  10 . The switching, adding and dropping operations of the ADM  6  are typically performed by one or more hardware cross-connect switching system cards having one or more hardware cross connect switching matrices. For more information on SONET/SDH formats, line-speeds, and theory of operation, see John Bellamy,  Digital Telephony , 2d Edition (1991), pp. 403-425.  
         [0019]    As shown in FIGS. 1 and 2, network element N 1  is coupled to two network systems Net 1  and Net 3 , via network access paths L 1  and L 3 , respectively. Also, network element N 3  is coupled to two network systems, Net 2  and Net 4 , via network access paths L 2  and L 4 , respectively. In the example illustrated by FIG. 2, the transport network  4  provides a transport network path TP between network systems Net 1  and Net 2  and a transport network path TP between network systems Net 3  and Net 4 . In the example of FIGS. 1 and 2, each of the network access paths L 1 -L 4  are Gigabit Ethernet paths. Because the transport network  4  in this example is only capable of providing STS-1 transport paths, STS-3c transport paths, STS-12c transport paths, or STS-48c transport paths, to provide a transport network path TP between network systems Net 1  and Net 2 , the transport network must dedicate an STS-48c path. Moreover, to provide a transport network path between network systems Net 3  and Net 4 , the transport network must dedicate a STS-48c path. Also, in this example, the network systems Net 1 , Net 2 , Net 3 , and Net 4  could be local area networks (LANs), metro area networks (MANs), wide area networks (WANs) or other type of Ethernet equipment or network.  
         [0020]    [0020]FIG. 3 is a block diagram of a preferred network element  12  that is capable of allowing the communication path between network systems Net 1  and Net 2  and the communication path between network systems Net 3  and Net 4  to share transport network path bandwidth thereby more efficiently utilizing the transport network bandwidth. The preferred network element  12  comprises a mapper module  14 , a cross-connect module  16 , and a line card  18 .  
         [0021]    With reference to FIG. 4, preferred network elements N 1  and N 3  view an STS-48c transport network path as 48 STS-1 transport network path channels, and the other network elements view the STS-48c transport network path as being one STS-48c path. The preferred network elements N 1  and N 3  use distinct STS-1 portions of the STS-48c to form a bigger payload envelope than the payload envelope for an individual STS-1 channel. The mapper module  14  in the preferred network element  12  maps a traffic port such as an Ethernet port onto the STS-48c. The mapper module  14  chooses a sufficient number of STS-1 channels to complete the mapping. The remaining STS-1 channels are available for mapping other traffic ports onto the STS-48c so that a more efficient use of the STS-48c is made. In the example of FIG. 4, the port # 1  is mapped into the first two STS-1 channels, the second port into the STS-1 channel numbers  2 ,  3  &amp;  4 , and so on. The number of STS-1 channels allocated to a port is not fixed but is determined by the needed bit rate for transporting traffic from that port.  
         [0022]    The mapper module  14  in the preferred network element  12  preferably performs both a mapping function and a de-mapping function. For traffic flowing from network system Net 1  to network system Net 2 , for example, the mapper module  14  at network element N 1  would map traffic from network access path L 1  onto STS-1 channels of the STS-48c transport network path. For traffic flowing from network system Net 2  to network system Net 1 , the mapper module  14  at network element N 1  would de-map traffic from STS-1 channels of the STS-48c transport network path to network access path L 1 . Similarly, a mapper module  14  would exist at network element N 3  to perform similar mapping and de-mapping functions. At the add point in the network, the port to be mapped uses a pre-configured number of STS-1 channels for its mapping. The traffic to be mapped is distributed among the different STS-1. At the drop point in the network, the STS-1 channels used to map the traffic are de-mapped to re-build the original payload.  
         [0023]    As illustrated in FIG. 5, cross-connect modules  16  at network elements N 1  and N 3  would perform the add/drop function for the network element, and line cards  18  at network elements N 1  and N 3  would interface with the communication paths  8 A,  8 B in the transport network.  
         [0024]    In the example of FIGS. 1 and 2, two Gigabit Ethernet ports can be mapped into a single STS-48c path. The 24 first STS-1 channels would be used to transport the first Gigabit Ethernet port and the last 24 STS-1 channels would be used for transporting the second port. Therefore, traffic from network system Net 1  to network system Net 2  would be mapped onto the first 24 STS-1 channels of transport network path TP and traffic from network system Net 3  to network system Net 4  would be mapped onto the last 24 STS-1 channels in the STS-48c transport network path TP. In another example, two Fast Ethernet ports can be mapped into an STS-3c transport network path. The first port could be mapped in the first STS-1 channel and the second into the last two STS-1 channels of the transport network path TP.  
         [0025]    Exemplary Mapper  
         [0026]    The mapper module preferably comprises network access path circuitry. The network access path circuitry receives traffic from the network access path and maps the received traffic onto a number of the network path channels. In the example of FIGS. 1 and 2, the network access path circuitry of the mapper module interfaces with a network access path such as network access path L 1  and maps traffic from the network access path L 1  onto 24 STS-1 channels of the STS-48c transport network path TP 1  from network system Net 1  to network system Net 2 . The network access path circuitry of the mapper module also receives traffic from 24 STS-1 channels of the STS-48c transport network path TP 2  from network system Net 2  to network system Net 1 , de-maps that traffic, and transmits it on network access path L 1 . In this example, the transport network path TP is a two-way network path and comprises a one-way transport network path TP 1  and a one-way transport network path TP 2  wherein each one-way path is an STS-48c path. Also, in this example, each STS-1 channel is a two-way channel having a one-way channel in the one-way transport network path TP 1  and a one-way channel in the one-way transport network path TP 2  wherein each one-way channel is a STS-1 channel.  
         [0027]    The mapper module preferably comprises at least one additional network access path circuitry. In the example of FIGS. 1 and 2, the second network access path circuitry receives traffic from network access path L 2  and maps traffic from the network access path L 2  onto the last 24 STS-1 channels of the STS-48c transport network path TP 1  from network system Net 3  to network system Net 4 . The second network access path circuitry of the mapper module also receives traffic from the last  24  STS-1 channels of the STS-48c transport network path TP 2  from network system Net 4  to network system Net 3 , de-maps that traffic, and transmits it on network access path L 2 .  
         [0028]    The exemplary mapper preferably performs its mapping function, channelized mapping, by using the payload capacity of the smallest high order signal in the transport network path. In the case of SONET, the mapper uses the payload capacity of STS-1 signals to carry traffic from a network system or network access path with traffic such as Ethernet traffic. The Ethernet traffic is organized into a concatenated payload. The concatenated payload is divided into “y” smaller chunks wherein each chunk is small enough to fit within the STS-1 payload of an STS-1 pipe. “Y” STS-1 pipes are used to map the Ethernet traffic. Therefore, to map the Ethernet traffic into the transport network path, the transport network path is divided into “x” STS-1 pipes. “Y” of these STS-1 pipes are considered one payload. The “new” payload formed by the “y” STS-1 pipes is used to map the Ethernet traffic onto the transport network path. The remaining STS-1 pipes within the transport network path (i.e., x-y STS-1 pipes) can be mapped with other payload. At the drop point for the mapped traffic, a mapper would de-map the “y” STS-1 pipes to re-form the Ethernet traffic.  
         [0029]    Exemplary Frame Structure  
         [0030]    Illustrated in FIG. 6 is an exemplary SONET frame structure for use in SONET channelized mapping. BellCore specifies that there are 3 different portions in the frame structure: the path overhead (“POH”); the fixed stuff; and the STS-xC Payload Capacity. When used for channelized mapping, the STS-xC Payload Capacity is divided into two different portions: unused columns and channelized payload.  
         [0031]    The unused columns are not used, preferably filled with all ‘1s’, and are present to make the number of columns divisible by x. The remainder of the channelized payload is divided into x emulated STS-1 channels. The first channelized payload column is for the emulated STS-1 channel # 1 , the second channelized payload column is for the emulated STS-1 channel # 2  and the next channelized payload column is for the next emulated STS-1 channel number and so forth. After the x th  channelized payload column is reached, the pattern is repeated and results in the same number of columns for each emulated STS-1 channel.  
         [0032]    Conclusion  
         [0033]    Other variations from these systems and methods should become apparent to one of ordinary skill in the art without departing from the scope of the invention defined by the claims. The preferred embodiments have been described with reference to SONET/SDH transport networks and Ethernet but the invention described by the claims could be applicable to other network systems.  
         [0034]    The embodiments described herein and shown in the drawings are examples of structures, systems or methods having elements corresponding to the elements of the invention recited in the claims. This written description and drawings may enable those skilled in the art to make and use embodiments having alternative elements that likewise correspond to the elements of the invention recited in the claims. The intended scope of the invention thus includes other structures, systems or methods that do not differ from the literal language of the claims, and further includes other structures, systems or methods with insubstantial differences from the literal language of the claims. It is also to be understood that the invention is not limited to use with SONET or SDH systems or Ethernet unless explicitly limited by the claims.