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10: Ethernet - Ethernet frame header, trailer, format, & structure (intro) part 10


Ethernet frame header, trailer, format, & structure

Ethernet Frame introduction

Framing : Role of the header and trailer lesson has shown some basic details of what a frame is and what it is composed of. However, it describes the role of the header and trailer in general, without delving into details and expounding each field profoundly. This present lesson is aimed to cover Ethernet frame in more details. Notwithstanding the constant development of Ethernet technology, including its media and standards, the Ethernet frame remains unchanged to the extent that the very first version of Ethernet is virtually the same as the current one.

Given the fact that Ethernet frame consists of fields, each with a specific function, it is of pivotal significance to have a firm grasp of them with a view to recognize the function of the whole frame, as well as the operation of Ethernet. Additionally, it is recommended to understand Ethernet frame in reference to the Data-link Layer, on the grounds that it is the layer where it is generated.

As you have seen throughout the OSI layers, Transport and Network layers hugely participate in the transmission of data by generating headers added to each piece of data. In the same way, Data-link layer also creates a header and a trailer that are added to the packet when arriving at Data-link layer. It seems as the following :
Ethernet frame header, trailer, format, & structure

The above drawing shows how Data-link layer’s frame is. This frame is itself the one that this lesson aims to clarify. It is currently referred to as Ethernet frame because of the fact that it was created by the same consortium of companies ( DEC, Intel, and Xerox), however, It is of pivotal significance to point out that there are three types of frame ; but they are all the same except for a slight difference in one field for each.

Ethernet II (DIX) frame, IEEE 802.2 (LLC) frame, and Ethernet SNAP frame are all the three Ethernet frames that this lesson is going to cover. Significantly, the predominant one is Ethernet II (DIX) frame, It  was the first implemented frame after the experimental Ethernet in 1973.  This Ethernet frame was intially used with 10Mb/s over thick coaxial cable in 1982. In 1983, this standard went through a formal IEEE standardization process which gives rise to the creation of a new standard called 802.3. In this standard’s frame, the Ethertype field was changed to a Length field, whose function is explained below. (see the next lesson)
10: Ethernet - Ethernet frame header, trailer, format, & structure (intro) part 10 Reviewed by BOUFTIRA on 3:28:00 PM Rating: 5

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