Virtual Concatenation of PDH Signals for Ethernet Transport
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Solution Overview
Problem
There is a lack of standardized methods for mapping native Ethernet signals into asynchronous/plesiochronous digital hierarchy (PDH) signals like DS1 and DS3, which limits the efficient transport of Ethernet connectivity over existing PDH networks, and existing solutions like ML-PPP and IMA have inefficiencies or require additional overhead, disrupting service during channel changes.
Innovation Solution
The virtual concatenation of PDH signals, such as DS1 and E1, involves encapsulating data packets and inserting an overhead packet to compensate for differential delays, allowing the creation of larger transport channels with minimal impact on payload capacity, using techniques like GFP and LCAS/VCAT to realign frames and manage channel size dynamically.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If Ethernet frames are mapped into multiple PDH signals using existing protocols like ML-PPP or IMA, then Ethernet connectivity can be provided over PDH networks, but additional per-packet overhead is introduced and service disruption occurs during channel changes
Solution Approach 1:
The patent extracts the overhead requirements from the per-packet domain and places them in the per-frame domain. By using GFP encapsulation, the overhead is taken out of the packet processing path and embedded in the GFP frame structure, eliminating the need for per-packet overhead protocols like ML-PPP or IMA.
Solution Approach 2:
The patent segments the Ethernet data stream at the GFP frame level rather than at the packet level. This segmentation allows the use of byte-level inverse multiplexing where GFP frames are distributed across multiple PDH channels, avoiding the need for complex per-packet sequencing and reassembly protocols.
2Quantity of substance
If byte-level inverse multiplexing is implemented without VCAT overhead, then payload capacity is maximized, but channel changes require long re-initialization periods disrupting service
Solution Approach 1:
The patent nests the VCAT overhead information within the GFP frame structure itself. The LCAS/VCAT overhead bytes are embedded in the GFP encapsulated data stream, allowing the overhead to be carried efficiently without requiring separate dedicated channels or permanent payload reservations.
Solution Approach 2:
The patent implements dynamic channel adjustment capability through LCAS (Link Capacity Adjustment Scheme). The nested overhead enables real-time addition, removal, or reconfiguration of PDH member channels without requiring long re-initialization periods, making the multiplexed channel dynamically adaptable to changing bandwidth requirements.
3Ease of operation
If VCAT overhead is carried in a permanent payload channel, then channel reconfiguration is simplified, but excessive capacity is lost
Solution Approach 1:
Instead of permanently reserving an entire payload channel for VCAT overhead, the patent uses partial action by embedding only the necessary overhead bytes within the GFP frame structure. This approach provides the full functionality of VCAT for simplified channel reconfiguration while using minimal capacity for overhead purposes.
4Adaptability or versatility
If Ethernet is terminated and remapped to ML-PPP, then inverse multiplexing can be performed, but Layer 2 transparency is lost and operational complexity increases
Solution Approach 1:
The patent makes the GFP encapsulation universal by designing it to carry various Layer 2 protocols including Ethernet, PPP, and ATM over PDH signals. This multi-functionality eliminates the need for protocol-specific inverse multiplexing solutions like ML-PPP or IMA, as GFP can directly encapsulate and transport the desired Layer 2 protocol frames with built-in inverse multiplexing capability.
Data Source
AI summary
Asynchronous/plesiochronous digital hierarchy (PDH) signals, such as DS1 and E1, are transported using virtual concatenation. The packetized data signals are frame encapsulated and subsequently inverse multiplexed into a plurality of PDH frames. An overhead packet is inserted in the transmitted frames to enable the receiver to determine the status of the frames and extract the differential delay experienced by various frames as they are routed through virtually concatenated channels. The extracted delays enables the receiver to realign the various frames of the PDH signal to reconstitute the originally transmitted signals that travel through different paths of the transport network linking the source and sink of the virtually concatenated channel.