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What is the OSI Model and what is it used for?

The OSI Model, or Open Systems Interconnection Mode, is a reference model developed by the International Organization for Standardization (ISO)

What are the 7 layers of the OSI model?

Layer 7: Application; Layer 6: Presentation; Layer 5: Session; Layer 4: Transport; Layer 3: Network; Layer 2: Data Link; Layer 1: Physical

What is the Pneumonic to memorize the 7 layers of the OSI Model?

Please Do Not Throw Sausage Pizza Away

What model do modern networks operate on today?

TCI/IP Model

How does data flow within the OSI model when receiving vs sending?

Data moves down the stack on the sending side (encapsulation) and up the stack on the receiving side (decapsulation). Each layer wraps the data from the layer above with its own header (and sometimes a trailer)

Sending: Top down

Receiving: Down up

What is PDU?

PDU, or Protocol Data Unit, is a generic term for referencing data at different layers of the of a network protocol stack, like the OSI model. PDU is the umbrella term for whatever the unit of data is called at a given layer

What is the PDU for each layer of the OSI Model?

Layer 5, 6, 7 (Application, Presentation, Session) - Data; Layer 4 (Transport) - Segments; Layer 3 (Network) - Packets; Layer 2 (Data Link) - Frames; Layer 1 (Physical) - Bits

What is the Pneumonic to memorize the PDU for each layer of the OSI Model?

Do Some People Fear Birthdays

What is Layer 1 and what does it do?

Layer 1 is the Physical layer. It is responsible for moving raw bits between devices over a physical medium

What is Modulation?

Modulation is the process of encoding bits onto a carrier signal by varying one or more of its properties (amplitude, frequency, or phase) according to the data being sent

What is the difference between Carrier and a Medium when it comes to Modulation?

The carrier is the wave that gets shaped to represent bits; the medium is the physical path it travels through (air, copper, fiber)

Why is Modulation used?

Modulation fits data to what the medium handles well

What is an RJ-45 Connector?

The head of an ethernet cable

What is TIA/EIA-568A & 568B?

TIA/EIA stands for Telecommunications Industry Association/ Electronic Industries Alliance and are standards for terminating twisted pair ethernet cables. Essentially, standards for pin lay outs in an RJ-45 connector.

What are Crossover Cables and Straight-Through Cables?

Crossover Cables are ethernet cables with different TIA/EIA heads (568A - 568B), used for connecting same devices (pc to pc, switch to switch, etc). Straight-Through Cables are ethernet cables with same TIA/EIA heads (568A - 568A, 568B - 568B), used for connecting different devices (pc to switch, router to pc)

What is Asynchronous and Synchronous communication?

Both describes how devices coordinate the timing of data transmission. Synchronous Communication is when data is transmitted based upon a shared clock. Asynchronous Communication is when data is transmitted without requiring a shared clock

What is Synchronous communication?

Is when data is transmitted and received according to a shared clock between sender and receiver. Sender and receiver coordinates when bits are transmitted and received

What is Asynchronous communication?

Is when data is transmitted and received without a shared clock. Each character or unit of data can be transmitted independently - start and stop bits help identify where each character begins and ends

What is Broadband and Baseband, and what is there distinction?

Broadband and Baseband describes how a communication medium uses its available frequency spectrum to transmit signals. Baseband: Uses the entire channel bandwidth for a single digital signal at a time. Broadband: Divides the channel into multiple frequency channels, allowing multiple signals or services to operate simultaneously.

What is Multiplexing and why is it needed in networking?

Multiplexing is the process of combining multiple signals or data streams so they can share a single communication medium. Multiple signals sharing one medium. Imagine a fiber-optic cable connecting two cities. Instead of installing 100 separate cables for 100 users, multiplexing allows multiple users' data to travel through the same cable.

What is MUX and DEMUX in Multiplexing?

MUX combines multiple signals into a single signal while DEMUX processes a single input into their original individual signals

What are Multiplexing techniques used for?

Multiplexing techniques, such as TDM, statistical TDM, FDM, etc are all various ways to allow multiple signals or data streams to share a single communication medium efficiently.

What is TDM?

TDM, or Time-Division Multiplexing, is a technique that allows multiple signals to share the same communication channel by assigning each signal a specific time slot.

What is FDM?

FDM (Frequency-Division Multiplexing) is a multiplexing technique that allows multiple signals to share one communication channel by assigning each signal a different frequency band.

What is the main difference between TDM and FDM?

TDM: Computers take turns transmitting using different time slots. FDM: Computers can transmit simultaneously because each uses a different frequency.

What is StatTDM?

StatTDM, or Statistical Time-Division Multiplexing, is essentially a more efficient TDM where time slots are assigned dynamically. Basically, it only assigns time slots to devices only when they have data to transmit.

What are some Layer 1 devices?

Devices that deal with physical signals and bits: Hubs; Repeaters; Media Converters; Cables (Fiber optic, Ethernet, Coaxial); Transceivers

What is Layer 2 and what does it do?

Layer 2 is the Data Link layer and it is responsible for packages bits into frames. The Data Link layer's primary job is to take data from the Network Layer (Layer 3) and package it into frames so it can travel across a physical network.

What are the four major responsibilities of Layer 2?

Framing: Takes Layer 3 packets and encapsulates them into frames. MAC addressing: Uses MAC addresses to identify devices on a local network. Error detection: Detects transmission errors using mechanisms such as FCS (Frame Check Sequence). Media access control: Determines how devices access and transmit over the communication medium.

What is a Mac Address?

A MAC address (Media Access Control address) is a unique hardware identifier assigned to a network interface (NIC) that allows devices to identify each other on a local network.

What is an LLC and what does it do?

An LLC, or Logical Link Control, is a sublayer of the Data Link layer and is responsible for providing the interface between layer 3 and layer 2. The LLC helps determine how incoming and outgoing data should be handled by higher-level network protocols.

What are the two sublayers of Layer 2?

LLC (Logical Link Control) and MAC (Media Access Control). LLC acts as the upper sublayer, acting as the interface between layer 2 and 3. MAC acts as the lower sublayer, responsible for identifying devices and managing access to the network medium.

What is a MAC (not MAC address) and what does it do?

MAC (Media Access Control) is the lower sublayer of the Data Link Layer (Layer 2) in the OSI model. Its primary responsibilities are: 1. Physical addressing: Uses MAC addresses to identify network interfaces. 2. Frame delivery: Helps determine where Ethernet frames should be delivered on a local network. 3. Media access: Defines how devices access and transmit data over the communication medium. Think of MAC as the part of Layer 2 responsible for identifying devices and managing access to the network medium.

What is a checksum?

A checksum is a value calculated from a piece of data and used to detect whether that data has been corrupted or changed during transmission or storage. Think of it as a way to verify that the data received matches what was originally sent.

What are some Layer 2 devices?

Layer 2 devices operate at the Data Link Layer of the OSI model. They primarily use MAC addresses to identify devices and forward frames across a local network: Switch; Bridge; Wireless Access Point (AP); Network Interface Card (NIC)

FDM

Different frequencies share the medium simultaneously.

TDM

Different users take turns transmitting in assigned time slots.

WDM

Different wavelengths of light share one fiber simultaneously.

CDM

What are some Layer 1 Devices?

Fiber Optic Cables; Ethernet Cables; Coaxial Cables