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ETHERNET CONTROLLER
Added by
Transmitter,
Stripped by
Receiver
Preamble
7-bit
DSAP = Destination service access point
CTRL = Control field
OUI = Origanizationally unique identifier
SFD = Starting frame delimiter
7.5.1.1 Options that affect the Standard MAC Frame
— There are a number of factors and options that can affect the standard MAC frame, as described in Table 7-
2:
— Some PHYs may deliver a longer or shorter preamble.
— Short frame mode permits LLC data fields with less than 46 bytes. Options are available to suppress padding
and to support the reception of short frames.
— Long frame mode supports LLC data fields with more than 1500 bytes. An option is also available to support
to reception of long frames.
— 'No CRC' mode suppresses the appending of a CRC field.
— 'Ignore CRC' mode allows the reception of frames without valid CRC fields.
7-38
Packet (Encoded on the Medium)
Data Frame (sent by user)
Data frame (delivered to user)
S
Destination
Source
F
Address
Address
D
1
6-byte
6-byte
LLC header
DSAP
SSAP
OR
DSAP
SSAP
1-byte
1-byte
Figure 7-5. Fields of an IEEE802.3/Ethernet Frame
Length or
LLC data
type
46 to 1500
2-byte
-byte
LLC information field
CTRL
IP/X.25/......
SNAP
CTRL
OUI
PID
1-byte
3-byte
2-byte
SSAP = Source service access point
SNAP = Subnetwork access protocol
PID = Protocol identifier
LLC = Logical lick control
FCS = Frame check sequence
Added by transmitter
Optionaly stripped
by receiver
PAD
FCS
0 to 46-
4-byte
byte
IP/X.25/......
S3C2500B
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