For example, are you running a DNS server on a system on which it is essential that other networking services be as highly responsive as possible? Consider moving the DNS component to a different server to free up that valuable bandwidth and to release the server from these particular duties. Take some time to plan what you want the server to do, and make sure that it isn't doing anything else. Buy additional servers if you have to in order to increase performance.
Likewise, make sure that other unnecessary networking components have not been installed. For example, do you have a NetWare server on your network? You can verify which components are installed on a particular connection by choosing Start Control Panel Network Connections and then choosing the network connection you wish to view.
On the status screen for the connection, click the Properties button to see a list of the components installed. Remove any that are not needed. Make sure network errors aren't a problem Not all performance tweaks can be performed at the server. Often, such tweaks, and network problems in general, are the result of problems on the physical network itself and not the server.
Ensuring there are no errors on the physical network may be the best way to begin improving server networking performance. By default, Windows will report only the total bytes sent and received on the network medium. However, by adding a key to the registry, you can allow Windows to report error statistics on the status page for any network connection.
To avoid confusion of duplicate sequence numbers, the TCP timestamp is used as an extension to the sequence number. Packets have current and progressing time stamps. An old packet has an older time stamp and is discarded. Before SACK, a receiver could only acknowledge the latest sequence number of a contiguous data stream that had been received, or the "left edge" of the receive window. With SACK enabled, the receiver continues to use the ACK number to acknowledge the left edge of the receive window, but it can also acknowledge other blocks of received data individually.
The data blocks are identified using the sequence number at the start and at the end of that block of data.
It's also known as the left and right edge of the block of data. Length is the length in bytes of this TCP option. With SACK enabled default , a packet or series of packets can be dropped. The receiver informs the sender which data has been received, and where there may be "holes" in the data. The sender can then selectively retransmit the missing data without a retransmission of blocks of data that have already been received successfully. The SackOpts value in the following registry key can be edited to control the use of selective acknowledgments:.
The valid binary value is 0 or 1, the default value is 1. The following Network Monitor trace illustrates a host acknowledging all data up to sequence number , plus the data from sequence number The missing data is from to As a review of normal retransmission behavior, TCP starts a retransmission timer when each outbound segment is handed down to the Internet Protocol IP.
If no acknowledgment has been received for the data in a given segment before the timer expires, then the segment is retransmitted. The timer for a given segment is doubled after each retransmission of that segment. Using this algorithm, TCP tunes itself to the normal delay of a connection. TCP retransmits data before the retransmission timer expires under some circumstances.
The most common cause is a feature known as fast retransmit. When a receiver that supports fast retransmit receives data with a sequence number beyond the current expected one, some data was likely dropped. To help inform the sender of this event, the receiver immediately sends an ACK, with the ACK number set to the sequence number that it was expecting. It will continue to do so for each additional TCP segment that arrives.
When the sender starts to receive a stream of ACKs that's acknowledging the same sequence number, a segment may have been dropped. The sender will immediately resend the segment that the receiver is expecting, without waiting for the retransmission timer to expire. This optimization greatly improves performance when packets are frequently dropped. The TcpMaxDupAcks value in the following registry key can be edited to control the number of ACKs necessary to start a fast retransmits:.
This parameter determines the number of duplicate ACKs that must be received for the same sequence number of sent data before fast retransmit is triggered to resend the segment that has been dropped in transit. Skip to main content. This browser is no longer supported. Download Microsoft Edge More info.
Contents Exit focus mode. Is this page helpful? Some network adapters set their receive buffers low to conserve allocated memory from the host. The low value results in dropped packets and decreased performance. Therefore, for receive-intensive scenarios, we recommend that you increase the receive buffer value to the maximum. If a network adapter does not expose manual resource configuration, either it dynamically configures the resources, or the resources are set to a fixed value that cannot be changed.
To control interrupt moderation, some network adapters expose different interrupt moderation levels, different buffer coalescing parameters sometimes separately for send and receive buffers , or both. You should consider interrupt moderation for CPU-bound workloads. When using interrupt moderation, consider the trade-off between the host CPU savings and latency versus the increased host CPU savings because of more interrupts and less latency.
If the network adapter does not perform interrupt moderation, but it does expose buffer coalescing, you can improve performance by increasing the number of coalesced buffers to allow more buffers per send or receive.
Many network adapters provide options to optimize operating system-induced latency. Latency is the elapsed time between the network driver processing an incoming packet and the network driver sending the packet back. This time is usually measured in microseconds. For comparison, the transmission time for packet transmissions over long distances is usually measured in milliseconds an order of magnitude larger.
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.
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