Methods and apparatus for protecting a communications network

The invention relates in general to a communications network, and more particularly, to methods and apparatus for protecting such a network. The methods and apparatus disclose the providision path protection in a communications network (14) having a plurality of nodes including at least one access node (24, 26, 28, 30). A connection-oriented worker path (23) is set up between a first distribution node (22) and the at least one access node. A connection-oriented protection path (21) is also set up between a second distribution node and the at least one access node. A connection-oriented interface path (52) is also set up between the first and second distribution nodes. Traffic from an upstream node (16, 18) is switched to the interface path (52) at one of the distribution nodes (20, 22). Traffic may be switched to the protection path (21) in response to detecting a fault (54) in the worker path.

This application is the U.S. national phase of International Application No. PCT/EP2009/051493 filed 10 Feb. 2009 which designated the U.S., the entire content of which is hereby incorporated by reference.

TECHNICAL FIELD

The invention relates in general to a communications network, and more particularly, to methods and apparatus for protecting such a network.

BACKGROUND

Telecommunications operators are continuing to develop triple play services which may include the provisioning of high-speed Internet, television/video, and telephone services via a single broadband connection. It is known to use a metro network, also known as a local network, which is a Connection Oriented—Packet Switched (CO-PS) network to provide such services. Technologies such as Multi Protocol Label Switching Transport Profile (MPLS-TP), and Provider Backbone Bridge Traffic Engineering (PBB-TE) have been used in the metro network for this purpose. Up until now such CO-PS networks and the corresponding technology have generally offered the required performance and reliability to satisfy market requirements for triple play services.

Within triple play services the demand for television and video services is increasing. Such television and video services require multicast distribution from a video server to many subscribers which may consume a large bandwidth, and place greater demands on the metro network and underlying technology. These increasing demands have an impact on the ability of telecommunications operators to guarantee the level of service and quality of service that the metro network architecture and technology can offer.

There are many types of protection mechanism that may be used in CO-PS networks to guarantee the level of service and quality of service. Such protection mechanisms aim to provide protection to a network in the event of failures of paths, links or devices within the network so that disruptions to communication services are minimised. A further aim of such protection mechanisms is to avoid loss of traffic in the event of failures within the network.

It is known to provide a redundancy mechanism such as Virtual Router Redundancy Protocol (VRRP) which utilises two edge routers in a core network which are connected to respective edge devices of the metro network. One router acts as a master and the other router operates in a standby condition until required to be used. Such a protection protocol provides protection for traffic passing from the core network to the metro network. The technique delegates protection to the core network at the cost of a complication in redundancy management for the router in the stand-by condition. If a failure is detected in the metro network a fail notification is reported to an edge switching node of the metro network which in turn reports it to the edge router of the core network. This activates protection and starts the sending of traffic towards the standby edge switching node of the core network.

A problem associated with such mechanisms is that they require that a fault in the metro network induces an action or modification in the core network. This is not a straight forward process due to the need for a failure message to propagate from Layer 2 in the metro network to Layer 3 in the core network. Furthermore, using the VRRP the edge switching nodes of the metro network may need to be aware of the master router and be able to modify its traffic forwarding status, or may be required to participate in the router control plane and elect which router is to be used. In addition, when the VRRP is used with an Ethernet tree configuration, each router of the core network is connected to respective edge devices of the metro network, which typically requires two Ethernet worker trees and two Ethernet protection trees to be configured and managed. Overall Layer 3 protocols such as the VRRP add cost and complexity to the metro network which is undesirable.

SUMMARY

What is required is an improved way of providing a protection mechanism to a communications network and to reduce the above-mentioned problems.

According to a first aspect of the invention, there is provided a method of providing path protection in a communications network having a plurality of nodes including at least one access node. The method comprises setting up a connection-oriented worker path between a first distribution node and the at least one access node, and switching traffic from an upstream node to the worker path at the first distribution node. The method includes setting up a connection-oriented protection path between a second distribution node and the at least one access node. The method includes setting up a connection-oriented interface path between the first and second distribution nodes. The method includes switching traffic from the upstream node to the interface path, and switching traffic from the interface path to the protection path at the second distribution node in response to detecting a fault in the worker path.

According to a second aspect of the invention there is provided a method of providing path protection in a communications network having a plurality of nodes including at least one access node. The method comprises setting up a connection-oriented worker path between a first distribution node and the at least one access node. The method comprises setting up a connection-oriented protection path between a second distribution node and the at least one access node. The method comprises setting up a connection-oriented interface path between the first and second distribution nodes. The method comprises switching traffic from an upstream node to the interface path at the second distribution node and switching traffic from the interface path to the worker path at the first distribution node. The method comprises switching traffic from the upstream node to the protection path at the second distribution node in response to detecting a fault in the worker path.

Such a way of providing path protection has the advantage that the involvement of the upstream node in protection mechanisms of the distribution nodes is reduced. Furthermore, when the fault is detected the upstream node, which may be located in a core network, is not required to implement protection switching. This may reduce cost and complexity of protection switching and may assist telecommunications operators to guarantee levels of service and quality of service. In the case of the first aspect of the invention, the traffic may be routed between the first distribution node and the second distribution node to utilise the interface path in response to determining the fault. In the case of the second aspect of the invention, the interface path may be used to relay traffic to the worker path, and traffic may be routed to the protection path in the event of the fault. Such arrangements provide a more robust way of providing protection to a communications network than prior techniques and is advantageous for the overall network reliability.

In one aspect the method may further include switching traffic from the upstream node to the interface path at the second distribution node and switching traffic from the interface path to the worker path at the first distribution node in response to a change of the distribution node receiving the traffic.

In another aspect the method may further include switching traffic from the upstream node to the worker path at the first distribution node in response to a change of the distribution node receiving the traffic.

Such arrangements may provide the advantage that a protection switching event of the upstream node does not require traffic to be switched from the worker path to the protection path.

Preferably the method further including sharing at least one common intermediate node in the worker path and/or the protection path to communicate with the at least one access node. This may further improve the protection provided by the protection path.

The method may further include transmitting the traffic from the first or second distribution node to a plurality of access nodes. The method further includes multicasting the traffic from the first or second distribution node to the plurality of access nodes.

In a preferred embodiment the method further includes using a worker tree or a protection tree for at least a part of the worker path and/or the protection path.

Preferably the method further includes using Multi Protocol Label Switching (MPLS), or Multi Protocol Label Switching-Transport Profile (MPLS-TP), or an Ethernet Protocol for at least a part of the worker path and/or the protection path and/or the interface path.

Preferably the method further includes using a control message from one distribution node to the other distribution node to initiate switching traffic. Preferably the method further includes using the interface path for communication of the control message.

The method may further include using an edge node of a local network for at least one of the distribution nodes. The method may further include using an edge router of a core network for the upstream node.

In one embodiment the method further includes providing connection-oriented paths between the first and second distribution nodes and respective upstream nodes.

According to a third aspect of the invention there is provided a node arrangement for a communications network having at least one access node. The node arrangement comprising a first distribution node and a second distribution node having a connection-oriented interface path between them. The first distribution node operable to switch traffic from an upstream node to a connection-oriented worker path to the at least one access node. The second distribution node having a connection-oriented protection path to the at least one access node. The first distribution node operable to switch traffic from the upstream node to the interface path, and the second distribution node operable to switch traffic from the interface path to the protection path in response to detection of a fault in the worker path.

According to a fourth aspect of the invention there is provided a node arrangement for a communications network having at least one access node. The node arrangement comprising a first distribution node and a second distribution node having a connection-oriented interface path between them. The first distribution node having a connection-oriented worker path to the at least one access node. The second distribution node having a connection-oriented protection path to the at least one access node. The second distribution node operable to switch traffic from the upstream node to the interface path, and the first distribution node operable to switch traffic from the interface path to the worker path. The second distribution node operable to switch traffic from an upstream node in response to detection of a fault in the worker path.

In one aspect the second distribution node is operable to switch traffic from the upstream node to the interface path, and the first distribution node is operable to switch traffic from the interface path to the worker path in response to a change of the distribution node receiving the traffic.

In another aspect the first distribution node is operable to switch traffic from the upstream node to the worker path in response to a change of the distribution node receiving the traffic.

Preferably the worker path and/or the protection path have at least one common intermediate node for communication with the at least one access node.

The first or second distribution node may be operable to transmit traffic to a plurality of access nodes. The first or second distribution node are operable to multicast the traffic to the plurality of access nodes.

In a preferred embodiment at least a part of the worker path and/or the protection path include a worker tree and/or a protection tree.

Preferably at least a part of the worker path and/or the protection path and/or the interface path are operable to use Multi Protocol Label Switching (MPLS), or Multi Protocol Label Switching-Transport Profile (MPLS-TP), or an Ethernet Protocol.

Preferably the node arrangement is operable to initiate switching traffic using a control message from one distribution node to the other distribution node. Preferably the interface path is operable for communication of the control message.

At least one of the distribution nodes may be an edge node of a local network. The upstream node may be an edge router of a core network.

In one embodiment each of the first and second distribution nodes are arranged to have a connected-oriented communication path with a respective upstream node.

According to a fifth aspect of the invention there is provided a communications network using a method of the first or second aspects of the invention, or including a node arrangement of the third or fourth aspects of the invention.

DETAILED DESCRIPTION

FIG. 1shows a communications network, generally designated10, comprising a core network12in communication with a metro network14according to an embodiment of the invention. The core network12is a Layer 3 transport network, for example, based on routers, whereas the metro network14is comprised of switching devices, such as bridges, which support Layer 2 traffic. The metro network14is a Connection Oriented Packet Switched (CO-PS) network, and the core network may be a CO-PS network or a Connectionless (CL) network. It will be appreciated that the core network12may also be known as a backbone network, and the metro network14may also be known as a local network.FIG. 1shows the normal operation of the core network12and the metro network14when no faults are present.

The core network12has two edge routers16,18which are connected to respective edge switching devices20,22, such as Ethernet bridges, of the metro network14. The edge switching devices20,22may alternatively be termed as a first distribution node22and a second distribution node20. The two edge routers16,18may alternatively be termed as upstream nodes16,18relative to the switching devices20,22.

The switching devices20,22of the metro network14form respective root nodes of a connection-oriented protection tree21, and a connection-oriented worker tree23which both communicate with four access nodes24,26,28,30. The protection tree21and the worker tree23may also be known as protection and worker paths respectively. The access nodes24,26,28,30are connected to respective user nodes32,34,36,38for connection to users. The metro network14also includes a plurality of intermediate nodes40,42,44,46,48,50which are arranged between the edge switching devices20,22and the access nodes24,26,28,30.FIG. 1also shows that the two edge switching devices20,22are connected to one another by a connection-oriented interface path52.

The protection tree21comprises the edge switching device20which is in communication with the intermediate node40. The intermediate node40is in communication with each of the access node24and the intermediate node44. The access node24is in communication with the intermediate node42which is in communication with the access node26. The intermediate node40is in communication with the intermediate node44. The intermediate node44is in communication with each of the access node28and the intermediate node46. The intermediate node46is in communication with the access node30. The protection tree21is shown with a dotted line.

The worker tree23comprises the edge switching device22which is in communication with the intermediate node48. The intermediate node48is in communication with the intermediate node50. The intermediate node50is in communication with each of the access nodes24,26,28,30. The worker tree21is shown with a solid line.

Under normal operation of the communications network10the edge router18of the core network12is the master router, and the edge router16is in a standby condition. Traffic from the core network12to the metro network14passes from the edge router18to the edge switching device22and on to the worker tree23. Alternatively, traffic from the core network12to the metro network14passes from the edge router18to the edge switching device20and on to the edge switching device22via the interface path52where it then passes to the worker tree23. The protection tree21provides redundancy for the worker tree23. The edge switching devices20,22and the wider metro network14are not required to be aware which edge router16,18is performing as the master router. However, each edge switching device20,22must be aware whether the worker tree23or the protection tree21is operational and sending traffic to the access nodes24,26,28,30.

Whereas the two edge routers16,18are shown at the edge of the core network12, and the edge switching devices20,22are shown at the edge of the metro network14, these devices may actually be anywhere within the core network12or the metro network14respectively. Where certain parts of the core network12and the metro network14begin and end within the overall network10may vary such that in some embodiments the edge routers16,18may not actually be at the edge of the core network12but slightly within the core network12. Furthermore in some embodiments the edge switching devices20,22may not be actually at the edge of the metro network14but slightly within the metro network14.

It will also be appreciated that the paths between the edge switching devices20,22, the intermediate nodes40,42,44,46,48,50, the access nodes24,26,28,30and the user nodes32,34,36,38are via links which may be optical fibres, such that there may be many paths within the same link.

FIG. 2shows the communications network10ofFIG. 1with a failure54in the metro network14. The failure54causes a break in the connection between the intermediate nodes48and50of the worker tree23such that communication with the access nodes24,26,28,30using the worker tree23has been lost. The failure54causes a failure message56to be sent from the intermediate node48to the edge switching device22. Such behaviour is achieved by using messages which are part of the Operations, Administration and Maintenance (OAM) capabilities embedded within Ethernet as described in the standard ITU-T Y(1731). The failure message56may be for example, an Alarm Indication Signal (AIS), or an Automatic Protection Switching (APS) message. The failure notification can also be based on relevant OAM capabilities within the forwarding plane, such as Multi Protocol Label Switching (MPLS).

In the case where traffic is passed from the edge router18to the edge switching device22, the failure message56causes the edge switching device22to switch traffic to the edge switching device20via the interface path52and on to the protection tree21. In the case where the traffic is passed from the router18to the edge switching device20, the failure message56causes the edge switching device20to switch traffic on to the protection tree. In either case the protection tree21is utilised for sending traffic to the access nodes24,26,28,30in the even of the failure54.

FIG. 3shows the communications network10ofFIG. 1with a failure58in the core network12. The failure58may be a failure of the edge router18, or a failure of the link between the edge router18and the edge switching device22, or any other failure requiring traffic to be sent from the core network12to the edge switching device20of the metro network14. In this situation the standby edge router16now becomes the master router. The failure58causes a break in the connection between the edge router18of the core network12and the switching device22of the metro network14such that communication with the access nodes24,26,28,30using the worker tree23has been lost. The failure58causes a failure message60, such as an OAM message, to be sent from the edge router18of the core network12to the edge router16of the core network. The failure message60may be any alert message associated to any protocol operating between the edge routers16,18. The failure message60causes the edge router16to send traffic to the edge switching device20and then on to the edge switching device22via the interface path52. In this arrangement the worker tree23is still utilised for sending traffic to the access nodes24,26,28,30.

Since the failure58is not initiated in the metro network14no fail notification is sent to the edge switching devices20,22. The edge switching devices20,22continue processing traffic independent of the edge router that is acting as the master router. Both edge switching devices20,22are configured to forward traffic to the trees providing service to the access nodes24,26,28,30, which in this scenario is the worker tree23, whereby the protection tree21is in a standby condition.

FIG. 4shows the arrangement of the edge switching devices20,22of the communications network ofFIG. 1under normal operation is shown with no faults present, generally indicated at70. Each edge switching device20,22has a respective selector device72,74. The selector device72of the edge switching device20has an input port76to receive traffic from the edge router18, and an output port78to transmit traffic to the worker path23. The selector device72also has a protection port80which can operate to receive traffic from the edge switching device22or to transmit traffic to the edge switching device22via the interface path52. In a similar manner, the selector device74of the edge switching device22has an input port82to receive traffic from the edge router16, and an output port84to transmit traffic to the interface path21. The selector device74also has a protection port86which is in communication with the protection port80to receive traffic from the edge switching device20or to transmit traffic to the edge switching device20via the interface path52.

InFIG. 4the worker tree23is shown to be active and the selector device72is shown to be operational to select the traffic flow from the input port76and pass it to the output port78. The edge switching device22knows that the worker tree23is the worker path and is ready to select the traffic flow from the input port82and pass it to the output port84towards the edge switching device20via the protection path52.

FIG. 5shows the failure in the metro network14ofFIG. 2in greater detail. InFIG. 5like features to the arrangement ofFIG. 4are shown with like reference numerals. InFIG. 5the fault54is shown to prevent the worker tree23from operating. The fault message56propagates a failure indication and informs the selector device72that it cannot send traffic from the edge switching device20to the worker tree23. A failure message59also propagates from the selector device72to the selector device74to notify the failure of the worker path23. Alternatively the selector device74of the edge switching device22may be informed of the failure54by the access nodes24,26,28,30detecting a loss of connectivity. In response the selector device72switches to send the traffic received at the input port76to the protection port80so that it is passed to the edge switching device22via the interface path52. The selector device74of the edge switching device22then operates to select the traffic flow from the protection port86and pass it to the output port84to the protect tree21. In an alternative arrangement when traffic is received from the core network12at the edge switching device22, the selector device74can select the traffic flow from the input port82of the selector device74and pass it to the output port84and on to the protect tree21. In either scenario the edge routers16,18of the core network are not aware of the failure54.

FIG. 6shows the failure in the core network12ofFIG. 3in greater detail. InFIG. 6like features to the arrangement ofFIG. 4are shown with like reference numerals. InFIG. 6the failure58in the core network12is shown to prevent the traffic from being received by the input port76of the selector device72. In response the selector device74receives traffic at the input port82from the edge router16and passes it to the protection port86and on to the selector device72via the interface path52. In response the selector device72then sends the traffic received at the protection port80to the output port78to the worker tree23. Both edge switching devices20,22know that the worker tree23is the worker path and forward traffic accordingly. Failure notification between the edge switching device20and the edge switching device22is optionally provided by the fault message59. The selector device74may also select the traffic flow from the input port82and pass it to the output port84and on to the protect tree21in case of failure of the working path23.

In the arrangements ofFIGS. 4-6the edge switching devices20,22are required to know which of the worker tree23and the protection tree21are operational at any given time so that traffic is passed to the access nodes24,26,28,30via the appropriate tree. Such notification is most conveniently performed using the OAM message56, and to optionally by the OAM message59. It will be appreciated that the interface path52is shown as a bidirectional link which may be provided by two unidirectional links in either direction.

FIG. 7is a flow diagram illustrating a method of providing path protection according to an embodiment of the invention, generally designated90. The method90relates to the metro network14which has a plurality of nodes including at least one access node, such as access nodes24,26,28,30. The method comprises setting up a connection-oriented worker path shown at92, which may be the worker tree23which permits traffic to flow between the first distribution node22and the at least one access node24,26,28,30. The first distribution node22is in communication with a node of the core network12which may be the edge router18. The method then includes setting up a connection-oriented protection path shown at94, which may be the protection tree21to permit traffic to flow between the second distribution node20of the metro network14and at least one access node24,26,28,30. The method then includes setting up a connection-oriented interface path52between the first and second distribution nodes as shown at96.

In one arrangement the method includes switching traffic from an upstream node16,18to the worker path at the first distribution node22as shown at98. The method then includes switching traffic from the upstream node16,18to the interface path52, and switching traffic from the interface path52to the protection path21at the second distribution node20in response to detecting a fault54in the worker path23, as shown at100. The method may further include switching traffic from the upstream node16,18to the interface path52at the second distribution node20and switching traffic from the interface path to the worker path23at the first distribution node22in response to a change of the distribution node20,22receiving the traffic, as shown at106

In another arrangement the method includes switching traffic from an upstream node16,18to the interface path52at the second distribution node20and switching traffic from the interface path52to the worker path23at the first distribution node22, as shown at102. The method then includes switching traffic from the upstream node16,18to the protection path21at the second distribution node20in response to detecting a fault54in the worker path23, as shown at104. The method may include switching traffic from the upstream node16,18to the worker path23at the first distribution node20in response to a change of the distribution node20,22receiving the traffic, as shown at108.

The method may include using at least one common intermediate node40,42,44,46,48,50in the worker path23and/or the protection path21to communicate with the at least one access node24,26,28,30. This may further improve the protection offered by the protection tree21.

It will be understood that the worker tree23and the protection tree21are both trees that may implement rooted multipoint Ethernet Virtual Connections (EVC), also known as point-to-multipoint EVCs. This may alternatively be known as a one-to-many connection, or broadcasting, or multicasting. The method may include using Multi Protocol Label Switching (MPLS), or Multi Protocol Label Switching-Transport Profile (MPLS-TP), or an Ethernet Protocol for at least a part of the worker path23and/or the protection path21and/or the interface path52.

The method may further include using a control message from one distribution node20,22to the other distribution node20,22to initiate switching traffic. The interface path52may be used for communication of the control message.

The above embodiment ofFIGS. 1-7describe 1:1 protection whereby the protection tree21is provisioned such that traffic is only switched to it upon receipt of the failure message56. Such 1:1 protection is more desirable in view of the large bandwidth that tree architectures use. It will be appreciated that the above embodiment may be used with 1+1 protection whereby traffic in the metro network14is actively transmitted on both the worker tree23and the protection tree21via the interface path52. With 1+1 protection the access nodes24,26,28,30are responsible for deciding which traffic flow to use by switching to the desired traffic flow from the worker tree23or the protection tree21. In the case of 1+1 protection for the failure54in the worker tree23as shown inFIG. 2the failure message56to notify the distribution nodes20or22is not required. Should such a failure message56be received by the distribution nodes20or22no action is necessary. For 1+1 protection in the case of the failure54, a Loss of Connectivity (LOCV) OAM message may be received at each of the access nodes24,26,28,30to indicate switching to the protection tree21. Overall from the perspective of the network operator the 1:1 protection is more appealing due to bandwidth saving considerations inside the metro network14.

For the provision of 1+1 protection the method includes transmitting the traffic from each of the two edge switching devices20,22of the metro network14to at least one access node24,26,28,30of the metro network14using the working path and the protection path. The method then includes selecting the traffic flow to use at the at least one access node24,26,28,30.

In the case of 1+1 protection it will be appreciated that the protection mechanisms described with reference toFIG. 1-7allow real time updating of the forward databases of the edge switching devices20,22. Such real time updating provides the added advantage that the possibility that traffic is lost in the event of the failure54,58is reduced. This is because the destination of the replicated traffic is always stored in the forward database of either of the edge switching devices20,22. This means that the connectivity with the user nodes32,34,36and38is improved and loss of traffic is minimised. The embodiments ofFIGS. 1-7with 1:1 protection do not have this added advantage because the traffic on the protection path is not copied and the protection path is merely provisioned.

It will be appreciated that the above embodiments described inFIGS. 1-7may be utilised with the known Virtual Router Redundancy Protocol (VRRP) whereby the edge router16is connected to each of the switching devices20,22, and the edge router18is connected to each of the switching devices20,22. Such a VRRP is an example of a Dual Homing Configuration. An advantage of the above described methods and apparatus is the ability to provide connection-oriented tree protection, for example, when a dual router configuration is used. The prior art VRRP used with tree connections typically require four tree connections to be configured and managed. In contrast, the embodiments of the invention described above only required two tree connections to be configured and managed which are the worker tree23from the edge switching device22, and the protection tree21from the edge switching device20. Such a reduction in Is trees from four to two decreases complexity in configuration and management of the network10.

It will be further appreciated that the above embodiments may be utilised when only one edge router is used in the core network12which is connected to each of the switching devices20,22. In this example the above described embodiments may be used to protect trees21,23from each of the switching devices20,22.

The above-described embodiments are particularly, but not exclusively, relevant to tree networks which can support video multicasting via a tree arrangement. The tree is a point-to-multipoint technology which is used to multicast traffic from the edge switching devices20,22, also known as head-end nodes, to the access nodes24,26,28,30.

The above-described embodiments have the advantage that the core network is not involved in protection mechanisms implemented by the metro network. Furthermore the edge switching devices20,22of the metro network14are not required to participate in protocols or protection mechanisms related to dual homing configuration such as VRRP. In this manner the protection mechanisms of the core network12and the metro network14are largely independent. Switch traffic between the edge switching devices20,22via the interface path52provides cost effective and efficient protection which consumes minimised resource when compared to prior art solutions. This may reduce cost and complexity of protection switching and may assist telecommunications operators to guarantee levels of service and quality of service.

Providing protection according to the embodiments of the invention has the advantage to improve network stability because traffic in the network is not rerouted unnecessary, which reduces inefficiencies in the network. For example, if traffic is rerouted there may be an increase of traffic congestion particularly in the case of multicast traffic composed of video or television services. Typically such video or television services use a dedicated protocol for traffic optimization such as Internet Group Management Protocol (IGMP) whereby protection switching usually requires such protocols to update their status to a new topology. In the case of protection switching for IGMP it is necessary to send video channel request messages to all nodes in a multicast protection path which results in a burst of control plane messages. Such a burst of control plane messages may cause traffic delivery inefficiencies to arise. A reduction of unnecessary protection switching, as provided by the embodiments of the present invention, reduces such inefficiencies and the associated disruptions in video or television services.