M1 Physical Layer

Explain how physical layer protocols, services, and network media support communications across data networks.

Wired

Physical connection of a device to a local network using a cable. Fast, stable, and predictable.

Wireless

Physical connection of a device to a local network using radio waves instead of cables. Devices connect to a wireless AP or wireless router. Convenient, flexible, but affected by obstacles and traffic.

AP

Access Point.

Wireless Router Components

• Wireless antennas (internal or external)

• Ethernet switchports (for wired devices)

• Internet/WAN port (connects to the ISP modem)

NIC

Network Interface Card. A device need this card to connect to a network.

2 Types of NIC

1. Ethernet NIC (Wired) - uses ethernet cable

2. WLAN NIC (Wireless) - uses Wi-fi

Physical connection

It means a device must connect to a local network using wired or wireless media.

Physical Layer

(OSI model Layer 1) is responsible for turning bits into signals and signals back into bits. It takes a frame from layer 2, converts it into electrical/optical/radio signals for transmission, and the receiving device converts those signals back into bits and passes the frame up to the Data Link Layer.

IEEE 802.3

Physical standard for Ethernet

IEEE 802.11

Physical standard for Wi-Fi

IEEE 802.15

Physical standard for Bluetooth

IETF

Govern the TCP/IP standards that are implemented in software. Layer 3 to Layer 7 of OSI model.

IEEE

Govern the physical layer standard that are implemented in hardware (Ethernet & Wi-Fi). Layer 1 and 2 of OSI model. Engineering organizations.

3 Major Functions of Layer 1

1. Physical Components

2. Encoding

3. Signaling

Physical Components

One of the three function of layer 1, which are the actual hardware pieces that allow bits to travel across a network.

Encoding

It is the method a device uses to convert bits (0s & 1s) into a pattern of signals that can travel across the physical medium.

Signaling

It is the method used to physically represent 1s and 0s on copper cables, fiber optic cables, and wireless radio waves. Think of it as the physical “voice” of the network.

Copper cable

It uses voltage changes to represent bits. High voltage = 1; Low voltage = 0.

Fiber Optic

It uses light instead of electricity to represent bits. Light pulse = 1; No light =0.

Wireless

It uses radio wave modulation to represent bits. There are 2 modulation types: AM, FM, and PM.

Amplitude Modulation

A radio wave modulation that change the height of the wave to represent bits. Higher amplitude = 1; Lower amplitude = 0

Frequency Modulation

A radio wave modulation that change the frequency of the wave to represent bits. Faster oscillation = 1; Slower Oscillation = 0

Phase Modulation

A radio wave modulation that change the phase (shift the wave). Phase shift = 1; No shift = 0

Bandwidth

Is the capacity of a medium to carry data. It tells you how many bits per second can be transmitted. It is not the speed of electricity or light. It is how many bits you can fit per second, not how fast they travel.

Data Transfer Terminologies

• Bandwidth

• Latency

• Throughput

• Goodput

Latency

Is the time it takes for data to travel from one point to another. The delay before data starts arriving. High would mean slow response.

Throughput

Is the real amount of data successfully transferred per second. The actual bits per second. It is not the same as bandwidth.

Bottleneck

This mean that Throughput cannot exceed the slowest link in the path.

Goodput

Is the amount of actual, usable data delivered per second. Useful data only. It removes: headers, ack, retransmissions, session setup overhead. It is the closest measurement to what the user actually experiences.

Signal Attenuation

The weakening of electrical signals when it travels through copper. Longer cable = weaker signal = more errors. Strict distance limits = 100 meters for most twisted-pair Ethernet.

Electromagnetic Interference / Radio Frequency Interference

It can distort the electrical signal, causing bit errors. Copper cables are vulnerable of this distortions.

Crosstalk

This occurs when the signal on one wire bleeds into an adjacent wire. Effects: bit errors, noise, and reduced performance.

2 Ways to Reduce Interference in Copper Cables

1. Twisting

2. Shielding

Twisting

Copper cable technique to reduce crosstalk. It works because magnetic fields cancel each other out. It creates a self-shielding effect.

Shielding

Copper cable technique to reduce EMI/RFI. It blocks external interference.

UTP

Unshielded Twisted-Pair Cable. Is the most common networking cable used in LANs. It contains 4 pairs of wires. Each pair is twisted together. It uses cancellation and twist rate variation to protect itself against interference.

STP

Shielded Twisted-Pair Cable. Is a type of copper cabling designed to provide extra protection against interference. Similar to UTP, but it includes metallic shielding around the wire pairs.

Coaxial Cable

Is an older copper-based medium that was once used in Ethernet networks. UTP has replaced this cable in LANs, but still widely used in wireless and cable internet installations. Two conductors sharing the same axis. Excellent shielding.

4 Main Layers of Coax

1. Inner Copper Conductor

2. Plastic Insulation

3. Metallic Shield

4. Outer Jacket

Cancellation

When two wires in a pair carry equal and opposite electrical currents: their magnetic fields cancel each other, this reduces crosstalk and EMI/RFI. It is the foundation of UTP’s noise resistance. It is the reason why UTP can work reliably without shielding.

ANSI/TIA-568

An organization that defines the commercial cabling standards used in LANs. It specifies: cable types, max cable lengths, connectors, termination standards, cable testing methods. This is the standard used by installers and network engineers.

IEEE

An organization that defines the electrical performance of copper cabling. It assigns categories based on performance.

Category 3

UTP Cable category. Is originally for voice. 10 Mbps.

Category 5e

UTP Cable category. It supports 1 Gbps. It is the minimum acceptable cable for modern networks.

Category 6

UTP Cable category. It has internal separator to reduce crosstalk. Supports 1 Gbps up to 100m. Supports 10 Gbps up to ~55m. Recommended for new installations.

Category 5

UTP Cable category. It supports 1 Gbps. It is the minimum acceptable cable for modern networks.

Category 6A

UTP Cable category. It supports 10 Gbps up to 100m. It has better shielding and twist control.

Category 7

UTP Cable category. It supports 10 Gbps. It is not officially recognized by ANSI/TIA.

Category 8

UTP Cable category. It supports 40 Gbps. For short distances (up to 30m). It is used in data centers.

RJ-45 Connectors

It is used to terminate UTP cables. It has a male and female version. The male inserts into the socket to complete the physical connection.

RJ-45 Plug

It is the male version of RJ-45. It is used to connect into a device or patch panel.

RJ-45 Socket

The female version of RJ-45. It is found on switches, routers, wall outlets, and patch panels.

3 Main Cable Types

1. Ethernet Straight-Through

2. Ethernet Crossover

3. Rollover (Cisco Console cable)

Ethernet Straight-Through

One of the 3 cables. Use case: Host → Switch; Switch → Router; Host → Hub. The connectors on both ends of the wiring should be the same. This is the most common Ethernet cable. Different devices.

Ethernet Crossover

One of the 3 types of cable. Use case: Switch ←→ Switch; Router ←→ Router; Host ←→ Host. Same devices connections. The connectors at the end of the wiring swaps the transmit and receive pairs: one end T568A and other end T568B.

Rollover

One of the 3 Types of cable. Use case: PC/workstation → Router console port; PC/workstation → Switch console port. Use for out-of-band management (CLI access). The connectors at the end is the reverse of the other: Pin 1 ←→ Pin 8; Pin 2 ←→ Pin 7. It is the console cable.