Source Packet Bridge for Isochronous Data Synchronization
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Solution Overview
Problem
The IEEE 1394.1 standard requires a common time base to be distributed across the network for synchronizing isochronous data streams, which is challenging due to variations in time bases between buses, leading to overruns and underruns, and is not optimal as it necessitates a cycle master on each bus and network-wide propagation of the master time reference, especially in distributed bridges with physically separated portals.
Innovation Solution
A communication function between ports on a node that recreates and timestamps data streams without requiring a common time base, using a source packet bridge method that samples data streams, calculates an offset value based on timestamp comparisons, and repacketizes the data for transmission, allowing isochronous traffic to be bridged without a common time base and eliminating the need for a cycle master on each bus.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a common time base is distributed across the network to synchronize isochronous data streams, then data transmission synchronization is improved, but device complexity increases due to requiring cycle master on each bus and network-wide propagation of master time reference
Solution Approach 1:
The patent extracts the time base distribution function from the network-wide synchronization mechanism. Instead of requiring a common time base to be propagated across the entire network, each bridge device generates and uses its own local time base for timestamping packets. This eliminates the need for cycle masters on each bus and network-wide time reference propagation, while still ensuring reliable data transmission through local timestamping and playback timing.
Solution Approach 2:
The patent segments the synchronization function into independent local operations at each bridge device. Rather than a centralized time base distribution system, each bridge independently manages its own time base, timestamps packets locally, and handles playback timing independently. This segmentation eliminates the complexity of network-wide synchronization while maintaining reliable data transmission through distributed autonomous operation.
2Reliability
If a common time base is distributed across the network, then isochronous data stream synchronization is improved, but ease of operation deteriorates due to challenges in distributed bridges with physically separated portals
Solution Approach 1:
The patent removes the requirement for physical proximity or centralized time base distribution in bridge operations. Each bridge device independently generates its own time base and performs timestamping without needing to receive or propagate a common time reference. This extraction of the time base distribution function simplifies operation of distributed bridges with physically separated portals, as each device operates autonomously using its local time base.
3Adaptability or versatility
If time base variations between buses are accommodated, then adaptability of the network is improved, but manufacturing precision deteriorates due to overruns and underruns in data transmission
Solution Approach 1:
The patent applies preliminary action by timestamping packets at the source bridge using the source bus time base before transmission. The timestamp captures the exact timing information needed for accurate playback, allowing the destination bridge to reconstruct the original data stream timing despite time base variations. This preliminary timestamping action ensures data transmission accuracy while accommodating network adaptability to different time bases.
Solution Approach 2:
The patent uses the packet timestamp as an intermediary that carries timing information across buses with different time bases. The timestamp acts as a mediator between the source bus time base and the destination bus time base, allowing accurate playback timing to be determined without requiring the destination bus to operate at the same time base as the source. This intermediary mechanism maintains data transmission precision while enabling network adaptability.
Data Source
AI summary
A communication function between ports on a node that does not require a common time base to be distributed across the network is disclosed. A data stream received over a first port is placed on an interlace between nodes using the time base of the first port; a second port samples the data stream on the interface and timestamps it using the time base of the second port. The data stream is timestamped by the second port and packetized before transmitted to the second node to another bridge or device. Alternatively, the first port extracts a time stamp from the data stream and calculates an offset using a cycle timer value from the bus connected to the first port. The offset is added to the cycle timer value on the bus connected to the second port and used to timestamp the data stream.