Intel Gigabit Ethernet Controllers User Manual

67

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

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