Abstract:
An apparatus comprising a path computation element (PCE) configured to communicate with a path computation client (PCC) and compute a point-to-multipoint (P2MP) path across an autonomous system (AS) domain. Also included is a network component comprising at least one processor configured to implement a method comprising obtaining a computation request for a P2MP path across a plurality of AS domains, attempting to calculate the P2MP path across the AS domains, thereby generating a computed path or a failure reason, and transmitting a reply comprising the computed path or an indication of the failure reason. Included is a method comprising exchanging a request message and a reply message about a P2MP path across an AS domain between a PCC and a PCE.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. Non-Provisional patent application Ser. No. 12/404,100 filed Mar. 13, 2009 by Huaimo Chen et al. and entitled “System and Method for Computing Point-to-Multipoint Label Switched Paths,” which claims priority to U.S. Provisional Patent Application No. 61/040,102 filed Mar. 27, 2008 by Huaimo Chen et al. and entitled “System and Method for Computing Point-to-Multipoint Label Switched Paths,” both of which are incorporated herein by reference as if reproduced in its entirety. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     REFERENCE TO A MICROFICHE APPENDIX 
     Not applicable. 
     BACKGROUND 
     In some networks, such as Multiprotocol Label Switching (MPLS) networks and Generalized MPLS (GMPLS) networks, a Traffic Engineering (TE) Label Switched Path (LSP) can be established by MPLS (GMPLS) with a path provided by a Path Computation Client (PCC) and a Path Computation Element (PCE). Specifically, the PCC requests a path or route from the PCE, which computes the path and forwards the computed path information back to the PCC. The path can be a point-to-point (P2P) path, which is computed across single or multiple areas or Autonomous System (AS) domains. The path can comprise a plurality of nodes and/or Label Switch Routers (LSRs) and extend from a source node or LSR to a destination node or LSR. Further, a plurality of P2P paths can be combined to constitute a Point-to-Multipoint (P2MP) path, which may be referred to as a path. However, the mechanisms for requesting and computing the P2MP path across multiple areas or AS domains using the PCC and PCE are still being developed. 
     SUMMARY 
     In one embodiment, the disclosure includes an apparatus comprising a PCE configured to communicate with a PCC and compute a P2MP path across an AS domain. 
     In another embodiment, the disclosure includes a network component comprising at least one processor configured to implement a method comprising obtaining a computation request for a P2MP path across a plurality of AS domains, attempting to calculate the P2MP path across the AS domains, thereby generating a computed path or a failure reason, and transmitting a reply comprising the computed path or an indication of the failure reason. 
     In yet another embodiment, the disclosure includes a method comprising exchanging a request message and a reply message about a P2MP path across an AS domain between a PCC and a PCE. 
     These and other features will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings and claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of this disclosure, reference is now made to the following brief description, taken in connection with the accompanying drawings and detailed description, wherein like reference numerals represent like parts. 
         FIG. 1  is a schematic diagram of an embodiment of a label switched system. 
         FIG. 2  is an illustration of one embodiment of a request/reply object. 
         FIG. 3  is a schematic diagram of an embodiment of a general-purpose computer system. 
     
    
    
     DETAILED DESCRIPTION 
     It should be understood at the outset that although an illustrative implementation of one or more embodiments are provided below, the disclosed systems and/or methods may be implemented using any number of techniques, whether currently known or in existence. The disclosure should in no way be limited to the illustrative implementations, drawings, and techniques illustrated below, including the exemplary designs and implementations illustrated and described herein, but may be modified within the scope of the appended claims along with their full scope of equivalents. 
     Disclosed herein are systems and methods for providing mechanisms for handling P2MP path or P2P path computations between a PCC and PCE. Accordingly, the paths may be computed across a single area or AS domain or across multiple areas or AS domains. The mechanisms may comprise declaring path computation capabilities between the PCC and PCE, for instance, using session establishment messages. The PCC and PCE may exchange a request message and reply message to compute new paths, to add branches to existing paths, or to store, delete, or re-optimize paths. Specifically, the messages exchanged between the PCC and PCE may indicate whether the computation request or reply is related to a P2MP path or P2P path. Additionally, the messages may comprise path computation information, which may be used to request or compute the path. For instance, the messages may comprise a request/reply (RP) object that indicates a P2MP path or P2P path related message and an end-points object that specifies a source and at least one destination node for the path. The reply message may also comprise an error object that indicates a computation failure, at least some nodes in the request message that may not be used, or both. 
       FIG. 1  illustrates one embodiment of a label switched system  100 , where P2P TE LSPs and P2MP TE LSPs may be established between at least some of the components. The label switched system  100  may comprise a label switched network  110 , a control plane controller  120 , and a PCE  130 . The label switched network  110 , control plane controller  120 , and PCE  130  may communicate with each other via optical, electrical, or wireless means. 
     In an embodiment, the label switched network  110  may be a packet switched network, where data traffic may be transported using packets or frames along network paths or routes. The packets may be routed or switched along a Traffic Engineering (TE) Label Switched Path (LSP) established by a signaling protocol, such as MPLS or GMPLS, based on a path computed or given. The label switched network  110  may comprise a plurality of nodes  112  coupled to one another using optical, electrical, or wireless links. 
     In an embodiment, the nodes  112  may be any devices or components that support transportation of the packets through the label switched network  110 . For example, the nodes  112  may include bridges, switches, routers, or various combinations of such devices. The nodes  112  may comprise a plurality of ingress ports for receiving packets from other nodes  112 , logic circuitry that determines which nodes  112  to send the frames to, and a plurality of egress ports for transmitting frames to the other nodes  112 . In some embodiments, at least some of the nodes  112  may be LSRs, which may be configured to modify or update the labels of the packets transported in the label switched network  110 . Further, some of the nodes  112  may be label edge routers (LERs), for example those at the edges of the label switched network  110 , which may be configured to insert or remove the labels of the packets transported between the switched network  110  and external networks. The first node  112  and the last node  112  along a path are sometimes referred to as the source node and the destination node, respectively. Although four nodes  112  are shown in the label switched network  110 , the label switched network  110  may comprise any quantity of nodes  112 . 
     In an embodiment, the control plane controller  120  may be configured to coordinate activities within the label switched network  110 , such as a Network Management System (NMS) or Operations Support System (OSS). Specifically, the control plane controller  120  may receive routing requests from the label switched network  110  and provide back the corresponding path information. In addition, the control plane controller  120  may communicate with the PCE  130 , for instance using a PCE Protocol (PCEP), provide the PCE  130  with information that may be used for path computation, receive the computed path from the PCE  130 , and forward the computed path to at least one of the nodes  112 . The control plane controller  120  may be located in a component outside of the label switched network  110 , such as an external server, or may be located in a component within the label switched network  110 , such as a node  112 . 
     In an embodiment, the PCE  130  may perform all or part of the path computation for the label switched system  110 . Specifically, the PCE  130  may receive the information that may be used for computing the path from the control plane controller  120 , from the node  112 , or both. The PCE  130  may process the information to obtain the path. For instance, the PCE  130  may compute the path, and determine the nodes  112  including the LSRs along the path. The PCE  130  may then send all or part of the computed path information to the control plane controller  120  or directly to at least one node  112 . Further, the PCE  130  may be coupled to or comprise a traffic-engineering database (TED), a P2MP Path database (PDB), a P2P path database, an optical performance monitor (OPM), a physical layer constraint (PLC) information database, or combinations thereof, which may be used to compute the path. The PCE  130  may be located in a component outside of the label switched network  110 , such as an external server, or may be located in a component within the label switched network  110 , such as a node  112 . 
     In an embodiment, the path computation request may be sent to the PCE  130  by a PCC. The PCC may be any client application requesting a path computation to be performed by the PCE  130 . The PCC may also be any network component that makes such a request, such as the control plane controller  120 , or any node  112 , such as a LSR. For instance, the PCC may request from the PCE a P2MP path or P2P path. Additionally, the PCC may send the PCE  130  at least some of the path required information. 
     In an embodiment, the packets transported between network nodes, such as the nodes  112 , are referred to as label switched packets, and may comprise labels that may be used to switch the packets along the nodes of a computed path. A path computed or given and signaled by MPLS for transporting or routing the label switched packets is referred to as a LSP. For example, the LSP may be a TE LSP established using a Resource Reservation Protocol—Traffic Engineering (RSVP-TE). The LSP may be a P2P TE LSP that extends from a source node to a destination node and may be unidirectional, where the packets may be transported in one direction along the path, e.g., from the source node to the destination node. Alternatively, the LSP may be a P2MP TE LSP, which may comprise a plurality of P2P TE LSPs that share the same source node. As such, the P2MP TE LSP may extend from a source or root node to a plurality of destination or leaf nodes. In some embodiments, the P2MP TE LSP is referred to as a P2MP tree and its P2P TE LSPs are referred to as Source-to-Leaf (S2L) sub-LSPs. Typically, the P2MP tree may be established by RSVP-TE based on a P2MP path for multicasting purposes, for example to transport the same packets to a plurality of destination nodes in label switched network. 
     In an embodiment, a PCC and a PCE, such as the PCE  130 , may declare their capabilities related to computing or establishing paths in the network during the session establishment between the PCC and the PCE. For instance, the PCC may send the PCE a first session establishment message, which may comprise at least one flag that may be set to indicate supporting functions related to establishing a P2MP tree or P2P TE LSP. The PCE may send the PCC a second session establishment message, which may comprise at least one flag that may be set to indicate supporting related functions, such as computation of P2MP paths across multiple areas or AS domains. In an embodiment, the second session establishment message may comprise a type length value (TLV) field. The value of the TLV field may indicate the capabilities of the PCE, for instance according to a TLV type number defined by the Internet Assigned Numbers Authority (IANA). Alternatively, the second session establishment message may comprise an open object as described in the PCE Discovery protocol, which may comprise the TLV field. Thus, the PCC may communicate with a plurality of PCEs and know their different capabilities. The PCC may then request specific functions from those PCEs that may support it, such as requesting new P2MP paths only from a PCE that is configured to compute such paths. 
     In an embodiment, a PCC may send a request message to a PCE to add or compute a new path, for instance across multiple areas or AS domains. Specifically, the request message may comprise a first flag, which may be used to request a P2P path computation or a P2MP path computation. For instance, the first flag may be set to request a P2MP path computation from the PCE. The request message may comprise a second flag, which may be used to indicate whether the path is represented in a compressed format. In some embodiments, the request message may comprise a RP object, which may comprise the first flag and the second flag. 
     The request message may also comprise information that may be used for computing the P2MP path. For example, the request message may comprise path constraints, such as bandwidth limitation, maximum quantity of nodes or LSRs, shortest or longest route requirement, etc. Additionally, the request message may specify a source or root node and a plurality of destination or leaf nodes for the requested P2MP path. For example, the request message may comprise the network addresses of the source node and the destination nodes for the P2MP path. In an embodiment, the request message may comprise an end-points object, which may comprise the source node and the destination nodes&#39; information. Alternatively, the flag may be cleared to request a P2P path computation and the request message may comprise information required to compute the P2P path. In some embodiments, the PCC may send a plurality of request messages to obtain at least one P2MP path from a plurality of PCEs  130 . 
     In some embodiments, the path information provided to the PCE may not fit in a single request message. As such, a plurality of request messages may be sent to the PCE, where the included path information in all the messages may be combined at the PCE to compute the requested path. To associate the multiple request messages with a single path computation request, the request messages may comprise the same request IDs. 
     The PCE may send a reply message to the PCC in return to the request message for computing a new path. The reply message may comprise the computed path information. Specifically, the reply message may comprise a first flag, which may be used to indicate a computed P2P path or P2MP path. For instance, the first flag may be set to indicate that the reply message comprises the computed P2MP path information across multiple areas or AS domains based on a set of path constraints. Alternatively, the first flag may be cleared to indicate a P2P path computation and the reply message may comprise information related to the computed P2P path. The reply message may comprise a second flag, which may be used to indicate whether the path is represented in a compressed format. The first flag and the second flag may be included in a RP object in the reply message. 
     In an embodiment, the PCC may send a request message to the PCE to obtain a plurality of new S2L paths for an existing P2MP path. The existing P2MP path may be previously computed using a request message or may be configured by the PCC. The request message may comprise the existing P2MP path information, such as the path nodes and branches. Additionally, the request message may comprise information to add new branches to the P2MP path, such as the network addresses of new destination nodes. Accordingly, the PCE may use the information in the request message to add new branches to the existing P2MP path, for example using the new destination nodes as leaf nodes. To indicate an existing P2MP path, the request message may comprise a P2MP path ID associated with the existing P2MP path. The existing P2MP path may be previously computed and stored at the PCE, for instance in a P2MP Path database (PDB). 
     The PCE may send a reply message to the PCC in return to a request for adding new branches to an existing P2MP path. The reply message may comprise a plurality of branches, such as S2L paths, to the existing P2MP path. Additionally, the reply message may comprise a flag that may be set to indicate that the computed information is related to a P2MP path. In some embodiments, the reply message may also comprise path constraints associated with the computed or modified path. Further, the reply message may comprise the P2MP path ID associated with the computed or modified path. 
     In an embodiment, the PCC and the PCE may negotiate whether the PCE may store the computed path information. For instance, the PCC may send the PCE a request message to store the path information and the PCE may return to the PCC a reply message to indicate whether the PCC request has been accepted. In some embodiments, the PCC may send the PCE a request message to add branches or leaf nodes to an existing path, and to store the new information at the PCE. The request message may comprise the P2MP path ID or P2P path ID in addition to information about the new leaf nodes, e.g., the network addresses of the leaf nodes. If the PCE accepts to store the path information, the PCE may store the computed path, for instance at the PDB, and send back a reply message to the PCC confirming that the information has been stored. The reply message may comprise the P2MP path ID or P2P path ID for the stored path. The PCC may receive the reply message and match the P2MP path ID or P2P path ID of the reply message to the P2MP path ID or P2P path ID of the request message. 
     If the PCE does not accept to store the path information, the PCE may return a reply message to the PCC to indicate that the computed path may not be stored at the PCE. Alternatively, the PCE may not return a reply message to the PCC to indicate that the PCE may not store the computed path information. In an embodiment, the PCC may wait for a predetermined time interval to detect a reply message from the PCE. If the PCC does not receive the reply message after the time interval expires, the PCC may send subsequent request messages to the PCE without P2MP path IDs or P2P path IDs. 
     In other embodiments, the PCC and the PCE may negotiate whether the PCE may store the computed path or the path information during session establishment between the PCC and the PCE. For instance, the PCC may send the PCE a first session establishment message to request storing the path information and the PCE may return to the PCC a second session establishment message, which may indicate whether the PCE will store the information. 
     In an embodiment, the PCC may send the PCE a request message to delete an existing path. The existing path information may be stored at the PCE, for instance at the PDB. 
     Specifically, the request message may comprise a flag, which may be used to indicate a request to delete an existing P2MP path or P2P path. Additionally, the request message may comprise the P2MP path ID or P2P path ID associated with the existing path. In some embodiments, the request message may be used to delete a plurality of existing paths. For instance, the request message may comprise a plurality of P2MP path IDs or P2P path IDs associated with the existing paths. In other embodiments, the request message may be used to delete all existing paths. For instance, the request message may comprise a global or “wild card” P2MP path ID or P2P path ID associated with all the existing paths. 
     In return to such request message, the PCE may send a reply message to the PCC to confirm whether the path has been deleted. The reply message may comprise a flag, which may be used to confirm deleting a P2MP path or P2P path. Additionally, the reply message may comprise at least one P2MP path ID or P2P path ID to indicate the deleted path to the PCC. Alternatively, the reply message may comprise a global or “wild card” P2MP path ID or P2P path ID to confirm the deletion of all the existing paths. 
     In some embodiments, the PCC may send a request message to the PCE to re-optimize an existing P2MP path or P2P path. For instance, the request message may indicate whether at least one or all the branches of an existing P2MP path are to be optimized. As such, the request message may comprise a plurality of nodes or paths that may be added, deleted, replaced, or combinations thereof. The nodes or paths may be represented using end-points objects, record route objects (RROs), or both and may be located across multiple areas or AS domains. The PCE may use such information to re-compute at least some of the branches of the path. 
     In some cases, the PCE may not complete the path computation as requested, for example based on a set of constraints. As such, the PCE may send a reply message to the PCC that indicates an unsuccessful path computation attempt. The reply message may comprise a PCEP-error object, which may comprise an error-value and error-type based on the PCEP. Hence, the request message may be rejected and the path computation request may be canceled. 
       FIG. 2  is an embodiment of a RP object  200 , which may be a part of the request message transmitted from the PCC or the reply message transmitted from the PCE. The RP object may indicate a P2MP path or P2P path related message. The RP object  200  may comprise a Reserved field  210 , a plurality of Flags  220 , and a Request-ID-number  230 . Additionally, the RP object  200  may optionally comprise at least one TLV  240 , for instance to indicate path computation capabilities, path constraints, or other path information. The Flags  220  may comprise an explicit route object (ERO)-compression bit (E) flag  221 , a P2MP bit (M) flag  222 , a Strict/Loose bit (O) flag  223 , a Bi-directional bit (B) flag  224 , a re-optimization (R) flag  225 , and a plurality of Priority bit (P) flags  226 . The Flags  220  may also comprise additional bits, which may be unassigned or reserved. For instance, the remaining bits may be set to zero and ignored. In an embodiment, each of the E flag  221 , M flag  222 , O flag  223 , B flag  224 , and R flag  225  may have a length of about one bit, the P flags may have a combined length of about three bits, the Request-ID-number  230  may have a length of about 32 bits, and the Reserved field  210  may have a length of about eight bits. 
     In an embodiment, the E flag  221  may be set to indicate that the path information is represented in a compressed format or may be cleared otherwise. The M flag  222  may be set to indicate whether the request message or reply message is related to a P2MP path or P2P path computation. Further, at least some of the fields of the RP object  200  may be configured based on the PCEP. For instance, the Reserved field  210  may be reserved for other purposes and/or may not be used. The O flag  223  may be set in a request message to indicate that a loose path is acceptable or may be cleared to indicate that a path comprising exclusively strict hops is required. On the other hand, the O flag  223  may be set in a reply message to indicate that the computed path is loose or may be cleared to indicate that the computed path comprises strict hops. The B flag  224  may be set to indicate that a path computation request relates to at least one bidirectional P2P TE LSP or S2L sub-LSP, which may have the same TE requirements in each direction, such as fate sharing, protection and restoration, LSRs, TE Links, resource requirements (e.g., latency and jitter), etc. Otherwise, the B flag  224  may be cleared to indicate that the LSP is unidirectional. The R flag  225  may be set to indicate that a computation request relates to re-optimizing an existing path or branch. The P flags  226  may be used to specify a recommended request priority. For instance, the P flags  226  may have a value from about one to about seven, which may be set locally at the PCC. Alternatively, the P flags  226  may be set to zero when the request priority is not specified. The Request-ID-number  230  may be combined with the source IP address of the PCC or the PCE network address to identify the path computation request context. The Request-ID-number may be changed or incremented each time a new request is sent to the PCE. 
     The network components described above may be implemented on any general-purpose network component, such as a computer or network component with sufficient processing power, memory resources, and network throughput capability to handle the necessary workload placed upon it.  FIG. 3  illustrates a typical, general-purpose network component  300  suitable for implementing one or more embodiments of the components disclosed herein. The network component  300  includes a processor  302  (which may be referred to as a central processor unit or CPU) that is in communication with memory devices including secondary storage  304 , read only memory (ROM)  306 , random access memory (RAM)  308 , input/output (I/O) devices  310 , and network connectivity devices  312 . The processor  302  may be implemented as one or more CPU chips, or may be part of one or more application specific integrated circuits (ASICs). 
     The secondary storage  304  is typically comprised of one or more disk drives or erasable programmable ROM (EPROM) and is used for non-volatile storage of data. Secondary storage  304  may be used to store programs that are loaded into RAM  308  when such programs are selected for execution. The ROM  306  is used to store instructions and perhaps data that are read during program execution. ROM  306  is a non-volatile memory device that typically has a small memory capacity relative to the larger memory capacity of secondary storage  304 . The RAM  308  is used to store volatile data and perhaps to store instructions. Access to both ROM  306  and RAM  308  is typically faster than to secondary storage  304 . 
     At least one embodiment is disclosed and variations, combinations, and/or modifications of the embodiment(s) and/or features of the embodiment(s) made by a person having ordinary skill in the art are within the scope of the disclosure. Alternative embodiments that result from combining, integrating, and/or omitting features of the embodiment(s) are also within the scope of the disclosure. Where numerical ranges or limitations are expressly stated, such express ranges or limitations should be understood to include iterative ranges or limitations of like magnitude falling within the expressly stated ranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4, etc.; greater than 0.10 includes 0.11, 0.12, 0.13, etc.). For example, whenever a numerical range with a lower limit, R 1 , and an upper limit, R u , is disclosed, any number falling within the range is specifically disclosed. In particular, the following numbers within the range are specifically disclosed: R=R 1 +k*(R u −R 1 ), wherein k is a variable ranging from 1 percent to 100 percent with a 1 percent increment, i.e., k is 1 percent, 2 percent, 3 percent, 4 percent, 5 percent, . . . , 50 percent, 51 percent, 52 percent, . . . , 95 percent, 96 percent, 97 percent, 98 percent, 99 percent, or 100 percent. Moreover, any numerical range defined by two R numbers as defined in the above is also specifically disclosed. Use of the term “optionally” with respect to any element of a claim means that the element is required, or alternatively, the element is not required, both alternatives being within the scope of the claim. Use of broader terms such as comprises, includes, and having should be understood to provide support for narrower terms such as consisting of, consisting essentially of, and comprised substantially of. Accordingly, the scope of protection is not limited by the description set out above but is defined by the claims that follow, that scope including all equivalents of the subject matter of the claims. Each and every claim is incorporated as further disclosure into the specification and the claims are embodiment(s) of the present disclosure. The discussion of a reference in the disclosure is not an admission that it is prior art, especially any reference that has a publication date after the priority date of this application. The disclosure of all patents, patent applications, and publications cited in the disclosure are hereby incorporated by reference, to the extent that they provide exemplary, procedural, or other details supplementary to the disclosure. 
     While several embodiments have been provided in the present disclosure, it should be understood that the disclosed systems and methods might be embodied in many other specific forms without departing from the spirit or scope of the present disclosure. The present examples are to be considered as illustrative and not restrictive, and the intention is not to be limited to the details given herein. For example, the various elements or components may be combined or integrated in another system or certain features may be omitted, or not implemented. 
     In addition, techniques, systems, subsystems, and methods described and illustrated in the various embodiments as discrete or separate may be combined or integrated with other systems, modules, techniques, or methods without departing from the scope of the present disclosure. Other items shown or discussed as coupled or directly coupled or communicating with each other may be indirectly coupled or communicating through some interface, device, or intermediate component whether electrically, mechanically, or otherwise. Other examples of changes, substitutions, and alterations are ascertainable by one skilled in the art and could be made without departing from the spirit and scope disclosed herein.