WO2012062386A1

WO2012062386A1 - A method and a system for managing transit connectivity failures in a ip/mpls network, and access node for such a system

Info

Publication number: WO2012062386A1
Application number: PCT/EP2011/004039
Authority: WO
Inventors: Javier JIMÉNEZ; Juan FERNÁNDEZ-PALACIOS; María Ángeles CALLEJO RODRÍGUEZ; Oscar GONZÁLEZ; Rafael CANTÓ
Original assignee: Telefonica, S.A.
Priority date: 2010-11-11
Filing date: 2011-08-11
Publication date: 2012-05-18
Also published as: AR083663A1

Abstract

A method and a system for managing transit connectivity failures in a IP/MPLS network, and access node for such a system The method comprises providing means to provide alternative connectivity, through a backup transit node, to one or more access nodes which have been affected by a transit connectivity failure, and requesting said alternative connectivity by each of said access nodes under a transit connectivity failure or by an intermediate node said access nodes are connected to. For a preferred embodiment, the transit level of said IP/MPLS network is designed as a single non-protected layer. The system and the access node are both arranged for implementing the method.

Description

A method and a system for managing transit connectivity failures in a IP/MPLS network, and access node for such a system

Field of the art

The present invention generally relates, in a first aspect, to a method for managing transit connectivity failures in a IP/MPLS network, and more particularly to a method which provides a mechanism to provide on-demand backup transit routing capacity to any node that has become isolated from the rest of the network due to any network failure. This mechanism permits a drastic reduction of the extra capacity needed for backup purposes in an IP/MPLS network.

The invention relates to the field of IP/MPLS networks and multi-layer IP/MPLS over dynamic transport networks, such as GMPLS-enabled WSON, OTN and MPLS-TP.

A second aspect of the invention relates to a system for managing transit connectivity failures in a IP/MPLS network adapted to implement the method of the first aspect.

A third aspect of the invention relates to an access node adapted to implement functions related to both: requesting and providing means to provision an alternative connectivity when it has been affected by a transit connectivity failure.

Prior State of the Art

Figure 1 exemplifies a typical IP/MPLS core network of a telecom operator providing Internet services to end customers. As it can be seen, this IP backbone is usually based on a hierarchy of routers interconnected through high speed point-to-point links.

At the lower level of the hierarchy, access routers aggregate traffic from metropolitan and access networks. At the highest level, interconnection routers connect the operator to other operators and the rest of the Internet. IP connectivity among access and interconnection routers, as well as among different access routers, is provided by one or many levels of transit routers. In the context of the present invention, whenever there are various levels of transit nodes, a transit node of a lower level will be considered as intermediate node with respect to a transit node of an upper level.

For resilience purposes, IP/MPLS network operators usually design partially meshed networks, so that connectivity failures can be solved by implementing IGP routing protocols (e.g. IS-IS or OSPF). In addition, and to provide protection for Internet services against single failures, a dual network design approach is known in the state of the art. According to said approach, every router in the network is actually duplicated, so that network is composed indeed by two overlapping and interconnected topologies: the even network and the odd one. This architecture offers a 1+1 protection scheme in case of router failures, as there is always a backup element for every single router, and in combination with the IGP recovery, it provides IP/MPLS services a very high degree of availability.

Figure 2 shows said dual-network approach for IP/MPLS networks.

The main concern with said traditional architecture is that it requires every node to be duplicated, and therefore derives in a 100% network over-provisioning.

There are various concepts and technologies which provide partial mechanisms to overcome such over-provisioning drawback, usually based on control plane enabled multilayer networks. They are briefly described next: - GMPLS [RFC3945], which is a generalization of MPLS to support packet switching, time division and wavelength multiplexing, is the current state of the art in terms of control plane for transport networks. The GMPLS protocol stack allows for the dynamic establishment, teardown and modification of transport connections. For this reason, GMPLS can be used as a mechanism to provide on-demand transport connectivity. In addition, and due to its multi-layer nature, a GMPLS integrated control plane can theoretically permit to implement multi-layer path restoration approaches, which could be used to reconsider said 1 +1 protection strategy at the IP/MPLS level.

However, the implementation of integrated GMPLS solutions is uncommon in real networks. On one side, most of already deployed IP/MPLS networks are based on IP/MPLS protocols (not GMPLS), and therefore are not interoperable with GMPLS. On the other side, a pure multi-layer GMPLS approach represents a significant challenge for multi-vendor scenarios (different vendors in each layer). The reason is that it would force the different GMPLS implementations to be fully compatible, something that is not available by default.

- Telefonica l+D International Application PCT/ES2010/070323 "IP Offloading Manager" provides a system and method to manage IP offloading, and focuses on the definition of a centralized system in charge of triggering connectivity changes on the transport network upon traffic changes or network failures, and reconfiguring the IP network according to these changes. Although this application also identifies a use case related to multi-layer restoration, the specific scenario and requirements of a 1 +1 IP/MPLS network was not deeply analyzed therein.

The main concern of using the IP offloading manager to reconsider the current 1+1 protection scheme at the IP layer is twofold:

- On one side, the multi-layer recovery use case proposed in the "IP offloading manager" application is very generic, and it does not specify a complete recovery process nor consider to any extent the specific requirements coming from the 1+1 IP/MPLS network architecture.

- On the other side, the IP offloading manager is a centralized system, which takes decisions on a unilateral basis. In some cases, it could be desirable to have a semi-distributed solution, in which multi-layer recovery actions are triggered by routers themselves.

In brief, although the IP offloading manager could be partially used to solve a challenge as the one described above, it does not currently provide a complete method to solve the problem (indeed, it should be extended with the specific issues of backup capacity management), and it follows a purely centralized approach, which could become a concern for real implementations, both for flexibility and scalability and issues.

- AT&T Patent Application N° US20090257742 on "Joint IP/Optical layer restoration after a router failure" defines a method and system for providing joint IP/Optical Layer restoration mechanisms for the IP over Optical Layer architecture, particularly for protecting against router failure within such based on the integration of optical and IP alarm management systems. According to this patent application, a router failure can be detected by the transport network, which would inform the source endpoint of the connection and subsequently trigger an alternative transport network connection to an alternative router. Although this alternative could be potentially adapted to solve the aforementioned problem statement, it requires the implementation of multi-layer alarm notifications, and most probably an integrated multi-layer control plane, that could facilitate enough information to the source node to perform the multi-layer restoration. In general, operators prefer to avoid such level of multi-layer integration between the IP/MPLS and the transport layer.

In summary, there is no solution in the current state of the art to provide a semi- distributed solution in which the access routers which become isolated due to a transit connectivity failure could request for alternative transit connectivity and without the use of an integrated multi-layer control plane. Even if the router could request for connectivity to the lower layer, it will not be able to identify an alternative transit router to be connected to unless a mechanism provides such information. Description of the Invention

It is necessary to offer an alternative to the state of the art which covers the gaps found therein.

To that end, the present invention provides, in a first aspect, a method for managing transit connectivity failures in a IP/MPLS network, comprising providing means for providing alternative connectivity, through a backup transit node, to an access node which has been affected by a transit connectivity failure.

In a characteristic manner, the method comprises requesting said alternative connectivity by said access node under a transit connectivity failure or by an intermediate transit node said access node is connected to.

A transit connectivity failure can be caused by a transit node failure, a failure in one or all the interfaces or ports of a transit node, or by any other failure that derives in a lost of connectivity for said access node to the rest of the network.

An alternative connectivity is achieved by establishing a new connection or link towards a backup transit node that can provide the connectivity that the failed transit node was providing.

The same method is applicable to transit node failures in higher levels of the hierarchy. In that case, the transit connectivity failure affects to at least one intermediate transit node, which becomes isolated, together with plurality of access nodes that are connected to said intermediate transit node, from the rest of the network.

Generally, the method comprises providing said alternative connectivity in two steps:

- Identifying an alternative transit node, or backup transit node, and

- Establishing a connection from the access node to that alternative transit node. For a preferred embodiment, the transit level of said IP/MPLS network is designed as a non-protected layer, such that the nodes thereof are interconnected through single links, without node redundancy.

For an embodiment, the method of the first aspect of the invention comprises requesting alternative connectivity by a plurality of access nodes under transit connectivity failures, or by at least one intermediate node said plurality of access nodes are connected to, and providing means for an alternative connectivity, through at least one backup transit node, to said plurality of access nodes under transit connectivity failures.

The method comprises, for an embodiment, carrying out:

- said requesting of said alternative connectivity by sending, each of the nodes under connectivity failure or each intermediate node, to a backup assignment policy manager, a backup transit request, and

- said providing of said alternative connectivity to each of the access nodes under connectivity failure or to each intermediate node, by sending back to each of the requesting nodes, said backup assignment policy manager, a response enabling the alternative connectivity, said response including, depending on the embodiment, at least an identifier for each backup transit node assigned to each requesting node, or the whole multi-layer route towards each backup transit node assigned to each requesting node.

Regarding the transport connection from the requesting node to the assigned backup transit node, the method comprises, as per an embodiment, after receiving said response, sending a transport connection request to the transport network, the latter sending, upon receiving said request, a transport connection response enabling said the requested transport connection.

According to different embodiments of the method, each of said access nodes and/or each of said intermediate nodes and/or each of said backup transit nodes is a router.

The present invention proposes therefore a mechanism to provide on-demand backup transit routing capacity to any node or router that has become isolated from the rest of the network due to any network failure. This mechanism permits a drastic reduction of the extra capacity needed for backup purposes in an IP/MPLS network.

Instead of following a 1+1 design, the transit level is preferably designed as a single non-protected layer. However, for some embodiments, each router is dimensioned so that it reserves extra capacity and interfaces, to provide occasional transit routing support for access nodes in a different region in case of failure of their transit router.

For an embodiment, in case of a transit node failure, a set of on-demand connections is triggered from every single access node affected by a connectivity loss towards an alternative backup transit (eventually located in other region). Once the new set of links is established and properly configured, the traffic will be diverted through the backup transit node. For an embodiment the IP/MPLS network is a multi-layer IP/MPLS over dynamic transport network, where the IP/MPLS and the transport layers are not coordinated through an integrated control plane.

A second aspect of the invention relates to a system for managing transit connectivity failures in a IP/MPLS network, comprising in a conventional manner:

- a plurality of nodes including access nodes connected through transit nodes to interconnection nodes and other access nodes; and

- means for identifying and providing an alternative connectivity, through a backup transit node, to each access node which has been affected by a transit connectivity failure, caused by the failure of the transit node to which said access node is connected.

In contrast to other known systems, in the system of the second aspect of the invention part or all of said access nodes comprise:

- first means intended for detecting the transit connectivity failure affecting at least the access node comprising said first means, and for sending a detection signal indicating said transit connectivity failure detection, and

- second means arranged for receiving said detection signal, and intended for at least requesting said alternative connectivity to said backup manager means.

According to an embodiment, said first means comprise an alarm manager connected to said second means, the latter comprising a backup transit connectivity searcher connected bidirectionally to said means for identifying and providing an alternative connectivity, namely the backup manager means, which comprises a backup assignment policy manager, in order to implement the actions of the method described above referring to the requesting of alternative connectivity and the providing of the corresponding response.

Depending on the embodiment, said alarm manager is arranged to detect and/or collect alarms related to transit connectivity failures affecting only its own access node or also other access nodes.

The system of the invention comprises, for an embodiment, a transit backup manager including said backup assignment policy manager, and which is external to said nodes of the system, and common to at least part of said access nodes.

For an alternative embodiment, said backup assignment policy manager is implemented into one or more of said access nodes.

For an embodiment, said backup assignment policy manager has access to data related to the topology and network status for IP/MPLS and transport network and implements algorithms which process said data to generate and assign an optimum alternative connectivity to the requesting node.

Regarding said backup transit connectivity searcher, for an embodiment, it is connected bidirectionally to a connection manager of the transport network, for implementing the actions of the method described above referring to transport connection request/response.

A third aspect of the invention relates to an access node for a system for managing transit connectivity failures in a IP/MPLS network, which is adapted to implement functions related to both: requesting and providing means for an alternative connectivity when it has been affected by a transit connectivity failure.

For an embodiment of the access node of the third aspect of the invention, it constitutes one of said access nodes of the system implementing said backup assignment policy manager, for the above referred alternative embodiment where the backup assignment policy manager is implemented into one or more of the access nodes of the system.

Brief Description of the Drawings

The previous and other advantages and features will be more fully understood from the following detailed description of embodiments, with reference to the attached drawings (some of which have already been described in the Prior State of the Art section), which must be considered in an illustrative and non-limiting manner, in which:

Figure 1 shows a generic IP hierarchical network architecture;

Figure 2 shows a dual-network approach to provide 1+1 protection in IP/MPLS networks;

Figure 3 shows an embodiment of the method of the invention, in the form of a scenario providing on-demand connectivity to an alternative transit node to recover from transit connectivity failure;

Figure 4 shows another embodiment of the method of the invention, in the form of a scenario providing on-demand connectivity to a generic backup node to recover from transit connectivity failure;

Figure 5 shows the system of the second aspect of the invention, for an embodiment, where the different elements forming part thereof are linked by dotted arrow lines according to a procedure architecture implementing the method of the first aspect of the invention; Figure 6 shows the same elements shown in Figure 5, but illustrating an implementation example based on the use of available protocols;

Figure 7 shows a workflow followed by the system of the second aspect of the invention for implementing the method of the first aspect;

Figure 8 shows two alternative embodiments for communications between the elements of the system shown in Figures 5 and 6 responsible for requesting/providing an alternative transit, the right view being related to the usage of a PCE architecture; and

Figure 9 shows an embodiment of the system of the second aspect of the invention regarding the usage of the ASON/GMPLS UNI to request for a transport network connection.

Detailed Description of Several Embodiments

As explained in a previous section, the present invention offers a mechanism to provide on-demand backup transit routing capacity to any router that has become isolated from the rest of the network due to any network failure. This mechanism permits a drastic reduction of the extra capacity needed for backup purposes in an IP/MPLS network.

The invention is based on the availability of a dynamic transport layer, capable of on-demand provisioning of point to point connectivity services between routers. Although GMPLS represents a good candidate to solve the automatic provisioning of transport connectivity, the present invention does not prevent any other technology or mechanism as long as it provides fast dynamic allocation of capacity over a transport network.

In summary, the present invention describes an access node, a system and a method to orchestrate the provisioning of connectivity towards a backup router in case of router failure in the default IP path.

The proposed mechanism actuates as follows, for an embodiment:

- Instead of a 1+1 design, every transit node is designed as a single network element, but with extra capacity and interfaces to provide occasional support for access nodes due to the failure of other transit routers.

- In case of a transit node failure, an on-demand connectivity request is triggered towards the generic backup resource (specifically, towards the slice representing the virtual backup node).

- Subsequently, an on-demand connectivity request is triggered by the access node towards an alternative transit node.

- Besides, any bandwidth upgrade between the generic backup transit and any other transit or the interconnection nodes will be triggered when needed. - Both the access and the backup transit nodes will discover each other, and a new IGP route towards the rest of the network will be provided.

- Finally, the traffic will be diverted through the backup transit node.

In this context, a new element is needed to process the "backup transit" requests from isolated routers, and to assign a backup transit router IP address to every single request, based on operator-specific policies. Said new element is the above referred as transit-backup manager, which will be described next in more detail with reference to the drawings. Scenarios:

The invention can be applicable to different scenarios. In the following, two main scenarios are described:

- On-demand connectivity to an alternative transit node to recover from transit connectivity failure.

- On-demand connectivity to a generic backup transit node to recover from transit connectivity failure.

These scenarios are depicted in Figures 3 and 4.

Figure 3 shows an embodiment of the method of the invention, in the form of said scenario providing on-demand connectivity to an alternative transit node to recover from transit connectivity failure, in which the alternative transit node is one of the transit nodes already providing conventional connectivity to at least one access node not undergoing under a transit connectivity failure. Particularly, referring to said Figure 3, for the situation there illustrated "Region A IP Transit node" has failed, and IP Access node of Region A is connected to "Region B IP Transit node" (connection indicated by a dotted arrow line) which is already providing a connection to IP Access node of Region B.

Figure 4 shows another embodiment of the method of the invention, in the form of said scenario providing on-demand connectivity to an alternative transit node to recover from transit connectivity failure, in which the alternative transit node is a generic backup transit node intended on purpose for carrying out said function of providing means for an alternative connectivity to one or more access nodes. Particularly, referring to said Figure 4, for the situation there illustrated "Region A IP Transit node" has failed, and IP Access node of Region A is connected to "Generic Backup Transit" node (connection indicated by a dotted arrow line) to which "Region A IP Transit node", "Region B IP Transit node" and "IP Interconnection node" are already connected. System architecture:

Figure 5 describes the architecture of the system of the second aspect of the invention, for an embodiment, adapted to implement the procedure for on-demand backup routing capacity assignment upon connectivity failures of the method of the first aspect of the invention. Dotted arrow lines indicate communication paths between the different blocks illustrated.

Specifically, Figure 5 depicts the next four main elements, or main blocks:

- the access router;

- the transit-backup router;

- the transport network;

- and the transit-backup manager, which is a new element provided by the present invention. The functional blocks illustrated in Figure 5 within the access router are the following:

- Backup-Transit Connectivity Searcher: new functional block in charge of triggering the search of an alternative transit in response to an "isolated router" situation due to a failure in the transit router.

- Alarm manager: provides real-time information about failures to the

Backup-Transit Connectivity Searcher (potentially by means of state-of- the-art mechanisms).

- Backup Requester: in charge of requesting the identification of a backup- transit node to the Transit-Backup Manager, to be used as new transit node by the access node, and to process the response obtained therefrom.

- Connection Manager: in charge of requesting to the transport network on- demand transport connectivity towards specific destinations, particularly a transport connection to the backup transit node assigned by the Transit- Backup Manager.

The new Transit-Backup Manager can be functionally decoupled into the following blocks, as indicated in Figure 5: - Backup Provider: in charge of receiving backup-transit node requests from the Backup requester, and transmitting the response of the Transit-Backup Manager to the access node.

- Backup Assignment Policy Manager: this module is in charge of performing multilayer path computation and back up resources assignment for every single backup transit request. This module executes multilayer optimization algorithms able to compute an optimum combination of both back up transit IP/MPLS and transport resources according to the information distributed by the routing protocols implemented in each network layer (e.g. IP/MPLS and WSON). Backup resources can be pre- calculated for each IP transit node failure in order to minimize the restoration time and the resources usage.

- Multi-layer TEDB (Traffic Engineering Data Base): in charge of maintaining a database with topology and network status both for IP/MPLS and transport network, to feed the Backup Assignment Policy Manager process. To achieve this, it listens to the routing protocols of both the IP/MPLS and the transport network, to learn the information from the respective TEDBs.

The Transit-Backup Router will be only involved in the process by the following means:

- IP/MPLS TEDB (Traffic Engineering Data Base): state-of-the-art module which resides in any router and maintains information about the IP/MPLS topology, network status and traffic engineering information. This module typically collects this kind of information through standard IGP routing protocols. Any new element (such as the Multi-layer TEDB) can use the same protocols to collect information from any of the IP/MPLS TEDB.

- Connection Manager: an optional module which is connected to the Transport Network, and which is in charge of terminating the end-to-end transport originated by the access node's Connection Manager.

Finally, the Transport Network provides an interface, the "Connection Manager" to request for (and receive confirmation of) on-demand transport connections to remote routers, in this case to potential transit-backup routers. In addition, the Transport Network contains a Transport TEDB to collect the information about the transport network status, specifically to feed the Multi-layer TEDB in the Transit-Backup Manager. As mentioned before, some of the functional blocks identified in the previous paragraphs with reference to Figure 5 can be implemented by means of standard protocols, as those presented in Figure 6. Note that the new elements proposed by this invention are depicted with dotted lines.

For instance, the interfaces towards the alarm manager can be implemented by available SMNP protocol, the collection of information to feed the Multi-Layer TEDB can be implemented by means of standard IGP protocols such as IS-IS or OSPF (with the -TE or GMPLS extensions when needed), the communication of on-demand connection requests between the routers and the transport network can be implemented by means of GMPLS protocols and/or IETF/OIF UNI interfaces, and the request/response of a backup- transit router to the Transit-Backup Manager can be implemented by means of the PCE architecture and PCEP protocol.

However, the present invention focuses on the method and system to provide on- demand backup routing, and therefore it does not prevent the utilization of other protocols or technical solutions.

Figure 7 shows an embodiment of the method of the first aspect of the invention, carried out by means of part of the blocks or modules of the system illustrated in Figures 5 and 6. Both the main message exchanges between the modules as well as the main processes carried out within the modules themselves are indicated in Figure 7, the first ones by means of respective dotted arrow lines and the latter by boxes A to D.

The whole method is initiated by a "isolated router" alarm triggered by the alarm manager. This message could be e.g. an SNMP trap configured so as to reflect a connectivity failure with the transit router and the unavailability of an alternative IGP or EGP route to a set of destinations.

Process "A" within the Backup-Transit Connectivity Searcher module will collect and align all the potential "isolated router" alarms, and will evaluate the necessity of requesting for an alternative route to some destinations. According to the result of this process, it will send a "Backup-Transit Request" to the Backup Assignment Policy Manager.

The communication between the "Backup-Transit Connectivity Searcher" and the "Backup Assignment Policy Manager", namely the "Backup-Transit Request" and the "Backup-Transit Response" messages, can be implemented by any means, but a potential implementation based on the use of the PCE architecture (see [RF4566]) is depicted in the right view of Figure 8 (and also in Figure 6), which on the left side depicts a simple embodiment where the particular implementation for said communication is not specified.

Process "B" within the Backup Assignment Policy Manager is in charge of collecting and eventually correlating Backup-Transit Requests from different access nodes (related to the fact that a transit router failure prevents a set of access nodes from having connectivity to the rest of the network).

The required transit resources at each layer are computed by the Transit Backup Manager, specifically by said Backup Assignment Policy Manager, according to the following procedure:

1.- Transit Backup Manager collects real time information about the transit connectivity failures and available networks resources from the multi-layer TEDB (available network resources) and from the Backup connectivity searcher (failures).

2 - Transit Backup Manager executes a multilayer optimization algorithm able to compute the optimum combination of IP/MPLS and transport transit resources for the existing failures. The algorithm could permit to redirect multiple the access nodes to the same backup-transit, to take interfaces availability into account, to perform load-balancing techniques or any other restriction or algorithm. The specific methodology to assign free backup-transit routing capacity to the different access nodes is out of scope of the present invention.

3.- Finally, the process B will provide the best-fit transit router and optionally the multi-layer path to reach it for every single backup request, by sending "Backup-Transit Response" messages in response to the received requests. These responses will include, at least, an identifier for the transit router assigned to the requesting access node, and may potentially include the whole multi-layer route towards the destination.

Within process "C", the access node processes the received message from the

Backup Assignment Policy Manager and it triggers a new connection request to the transport network, by means of the eventual usage of a "connection manager" module sending a "Transport Connection Request" to the Transport Network. In the end, both IP/MPLS and transport resources computed by the Transit Back up Manager are allocated by means of IP/MPLS and transport signalling protocols.

As an example, the communication between the "Backup-Transit Connectivity Searcher" and the "Transport Network", namely the "Transport Connection Request" and the "Transport Connection Response" messages, can be implemented by means of the collaboration of any kind of connection managers, as generically indicated by left view of Figure 9. A potential implementation based on the use of the UNI interface (see [RFC4208], [OIFUNI]) is depicted in the right view of Figure 9 (and also in Figure 6), which also illustrates the communication between the Transport Network and a Transit-Backup router also by means of a UNI interface.

Finally, process "D", within the transport network is in charge of the actual provisioning of the transport network connection (and could be implemented by standard or proprietary control or management solutions), but the actual implementation is out of scope of the present invention.

The fundamental novelty of this invention is related to the whole method and system, but especially to the "Backup-Transit Connectivity Searcher" module and its main processes, "A" and "C", as well as the "Backup Assignment Policy Manager" with its process "B". In addition, process "C" will be in charge of the reconfiguration of the involved interfaces/ports as well as protocols to be used over the new connection.

Although the system of the second aspect of the invention illustrated by Figures 5 and 6 has been described as being centralized, i.e. with a "Transit-Backup Manager" which is external and common to all the access nodes, for other embodiments, not illustrated, the system is arranged forming a distributed architecture, including several "Transit-Backup Managers", each for one or more access nodes, and even, depending on the embodiment, with said "Transit-Backup Managers", or at least the "Backup Assignment Policy Managers" included therein, implemented into the access routers themselves.

Advantages of the Invention:

The main advantages of the proposed invention are the following:

- It permits to drastically reduce the over-provisioning in IP/MPLS transit routing capacity for resilience purposes, as it provides a dynamic mechanism to reallocate the routing capacity and the connectivity from the access nodes to the backup transit nodes whenever it is needed.

It allows achieving the previous benefit in a scenario in which the IP/MPLS and the transport layer are not coordinated through an integrated control plane.

It permits to deploy a semi-distributed architecture, in which the connectivity requests are triggered by the access routers and no centralized active manager is needed.

- It permits a very simple integration with standard state-of-the-art tools such as the PCE and the UNI. In summary, the proposed system, access node and method permit to reduce the over-provisioning in IP/MPLS transit capacity with a centralized or decentralized policy, depending on the embodiment, and a distributed triggering, and based on standard protocols, without the need for a fully integrated multi-layer control plane.

A person skilled in the art could introduce changes and modifications in the embodiments described without departing from the scope of the invention as it is defined in the attached claims.

ACRONYMS AND ABBREVIATIONS

ASON Automatically Switched Optical Network

EGP Exterior Gateway Protocol

GMPLS Generalized Multi-Protocol Label Switching

IETF Internet Engineering Task Force

IGP Interior Gateway Protocol

IP Internet Protocol

IS-IS Intermediate System-to-lntermediate System

LDP Label Distribution Protocol

LSP Label Switched Path

MPLS Multi-Protocol Label Switching

MPLS-TP Multi-Protocol Label Switching - Transport Profile

OSPF Open Shortest Path First

OTN Optical Transport Network

PCE Path Computation Element

PCEP Path Computation Element Protocol

RSVP Resource Reservation Protocol

SNMP Simple Network Management Protocol

TE Traffic Engineering

TEDB Traffic Engineering Database

UNI User-Network Interface

WDM Wavelength Division Multiplex

REFERENCES

[RFC3945] Mannie, E., "Generalized Multi-Protocol Label Switching (GMPLS) Architecture", RFC 3945, October 2004. [RFC4655] A. Farrel, J. -P. Vasseur, J. Ash, "A Path Computation Element (PCE)- Based Architecture", RFC 4655, August 2006.

[OIFUNI] OIF, "User Network Interface (UNI) 2.0 Signalling", February 2008.

[RFC4208] G. Swallow et al, "Generalized Multiprotocol Label Switching (GMPLS) User-Network Interface (UNI): Resource Reservation Protocol-Traffic Engineering (RSVP- TE) Support for the Overlay Model", RFC 4208, October 2005

[WSON] WSON definition: draft-ietf-ccamp-wavelength-switched-framework (http://tools.ietf.org/html/draft-ietf-ccamp-rwa-wson-framework-03)

Claims

1. - A method for managing transit connectivity failures in a IP/MPLS network, of the type which comprises providing means for the establishment of an alternative connectivity, through a backup transit node, to an access node which has been affected by a transit connectivity failure, characterised in that the method comprises requesting said alternative connectivity by said access node under a transit connectivity failure or by an intermediate node said access node is connected to.

2. - A method as per claim 1 , comprising requesting alternative connectivity by a plurality of access nodes under transit connectivity failures, or by at least one intermediate node said plurality of access nodes are connected to, and providing means for an alternative connectivity, through at least one backup transit node, to said plurality of access nodes under transit connectivity failures.

3. - A method as per claim 1 or 2, wherein the transit level of said IP/MPLS network is designed as a single non-protected layer, such that the nodes thereof are interconnected through single links, without node redundancy.

4. - A method as per any of the previous claims, comprising carrying out:

- said providing of said alternative connectivity to each of the access nodes under connectivity failure or to each intermediate node, by sending back to each of the requesting nodes, said backup assignment policy manager, a response enabling the alternative connectivity.

5.- A method as per claim 4, wherein said response includes at least an identifier for each backup transit node assigned to each requesting node.

6. - A method as per claim 5, wherein said response includes the whole multi-layer route towards each backup transit node assigned to each requesting node.

7. - A method as per claim 4, 5 or 6, comprising, by means of each requesting node, after receiving said response, sending a transport connection request to the transport network, the latter sending, upon receiving said request, a transport connection response enabling said the requested transport connection.

8. - A method as per any of the previous claims, wherein each of said access nodes and/or each of said intermediate nodes and/or each of said backup transit nodes is a router.

9. - A method as per any of the previous claims, wherein said IP/MPLS network is a multi-layer IP/MPLS over dynamic transport network, where the IP/MPLS and the transport layers are not necessarily coordinated through an integrated control plane.

10. - A system for managing transit connectivity failures in a IP/MPLS network, of the type which comprises:

- a plurality of nodes including access nodes connected through transit nodes to interconnection nodes and other access nodes;

- means for identifying and providing alternative connectivity, through a backup transit node, to each access node which has been affected by a transit connectivity failure, caused by the failure of the transit node to which said access node is connected, characterised in that at least part of said access nodes comprises:

11. - A system as per claim 10, wherein said first means comprise an alarm manager connected to said second means, the latter comprising a backup transit connectivity searcher connected bidirectionally to said means for identifying and providing an alternative connectivity, namely the backup manager means, which comprise a backup assignment policy manager, in order to implement the actions of the method as per any of claims 4 to 6.

12. - A system as per claim 11 , comprising a transit backup manager including said backup assignment policy manager, and which is external to said nodes of the system, and common to at least part of said access nodes.

13. - A system as per claim 10, wherein said backup assignment policy manager is implemented into at least part of said access nodes.

14. - A system as per claim 11 , wherein said backup transit connectivity searcher is connected bidirectionally to a connection manager of the transport network, for implementing the actions of the method as per claim 7.

15. - A system as per claim 11 , wherein said backup assignment policy manager has access to data related to the topology and network status for IP/MPLS and transport network and implements algorithms which process said data to generate and assign an optimum alternative connectivity to the requesting node.

16. - A system as per claim 11, wherein said alarm manager is arranged to collect alarms related to transit connectivity failures affecting other access nodes.

17. - A system as per any of claims 10 to 16, wherein said backup transit node is a generic backup transit node intended on purpose for carrying out said function of providing means for an alternative connectivity to at least one access node.

18. - A system as per any of claims 10 to 16, wherein said backup transit node is one of said transit nodes already providing conventional connectivity to at least one access node not undergoing under a transit connectivity failure.

19. - An access node for a system for managing transit connectivity failures in a IP/MPLS network, characterised in that it is adapted to implement functions related to both: requesting and providing means to provision an alternative connectivity when it has been affected by a transit connectivity failure.

20. - An access node as per claim 19, wherein it constitutes one of said access nodes of the system as per claim 13 which implements said backup assignment policy manager for carrying out said function of providing said alternative connectivity.