PTP Transparent Clock Inter-VLAN Forwarding via TCAM
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Solution Overview
Problem
Current Precision Time Protocol (PTP) transparent clocks, as defined by the IEEE standard, are not capable of forwarding PTP messages between Virtual Local Area Networks (VLANs) due to their adherence to Layer 2 switch forwarding rules, making it difficult to design cost-effective LANs with PTP synchronization throughout.
Innovation Solution
A PTP transparent clock is extended to include a Layer 2 switch with a PTP module that detects and forwards PTP frames between VLANs by configuring forwarding rules in a Ternary Content-Addressable Memory (TCAM), allowing PTP messages to be transmitted between different VLANs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a Boundary Clock is used to forward PTP messages between VLANs, then PTP inter-VLAN forwarding capability is achieved, but device cost increases significantly
Solution Approach 1:
The patent makes the Transparent Clock multi-functional by enabling it to forward PTP messages between VLANs through TCAM rule configuration, a function traditionally only available in Boundary Clocks. This allows a single device type to perform multiple roles (both transparent clocking and inter-VLAN PTP forwarding), eliminating the need for expensive Boundary Clock hardware while achieving the same functional outcome.
Solution Approach 2:
The patent replaces expensive Boundary Clock devices with cheaper Transparent Clock devices that have enhanced functionality through software/configuration (TCAM rules). This substitution uses a lower-cost device type to achieve the required function, significantly reducing overall system cost while maintaining PTP synchronization capability across VLANs.
2Ease of operation
If standard Layer 2 switch forwarding rules are applied in Transparent Clock, then forwarding simplicity is maintained, but inter-VLAN PTP forwarding is blocked
Solution Approach 1:
The patent introduces TCAM (Ternary Content-Addressable Memory) as an intermediary layer between the standard Layer 2 switching fabric and the PTP forwarding function. The TCAM stores special forwarding rules that intercept PTP messages and redirect them across VLAN boundaries, while leaving normal data traffic to follow standard Layer 2 rules. This intermediary mechanism enables inter-VLAN PTP forwarding without disrupting the simplicity of standard switching operations.
Solution Approach 2:
The patent applies different forwarding behaviors to different types of traffic: standard Layer 2 forwarding rules apply to normal data traffic, while special TCAM-based rules apply specifically to PTP messages. This local differentiation allows the system to maintain forwarding simplicity for the majority of traffic while providing enhanced inter-VLAN capability specifically for PTP synchronization messages.
Data Source
AI summary
There is described a Precision Time Protocol (“PTP”) transparent clock for inter-VLAN forwarding comprising a Layer 2 switch and a PTP module. The switch includes a first port associated with a first VLAN and a second port associated with a second VLAN. The switch detects a PTP frame at the first port and the PTP module receives the PTP frame. The switch forwards the PTP frame to the second port in response to the PTP module determining that the PTP frame is a forwardable frame. For another embodiment, the switch includes a ternary content-addressable memory (“TCAM”), and the PTP module configures the TCAM to include forwarding rules. The Layer 2 switch forwards the PTP frame to the second port in response to identifying a particular forwarding rule associated with forwarding the PTP frame.