IGP-Based Path MTU Discovery Without ICMP

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Solution Overview

Problem

Path Maximum Transmission Unit (MTU) discovery in data communication networks is hindered by ICMP message filtering or blocking, leading to failures in adapting data packet frame sizes, resulting in packet fragmentation, performance issues, and reordering, especially in mobile backhaul networks.

Innovation Solution

A method and apparatus for determining the path MTU size by acquiring link interface MTU sizes and updating routing tables to calculate and select the lowest MTU size for each transmission path, using link-state routing protocols like IS-IS and OSPF, to ensure efficient data transmission without fragmentation, using new TLVs and LSAs for distributing MTU information.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If path MTU discovery uses ICMP messages to adapt data packet frame sizes, then packet fragmentation is avoided, but ICMP message filtering or blocking causes the discovery process to fail

Engineering Contradiction:

ImprovePath MTU discovery reliabilityVSAvoidICMP message filtering or blocking

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent uses IGP protocol messages (OSPF LSA or IS-IS TLV) as an intermediary carrier to transmit MTU size information throughout the network. Instead of relying on ICMP messages that are blocked by firewalls, the MTU information is embedded in routing protocol advertisements that are trusted and allowed to pass through network security boundaries, thus resolving the blocking issue while maintaining reliable path MTU discovery

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent performs preliminary action by pre-calculating and storing the path MTU size in routing tables before actual data transmission occurs. The IGP messages carry MTU information that is processed in advance to determine the minimum MTU along each path, so when data packets need to be sent, the appropriate MTU size is already known and stored, eliminating the need for reactive ICMP-based discovery

Inventive Principle:

Principle #10Preliminary action

2Productivity

If larger MTU size is used to improve throughput efficiency, then fewer packets need to be processed, but large packets occupy slow links longer causing increased jitter and latency

Engineering Contradiction:

ImproveThroughput efficiencyVSAvoidJitter and latency

Core Design Contradiction:

ProductivityVSLoss of time

Solution Approach 1:

The patent dynamically changes the MTU size parameter based on the specific path characteristics. By determining the minimum MTU size along each transmission path and storing it in the routing table, the system adapts the packet size parameter to match the bottleneck link capacity, optimizing throughput for each path while preventing excessive packet sizes that would cause jitter and latency on slower links

Inventive Principle:

Principle #35Parameter changes

3Productivity

If larger MTU size is used to reduce packet processing overhead, then bulk protocol throughput improves, but packet corruption probability increases requiring retransmission

Engineering Contradiction:

ImproveBulk protocol throughputVSAvoidPacket transmission reliability

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent optimizes the MTU size parameter by setting it to the minimum MTU value along the transmission path. This prevents using excessively large MTU sizes that would increase corruption probability on links with smaller capacity or higher error rates, while still achieving efficient throughput by avoiding unnecessary packet fragmentation and processing overhead

Inventive Principle:

Principle #35Parameter changes

4Adaptability or versatility

If MTU size varies in different network segments due to multiple encapsulation protocols, then network flexibility is improved, but packet fragmentation and performance degradation occur

Engineering Contradiction:

ImproveNetwork encapsulation flexibilityVSAvoidPacket transmission performance

Core Design Contradiction:

Adaptability or versatilityVSProductivity

Solution Approach 1:

The patent performs preliminary calculation of the path MTU size by examining all link interfaces along the transmission path, including those with different encapsulation protocols. The minimum MTU value is pre-determined and stored in the routing table, allowing the network to maintain flexibility with multiple encapsulation protocols while ensuring packets are sized appropriately to avoid fragmentation across any segment of the path

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentEP2865142B1Adaptive MTU size optimization using igp

Publication Date: 2019.11.27 TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

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AI summary

The present invention relates to methods and routing and/or switching devices for determining a path maximum transmission unit MTU P(n) size for transmission paths between edge nodes in a data communications network and for updating routing tables associated with the routing and/or switching devices in said edge nodes, which are linked together with link interfaces L(i) constituting transmission paths P(n) for data packet transmission, each link interface L(i) having a link interface maximum transmission unit MTU L(i) size. The methods involve the acquisition of a link interface maximum transmission unit MTU L(i) size for a link interface L(i), and the updating the routing table by calculating the path maximum transmission unit MTU P(n) size for each destination wherein the link interface L(i) for the acquired link interface maximum transmission unit MTU L(i) size is involved. New link-state protocols for distributing the link interface maximum transmission unit MTU L(i) size is also provided.