USB 3.0 Extension Devices Latency Compensation
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Solution Overview
Problem
The existing USB specifications limit SuperSpeed connections to a maximum cable length of 3 meters due to timing and signaling requirements, restricting the distance between host and USB devices, necessitating a method to extend USB communication beyond this range without compromising data integrity.
Innovation Solution
The implementation of upstream and downstream facing port devices with extension interfaces that use non-USB extension media, such as networks, to facilitate communication between host and USB devices by generating synthetic request and response packets, compensating for latency introduced by the extension medium, and synchronizing service intervals to maintain compliant USB communication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a regular copper cable is used for a SuperSpeed connection, then data transmission speed is maintained at 5 Gbps or 10 Gbps, but the maximum cable length is limited to 3 meters due to timing and signaling requirements
Solution Approach 1:
The patent introduces an extension medium (such as Ethernet cable or wireless network) as an intermediary between the host device and USB device. The USB extension devices convert USB packets into packets suitable for transmission over the extension medium, enabling communication beyond the 3-meter limit while maintaining SuperSpeed data rates through protocol conversion and latency compensation mechanisms
Solution Approach 2:
The patent divides the USB communication path into multiple segments: host device to USB extension device (via USB connection), USB extension device to USB extension device (via extension medium), and USB extension device to USB device (via USB connection). Each segment handles specific protocol requirements, allowing the system to overcome the cable length limitation while preserving data transmission speed
2Length of stationary object
If the cable length is extended beyond 3 meters, then communication distance is increased, but timing mandates and signaling techniques cannot properly support the SuperSpeed connection
Solution Approach 1:
The USB extension devices perform preliminary actions by measuring and characterizing the latency of the extension medium during initialization. This pre-measured latency information is then used to compensate for timing delays in subsequent USB transactions, ensuring that timing mandates are met even when communication distance exceeds 3 meters
Solution Approach 2:
The patent implements feedback mechanisms where USB extension devices measure actual transmission latency and use this information to adjust timing parameters. The system continuously monitors and compensates for timing variations introduced by the extension medium, maintaining signaling integrity and timing compliance throughout the extended communication distance
3Length of stationary object
If USB communication is extended beyond 3 meters using extension media, then cable length limitation is overcome, but additional latency is introduced by the extension medium
Solution Approach 1:
The USB extension devices perform preliminary latency measurement during the initialization phase by exchanging test packets through the extension medium. The measured latency value is stored and used to pre-compensate for timing delays in all subsequent USB transactions, reducing the effective impact of extension medium latency on data transmission
Solution Approach 2:
The patent dynamically adjusts USB transaction timing parameters based on the measured extension medium latency. By modifying interval times and synchronization parameters according to the actual latency conditions, the system optimizes data transmission efficiency while maintaining compliance with USB timing requirements despite the added delay from the extension medium
Data Source
AI summary
An upstream facing port device (UFP device) and a downstream facing port device (DFP device) allow a host device and a USB device to conduct SuperSpeed communication via a non-USB compliant extension medium. In some embodiments, the UFP device helps overcome increased latency by generating synthetic packets to be transmitted to the DFP device in order to pre-fetch more data packets from the USB device than requested by the host device. In some embodiments, the DFP device adjusts service interval timing or caches data packets from the host device in order to compensate for the increased latency. In some embodiments, the DFP device transmits a synthetic acknowledgement packet to the UFP device to indicate a larger amount of free buffer space than is present on the USB device to help overcome the increased latency.