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Method for hitless Internet multicast forwarding using shared tree-to-source tree switching

IP.com Disclosure Number: IPCOM000146689D
Publication Date: 2007-Feb-19
Document File: 4 page(s) / 65K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for hitless Internet multicast forwarding using shared tree-to-source tree switching. Benefits include improved functionality and improved reliability.

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Method for hitless Internet multicast forwarding using shared tree-to-source tree switching

Disclosed is a method for hitless Internet multicast forwarding using shared tree-to-source tree switching. Benefits include improved functionality and improved reliability.

Background

      Internet multicasting is standardized by several specifications, including the following:

•     “Host extensions for IP multicasting”, RFC1112, dated August 1989 by Internet Engineering Task Force

•     “Protocol Independent Multicast-Sparse Mode (PIM-SM): Protocol Specification”, RFC2362, dated June 1998 by Internet Engineering Task Force

      Multitasking standards specify two different service models, any source multicast (ASM) and source-specific multicast (SSM). ASM is the conventional multicast approach that includes a datagram with a destination Internet multicast address, G, that is delivered to all hosts that have requested the datagram. Its transmission path is called a multicast distribution tree and is one of two types, a source tree or a shared tree.

      A source tree is the shortest path tree. Multicast routing protocols look up the source address, S, and the destination address, G, to build SSM trees using an (S,G) path. They are not shared and are unidirectional. 

      A shared tree is a group-based (*,G) tree. Multicast routing protocols look up the destination address, G. Multiple sources send data to G using the same multicast distribution tree. Shared trees are either unidirectional or bidirectional.

      Sparse-mode multicast distribution requires switching from the source tree to the shared tree and back to the source tree. The switching is conventionally coordinated by control plane protocols. These protocols perform the packet data unit (PDU) exchanges for disconnecting from one tree and joining the other tree. The transport mechanism for the PDUs is unreliable and error recovery is based on timers and retransmission. Joining one tree and leaving the other tree depends upon the robustness index and congestion level of the network (see Figure 1).

      A problem occurs with the algorithm when the packet is transferred using the shared tree. The packet arrives at the address (S,G) and can be dropped due to random pattern filter (RPF) check failure. Alternatively, the packet can be routed to the control plane and overload it. While switching over from a shared tree to a source tree, the data plane must be synchronized with the control plane. When the packet has exited from the shared tree, the control plane must create an appropriate entry for the source tree.

     

Description

      The disclosed method is hitless Internet multicast forwarding using shared tree-to-source tree switching. The method decouples the data plane operation from control plane operation. An embedded group (*,G) lookup is performed in case of RPF fail...