C01:Network Models/Protocol

• A protocol is a collection of guidelines that controls how computers communicate with one another over a network.
• These regulations contain recommendations for controlling a network's access method, permitted physical topologies, cable kinds, and data transfer speed.
  

The two widely used models: the OSI reference model and the TCP/IP model. Both models are founded on the idea of layering, which enables us to deal with various aspects of networks abstractly when using formal models.

Layering is to divide a task into sub-tasks and then solve each sub-task independently.

OSI Model

• The seven levels that computer systems employ to interact over a network are described by the Open Systems Interconnection (OSI) model.
• Early in the 1980s, all significant computer and telecommunications businesses accepted it as the first industry standard for network communications.

1. Physical Layer: The physical layer is responsible for the physical cable or wireless connection between network nodes. It defines the connector, the electrical cable or wireless technology connecting the devices, and is responsible for transmission of the raw data, which is simply a series of 0s and 1s, while taking care of bit rate control.
2. Data Link Layer: The data link layer creates and breaks connections between two network nodes that are physically close to one another. Frames are created from packets, which are then sent from source to destination. This layer is made up of two components: Media Access Control (MAC), which utilizes MAC addresses to connect devices and specifies permissions to transmit and receive data, and Logical Link Control (LLC), which identifies network protocols, does error checking, and synchronizes frames.
3. Network Layer: The network layer serves two primary purposes. One is dividing segments into network packets, which are then put back together at the other end. The alternative method of packet routing involves finding the optimum route through a physical network. In order to route packets to a destination node, the network layer needs network addresses, which are commonly Internet Protocol addresses.
4. Transport Layer: Data transferred in the session layer is divided into "segments" by the transport layer at the receiving end. On the receiving end, it is in charge of putting the segments back together in order to create data that the session layer may use. The transport layer performs error control, which determines whether data was received wrongly and, if not, requests it again, as well as flow control, which sends data at a pace that matches the connection speed of the receiving device.
5.  Session Layer: The session layer establishes sessions, or channels of communication, between devices. It is in charge of starting sessions, making sure they are active and open while data is being exchanged, and shutting them down once communication is complete. The session layer can also establish checkpoints during a data transmission, allowing devices to pick up where they left off in the event that the session is terminated.
6. Presentation Layer: Data is prepared for the application layer by the presentation layer. In order for data to be correctly received on the other end, it specifies how two devices should encode, encrypt, and compress data. Any data transmitted by the application layer is processed by the presentation layer before being delivered via the session layer.
7. Application Layer: End-user applications like web browsers and email clients operate at the application layer. It offers protocols that let computer programs transmit and receive data and give consumers useful information. The Hypertext Transfer Protocol (HTTP), File Transfer Protocol (FTP), Post Office Protocol (POP), Simple Mail Transfer Protocol (SMTP), and Domain Name System (DNS) are a few examples of application layer protocols.

TCP/IP Model

• consists of 4 layers

1. Application Layer: This layer is comparable to the OSI model's transport layer. It is in charge of ensuring seamless end-to-end connection and error-free data transfer. It protects the higher-layer applications from the data complexity. This layer's three primary protocols are as follows: 

• TELNET
• FTP
• HTTP

2.  Transport layer: To make sure that packets arrive in the correct order and without errors, the TCP/IP transport layer protocols exchange data reception acknowledgments and retransmit any that are lost. Communication from beginning to conclusion is referred to as such. User Datagram Protocol (UDP) and Transmission Control Protocol (TCP) are transport layer protocols at this level.

3. Internet layer: This layer performs similar tasks as the Network layer of the OSI model. It outlines the protocols in charge of logical data transmission over the whole network. The Internet Layer is a layer in the IP suite, a group of protocols that together define the Internet. Data packets must be routed from one device to another over a network by the Internet Layer. It achieves this by giving every device a special IP address, which is used to distinguish each one and specify the path that packets should travel in order to reach them.

4. Host-to-network: It is the TCP/IP model's lowest layer and is also referred to as the network interface layer. This layer's function is to link the host to the network.

Similarities between OSI layer and TCP/IP layer

• Both are models for logic.
• Both specify networking protocols.
• Both offer a framework for developing and putting into use networking standards and tools.
• Both create levels for the network communication process.

Differences between OSI and TCP/IP

TCP/IP	OSI
TCP refers to Transmission Control Protocol.	OSI refers to Open Systems Interconnection.
TCP/IP uses both the session and presentation layer in the application layer itself.	OSI uses different session and presentation layers.
TCP/IP follows connectionless a horizontal approach.	OSI follows a vertical approach.
The Transport layer in TCP/IP does not provide assurance delivery of packets.	In the OSI model, the transport layer provides assurance delivery of packets.
Protocols cannot be replaced easily in TCP/IP model.	While in the OSI model, Protocols are better covered and are easy to replace with the technology change.
TCP/IP model network layer only provides connectionless (IP) services. The transport layer (TCP) provides connections.	Connectionless and connection-oriented services are provided by the network layer in the OSI model.