Asynchronous Optical Transport Network Variable Overhead Ratio Clocking
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current optical transport networks (OTNs) require costly phase locked loop (PLL) circuitry and crystal oscillators for synchronous clocking, leading to high system costs and complexity, especially when handling different client signal protocols like 10 GbE and OC192, as they need to maintain accurate clock synchronization across nodes.
Innovation Solution
Implementing an asynchronous optical transport network (AOTN) with a variable overhead ratio (V-OHR) that allows intermediate nodes to operate with a single local frequency clock, eliminating the need for expensive clocking devices by asynchronously remapping client signals using Optical-Electronic-Optical (OEO) conversions and FEC encoding, thereby maintaining a constant line rate throughout the network.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If synchronous clocking is used to maintain accurate timing across network nodes, then signal synchronization and timing accuracy are improved, but system cost and device complexity increase due to required PLL circuitry and crystal oscillators
Solution Approach 1:
The network is divided into asynchronous segments where each node operates independently with its own local clock, eliminating the need for complex synchronous clocking systems. Each node handles timing locally without requiring coordinated PLL circuitry across the entire network.
Solution Approach 2:
The system changes from fixed synchronous clocking to variable asynchronous clocking, allowing each node to operate at its own clock rate. This parameter change enables cost reduction while maintaining functionality through flexible timing management at each node.
2Reliability
If accurate clock synchronization is implemented at each node, then signal timing consistency is improved, but manufacturing cost increases due to expensive crystal oscillators and PLL circuitry
Solution Approach 1:
The patent replaces expensive, long-lasting crystal oscillators and PLL circuitry with simpler, less expensive local reference clocks at each node. These cheaper clocking devices suffice for asynchronous operation where exact synchronization is not required, significantly reducing manufacturing costs.
Solution Approach 2:
The complex clock synchronization functionality is extracted from each individual node, allowing nodes to operate independently with simple local clocks. The synchronization function is replaced by asynchronous mapping and remapping mechanisms that handle timing differences without requiring expensive hardware at each node.
3Device complexity
If a fixed overhead ratio is used in digital wrapper frames, then frame structure simplicity is maintained, but adaptability to different client signal protocols is reduced
Solution Approach 1:
The overhead ratio is changed from fixed to variable, allowing the digital wrapper frame structure to dynamically adapt to different client signal protocols. Each node can adjust the overhead ratio according to the specific protocol being handled, enabling support for multiple protocols like 10 GbE and OC192 while maintaining frame structure flexibility.
Solution Approach 2:
The digital wrapper frame structure is designed to be universal by allowing variable overhead ratios, enabling a single frame format to handle multiple different client signal protocols. This multi-functionality is achieved through flexible mapping and remapping capabilities at each node.
4Ease of manufacture
If asynchronous operation with variable overhead ratio is implemented, then system cost is reduced by eliminating PLL and crystal oscillators, but clock synchronization and timing accuracy are compromised
Solution Approach 1:
Asynchronous mapping and remapping mechanisms serve as intermediaries that handle the timing differences between nodes. These mechanisms mediate between the independent local clocks and the overall network timing, allowing cost reduction while maintaining acceptable timing performance through software-based synchronization rather than hardware-based precision clocking.
Data Source
AI summary
An optical transmission network is inherently asynchronous due to the utilization of a variable overhead ratio (V-OHR). The network architecture makes extensive use of OEO regeneration, i.e., deals with any electronic reconditioning to correct for transmission impairments, such as, for example, FEC encoding, decoding and re-encoding, signal reshaping, retiming as well as signal regeneration. The optical transmission network includes a plesiochronous clocking system with intermediate nodes designed to operate asynchronously with a single local frequency clock without complicated network synchronization schemes employing high cost clocking devices such as phase locked loop (PLL) control with crystal oscillators and other expensive system components. The asynchronous network operation provides for asynchronous remapping or remapping of any client signal utilizing any type of transmission protocol where the line side rate or frequency is always the same frequency for the payload signal and the local frequency at an intermediate node is set to a local reference clock in accordance with the payload type and its overhead ratio, i.e., the overhead ratio is varied to meet the desired difference between the line rate or frequency and the desired client signal payload rate or frequency for the particular client signal payload type.