Clock Recovery Loop for Timing Transparency in Client Data Transport
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Solution Overview
Problem
Existing clock recovery methods in communications networks require a common clock and overhead bytes to synchronize nodes, which is not feasible in all systems, especially those without a reference clock, leading to inefficiencies in data transmission due to jitter and wander issues.
Innovation Solution
An apparatus and method that uses a clock recovery loop within the egress data path to derive a client data reference clock from a depth indicator of client data in memory, eliminating the need for a common clock and overhead bytes, allowing for timing transparency in client data transport.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a differential clock recovery method using overhead bytes is used, then phase information can be transmitted between network nodes, but the system requires a common clock and complex circuits to support reference clocks and phase corrections
Solution Approach 1:
The invention extracts the clock recovery function from the traditional differential method that requires common clocks and overhead bytes. By using a unidirectional approach where only the egress node performs clock recovery using locally stored depth information, the system eliminates the need for complex bidirectional phase information exchange and common clock infrastructure, thereby reducing device complexity while maintaining reliability
Solution Approach 2:
The egress node performs self-contained clock recovery using its own locally stored depth information from the FIFO buffer. The node recovers the client clock frequency by analyzing the relationship between transmitted data and its own internal clock, eliminating the need for external reference clocks or complex synchronization mechanisms from other nodes
2Measurement precision
If a common clock is available to both ingress and egress sides, then phase information can be accurately recovered, but not all systems or network architectures include a reference clock
Solution Approach 1:
The system enables each node to perform self-contained clock recovery using its own internal clock and locally stored depth information. The egress node calculates the client clock frequency by comparing its own clock against the depth changes in the FIFO buffer, eliminating the requirement for external reference clocks or common clock infrastructure while maintaining accurate phase recovery
Solution Approach 2:
The invention changes the approach from using absolute phase information requiring common clocks to using relative depth changes in the FIFO buffer. By monitoring how the buffer depth changes over time and comparing this against the egress node's internal clock, the system derives the client clock frequency without needing synchronized reference clocks at both ends
3Reliability
If overhead bytes are used to send phase information, then clock recovery can be assisted, but the data transmission efficiency is reduced and the system becomes more complex
Solution Approach 1:
The invention removes the need for dedicated overhead bytes for phase information transmission. Instead, it uses the existing FIFO buffer depth information that is already present in the data path to perform clock recovery. This eliminates the overhead burden while maintaining reliable clock recovery capability through the unidirectional depth-based method
Data Source
AI summary
Clock recovery is used in a variety of communications network applications to enable nodes using different clocks to operate in an effectively synchronized manner. Example embodiments of the present invention include an apparatus and corresponding method for supporting client data transport with timing transparency and require neither a common clock to be available at both the ingress and egress sides of the connection nor overhead bytes to recover a client clock. Rather, client traffic clock recovery may be performed in example embodiments of the present invention entirely in the egress data path using the client data received from the ingress side after removing the clients signal from a higher level carrier signal.