WO2015131703A1

WO2015131703A1 - Method and apparatus for path selecting

Info

Publication number: WO2015131703A1
Application number: PCT/CN2015/071468
Authority: WO
Inventors: Sandeep Kumar BOINA; Reeja PAUL; Dhruv Dhody
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2014-03-06
Filing date: 2015-01-23
Publication date: 2015-09-11
Also published as: CN106068632B; CN106068632A

Abstract

The embodiments of the present invention provide a method and an apparatus for selecting path in a network, the method comprising: receiving, by a PCE, a PCReq message transmitted by a PCC or another PCE, wherein the PCReq message is used to request a path, the PCReq message includes a Backward Recursive Path Computation (BRPC) flooding flag and identifiers of leaf nodes which are on the path; removing, by the PCE, an identifier of a leaf node existed in a domain where the PCE is in from the PCReq message, when at least one leaf node of the leaf nodes does not exist in the domain; and forwarding, by the PCE, the PCReq message with the identifier of the leaf node in the domain removed, to other PCEs in all adjacent domains. According to the method of the embodiment of the present invention, a BRPC flooding mechanism is used to compute inter-domain TE LSP when destination domain or domain tree is unknown, this mechanism requires least changes in PCEP architecture or other components, and reduces the computational complexity.

Description

Method and Apparatus for Path Selecting

FIELD OF THE INVENTION

This application relates to telecommunications, in particular, to a method and apparatus for path selecting in a nework.

BACKGROUND

Draft-ietf-pce-pcep-inter-domain-p2mp-procedures-02 [PCE-based Computation Procedure To Compute Shortest Constrained P2MP Inter-domain Traffic Engineering Label Switched Paths] describes a mechanism to compute inter-domain constrained paths by cooperating PCE (Path Computation Elements, PCE) . The procedure can be implemented successfully when the sequence of domains to be traversed is either administratively predetermined or discovered by some means.

BRPC (Backward Recursive Path Computation, BRPC) based core tree path computation procedure is as follows:

1. Using the BRPC procedures to compute the VSPT (i) (Virtual Shortest Path Tree, VSPT) for each leaf BN (i) (Boundary Node, BN) , i＝1 to n, where n is the total number of entry nodes for all the leaf domains. In each VSPT (i) , there are a number of P (i) paths.

2. When the root PCE has computed all the VSPT (i) , i＝1 to n, take one path from each VSPT (Virtual Shortest Path Tree, VSPT) and form a set of paths, we call it a PathSet (j) , j＝1 to M, where M＝P (1) × P (2) ... × P (n) .

3. For each PathSet (j) , there are n S2L (Source to Leaf BN (Boundary Node, BN)) paths and form these n paths into a Core Tree (j) .

4. There will be M number of Core Trees computed from step3. Apply the OF (Objective Function, OF) to each of these M Core Trees and find the optimal Core Tree.

Note that the application of BRPC in the aforementioned procedure differs from the typical one since paths returned from a downstream PCE are not necessary pruned from the solution set by intermediate PCEs.

The reason for this is that if the PCE in a downstream domain does the pruning and returns the single optimal sub-path to its parent PCE, BRPC insures that the ingress PCE will get all the best optimal sub-paths for each LBN (Leaf Border Node, LBN) , but the combination of these single optimal sub-paths into a P2MP (Point to Multi-Point, P2MP) tree is not necessarily optimal even if each S2L (Source-to-Leaf, S2L) sub-path is optimal.

Without trimming, the ingress PCE will get all the possible S2L sub-paths set for LBN, and eventually by looking through all the combinations, and taking one sub-path from each set to built one P2MP tree it finds the optimal tree.

The proposed method may present a scalability problem for the dynamic computation of the Core Tree, specially with dense/meshed domains. Considering a domain sequence D1, D2, D3, D4, where the Leaf border node is at domain D4, PCE (4) will return 1 path. PCE (3) will return N paths, where N is E (3) × X (3) , where E (k) × X (k) denotes the number of entry nodes times the number of exit nodes for that domain. PCE (2) will return M paths, where M＝E (2) × X (2) × N＝E (2) × X (2) × E (3) × X (3) × 1, etc. Generally speaking, the number of potential paths at the ingress PCE Q＝\prod E (k) × X (k) .

Consequently, it is expected that the core path will be typically computed offline, without precluding the use of dynamic, online mechanisms such as the one presented here, in which case it should be possible to configure transit PCEs to control the number of paths sent upstream during BRPC.

However the applicant found that, when P2MP leaf domain is unknown, the above core-tree procedure cannot be applied, moreover, the core-tree procedure also requires the domain-tree (list of domain-sequences) to be known, in case administrator cannot configure or pre-determine the domain-tree by some external means, this core-tree procedure can not be applied.

SUMMARY

The object of the present invention is to provide a method, apparatus and system for path selecting, so that in case P2MP destinations domain or domain tree is unknown, P2MP-BRPC-Flooding mechanism can be applied without any modifications in other protocols or components.

According to a first aspect, a method for selecting a path is provided, the method includes:

receiving, by a Path Computation Element (PCE) , a Path Computation Request (PCReq) message transmitted by a Path Computation Client (PCC) or another PCE, wherein the PCReq message is used to request a path, the PCReq message includes a Backward Recursive Path Computation (BRPC) flooding flag and identifiers of leaf nodes which are on the path；

removing, by the PCE, an identifier of a leaf node existed in a domain where the PCE is in from the PCReq message, when at least one leaf node of the leaf nodes does not exist in the domain； and

forwarding, by the PCE, the PCReq message with the identifier of the leaf node in the domain removed, to other PCEs in all adjacent domains.

In a first possible implementation of the method for selecting a path according to the first aspect, before the step of forwarding, the method further includes:

determining, whether the BRPC flooding flag is included in the PCReq message； and

performing the step of forwarding, when the BRPC flooding flag is included in the PCReq message.

In a second possible implementation of the method for selecting a path according to the first aspect or according to the first implementation form of the first aspect, the method further includes:

calculating, Virtual Shortest Path Trees (VSPTs) of all the leaf nodes, when all the leaf nodes exist in the domain； and

returning, a Path Computation Reply (PCRep) message including the VSPTs, to the PCC or the another PCE.

In a third possible implementation of the method for selecting a path according to the first aspect or according to the first implementation form of the first aspect, the method further includes:

calculating, a VSPT of a leaf node existed in the domain, when at least one leaf node of the leaf nodes does not exist in the domain； and

storing, the VSPT.

In a fourth possible implementation of the method for selecting a path according to the third implementation form of the first aspect, the step of forwarding includes:

determining, whether an adjacent domain exists；

generating, a plurality of PCReq messages for all adjacent domains according to the PCReq message with the identifier of the leaf node in the domain removed, when the adjacent domain exists； and

forwarding, the plurality of PCReq messages to the other PCEs in all adjacent domains.

In a fiveth possible implementation of the method for selecting a path according to the fourth implementation form of the first aspect, the step of forwarding further includes:

determining, whether a VSPT of at least one leaf node existed in the domain is calculated, when the adjacent domain does not exist；

returning, a PCRep message including the VSPT to the PCC or to the another PCE, when the VSPT of at least one leaf node existed in the domain is calculated.

In a sixth possible implementation of the method for selecting a path according to the first aspect, when a PCRep message transmitted by the other PCEs in all adjacent domains is received by the PCE, the method further includes:

determining, whether a path where at least one leaf node is on is found according to the PCRep message；

calculating, a VSPT of the at least one leaf node according to a BRPC procedure and returning a PCRep message including the calculated VSPT to the PCC or the another PCE, when the path where the at least one leaf node is on is found.

According to a second aspect, a PCE for selecting a path is provided, the PCE includes:

a receiving unit, configured to receive a Path Computation Request (PCReq) message transmitted by a Path Computation Client (PCC) or another PCE, wherein the PCReq message is used to request a path, the PCReq message includes a Backward Recursive Path Computation (BRPC) flooding flag and identifiers of leaf nodes which are on the path；

a removing unit, configured to remove an identifier of a leaf node existed in a domain where the PCE is in from the PCReq message, when at least one leaf node of the leaf nodes does not exist in the domain； and

a forwarding unit, configured to forward the PCReq message with the identifier of the leaf node in the domain removed, to other PCEs in all adjacent domains.

In a first possible implementation of the PCE for selecting a path according to the second aspect, the PCE further includes:

a first determining unit, configured to determine whether the BRPC flooding flag is included in the PCReq message；

the forwarding unit forwards the PCReq message to the other PCEs, when the BRPC flood flag is included in the PCReq message.

In a second possible implementation of the PCE for selecting a path according to the second aspect or the first implementation form of the second aspect, the PCE further includes:

a first calculating unit, configured to calculate VSPTs of all the leaf nodes, when all the leaf nodes exist in the domain； and

a returning unit, configured to return a Path Computation Reply (PCRep) message including the VSPTs, to the PCC or the another PCE.

In a third possible implementation of the PCE for selecting a path according to the second aspect or the second implementation form of the second aspect, the PEC further includes:

a second calculating unit, configured to calculate a VSPT of a leaf node existed in the domain, when at least one leaf node does not exist in the domain； and

a storing unit, configured to store the VSPT.

In a fourth possible implementation of the PCE for selecting a path according to the third implementation form of the second aspect, the forwarding unit includes:

a first determining module, configured to determine whether an adjacent domain exists；

a generating module, configured to generate a plurality of PCReq messages for all adjacent domains according to the PCReq message with the identifier of the leaf node in the domain removed, when the adjacent domain exists； and

a forwarding module, configured to forward the plurality of PCReq messages to the other PCEs in all adjacent domains.

In a fiveth possible implementation of the PCE for selecting a path according to the fourth implementation form of the second aspect, the forwarding unit further includes:

a second determining module, configured to determine whether a VSPT of at least one leaf node existed in the domain is calculated, when the adjacent domain does not exist；

a returning module, configured to return a PCRep message including the VSPT to the PCC or to the another PCE, when the VSPT of at least one leaf node existed in the domain is calculated.

In a sixth possible implementation of the PCE for selecting a path according to the second aspect, the PCE further includes:

a second determining unit, configured to determine whether a path where at least one leaf node is on is found according to a PCRep message transmitted by the other PCEs in all adjacent domains, when the PCRep message is received by the PCE；

a processing unit, configure to calculate a VSPT of the at least one leaf node according to a BRPC procedure and return a PCRep message including the updated VSPT to the PCC or to the another PCE, when the path where the at least one leaf node is on is found.

The advantages of the present invention exist in that the embodiments of the present invention provide with a way (BRPC-Flooding) to be used to calculate inter-domain TE (Traffic Engineering, TE) LSP (Label Switched Path, LSP) when destination domain or domain tree is unknown. This mechanism requires least changes in PCEP (Path Computation Element Communication Protocol, PCEP) architecture or other components.

With reference to the following description and drawings, the particular embodiments of the present invention are disclosed in detail, and the principle of the present invention and the manners of use are indicated. It should be understood that the scope of the embodiments of the present invention is not limited thereto. The embodiments of the present invention contain many alternations, modifications and equivalents within the spirits and scope of the terms of the appended claims.

Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in combination with or instead of the features of the other embodiments.

It should be emphasized that the term “includes/including” when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

BRIEF DESCRIPTION OF THE DRAWING

The drawings are included to provide further understanding of the present invention, which constitute a part of the specification and illustrate the preferred embodiments of the present invention, and are used for setting forth the principles of the present invention together with the description. The same element is represented with the same reference number throughout the drawings.

Figure 1 is a flowchart of a method according to one embodiment of the present invention.

Figure 2 is a flowchart of a method on receiving path request according to another embodiment of the present invention.

Figure 3 is a flowchart of a method on receiving path reply according to another embodiment of the present invention.

Figures 4-16 are schematic diagram of application scenarios of the method according to the embodiment of the present invention.

Figure 17 is a schematic diagram of an apparatus for selecting path according to the embodiment of the present invention.

Figure 18 is a schematic structure diagram of the node according to an embodiment of the present invention.

DETAILED DESCRIPTION

The many features and advantages of the embodiments are apparent from the detailed specification and, thus, it is intended by the appended claims to cover all such features and advantages of the embodiments that fall within the true spirit and scope thereof. Further, since numerous modifications and changes will readily occur to a person skilled in the art, it is not desired to limit the inventive embodiments to the exact construction and operation illustrated and described, and accordingly all suitable modifications and equivalents may be resorted to, falling within the scope thereof.

In the present application, embodiments of the invention are described primarily in the context of PCC and PCE in a network. However, it shall be appreciated that the invention is not limited to the context of PCC and PCE, and may relate to any type of appropriate electronic apparatus having the function of path computation.

The embodiments of the present invention are described as follows in reference to the drawings.

Embodiment 1

One embodiment of the present invention provides a method for selecting path in a network. Figure 1 is a flowchart of the method according to the embodiment of the present invention. As shown in Figure 1, the method includes:

step 101: a PCE receives a PCReq message transmitted by a PCC or another PCE, wherein the PCReq message is used to request a path, the PCReq message includes a BRPC flooding flag and identifiers of leaf nodes which are on the path；

step 102: the PCE removes an identifier of a leaf node existed in a domain where the PCE is in from the PCReq message, when at least one leaf node of the leaf nodes does not exist in the domain； and

step 103: the PCE forwards the PCReq message with the identifier of the leaf node in the domain removed, to other PCEs in all adjacent domains.

In step 101, the PCReq message indicates leaf nodes for which paths need to be selected, and it can be transmitted by a PCC to a PCE in a domain where the PCC and the PCE are located, and it also can be forwarded by a PCE to another PCE which is located in another domain adjacent to the domain of the PCE.

In the embodiment, the PCReq can also be called as BRPC flood path computation request or path request, the meaning of the different versions is the same.

In step 102, when at least one leaf node of the leaf nodes does not exist in the domain, i.e., not all the leaf nodes are in the current domain, in order to find a path where a leaf node which is not in in the current domain is in, the PCE may forward the PCReq message, beore forwarding the PCReq message, the PCE may remove the identifiers of leaf nodes which are in the current domain from the PCReq message.

In an embodiment, the PCE may calculate a Virtual Shortest Path Trees (VSPT) of a leaf node which is in the current domain. For example, when all the leaf nodes exist in the current domain, the PCE may calculate VSPTs of all the leaf nodes, and return the calculation result to the PCC or the another PCE who transmit the PCReq message, such that the PCC or the another PCE may determine the VSPTs of all the leaf nodes and the path of all the leaf nodes. when not all the leaf nodes exist in the current domain, such as some leaf nodes exist in the current domain, and other leaf nodes exist in adjacent domains, the PCE may calculate VSPTs of the leaf nodes that in the current domain and store the calculation result, such that updates or returns the VSPTs after receiving a RCRep message transmitted by other PCEs.

In step 103, after removing the identifiers of the leaf nodes which are in the current domain from the PCReq message, the PCE may forward the PCReq message to other PCEs of all the adjacent domains, such that the paths of leaf nodes which are not in the current domain can be found, and the VSPTs of the leaf nodes which are not in the current domain can be obtained.

In an embodiment, the PCE may add the current domain to the domain list included in the PCReq message to avoid domain-sequence loop.

With the method of the embodiment, when destination domain (leaf node domain) or domain tree is unknown, the PCReq message (referred to as path request) can be flood to every neighboring domain, and carrying the already visited domains to avoid loop, thus the path selecting can be achieved without any changes in any external protocol and component.

In one implementation of the embodiment of the present invention, a BRPC flood flag can be set in the path request to indicate whether the method of the embodiment of the present invention can be used. When a BRPC flood flag is set in the path request, the method of the embodiment of the present invention can be used, otherwise, the method of the embodiment of the present invention can not be used, and normal core tree processing as described in the background is used to process the path request.

Therefore, in the implementation, before the step 103, the method further includes a step of determining whether a BRPC flood flag is set in the PCReq message. When the judging result is positive, i.e. the BRPC flood flag is set in the path request, step 103 can be processed, or else a normal core tree processing is processed.

With the implementation, the normal method and the mothod of the embodiment of the present invention can be two options for selecting, the flexibility of path selecting can be improved.

In another implementation of the embodiment of the present invention, leaf nodes are located in the domain where the PCE of the embodiment of the present invention who received the path request is present. In this implementation, the path request can be handed as intra-domain P2MP request.

For example, in case the PCC determines a PCE capable of serving its path computation request in a domain where the PCC is located, and transmits the path request to the PCE (the PCE of the embodiment of the present invention) . The PCE of the embodiment of the present invention receives the path request from the PCC. When leaf nodes are in the domain where the PCC and the PCE are located, this can be handed as intra-domain P2MP request.

For example, in case a PCE forwards the path request to the PCE of the embodiment of the present invention, the PCE of the embodiment of the present invention may receive the path request from the PCE (called as another PCE) . When leaf nodes are in the domain where the PCE of the embodiment of the present invention is present, the PCE may calculate VSPTs for leaf nodes and returns the VSPTs to the another PCE.

With the implementation, when leaf nodes are in the domain where the PCE who received the path request is present, the VSPT can be computed in one step, and the path selecting can be easily achieved.

In another implementation of the embodiment of the present invention, not all the leafs are in the domain where the PCE of the embodiment of the present invention who receiving the path request is present, in case at least one leaf node exists in the domain, the PCE may calculate the VSPT for the at least one leaf node, store the calculation result, and remove identifiers of the at least one leaf node from the path request before forwarding； in case all the leaf nodes are not in the domain, the PCE may forward the path request to PCEs in adjacent domains or return a path reply (PCRep message) to the PCC or the another PCE who transmit the path request.

In the implementation, the step 102 includes: the PCE judges whether at least one leaf node of all the leaf nodes does not exist in the domain.

If at least one leaf node does not exist in the domain, the PCE may calculate VSPT for leaf nodes exist in the domain. Where, the PCE can also store the VSPT and returen a path reply with the VSPT to the PCC or the another PCE who transimts the path request at an appropriate time. Where, when there are adjacent domains, the PCE may also remove the identifiers of the leaf nodes which are in the domain from the path request and forwards the path request to PCEs in the adjacent domains, when there are not adjacent domains, the PCE may return a pathe reply to the PCC or the another PCE who transmit the path request.

In an embodiment, the step 103 further includes: the PCE determines whether an adjacent domain exists.

If there are adjacent domains, the PCE will generate a plurality of path requests for all the adjacent domains which do not cause domain-sequence loop, and forward the plurality of path requests to PCEs of all the adjacent domains. In an emplementation, the PCE should also add the current domain to the already visited domain list included in the path request to avaoid loop.

Where, when at least one leaf node exists in the domain, an identifier of the at least one leaf node may be removed from the path requests that the PCE generates for all the adjacent domains.

If there are not adjacent domains, and the VSPT of at least one local leaf node (exists in the domain) is success (calculated) , the PCE may return a path reply with the VSPT to a node which transmit the path request.

If ther are not adjacent domains, and no the VSPT of local leaf node is not success, the PCE may return a path reply with no-path to a node which transmit the path request.

Figure 2 is a flowchart of the method processed by a PCE according to the method of the embodiment of the present invention when receiving a path request, referring to figure 2, the method includes:

step 201: judging whether a BRPC flood flag is set in a path request received by the PCE？ If it is YES, run to step 203, or else run to step 202；

step 202: do normal core tree processing；

step 203: judging if leaf nodes exist in current domain？ If it is YES, run to step 205, or else run to step 204；

where, current domain means the domain where the PCE is present.

step 204: calculating VSPTs for all the leaf nodes and returning the VSPTs to PCC or another PCE who transmit the path request；

step 205: judging if at least one leaf node exists in current domain？ If it is YES, run to step 206, or elso run to step 207；

step 206: calculating VSPTs for leaf nodes exist in the current domain, store the calculation result and remove the identifiers of the leaf nodes from the path request；

step 207: judging if there are any new adjacent domains？ If it is YES, run to step 208, or else run to step 209；

step 208: generating a multiple of path requests for all the adjacent domains which do not cause domain-sequence loop； add the current domain to the domain list included in the path request；

step 209: judging whether a VSPT of at least one local leaf node is success？ If it is YES, run to step 210, or else run to step 211；

step 210: returning a path reply with the VSPT to a node who transmit the path request；

step 211: returning path reply with no-path to a node who transmit the path request.

In the embodiment of the present invention, when receiving a path reply (with VSPT or no-path) , the PCE may attach the path reply to the main request, and store the result.

In one implementation, similar to the process on receiving a path request, the PCE can check for the BRPC flood flag first, when BRPC flood flag is set in the path reply, the PCE attachs the path reply to the main request, otherwise, the PCE does normal core tree processing.

In the embodiment, the PCE waits for the path reply with VSPT or no-path received from all the adjacent domains. When at least one path (local or received) is success, then VSPT is generated as described in the background.

In the embodiment, when a PCRep message (referred to as path reply) transmitted by another PCE is received by the PCE, the PCE judges whether there are at least one success path, i.e., whether a path where at least one leaf node is on is found according to the PCRep message, when there are at least one success path, the PCE may update a VSPT of the at least one leaf node based on a BRPC procedure and return a PCRep message with the VSPT to the another PCE； when there are no success path, the PCE returns a path computation reply with no path to the another PCE.

Figure 3 is a flowchart of the method processed by a PCE according to the method of the embodiment of the present invention when receiving a path reply, referring to figure 3, the method includes:

step 301: judging whether a BRPC flood flag is set in the path reply？ If it is YES, run to step 302, or else run to step 303；

step 302: doing normal core tree processing；

step 303: attaching the reply to the main request, store result；

step 304: judging if path replies are received from all adjacent domains？ If it is YES, run to step 306, or else run to step 305；

step 305: waitting for path reply from all adjacent domains；

step 306: judging if there is at least one success path result？ If it is YES, run to step 307, or else run to step 308；

step 307: updating VSPT based on BRPC procedure and returning a path reply with the VSPT；

step 308: returning a path reply with no-path.

When received the VSPT of leaf nodes for path selecting from all adjacent PCEs with all possible domain sequence, the first PCE (1) can slect appropriate path. Thus, with the method of the embodiment of the present invention, when destination domain or domain tree is unknown, with least changes in PCEP architecture or other components, path selecting can be achieved.

For easy understanding of the method for path selecting of the embodiments of the present invention, the method of this embodiment shall be described below with reference to figures 4-16.

Figures 4-16 are schematic diagram of application scenarios of the method according to the embodiment of the present invention. Reference to figures 4-16, there are five domains in the application scenarios, PCC1and PCE1are located in domain #1, PCE2 and leaf node A1 are located in domain #2, PCE3 and leaf node B1 are located in domain #3, PCE4 and leaf node C1 are located in domain #4, PCE5 is located in domain #5.

As shown in Figure 4, PCC1 is the ingress of the path selecting, and A1, B1 and C1 are the egresses of the path selecting.

As shown in Figure 5, PCC1 transmits the path request to PCE1 serving its domain. And the path request includes identifiers of leaf nodes on the egresses, such as A1, B1and C1.

As shown in Figure 6, since there are two domains (domain #2 and domain #4 adjacent to the domain where PCC1 and PCE1 are located (domain #1) , the two domains are called as adjacent domains, PCE1 generates two path requests for the two domains, and forwards the two path requests to the PCE2 and PCE4 of the two adjacent domains. Since A1, B1and C1 are not in the domain where the PCE1 is located (i.e. domain #1) , in each of the path requests generated by the PCE1, including the identifers of A1, B1 and C1.

As shown in Figure 7, PCE2 may receive a path request forwarded by PCE1, and since PCE2 and leaf node A1 are in the domain #2, PCE2 may exclude identifier of leaf node A1 from the path request and forward the updated path request to adjacent domains, i.e. domain #3. Where, only identifiers of B1 and C1 are in the updated path request. Where, PCE2 may calculate VSPT for A1 and store the result of calculation.

As shown in Figure 8, similar to PCE2, PCE3 may receive a path request forwarded by PCE2, and since PCE3 and leaf node B1 are in the domain #3, PCE3 may exclude identifier of leaf node B1 from the path request and forward the updated path request to adjacent domains, i.e. domain #4 and domain #5. Where, only identifier of C1 is in the updated path request. Where, PCE3 may calculate VSPT for B1 and store the result of calculation.

As shown in Figure 9, PCE4 and PCE5 may receive a path request forwarded by PCE3. Since identifier of leaf node C1 is in the path request, and, PCE4 and leaf node C1 are in the same domain, after receiving the path request, PCE4 may calculate VSPT for leaf node C1 and return a path reply with the VSPT of C1 to PCE 3. Since leaf node C1 is not in the domain where PCE5 is located, PCE5 may return a path reply with no-path in it.

As shown in Figure 10, PCE3 may receive path replies from PCE4 and PCE5, attach VSPT of C1 (received from PCE4) and B1 (local, i.e. calculated by the PCE3) to a path reply and return the path reply to PCE2.

As shown in Figure 11, similar to PCE2, PCE4 may receive a path request forwarded by PCE1, and since PCE4 and leaf node C1 are in the domain #4, PCE4 may exclude identifier of leaf node C1 from the path request and forward the updated path request to adjacent domains, i.e. domain #3. Where, only identifiers of A1 and B1 are in the updated path request. Where, PCE4 may also calculate VSPT for C1 and store the result of calculation.

As shown in Figure 12, similar to PCE4, PCE3 may receive a path request forwarded by PCE4, and since PCE3 and leaf node B1 are in the domain #3, PCE3 may exclude identifier of leaf node B1 from the path request and forward the updated path request to adjacent domains, i.e. domain #2 and domain #5. Where, only A1 is in the updated path request. Where, PCE3 may also calculate VSPT for B1 and store the result of calculation.

As shown in Figure 13, PCE2 and PCE5 may receive a path request forwarded by PCE3. Since identifier of leaf node A1 is in the path request, and, PCE2 and leaf node A1 are in the same domain, after receiving the path request, PCE2 may calculate VSPT for leaf node A1 and return a path reply with the VSPT of A1 to PCE 3. Since leaf node A1 is not in the domain where PCE5 is located, PCE5 may return a path reply with no-path in it.

As shown in Figure 14, PCE3 may receive path replies from PCE2 and PCE5, attach VSPTs of A1 (received from PCE2) and B1 (local, i.e. calculated by the PCE3) to a path reply and return the path reply to PCE4.

As shown in Figure 15, after receiving the path reply with VSPTs of B1 and C1 from PCE3, PCE2 may attach the VSPT of A1 to the path reply, and return the path reply with VSPTs of A1, A2 and A3 to PCE1. Similarly, after receiving the path reply with VSPTs of A1 and B1 from PCE3, PCE4 may attach the VSPT of C1 to the path reply, and return the path reply with VSPTs of A1, A2 and A3 to PCE1.

As shown in Figure 16, finally, PCE1 may receive the VSPTs of A1, A2, and A3 from all adjacent PCEs with all possible domain sequence, select the best path and forward the result to PCC1.

According to the method of the embodiment of the present invention, a BRPC flooding mechanism is used to calculate inter-domain TE LSP when destination domain or domain tree is unknown, this mechanism requires least changes in PCEP architecture or other components, and reduces the computational complexity.

An embodiment of the present invention further provides a PCE for selecting path in a network, as stated below. As the principle for solving problems is identical to that of the method of Embodiment 1, the implementation of Embodiment 2 may be referred to for the implementation of this method and the repeated parts shall not be described herein any further.

Embodiment 2

The embodiment of the present invention provides a PCE for selecting path in a network. Figure 17 is a schematic diagram of the PCE according to an embodiment of the present invention. Other parts of the PCE can refer to the existing technology of PCE and not be described in the present application.

As shown in figure 17, the PCE includes a receiving unit 171, a removing unit 172 and a forwarding unit 172.

Wherein, the receiving unit 171 is configured to receive a Path Computation Request (PCReq) message transmitted by a Path Computation Client (PCC) or another PCE, wherein the PCReq message is used to request a path, the PCReq message includes a Backward Recursive Path Computation (BRPC) flooding flag and identifiers of leaf nodes which are on the path.

Wherein, the removing unit is configured to remove an identifier of a leaf node existed in a domain where the PCE is in from the PCReq message, when at least one leaf node of the leaf nodes does not exist in the domain.

Wherein, the forwarding unit 172 is configured to forward the PCReq message with the identifier of the leaf node in the domain removed, to other PCEs in all adjacent domains.

In one implementation of the embodiment, the PCE further includes: a first determining unit 174 which is configured to determine whether the BRPC flooding flag is included in the PCReq message, when the BRPC flood flag is set included in the PCReq message, the forwarding unit 173 forwards the PCReq message to the other PCEs.

In one implementation of the embodiment, the PCE further includes: a first calculating unit 175 and a returning unit 176.

If all the leaf nodes exist in the domain, the first calculating unit 175 is configured to calculate VSPTs of all the leaf nodes, the returning unit 176 is configured to return a PCRep message including the VSPTs to the PCC or the another PCE.

In one implementation of the embodiment, the PCE further includes: a second calculating unit 177 and a storing unit178.

If at least one leaf node does not exist in the domain, the second calculating unit 177 is configured to calculate a VSPT of a leaf node existed in the domain, the storing unit 178 is configured to store the VSPT.

In one implementation of the embodiment, the forwarding unit 173 includes: a first determining module1731, a generating module1732, and a forwarding module1733.

The first determining module 1731 is configured to determine whether an adjacent domain exists, when the adjacent domain exists, the generating module 1732 is configured to generate a plurality of PCReq messages for all adjacent domains according to the PCReq message with the identifier of the leaf node in the domain removed, and the forwarding module 1733 is configured to forward the plurality of PCReq messages to the other PCEs in all adjacent domains.

In one implementation of the embodiment, the forwarding unit 173 further includes: a second determining module 1734 and a returning module 1735.

If the adjacent domain does not exist, the second determining module 1734 is configured to determine whether a VSPT of at least one leaf node existed in the domain is calculated, and when the VSPT of at least one leaf node existed in the domain is calculated, the returning module is configured to return a PCRep message including the VSPT to the PCC or to the another PCE.

In one implementation of the embodiment, the PCE further includes: a second determining unit 179 and a processing unit 1710.

The second determining unit 179 is configured to determine whether a path where at least one leaf node is on is found according to a PCRep message transmitted by the other PCEs in all adjacent domains, when the PCRep message is received by the PCE. The processing unit 1710 is configure to update a VSPT of the at least one leaf node according to a BRPC procedure and return a PCRep message including the updated VSPT to the PCC or to the another PCE, when the path where the at least one leaf node is on is found.

According to the PCE of the embodiment of the present invention, a BRPC flooding mechanism is used to calculate inter-domain TE LSP when destination’s domain or domain tree is unknown, this mechanism requires least changes in PCEP architecture or other components, and reduces the computational complexity.

Embodiment 3

This embodiment of the present invention further provides a node in a network. Figure 18 is a schematic structure diagram of the node according to an embodiment of the present invention. As shown in Figure 18, the node includes a processor 181 and a memory 182 coupled to the processor 181.

The memory 182 is configured to store program. Specifically, the program can includes program code, the program code includes computer operating instruction.

The processor 181 is configured to receive a PCReq message transmitted by a PCC or another PCE, wherein the PCReq message is used to request a path, the PCReq message includes a BRPC flooding flag and identifiers of leaf nodes which are on the path； remove an identifier of a leaf node existed in a domain where the node is in from the PCReq message, when at least one leaf node of the leaf nodes does not exist in the domain； and forward the PCReq message with the identifier of the leaf node in the domain removed, to other PCEs in all adjacent domains.

The memory 182 may include a high speed RAM and a non-volatile memory.

The processor 181 may be a Central Processing Unit (CPU) , or can be Application Specific Integrated Circuit (ASIC) , or can be configured to one or more ASIC.

According to the above node, a BRPC flooding mechanism is used to calculate inter-domain TE LSP when destination’s domain or domain tree is unknown, this mechanism requires least changes in PCEP architecture or other components, and reduces the computational complexity.

The processor 181 is further configured to determine whether the BRPC flooding flag is included in the PCReq message； and when the BRPC flooding flag is included in the PCReq message, remove the identifier and forward the PCReq message as described above.

The processor 181 is further configured to calculate a VSPT of all the leaf nodes, when all the leaf nodes exist in the domain； and return a PCRep message including the VSPT, to the PCC or to the another PCE.

The processor 181 is further configured to calculatie a VSPT of a leaf node existed in the domain, when at least one leaf node of the leaf nodes does not exist in the domain； and, store the VSPT.

The processor 181 is further configured to determine whether an adjacent domain exists； generate a plurality of PCReq messages for all adjacent domains according to the PCReq message with the identifier of the leaf node in the domain removed, when the adjacent domain exists； and forward the plurality of PCReq messages to the other PCEs in all adjacent domains.

The processor 181 is further configured to determine whether a VSPT of at least one leaf node existed in the domain is calculated, when the adjacent domain does not exist； and return a PCRep message including the VSPT to the PCC or to the another PCE, when the VSPT of at least one leaf node existed in the domain is calculated.

The processor 181 is further configured to determine whether a path where at least one leaf node is on is found according to a PCRep message received by the node and transmitted by the other PCEs in all adjacent domains； update a VSPT of the at least one leaf node according to a BRPC procedure, and return a PCRep message including the updated VSPT to the PCC or the another PCE, when the path where the at least one leaf node is on is found.

The embodiments of the present invention further provide a computer-readable program, wherein when the program is executed in an PCE, the program enables the computer to carry out the method for selecting path as descrideb in embodiment 1.

The embodiments of the present invention further provide a storage medium in which a computer-readable program is stored, wherein the computer-readable program enables the computer to carry out the method for selecting path as descrideb in embodiment 1.

It should be understood that each of the parts of the present invention may be implemented by hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods may be realized by software or firmware that is stored in the memory and executed by an appropriate instruction executing system. For example, if it is realized by hardware, it may be realized by any one of the following technologies known in the art or a combination thereof as in another embodiment: a discrete logic circuit having a logic gate circuit for realizing logic functions of data signals, application-specific integrated circuit having an appropriate combined logic gate circuit, a programmable gate array (PGA) , and a field programmable gate array (FPGA) , etc.

The description or blocks in the flowcharts or of any process or method in other manners may be understood as being indicative of comprising one or more modules, segments or parts for realizing the codes of executable instructions of the steps in specific logic functions or processes, and that the scope of the preferred embodiments of the present invention comprise other implementations, wherein the functions may be executed in manners different from those shown or discussed, including executing the functions according to the related functions in a substantially simultaneous manner or in a reverse order, which should be understood by those skilled in the art to which the present invention pertains.

The logic and/or steps shown in the flowcharts or described in other manners here may be, for example, understood as a sequencing list of executable instructions for realizing logic functions, which may be implemented in any computer readable medium, for use by an instruction executing system, device or apparatus (such as a system including a computer, a system including a processor, or other systems capable of extracting instructions from an instruction executing system, device or apparatus and executing the instructions) , or for use in combination with the instruction executing system, device or apparatus.

The above literal description and drawings show various features of the present invention. It should be understood that those skilled in the art may prepare appropriate computer codes to carry out each of the steps and processes as described above and shown in the drawings. It should be also understood that all the terminals, computers, servers, and networks may be any type, and the computer codes may be prepared according to the disclosure to carry out the present invention by using the apparatus.

Particular embodiments of the present invention have been disclosed herein. Those skilled in the art will readily recognize that the present invention is applicable in other environments. In practice, there exist many embodiments and implementations. The appended claims are by no means intended to limit the scope of the present invention to the above particular embodiments. Furthermore, any reference to “a device to…” is an explanation of device plus function for describing elements and claims, and it is not desired that any element using no reference to “a device to…” is understood as an element of device plus function, even though the wording of “device” is included in that claim.

Although a particular preferred embodiment or embodiments have been shown and the present invention has been described, it is obvious that equivalent modifications and variants are conceivable to those skilled in the art in reading and understanding the description and drawings. Especially for various functions executed by the above elements (portions, assemblies, apparatus, and compositions, etc.) , except otherwise specified, it is desirable that the terms (including the reference to “device” ) describing these elements correspond to any element executing particular functions of these elements (i.e. functional equivalents) , even though the element is different from that executing the function of an exemplary embodiment or embodiments illustrated in the present invention with respect to structure. Furthermore, although the a particular feature of the present invention is described with respect to only one or more of the illustrated embodiments, such a feature may be combined with one or more other features of other embodiments as desired and in consideration of advantageous aspects of any given or particular application.

Claims

A method for selecting a path in a network, comprising:

receiving, by a Path Computation Element (PCE) , a Path Computation Request (PCReq) message transmitted by a Path Computation Client (PCC) or another PCE, wherein the PCReq message is used to request a path, the PCReq message includes a Backward Recursive Path Computation (BRPC) flooding flag and identifiers of leaf nodes which are on the path；

removing, by the PCE, an identifier of a leaf node existed in a domain where the PCE is in from the PCReq message, when at least one leaf node of the leaf nodes does not exist in the domain； and

forwarding, by the PCE, the PCReq message with the identifier of the leaf node in the domain removed, to other PCEs in all adjacent domains.
The method according to claim 1, wherein, before the step of forwarding, the method further comprises:

determining, whether the BRPC flooding flag is included in the PCReq message； and

performing the step of forwarding, when the BRPC flooding flag is included in the PCReq message.
The method according to claim 1 or 2, wherein, the method further comprises:

calculating, a Virtual Shortest Path Tree (VSPT) of all the leaf nodes, when all the leaf nodes exist in the domain； and

returning, a Path Computation Reply (PCRep) message including the VSPT, to the PCC or the another PCE.
The method according to claim 1 or 2, wherein, the method further comprises:

calculating, a VSPT of a leaf node existed in the domain, when at least one leaf node of the leaf nodes does not exist in the domain； and

storing, the VSPT.
The method according to claim 4, wherein, the step of forwarding comprises:

determining, whether an adjacent domain exists；

generating, a plurality of PCReq messages for all adjacent domains according to the PCReq message with the identifier of the leaf node in the domain removed, when the adjacent domain exists； and

forwarding, the plurality of PCReq messages to the other PCEs in all adjacent domains.
The method according to claim 5, wherein, the step of forwarding further comprises:

determining, whether a VSPT of at least one leaf node existed in the domain is calculated, when the adjacent domain does not exist；

returning, a PCRep message including the VSPT to the PCC or to the another PCE, when the VSPT of at least one leaf node existed in the domain is calculated.
The method according to claim 1, wherein, when a PCRep message transmitted by the other PCEs in all adjacent domains is received by the PCE, the method further comprises:

determining, whether a path where at least one leaf node is on is found according to the PCRep message；

updating, a VSPT of the at least one leaf node according to a BRPC procedure and returning a PCRep message including the updated VSPT to the PCC or the another PCE, when the path where the at least one leaf node is on is found.
A Path Computation Element (PCE) for selecting a path in a network, comprising:

a receiving unit, configured to receive a Path Computation Request (PCReq) message transmitted by a Path Computation Client (PCC) or another PCE, wherein the PCReq message is used to request a path, the PCReq message includes a Backward Recursive Path Computation (BRPC) flooding flag and identifiers of leaf nodes which are on the path；

a removing unit, configured to remove an identifier of a leaf node existed in a domain where the PCE is in from the PCReq message, when at least one leaf node of the leaf nodes does not exist in the domain； and

a forwarding unit, configured to forward the PCReq message with the identifier of the leaf node in the domain removed, to other PCEs in all adjacent domains.
The PCE according to claim 8, wherein, the PCE further comprises:

a first determining unit, configured to determine whether the BRPC flooding flag is included in the PCReq message；

the forwarding unit forwards the PCReq message to the other PCEs, when the BRPC flood flag is included in the PCReq message.
The PCE according to claim 8 or 9, wherein, the PCE further comprises:

a first calculating unit, configured to calculate a VSPT of all the leaf nodes, when all the leaf nodes exist in the domain； and

a returning unit, configured to return a Path Computation Reply (PCRep) message including the VSPT, to the PCC or the another PCE.
The PCE according to claim 8 or 9, wherein, the PEC further comprises:

a second calculating unit, configured to calculate a VSPT of a leaf node existed in the domain, when at least one leaf node does not exist in the domain； and

a storing unit, configured to store the VSPT.
The PCE according to claim 11, wherein, the forwarding unit comprises:

a first determining module, configured to determine whether an adjacent domain exists；

a generating module, configured to generate a plurality of PCReq messages for all adjacent domains according to the PCReq message with the identifier of the leaf node in the domain removed, when the adjacent domain exists； and

a forwarding module, configured to forward the plurality of PCReq messages to the other PCEs in all adjacent domains.
The PCE according to claim 12, wherein, the forwarding unit further comprises:

a second determining module, configured to determine whether a VSPT of at least one leaf node existed in the domain is calculated, when the adjacent domain does not exist；

a returning module, configured to return a PCRep message including the VSPT to the PCC or to the another PCE, when the VSPT of at least one leaf node existed in the domain is calculated.
The PCE according to claim 8, wherein, the PCE further comprises:

a second determining unit, configured to determine whether a path where at least one leaf node is on is found according to a PCRep message transmitted by the other PCEs in all adjacent domains, when the PCRep message is received by the PCE；

a processing unit, configure to update a VSPT of the at least one leaf node according to a BRPC procedure and return a PCRep message including the updated VSPT to the PCC or to the another PCE, when the path where the at least one leaf node is on is found.