Ethernet & Ethernet Frames Explained

Ethernet & Ethernet Frames Explained

What is Ethernet and Ethernet Frames?

We’ve already discovered that an Ethernet frame is encapsulated data specified by the Network Access layer. An Ethernet frame begins with a header, which includes the source and destination MAC addresses as well as other details. The actual data is in the center of the picture. The frame concludes with a field known as Frame Check Sequence (FCS).

Ethernet Explained – What does it consist of?

Ethernet is a method of linking computers in a local area network, also known as a LAN. Since the 1990s, it has been the most commonly used method of connecting computers in LANs. The basic concept behind its architecture is that several computers can access it and submit data at any time. Ethernet frames is the bits of information that is sent upon the network being established.

The IEEE 802.3 specification defines the Ethernet frame structure. Here’s a graphical representation of an Ethernet frame, along with a definition of each field:

Ethernet is the most widely used networking technology for local area networks (LANs) today. It specifies the wiring and signaling for the OSI model’s Physical layer. It specifies frame formats and protocols for the Data Link layer.

The IEEE 802.3 standard is used to characterize Ethernet. It supports speeds of up to 100 Gbps and employs the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) access process. It is compatible with coaxial, twisted pair, and fiber optic cables. To deliver data over Ethernet, frames with source and destination MAC addresses are used.

Ethernet Frames Explained

The Ethernet frame structure as described and defined in IEEE 802.3 standard.

The Ethernet frames explained in the table below:

Preamble Start frame delimiter (SFD)8 bytesSynchronization of the receivers Bit sequence that initiates the frame
Destination address (MAC)6 bytesHardware address of the destination network adapter
Source address (MAC)6 bytesHardware address of the source network adapter
Tag4 bytesOptional VLAN tag for integration in VLAN networks (IEEE 802.1q)
Type2 bytesEthernet II: labeling of layer 3 protocols
Length2 bytesLength information about the record
Destination service access point (DSAP)1 byteIndividual address of the addressed service access point
Source service access point (SSAP)1 byteSource address of the sending device
Control1 byteDefines the LLC frame (logical link)
SNAP5 bytesField for the definition of the organizationally unique identifier (OUI) of the manufacturer and the protocol number (like “Type”)
Data44-1,500 bytes (limit depending on frame structure)The data to be transmitted
Frame check sequence (FCS)4 bytesChecksum that computes the entire frame
Inter frame gap (IFS)Transmission break of 9.6 μs


A note on Runt Frames in Ethernet Frame.

Runt Frames – A runt frame is an Ethernet frame that is less than the minimum length of 64 octets specified by IEEE 802.3. Collisions are the most common cause of runt frames; other potential causes include a faulty network card, buffer underrun, duplex mismatch, or software problems.


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