Reliable Multicast via Redundant Unicast Overlay
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Solution Overview
Problem
Traditional link state routing protocols, such as OSPF and IS-IS, experience prolonged convergence times when a link or router fails, leading to delayed adaptation of forwarding tables, which can result in traffic loss and negatively impact VoIP and multimedia applications. Service providers require faster failure detection and recovery times, typically less than 50 milliseconds.
Innovation Solution
The implementation of a parallel connection-oriented distribution tree using reliable overlay connections between adjacent nodes of a multicast distribution tree, allowing for the creation of a redundant network path for multicast traffic. This involves creating TCP connections between routers to replicate and ensure the reliable delivery of multicast packets, with mechanisms for acknowledging packet receipt and filling gaps in packet sequences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional link state routing protocols (OSPF, IS-IS) are used for multicast traffic forwarding, then routing convergence is achieved through shortest path recalculation, but convergence time is prolonged (500 milliseconds to several seconds)
Solution Approach 1:
The patent establishes TCP connections between adjacent routers in the multicast distribution tree in advance, before failures occur. These pre-established connections enable immediate packet forwarding upon failure detection, eliminating the need for time-consuming shortest path recalculation and achieving convergence times under 50 milliseconds
Solution Approach 2:
The patent creates a parallel connection-oriented distribution tree that mirrors the traditional multicast distribution tree. Multicast packets are replicated and sent through both the traditional tree and the TCP-based overlay network, ensuring continuous delivery during failures while maintaining protocol independence
2Reliability
If redundant unicast overlay network with TCP connections is established between adjacent routers, then packet delivery reliability is improved and convergence time is reduced, but network complexity increases
Solution Approach 1:
The patent introduces a TCP-based overlay network as an intermediary layer between traditional multicast routers. This overlay provides reliable packet delivery mechanisms (acknowledgments, retransmissions, gap filling) without modifying the underlying multicast routing protocols, thereby improving reliability while maintaining protocol independence and limiting complexity increase to the overlay layer only
Data Source
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AI summary
Techniques are described for redundantly forwarding encapsulated multicast traffic of a multicast distribution tree, using reliable overlay connections established between adjacent nodes of the multicast distribution tree. An example router of this disclosure is configured to receive first multicast packets of a multicast flow via a multicast distribution tree, to receive second multicast packets of the multicast flow via a transmission control protocol (TCP) connection of a connection-oriented distribution tree implemented in parallel to the multicast distribution tree, and in response to determining that the LHR has received a multicast packet of the first multicast packets via the multicast distribution tree out of order to create a gap of one or more of the first multicast packets for the multicast flow, forward, to at least one interested receiver positioned downstream of the router, the second multicast packets.