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What is an Ethernet frame? Definition, structure and variants

Know-how   2020-06-21 19:23:36

[if IE 9]> " style = "max- height: 400px; max-width: 99%; "> Ethernet frame: definition and variants of the network frame In an IEEE 802.3 Ethernet network, devices share data packets with each other, also known as Ethernet packets. Their content includes the Ethernet frame (often called a data frame), which in turn is divided into multiple sets of data . These datasets consist of binary code that provides important information, including addresses, control information, user data, and checksums. According to the Ethernet standard, Ethernet frames are structured differently and can contain more or less data fields, depending on the network protocol . Definition When transmitting data via Ethernet, the Ethernet frame is mainly responsible for controlling correct and successful transmission of the data packets. The data sent via Ethernet is almost transported by the frame. An Ethernet frame has a size between 64 bytes and 1518 bytes, depending on the size of the data to be transported. In the OSI model , the frame is located on the link layer which is responsible for error-free transmission and separates the binary data stream into blocks or frames. The first version of Ethernet (Ethernet I) was still based on 16-bit data fields with no defined modern Ethernet was used for the first time in the so-called Ethernet II structure before Ethernet was developed in 1983 by the IEEE (Institute of Electrical and Electronics Engineers) in the standard protocol IEEE 802.3 (first IEEE 802.3raw). In the course of technical progress, the structure of the managers has been adapted several times so that the managers can carry more precise information data. In IEEE 802.3 format, the basic MAC frame and the SNAP frame for the multiplex method and for the manufacturer"s identification data were created. For the development of wifi, the Ethernet II frame and the IEEE 802.3 Ethernet frame were developed as tagged variants , that is to say they have a special label. This tag contains control data that can assign the frame to a specific VLAN. Summary "> Ethernet II Ethernet 802.3raw Ethernet IEEE 802.3 Ethernet IEEE 802.3 SNAP VLAN 802.1q - Ethernet II Tagged and IEEE 802.3 Tagged Overview: basic components of frames ethernet Ethernet II [if IE 9]> " style = "max- height: 400px; max-width: 99%; "> the classic Ethernet 802.3raw frame structure An Ethernet frame must have a size of at least 64 bytes by default for collision detectionworks, and can have a maximum size of 1518 bytes . The packet always starts with a preamble , which controls the synchronization between the transmitter and the receiver, and a Start Frame Delimiter ( SFD ), which defines the frame. The two pieces of information are a sequence of bits in the format 10101010 .... The actual frame contains information on the destination and source addresses (MAC format) and control information (in the case of Ethernet II, the type field , later a length specification), followed by all the data to be transmitted. A Frame Check Sequence ( FCS ) closes the entire frame (except for the preamble and the SFD) as a checksum. The packet is terminated by an Inter Frame Gap , which defines a transmission pause of 9.6 µs. Ethernet II uses the conventional frame structure, which includes the type field , which defines different protswitching layer oceans. In the OSI model, the network layer is important for switching connections and providing network addresses. In later frame formats, the type field has been replaced by a length specification. Note The type field in Ethernet II determines the switching protocols used. This is important to segment the data flow and avoid data stuffing. The Ethernet II frame was defined in 1982 and is the cornerstone of subsequent frames. However, the format is still very popular today, mainly because it gives the most space to the data field.current (up to 1,500 bytes). Ethernet 802.3raw [if IE 9]> The standardized frame structure of Ethernet 802.3. The new features are DSAP and SSAP which replace the type field and the control field which contains the LLC frame]. Novell released this supposed raw version of the 802.3 packet with the popular IPX / SPX protocol before the establishment of the IEEE 802.3 standard and unfortunately called it Ethernet 802.3, which often led to confusion with the I standardEEA . Therefore, Novell added raw. Unlike the conventional Ethernet II model, this frame defines for the first time an exact end of the bit sequence for the SFD. This means that the data packet is identified by the receiver as an 802.3 standard. Instead, the type field, which is replaced by a length specification, no longer exists. This frame type does not contain a protocol identifier because it can only be used for Novell IPXes. In addition, the data to be transmitted is always preceded by 2 bytes, which always consist of several bytes. This is the only way to distinguish a “raw" frame from other frames in the 802.3 family. The IEEE 802.3raw frame can only be used for the IPX protocol because the protocol ID of the type field is missing. The name IEEE 802.3raw is also slightly misleading because Novell used the name of the protocol without involving the IEEE in the development of the frame. LUsing this frame represents an extra effort for the user , as compatibility issues between devices may arise. Since 1993, Novell has recommended the Ethernet 802.2 format for its Netware, which is nothing more than the IEEE 802.3 framework below (to avoid any risk of confusion with the raw framework). In addition, Novell now also supports the official IEEE 802.3 standard. Ethernet IEEE 802.3 [if IE 9]> The standardized frame structure of Ethernet 802.3. The new features are DSAP and SSAP which replace the type field and the control field which contains the LLC] frame. This standardized version of the 802.3 Ethernet frame can in turn define up to 256 compatible protocols. In addition, important protocol information is now integrated into the data field. The fields " D estination S ervice A ccess P anointed (DSAP) and" S ource S ervice A ccess P anointed (SSAP) are also included. The new control field defines the logical link (LLC) of the protocol. This point ensures transparency in media sharing procedures. In addition, information for controlling data flow is stored there, among other things. Ethernet IEEE 802.3 is by far the most popular LAN frame structure and the no longer usedtoday. However, some networks and protocols require more space for certain information. Therefore, there are variants of the IEEE 802.3 frame that provide additional data blocks for specific information, including the SNAP extension and the VLAN tag. Ethernet IEEE 802.3 SNAP [if IE 9]> Classic 802.3SNAP Ethernet frame structure. The SNAP field is a special feature. The SNAP (Subnetwork Access Protocol) field allows you to define more256 protocols. It provides 2 bytes for the protocol number. The manufacturer can also integrate a unique identifier (3 bytes). Unlike its predecessors, SNAP also provides backward compatibility with Ethernet II. DSAP, SSAP and Control are defined here. With the addition of a protocol information space, IEEE 802.3 SNAP is extremely versatile and allows compatibility between many different protocols on a network. However, the space for actual data is a bit smaller. VLAN 802.1q - Ethernet II Tagged and IEEE 802.3 Tagged [if IE 9]> The classic structure of an Ethernet II Tagged frame. The tag field contains important information for VLAN integration. Frames tagged contain a VLAN tag that allows them to be assigned to a Virtual Local Area Network (VLAN). The VLAN separates the network structure into physical and logical levels. This means that VLANs can be used to implement subnets without having to install additional hardware: the subnet is therefore virtual and is not physically implemented. The tag field is necessary for the identification of Ethernet frames in a VLAN. On a physical level, VLANs operate via switches. In the OSI layer model, the VLAN works on the link layer (layer 2) and thus controls the control of data flow. With VLAN, more efficient networks can bedeveloped by dividing a network into subnets . The labeled frames are responsible for the information processed by the switch. In the Ethernet II frame, the tag field is implemented before the type field and occupies 4 bytes. It also increases the minimum size of the Ethernet II frame by 4 bytes. [if IE 9]> The classic frame structure of Ethernet 802.3 Tagged. The Tag field contains important information for VLAN integration Of course, VLAN tags can also be installed in today"s most popular IEEE 802.3 frame format. Within this framework, the tag field is implemented with a size of 4 bytes before the length. The minimum size of the image is thus reduced from 4 bytes to 68 bytes. : basic components of Ethernet frames Component Size Function Preamble Start Frame Delimiter (SFD) 8 bytes Recipient synchronization Sequence bit which introduces the frame Destination address (MAC) 6 bytes Hardware address of the target network adapter Source address (MAC) 6 bytes Hardware address of the source network adapter Tag 4 bytes Optional VLAN tag for integration into VLANs (IEEE 802.1q ) Type 2 bytes Ethernet II: marking of layer 3 protocols Length 2 bytes Information about the length of the dataset Destination Service Access Point ( DSAP) 1 byte Individual address of the access point to the targeted service Source Service Access Point (SSAP) 1 byte Source address of the sending device Control 1 byte Defines the LLC framework (logical link) SNAP 5 bytes Field used to define the unique organization identifier (YES) from the manufacturer and the protocol number (such as Type) Data 44–1,500 bytes (the limits depend on the frame structure) Data to be transmitted FrameCheck Sequence (FCS) 4 bytes Checksum that calculates the entire frame Inter Frame Gap (IFS) - 9.6 µs pause between transmissions