Traffic Generation
71
size accepted without declaring the OverS defect. Standard IEEE 802.3 specifies an
MTU of 1518 bytes for ordinary Ethernet frames but 1522 is admitted for VLAN frames
and 1526 is valid for frames carrying two VLAN tags (IEEE 802.3ad, Q-in-Q). Some
switches provide support for much larger frames known as jumbo frames. These
frames are more efficient because the ratio of header bytes to payload bytes is smaller
for larger frames but they are currently not accepted by any international standard.
The following steps illustrate the frame configuration procedure in xGenius. Both the
port-wide and flow-specific configuration is included.
Figure 4.1: MAC frame structure: IEEE 802.3 and DIX
Preamble
bits
13 57
2
468
FCS
DA
SA
6
6
2
4
8
bytes
DIX Frame
Type
Preamble
13 57
SDF
2468
FCS
DA
SA
1
6
6
2
4
7
bytes
IEEE 802.3 Frame
Type / Length
bits
Data
LLC
DSAP (0xaa)
13 5 7
Control (0x03)
2
468
1
1
1
bytes
SSAP (0xaa)
Payload
LLC frame (IEEE 802.2 / RFC 1042)
Pad
Protocol ID
13 5 7
2
468
3
bytes
Payload
SNAP frame (IEEE 802.2 / RFC 1042)
Type
(0x00-00-00)
2
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