IGMP Fastleave via Listener Reference Count
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Solution Overview
Problem
Standard IGMP protocols experience latency issues during channel zapping, leading to unnecessary resource accumulation on CPE devices and potential stream loss for other clients when one device leaves a multicast group, as the gateway immediately reports leaving the group without verifying if it is the last listener.
Innovation Solution
Implementing a listener reference count system where a gateway proxy maintains a database of listeners for each multicast group, allowing immediate leave reporting if the leaving device is the last listener, and sending a query otherwise to verify the presence of other listeners.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the gateway immediately reports leaving the multicast group when receiving a leave report, then the leave latency is reduced, but other clients listening to the same group will lose the stream
Solution Approach 1:
The patent introduces an intermediary verification mechanism where the gateway sends a leave report to a verification device (CMTS or another gateway) before actually leaving the multicast group. This intermediary step allows the gateway to verify whether it is the last listener of the group, thereby preventing premature group departure that would cause stream loss for other clients while still enabling fast leave when appropriate.
2Reliability
If the gateway waits for query expiration to verify last listener status, then other clients are protected from stream loss, but leave latency increases and resources accumulate
Solution Approach 1:
The patent applies preliminary action by performing a verification check before the gateway actually leaves the multicast group. The gateway sends a leave report to the verification device in advance, receives confirmation of its last listener status, and only then proceeds to leave the group. This preliminary verification prevents resource accumulation and unnecessary group membership maintenance while avoiding stream loss for other clients.
3Loss of time
If normal fastleave is enabled, then leave latency is reduced, but resource accumulation occurs on CPE and headend devices
Solution Approach 1:
The patent implements a feedback mechanism where the gateway receives verification results from the CMTS or another gateway about its last listener status. Based on this feedback, the gateway intelligently decides whether to leave the multicast group immediately or wait for query expiration. This feedback-driven approach prevents resource accumulation by ensuring the gateway only leaves when confirmed as the last listener, while still enabling fast leave when appropriate.
Data Source
AI summary
Methods, systems, and computer readable media described herein can be operable to facilitate an IGMP fastleave using a listener reference count. A gateway proxy saves each listener for every specific multicast group, thus the gateway knows if a listener is the last one in the group when it receives a leave report from a listener. The gateway leaves the group immediately without sending specific query if the leave report comes from the last listener of the current group, thereby significantly reducing the leave latency. Otherwise, the standard procedure wins, and the gateway sends out a specific query when the leave report is not from the last listener.