SE Articles From the Field
Summary
In CommandCTRL, administrators may observe RDP session latency reported around ~400 ms. This is not indicative of actual network latency and typically occurs when RDP is using UDP transport (RDPEUDP).
Symptoms
- Latency displays approximately 400 ms
- Latency appears static or inconsistent with user experience
- Session performance appears normal
- No packet loss or degradation observed
Example
The screenshots below illustrate this behavior:
- The first image shows ~400 ms latency when UDP transport is in use
- The second image shows low latency (~2 ms) when UDP is disabled and TCP is used
Cause
Modern RDP uses a dual transport model:
- TCP for session control and fallback
- UDP (RDPEUDP) for primary data transport when available
When UDP is active, traditional round-trip time (RTT) is not consistently measured, leading to inaccurate latency reporting.
Why ~400 ms Appears
When UDP is in use:
- Latency metrics are not based on true RTT
- Values may become static or synthetic
- Commonly observed around ~400 ms
Resolution / Guidance
If latency shows ~400 ms but the session is performing well:
- This is expected behavior
- It indicates UDP transport is likely in use
To validate:
1. Disable UDP via GPO (Turn Off UDP On Client = Enabled)
2. Reconnect and observe latency returning to normal values (e.g., 2–40 ms)
Best Practices
- Do not interpret 400 ms latency as a network issue
- Correlate with user experience and packet loss
- Use TCP-only testing for accurate latency validation
Key Takeaway
A latency value around 400 ms in CommandCTRL typically indicates UDP transport is in use and does not reflect actual network latency.