WG82574L S LBA8 Intel, WG82574L S LBA8 Datasheet - Page 164

• Manufacturer Part Number: WG82574L S LBA8
• Manufacturer: Intel

Specifications of WG82574L S LBA8

• Operating Supply Voltage (typ): 3.3V
• Operating Temp Range: 0C to 85C
• Operating Temperature Classification: Commercial
• Mounting: Surface Mount
• Pin Count: 64
• Lead Free Status / RoHS Status: Compliant

7.2.11.7
7.3
Note:
7.3.1
Note:
7.3.2
164
VLAN
The VLAN field is used to provide the 802.1Q tagging information. The special field is
ignored if the VLE bit in the DCMD command byte is 0b.
TCP Segmentation
TCP segmentation is an offloading option of the TCP/IP stack. This is often referred to
as Transmit Segmentation Offloading (TSO). This feature obligates the software device
driver and hardware to carve up TCP messages, larger than the Maximum Transmission
Unit (MTU) of the medium, into MSS sized frames that have appropriate layer 2, 3 (IP),
and 4 (TCP) headers. These headers must have the correct sequence number, IP
identification, checksum fields, options and flag values as required. This is done by
breaking up the data into segments smaller than or equal to the MSS.
Note that some of these values (such as the checksum values) are unique for each
packet of the TCP message, and other fields such as the source IP address are constant
for all frames associated with the TCP message.
The offloading of these mechanisms to the software device driver and the 82574 saves
significant CPU cycles. The software device driver shares the additional tasks to support
these options with the 82574.
TCP Segmentation Performance Advantages
Performance advantages for a hardware implementation of TCP segmentation offload
include:
TCP segmentation requires the transmit context descriptor format and the transmit
data descriptor format.
Ethernet Packet Format
A TCP message can be fragmented across multiple pages in host memory. The 82574
partitions the data packet into standard Ethernet frames prior to transmission. The
82574 supports calculating the Ethernet, IP, TCP, and UDP headers, including
checksum, on a frame-by-frame basis.
• The stack does not need to partition the block to fit the MTU size, saving CPU
• The stack only computes one Ethernet, IP, and TCP header per segment (entire
• The stack interfaces with the software device driver only once per block transfer,
• Interrupts are easily reduced to once per TCP message instead of once per frame.
• Fewer I/O accesses are required to command the the 82574.
15
cycles.
packet), saving CPU cycles.
instead of once per frame.
PRI
13
CFI
12
11
VLAN ID
82574 GbE Controller—Inline Functions
0