Multicast Preview Streams for Latency Reduction in CDN Switching

Solution Overview

Problem

Multicast content-delivery networks experience significant latency when subscribers switch between streams due to the time-consuming process of setting up and maintaining multicast distribution trees, particularly in handling control packets like IGMP reports and PIM joins.

Innovation Solution

Generating and multicasting 'preview multicast streams' that contain pre-recorded content of desired streams, allowing subscribers to receive pre-recorded content during the setup of new distribution trees, thereby minimizing latency when switching between streams.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If control packet processing is performed for each multicast stream switch, then the multicast distribution tree can be properly set up, but substantial latency is introduced due to the time-consuming processing of IGMP reports and PIM joins

Engineering Contradiction:

Improvemulticast distribution tree setupVSAvoidlatency during stream switching

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent applies preliminary action by pre-establishing multicast distribution trees for multiple streams before the subscriber actually needs to switch between them. The system maintains ready-to-play content and pre-configured routing paths in advance, so when a stream switch is requested, the subscriber can immediately receive content without waiting for real-time tree setup. This eliminates the latency caused by processing control packets at the moment of switching.

Inventive Principle:

Principle #10Preliminary action

2Adaptability or versatility

If multiple multicast streams are subscribed to within a time window, then the subscriber can access multiple channels, but additional processing and bandwidth allocation are required leading to increased latency

Engineering Contradiction:

Improvemulti-channel switching capabilityVSAvoidprocessing time for multiple streams

Core Design Contradiction:

Adaptability or versatilityVSLoss of time

Solution Approach 1:

The system pre-establishes multiple multicast distribution trees for different streams that the subscriber might want to switch between. By maintaining ready-to-play content and pre-configured paths for multiple streams simultaneously, the system enables rapid switching without requiring additional real-time processing when the subscriber switches between channels within a time window.

Inventive Principle:

Principle #10Preliminary action

3Adaptability or versatility

If control packets are processed in real-time for each stream switch, then the multicast routing protocol can adapt to dynamic membership, but substantial processing time is consumed by routers

Engineering Contradiction:

Improvedynamic multicast group membershipVSAvoidstream switching speed

Core Design Contradiction:

Adaptability or versatilityVSProductivity

Solution Approach 1:

The patent applies preliminary action by pre-establishing multicast distribution trees for multiple streams before the subscriber actually needs to switch between them. The system maintains ready-to-play content and pre-configured routing paths in advance, so when a stream switch is requested, the subscriber can immediately receive content without waiting for real-time tree setup. This eliminates the latency caused by processing control packets at the moment of switching.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS7995576B2Method and system for reducing latency in a multi-channel multicast streaming environment in content-delivery networks

Publication Date: 2011.08.09 CISCO TECHNOLOGY INC

AI summary

Methods, systems and apparatus for reducing apparent latency in content-delivery networks are provided. Sources multicast certain ‘preview multicast streams’ to multiple subscribers. These preview multicast streams provide pre-recorded content of multicast streams. When a subscriber switches to a desired multicast stream, pre-recorded content of the desired multicast stream is reconstructed from a preview multicast stream. Thereafter, the pre-recorded content is played during the setup of the new multicast distribution tree to minimize latency. Once the distribution tree is setup, live content of the desired multicast stream is made available to the subscriber.