TJ Week 1 - Shadowsarespooky/TechJournal GitHub Wiki

Intro to OSI Model

Open Systems Interconnection (OSI)

Made up of 7 layers, it is the stages data goes through to travel across device over a network. Some phrases to remember the names (All People Seem To Need Data Processing) or (Please Do Not Throw Sausage Pizza Away) Headers from each layer is added to the packets traveling from one device to another. However depending on the packet, an UDP packet would not have much data to add as a header, such as encryption like a TCP would add.

Application Layer (7)

Network: The data that the computer is sending/receiving

Letter: The body of the letter

Presentation Layer (6)

Network: Compression, encryption, other encoding

Letter: Is it in code, abbreviated (texting?)

Session Layer (5)

Network: Session set up and teardown

Letter: Tracking Number

A session is setting up a tunnel or connection temporarily between devices, such as used by VPNS or accessing a website.

Transport Layer (4)

Network: Port numbers tell receiver what application the data is for Port 80 – HTTP web traffic Port 25 – SMTP e-mail Port 22 - SSH

Letter: Internal routing info on envelope Suite 36 Dept. C9

Network Layer (3)

Network: IP addresses of sender and receiver

Letter: Street address and zip code of sender and receiver

Datalink Layer (2)

Network: Defines how the packets get onto the media When is it safe to send – prevent collisions Is the recipient ready to receive

Letter: How do you get it to the postal service? Carrier pick up from your mailbox Take it to Post Office Drop it in mailbox

Physical Layer (1)

Network: Physically send the bits over media Copper wires Fiber optic Radio waves

Letter: What service to use: USPS, UPS, FedEx

Why does OSI Matter?

The OSI Model gives a visual reference of the layers in a networking system. This helps with figuring out problems, development and coding, and to help customers understand products that work with what layer.

Benefits

Packets