Intro to OSI - Dleifnesor/NET-150 GitHub Wiki

Open systems interconnection

the way data travels through a network to and from IP addresses

A Priest Saw Two Nuns Doing Pushups

Application - the data that the computer is sending

Presentation - Compression, encryption, other encoding

Session - Session setup and teardown

Transport - Port numbers tell receiver what application the data is meant for

Network - IP addresses of sender and receiver

Data link - Defines how packets are sent over the layer, prevents data collisions (makes it safe to send, ie waiting to send to prevent an overflow of data)

Physical layer - How bits are physically sent over media (ethernet cables, fiber optic)

(port 80 - HTTP, port 25 - SMPT, port 22 - SSH)

Having separation of OSI layers is helpful for troubleshooting, as it helps narrow down problems to a layer(s)

IPv4 - xxx.xxx.xxx.xxx 0-255 Ipv6 - xx:xx:xx:xx:xx:xx 0-9, A-F

Dividing protocols into layers helps to manage the complexity of a network into separate processes

Data link - mac addresses

network - IP

DNS - application

TCP, UDP - transport

Layered models assist in protocol design, as protocols that operate at a specific layer have defined information that they act upon and a defined interface to the layers above and below also prevents technology or capability changes in one layer from affecting other layer above and below provides a common language to describe networking functions