LAN Technologies | ETHERNET

A local Area Network (LAN) is a data communication network connecting various terminals or computers within a building or limited geographical area. The connection among the devices could be wired or wireless. Ethernet, Token Ring and Wireless LAN using IEEE 802.11 are examples of standard LAN technologies. 
LAN has the following topologies:

• Star Topology
• Bus Topology
• Ring Topology
• Mesh Topology
• Hybrid Topology
• Tree Topology

Ethernet:-
Ethernet is the most widely used LAN technology, which is defined under IEEE standards 802.3. 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 topologies that are allowed. Ethernet generally uses Bus Topology. 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 DLL. In order to handle collision, the Access control mechanism used in Ethernet is CSMA/CD. 
Manchester Encoding Technique is used in Ethernet. 

Since we are talking about IEEE 802.3 standard Ethernet, therefore, 0 is expressed by a high-to-low transition, a 1 by the low-to-high transition. In both Manchester Encoding and Differential Manchester, the Encoding Baud rate is double of bit rate. 

Some of the key features of Ethernet include:

Speed: Ethernet is capable of transmitting data at high speeds, with current Ethernet standards supporting speeds of up to 100 Gbps.

Flexibility: Ethernet is a flexible technology that can be used with a wide range of devices and operating systems. It can also be easily scaled to accommodate a growing number of users and devices.

Reliability: Ethernet is a reliable technology that uses error-correction techniques to ensure that data is transmitted accurately and efficiently.

Cost-effectiveness: Ethernet is a cost-effective technology that is widely available and easy to implement. It is also relatively low-maintenance, requiring minimal ongoing support.

Interoperability: Ethernet is an interoperable technology that allows devices from different manufacturers to communicate with each other seamlessly.

Security: Ethernet includes built-in security features, including encryption and authentication, to protect data from unauthorized access.

Manageability: Ethernet networks are easily managed, with various tools available to help network administrators monitor and control network traffic.

Compatibility: Ethernet is compatible with a wide range of other networking technologies, making it easy to integrate with other systems and devices.

Scalability: Ethernet is highly scalable, which means it can easily accommodate the addition of new devices, users, and applications without sacrificing performance or reliability.

Availability: Ethernet is a widely available technology that can be used in almost any setting, from homes and small offices to large data centers and enterprise-level networks.

Simplicity: Ethernet is a simple technology that is easy to understand and use. It does not require specialized knowledge or expertise to set up and configure, making it accessible to a wide range of users.

Standardization: Ethernet is a standardized technology, which means that all Ethernet devices and systems are designed to work together seamlessly. This makes it easier for network administrators to manage and troubleshoot Ethernet networks.

Scalability: Ethernet is highly scalable, which means it can easily accommodate the addition of new devices, users, and applications without sacrificing performance or reliability.

Broad compatibility: Ethernet is compatible with a wide range of protocols and technologies, including TCP/IP, HTTP, FTP, and others. This makes it a versatile technology that can be used in a variety of settings and applications.

Ease of integration: Ethernet can be easily integrated with other networking technologies, such as Wi-Fi and Bluetooth, to create a seamless and integrated network environment.

Ease of troubleshooting: Ethernet networks are easy to troubleshoot and diagnose, thanks to a range of built-in diagnostic and monitoring tools. This makes it easier for network administrators to identify and resolve issues quickly and efficiently.

Support for multimedia: Ethernet supports multimedia applications, such as video and audio streaming, making it ideal for use in settings where multimedia content is a key part of the user experience.

 Ethernet is a reliable, cost-effective, and widely used LAN technology that offers high-speed connectivity and easy manageability for local networks

Advantages of Ethernet:

Speed: When compared to a wireless connection, Ethernet provides significantly more speed. Because Ethernet is a one-to-one connection, this is the case. As a result, speeds of up to 10 Gigabits per second (Gbps) or even 100 Gigabits per second (Gbps) are possible.

Efficiency: An Ethernet cable, such as Cat6, consumes less electricity, even less than a wifi connection. As a result, these ethernet cables are thought to be the most energy-efficient.

Good data transfer quality: Because it is resistant to noise, the information transferred is of high quality.

 Baud rate = 2* Bit rate 

Ethernet LANs consist of network nodes and interconnecting media or links. The network nodes can be of two types: 
Data Terminal Equipment (DTE):- Generally, DTEs are the end devices that convert the user information into signals or reconvert the received signals. DTEs devices are: personal computers, workstations, file servers or print servers also referred to as end stations. These devices are either the source or the destination of data frames. The data terminal equipment may be a single piece of equipment or multiple pieces of equipment that are interconnected and perform all the required functions to allow the user to communicate. A user can interact with DTE or DTE may be a user. 

Data Communication Equipment (DCE):- DCEs are the intermediate network devices that receive and forward frames across the network. They may be either standalone devices such as repeaters, network switches, routers, or maybe communications interface units such as interface cards and modems. The DCE performs functions such as signal conversion, coding, and maybe a part of the DTE or intermediate equipment. 

Currently, these data rates are defined for operation over optical fibres and twisted-pair cables: 
i) Fast Ethernet
Fast Ethernet refers to an Ethernet network that can transfer data at a rate of 100 Mbit/s. 

ii) Gigabit Ethernet
Gigabit Ethernet delivers a data rate of 1,000 Mbit/s (1 Gbit/s). 

iii) 10 Gigabit Ethernet
10 Gigabit Ethernet is the recent generation and delivers a data rate of 10 Gbit/s (10,000 Mbit/s). It is generally used for backbones in high-end applications requiring high data rates. 

 disadvantages Ethernet:

Distance limitations: Ethernet has distance limitations, with the maximum cable length for a standard Ethernet network being 100 meters. This means that it may not be suitable for larger networks that require longer distances.

Bandwidth sharing: Ethernet networks share bandwidth among all connected devices, which can result in reduced network speeds as the number of devices increases.

Security vulnerabilities: Although Ethernet includes built-in security features, it is still vulnerable to security breaches, including unauthorized access and data interception.

Complexity: Ethernet networks can be complex to set up and maintain, requiring specialized knowledge and expertise.

Compatibility issues: While Ethernet is generally interoperable with other networking technologies, compatibility issues can arise when integrating with older or legacy systems.

Cable installation: Ethernet networks require the installation of physical cables, which can be time-consuming and expensive to install.

Physical limitations: Ethernet networks require physical connections between devices, which can limit mobility and flexibility in network design.

ALOHA
The Aloha protocol was designed as part of a project at the University of Hawaii. It provided data transmission between computers on several of the Hawaiian Islands involving packet radio networks. Aloha is a multiple access protocol at the data link layer and proposes how multiple terminals access the medium without interference or collision. 

There are two different versions of ALOHA: 
1. Pure Aloha
Pure Aloha is an un-slotted, decentralized, and simple to implement the protocol. In pure ALOHA, the stations simply transmit frames whenever they want data to send. It does not check whether the channel is busy or not before transmitting. In case, two or more stations transmit simultaneously, the collision occurs and frames are destroyed. Whenever any station transmits a frame, it expects acknowledgement from the receiver. If it is not received within a specified time, the station assumes that the frame or acknowledgement has been destroyed. Then, the station waits for a random amount of time and sends the frame again. This randomness helps in avoiding more collisions. This scheme works well in small networks where the load is not much. But in largely loaded networks, this scheme fails poorly. This led to the development of Slotted Aloha. 
To assure pure aloha: Its throughput and rate of transmission of the frame to be predicted. 
For that to make some assumptions: 
i) All the frames should be the same length. 
ii) Stations can not generate frames while transmitting or trying to transmit frames. 
iii)The population of stations attempts to transmit (both new frames and old frames that collided) according to a Poisson distribution. 

 Vulnerable Time = 2 * Tt 

The efficiency of Pure ALOHA:

Spure= G * e^-2G 
where G is number of stations wants to transmit in Tt slot. 

Maximum Efficiency:
Maximum Efficiency will be obtained when G=1/2

(Spure)max = 1/2 * e^-1
           = 0.184 

Which means, in Pure ALOHA, only about 18.4% of the time is used for successful transmissions.

2. Slotted Aloha
This is quite similar to Pure Aloha, differing only in the way transmissions take place. Instead of transmitting right at demand time, the sender waits for some time. In slotted ALOHA, the time of the shared channel is divided into discrete intervals called Slots. The stations are eligible to send a frame only at the beginning of the slot and only one frame per slot is sent. If any station is not able to place the frame onto the channel at the beginning of the slot, it has to wait until the beginning of the next time slot. There is still a possibility of collision if two stations try to send at the beginning of the same time slot. But still, the number of collisions that can possibly take place is reduced by a large margin and the performance becomes much well compared to Pure Aloha. 

Collision is possible for only the current slot. Therefore, Vulnerable Time is Tt. 

The efficiency of Slotted ALOHA:

 Sslotted = G * e^-G

Maximum Efficiency:
(Sslotted)max = 1 * e^-1 
              = 1/e = 0.368 
Maximum Efficiency, in Slotted ALOHA, is 36.8%.

Image Reference: Wikipedia, Technical University of Munich

References: 
https://www.cisco.com/c/en/us/tech/lan-switching/ethernet/index.html 
https://en.wikipedia.org/wiki/Ethernet 

This article is contributed by Sheena Kohli and Abhishek Agrawal