ONU Startup via Optical Loopback for Low-Latency PON
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Solution Overview
Problem
In optical communication networks, the use of quiet windows for ONU ranging introduces significant latency, which is unacceptable for applications requiring low latency, such as mobile fronthauling, especially when dynamic bandwidth allocation is turned off and data buffering grows infinitely.
Innovation Solution
A method that allows new ONUs to start communication without quiet windows by using a power splitter to receive upstream optical signals from operational ONUs, determining a temporal position of unused time slots, and calculating equalization delays based on these signals to synchronize with existing ONUs, thereby eliminating the need for quiet windows.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If quiet windows are used for ONU ranging, then new ONUs can be registered and synchronized, but significant latency is introduced into upstream data transmission
Solution Approach 1:
The patent applies preliminary action by having the new ONU determine its equalization delay before actually transmitting upstream data. The ONU calculates the delay based on downstream frame reception time and upstream burst transmission time, so that when normal transmission resumes, the ONU is already synchronized and can transmit immediately without waiting for quiet windows. This eliminates the latency caused by periodic quiet windows while ensuring proper synchronization.
2Reliability
If quiet windows are used for ONU ranging, then new ONUs can be discovered and registered, but upstream traffic must be buffered periodically causing infinite buffer growth with fixed bandwidth allocation
Solution Approach 1:
The patent applies self-service by enabling the new ONU to autonomously determine its equalization delay using information already available in the downstream and upstream signals. The ONU calculates the delay based on the reception time of downstream frames and the transmission time of upstream bursts, without requiring the OLT to coordinate quiet windows or buffer traffic. This self-determined synchronization allows continuous upstream transmission without buffering, preventing infinite buffer growth while still enabling proper ONU registration.
3Reliability
If quiet windows are used for ONU ranging, then new ONUs can be synchronized to avoid collision, but the ranging protocol requires periodic repetition of quiet windows
Solution Approach 1:
The patent applies continuity of useful action by enabling the new ONU to determine its equalization delay and begin continuous upstream data transmission without periodic interruptions. The ONU calculates the delay once based on downstream frame reception and upstream burst transmission timing, then maintains this synchronization continuously. This eliminates the need for periodic quiet windows, allowing uninterrupted upstream transmission and significantly improving productivity for applications requiring continuous data flow.
Data Source
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AI summary
The present invention discloses an Optical Network Unit (ONU) start up procedure with optical loopback for Passive Optical Network. In one embodiment, there is provided a method in a first ONU (130c), of starting up a communication with an Optical Line Terminal, OLT (110), the OLT (110) being communicatively coupled to the first ONU (130c), and a first number of ONUs (130a, 130b, 130d) that are already in operation, the first number being a natural number, each of the first number of ONUs (130a, 130b, 130d) being assigned to a time interval within an upstream frame to transmit an upstream bursts to the OLT (110), at least one predetermined time slot in the upstream frame being not assigned to any of the first number of ONUs (130a, 130b, 130d); the method comprising: a) receiving an information about at least one of the first number of ONUs (130a), from the OLT (110); b) receiving a downstream frame from the OLT (110), and obtaining a time of reception of a predetermined bit of the downstream frame; c) receiving an upstream optical signal from a first network node communicatively coupled to the first ONU (130c) and the first number of ONUs (130a, 130b, 130d), and detecting an envelope of the upstream optical signal, the upstream optical signal comprising burst signals transmitted by the first number of ONUs (130a, 130b, 130d) in response to the downstream frame respectively on the time interval assigned to them; d) determining a temporal position of the at least one predetermined time slot that is not used by the first number of ONUs (130a, 130b, 130d) in an upstream frame based on the envelope of the upstream optical signal; e) determining a first equalization delay based on the envelope of the upstream optical signal, the time of reception of a predetermined bit of the downstream frame and the information about the at least one of the first number of ONUs (130a); f) transmitting a first signal to the OLT (110) using the at least one predetermined time slot based on the first equalization delay