Label switched routing system and method

A method to be executed at a node within a network of interconnected nodes within which a hierarchical plurality of LSP/FA-LSPs has been defined of performing label switching of packets having an LSP label and having a possibly empty components label, the method comprising:

• the node maintaining information for each LSP/FA-LSP comprising an LSP label, an identification of a source node, transit nodes if any, and a destination node, and for each LSP/FA-LSP an identification of all possible next lowest level LSP/FA-LSPs which may use the LSP/FA-LSP;
• the node obtaining the LSP label, the LSP label defining a current LSP/FA-LSP of a packet to be routed;
• the node obtaining the components label of the packet;
• the node looking up the information for the current LSP/FA-LSP;
• in the event the node is a source node of a next higher level FA-LSP of which the current LSP/FA-LSP forms a component, switching the LSP label to contain the label of the next higher level FA-LSP which is used by the current LSP/FA-LSP, and adding to the components label to include in an additional component identifier an identifier of the current LSP/FA-LSP;
• in the event the node is the destination node of the current LSP/FA-LSP, determining from the components label and the maintained information another LSP label for a lower level LSP/FA-LSP from a component identifier for the lower level and removing the component identifier for the lower level from the components label, and changing the LSP label to the another LSP label for the lower level hierarchy determined from the components label;
• the node re-applying the components label to the packet;
• the node re-applying the LSP label to the packet;
• and
• the node changing an output interface such that the packet is forwarded to an appropriate next node.

A packet routing/switching system comprising:

• a network of interconnected nodes through which is defined a hierarchical plurality of label switched paths (LSP)/forwarding adjacency-label switched paths (FA-LSP) from a lowest (least-nested) level in which LSPs are defined between edge nodes of the network to a highest (most-nested) level, each LSP/FA-LSP comprising a respective sequence of nodes comprising at least a source node and a destination node and possibly one or more transit nodes;
• wherein each edge node is adapted to maintain a mapping between each packet flow entering the network at the edge node and a respective first LSP of the hierarchical plurality of LSP/FA-LSPs defined between the edge node and a destination node in the network for the packet flow;
• wherein each edge node is further adapted to add to each packet of a given packet flow switched routing information comprising an LSP label identifying the respective first LSP to which the packet flow is mapped and to send the packet to subsequent node(s) in the sequence of nodes defined for the respective first LSP;
• wherein each node other than an edge node is adapted to perform label switching by:
• i) if the node is a source node of a higher level FA-LSP than the LSP/FA-LSP identified by the LSP label of the packet, changing the LSP label in the label switched routing information to indicate the source node of the higher level FA-LSP, and including in the label switched routing information hierarchy information in respect of all lower level LSP/FA-LSPs in the hierarchy leading up to the higher level FA-LSP and forwarding the packet to the next node in the sequence of nodes defined for the higher level FA-LSP;
• ii) if the node is only a transit node, forwarding the packet to the next node in the sequence of nodes defined for the LSP/FA-LSP identified by the LSP label;
• iii) if the node is a destination node of a higher level FA-LSP, changing the LSP label in the label switched routing information to indicate the source node of the next lower level LSP/FA-LSP indicated by the hierarchy information, and changing the hierarchy information to include only hierarchy information in respect of LSP/FA-LSPs in the hierarchy leading up to but not including the next lower level LSP/FA-LSP, and forwarding the packet to the next node in the sequence of nodes defined for the next lower level LSP/FA-LSP.

A network node within a network of interconnected nodes within which a hierarchical plurality of LSP/FA-LSPs has been defined, the network node comprising:

• a network information repository comprising for each LSP/FA-LSP an LSP label, an identification of a source node, transit nodes if any, and a destination node, and for each LSP/FA-LSP an identification of all possible next lowest level LSP/FA-LSPs which may use the LSP/FA-LSP;
• a packet router adapted to route each packet by:
• obtaining an LSP label of the packet, the LSP label defining a current LSP/FA-LSP of the packet;
• obtaining a components label of the packet;
• looking up the information in the network information repository for the current LSP/FA-LSP;
• in the event the node is a source node of a next higher level FA-LSP of which the current LSP/FA-LSP forms a component, switching the LSP label to contain the label of the next higher level FA-LSP which is used by the current LSP/FA-LSP, and adding to the components label to include in an additional component identifier an identifier of the current LSP/FA-LSP;
• in the event the node is the destination node of the current LSP/FA-LSP, determining from the components label and the maintained information another LSP label for a lower level LSP/FA-LSP from a component identifier for the lower level and removing the component identifier for the lower level from the components label, and changing the LSP label to the another LSP label for the lower level hierarchy determined from the components label;
• re-applying the components label to the packet;
• re-applying the LSP label to the packet;
• and
• changing an output interface such that the packet is forwarded to an appropriate next node.