HDX Protocol RTT Measurement via Intermediary Bit Manipulation
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Solution Overview
Problem
Existing methods for measuring round trip time (RTT) in network devices between a network intermediary and endpoints are inaccurate when there are network intermediaries like Firewalls and WAN Optimizers present, as they interfere with the TCP connection measurements.
Innovation Solution
The solution involves an intermediary device that identifies and modifies HDX protocol packets to measure client-side and server-side RTT separately, even when the host is not measuring active latency, by setting and resetting an active latency bit in the packets, allowing for accurate RTT calculation without upgrading clients or hosts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If RTT is measured by monitoring TCP connection between network device and endpoints, then RTT measurement is simple, but measurement accuracy deteriorates when network intermediaries like Firewalls and WAN Optimizers are present
Solution Approach 1:
The patent introduces an intermediary mechanism within the HDX protocol itself to measure RTT accurately. Instead of relying on external TCP connection monitoring that fails in the presence of network intermediaries, the solution embeds RTT measurement functionality directly into the existing HDX protocol packets, allowing accurate measurement even when Firewalls and WAN Optimizers are present in the network path.
Solution Approach 2:
The patent modifies the HDX protocol by changing specific parameters within the packets - specifically setting and resetting the 'active latency' bit. This parameter change enables the intermediary device to accurately measure RTT by identifying packets with the bit set, without requiring upgrades to clients or hosts, thus resolving the contradiction between measurement simplicity and accuracy.
2Measurement precision
If Active Latency measurement feature is enabled on host, then client-side RTT can be measured accurately, but system complexity increases and upgrades to hosts are required
Solution Approach 1:
The intermediary device acts as a mediator that enables Active Latency measurement without requiring host upgrades. It intercepts HDX packets, sets the 'active latency' bit when the host is not measuring, and resets it before forwarding to the host. This approach achieves accurate client-side RTT measurement while keeping the host system unchanged.
Solution Approach 2:
Instead of requiring full Active Latency measurement capability on the host, the patent applies partial action by having the intermediary device selectively set and reset the 'active latency' bit only when needed for measurement. This partial intervention achieves the measurement goal without the complexity and upgrade requirements of full host-based Active Latency measurement.
Data Source
AI summary
The present disclosure is directed towards systems and methods for measuring round trip time (RTT) in network devices between the device and an endpoint. A network device may be deployed as an intermediary to provide many security and visibility functions. For measuring the server side RTT between the network device and host, the intermediary device identifies the packet that has been sent by the client when it initiated the RTT measurement. The network device remembers the moment T1 when it sees this packet. The host (e.g., the server) will respond to this with a packet that contains the response. The intermediary device remembers the moment T2 when it sees this response. Server side RTT is calculated by the network device as T2−T1. For measuring the client side RTT the network device and client, the intermediary device identifies the packet that the host sends to initiate measurement of RTT. As per the HDX protocol, the client will respond immediately with a new packet or with a bit set in any packet being sent to the host. Just as for server side RTT, the intermediary device can identify these packets and measure the times to calculate the client side RTT.