NDIS 6.0 supports an architecture for full TCP offload. This architecture is called a "chimney offload" architecture because it provides a direct connection, called a "chimney," between applications and an offload-capable NIC. The chimney enables the NIC to perform TCP processing for offloaded connections, including maintaining the protocol state.

The chimney offload architecture reduces host network processing for network-intensive applications. This allows networked applications to scale more efficiently while also reducing end-to-end latency. Fewer servers are needed to host an application, and servers are able to use the full Ethernet bandwidth.

The TCP chimney offloads all TCP processing for one or more TCP connections. The primary performance gains are obtained from offloading segmentation and reassembly (SAR), offloading processing that ensures reliable connections (for example, ACK processing and TCP retransmission timers), and reducing interrupt loading.

Note  The Windows Vista operating system continues to support the individual TCP task offloads available in earlier versions of the operating system. These tasks can be offloaded on connections that have not been offloaded through a chimney. An offload-capable NIC should support both chimney offloads and task offloads. Such a NIC provides the highest degree of offload optimization.

How To Obtain the NDIS 6.0 TCP Chimney Offload Documentation

For information on NDIS 6.0 TCP chimney offload, including documentation, use the following procedure:

1. Go to the Microsoft Connect Web site.
2. Click Invitations on the left navigation bar.
3. Enter the e-mail address and password from your Microsoft Live or .NET Passport account, and click Sign In. If you do not have an account, create one by clicking Sign Up Now.
4. Enter one of the Invitation IDs from the following table, and click Go.

   Windows Network Devices Program	Invitation ID
   NDIS	NDIS-B4JF-H9C9
   NDIS Test	NTst-CY36-J9MX
   Wireless	WLSS-K6QQ-VQT9

5. On the Complete Required Registration Information page, click Continue.
6. On the Register page, provide all required information for access. Please also include Company/Organization Name to ensure access to this program. Click Continue.
7. Your enrollment status will be displayed. When you are accepted for participation, you will be contacted with information on NDIS 6.0 TCP Chimney Offload, including how to obtain the documentation.

Important  For legal information about TCP chimney offload, see Legal Information.