Network Model  / Protocol

protocol- is the set of rules that governs the communication between computer on nertork.

rules includes:

1. guidelines 

2. access method

3. allowed physical method

4. types of cabling

5. speed of data transfer.

layer- divide the task into sub-task and then solve each sub-task independently.

OSI(Open System interconnection Reference Model)- is the description for layered communication and computer network protocol  communication and computer network protocol and transmission design.

it divides data movement into seven layer from to to bottom, that are:

1. application layer

• is the responsible to identify communication methods to allow users and hosts to interact with the software applications available on the internet.
• this layer help to identify communication partner, and synchronizing communication.
• this layer allows users to interact with other software application.
  

2. presentation layer

•  this layer establishes a context between Application Layer entities.
• the higher-layer entities can use different syntax and semantics, as long as the presentation service understands both and the the mapping between them.

3. session layer

•  is the layer of the ISO open systems interconnection model that controls the dialogues(connections) between computers.
• It establishes, manages, and terminates the connections between the local and remote application.

4. transport layer

•  provides transparent transfer of data between end users, providing reliable data transfer services to the upper layers.
• this layer control the reliability of a given link through flow control, segmentation and de-segmentation and error control.

5. network layer

•  provides the functional and procedural means of transferring data from source to a destination.
• this layer performs networking routing function, sending data through extended network and making internet possible.

6. data link layer

•  is the functional and procedural means to transfer data between networks entities.
• its major role is to ensure error-free transmission of information.

7. physical layer

• is the first and lowest layer of the OSI communication model.
• it provides the encoding of signals if required.
•  It also provides the bit synchronization for the transmission of bits in both synchronous 

it also refer as OSI Seven Layer Model

TCP/IP Model

• used by ARPANET

FOUR layers of TCP

1. host-to-network
2. internet
3. transport
4. application

Host to Network Layer

• is the lowest layer of the TCP/IP model and is connect with the physical transmission of data.
• it is also called a network interface layer and link layer.
• it can be considered as the combination of physical layer and data link layer of the OSI model.

Internet layer

• it is also known as network layer or IP layer
• accepts and deliver packets for the network.

Network Protocol

• is a protocol, or set of rules, for routing and addressing packets of data so that they can travel across networks and arrive at the correct destination.

TCP

• Transport layer used TCP for reliable connection oriented service.

The function of TCP are

1. error control
2. flow control
3. sequencing

UPD

Transport layer used this protocol for unreliable connectionless service.

Application layer

• this layer is the connection of application, presentation, and session layer of the OSI model.
• it includes high-level protocol that used for wide variety of application:

1. TELNET(terminal network)-used to remote login
2. FTP(File Transfer Protocol)- for transfer of file from one system to another
3. HTTP(Hyper Text Transfer Protocol)-fetching web page on world wide web