MPLS-TP Communication Device MTU Discovery Mechanism
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Solution Overview
Problem
In MPLS-TP networks, determining the end-to-end MTU value accurately and efficiently is challenging due to label stacking, which can lead to frames exceeding the MTU, preventing end-to-end transfer, and existing methods like Path MTU Discovery and CC functions are either IP-layer dependent or inefficient in accuracy and speed.
Innovation Solution
A communication device and method that includes a transfer unit, calculation unit, notification unit, and retransmission unit to determine the MTU by generating and processing MTU confirmation and response frames, ensuring frames are adjusted to fit within the transmittable size, and correcting sizes when necessary, thereby efficiently discovering the path MTU.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If label stacking is performed in MPLS-TP network to establish hierarchical paths, then path monitoring and maintenance capabilities are improved, but frame size exceeds MTU preventing end-to-end transfer
Solution Approach 1:
The patent segments the frame transmission process into multiple stages: sending OAM frames with different payload sizes (from 1 byte to maximum size in incremental steps), allowing the system to identify the maximum transmittable frame size without exceeding MTU limits. This segmentation enables reliable path monitoring while avoiding the harmful effect of oversized frames.
Solution Approach 2:
The patent performs preliminary MTU discovery actions before actual data transmission. The communication device sends test OAM frames with incrementally increasing payload sizes to pre-determine the maximum transmittable frame size, storing this information for subsequent transmissions. This preliminary action prevents frame size issues before they occur during normal operation.
2Measurement precision
If Path MTU Discovery protocol is used to determine MTU, then MTU information can be obtained, but the method is dependent on IP layer and not suitable for MPLS-TP
Solution Approach 1:
The patent introduces OAM (Operations, Administration, and Maintenance) frames as an intermediary mechanism to perform MTU discovery in MPLS-TP networks. These OAM frames operate independently of the IP layer, using MPLS labels and OAM-specific protocols to carry test payloads and discover the maximum transmittable unit size. This intermediary approach maintains measurement precision while removing IP layer dependency.
3Reliability
If CC function is used for MTU discovery, then path monitoring is performed, but the accuracy and speed of MTU determination are insufficient
Solution Approach 1:
The patent implements a dynamic MTU discovery process where the OAM frame payload size is adjusted dynamically in incremental steps (1 byte, 2 bytes, 4 bytes, 8 bytes, 16 bytes, 32 bytes, 64 bytes, 128 bytes, 256 bytes, and maximum size). This dynamic adjustment allows the system to efficiently converge on the maximum transmittable frame size with high precision, improving both accuracy and speed compared to static or less granular approaches.
4Measurement precision
If incremental OAM frame transmission is performed to discover MTU, then high accuracy MTU value is obtained, but the number of transmissions increases and time is extended
Solution Approach 1:
The patent employs periodic action with exponentially increasing intervals between transmission attempts. The device sends OAM frames with payload sizes following a periodic pattern of incremental doubling (1, 2, 4, 8, 16, 32, 64, 128, 256, maximum bytes). This periodic progression with increasing steps balances the need for high measurement precision with the constraint of minimizing total discovery time, as larger jumps are made once the approximate MTU range is identified.
Data Source
AI summary
A communication device including: a transfer unit transferring a received frame based on an identifier included in the received frame; a calculation unit calculating a size of the received frame to which the identifier is added when the received frame is a specific frame; a notification unit adding a value indicating a transmittable size or a size less than the transmittable size, when the size of the received frame after the identifier added is larger than the size that can be transmitted to a next destination communication device on a communication path, generating a transmission impossible notification frame addressed to a source communication device of the received frame, and transferring the transmission impossible notification frame to the transfer unit; and a retransmission unit correcting the size of the specific frame to be smaller than or equal to the transmittable size, when the transmission impossible notification frame is received and transferring the transmission impossible notification frame to the transfer unit.