CBR Transport Over Packet Interfaces Without Stratum Clocks
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Solution Overview
Problem
Existing methods for transmitting Constant Bit Rate (CBR) client signals across packet interfaces lose phase information, leading to challenges in maintaining phase and frequency synchronization, particularly in networks that require seamless evolution from CBR to data traffic, and are costly due to the need for common stratum reference clocks.
Innovation Solution
The method involves segmenting CBR client streams into variable-sized packets or GFP frames, where phase and frequency information is regenerated based on segment sizes, eliminating the need for overhead bytes and allowing phase-locking without requiring source and sink network elements to share a common stratum reference clock.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If CBR client signals are converted into packets for transmission across a packet interface, then the signals can be transported over packet fabrics, but the phase and frequency information is lost in the process
Solution Approach 1:
The patent applies preliminary action by capturing and storing phase and frequency information from the incoming CBR signal before packetization occurs. The ingress network element measures and records these timing characteristics in advance, so they can be recovered later at the egress element to reconstruct the original signal properties without being lost during packet transmission
Solution Approach 2:
The patent uses an intermediary mechanism by introducing measurement and signaling functions that extract phase and frequency information from the CBR signal and convey it through the packet network. This intermediary process allows the timing information to be transported alongside or with the packetized CBR data, enabling recovery at the destination
2Adaptability or versatility
If separate CBR and Packet fabrics are used to support both CBR and Data traffic, then both traffic types can be handled, but the network cost increases due to requiring 100% bandwidth in both fabrics
Solution Approach 1:
The patent applies universality by designing a single packet fabric that can handle both CBR and Data traffic. By packetizing CBR signals and transporting them through the same packet fabric used for data, the network eliminates the need for separate dedicated CBR fabrics, reducing overall network cost and bandwidth requirements while maintaining full functionality for both traffic types
Solution Approach 2:
The patent merges previously separate CBR and Data traffic handling into a unified packet-based architecture. Both CBR and Data clients are switched through the same packet fabric, consolidating network resources and eliminating redundant infrastructure while preserving the ability to handle both traffic types effectively
3Loss of information
If timestamps are inserted into packet overhead to signal phase information, then phase can be recovered at egress, but the potential throughput of the fabric is reduced by the bandwidth consumed by timestamps
Solution Approach 1:
The patent extracts phase and frequency information from the CBR signal at the ingress element and separates it from the main data stream. By taking out these timing characteristics and handling them through dedicated measurement and signaling mechanisms rather than embedding them in every packet overhead, the solution minimizes the bandwidth consumption dedicated to timing information while ensuring complete phase recovery capability
Data Source
AI summary
A method and apparatus are described for signaling the phase and frequency of constant bit rate (CBR) clients over a network or fabric. An incoming CBR client stream is segmented into variable sized segments, such as packets or general framing protocol (GFP) frames, and is regenerated on the other side of a fabric or network phase-locked to the incoming stream. Regeneration of the CBR client clock is based solely on segment sizes, and in the case of GFP frames, the rate of the SONET Path or OTN ODUk stream carrying the GFP frames. No overhead bytes are inserted into the GFP frames to convey phase and frequency information. The method disclosed is important for reducing the cost and complexity of communications networks by allowing CBR clients to be transported with low jitter and wander without requiring the source and sink network elements to be phase-locked to a common stratum reference.