To determine the optimal size for the receive window, the receive window autotuning feature measures the product of the network delay and bandwidth, and also looks at the application retrieve-rates.
Then, the receive window autotuning feature changes the receive window size of the ongoing transmission to take advantage of any unused bandwidth. When the receive window autotuning feature is enabled, older routers, older firewalls, and older operating systems that are incompatible with the receive window autotuning feature may sometimes cause slow data transfer or a loss of connectivity between Vista clients. When this occurs, users may experience slow performance.
Or, the applications may crash. These older devices do not comply with the RFC standard. Some device manufacturers provide software that works around the hardware limitations. Note Contact the device manufacturer to determine whether this kind of software is available.
If the incompatible devices are outside your organization, and you cannot change the devices, this issue will remain. In order to determine whether the issue is caused by faulty firewalls, Vista SP1 contains an autotuning diagnostic tool that determines whether a faulty device is in the path from your computer. If the diagnostic tool detects a faulty device on the network, it reduces the degree of optimization performed by the receive window autotuning feature.
The user may not notice that the window autotuning feature was turned down and may continue to use the computer as before. However, the state of the computer is changed. In order to control the state of the autotuning feature, the user may want to disable the diagnostic tool. This tuning will not reduce the time a packet spends in transit. However, note that this is system and BIOS dependent, and some systems will provide higher performance if the operating system controls power management.
You can check and adjust your power management settings from Settings or by using the powercfg command. For more information, see Powercfg Command-Line Options. This setting does not work properly if the system BIOS has been set to disable operating system control of power management.
Enable static offloads. If the traffic is multi-streamed, such as when receiving high-volume multicast traffic, enable RSS. Disable the Interrupt Moderation setting for network card drivers that require the lowest possible latency. Remember, this configuration can use more CPU time and it represents a tradeoff. Handle network adapter interrupts and DPCs on a core processor that shares CPU cache with the core that is being used by the program user thread that is handling the packet.
CPU affinity tuning can be used to direct a process to certain logical processors in conjunction with RSS configuration to accomplish this. Using the same core for the interrupt, DPC, and user mode thread exhibits worse performance as load increases because the ISR, DPC, and thread contend for the use of the core.
If you need to achieve the lowest latency, you should request a BIOS version from your hardware provider that reduces SMIs to the lowest degree possible. The operating system cannot control SMIs because the logical processor is running in a special maintenance mode, which prevents operating system intervention.
In earlier versions of Windows, the Windows network stack used a fixed-size receive window 65, bytes that limited the overall potential throughput for connections.
The total achievable throughput of TCP connections could limit network usage scenarios. TCP receive window autotuning enables these scenarios to fully use the network. For a TCP receive window that has a particular size, you can use the following equation to calculate the total throughput of a single connection. For example, for a connection that has a latency of 10 ms, the total achievable throughput is only 51 Mbps.
This value is reasonable for a large corporate network infrastructure. However, by using autotuning to adjust the receive window, the connection can achieve the full line rate of a 1-Gbps connection. Some applications define the size of the TCP receive window. Window Auto-Tuning feature is enabled by default in Windows 10 and makes data transfers over networks more efficient.
But if your network uses an old router or your firewall software does not support this feature, then you may experience slow data transfers or even loss of connectivity. To check the status of Auto-Tuning feature on your system, in an elevated command prompt windows, type the following and hit Enter:.
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