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Network+ Exam

Layer 1 - (Physical)

October 29, 2025

  • #network+

Layer 1 - (Physical)

Where transmission of bits across the network occurs. Includes the physical and electrical network characteristics. It is bits, 1 and 0. Yes and no on and off. If it’s a copper wire it’s 0 volts for 0 and .1 volts for 1.

  • Transition Modulation. If it changes during the clock ttime. if it changes during the cicle it’s represented as 1 if not is’s a 0.

The cables are a part of the physical network. The connete is wired is tepend on the standard

  • crossover cables 568 A on one side and B on the other side.
  • straight - through cables 568B on both sides.

Topology of the network: - Layer 1 devices view a network from a physical topology perspective. If you drew them out what pattern would it make.

Data Syncrinization: -

  • acricinious syncrinizaiton: One can talk at a time, you do it and another person does it. Use a start and stop bit to indicaansmissions orccur from the sender to reciver. te when tr
  • Syncrinious: If both are talking at the stame time. Uses a refrence clock to coodinate the transmissions by both sender and reciver.

How to use the bandwidth of the cable.

Broadband: divide the bandwidth into separate channels.

Baseband:sue all aailable frequencies all of the time. telephone. - uses a refrence clock. Wired home ethereth.

Time - Division Multiplexing - each session takes a turn using the time slocs, to share the medium between all users.

Statistical time-Division Multiplexing (StatTDM)- Allocates the time clots on an as needed basis. everyont takes turns based on the needs.

Multiplesxing involves optimizing a limited amount of resources for more efficent utilization

Multiplexing enables simultainius use of a base band connetion by multple users.

Examples:

Media: Fiber optic cable, Ethernet Cable, Coaxial cable

Wireless: Bluetooth, Wi-fi, NFC

Infrastructure: Hubs, Accesspoints, Media converters/

Layer 1 devices are just repeaters.

🧱 OSI Layer 1 — Physical Layer

Where raw bit transmission occurs

Concerned with physical and electrical characteristics of the network — 1s and 0s, on/off signals, voltages, light pulses, and radio waves.

🧬 Core Concepts

  • Bit Transmission: Raw data (bits) is transmitted across physical media (copper, fiber, RF).
  • Signal Representation:
    • On copper: 0 volts = binary 0, small voltage (e.g. 0.1v) = binary 1
    • Light (fiber) or radio signals may use different representations

🔄 Transition Modulation

  • Interprets bits based on changes in signal during the clock cycle:
    • Change = 1
    • No change = 0

🔌 Media & Cabling

  • Part of the physical layer (cables literally are Layer 1):
    • Ethernet cables
    • Fiber optic
    • Coaxial cable

Ethernet Cable Types:

  • Straight-through cable: Same standard on both ends (e.g. 568B ↔ 568B)

    Used to connect unlike devices (PC → Switch).

  • Crossover cable: 568A on one end, 568B on the other

    Used to connect like devices (PC → PC, Switch → Switch).

🛰️ Network Topology (Physical)

  • Layer 1 devices only see physical topology:
    • What shape would the network make if you drew out all the cables?
    • Examples: star, mesh, ring, bus.

🕰️ Data Synchronization Types

1. Asynchronous Transmission:

  • Only one party transmits at a time
  • Uses start and stop bits to indicate transmission boundaries

2. Synchronous Transmission:

  • Both sender and receiver share a reference clock
  • Enables simultaneous transmission and better efficiency

📶 Bandwidth Usage

| Term | Description | | --- | --- | | Baseband | Uses the entire bandwidth for one channel. Example: Ethernet | | Broadband | Splits bandwidth into multiple channels. Example: Cable TV |

⏱️ Multiplexing (MUX)

Used to optimize limited bandwidth by allowing multiple signals to share the same medium.

Types:

  • TDM (Time Division Multiplexing):
    • Each session gets a turn in fixed time slots
  • Statistical TDM (StatTDM):
    • Time slots allocated as needed, more efficient

🧱 Layer 1 Devices (Physical Layer Hardware)

| Device Type | Description | | --- | --- | | Repeater | Regenerates signals to extend distance (true Layer 1 device) | | Hub | Multiport repeater — broadcasts all incoming traffic | | Media Converter | Converts media types (e.g., fiber ↔ Ethernet) | | Transceivers (SFP, GBIC) | Send and receive signals over different mediums | | Access Point | (Partially Layer 1 for RF, also Layer 2) | | Cables and Connectors | Copper, fiber, coax, RJ45, etc. |

📡 Layer 1 Examples

Media:

  • Ethernet cable
  • Fiber optic cable
  • Coaxial cable

Wireless Signals:

  • Bluetooth
  • Wi-Fi
  • NFC (Near Field Communication)

Infrastructure Devices:

  • Hubs
  • Access points (partial Layer 1)
  • Media converters