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Ethernet

Written By: 

Preeti Jain

 

Networking is playing vital role in current IT era where data distribution and access is critically important. As the use of communication between two or more entities increases the networking technologies need to be improved and refurbished over time.  Similarly the transmission media, the heart of a network, has been changed with the time improving on the previous one. If you know a little bit about networking you surely have heard the term Ethernet which is currently the dominant network technology.  Wide spread of the Ethernet technology made most of the offices, universities and buildings use the technology for establishment of local area networks (LANs).

Image Showing a Typical Ethernet Network
Fig. 1: Image Showing a Typical Ethernet Network
 
To understand what actually Ethernet is, we need to know about IEEE first which is a short of Institute of Electrical and Electronics Engineers. IEEE is a part of International Organization for Standardization (ISO) whose standard IEEE 802.3 is defined for Local Area Network. The standard 802.3 commonly known as ETHERNT defines the communication standards for how data is transferred from one network device to another in a local area network. Since the limit for Ethernet cable is few hundred meters Ethernet is commonly deployed for networks lying in a single building to connect devices with close proximity. The same standard for Ethernet enables manufactures from around the earth to manufacture Ethernet products in accordance with the ISO standards that are feasible for all computing devices worldwide.
 
Local Area Network
A LAN is an interconnected group of computers that span over a relatively small area. Generally LANs are limited to a single building or a group of buildings where a wired or wireless communication channel is used for connecting the computers.  A LAN consists of following components:
      ·         Two or more computers
      ·         NIC (Network Interface Card) cards embedded in each computer.
Pictorial Representation of a LAN Network
Fig. 2: Pictorial Representation of a LAN Network

 
 
      ·         A switch or hub to centrally connect all the computers and controlling traffic.
      ·         An Ethernet cable to connect each computer’s NIC to hub/switch.
      ·         Networking software.
A NIC is installed on each computer and is assigned a unique address. The Ethernet cable connects all computers through hub or switch where each computer is directly connected to the central hub/switch. In wireless LANs also called Wi-Fi, a wireless NIC is used in lieu of cables and data is transferred through radio waves.
 
History

Ethernet was developed by Robert Metcalfe at Xerox PARC between 1973 and 1974 and first documented on May 22, 1973. Later it was successfully deployed at PARC in 1976. After two years Xerox developed X-Wire - a 10 Mbit/s Ethernet running on a coaxial cable.

In June 1979, Robert Metcalfe left Xerox and founded 3Com to commercialize the Ethernet. He convinced Gordon Bell at DEC, David Liddle at Xerox and Phil Kaufman at Intel to jointly develop an Ethernet specification based on X-Wire. This specification was called DIX Ethernet which specifies a 10 Mbit/s ethernet cable.

In 1982 Sun Microsystems was founded to develop UNIX workstations with Ethernet. Later soon Intel introduced the first Ethernet interface card. In November 1982, the second version of ethernet was launched known as Ethernet II. Next year the 802.3 specification was formally approved by IEEE and it was adopted by ISO.  Soon there were many new companies like Novell, Cabletron, CISCO, Network General, and SynOptics to develop a variety of devices for Ethernet LAN. Ethernet became the major technology in computer networking by the end of 1980’s. Since then the technology is continuously evolving data speeds and reliability measures.
 
Ethernet terms
Ethernet specification defines all aspects of local area network communication. To understand its actual working, below are some important terminologies that are frequently used in Ethernet networking
·         Medium - An Ethernet medium is the cable used for data travelling. The earlier medium that was used in Ethernet systems was co-axial copper cable which was replaced by twisted pair cables.
·         Segment – A piece of the medium that is used in a single connection is known as segment.
·         Node – The end devices which are connected through segments.
·         Frame – Data and information is divided into frames, where each frame is a short message that travels from source node to destination node. Each frame is constructed according to the protocols and contains a source and destination address.
 

OSI Model & Structure

Open System Interconnection (OSI) Model
      OSI Model is a characterization for standardization of working of a communication system. The model divides the central tasks of data communication into seven layers. Each layer is built upon the one beneath it, acting as an instance which carries out its tasks according to rules defined by protocols which can extend over several layers. These layers are –
       1.      Physical Layer
       2.      Data Link Layer
       3.      Network Layer
       4.      Transport Layer
       5.      Session Layer
       6.      Presentation Layer
       7.      Application Layer
Data transmission on an Ethernet network works in accordance with OSI model layers. For simplicity first two layers are commonly called as physical layers, network and transport layers are termed as transmission layers however each layer has the different tasks to be done. The first – physical layer defines the electrical, mechanical and functional interface to the transmission medium. The second layer – Data Link Layer defines data addressing and reliable data connection between end devices and communication channel by using error detection functions. The network layer controls data transmission timing and logic while transport layer segment data and assigns it to applications. The last three layers – session, presentation and application layer, as all the programs and applications have a direct access to these layers, they are summarized to application layers.
The Ethernet protocol mainly implements the bottom two layers of the OSI 7-layer model, i.e., the data link and physical layers. It uses Carrier Sense Multiple Access/Collision Detection (CSMA/CD) to support the data link layer. CSMA/CD, a protocol to determine how network devices respond when two devices attempt to use a data channel simultaneously, checks the media for other devices before transmitting data to minimize the number of collisions.
The systems communicating over Ethernet send information dividing it to a stream of data into shorter pieces called frames. Each frame contains source and destination addresses and error-checking data so that damaged data can be detected and re-transmitted. There are specific rules for generating frames to send over the Ethernet network:
Length of a frame varies
A frame must contain the source and destination address
There should be a unique address for each device in the network.
A node should be uniquely identified.
 
Structure of Ethernet Frame
An Ethernet frame is made up of five fields: the Destination and the Source MAC address field, the Ethertype field that contains some control information,   a Payload (data) field, and a trailing Frame Check Sequence field that holds a checksum for the frame. The Ethernet frame starts with preamble and start frame delimiter, followed by an ethernet header containing MAC address of source and destination devices. The middle section of the frame consists of payload data including headers for other protocols such as internet protocol, carried in the frame. The end part of the frame consist a 32-bit cyclic redundancy check which detects the errors in transmission. The standard data frame has a maximum length of 1518 bytes, and contains a Payload field of at least 46 and up to 1500 bytes.
The Data Link layer receives data in bit form and combines them into bytes which are combined into frames. These frames encapsulate data packets from the Network layer for. A MAC frame format is used by Ethernet devices to pass data frames and perform a cyclic redundancy check (CRC) for error detection.

Types of Ethernet cabling

Types of Ethernet cabling
The Ethernet physical layer evolved over a considerable time span and encompasses coaxial, twisted pair and fiber optic physical media interfaces and speeds from 10 Mbit/s to 100 Gbit/s. Depending on the requirement and use, Ethernet cables are divided into various categories.
 
Image Showing Different Types of Ethernet Cables
Fig. 3: Image Showing Different Types of Ethernet Cables
 
Straight through and crossover are two types of cables used in networking. Straight through is used for connecting two different types of network devices such as PC and Hub while Crossover cables are used for connecting two same type of networking devices such as PC to PC or Hub to Hub. Besides this simple categorization there are some other things that vary in different Ethernet cables.
Cat 3 – It is used for voice cabling and 10Mb Ethernet
Cat 5 – It is used for 10/100Mb Ethernet and works for voice as well
Cat 5E – It is an enhanced Cat 5 cabling that helps to prevent cross-talk, works for 10/100Mb and 1000Mb (or Gigabit Ethernet)
Cat 6 – It is similar to Cat 5E but with larger gauge wires, works for 10/100/1000Mb. This cable is better than Cat 5e for Gigabit Ethernet.
Cat 7 – Also called Class F, Cat 7 cables are fully-shielded cabling and support up to 600Mhz. This is a relatively new type of cabling and has not been used much.
Besides the new advancements in Ethernet cabling, Category 5E is still in wide use as it works for 100 Mbit/s and is economical compared to the higher categories of cabling.
 Get in depth detail about a conventional ethernet cable through exclusive images and thorough explanation through Insight of ethernet cable.
Wired Vs Wireless LAN
Generally the cables used in wired LANs are Ethernet cables consisting twisted pair cable with RJ45 connectors at both ends. All the data transfer occurs through this cable. Similar like wired LAN, a wireless LAN, commonly known as Wi-Fi can also be established where radio waves are used for data communication instead of a cable. There are particular wirelesses LAN cards are used instead of simple LAN cards. A small antenna situated in wireless network card receives radio signals from computers or hub or switches.