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Ethernet Networking Study Notes

1.0 Network Fundamentals

1.1 h Power over Ethernet (PoE)

Power over Ethernet (PoE) technology enables standard twisted-pair cabling in an Ethernet network to transmit electrical power along with data. This technology is particularly useful for powering devices such as IP phones (Voice over IP), wireless LAN access points, network cameras, remote network switches, and embedded computers where it would be costly or impractical to run separate power supplies.

  • PoE Standard: 802.3af

  • PoE+ Standard: 802.3at, delivers up to 30 W and is compatible with Gigabit Ethernet using four wire pairs.

  • Power can be delivered from a powered switch port or through a power injector (only one method can be used at a time).

1.3 Compare Physical Interface and Cabling Types

1.3 a. Single-mode Fiber, Multimode Fiber, Copper

Ethernet utilizes different types of cables to connect devices. Each type has distinct specifications and use cases:

  1. Single-mode fiber: Generally used for long-distance communications as it allows only one mode of light to propagate, enabling higher bandwidth and longer distances.

  2. Multimode fiber: Used for shorter distances and allows multiple modes of light to travel, making it less suitable for long-distance transmission due to modal dispersion.

  3. Copper cabling: Various types include twisted pair cables (like UTP) and coaxial cables, commonly used for local area networks.

1.3 b. Connections (Ethernet Shared Media and Point-to-Point)

Ethernet can use shared media infrastructure (loading, such as hubs and access points) or point-to-point connections (like direct connections between switches or routers).

1.4 Identify Interface and Cable Issues

Collision Issues

Collisions occur when two devices attempt to send data on the same medium simultaneously. This can significantly reduce network performance, so strategies must be employed to minimize collisions.

Errors and Problems Requiring Resolution

  • Collisions: When two or more devices transmit at the same time.

  • Errors: May arise from issues like signal degradation over long distances or faulty cables.

  • Mismatch duplex/speed: Proper settings on devices are critical to facilitate communication without errors.

2.0 Ethernet

Today, Ethernet is pivotal in networking due to its simplicity and scalability. Key topics include:

2.1 Collision Domain

A collision domain is a network segment where devices share bandwidth. A collision occurs when two devices transmit simultaneously. In legacy networks (like those using hubs), only one device could transmit data at a time.

  • Figure 2.1 shows a legacy collision domain; only one host can transmit simultaneously.

2.2 Broadcast Domain

A broadcast domain is a logical segment where all devices can receive broadcast frames sent by any device in a network. Routers create boundaries for broadcast domains, and switches help in managing collision domains.

  • Figure 2.3 illustrates how routers separate broadcast domains in a design still relevant today.

3.0 CSMA/CD: Carrier Sense Multiple Access with Collision Detection

CSMA/CD allows devices to transmit and hear transmissions from other devices, minimizing the chance of collisions and managing retransmissions.

How CSMA/CD Works:

  1. A device checks if the medium is free before sending.

  2. If busy, the device waits and monitors the channel.

  3. In the event of a collision, a jam signal is sent to all devices, which then wait for a random backoff period before attempting to transmit again.

  4. After collisions, if retries exceed 15, nodes will timeout.

Identifier for Half-Duplex and Full-Duplex Modes

  • Half-duplex: Allows transmission in one direction at a time.

  • Full-duplex: Permits simultaneous transmission in both directions, effectively using two pairs of wires, preventing collisions.

4.0 Ethernet Addressing at the Data Link Layer

MAC Addressing

Ethernet addresses use Media Access Control (MAC) addresses, which are 48 bits (6 bytes) encoded in hexadecimal format.

MAC Address Format:

  • 24 Bits Organizationally Unique Identifier (OUI) assigned by IEEE.

  • 24 Bits: Vendor-assigned individual address.

Breaking Down the MAC Address

  • Individual/Group (I/G) bit: If 0, it indicates a device MAC; if 1, indicates a broadcast or multicast.

  • Global/Local (G/L) bit: 0 indicates a globally administered address, while 1 indicates a locally administered address.

5.0 Ethernet Frame Structure at the Data Link Layer

An Ethernet frame encapsulates packets from the Network layer. It includes:

  1. Preamble: Used for clock synchronization; consists of 7 bytes.

  2. Start Frame Delimiter (SFD): A marker indicating the start of data transmission.

  3. Destination and Source Addresses: Identifying sending and receiving devices, with both being 48 bits.

  4. Type/Length: Indicates the protocol and size of data.

  5. Data and Padding: Contains the actual payload (46-1500 bytes).

  6. Frame Check Sequence (FCS): Ensures error detection through CRC for integrity validation.

6.0 Ethernet Standards and Physical Layer Specifications

Standard Ethernet types include:

  • 10Base-T: 10 Mbps over Category 3 Cable, max distance 100m.

  • 100Base-TX (Fast Ethernet): 100 Mbps over Category 5, 5E, 6 cables, max distance 100m.

  • 1000Base-T (Gigabit Ethernet): 1 Gbps over Category 5 up to 100m.

  • 10GBase-T: 10 Gbps connection using encodings that allow for 100-meter reach over existing UTP.

Fiber-Optic Connectivity

Involves transmitting data as light signals through glass or plastic fibers. Fiber-optic cables include:

  1. Single-mode fiber: Designed for long distances, smaller core diameter.

  2. Multimode fiber: Used for shorter distances, larger core diameter that allows multiple light modes.