Which Three Options Are Fields In A Basic Ethernet Data Frame

This tutorial explains the format, parts, and types of an Ethernet frame in detail. Learn what does an Ethernet frame contains and how to interpret the Ethernet format.

What is the Ethernet frame?

An Ethernet frame is a piece of data along with the data that is required to transport and deliver that slice of data. In networking reference models, such as; OSI Seven Layers model and TCP/IP, the Ethernet frame is defined in the Data link layer.

Ethernet format

An Ethernet frame contains iii parts; an Ethernet header (Preamble, SFD, Destination, Source, and Blazon), Encapsulated information (Data and Pad), and an Ethernet trailer (FCS).

The following image shows an example of an Ethernet frame.

Ethernet header

Ethernet header contains five fields; Preamble, SFD, Destination, Source, and Type. Let's understand each field in detail.

The preamble field

The preamble field is 7 bytes long. It contains a cord of seven bytes. Each byte alternatively stores 1 and 0 to make the design '10101010'. Preamble bytes assist the receiving device to place the first of an Ethernet frame. When a device receives vii continuous bytes of the aforementioned pattern (10101010), it assumes that the incoming data is an Ethernet frame and it locks the incoming bit-stream.

The SFD field

The SFD (Start Frame Delimiter) field is one byte long. Information technology contains a string of one byte. This byte also stores the aforementioned pattern, except the concluding fleck. In the concluding bit, it stores 1 instead of the 0. The post-obit image shows both fields with their related bytes respectively.

The SFD byte indicates the receiving device that the side by side byte is the destination MAC address of the Ethernet frame.

Destination MAC accost

This field is half dozen bytes long. It contains the MAC address of the destination device. MAC address is six bytes or 48 $.25 (1 byte = viii $.25, 6x8 = 48bits) long. For convenience, unremarkably, information technology is written as 12-digit hexadecimal numbers (such as 0000.0A12.1234).

The destination MAC accost allows the receiving device to make up one's mind whether an incoming frame is intended for information technology or non. If a frame is not intended for the receiving device, the receiving device discards that frame.

Source MAC address

This field is also 6 bytes long. Information technology contains the MAC address of the source device. It helps the receiving device in identifying the source device. The following epitome shows an example of both types of address in the frame.

Type field

This field is 2 bytes long. This field stores information most the protocol of the upper layer (network layer).

The Information Link layer of the source computer prepares, packs and loads the Ethernet frame in the media. The Data link layer of the destination computer picks the Ethernet frame from the media. Later on picking the Ethernet frame, the Data link layer of the destination calculator unpacks, processes, and easily over that Ethernet frame to the upper layer for further processing.

If multiple protocols are running in the upper (network) layer of the destination estimator, the information link layer volition fail to hand over the received frame to the upper layer every bit it does not know to which protocol it should give the received frame.

To learn more than virtually how layers exchange and procedure information, you can check this tutorial.

Data Encapsulation and De-encapsulation Explained

The blazon field solves this result. This field allows the sender computer to insert the data of the upper layer protocol. Through this information, the data link layer of the destination computer can easily decide the upper layer protocol to which it should hand over the received frame.

Modern LAN implementations by and large use the IP protocol in the network layer. In that location are two variants of the IP protocol; IPv4 and IPv6. If the type field has value IP or ox800, the frame is carrying the data of the IPv4 protocol. If the type field has value IPv6 or 0x86dd, the frame is carrying the data of the IPv6 protocol.

The post-obit paradigm shows an example of the type field for both IP variants.

Data and Pad field

This field stores the encapsulated data of the upper layer. This field has a size limit of 46 bytes (minimum) to 1500 bytes (maximum). Due to this limit, the network (upper) layer can't pack more or less data in a single packet (encapsulated data of the upper layer). If data is less than the minimum requirement, padding is added. If data is more the maximum limit, extra information is packed in the side by side parcel.

FCS (Frame Check Sequence)

This field is four bytes long. This field stores a four bytes value that is used to check whether the received frame is intact or not. The sender device takes all fields of the frame except the FCS field, and runs them through an algorithm, known as the CRC (Circadian Redundancy Cheque). The CRC algorithm generates a 4-byte event, which is placed in this FCS field.

When the destination device receives a frame, it takes the same fields and runs them through the same algorithm. If the consequence matches with the value stored in the FCS field, the frame is considered proficient and is processed farther. If both values do not match, the frame is considered bad and is dropped.

That's all for this tutorial. If y'all like this tutorial, delight don't forget to share information technology with friends through your favorite social platform.

By ComputerNetworkingNotes Updated on 2019-09-05 05:38:37 IST