Intel PCI-X, Intel Gigabit Ethernet Controllers manual 9.1 TCP/IP/UDP Header for the First Frame

Receive and Transmit Description

3.5.9.1TCP/IP/UDP Header for the First Frame

The hardware makes the following changes to the headers of the first packet that is derived from each TCP segmentation context.

•IPv4 Header

—IP Total Length = MSS + HDRLEN – IPCSS

—IP Checksum

—IPv6 Header

—Payload Length = MSS + HDRLEN - IPCSS

•TCP Header

—Sequence Number: The value is the Sequence Number of the first TCP byte in this frame.

—If FIN flag = 1b, it is cleared in the first frame.

—If PSH flag =1b, it is cleared in the first frame.

—TCP Checksum

•UDP Header

—UDP length: MSS + HDRLEN - TUCSS

—UDP Checksum

3.5.9.2TCP/IP/UDP Header for the Subsequent Frames

The hardware makes the following changes to the headers for subsequent packets that are derived as part of a TCP segmentation context:

Note: Number of bytes left for transmission = PAYLEN – (N * MSS). Where N is the number of frames that have been transmitted.

•IPv4 Header

—IP Identification: incremented from last value (wrap around)

—IP Total Length = MSS + HDRLEN – IPCSS

—IP Checksum

•IPv6 Header

•Payload Length = MSS + HRDLEN - IPCSS

•TCP Header

—Sequence Number update: Add previous TCP payload size to the previous sequence number value. This is equivalent to adding the MSS to the previous sequence number.

—If FIN flag = 1b, it is cleared in these frames.

—If PSH flag =1b, it is cleared in these frames.

—TCP Checksum

•UDP Header

—UDP Length: MSS + HDRLEN – TUCSS

—UDP Checksum

Software Developer’s Manual 67