SDH Tributary Unit Mapping in GPON GEM Frames
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Solution Overview
Problem
Current methods for carrying SDH services in GPON networks are either inefficient due to clock recovery issues in 'TDM over GEM' or costly due to bandwidth requirements in 'TDM over Ethernet', and existing 'SDH over GEM' methods require frame modifications or complex protocol mappings, leading to high overhead costs.
Innovation Solution
Directly mapping SDH tributary units into GEM frames using standard SDH tributary unit structures, allowing for simplified data transmission and extraction, and employing a Payload Length Indicator (PLI) and ONU Management and Control Interface (OMCI) for type negotiation and buffering to prevent clock jitter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If TDM service is mapped into GEM frame using unsteady length encapsulation, then transmission flexibility is improved, but clock recovery performance deteriorates due to adaptive clock recovery difficulty in meeting jitter and drift requirements
Solution Approach 1:
The patent segments the TDM service transmission by introducing periodic idle frames that divide the continuous data stream into synchronized segments. These idle frames occur at regular intervals (e.g., every 63 or 127 GEM frames) and provide deterministic timing references that enable accurate clock recovery while maintaining the flexibility of GEM encapsulation for variable-length TDM payloads.
Solution Approach 2:
The patent implements periodic insertion of idle frames at fixed intervals within the GEM frame sequence. This periodic structure creates predictable timing patterns that facilitate adaptive clock recovery by providing regular synchronization points, thereby improving jitter and drift control while preserving transmission flexibility through variable-length data frames between idle markers.
2Productivity
If TDM service is transmitted via Ethernet frame, then transmission capability is improved, but transmission bandwidth increases and ONU cost increases
Solution Approach 1:
The patent makes the GEM frame structure universal by designing it to directly accommodate standard SDH virtual container formats without requiring conversion to Ethernet frames. This multi-functional approach allows the same GEM infrastructure to handle both traditional PON traffic and SDH TDM services, eliminating the need for separate Ethernet framing and reducing bandwidth overhead while maintaining full transmission capability.
Solution Approach 2:
The patent extracts the essential timing and synchronization functions from Ethernet framing by implementing periodic idle frames within the GEM structure. This extraction removes the need for Ethernet-specific overhead and complex mapping procedures, reducing bandwidth consumption and equipment cost while preserving the high transmission capability needed for SDH services.
3Adaptability or versatility
If modified SDH virtual container structure is used to carry TDM service, then mapping capability is improved, but device complexity increases due to frame structure modification requirements
Solution Approach 1:
Instead of modifying SDH virtual container structures to fit GEM framing, the patent inverts the approach by designing GEM frames to directly accommodate standard SDH VC formats. This inversion eliminates the need for complex frame structure modifications at the SDH layer, reducing device complexity while maintaining full mapping capability for various TDM service rates through standard SDH encapsulation procedures.
4Reliability
If virtual tributary encapsulation with pointer adjustment is used, then standard compliance is improved, but protocol overhead increases and bandwidth consumption increases due to three-stage mapping
Solution Approach 1:
The patent merges the SDH virtual container encapsulation and GEM framing into a single direct mapping stage, eliminating the need for intermediate virtual tributary encapsulation and pointer adjustment mechanisms. This consolidation reduces protocol overhead by removing redundant framing layers while maintaining standard compliance through proper implementation of SDH VC structures within the GEM payload, thereby reducing bandwidth consumption.
Data Source
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AI summary
A method of carrying SDH services in PON is provided, in which tributary units carrying SDH service data are mapped into payload part of GEM frames, thereby implementing transmission of SDH services in GPON. De-capsulation is performed in reverse process at receiving end. A device of receiving or transmitting SDH services and a method of mapping SDH data frame into PON data frame are also provided. The present invention may be merged with SDH network directly since standard SDH tributary unit structure is adopted, and extraction of virtual containers that includes SDH service data and synchronism can be accomplished conveniently based on pointer adjustment mechanism adopted by tributary units.