WO2015135570A1

WO2015135570A1 - Automatic backup path re-optimization

Info

Publication number: WO2015135570A1
Application number: PCT/EP2014/054639
Authority: WO
Inventors: Franz Rambach; Cyril Margaria; Svetoslav Duhovnikov
Original assignee: Nokia Solutions And Networks Gmbh & Co Kg
Priority date: 2014-03-11
Filing date: 2014-03-11
Publication date: 2015-09-17

Abstract

The present invention provides a method, apparatus and computer program product for automatic backup path re-optimization. The present invention includes composing, at a first network entity, a request message for requesting a second network entity to perform path computation, the request message including a indicator indicating whether the second network entity is requested to perform a re-optimization of a backup path, and transmitting the request message to the second network entity.

Description

DESCRIPTION

Automatic Backup Path Re-Optimization Field of the invention

The present invention relates to apparatuses, methods, systems, computer programs, computer program products and computer-readable media regarding automatic backup path re- optimization .

Background of the invention

A network can incur failures due to malfunctioning of one or multiple of its hardware or software contained components. In such a case, a problem occurs in IP (Internet Protocol) or Transport network, and the affected traffic needs to be restored. This is done by either switching or re-routing on a path which is diverse from the failed resource.

The new route can be found on demand after the failure is detected or pre-calculated and stored in every ingress network element. In case of pre-calculated restoration options, there exists a path for every (protected) traffic demand and every possible failure scenario.

When the backup paths are stored inside the network elements, each time the topology changes or more resources are used, the backup paths must be recomputed to avoid contentions in case of failures. Every time resources are released by a service, it is also possible to do re-optimization for the backup paths .

For a path which stays inside a single domain, the corresponding ingress node can detect a topology or new resource usage. Therefore, it can trigger the re-optimization.

However, in case of multi-domain paths, the ingress node has no knowledge of the topology of the other domains. Therefore, it cannot detect, if resource or topology changes happened in other domains and also if these events in the other domains have any impact on the pre-calculated restoration paths. Therefore, the re-optimization cannot be triggered by the ingress node.

As a result, today it is not possible to avoid contentions of the (stored) backup path for a multi-domain (MD) path.

In the following explanations, it is assumed that a centralized path computation element (PCE) performs the mentioned re-optimization.

A Path Computation Element (PCE) is an entity that is capable of computing a network path or route based on a network graph, and of applying computational constraints during the computation. The PCE entity is an application that can be located within a network node or component, on an out-of- network server, etc. For example, a PCE would be able to compute the path of a TE LSP (Traffic Engineering Label Switched Path) by operating on the TED (Traffic Engineering Database) and considering bandwidth and other constraints applicable to the TE LSP service request (cf. document [1]) .

As mentioned above, the re-optimization for single domain scenarios can be triggered in principle by the ingress node acting as a path computation client (PCC) . As defined in document [1], a PCC is any client application that requests a path computation to be performed by the PCE.

However, in case of a topology/resource change, all ingress nodes, which store affected backup paths, would send corresponding re-optimization requests to the PCE. As a result the PCE will be flooded by Path Computation Requests (PCReqs), i.e. the PCE will be highly loaded. This will significantly slow down the performance of the PCE and it could delay the calculation of requests for pending services that are about to be established. Furthermore, the re-optimization cannot be triggered by the ingress node for MD paths.

Thus, there is a need for mechanisms, which realize this re- optimization for MD scenarios.

Related documents:

[1] : IEFT RFC 4655, http://www.ietf.org/rfc/rfc4655.txt; [2]: IETF RFC 5440, http://tools.ietf.org/html/rfc5440; [3]: IETF RFC 5521, http://tools.ietf.org/html/rfc5521; Summary of the Invention

It is therefore an object of the present invention to overcome the above mentioned problems and to provide apparatuses, methods, systems, computer programs, computer program products and computer-readable media regarding automatic backup path re-optimization .

According to an aspect of the present invention there is provided a method comprising:

composing, at a first network entity, a reguest message for reguesting a second network entity to perform path computation,

the reguest message including a indicator indicating whether the second network entity is reguested to perform a re-optimization of a backup path, and

transmitting the reguest message to the second network entity .

According to another aspect of the present invention there is provided a method comprising:

receiving a reguest message for reguesting path computation from a first network entity at a second network entity, analyzing, by the second network entity, whether the request message includes an indicator indicating to perform re-optimization of backup paths, and

if it is determined that the indicator indicates to perform the re-optimization of the backup paths,

triggering, at the second network entity, re-optimization of the backup paths when a predetermined condition is fulfilled.

According to another aspect of the present invention there is provided an apparatus for use in first network entity, comprising at least one processor, and at least one memory for storing instructions to be executed by the processor, wherein the at least one memory and the instructions are configured to, with the at least one processor, cause the apparatus at least to perform a method as defined in any one of the above aspects .

According to another aspect of the present invention there is provided an apparatus for use in second network entity, comprising at least one processor, and at least one memory for storing instructions to be executed by the processor, wherein the at least one memory and the instructions are configured to, with the at least one processor, cause the apparatus at least to perform a method as defined in any one of the above aspects .

According to another aspect of the present invention there is provided an apparatus, comprising means for composing, at a first network entity, a reguest message for reguesting a second network entity to perform path computation,

means for transmitting the reguest message to the second network entity.

According to another aspect of the present invention there is provided an apparatus, comprising means for receiving a reguest message for reguesting path computation from a first network entity at a second network entity,

means for analyzing, by the second network entity, whether the reguest message includes an indicator indicating to perform re-optimization of backup paths, and

if it is determined that the indicator indicates to perform the re-optimization of the backup paths, means for triggering, at the second network entity, re- optimization of the backup paths when a predetermined

condition is fulfilled.

According to another aspect of the present invention there is provided a computer program product comprising code means adapted to produce steps of any of the methods as described above when loaded into the memory of a computer.

According to a still further aspect of the invention there is provided a computer program product as defined above, wherein the computer program product comprises a computer-readable medium on which the software code portions are stored.

According to a still further aspect of the invention there is provided a computer program product as defined above, wherein the program is directly loadable into an internal memory of the processing device.

Further aspects and features according to example versions of the present invention are set out in the appending claims.

Brief Description of the Drawings

These and other objects, features, details and advantages will become more fully apparent from the following detailed description of aspects /embodiments of the present invention which is to be taken in conjunction with the appended drawings, in which:

Fig. 1 is a diagram illustrating an example of a format of a reguest parameter object;

Fig. 2 is a diagram illustrating an example of a modified format of the reguest parameter object according to example versions of the present invention;

Fig. 3 is a flowchart illustrating an example of a method according to example versions of the present invention;

Fig. 4 is a flowchart illustrating another example of a method according to example versions of the present invention;

Fig. 5 is a diagram illustrating an example of an apparatus according to example versions of the present invention.

Detailed Description

According to example versions of the present invention, the PCE triggers the re-optimization based on topology/resources change, on PCE load and on policy and pushes actively the re- optimized paths to the PCC . It is noted that this re- optimization happens in the idle periods of the PCE, i.e. not affecting or delaying any pending reguests for new service establishment . According to example versions of the present invention, the following steps are involved:

1. The PCC indicates in the PCReq message, if the backup paths should be automatically re-optimized and pushed to the PCC by the PCE.

2. The PCE triggers a re-optimization of the backup paths, which should be re-optimized on demand (as indicated in step 1)

a. if it sees a topology change in its own domain or b. if it gets informed that a topology change happened in another domain

c. in case of new resource utilization which invalidates some of the already provided back-up paths

d. Based on operator policy or policy change.

3. The PCE sends the re-optimized computed paths to the corresponding PCCs.

For the single domain case, the PCE is aware of any topology changes, if it is listening to the interior gateway protocol, e.g. OSPF-TE (Open Shortest Path First - Traffic Engineering). Hence, it knows when it should do the re-optimization.

For the multi domain (MD) case, there are two general possibilities .

According to a first possibility, the PCE gets informed actively by another PCE. In this case, the PCE which is responsible for the ingress node, has to re-compute the backup paths as it has done originally, e.g. by using Backward- Recursive PCE-Based Computation (BRPC) . It is noted that in case of topology change in a domain, this information, i.e. a change in a specified domain, is flooded to all PCEs.

According to a second possibility, the PCE automatically receives new computed parts of the backup paths from other PCEs responsible for the domain where the topology or resource utilization has changed. As explained before, the PCE triggers a re-computation of all the backup paths, if the "local" topology changes. It will send the new computed path to the corresponding PCCs.

However, if the PCC is actually a PCE, which is responsible for some MD path, it will automatically receive (locally) re- optimized backup paths. Using this information, it can construct again the complete backup path and sends it to the corresponding PCCs, which have requested the MD paths.

Hence, in general the same mechanism is applied for the inter- PCE backup path re-optimization as the mechanism described for the single domain scenario.

In the following, an implementation of example versions of the present invention with respect to the PCE concept will be described in detail.

However, it is noted that despite the fact that example versions of the present invention are explained using the PCE concept, the implementation of the example versions of the present invention is of course not limited thereto. For example, the whole mechanism can in principle also be applied to management systems. This implies that the management system automatically does a re-optimization in case of topology or resource change and configures the updated backup paths at the network elements.

The communication between the network element, i.e. the PCC, and the PCE is done via the PCEP protocol as specified in document [2] . For the path computation of the working path and the backup path, the PCC reguests on the one hand the computation for the working path and on the other hand another computation for each possible failure case. The latter reguests include an exclude route object (XRO) (as specified by document [3]), which specifies the resource that is expected to fail.

Additionally, extensions of the PCEP protocol are reguired to indicate that the backup path should be re-optimized in case of topology or resource change .

Fig. 2 shows an example of the RP (Reguest Parameter) object as defined in document [2] . The RP object is carried in each PCReg message and is used to specify various characteristics of the path computation reguest. A description of the individual flags of the RP object can be found in chapter "7.4. RP Object" in document [2].

Fig. 3 illustrated an example of the modified format of the RP object according to example versions of the present invention.

As shown in Fig. 2, according to example versions of the present invention, it is proposed to add an additional 'Ρ' flag in the RP object of the PCEP reguest message to indicate that this (backup) path should be re-optimized in case of topology/resource change and it should be automatically pushed to the PCC.

If the P flag is set, than this reguest should be re-optimized and pushed to the PCC in case of topology/resource changes.

This P flag is mirrored in the response, if understood by the PCE, allowing the PCC to adapt its behaviour.

When the PCE has recomputed a backup path, it sends a PCRep (Path Computation Reply) with the same reguest ID as the original reguest.

As already mentioned above, in case of a failure, the PCC uses a pre-calculated backup path.

There are two options how the PCE reacts in this case:

• Since the PCE gets informed about the failure, it can deduce which of the working paths are affected. Based on this information it knows which backup paths are now used .

• The other option is that the PCC informs actively the PCE that it is now using the backup path and re-optimization is no longer needed.

To inform the PCE about this, according to example versions of the present invention, it is proposed to use a PCNtf (PC Notify) message, which includes the RP object with the additional 'Ρ' flag set to 'Ο'. If such a PCNtf message is send with the 'Ρ' flag set to 1, this indicates that re- optimization is needed again for this path. The RP object is put inside the notification object (described in chapter 7.14. NOTIFICATION Object in document [2]) as the "optional TLVs".

The RP object includes the Reguest-ID and with this number, the reguest which should be (no longer) re-optimized is identified .

This just described message can be used to indicate in any general case that re-optimization should no longer be done for this backup path. Different reasons for this case exist, e.g. the PCC decides that the corresponding working path should not be protected any more.

Note that this PCNtf message includes only some information, but it does not trigger any direct path computation. Hence, this message results in no additional (or in a negligible) load at the PCE side.

Note that - as already mentioned - the other possible implementation involves the management plane. In this case the management plane computes the backup paths and does a re- optimization in case of topology or resource change. (The actual path computation can be either done directly inside the management system or the management system triggers a PCE for the path computation.) After the re-optimization, the management system updates the backup paths inside the network elements .

In the foregoing, example versions of the present invention have been described in detail with respect to the PCE concept. In the following, a more general description of example versions of the present invention is made with respect to Figs . 3 to 5.

Fig. 3 is a flowchart illustrating an example of a method according to example versions of the present invention.

According to example versions of the present invention, the method may be implemented in a first network node and comprises composing, at a first network node, a reguest message for reguesting a second network entity to perform path computation in a step S31. The reguest message includes a indicator indicating whether the second network entity is reguested to perform a re-optimization of a backup path. Further, the method comprises transmitting the reguest message to the second network entity in a step S32.

According to example versions of the present invention, the method further comprises transmitting, by the first network entity, a notification message to the second network entity, including an indicator informing the second network entity that re-optimization of the backup path is no longer needed.

According to example versions of the present invention, the indicator is a flag added to the reguest message or the notification message.

Fig. 4 is flowchart illustrating another example of a method according example versions of the present invention According to example versions of the present invention, the method may be implemented in a second network entity and comprises receiving a reguest message for reguesting path computation from a first network entity at a second network entity in a step S41, and analyzing, by the second network entity, whether the reguest message includes an indicator indicating to perform re-optimization of backup paths in a step S42. If it is determined that the indicator indicates to perform the re-optimization of the backup paths, the method further comprises triggering, at the second network entity, re-optimization of the backup paths when a predetermined condition is fulfilled in a step S43.

According to example versions of the present invention, the method further comprises transmitting the re-optimized backup paths to the first network entity.

According to example versions of the present invention, it is determined that the predetermined condition is fulfilled if the second network entity recognizes a topology change in its own domain, or if the second network entity is informed about a topology change in another domain. As an alternative it is determined that the predetermined condition is fulfilled in case of new resource utilization which invalidates at least one backup path previously provided to the first network element. Moreover, as a further alternative, the determination is made depending on operator policy or policy change.

According to example versions of the present invention, the method further comprises, if the second network entity is informed about a topology change or new resource utilization in another domain, receiving, at the second network entity, a part of re-computed backup paths from other network entities according to the domain in which the topology or the resource utilization has changed, and constructing a complete re- optimized backup path based on the received part of the backup path .

According to example versions of the present invention, the method further comprises receiving, at the second network entity, a notification message from the first network entity, including an indicator informing the second network entity that re-optimization of the backup path is no longer needed.

Fig. 5 is a block diagram showing an example of an apparatus according to example versions of the present invention.

In Fig. 5, a block circuit diagram illustrating a configuration of an apparatus 50 is shown, which is configured to implement the above described aspects of the invention. It is to be noted that the apparatus 50 shown in Fig. 5 may comprise several further elements or functions besides those described herein below, which are omitted herein for the sake of simplicity as they are not essential for understanding the invention. Furthermore, the apparatus may be also another device having a similar function, such as a chipset, a chip, a module etc., which can also be part of an apparatus or attached as a separate element to the apparatus, or the like.

The apparatus 50 may comprise a processing function or processor 51, such as a CPU or the like, which executes instructions given by programs or the like related to the flow control mechanism. The processor 51 may comprise one or more processing portions dedicated to specific processing as described below, or the processing may be run in a single processor. Portions for executing such specific processing may be also provided as discrete elements or within one or more further processors or processing portions, such as in one physical processor like a CPU or in several physical entities, for example. Reference sign 52 denotes transceiver or input/output (I/O) units (interfaces) connected to the processor 51. The I/O units 52 may be used for communicating with one or more other network elements, entities, terminals or the like. The I/O units 52 may be a combined unit comprising communication eguipment towards several network elements, or may comprise a distributed structure with a plurality of different interfaces for different network elements. Reference sign 53 denotes a memory usable, for example, for storing data and programs to be executed by the processor 51 and/or as a working storage of the processor 51.

The processor 51 is configured to execute processing related to the above described aspects.

In particular, the apparatus 50 may be implemented in or may be part of a first network entity and may be configured to perform a method as described in connection with Fig. 3. Thus, the processor 51 is configured to perform composing a reguest message for reguesting a second network entity to perform path computation, the reguest message including a indicator indicating whether the second network entity is reguested to perform a re-optimization of a backup path, and transmitting the reguest message to the second network entity.

According to example versions of the present invention, the apparatus 50 may also be implemented in or may be part of a second network entity and may be configured to perform a method as described in connection with Fig. 4. Then, the processor 51 is configured to perform receiving a reguest message for reguesting path computation from a first network entity at a second network entity, analyzing, whether the reguest message includes an indicator indicating to perform re-optimization of backup paths, and if it is determined that the indicator indicates to perform the re-optimization of the backup paths, triggering re-optimization of the backup paths when a predetermined condition is fulfilled.

Thus, according to example versions of the present invention, there are provided two apparatuses 50, one for the first network entity and one for the second network entity, and the apparatuses each have a structure as illustrated in Fig. 5.

For further details regarding the functions of the apparatus 50, reference is made to the description of the methods according to example versions of the present invention.

The first network entity may be path computation client and the second network entity may be a path computation element according to a PCE concept. The first network entity and the second network entity may be located in separate network elements. Alternatively, the first network entity and the second network entity may be located in the same network element .

However, as already mentioned above, the example versions of the present invention are not limited thereto and are also applicable to a management plane Thus, the first network node may also be a management entity in the management plane.

According to example versions of the present invention, the following advantages are provided.

The network elements always have the optimal backup paths for any of their traffic demands.

Further, re-optimization is automatically scheduled in an optimized and controlled way, for instance in the idle cycles, if topology or resource has changed.

Furthermore, flow and computation complexity is less compared to multiple single reguests, since the PCE can compute all the backup paths in parallel and achieve better network utilization .

Moreover, PCE can take into account the non-disjoint working paths and provides backup path, which do not overload the links. Hence no crankback is needed in failure scenarios. Additionally, there are provided reductions of routing reguests send to a PCE in case of failures, since backup paths are already known and valid. This lowers the peak load of the PCE .

As a further matter, example versions of the present invention provide improved restoration time, backup paths are pre- computed and crankback are avoided beforehand.

As another advantage, there is achieved improved scalability by reducing the signalling and path computation reguest load.

Furthermore, predictability is improved, backup paths are pre- computed taking into account all the known demands, and contention is reduced.

Further, as backup path computation is done at a central PCE, the PCC can delegate the backup path computation policy and management to the PCE .

As a further advantage, the PCE does not have to be fully stateful, but only partially stateful, i.e. PCE only needs to know the working path of all demands for which the backup re- optimization is done.

In the foregoing exemplary description of the apparatus, only the units/means that are relevant for understanding the principles of the invention have been described using functional blocks. The apparatus may comprise further units/means that are necessary for its respective operation, respectively. However, a description of these units/means is omitted in this specification. The arrangement of the functional blocks of the apparatus is not construed to limit the invention, and the functions may be performed by one block or further split into sub-blocks .

When in the foregoing description it is stated that the apparatus (or some other means) is configured to perform some function, this is to be construed to be eguivalent to a description stating that a (i.e. at least one) processor or corresponding circuitry, potentially in cooperation with computer program code stored in the memory of the respective apparatus, is configured to cause the apparatus to perform at least the thus mentioned function. Also, such function is to be construed to be eguivalently implementable by specifically configured circuitry or means for performing the respective function (i.e. the expression "unit configured to" is construed to be eguivalent to an expression such as "means for") .

For the purpose of the present invention as described herein above, it should be noted that

- method steps likely to be implemented as software code portions and being run using a processor at an apparatus (as examples of devices, apparatuses and/or modules thereof, or as examples of entities including apparatuses and/or modules therefore), are software code independent and can be specified using any known or future developed programming language as long as the functionality defined by the method steps is preserved; - generally, any method step is suitable to be implemented as software or by hardware without changing the idea of the aspects/embodiments and its modification in terms of the functionality implemented;

- method steps and/or devices, units or means likely to be implemented as hardware components at the above-defined apparatuses, or any module(s) thereof, (e.g., devices carrying out the functions of the apparatuses according to the aspects/embodiments as described above) are hardware independent and can be implemented using any known or future developed hardware technology or any hybrids of these, such as MOS (Metal Oxide Semiconductor), CMOS (Complementary MOS), BiMOS (Bipolar MOS), BiCMOS (Bipolar CMOS), ECL (Emitter Coupled Logic), TTL (Transistor-Transistor Logic), etc., using for example ASIC (Application Specific IC (Integrated Circuit)) components, FPGA (Field-programmable Gate Arrays) components, CPLD (Complex Programmable Logic Device) components or DSP (Digital Signal Processor) components;

- devices, units or means (e.g. the above-defined apparatuses, or any one of their respective units/means) can be implemented as individual devices, units or means, but this does not exclude that they are implemented in a distributed fashion throughout the system, as long as the functionality of the device, unit or means is preserved;

- an apparatus may be represented by a semiconductor chip, a chipset, or a (hardware) module comprising such chip or chipset; this, however, does not exclude the possibility that a functionality of an apparatus or module, instead of being hardware implemented, be implemented as software in a (software) module such as a computer program or a computer program product comprising executable software code portions for execution/being run on a processor;

- a device may be regarded as an apparatus or as an assembly of more than one apparatus, whether functionally in cooperation with each other or functionally independently of each other but in a same device housing, for example.

In general, it is to be noted that respective functional blocks or elements according to above-described aspects can be implemented by any known means, either in hardware and/or software, respectively, if it is only adapted to perform the described functions of the respective parts. The mentioned method steps can be realized in individual functional blocks or by individual devices, or one or more of the method steps can be realized in a single functional block or by a single device .

Generally, any method step is suitable to be implemented as software or by hardware without changing the idea of the present invention. Devices and means can be implemented as individual devices, but this does not exclude that they are implemented in a distributed fashion throughout the system, as long as the functionality of the device is preserved. Such and similar principles are to be considered as known to a skilled person .

Software in the sense of the present description comprises software code as such comprising code means or portions or a computer program or a computer program product for performing the respective functions, as well as software (or a computer program or a computer program product) embodied on a tangible medium such as a computer-readable (storage) medium having stored thereon a respective data structure or code means /portions or embodied in a signal or in a chip, potentially during processing thereof.

It is noted that the aspects/embodiments and general and specific examples described above are provided for illustrative purposes only and are in no way intended that the present invention is restricted thereto. Rather, it is the intention that all variations and modifications which fall within the scope of the appended claims are covered.

Abbreviations :

MD multi-domain

ML multi-layer

OSPF Open Shortest Path First

PCC Path Computation Client

PCE Path Computation Element

PCEP PCE Protocol

PCNtf PC notify

PCReq Path Computation Request Message

RP Request Parameters

TE Traffic Engineering

TED Traffic Engineering Database

TLV Type Length Value

XRO exclude Route Object

Claims

1. A method, comprising:

transmitting the reguest message to the second network entity .

2. The method according to claim 1, further comprising:

transmitting, by the first network entity, a notification message to the second network entity, including an indicator informing the second network entity that re-optimization of the backup path is no longer needed.

3. The method according to claim 1 or 2, wherein

the indicator is a flag added to the reguest message or the notification message.

4. A method, comprising:

receiving a reguest message for reguesting path computation from a first network entity at a second network entity,

analyzing, by the second network entity, whether the reguest message includes an indicator indicating to perform re-optimization of backup paths, and

if it is determined that the indicator indicates to perform the re-optimization of the backup paths, triggering, at the second network entity, re-optimization of the backup paths when a predetermined condition is fulfilled.

5. The method according to claim 4, further comprising

transmitting the re-optimized backup paths to the first network entity.

6. The method according to claim 4 or 5, wherein it is determined that the predetermined condition is fulfilled

if the second network entity recognizes a topology change in its own domain, or

if the second network entity is informed about a topology change in another domain, or

in case of new resource utilization which invalidates at least one backup path previously provided to the first network entity, or

depending on operator policy.

7. The method according to claim 6, further comprising

if the second network entity is informed about a topology change or new resource utilization in another domain,

receiving, at the second network entity, a part of recomputed backup paths from other network elements according to the domain in which the topology or the resource utilization has changed, and

constructing a complete re-optimized backup path based on the received part of the backup path.

8. The method according to any one of claims 4 to 7, further comprising receiving, at the second network entity, a notification message from the first network entity, including an indicator informing the second network node that re-optimization of the backup path is no longer needed.

9. The method according to any one of claims 4 to 8, wherein the indicator is a flag added to the reguest message or the notification message.

10. The method according to any one of claims 1 to 9, wherein the first network entity is a path computation client and the second network entity is a path computation element according to a Path Computation Element concept.

11. The method according to any one of claims 1 to 10, wherein the first network entity and the second network entity are located in separate network elements.

12. The method according to any one of claims 1 to 10, wherein the first network entity and the second network entity are located in the same network element .

13. An apparatus for use in first network entity, comprising at least one processor, and at least one memory for storing instructions to be executed by the processor, wherein the at least one memory and the instructions are configured to, with the at least one processor, cause the apparatus at least to perform a method as defined in any one of claims 1 to 3 and 10 to 12.

14. An apparatus for use in second network entity, comprising at least one processor, and at least one memory for storing instructions to be executed by the processor, wherein the at least one memory and the instructions are configured to, with the at least one processor, cause the apparatus at least to perform a method as defined in any one of claims 4 to 12.

15. A computer program product including a program for a processing device, comprising software code portions for performing the steps of any one of claims 1 to 12 when the program is run on the processing device.

16. The computer program product according to claim 15, wherein the computer program product comprises a computer- readable medium on which the software code portions are stored .

17. The computer program product according to claim 15, wherein the program is directly loadable into an internal memory of the processing device.

18. An apparatus, comprising:

means for composing, at a first network entity, a reguest message for reguesting a second network entity to perform path computation,

means for transmitting the reguest message to the second network entity.

19. An apparatus, comprising:

means for receiving a reguest message for reguesting path computation from a first network entity at a second network entity,

means for triggering, at the second network entity, re- optimization of the backup paths when a predetermined

condition is fulfilled.