Specifications

Ethernet Data Frames
4-6 Ethernet Data Frames
Ethernet II Frame Type
In the early days of computer networks, Digital, Intel, and Xerox got
together and specified a networking standard that they called Ethernet.
This standard included the definition of a data link level access method
and a packet format that shared the Ethernet name (it is now called
Ethernet II because it is in its second revision). Table 4-1 shows the fields
defined for Ethernet II data frames.
The Ethernet II standard specified that a header (consisting of the
Preamble, Source and Destination addresses, and frame type) be added to
the data before sending it on the network medium. The frame format
follows the rules to access a network using the CSMA/CD access method.
Ethernet “Raw” Frame Type
Eventually, both the Ethernet media and packet format were pursued by
the standards committees of the IEEE. Working from the original DIX
specification, IEEE proposed its own Ethernet standard which they called
802.3 (named after the committee that worked on it). Table 4-2 describes
each of the Ethernet 802.3 frame fields (also known as “raw” frames).
Table 4-1. Ethernet II Frame Type
Field Name Field Size Field Definition
Preamble 8 bytes Signals beginning of the packet.
Destination
Address
6 bytes
Contains address of the destination of the
frame.
Source Address 6 bytes Contains address of the packet’s origin.
Type Field 2 bytes Specifies the upper layer protocol used.
Data 46–1500 bytes Contains the data to be transferred.
Frame Check
Sequence
4 bytes Verifies the integrity of the frame.