IPTV Terminal Synchronization via Low-Delay Feedback Channels
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Solution Overview
Problem
Existing IPTV systems face challenges in achieving group-synchronization of terminals without modifying the network infrastructure, particularly due to the difficulty in synchronizing local clocks and the limited scalability of central synchronization masters.
Innovation Solution
A method that utilizes low-delay communication channels between terminals and a synchronization unit to calculate and transmit delay information, allowing terminals to synchronize their outputs without the need for an absolute clock or network-wide variable delay buffers, by using a separate high-quality communication channel for synchronization information exchange.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a central synchronization master is used to collect timing information from all terminals, then group-synchronization can be achieved, but the system complexity increases and scalability is limited
Solution Approach 1:
Each terminal independently determines its own synchronization delay by analyzing the timing of synchronization packets received from other terminals. The terminal uses its local clock and buffer to calculate the delay needed to align its media stream output with other terminals, eliminating the need for a central synchronization master to make these decisions.
Solution Approach 2:
Terminals exchange synchronization information packets that contain timing data about when media units were received and output. Each terminal uses this feedback from other terminals to adjust its own variable delay buffer, creating a distributed feedback loop that achieves synchronization without central control.
2Reliability
If local clocks are synchronized using an absolute or central clock, then inter-destination synchronization can be achieved, but the implementation becomes difficult in practice
Solution Approach 1:
Instead of directly synchronizing local clocks to an absolute clock, the invention uses synchronization packets as an intermediary carrier. These packets contain timing information that allows terminals to indirectly coordinate their output timing without requiring direct clock synchronization or access to an absolute time reference.
Solution Approach 2:
The synchronization mechanism copies timing information from received media units into synchronization packets. Terminals exchange these copied timing data rather than exchanging actual clock signals, making the synchronization process easier to implement while achieving the same effect.
3Reliability
If dedicated multicast channels are used for distributing synchronization control packets, then synchronization can be achieved, but the scalability is limited due to limited network resources
Solution Approach 1:
The variable delay buffer serves multiple functions: it not only delays media packets for timing adjustment but also stores synchronization information packets from other terminals. This multi-functionality eliminates the need for separate dedicated multicast channels for synchronization, allowing the same network infrastructure to handle both media streaming and synchronization control.
Solution Approach 2:
The invention merges the synchronization control function with the existing media stream transmission. Synchronization packets are integrated into the same network traffic flow as media packets, using the same multicast channels and network resources, thereby improving scalability without sacrificing synchronization reliability.
Data Source
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AI summary
A Method is described for synchronizing the output of terminals. The method according to the invention may be used in a system comprising a station, which transmits a packetized stream to at least a first and second terminal. Each terminal comprises a variable delay unit and each terminal is connected through a low-delay communication channel to at least one synchronization unit for calculating delay information. Further, each terminal is capable of determining media reference information of a received media unit from the stream. The method comprising the steps of providing one or more low delay communication channels between the terminals and a synchronization unit; the synchronization unit calculating delay information on the basis of synchronization information received from the terminals via the one or more low delay communication channels; and transmitting the delay information to at least one of the terminals allowing the at least one terminal to delay its output such that the output of the terminals are substantially synchronized.