Ethernet Standards & Frames

Instructor: Lyna Griffin

Lyna has tutored undergraduate Information Management Systems and Database Development. She has a Bachelor's degree in Electrical Engineering and a Masters degree in Information Technology.

In this lesson we will examine and understand the different Ethernet standards that govern LAN Technology. We will understand the differences in technology employed for twisted pairs wires, Ethernet links and Fiber Optics. We will also understand the components of an Ethernet frame.

What is Ethernet?

Networking has been the foundation of modern connectivity and technology today. At the foundation of this networking phenomenon is Local Area Network(LAN). A LAN is a group of computers or devices that share a common mode of communication, be it a communications line or a wireless link, which is connected to a main server. The medium of communication which they share can be linked to a national transport system used by humans, cars, buses, trains and planes (computers or nodes). These communication links are used to send and receive packets of information (transport goods and services). The Ethernet is the most commonly used LAN technology. It dictates the technical specifications of hardware for connectivity; the number of connections permitted, performance thresholds and the overall framework that governs data transmission(types of vehicles, maximum height and speed limit). Think of the Ethernet as the respective air and land traffic regulations with each having different governing principles depending on what is used.

The Ethernet standard is developed by the Institute of Electrical and Electronic Engineers (IEEE).It is known as the Ethernet standard 802.3. Networking equipment and protocols communicate more efficiently when these standards are adhered to.

Ethernet Standards

There are different standards developed by IEEE that govern the different aspects of Ethernet. We will examine the following standards:

CSMA/CD Standard

One of the main standards of the Ethernet technology is the Carrier Sense Multiple Access/ Collision Detection (CSMA/CD). Ethernet usually permits each node in the network to transmit data packets at any time without any system of waiting. This creates a high possibility for data collisions.

Collisions occur when two or more nodes initiate data transmissions on the same channel simultaneously. When this happens, a packet collision is said to occur. Think of a busy road intersection with no traffic lights. When each driver crosses the intersection at will, a collision is likely to occur. For Ethernet to efficiently manage these collisions the protocol CSMA/CD is employed. CSMA/CD therefore defines how the devices involved in the collision must respond. These definitions dictate how long a device should wait to proceed with data transmission. If repeated collisions occur devices may wait twice as long before re-transmitting.

There are various access modes in CSMA:

1-Persistent - Device waits for the channel to be idle then transmits data. Often used by CSMA/CD systems like Ethernet

P-Persistent - Device waits for the channel to be idle then transmits data with success at probability P. If the transmission fails at probability (1-P) the device waits for the channel to be idle again and re-transmits. This is used by CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance) systems like Wi-Fi.

O-Persistent - which develops a transmission queue called a Transmission Order for each device or node. When the channel is idle the node or device next in line transmits data.

Standards for Cable

Standard: IEEE 802.3u

The IEEE 802.3u is known as the Fast Ethernet standard. This is the standard that governs Ethernet cabled networks. It was established to accommodate high transmission speeds in cables. The standard accommodates speeds from 10 Mbps to 100 Mbps providing high throughput for strong error detection and correction, multimedia and browsing.

There are three types of Fast Ethernet as shown in the table below:

Standard Media Type Cabling Distance Transfer Speed
100 Base - TX Category 5, 5e or 6 UTP cables 100 meters 100Mbps
100 Base - FX Multi-mode (two strands 62.5/125) Optical Fiber 412 meters - 2000 meters (Half-Duplex/full-duplex) 100Mbps
100 Base - T 3 UTP cables 100 meters 10Mbps

10 Gigabit Ethernet

When it comes to speed, 10 Gigabit Ethernet is one of the fastest Ethernet standards. This standard, also known as IEEE 802.3ae, is designed with speeds up to 10 Gbits/s. This is 10 times faster than other standards discussed earlier and is designed specifically for Optical Fiber networks. It is designed to meet the needs of multimedia as well as VoIP (Voice over IP) applications making it an essential enterprise backbone. There are three categories within this standard determined by cabling distance.

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