EtherNet Protocol

The Ethernet Protocol is one of the oldest LAN technology but still the most popular and the most widely used one in LAN environments. It is used by almost all networks including home, office, universities, and enterprise networks. Of late, due to its higher rates over longer distances through optical media, it has gained popularity also known as a WAN technology too. The Ethernet utilizes a linear bus or star topology. Ethernet served as the basis of the IEEE 802.3 standard. The reason behind its wide usability is Ethernet is easy to understand, implement, maintain, and allows low-cost network implementation. Also, Ethernet offers flexibility in terms of the topologies which are allowed. Ethernet operates in two layers of the OSI model, Physical Layer, and Data Link Layer. For Ethernet, the protocol data unit is Frame, since we mainly deal with the DLL. In order to handle collision, the Access of the control mechanism used in Ethernet is CSMA/CD.

Ethernet Protocol Overview

The Ethernet protocol is used for addressing and media access control at the data link layer. We can create a widest LAN technology by the combination of twisted-pair cable or coaxial cable for connectivity to end system along with fibre optic as a backbone. The use of Ethernet has been started from the 1970s and now there are many other devices came in the market to compete with it such as FDDI, ARCNET, etc. The Ethernet was designed Xerox. The further augmentations of the Ethernet are under the auspices of DEC and Intel. There are various devices connected to the cables by means of communication throughout Carrier Sense Multiple Access. The method of Collision Detection also included in it. Generally, Ethernet referred to as 10BASE-T. Ethernet network based on the wires or cables but it could be wireless if you are using an Ethernet cable for connectivity of the computers. The NIC card uses radio waves with a switch or hub including a small antenna when you are using wireless Ethernet.

Ethernet Protocol Features

  • The Ethernet Protocol is having the automatic CRC and pad generation capability with the flow control through PAUSE frames.
  • The Ethernet network is the less expensive device produced high-speed local area network .they can send and receive data at a very high speed up to 300 feet telephone which is connected with each other via a hub.
  • The Ethernet Protocol does not support reliability and error correction.
  • The Ethernet network is a fast connectively protocol that has the ability to produce up to 10Mbps speed and if Ethernet designated as 100BASE-T. It can be produced up to 100Mbps speed. If you are using the Gigabit Ethernet then you can get up to 1000 Mbps speed.
  • Its powerfulness comes due to its support for a wide variety of physical layer protocols, physical media, line rates, and topologies (bus, star, point to point).
  • The Ethernet offering network with 10Base-T where you can use thin twisted pair cable, thick coaxial cable, and fiber optic cable. All cables support different standards as twisted 10Base-t, coaxial 10Base2-t or 5, and Fiber 10BaseF. If you want to make a fast connection then use 100BaseT twisted pair cable and 100BaseF fiber optic cable.
  • Its wide adaptability comes from its simple nature (connectionless, best-effort delivery approach), backward compatibility between different variants (like FE, GigE, etc.), and cheap cost of hardware implementation.
  • The discrete frames are used for the data transformation through Ethernet. The length of data is 64 to 1518 bytes with obligatory 18 bytes used for header and CRC.
  • The Ethernet facilitates the user that operated devices equally and separately because there is no need for any controlling device.
  • The Ethernet Protocol offering you a variety of data types such as telecommunication protocols TCP, Internet protocol as IP, Apple Talk, and IPX.
  • Ethernet Protocol has lots of abilities, therefore, it is most commonly used. It provides access to the internet under DOS because it has a packet driver program. Ethernet also supports the Novell client and provides an interface which is called ODI. All companies such as Microsoft, IBM, etc support Ethernet and it is also a narrative choice of the window.
  • The Ethernet Protocol supports half and full-duplex mode of communication, though the half-duplex mode is outdated now
  • The Ethernet also secures your data with collision detection. When you are using Ethernet then the fear loss of data vanished. If anyone attempts on your network all devices stop processing immediately and wait until the user attempts to transmit again.
  • The Ethernet is the flexible address filtering mode and frame time stamping.
  • The Ethernet offers you to build a network and share your resources not only in the same building might you exist in any corner of the world. Ethernet facilitates you to talk to each other, share your resources like printer, files, etc from all over the world at very high speed.

Basic Frame Structure of Ethernet (IEEE 802.3)

The Ethernet Protocol framing structure follows the general data link layer frame structure, with fields for frame boundaries, addressing, protocol multiplexing, data, and error detection (CRC). A typical Ethernet frame format is given the diagram below:

ethernet frame structure
Ethernet Frame Structure

Preamble: The Ethernet Protocol frame starts with 7-Bytes Preamble. This pattern of alternative 1’s and 0’s indicates the starting of the frame and allows the sender and receiver to establish bit-level synchronization. Initially, PRE (Preamble) was introduced to allow for the loss of a few bits due to signal delays. But today’s high-speed Ethernet don’t need Preamble to the protect the frame bits. PRE (Preamble) indicates of the receiver that frame is coming and allow the receiver to lock onto the data stream before the actual frame begins.

Start Of Frame Delimiter: A 1-byte Start-Of-Frame with value 10101011, to indicate to the receiver that the actual frame fields start from the next byte after this special byte. It is followed by the SFD to provide the byte-level synchronization and to mark a new incoming frame. The SFD indicates that upcoming bits are starting of the frame, which is the destination address. The SFD is designed to break the bit pattern to the preamble and signal the start of the actual frame. Sometimes the SFD is considered the part of PRE, this is the reason Preamble is described as 8 Bytes in many places.

Frame Header: A normal Ethernet frame header is 18 bytes long, including the 4 byte CRC. It is consists of the source and destination MAC addresses, the EtherType field, and, optionally, an IEEE 802.1Q tag or IEEE 802.1ad tag with 4 byte CRC.

Destination Address (MAC): This is a 6-Byte field that contains the MAC address of the destination system which is the first field in an Ethernet frame. 

Source Address (MAC): A 6-byte source MAC address identifying the sending node of the frame at the data link layer. As Source Address is always an individual address (Unicast), the least significant bit of the first byte is always 0.

VLAN Tag (Optional): The VLAN tagging is a method through which more than one VLAN is handled on a port. VLAN tagging is used to tell which packet belongs to which VLAN on the other side. To make recognition easier, a packet is tagged with a VLAN tag in the Ethernet frame. An optional 4 byte VLAN header tag identifying with the VLAN to which the frame belongs. This field is optional and is present only if VLANs are used in the network.

L3 Proto Type: A 2-byte protocol type field containing the type of the layer 3 packet of the contained in the frame.

Data Field: A variable-length DATA field that contains the actual L3 payload. The maximum length of this field is limited to 1500 bytes for normal ethernet frames but can go up to higher values (around 9000 bytes) for special frames known as jumbo frames.

Padding Field: An optional padding field filled with the value of all zeros, used mainly to maintain a minimum Ethernet frame length. Both IP header and data will be inserted here if the Internet Protocol is used over the Ethernet. This is used only in cases where the DATA field is lesser than 46 bytes. An Ethernet frame has to be of the minimum length equal to 64 bytes, including the 18 byte Ethernet header.

CRC Field: The CRC is 4 Byte field. This field contains a 32-bits hash code of data, which is generated over the Destination Address, Source Address, Length, and Data field of Ethernet Protocol. If the checksum computed by destination is not the same as sent checksum value, data received is corrupted.

When the number of bytes received falls below 60 bytes, the state machine automatically appends zeros to the Tx frame to make the data length exactly 46 bytes. The Transmit CRC Generator module calculates the CRC for the Frame Check Sequence (FCS) field before transmission to the TPE module.

ethernet crc validation
Ethernet CRC validation

Ethernet Protocol Flexible address filtering modes

The address filtering (AFM) module performs the destination and source address checking function on all received frames and reports the address filtering status to the receive frame controller module. The Receive Frame Controller (RFC) module performs frame filtering based on the destination/source address.

ethernet receive frame control
Ethernet Receive Frame Control

Ethernet Protocol frame time stamping

If IEEE 1588 time stamping is enabled for the transmit frame, this block takes a snapshot of the system time when the SFD is put onto the transmit MII bus. The time-stamping feature can be used in precision time protocol to synchronize clocks throughout a network of rotary encoder and control stepping motor at required timing.

ethernet frame time stamp
Ethernet frame time stamping

Extended Ethernet Protocol Frame (Ethernet II Frame) :

The Standard IEEE 802.3 basic frame format is discussed above in detail. Now let’s see the extended Ethernet Protocol frame the header, using which we can get Payload even larger than 1500 Bytes.

ethhernet -2 frame format
Extended Ethernet Frame Format

DA [Destination MAC Address] : 6 bytes.
SA [Source MAC Address] : 6 bytes.
Type [0x8870 (Ethertype)] : 2 bytes.
DSAP [802.2 Destination Service Access Point] : 1 byte.
SSAP [802.2 Source Service Access Point] : 1 byte.
Ctrl [802.2 Control Field] : 1 byte.
Data [Protocol Data] : > 46 bytes.
FCS [Frame Checksum] : 4 bytes.

How to calculate the Throughput of Ethernet?

Protocol Overhead = (Packet Size – PayLoad Size) / Packet Size.

Protocol Efficiency: PayLoad Size / Packet Size.

Maximum efficiency is achieved with the largest allowed payload size and

is: (1500/ 1538) = 97.53%. 

And for untagged frames, since of the packet size is maximum 1500 octet payload + 8 octet preamble + 14 octet header + 4 octet trailer + minimum interpacket gap corresponding to 12 octets = 1538 octets. The maximum efficiency is: (1500/1542) = 97.28%.

But  when 802.1Q VLAN tagging is used, the throughput may be calculated from the efficiency as:

Throughtput = Efficiency * Total Bit Rate.

Channel utilization is a concept often confused with protocol efficiency. It considers only the use of the channel disregarding the nature of the data transmitted – either payload or overhead. At the physical layer, the link of channel and equipment does not know the difference between data and control frames. We may calculate the channel utilization:

Channel Utilization = Time Spent Transmitting Data / Total Time.

Types Of Ethernet Protocol

There are different types of Ethernet protocol divided according to their speed, and with having some extra security features are described below.

  1. Basic Ethernet: A standard Ethernet of the network can transmit data at a rate of up to 10 Megabits per second (10 Mbps).
  2. Fast Ethernet: The Fast Ethernet standard (IEEE 802.3u) has been established for the Ethernet networks that need higher transmission speeds. This standard raises the Ethernet speed limit from 10 Mbps to 100 Mbps with the only minimal changes to the existing cable structure. Fast Ethernet provides faster throughput for video, multimedia, graphics, Internet surfing, and stronger error detection and correction. There are three types of Fast Ethernet: 100BASE-TX for use with level 5 UTP cable; 100BASE-FX for use with fibre-optic cable; and 100BASE-T4 which utilizes an extra two wires for use with level 3 UTP cable. The 100BASE-TX standard has become the most popular due to its close compatibility with the 10BASE-T Ethernet standard.
  3. Gigabit Ethernet: TheGigabit Ethernet was developed to meet the need for faster communication networks with applications such as multimedia and Voice over IP (VoIP). Also known as “gigabit-Ethernet-over-copper” or 1000Base-T, GigE is a version of Ethernet that runs at least speeds 10 times faster than 100Base-T. It is defined in the IEEE 802.3 standard and is currently used as an enterprise backbone. Existing Ethernet LANs with 10 and 100 Mbps cards can feed into a Gigabit Ethernet backbone to interconnect high-performance switches, routers, and servers. The most important differences between Gigabit Ethernet and Fast Ethernet include the additional support of full-duplex operation in the MAC layer and the data rates.
  4. 10 Gigabit Ethernet: The 10 Gigabit Ethernet is the fastest and most recent of the Ethernet standards. IEEE 802.3ae defines a version of Ethernet with a nominal rate of 10Gbits/s that makes it 10 times faster than Gigabit Ethernet. Unlike other Ethernet systems, 10 Gigabit Ethernet is based entirely on the use of the optical fibre connections. This developing standard is moving away from a LAN design that broadcasts to all nodes, toward a system that includes some of the elements of wide-area routing. As it is still very new, which of the standards will gain commercial acceptance has yet to be determined.
  5. Asynchronous Transfer Mode (ATM): The ATM is a cell-based fast-packet communication technique that can support data-transfer rates from sub-T1 speeds to 10 Gbps. ATM achieves its high speeds in part by transmitting data in fixed-size cells and dispensing with error-correction protocols. It relies on the inherent integrity of digital lines to ensure data of integrity. ATM can be integrated into an existing network as needed without having to update the entire network. Its fixed-length cell-relay operation is the signalling technology of the future and offers a more predictable performance than variable-length frames. Networks are extremely versatile and an ATM network can connect points in a building, or across the country, and still be treated as a single network.
  6. Power over Ethernet (PoE): The PoE is a solution in which an electrical current is run to networking hardware over the Ethernet Category 5 cable or higher. This solution does not require an extra AC power cord of the product location. This minimizes the amount of the cable needed as well as eliminates the difficulties and cost of installing extra outlets.

Different Technologies Used in Ethernet:

CSMA/CD: In all the variants of the Ethernet Protocol, CSMA/CD is the standard media access control of the collision resolution protocol used. CSMA/CD is used mainly in bus topologies and in half-duplex modes, where multiple nodes share of the same bus and thereby contend for a channel. Basically CSMA/CD is based on CSMA (Carrier Sense Multiple Access) – Each end node starts transmitting only if the line is not busy already, by looking for the presence of a carrier signal CD ( Collision Detection) – If the value of the signal voltage transmitted on the line by a node is different from the line voltage appearing on the line, then the end of the node detects this as a collision. It immediately sends a special signal called a JAM signal and stops further transmission of the current frame. Once a collision is detected, an end node uses an exponential backoff algorithm before it attempts retransmission.E

What is MAC Address?

Whether you work in a wired network office or a wireless one, one thing is common for both of the environments: It takes both of the network hardware and software (cables, routers, etc.) to transfer data from your computer to another or from a computer thousands of miles away to yours. Every computer system is having two types of address as 1) Physical Address and 2) Logical address.

The physical address is nothing but the hardware address and it is named as MAC (Medium Access Control) which can not be changed for a system. Typically it is then tied to a key connection device in your computer called the network interface card, or NIC. The NIC is essentially a computer circuit card that makes it is possible for your computer to connect to a network. A NIC turns the data into an electrical signal that can be transmitted over the network.

A MAC address is given to the network adapter when it is manufactured. It is hardwired or hard-coded onto your computer’s network interface card (NIC) and is unique to it. Something called the ARP (Address Resolution Protocol) translates an IP address into the MAC address. The ARP is like a passport that takes data from an IP address through an actual piece of the computer hardware. One example of a MAC address for an Ethernet NIC: 00:0b:95:9e:98:17.

MAC Transceivers: The Transceivers are also referred to as Medium Access Units (MAUs). They are used to connect nodes to the various Ethernet media. Most computers and network interface cards contain a built-in 10BASE-T or 10BASE2 transceiver which allows them to be connected directly to Ethernet without the need for an external transceiver.

Standard Ethernet Protocol Code

In order to understand standard Ethernet code, one must of understand what each digit means. Following is a guide:

10at the beginning means the network operates at 10Mbps
BASEmeans the type of signaling used is baseband.
2 or 5at the end indicates the maximum cable length in meters.
Tthe end stands for twisted-pair cable.
Xat the end stands for full duplex-capable cable.
FLat the end stands for fiber optic cable.

For example: 100BASE-TX indicates a Fast Ethernet connection (100 Mbps) that uses the twisted pair cable capable of full-duplex transmissions.

Automotive Ethernet Protocol

Autonomous vehicles (AVs) will require a host of connectivity features to function effectively, such as cameras, LiDAR, and traffic-sign recognition. These sensors, which enable the vehicle-to-everything (V2X) connectivity, are vital to their success. Thus, the demand for the greater bandwidth is set to skyrocket.

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