OSI model

Layer 1 – Physical Layer

Responsible for sending bits via wired or wireless transmission.

The physical layer (layer 1) can convert digital data into

electrical, light, or radio signals for transmission across media.

Layer 1 – Physical Layer: Transmission Types:

• Wavelengths in the air (wireless).

• Voltage on copper wire (Ethernet cabling).

• Light through fiber-optic cabling.

Devices Operating at Layer 1:

• Hubs

• Repeaters

• Modems

• Network Interface Cards (NICs)

• Network cabling (Ethernet cables, fiber optics)

• Transceivers

Layer 1 Key Function:

Handles the raw transmission of bits (1s and 0s) and manages the electrical and physical specifications — including signal encoding, cable standards, and hardware connectors.

What is layer 2?

Data Link

Layer 2 – Data Link Layer is responsible for

reliable transmission of data across the Physical Layer.

Layer 2 (data link layer) provides error detection and correction, as well as…

frame synchronization, and flow control.

What is layer 2’s function?

Packages data into frames and establishes logical links between directly connected nodes. Detects and corrects Physical Layer errors, manages medium access, and uses MAC addresses for identification.

The sublayers in layer 2 are what?

LLC AND MAC

LLC

Manages error checking, frame synchronization, and identifies Network Layer protocols.

MAC

Controls access to the medium and transmission timing.

Devices in layer 2 contain:

Switches (sends info to a specific part), Bridges (links multiple switches together), and NICs

Layer 2 – Data Link Layer is also called

Frame

What is the name of Layer 3?

Network Layer

Layer 3 – Network Layer is responsible for

logical addressing, routing, and path determination to move data between networks.

The function of layer 3 is to

determine the best path for data using IP addresses, managing packet forwarding, fragmentation/reassembly, sequencing, and traffic control to ensure efficient delivery across networks.

Devices in layer 3:

Routers, Switches

What is layer three (network layer) also called?

Packet

Layer three can also operate as

layer 2.

What is the name of layer 4?

Transport layer

Layer four is responsible for

reliable end-to-end communication between devices.

What does the Transport Layer ensure during transmission?

That all data is completely and correctly transferred with error recovery and flow control.

What are the main functions of the Transport Layer?

It segments data, assigns port numbers, manages connections, handles error detection/retransmission, and controls data flow to prevent overload.

What protocol provides reliable, connection-oriented transport?

TCP

What protocol provides fast, connectionless transport?

UDP

What devices operate at the Transport Layer?

Gateways, firewalls, and load balancers

What is the PDU for the Transport Layer?

segment (TCP) or Datagram (UDP)

What is the purpose of the Transport Layer?

To ensure accurate data delivery between applications running on different hosts.

What is the name of layer 5?

Session layer

What is the main purpose of the Session Layer?

It manages and controls dialogues (sessions) between computers.

What does the Session Layer establish, maintain, and terminate?

Sessions between applications on different devices.

How does the Session Layer improve communication?

It synchronizes data exchange and provides checkpoints for recovery if a session is interrupted.

Layer 5 decides if it needs to speed up, slow down, or

be one way or two ways.

What is the purpose of the Presentation Layer?

It translates, encrypts, and compresses data between the application and network.

How does the Presentation Layer act?

Like a translator — converting data into a format usable by the Application Layer.

What is the name of layer 6?

Presentation layer

Layer 6/ Presentation layer is the last layer that

changes/touches the data (physically).

What are the key functions of the Presentation Layer?

Data translation, encryption/decryption, and compression/decompression.

What is the name of layer 7?

application layer

Layer 7 is the protocol in coding from data you created and what does it?

Puts it in format.

How does the Application Layer differ from applications themselves?

It’s the interface between the user’s app and the network, not the app itself.

What protocols or standards operate at the Physical Layer?

Ethernet (physical signaling), USB, Bluetooth, Wi-Fi (IEEE 802.11), DSL, SONET, RS-232, DOCSIS

What protocols are used at the Data Link Layer?

Ethernet (MAC & LLC), PPP (Point-to-Point Protocol), HDLC, Frame Relay, ATM, ARP, MAC addresses (IEEE 802.3)

What protocols are found at the Network Layer?

IP (IPv4/IPv6), ICMP, IPsec,

What protocols are used at the Transport Layer?

TCP