OSI Model Layer 1

Physical Layer

Responsible for actual sending of bits across the network hardware. 

Includes wires, cables, fiber, wireless signals, network hardware.

OSI Model : Layer 2

Data Link Layer

Responsible for interfacing with hardware only on the local network.

Also know as just the "Link Layer"

Protocols Include: Ethernet, Wi-Fi

Control Information : Adds a trailer at the end of a frame

OSI Model Layer 3

Network Layer

Moves information from one node on the network to another node on the network.

IP Address for EVERY node.

Fragmentation needs determined here.

Protocols Include: IP, ICMP, ARP

Control Info: Header added at beginning info and then called a packet or datagram.

OSI Model Layer 4

Transport Layer

Responsible for transporting application payloads from one app to another. 

*Fragmented portions of data called segments.

*Encapsulation heavily involved at this layer.

Protocols: TCP and UDP

Control Info: Header with port information added to beginning of packet / datagram

OSI Model Layer 5

Session Layer

Describes how data between apps is synced and recovered if delivery fails.

APIs (Application Programming Interfaces) often merge functions of layers 5-7 making it difficult to differentiate which layer is doing what.

OSI Model Layer 6

Presentation Layer

Responsible for reformatting, compressing and/or encoding/encrypting data. 

OSI Model Layer 7

Application Layer

Describes interface between 2 apps, each on separate devices.

Protocols fall into 2 categories:

A) Services to users such as web browsers

B) Services to the system such as SNMP

Protocols: HTTP, SMTP, POP3, IMAP(#) - 4 is current, FTP, Telnet, RDP

OSI Model

Open Systems Interconnection Model