Round Trip Time

Technical Classification

Type: JavaScript Property (navigator.connection.rtt)

Data Source: Browser's Network Information API

When Available: Chromium-based browsers (Chrome, Edge, Opera, Brave), not supported in Firefox or Safari

Return Type: Number (milliseconds)

Background & Purpose

The navigator.connection.rtt property returns an estimate of the round-trip time (RTT) in milliseconds. RTT represents the time it takes for a data packet to travel from the browser to a server and back. This is also commonly known as "latency" or "ping time."

Historical Context:

Part of the W3C Network Information API specification
RTT measurement has been fundamental to networking since early TCP/IP days
Enables applications to adapt to network latency conditions
Based on application-layer RTT measurements, not ICMP ping
Implemented primarily in Chromium-based browsers
Firefox and Safari don't support due to privacy and fingerprinting concerns

What is Round Trip Time?

Definition: Time for request to reach server + time for response to return
Components: Propagation delay + transmission delay + processing delay + queuing delay
Impact: Lower RTT = more responsive web experience
Also called: Latency, ping, lag

Key Characteristics:

Represents an estimate based on recent network activity
Rounded to nearest 25ms to reduce fingerprinting precision
Updates dynamically as network conditions change
More stable than downlink (changes less frequently)
Not based on ICMP ping, but actual HTTP request/response timing

RTT Values & Interpretation

Typical Value Ranges:

RTT (ms)	Quality	Connection Types	User Experience
0-50	Excellent	Local network, nearby servers, fiber	Instantaneous response, perfect for gaming and video calls
50-100	Very Good	Fast cable/fiber, good 4G/5G	Barely noticeable delay, great for all applications
100-200	Good	Standard broadband, 4G LTE	Slight delay noticeable in interactive apps
200-400	Fair	Slow broadband, 3G, distant servers	Noticeable lag, acceptable for browsing
400-1000	Poor	Slow 3G, 2G, satellite, heavily congested	Significant lag, frustrating for interactive use
1000+	Very Poor	2G, satellite, extreme congestion	Severe lag, barely usable

Real-World Examples:

Local network (same city server): 5-20ms
Fast home internet (regional server): 20-50ms
Cross-country (US coast to coast): 60-90ms
Transatlantic (US to Europe): 80-150ms
Transpacific (US to Asia): 150-300ms
Satellite internet: 500-700ms (due to distance to space)
Mobile 4G (good signal): 40-80ms
Mobile 3G: 100-500ms

Factors Affecting RTT:

Physical Distance: Speed of light limits - further = higher RTT
Routing: Number of hops between client and server
Network Congestion: Busy networks add queuing delays
Connection Type: Fiber faster than cable, cable faster than DSL
Server Load: Busy servers take longer to respond
ISP Quality: Better routing and infrastructure = lower RTT

Common Uses

Legitimate Uses:

Interactive Applications: Adjust UI responsiveness based on latency
Gaming: Warn users about high latency that affects gameplay
Video Conferencing: Optimize for low-latency vs high-quality modes
Real-Time Apps: WebRTC, collaborative editing tools adapt to latency
Prefetching Strategy: Only prefetch on low-latency connections
Timeout Configuration: Set appropriate request timeouts based on RTT
UX Optimization: Provide immediate feedback on high-latency connections
Server Selection: Choose geographically closer servers for better performance

Application-Specific Examples:

Online Gaming: Display "high ping" warning when RTT > 150ms
Video Calls: Reduce video quality to prioritize audio on high RTT
Trading Platforms: Critical for time-sensitive financial transactions
Cloud Gaming: Require RTT < 80ms for acceptable experience
Collaborative Tools: Adjust sync frequency based on latency

Combined with Other Metrics:

High RTT + low downlink = distant or congested connection
Low RTT + high downlink = ideal connection (nearby, fast)
Used with effectiveType to determine overall connection quality

Platform Differences

Browser Support:

Browser	Support	Notes
Chrome	Yes (v61+)	Full support, reliable measurements
Edge	Yes (v79+)	Full support on Chromium-based Edge
Opera	Yes (v48+)	Full support
Brave	Yes	Supported, may be limited in strict modes
Firefox	No	Not implemented; `navigator.connection` undefined
Safari	No	Not implemented; privacy concerns
Mobile Chrome	Yes	Works on Android, readings more variable
Mobile Safari	No	Not supported on iOS

Measurement Methodology:

Chrome: Based on actual HTTP request/response timing from recent traffic
Not ICMP: Different from traditional "ping" command
Application Layer: Includes processing time, not just network transit
Rolling Average: Smoothed over recent requests to avoid spikes

Why Limited Support?:

Fingerprinting Concerns: Can reveal geographic/network information
Privacy Philosophy: Firefox and Safari prioritize user privacy
Timing Attacks: Precise timing information can enable certain attacks
Standardization: W3C spec progress has been slow

Fallback Strategies:

Always check: if (navigator.connection?.rtt)
Provide sensible defaults (assume ~100ms for unknown)
Consider manual RTT measurement via fetch requests if needed
Use effectiveType as alternative quality indicator

Privacy Implications

Tracking Risk: LOW

Privacy Concerns:

Geographic Inference: Consistently low RTT suggests proximity to major data centers
ISP Quality: Reveals information about internet service quality
Connection Type Hints: Satellite (very high), mobile (variable), wired (stable)
Network Path: RTT patterns can hint at routing and infrastructure
Fingerprinting Component: Adds entropy when combined with other network metrics
Temporal Patterns: RTT variations throughout day may reveal usage patterns

Why Low Risk:

Rounded Values: Rounded to 25ms increments reduces precision
Limited Uniqueness: Most users fall into common ranges
Variable: Changes with network conditions, less stable for tracking
Limited Browser Support: Not available in Firefox or Safari
Broad Categories: Many users share similar RTT values
Context-Dependent: Depends on which servers browser recently contacted

Entropy Analysis:

Rounded to 25ms increments: ~40 possible values from 0-1000ms
Most users cluster in 50-150ms range (major population centers)
Adds roughly 2-3 bits of entropy to browser fingerprint
More valuable when combined with downlink and effectiveType
Significantly less identifying than timezone or screen resolution

Comparison to Other Metrics:

Less risky than: timezone (HIGH), canvas fingerprint (HIGH), fonts (MEDIUM-HIGH)
Similar risk to: connection type (LOW-MEDIUM), downlink (LOW)
Main concern is when combined with other attributes for comprehensive fingerprinting

User Control & Protection

How to Control RTT Reporting:

Browser Selection:

Firefox: Does not support Network Information API - no RTT exposed
Safari: Does not support Network Information API - no RTT exposed
Chrome/Edge: No native option to disable this API
Brave: Supports API but may limit in aggressive privacy modes

Privacy Extensions:

Fingerprint protection extensions can block or spoof navigator.connection
Canvas Defender, Chameleon, Trace may modify or block this API
uBlock Origin with advanced settings can block JavaScript APIs
Check extension documentation for "Network Information API" controls

Testing Your RTT:

Console: navigator.connection?.rtt
Returns number in milliseconds if supported, undefined otherwise
Monitor changes: setInterval(() => console.log(navigator.connection?.rtt), 5000)

VPN and Proxies:

VPN increases RTT due to additional routing
Reported RTT will be to VPN server, not actual location
Can make fingerprint less consistent with IP-based geolocation
May actually increase uniqueness if RTT/location mismatch is unusual

Limitations of Control:

No built-in Chrome/Edge setting to disable without extension
Blocking may break latency-sensitive applications
Spoofing can cause poor UX (e.g., gaming apps may misbehave)
Limited practical benefit due to low privacy risk

Privacy Best Practices:

Use browsers that don't expose this API (Firefox, Safari) if concerned about comprehensive fingerprinting
Focus on higher-impact privacy measures (VPN, tracker blocking, cookie management)
Accept that RTT alone provides minimal identifying information
Consider comprehensive fingerprinting protection extensions
Be aware that blocking all APIs can break legitimate functionality

For Developers:

Always feature-detect: if (navigator.connection?.rtt)
Provide fallbacks for unsupported browsers
Don't rely solely on this for critical functionality
Consider manual RTT measurement if precise values needed

Additional Resources

MDN: NetworkInformation.rtt
Comprehensive documentation for the RTT property
MDN: Network Information API
Complete overview of the Network Information API
W3C: Network Information API Specification
Official W3C specification for the API
Wikipedia: Round-Trip Delay
Technical explanation of RTT in networking
Web.dev: Adaptive Loading Based on Network Quality
Using RTT and other network metrics for adaptive content
Can I Use: Network Information API
Browser compatibility information for Network Information API
Cloudflare: What is Latency?
Comprehensive guide to understanding network latency

Your Current Round Trip Time