Ethernet (802.3) | Computer Networks - Computer Science Engineering (CSE) PDF Download

Introduction to Ethernet

Ethernet was developed in the mid-1970s by researchers at the Xerox Palo Alto Research Center (PARC). It serves as a practical example of a broader technology called carrier sense, multiple access with collision detection (CSMA/CD), which is used in local area networks.Ethernet (802.3) | Computer Networks - Computer Science Engineering (CSE)

In CSMA/CD, "carrier sense" refers to the ability of all nodes to determine whether a network link is idle or busy. "Collision detect" means that while nodes are sending data, they listen for any interference, or collision, with frames from other nodes.

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Try yourself:Ethernet frame consists of ____________
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Key Features

  • Standardized by: IEEE 802.3

  • Media: Twisted pair cables, fiber optics, and coaxial cables.

  • Data Rates: Ranges from 10 Mbps to 400 Gbps and beyond (like 800 Gbps being developed)

  • Topology: Primarily star (modern) or bus (legacy)

  • Access Method: CSMA/CD (Carrier Sense Multiple Access with Collision Detection) — though mostly obsolete in switched Ethernet.

Physical Properties of Ethernet

Coaxial Cable: An Ethernet segment uses a coaxial cable similar to that used for cable TV, but with some differences. The Ethernet cable can be up to 500 meters long and typically has an impedance of 50 ohms, whereas cable TV cables usually have an impedance of 75 ohms. To set up the segment, taps (connection points) need to be spaced at least 2.5 meters apart.

Transceiver: A transceiver is a small device attached to the tap on the coaxial cable. Its functions include:

  • Detecting when the Ethernet line is not in use.
  • Sending signals when a host is transmitting data.
  • Receiving incoming signals.

The transceiver connects to an Ethernet adapter, which is then plugged into the host computer or device.Ethernet (802.3) | Computer Networks - Computer Science Engineering (CSE)

Repeaters: Multiple Ethernet segments can be connected using a repeater. A repeater’s role is to forward digital signals, similar to how an amplifier boosts analog signals. However, there are limitations: no more than four repeaters can be placed between any two hosts, which restricts the total range of an Ethernet network to 2,500 meters.

Maximum Hosts: Under specific standards, an Ethernet network can support a maximum of 1,024 hosts. At the end of each segment, terminators are used to absorb the signal. This absorption prevents the signal from bouncing back and causing interference with subsequent signals, ensuring smoother data transmission.

Standards of Ethernet

There are several standards of Ethernet, each with its own specifications:Ethernet (802.3) | Computer Networks - Computer Science Engineering (CSE)Ethernet Cable Standards

  • 10Base5: This is the first physical standard defined in the IEEE 802.3 model. It is also known as thick net or thick Ethernet. A segment of the original 10Base5 cable can be up to 500 meters long.
  • 10Base2: The second implementation defined by the IEEE 802 series is called 10Base2. It is also known as thin-net, cheapnet, or thin Ethernet. In this standard, '10' indicates a network operation speed of 10 Mbps, 'Base' signifies the use of a baseband system, and '2' denotes a segment length limit of 200 meters.
  • 10Base-T: This is the most popular standard defined in the IEEE 802.3 series, known as 10Base-T or twisted pair Ethernet. The "T" refers to twisted pair cabling. A 10Base-T segment is typically limited to a length of less than 100 meters.
The document Ethernet (802.3) | Computer Networks - Computer Science Engineering (CSE) is a part of the Computer Science Engineering (CSE) Course Computer Networks.
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FAQs on Ethernet (802.3) - Computer Networks - Computer Science Engineering (CSE)

1. What are the physical properties of Ethernet?
Ans. Ethernet has several physical properties, including: - Speed: Ethernet can support different speeds, such as 10 Mbps, 100 Mbps, 1 Gbps, 10 Gbps, and even higher. - Cable Type: Ethernet can use different cable types, such as twisted-pair copper cables (e.g., Cat5e, Cat6), coaxial cables, or fiber optic cables. - Cable Length: Ethernet has a maximum cable length limit, which varies depending on the type of cable and the speed of the Ethernet connection. - Connectors: Ethernet uses different types of connectors, such as RJ-45 for twisted-pair cables and SC or LC connectors for fiber optic cables. - Network Topology: Ethernet can be used in different network topologies, such as star, bus, or ring.
2. What is the significance of the Ethernet standard (802.3) in computer science engineering?
Ans. The Ethernet standard (802.3) is significant in computer science engineering for several reasons: - Compatibility: The Ethernet standard ensures compatibility between different devices and network equipment, allowing them to communicate seamlessly. - Scalability: Ethernet provides scalability, allowing networks to easily expand by adding more devices or increasing network speed. - Reliability: The Ethernet standard is known for its reliability, ensuring that data transmission is consistent and error-free. - Interoperability: The Ethernet standard enables interoperability between different vendors' equipment, ensuring that devices from different manufacturers can work together. - Industry Standard: The Ethernet standard is widely adopted in the industry, making it a fundamental technology for computer science engineering.
3. What are the common applications of Ethernet in computer networks?
Ans. Ethernet is commonly used in computer networks for various applications, including: - Local Area Networks (LANs): Ethernet is the most common technology used for LANs, connecting computers, servers, printers, and other network devices in a small area. - Wide Area Networks (WANs): Ethernet can be used to connect different LANs together to create a WAN, allowing remote sites to communicate with each other. - Internet Access: Ethernet is used by Internet Service Providers (ISPs) to provide broadband internet access to homes and businesses. - Data Centers: Ethernet is extensively used within data centers to connect servers, storage systems, and networking equipment, forming the backbone of cloud computing and other data-intensive applications. - Industrial Automation: Ethernet is increasingly used in industrial automation systems to connect sensors, actuators, and control devices, enabling real-time data exchange and control.
4. What are the key differences between twisted-pair copper cables and fiber optic cables in Ethernet?
Ans. Twisted-pair copper cables and fiber optic cables have key differences in Ethernet: - Transmission Medium: Twisted-pair cables use copper wires to transmit data, while fiber optic cables use thin strands of glass or plastic to transmit data using light signals. - Bandwidth and Speed: Fiber optic cables have a much higher bandwidth and can support higher speeds compared to twisted-pair cables. Fiber optics can transmit data at speeds of several terabits per second, while twisted-pair cables have speed limitations depending on the category (e.g., Cat5e, Cat6). - Distance: Fiber optic cables can transmit data over longer distances without signal degradation compared to twisted-pair cables. Fiber optics can transmit data over several kilometers, while twisted-pair cables have distance limitations depending on the category and speed. - Immunity to Interference: Fiber optic cables are immune to electromagnetic interference, making them more reliable in environments with high electromagnetic noise. Twisted-pair cables are more susceptible to interference. - Cost: Twisted-pair cables are generally less expensive compared to fiber optic cables, making them more commonly used for shorter distance applications. Fiber optics are more expensive but are preferred for long-distance and high-bandwidth applications.
5. What is the role of Ethernet standards in ensuring interoperability between devices from different manufacturers?
Ans. Ethernet standards play a crucial role in ensuring interoperability between devices from different manufacturers by establishing a common set of rules and specifications. These standards define the physical layer characteristics, data link layer protocols, and network layer functionalities that Ethernet devices must adhere to. By complying with the Ethernet standards, manufacturers ensure that their devices can communicate with other Ethernet devices regardless of the brand or model. This interoperability allows users to create mixed-vendor networks, where devices from different manufacturers can seamlessly exchange data and participate in network activities. Ethernet standards also facilitate the development of compatible networking equipment, such as switches, routers, and network interface cards, by providing a clear framework for designing and implementing Ethernet technology. This promotes healthy competition in the market and gives users the freedom to choose the best-suited devices for their network requirements, without being limited to a single vendor.
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