Ethernet is a networking technology. It involves the physical layer and the data-link layer of the OSI model of networks. It was invented by Robert Metcalfe. Ethernet was originally designed in 1980 but it was standardized in 1983 by Institute of Electrical and Electronics Engineers (IEEE) as IEEE 802.3. The originally designed Ethernet provided a speed of 10 Mbps (Megabits per second). Today, Ethernet is the most widely implemented LAN (Local Area Network) standards. Ethernet provides a reliable, efficient and secure access to information.
Almost all of the organizations, schools, and enterprises use Ethernet to connect their computer systems. Although the size of an Ethernet cable is not usually more than 100 m, Network Bridges are employed to connect several computers. Since 1983, Ethernet has evolved and now provides a maximum connection speed of 100 Gbps (Gigabits per second). Higher level network protocols use Ethernet as the transmission medium. The data is transferred as frames. A frame is unit from the stream of data which includes the data itself and a header which comprises of the source and destination address and some error correcting mechanism as well so that in case of a damaged frame, the frame can be re-transmitted.
Taking an example here, let us suppose that computer A wants to print a document. So it sends a command over the Ethernet medium. Since this command travels as a packet, it has its destination address with it. So, regardless of how many systems are connected to the network, the command is sent only to the device whose address matches the destination address of the packet.
One interesting thing about the addresses is the broadcast address. A frame with the destination address equal to the broadcast address will be delivered to all the devices connected onto the Ethernet. The broadcast address is usually the one in which the last octet of the IP address has a decimal equivalent of 255. Ethernet is interfaced to a computer by an Ethernet port. An Ethernet port is an opening on computer network equipment that Ethernet cables plug into. These ports are alternatively called jacks or sockets. Ethernet ports accept cables with RJ-45 connectors.
Protocol Used by Ethernet
The Ethernet regulates its communication over the network using CSMA/CD protocol. CSMA/CD stands for Carrier Sense Multiple Access with Collision Detection. It is a media access control method. It uses a carrier sensing mechanism in which a station, transmitting data, detects other signals while transmitting a frame, and stops transmitting that frame, transmits a jam signal and then waits for a random time interval before trying again. This results in an improvement in performance because as soon as a collision is detected the transmission is terminated, thus shortening the time interval before attempting a retry. We can summarize the procedure into steps as follows:
- Checks if the frame is ready for transmission
- Checks if the medium is idle. If false, then waits for the medium to become idle
- Starts transmission of the frame
- Senses if a collision has occurred. If yes, resets transmission counters and end frame transmission
After detecting the collision, the procedure follows like this:
- Transmission is continued until minimum packet time is reached to ensure that all receivers detect the collision.
- Re-transmission counter is incremented.
- If maximum number of re-transmissions was reached, then the transmission is aborted.
- Based on the number of collisions, a waiting time, called back off time is calculated.
- Re-transmission starts again.
Over the years, IEEE has revised various Ethernet standards. Below is a table which enlists them all. Ethernet connects devices over a medium through which the data flows.
|Ethernet Standards||Brief Description|
a.k.a Thin Ethernet or Thinnet or Thinwire
|Speed – 10Mbps
Medium – Coaxial Cable
Max Distance – 185 m
a.k.a Thick Ethernet or Thicknet or Thick Wire
|Speed – 10 Mbps
Medium – Coaxial Cable
Max Distance – 500 m
|10 Base-36||Speed – 10 Mbps
Medium – Multi-channel coaxial cable
Max Distance – 3600 m
|10 Base-F||Speed – 10Mbps
Medium – Optical Fiber
|10 Base-FB||Speed – 10 Mbps
Medium – Multi-mode optical fiber
|10 Base-FL||Speed – 10 Mbps
Medium – Two optical fibers (Optional Asynchronous Hub)
|10 Base-FP||Speed – 10 Mbps
Medium – Two Optical Fibers (Passive Hub)
|10 Base-T||Speed – 10 Mbps
Medium – Twisted Pair Cables
Max Distance – 100 m
|10 Broad-36||Speed – 10 Mbps
Medium – Three channel cable TV system
Max Distance – 3600 m
|10 Gigabit||Speed – 10 Gbps
Medium – Optical Fiber
Max Distance – 300 m (Multi-mode fiber) and 40 km (Single mode fiber)
|100 Base-FX||Speed – 100 Mbps
Medium – Two multi-mode optical fibers
|100 Base-T||Speed – 100 Mbps
Medium – Twisted pair cable
|100 Base-T2||Speed – 100 Mbps
Medium – Two pairs of category 3 twisted pair cable
|100 Base-T4||Speed – 100 Mbps
Medium – Four pairs of category 3 twisted pair cable
|100 Base-TX||Speed – 100 Mbps
Medium – Two pairs of category 4 twisted pair cable
|100 Base-X||Speed – 100 Mbps|
|1000 Base-CX||Speed – 1000 Mbps
Medium – Two pairs of 150 shielded twisted pair cable
|1000 Base-LX||Speed – 1000 Mbps
Medium – Two multi-mode or single-mode optical fibers using long-wave laser optics
|1000 Base-SX||Speed – 1000 Mbps
Medium – Two multi-mode optical fibers using short-wave optics
|1000 Base-T||Speed – 1000 Mbps
Medium – Four pairs of category 5 unshielded twisted pair cables
|1000 Base-X||Speed – 1000 Mbps|
To this point, we know that Ethernet can be share via an Ethernet cable. But practically, there are many limitations put on the Ethernet. The data through the Ethernet cables flow as electrical signals from one point to the other. It is an inherent property of the electrical signals that they weaken as they travel and are vulnerable to various kinds of external interference like from radio waves, florescent lights etc., and hence the signal might get scrambled. Hence, a network cables has to be appropriately small for transmitting the data to the destination with scrambling. This puts a limitation on the maximum separation of distance any two devices can have over the Ethernet. It is called Network Diameter. Moreover, in CSMA/CD protocol, only one device can transmit at any given point of time which puts a practical limit on the number of devices that can co-exist in an Ethernet network.
Ethernet has a distance limit of 100 Meters, or 328 feet. To extend a network segment beyond that distance, Ethernet Extenders are frequently used. Ethernet Extenders enable you to run a network segment as far as 6 miles over copper. Far greater distances can be covered by Fiber Ethernet Extenders which use fiber optic cable. Most Ethernet Extenders work over a single twisted pair of copper wire in a CAT3, CAT5, or CAT6 cable. They convert Ethernet to some form of DSL…then back to Ethernet at the far end. Ethernet Extenders are typically sold in pairs with a unit for each end, local and remote and they use different DSL modulation schemes depending on distance and bandwidth requirements.
To address the same issue, most of the times, Repeaters are also employed. Repeaters connect multiple Ethernet segments, listening to each segment and repeating the signal heard on one segment onto every other segment connected to the repeater. By running multiple cables and joining them with repeaters, you can significantly increase your network diameter. There are various other techniques like segmentation and bridging which is covered in another post.
Ethernet is the most widely used technology used to connect devices on the network. Although, it is being replaced by WLAN at some places still large organizations prefer Ethernet as the medium for networking across all the devices.
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