OSI ISO | TCP/IP Model

ISO OSI Model Layers

1. Physical

2. Data Link

3. Network

4. Transport

5. Session

6. Presentation

7. Application

Physical Layer

Defines electrical, mechanical, procedural and function specifications for activating maintaining and de activating the physical link between devices.

Define line encoding, voltage levels, timing, data rates, physical connectors and other attributes.

Only layer implemented solely in hardware.

Data Link Layer

Defines how data is formatted for transmission and controlled access to physical media.

Typically includes Error Detection & Correction

Involves NIC-to-NIC communication within the same network or subnet.

Uses Physical Address called a MAC address to identify hosts.

Network Layer

Provides connectivity and path selection all the way from source to destination.

Uses logical addressing to manage connectivity.

Transport Layer

Defines the segmenting and reassembling of data for reliable delivery between hosts.

Serves the upper layers, which in turn interface many user applications.

Session Layer

Establishes, manages and terminates sessions between 2 communicating hosts to allow them to exchange data over a prolonged period of time.

*Mainly concerned with issues that application processes may encounter and not with lower layer connectivity issues.

Also called Dialogs, can determine whether to handle data in one direction at a time or both directions simultaneously.

Presentation Layer

Helps ensure that data sent by the application layer of one system is “readable” by the application layer of another system.

Provides special data processing that must be done before transmission.

It may compress or decompress data to improve throughput

Application Layer

OSI Layer closest to the user.

Provides services to user applications that want to use the network.

OS also use the application layer when performing tasks triggered by actions that dont involve communication over the network.

Does not provide services to any other OSI layer.

TCP/IP Layers

1. Link Layer

2. Internet Layer

3. Transport Layer

4. Application Layer (Payload)

TCP/IP Link Layer

Known as media access layer but also referred to as network interface or network access layer

Defines protocols used to interface the directly connected network

Introduces physical addresses sometimes called MAC addresses

TCP/IP Internet Layer

Routes data from the source to the destination, and reports errors.

Provides logical addressing to help ensure a host is uniquely identified.

Logical Address = IP Address

Serves the upper transport layer and passes info to the link layer

TCP/IP Transport Layer

Core of the TCP/IP Architecture

Two main protocols are - TCP & UDP

Transport services prepare application data for transfer over the network.

TCP/IP Application Layer

Mainly deals with user interaction.

Supports API’s that allow programs to access the network services, regardless of OS.

PDU for Application Layer

Data

PDU for Transport Layer

Segment

PDU for Internet Layer

Packet

PDU for Link Layer

Frame

TCP/IP Application Layer corresponds to which OSI Layer(s)

5. Session

6. Presentation

7. Application

TCP/IP Transport Layer corresponds to which OSI Layer(s)

4. Transport

TCP/IP Internet Layer corresponds to which OSI Layer(s)

3. Network

TCP/IP Link Layer corresponds to which OSI Layer(s)

1. Physical

2. Data Link