> Source: [sk183805](https://support.checkpoint.com/results/sk/sk183805)

# sk183805 - Windows Multimedia Scheduler and Network Throttling Limits Windows Remote Access Client's Throughput

| Property | Value |
|----------|-------|
| Solution ID | sk183805 |
| Date Created | 2025-09-02 |
| Last Modified | 2025-09-08 |
| Technical Level | Advanced |
| Products | Security Gateway, Endpoint Security |
| Versions | R82.10, R82, R81.20, Cloud, E89.X, E88.X |
| OS | Windows |
| Platform | Open Server |

## Symptoms

- * VPN throughput is reduced to 10--52 Mbps despite high-bandwidth connectivity.
* VPN speed drops when Microsoft Teams or Zoom are running, even when not in active use.
* CPU usage remains normal.
* Affects Windows Vista and newer versions.

## Cause

When multimedia applications such as Microsoft Teams or Zoom register with the Windows Multimedia Class Scheduler Service (MMCSS), the operating system enforces network throttling to prioritize real-time audio and video traffic. This throttling applies system-wide, even when these applications are running in the background, and can significantly reduce VPN throughput. This behavior is by design and affects Windows Remote Access VPN clients in high-speed network environments.  

Default MMCSS throttling behaviour - Windows enforces a cap of 10,000 packets per second on system-wide network processing when MMCSS is triggered.  

**Technical Details**   

When using the built-in Windows VPN client, traffic is routed through a Virtual Network Adapter (VNA), which encapsulates application traffic into an encrypted VPN tunnel.  

* Each packet in the VPN tunnel generates two system-level packets:
  * Clear packet (App ? VNA)
  * Encrypted packet (VPN Client ? NIC)
* VNA MTU: 1350 bytes
* Estimated Payload per packet: \~1300 bytes (after removing headers overhead)

**Throughput Calculation (MMCSS Throttling Enabled)**   

|------------------------------|---------------------|
| **Metric**                   | **Value**           |
| MMCSS packet cap             | 10,000 pps          |
| VPN encapsulation multiplier | 2x                  |
| App-level packets allowed    | 5,000 pps           |
| Payload per packet           | 1,300 bytes         |
| VNA Max throughput           | 6.75 MB/s ? 52 Mbps |
| Payload max throughput       | 6.5 MB/s ? 52 Mbps  |

<br />

? Effective VPN throughput is capped at \~52 Mbps, even if the underlying link supports 1 Gbps or higher.  
For non-VPN traffic, the MMCSS cap results in \~10,000 pps � 1,500 bytes ? 120 Mbps on a standard Ethernet MTU.

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