In-band Flow Control for SPI-3 Backpressure
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Solution Overview
Problem
The SPI-3 interface standard falls short in supporting high channel count packet-based applications, particularly in OC-12 channelized links, as it fails to provide adequate flow control for all DS0 channels, leading to inefficiencies in link utilization and traffic management.
Innovation Solution
An in-band flow control mechanism is introduced, where backpressure information is transmitted from a physical layer device to a link layer device using a flow control message, enabling improved traffic shaping and detection, even in high channel count applications, without requiring additional MPHY polling address lines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the SPI-3 interface standard is used for physical layer device communication, then the interface provides standardized flow control mechanisms, but it fails to support adequate flow control for high channel count applications with up to 8064 DS0 channels
Solution Approach 1:
The patent segments the flow control mechanism by introducing separate in-band flow control messages for each MPHY (physical channel). Instead of relying on a single polling mechanism, the system divides flow control into individual channel-specific messages that can be independently managed, allowing support for high channel count applications while maintaining standardized interface compatibility.
Solution Approach 2:
The patent adds a new dimension to flow control by implementing in-band flow control messages that carry backpressure information within the existing SPI-3 interface framework. This dimensional addition allows the system to maintain backward compatibility while extending flow control capabilities to support thousands of channels beyond the original 256 MPHY limitation.
2Loss of information
If polling of MPHY addresses is used for backpressure detection, then flow control information can be obtained, but the SPI-3 interface only supports a maximum of 256 MPHYs which is insufficient for OC-12 channelized links requiring support for up to 8064 DS0 channels
Solution Approach 1:
The patent introduces in-band flow control messages as an intermediary mechanism between the physical layer device and link layer device. These messages serve as a mediator that carries backpressure information for individual MPHYs without requiring the link layer device to poll each MPHY address, thereby maintaining accurate backpressure detection while eliminating the 256 MPHY polling limitation.
3Ease of manufacture
If the SPI-3 interface standard is implemented, then a systematic approach to physical layer communication is provided, but it falls short of providing per-DS0 access and flow control for all DS0 channels in OC-12 facility
Solution Approach 1:
The patent applies universality by designing in-band flow control messages that can serve multiple functions: they maintain compatibility with the standardized SPI-3 interface while simultaneously providing per-channel flow control capability. The same message structure works for both standardized communication and extended high-channel-count applications, making the system universally applicable across different deployment scenarios.
Data Source
AI summary
Backpressure information is communicated from a physical layer device to a link layer device in a communication system by generating a flow control message in the physical layer device responsive to a detected condition relating to at least a given one of a plurality of queues of the physical layer device, and transmitting the flow control message from the physical layer device to the link layer device. The flow control message may comprises backpressure information associated with a given egress queue of the physical layer device and is transmitted from the physical layer device to the link layer device as an in-band message over an interface between the physical layer device and the link layer device. Multiple-rate traffic shaping or other types of traffic shaping may be provided responsive to the flow control message.