Specifications

Ethernet Data Frames 4-5
Ethernet Data Frames
Due to inherent propagation delays in electronics and cabling it would
make sense that within 25.6 µs (half of 51.2 µs) our transmitted signal
should have reached the farthest point on the network. If a collision were
to happen at the farthest point on the network the collision signal will
have the remaining 25.6 µs to travel back to the transmitting node thus
alerting the node that its transmission needs to be re-sent. The 25.6 µs one
way propagation window is also called the collision domain.
Data Frame Types
Ethernet data frames are packaged one of four ways:
• Ethernet II (DIX)
• 802.3 “raw”
• Ethernet 802.2
• Ethernet SNAP
Figure 4-3 shows each of the Ethernet frame types. The Ethernet 802.2 and
Ethernet SNAP frames are extensions of the 802.3 “raw” frame format,
while the Ethernet II frame is formatted differently. The following sections
describe each frame type.
Figure 4-3. Ethernet Frame Types
1913-07
802.3 "Raw" Frame
Preamble
7 bytes
FCS
4 bytes
Start Frame
Delimiter
1 byte
Source
Address
6 bytes
Length
2 bytes
Data
46 - 1,500 bytes
Destination
Address
6 bytes
Ethernet II Frame
Preamble
8 bytes
FCS
4 bytes
Destination
Address
6 bytes
Source
Address
6 bytes
Type
2 bytes
Data
46 - 1,500 bytes
FCS
4 bytes
Preamble
7 bytes
Ethernet 802.2 Frame
Start Frame
Delimiter
1 byte
Source
Address
6 bytes
Length
2 bytes
Data
43 - 1,497 bytes
Destination
Address
6 bytes
DSAP
1 byte
SSAP
1 byte
Control
1 byte
Ethernet SNAP Frame
Start Frame
Delimiter
1 byte
Source
Address
6 bytes
Length
2 bytes
Data
37 - 1,492 bytes
Destination
Address
6 bytes
DSAP
1 byte
SSAP
1 byte
Control
1 byte
Protocol
Identifier
5 bytes
Preamble
7 bytes
FCS
4 bytes