Day 3 Remediation | OSI & TCP/IP

Application Layer (7)

Closest to the end user:

• Interacts with software applications that have some communication component

• HTTP or HTTPs

• Identifying communication partners

• Synchronizing communication

• Provides process-to-process communication (specific task of delivering data to the correct application process on those hosts)

Presentation Layer (6)

Translates data to the appropriate format:

• Encryption of data as it is sent, so that only the intended recipient can read it

• And of course decryption as it is received.

Session Layer (5)

Controls dialogues between communicating hosts:

• Establishes, manages, and terminates connections between the local application

Transport Layer (4)

Segments and reassembles data for communications between end hosts.

• Breaks large pieces of data into smaller segments which can be easily sent over the network and are less likely to cause transmission problems if errors occur. 

• Provides host-to-host communication, also known as end-to-end communication (complete delivery of data from a source host to a destination host across a network.)

Network Layer (3)

Provides connectivity between end hosts on different networks

• Provides logical addressing, in the form of IP addresses

• Provides path selection between source and destination; provides the means of selecting the best path.

• Routers operate here

Data Link Layer (2)

Provides node-to-node connectivity and data transfer (for example, direct connections between a PC and a switch, or a switch and a router, or a router and a router)

• Defines how data is formatted for transmission over a physical medium

• Detects, and possibly corrects, errors that occur on the physical layer.

• Uses an addressing system

• Switches look at the destination Layer address to determine where to send the data

Physical Layer

Defines characteristics of the medium used to transfer data between devices.

• For example, voltage levels, maximum transmission distances, maximum cable length, physical connectors, cable specifications, etc.

• Digital bits are converted into electrical signals, for wired connections, or radio signals, for wireless connections, like Wi-Fi.

• Cables and pin layouts are relate

Layer 1 PDU

Bits

A Layer 2 header and trailer are added at the Data Link layer

Frame

Layer 3 header is added on at the Network layer which includes the IP address

Packet

Data plus Layer 4 header

Segment