Ethernet Tutorial

Ethernet frames and packets

What are frames?

A frame can be defined as the unit of data transferred across the network, defined at the datalink (network access) layer of the protocol stack.

What are packets?

A packet can be defined as the unit of data at any layer of the protocol stack, prior to, or after transmission.

Is it really that simple?


It's not really quite that simple because some people prefer to further define data in terms of each layer of the TCP/IP protocol suite.

As data descends the source protocol stack, successive levels encapsulate the data with additional information. After a frame has been received at its destination, successive layers then de-encapsulate the data as it travels up the destination protocol stack.

Therefore, a packet can be discussed in terms of its subsets - messages, segments and datagrams.

Frames are not discussed in any other terms, they simply encapsulate the data with a header and addressing information.

What does a frame look like?

The diagram below illustrates the IEEE 802.3 frame:

An octet is defined as eight bits of data.

The ethernet Version 2.0 frame is similar to the IEEE 802.3 frame. For a device to be 802.3 compliant, it must be able to communicate with legacy Version 2.0 devices.

What does each field do?

Tell me more!

Ethernet and IEEE 802.3 Frame Formats From the Cisco web site
Kansas State University Basic frame details
Temple University frame FAQ Easy to follow slide show

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