Specifications
Appendix C Operating Environment Installation and Operation Manual
C-14 Ethernet Transmission Technology FCD-E1LC Ver. 1.0
Basic Ethernet Frame Structure
The frame transmitted by each node contains routing, management and error
correction information. For Ethernet LANs, the characteristics of frames are
defined by IEEE Standard 802.3.
Basic frame lengths can vary from 72 to 1526 bytes and have the typical
structure shown in
Figure A-4
.
Preamble
(7 Bytes)
SFD
(1 Byte)
MAC Destination
Address
(6 Bytes)
Length/Type
(2 Bytes)
Padding
Bytes
MAC Client Data
(0 to 1500 Bytes)
Frame
Check
Sequence
(4 Bytes)
MAC Source
Address
(6 Bytes)
72 to 1526 Bytes
Start Frame
Delimiter
Figure C-4. Basic Ethernet Frame Structure
• Preamble. Each frame starts with a preamble of seven bytes. The preamble is
used as a synchronizing sequence for the interface circuits, and helps bit
decoding.
• Start-Frame Delimiter (SFD) field – consists of one byte. The SFD field
indicates where the useful information starts.
• Medium-Access (MAC) Destination Address (DA) field – consists of six bytes.
The MAC DA field carries the address of the destination node.
• Medium-Access (MAC) Source Address (SA) field – consists of six bytes. The
MAC SA field carries the address of the source node.
In writing, MAC addresses are represented as 6 pairs of hexadecimal digits,
separated by dashes, for example, 08-10-39-03-2F-C3.
• Length/Type field – consists of two bytes that indicate the number of bytes
contained in the logical link control (LLC) data field. In most Ethernet protocol
versions, this field contains a constant indicating the protocol type (in this
case, this field is designated EtherType).
• MAC Client Data field. The MAC client data field can contain 0 to 1500 bytes
of user-supplied data.
• Padding field. The optional padding field contains dummy data, that is used
to increase the length of short frames to at least 64 bytes.
• Frame Check Sequence (FCS) field – contains four check bytes generated by a
cyclic redundancy check (CRC) code. The FCS field is used to detect errors in
the data carried in the frame.
Note