TECHNICAL FIELD

Examples of the present disclosure relate to tearing down a label switched path (LSP) through a communications network.

BACKGROUND

Some communication networks, such as for example Optical Transport Networks specified in the ITU-T G.709 recommendation, may have a control plane to control nodes of such networks to reserve (set up) new paths by reserving resources at each node.

The RSVP (Resource reSerVation Protocol) [RFC2205] signaling protocol is a protocol for messages sent between nodes to set up new paths. RSVP-TE (RSVP-Traffic Engineering) [RFC3209] extends RSVP in order to provide a way to establish Label Switched Paths (LSPs) in MPLS (Multi-Protocol Label Switching). To reserve a path, an RSVP-TE (Traffic Engineering) PATH message, in the form of a Generalized Label Request, is sent out from a first node on the path (which acts as an ingress node) via one or more intermediate nodes along the proposed path, to the last node along the path (acting as an egress node). The egress node returns an RSVP-TE RESV message to the ingress node, back along the path via the same nodes, to cause the nodes along the path to confirm the reservation of resources, such as for example bandwidth on switch paths and ports, for the requested path, for traffic of a signal type specified in the message.

In some example communication networks, there may be multiple network domains, and a LSP may traverse multiple domains. In such examples, a node at which a path enters a domain may be referred to as an ingress node for the domain, and a node at which a path leaves a domain may be known as an egress node for the domain.

SUMMARY

One aspect of the present disclosure provides a method for tearing down a label switched path (LSP) through a communications network. The method comprises sending a first message towards an egress node of the LSP informing nodes of the LSP and the egress node of a tear down of the LSP, determining that one of the nodes of the LSP has not forwarded the first message along the LSP, and sending a second message to a controller of the communications network to cause the controller to communicate directly with the one of the nodes to inform the one of the nodes of the tear down of the LSP.

Another aspect of the present disclosure provides a method for tearing down a label switched path (LSP) through a communications network. The method comprises, in response to a first message being sent from an ingress node of the LSP towards an egress node of the LSP informing nodes of the LSP and the egress node of a tear down of the LSP, receiving a notification from a first node of the LSP that a second node of the LSP has not forwarded the first message along the LSP. The method also comprises sending, in response to the notification, a second message directly to one or more nodes in the LSP later than the first node informing the one or more nodes in the LSP later than the first node of the tear down of the LSP.

A further aspect of the present disclosure provides apparatus for tearing down a label switched path (LSP) through a communications network. The apparatus comprises a processor and a memory. The memory contains instructions executable by the processor such that the apparatus is operable to send a first message towards an egress node of the LSP informing nodes of the LSP and the egress node of a tear down of the LSP, determine that one of the nodes of the LSP has not forwarded the first message along the LSP, and send a second message to a controller of the communications network to cause the controller to communicate directly with the one of the nodes to inform the one of the nodes of the tear down of the LSP.

A still further aspect of the present disclosure provides apparatus for tearing down a label switched path (LSP) through a communications network. The apparatus comprises a processor and a memory. The memory contains instructions executable by the processor such that the apparatus is operable to receive, in response to a first message being sent from an ingress node of the LSP towards an egress node of the LSP informing nodes of the LSP and the egress node of a tear down of the LSP, a notification from a first node of the LSP that a second node of the LSP has not forwarded the first message along the LSP, and send, in response to the notification, a second message directly to one or more nodes in the LSP later than the first node informing the one or more nodes in the LSP later than the first node of the tear down of the LSP.

