Windows 7 / Networking

---

Scalable Networking

As LAN bandwidth has increased beyond gigabit speeds, other components of a computer have become bottlenecks, limiting network performance. For example, a computer connected to a 10-gigabit network might not be able to saturate the link fully because the processor would be fully utilized processing network traffic.

Windows Vista, Windows 7, and Windows Server 2008 support the following scalable networking technologies (which require compatible hardware):

• TCP Chimney Offload The computer's processor must assemble data from multiple TCP packets into a single network segment. TCP Chimney Offload allows the network adapter to handle the task of segmenting TCP data for outgoing packets, reassembling data from incoming packets, and acknowledging sent and received data. TCP Chimney Offload is not compatible with QoS or adapter teaming drivers developed for earlier versions of Windows. TCP Chimney Offload does not change how non-TCP packets are handled, including Address Resolution Protocol (ARP), Dynamic Host Configuration Protocol (DHCP), ICMP, and UDP. TCP Chimney Offload still requires the operating system to process every application input/output (I/O). Therefore, it primarily benefits large transfers, and chatty applications that transmit small amounts of data will see little benefit. For example, file or streaming media servers can benefit significantly. However, a database server that is sending 100-500 bytes of data to and from the database might see little or no benefit.
  Note To examine TCP Chimney Offload performance testing data, read "Boosting Data Transfer with TCP Offload Engine Technology" at http://www.dell.com/downloads /global/power/ps3q06-20060132-broadcom.pdf and "Enabling Greater Scalability and Improved File Server Performance with the Windows Server 2003 Scalable Networking Pack and Alacritech Dynamic TCP Offload" at http://www.alacritech.com/Resources /Files/File_Serving_White_Paper.pdf. For more information about TCP Chimney Offload, read "Full TCP Offload" at http://msdn.microsoft.com/en-us/library/aa503758.aspx.
• Receive-side scaling (RSS) With NDIS 6.0 and in Windows Vista, Windows 7, and Windows Server 2008, incoming packets can be processed by multiple processors. In earlier versions of Windows, packets had to be processed by a single processor. Because more new computers have multiple cores and processors, this can alleviate an important bottleneck when used with a network adapter that supports RSS.
  Note For detailed information about RSS, read "Scalable Networking: Eliminating the Receive Processing Bottleneck-Introducing RSS" at http://download.microsoft.com/download/5/D/6/5D6EAF2B-7DDF-476B-93DC-7CF0072878E6/NDIS_RSS.doc.
• NetDMA NetDMA moves data directly from one location in the computer's main memory directly to another location without requiring the data to be moved through the processor, reducing the processor overhead. NetDMA requires the underlying hardware platform to support a technology such as Intel I/O Acceleration Technology (Intel I/OAT). NetDMA and TCP Chimney Offload are not compatible. If a network adapter supports both NetDMA and TCP Chimney Offload, Windows Vista and Windows 7 will use TCP Chimney Offload.
• IPsec Offload IPsec authentication and encryption requires some processor overhead. Although the IPsec generated by a typical workstation will not significantly affect processor utilization, a workstation that is transferring large amounts of data (typically at greater than gigabit speeds) can dedicate a significant amount of processing time to IPsec. IPsec Offload moves IPsec processing to the network adapter, which typically has a processor optimized for handling authentication and encryption tasks.