The Internet is a massive network of networks in which computers communicate with each other via use of different communication protocols. The Internet includes packet-routing devices, such as switches, routers and the like, interconnecting many computers. To support routing of information such as packets, each of the packet-routing devices typically maintains routing tables to perform routing decisions in which to forward traffic from a source computer, through the network, to a destination computer.
One way of forwarding information through a provider network over the Internet is based on MPLS (Multiprotocol Label Switching) techniques. In an MPLS-network, incoming packets are assigned a label by a so-called LER (Label Edge Router) receiving the incoming packets. The packets in the MPLS network are forwarded along a predefined Label Switch Path (LSP) defined in the MPLS network based, at least initially, on the label provided by a respective LER. At internal nodes of the MPLS-network, the packets are forwarded along a predefined LSP through so-called Label Switch Routers. LDP (Label Distribution Protocol) and/or RSVP-TE are used to distribute appropriate labels for label-switching purposes.
Each Label Switching Router (LSR) in an LSP between respective LERs in an MPLS-type network makes forwarding decisions based solely on a label of a corresponding packet. Depending on the circumstances, a packet may need to travel through many LSRs along a respective path between LERs of the MPLS-network. As a packet travels through a label-switching network, each LSR along an LSP strips off an existing label associated with a given packet and applies a new label to the given packet prior to forwarding to the next LSR in the LSP. The new label informs the next router in the path how to further forward the packet to a downstream node in the MPLS network eventually to a downstream LER that can properly forward the packet to a destination.
MPLS service providers have been using unicast technology to enable communication between a single sender and a single receiver in label-switching networks. The term unicast exists in contradistinction to multicast, which involves communication between a single sender and multiple receivers. Both of such communication techniques (e.g., unicast and multicast) are supported by Internet Protocol version 4 (Ipv4).
Service providers have been using so-called unicast Fast Reroute (FRR) techniques for quite some time to provide more robust unicast communications. In general, fast rerouting includes setting up a backup path established prior to the occurrence of the failure for transmitting data in the event of a network failure so that a respective user continues to receive data even though the failure occurs.
One of the key drivers for the deployment of MPLS Traffic Engineering Point to Multipoint is the ability to provide fast restoration in case of link/shared risk link group (SRLG)/node failure for sensitive traffic such as video (particularly sensitive to traffic loss: even with forward error correction (FEC) techniques, the impact of a link or node failure on the traffic is very significant and requires local protection recovery techniques).
MPLS TE Fast Reroute can be used to protect a P2MP (Point To Multipoint) LSP in case of link, SRLG and node failure if the node is not a branching node. Conversely, if the node is a branching node (thus performing the traffic replication), the problem becomes more complex and two methods can be used. The first method used makes use of point to point (P2P) backup tunnels to protect a point-to-multipoint (P2MP) TE LSP against a branching node failure, and the second method used makes use of P2MP backup tunnels to protect a P2MP TE LSP against a branching node failure. Furthermore additional constraints such as the optimal location for restoration (the head-end of the backup, in other words the repairing node) make the problem even more difficult to solve.