Selective Join Forwarding for Multicast Latency Reduction

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Solution Overview

Problem

In L2 multicast multi-tier networks, channel-switching can lead to user experience degradation due to high control plane traffic and propagation delays, especially when hosts leave a multicast group, causing multiple messages to be exchanged through cascading switches.

Innovation Solution

Implementing selective join forwarding and distributed querying host functionality to reduce control plane traffic by tracking join messages, consolidating them when meeting a predetermined threshold, and distributing querying responsibilities among intermediate switches.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If IGMP functionality is implemented in cascading switches to handle multicast group management, then multicast group management capability is improved, but control plane traffic and processing latency increase due to multiple CPU lookups and message propagation through each switch level

Engineering Contradiction:

Improvemulticast group management capabilityVSAvoidcontrol plane latency

Core Design Contradiction:

Adaptability or versatilityVSLoss of time

Solution Approach 1:

The patent extracts the IGMP query host functionality from the cascading switch hierarchy and consolidates it at the root switch level. This eliminates the need for each intermediate switch to perform CPU lookups and forward IGMP messages, thereby reducing control plane latency while maintaining multicast group management capability.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent creates an asymmetric architecture where the root switch performs all IGMP processing operations while intermediate switches simply forward multicast data packets. This asymmetric division of labor eliminates the need for symmetric IGMP processing at each switch level, reducing control plane traffic and latency.

Inventive Principle:

Principle #4Asymmetry

2Reliability

If multiple messages are exchanged between hosts and IGMP querying host through cascading switches when a host leaves a multicast group, then multicast group membership accuracy is improved, but user experience deteriorates due to traffic loss and screen freezes

Engineering Contradiction:

Improvemulticast group membership accuracyVSAvoiduser experience during channel switching

Core Design Contradiction:

ReliabilityVSEase of operation

Solution Approach 1:

The patent implements preliminary action by having the root switch maintain up-to-date multicast group membership information in advance. When a host leaves a group, the root switch already has the current membership state and can immediately update forwarding rules without waiting for multiple IGMP message exchanges, thereby preventing traffic loss and screen freezes.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The root switch acts as an intermediary that consolidates all IGMP messaging between hosts and the network. By centralizing IGMP processing at the root switch, the patent eliminates the need for multiple message exchanges through intermediate switches, reducing latency and improving user experience while maintaining membership accuracy.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Loss of information

If join messages from multiple hosts are forwarded to the IGMP querying host through intermediate switches, then multicast group membership tracking is improved, but control plane traffic increases proportionally with the number of hosts and switch levels

Engineering Contradiction:

Improvemulticast group membership tracking accuracyVSAvoidcontrol plane traffic volume

Core Design Contradiction:

Loss of informationVSQuantity of substance

Solution Approach 1:

The patent merges all join message processing at the root switch level. Instead of each intermediate switch forwarding individual join messages upward through the hierarchy, all hosts send join messages directly to or through the root switch, which consolidates membership tracking. This combining approach maintains accurate membership tracking while dramatically reducing control plane traffic volume.

Inventive Principle:

Principle #5Merging (Combining)

Data Source

PatentUS20250047517A1Handling multicast device latencies through selective join forwarding

Publication Date: 2025.02.06 HEWLETT PACKARD ENTERPRISE DEV LP

AI summary

A switch receives a first query which requests a response from all hosts in the network, wherein the switch is a next-hop switch of a first set of the hosts in a multicast group, wherein the first query is an Internet Group Management Protocol (IGMP) all-host query message, and wherein the first query is generated by an IGMP querying host and transmitted via one or more intermediate switches. The switch tracks join messages received from the first set of the hosts in response to the first query, wherein a respective join message indicates that a corresponding host is to remain in the multicast group. Responsive to determining that the tracked join messages meet a predetermined threshold, the switch consolidates the tracked join messages by forwarding a reduced number of join messages, thereby reducing a total number of join messages propagated to the IGMP querying host via the intermediate switches.