TCP RTT Measurement Using ACK Sequence Number Matching
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Solution Overview
Problem
Existing methods for calculating packet round trip time (RTT) require software installation on sending or receiving nodes, limiting their applicability.
Innovation Solution
Deploy sensors at various network devices to sense network flows and analyze data packets, determining RTT based on expected and actual ACK sequence numbers without installing software on sending or receiving nodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If software is installed on sending or receiving nodes to calculate RTT, then RTT measurement accuracy is improved, but device complexity and installation requirements increase
Solution Approach 1:
The patent introduces a third packet (a specially crafted TCP packet with specific flags and sequence numbers) as an intermediary mechanism to enable RTT measurement without software installation. This intermediary packet carries timing information and triggers automated RTT calculation through standard TCP stack behavior, eliminating the need for custom software while maintaining measurement accuracy
Solution Approach 2:
The system enables RTT measurement through self-service by utilizing the existing TCP protocol stack's automatic acknowledgment behavior. The TCP stack inherently tracks sequence numbers and generates ACKs, which are leveraged to calculate RTT without requiring additional software processes. The measurement is performed automatically using existing protocol mechanisms
2Ease of operation
If sensors are deployed at network devices to measure RTT, then ease of operation is improved, but device complexity increases
Solution Approach 1:
The patent makes existing network devices universal by enabling them to perform RTT measurement through their standard packet forwarding function. Instead of adding specialized sensing capabilities, the solution uses the inherent packet inspection and forwarding abilities of routers and switches to capture timing information, making any standard network device capable of RTT measurement
3Measurement precision
If conventional RTT measurement methods are used, then measurement precision is improved, but adaptability worsens due to node-specific requirements
Solution Approach 1:
The patent segments the RTT measurement function into independent components that can be performed by different network devices along the packet path. Instead of requiring end-to-end software coordination, the measurement is divided into packet injection at one node, timing capture at intermediate nodes, and acknowledgment tracking at the destination, with each segment handled by standard device functions
Solution Approach 2:
The patent inverts the conventional approach by having network infrastructure devices perform RTT measurement rather than endpoint applications. Instead of applications on end nodes measuring RTT through software, the solution enables network devices to measure RTT using packet metadata and timing information captured during normal packet forwarding operations
Data Source
AI summary
Systems, methods, and computer-readable media are provided for determining a packet's round trip time (RTT) in a network. A system can receive information of a packet sent by a component of the network and further determine an expected acknowledgement (ACK) sequence number associated with the packet based upon received information of the packet. The system can receive information of a subsequent packet received by the component and determine an ACK sequence number and a receiving time of the subsequent packet. In response to determining that the ACK sequence number of the subsequent TCP packet matches the expected ACK sequence number, the system can determine a round trip time (RTT) of the packet based upon the received information of the packet and the received information of the subsequent packet.