Interpacket Gap Adjustment for Clock-Mismatched Loopback Links
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Solution Overview
Problem
Communication devices with loopback functionality experience packet throughput issues due to clock frequency mismatches, leading to packet drops and buffer overflow, and existing solutions compromise clock quality or range of operation.
Innovation Solution
A communication device with a CDR unit, receiver unit, transmitter unit, and IPG adjustment unit that adjusts interpacket gaps based on a comparison of recovered and local reference clocks, allowing loopback operation without packet drops and maintaining clock quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the loopback device uses the same exact frequency on both the transmitter and receiver by transmitting out based on the recovered clock, then the packet throughput problem is solved and there is no excess packet build up, but the transmitter suffers from negative effects such as clock jitter multiplication and noise coupling since it is not transmitting from a clean crystal reference
Solution Approach 1:
The patent changes the parameter of interpacket gap (IPG) length to resolve the contradiction. By dynamically adjusting the IPG length based on clock frequency differences, the system maintains packet throughput while allowing the transmitter to operate from a clean crystal reference, thus avoiding clock jitter multiplication and noise coupling.
Solution Approach 2:
The patent introduces dynamic adjustment of the interpacket gap length based on real-time clock frequency comparison. The IPG adjustment unit dynamically modifies the gap between packets to compensate for clock frequency differences, enabling the system to adapt to varying clock conditions while maintaining both throughput and clock quality.
2Speed
If the sending communication device sends a stream of packets with minimum interpacket gap when operating with a faster reference clock, then the transmission speed is maximized, but the transmitter of the receiving communication device will be unable to keep up resulting in excess packet build-up and buffer overflow
Solution Approach 1:
The patent changes the interpacket gap parameter dynamically to match clock frequency differences. When the sending device operates with a faster reference clock, the IPG is extended to allow the receiving device to process packets at its slower clock rate, preventing buffer overflow while maintaining high transmission speed.
3Reliability
If a buffer is implemented to temporarily store excess packets, then packet loss is reduced, but there is no buffer size that can be guaranteed not to overflow and packet drops still occur to match packet flow rates
Solution Approach 1:
The patent applies preliminary action by adjusting the interpacket gap length before packets are transmitted, based on pre-calculated clock frequency differences. This prevents packet flow rate mismatches before they occur, eliminating the need for large buffers and complex buffer management mechanisms.
Data Source
AI summary
A communication device includes a CDR (clock data recover) unit, a receiver unit, a transmitter unit, and an IPG (interpacket gap) adjustment unit. The CDR unit recovers a recovered clock of incoming packets. The receiver unit is coupled to the CDR unit and receives the incoming packets. The transmitter unit transmits outgoing packets and IPGs therebetween. The IPG adjustment unit is coupled between the transmitter unit and the CDR unit and outputs the IPG adjustment signal based on a comparison of the recovered clock and the local reference clock. An IPG adjustment method of the communication device is also provided.