OSI Layers

  • Layer 1: Physical Layer - Responsible for the transmission and reception of raw bit streams over a physical medium.

  • Layer 2: Data Link Layer - Provides node-to-node data transfer and handles error correction from the Physical Layer.

  • Layer 3: Network Layer - Manages data routing and forwarding, including addressing of packets.

  • Layer 4: Transport Layer - Ensures complete data transfer and provides error recovery and flow control.

  • Layer 5: Session Layer - Manages sessions and controls dialogues between computers.

  • Layer 6: Presentation Layer - Translates data formats, performs encryption, and data compression.

  • Layer 7: Application Layer - Provides network services to end-user applications and interfaces.

Layer 1 - The physical layer

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What’s the purpose of the physical layer?

The physical layer provides the means to transport the bits that make up a data link layer frame across the network media

What is a NIC?

A Network Interface Card (NIC) is a hardware component that connects a computer or device to a network, enabling communication over the physical layer by converting digital data into signals suitable for transmission over the network medium.

What is a NIC used for?

Physical Layer Standards address 3 standards:

  • Physical Components: The hardware elements involved in the network, such as cables, switches, and NICs.

  • Encoding: The method used to convert data into a form that can be transmitted over the physical medium, ensuring that it is accurately represented.

  • Signaling: The electrical, optical, or radio waves that carry the encoded data across the physical medium to the intended destination.

What is Bandwidth?

The capacity at which a medium can carry data.

How is Bandwidth measured?

Bits per second - 1 bps

Kilobits per second - 1 Kbps = 1,000 bits per second

Megabits per second - 1 Mbps = 1,000,000 bits per second.

Gigabits per second - 1 Gbps = 1,000,000,000 bits per second.

What are the Terms used to measure the quality of Bandwidth?

Latency

  • The time it takes for a data packet to travel from the source to the destination and back, measured in milliseconds (ms).

Throughput

  • The measure of bits transferred over a network in a given amount of time, typically expressed in bits per second (bps).

Goodput

  • The measure of usable data transferred over a given period of time (Goodput = Throughput - traffic overhead for establishing connections

Properties of UTP Cabling

  • UTP (Unshielded Twisted Pair) cabling consists of pairs of wires twisted together to reduce electromagnetic interference and crosstalk.

  • Typically used for network wiring in local area networks (LANs), UTP cabling is categorized by different standards (Cat5, Cat5e, Cat6, Cat6a, etc.), which define their transmission speeds and distances. (Cables in higher categories generally can support higher data rates and transmit over longer distances

How Cancellation Works:

When two wires in an electrical circuit carry equal but opposite signals, they cancel each other out, effectively reducing noise and improving the integrity of the transmitted data.

  • Advantages of UTP Cabling:

    • Cost-effective compared to other cabling options (e.g., fiber optics).

    • Flexible and easy to install, which makes it suitable for various applications.

    • Compatible with a wide range of networking equipment and protocols, ensuring versatility.

Straight-through and Crossover UTP Cables:

Ethernet Straight-Through - used to connect different types of devices, such as a computer to a switch, allowing for seamless communication within a network.

Ethernet Crossover - used to connect similar devices, such as switch to switch or computer to computer, enabling direct communication by facilitating the appropriate configuration of the transmit and receive pairs.

Rollover - Cisco proprietary cables which are typically used to connect a computer to a Cisco router's console port, allowing for device management and configuration through a serial connection.

Properties of Fiber-Optic Cabling

  • High bandwidth capacity: Supports data rates of several gigabits per second.

  • Long-distance transmission: Capable of transmitting signals over several kilometers without significant signal loss.

  • Immunity to electromagnetic interference: Unlike copper cables, fiber-optic cables are not affected by electromagnetic fields, ensuring a clearer signal.

  • Lightweight and thin: Easier to install and manage compared to traditional copper cables.

  • Secure: Fiber-optic cables are difficult to tap into, providing enhanced security for sensitive information.

Types of Fiber Media:

  • Single-mode fiber: Designed for long-distance communication, it allows the transmission of light over a single path, reducing signal loss.

  • Multi-mode fiber: Suitable for shorter distances, it enables multiple light paths but has higher signal attenuation compared to single-mode fiber.

How is Fiber Optic Cabling being used?

  • Enterprise Networks - Used for backbone cabling applications and interconnecting infrastructure devices

  • Fiber-to-the-Home - Used to provide always-on broadband services to homes and small businesses

  • Long-Haul Networks - Used by service providers to connect countries and cities over long distance

  • Submarine Cable Networks - Used to provide reliable high speed internet connectivity across continents via underwater cables.

Types of Fiber Connectors:

  • Straight-Tip(ST)

  • Subscriber Connector(SC)

  • Lucent Connector(LC)

  • Duplex Multimode LC connectors

Fiber Patch Cords:

What do they do?

They connect duplex multimode fibers for high-speed data transmission, ensuring effective signal integrity and reliable communication across network layers.

What are the types of Fiber Patch Cords?

  • SC-SC Multimode Patch Cord

  • LC-LC Single-Mode Patch Cord

  • ST-LC Multimode Patch Cord

  • SC-ST Single-Mode Patch Cord

Wireless Media

Limitations of Wireless Media:

  • Limited range and coverage due to signal attenuation

  • Susceptibility to interference from other wireless devices and physical obstructions

  • Security vulnerabilities associated with unauthorized access to wireless signals

  • Variability in signal quality affected by environmental factors such as weather and obstacles.

  • Shared medium means that WLANs operate ata single frequency range, leading to potential competition for bandwidth among users and increasing the chance of data collisions within the network.

Wireless Standards:

  • Wi-Fi (IEEE 802.11) - WLAN uses a contention-based protocol known as Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA), which helps manage access to the shared medium by detecting potential collisions before they occur and thus maintaining more efficient communication.

  • Bluetooth (IEEE 802.15) - Another wireless standard that utilizes a similar contention-based access method but is designed for short-range communication, allowing devices to communicate while minimizing interference and optimizing data transfer rates.

  • WiMax (IEEE 802.16) - Commonly known as Worldwide Interoperability for Microware Access. this wireless standard uses a point-to-Multipoint topology to provide wireless broadband access over long distances

  • Zigbee (IEEE 802.15.4) - Zigbee is a low-power, low-data-rate wireless communication standard designed primarily for applications such as home automation, industrial control, and sensor networks.

Terms to Know:

Frame Encoding - the process of taking raw data and formatting it into a structured frame so it can be transmitted over a network. It adds things like headers, trailers, and control information so devices can understand where the data starts, ends, and how to handle it.

Cancellation - When two wires carry equal but opposite signals , resulting in the cancellation of the signals at the receiver, effectively reducing noise and enhancing the overall signal integrity in communication systems.