Link State Message Fragmentation for IS-IS Routing

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Solution Overview

Problem

IS-IS link state routing protocol lacks an underlying datagram fragmentation capability, leading to disruptions in data forwarding due to incomplete link state messages, as receivers may prematurely perform route computations based on incomplete sets of messages exceeding the fixed maximum message size.

Innovation Solution

Implementing a method for generating and transmitting a complete set of link state messages with specified information indicating their coherence, and using modules to delay route computations until the complete set is received, ensuring accurate routing table updates and avoiding data forwarding disruptions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If link state messages are transmitted without fragmentation capability, then message transmission is simple, but data forwarding disruptions occur due to incomplete messages

Engineering Contradiction:

Improvedata forwarding continuityVSAvoidmessage transmission mechanism

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent segments link state messages into multiple fragments when the complete message exceeds the maximum message size. Each fragment is transmitted separately with identification information, and the receiving router reassembles them before processing. This resolves the contradiction by enabling reliable complete message delivery without requiring complex fragmentation capability in the underlying datagram protocol.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent implements preliminary actions by transmitting a notification before the complete set of link state messages indicating the total number of messages to be transmitted. The receiving router uses this information to wait for the complete set before performing route computations. This prevents data forwarding disruptions by ensuring route calculations are only performed when all message fragments are received.

Inventive Principle:

Principle #10Preliminary action

2Productivity

If receivers perform route computations immediately upon receiving link state messages, then routing updates are fast, but incorrect computations occur due to incomplete message sets

Engineering Contradiction:

Improverouting update speedVSAvoidroute computation accuracy

Core Design Contradiction:

ProductivityVSMeasurement precision

Solution Approach 1:

The patent implements a feedback mechanism where the receiving router counts the received link state message fragments and compares this count against the total number indicated in the preliminary notification. Route computations are triggered only when the received count matches the expected total, ensuring accuracy. This feedback loop maintains routing update speed by automatically initiating computations as soon as the complete set is verified.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The receiving router performs preliminary verification by checking whether the complete set of link state messages has been received before initiating route computations. This preliminary check ensures computation accuracy by preventing premature calculations on incomplete data, while the automated nature of the check minimizes the delay before accurate computations can proceed.

Inventive Principle:

Principle #10Preliminary action

3Quantity of substance

If the maximum message size is increased to accommodate complete link state information, then fewer messages need to be transmitted, but message size constraints are violated

Engineering Contradiction:

Improvelink state information completenessVSAvoidmessage size

Core Design Contradiction:

Quantity of substanceVSLength of stationary object

Solution Approach 1:

The patent segments large link state messages that would exceed the maximum message size into multiple smaller fragments. Each fragment is transmitted as a separate message within the size constraint, and the receiving router reassembles them using identification information. This resolves the contradiction by delivering complete link state information while adhering to message size limitations.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent adds a temporal dimension to message transmission by sending multiple fragmented messages sequentially over time rather than requiring a single large message. The preliminary notification provides metadata about the complete set, allowing the receiver to accumulate fragments until the complete information is available. This transforms the size constraint problem into a time-based delivery solution.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Data Source

PatentUS8830867B2Methods and network elements operable to specify and determine complete sets of link state messages for link state routing protocols

Publication Date: 2014.09.09 TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

AI summary

A method, performed by a transmitter network element utilizing a link state routing protocol which has a maximum link state message size. The method is for providing information to avoid a disruption in data forwarding that would result from a receiver network element performing preferred route computations based on an incomplete set of link state messages. The method includes generating a complete set of link state messages having information indicating that the link state messages are the complete set of the link state messages. The complete set of the link state messages are collectively coherent with a link state of the transmitter network element. The method also includes transmitting the complete set of the link state messages, and the information indicating that the link state messages are the complete set of the link state messages, to a network. Also disclosed are transmitter network elements, receiver network elements, and methods thereof.