a. OSI reference model:
It was created by the International Organization for Standardization (ISO) to provide a logical framework for how data communication processes should interact across networks. Standards were created for the computer industry allowing different networks to work together efficiently.
There are 7 layers in the OSI model. Each layer is responsible for a particular aspect of data communication. For example, one layer may be responsible for establishing connections between devices,
1. Application Layer:
Provides network services to user applications, it is responsible for exchanging information between programs running on the machine, such as an e-mail program, and other services running on a network.
2. Presentation Layer:
Concerned with how data is converted and formatted for data transfer. This layer performs code conversion, data translation, compression, and encryption.
3. Session Layer:
Determines how two devices establish, maintain and manage a connection - how they talk to each other. These connections are called sessions.
4. Transport Layer:
Responsible for breaking the data into segments, establishing an end-to-end logical connection between machines, and providing for error handling.
5. Network Layer:
Responsible for determining addressing on the network, determining the routes that information will take on its journey, and managing network traffic congestion. Data at this level is packaged into packets.
6. Data Link Layer:
It provides the link for how data, packaged into frames are communicated through hardware to be transported across a medium. It communicates with network cards, manages physical layer communications between connecting systems and handles error notification.
7. Physical Layer:
Specifies how data is processed into bits and physically transferred over medium, such as cables. It’* responsible for activating and maintaining the physical link between systems.
b. TCP/IP:
TCP/IP stands for “Transmission Control Protocol / Internet Protocol”. It is basically a network protocol that defines the details of how data is sent and received through network adapters, hubs, switches, routers, and other network communications hardware. It was developed by the US department of defense for the purpose of connecting government computer systems to each other through a global, fault-tolerant, network.
It has become the most popular networking protocol throughout the world and well supported by almost all computer systems and networking hardware.
TCP, Transmission Control Protocol, breaks data up into packets that the network can handle efficiently, verifies that all the packets arrive at their destination, and reassembles the data.
IP, Internet Protocol, envelopes and addresses the data, enables the network to read the envelope and forward the data to its destination and defines how much data can fit in a single packet.
After TCP/IP was developed, many more protocols included, Simple Mail Transfer Protocol ( SMTP) used for transferring email across the internet, File Transfer Protocol (FTP) used to upload and download files, and Hyper Text Transfer Protocol (HTTP) the protocol used to .transport web pages.
*The TCP/IP model’ protocol layers**
TCP/IP must be responsible for the following tasks:
- Dividing messages into manageable chunks of data that will pass efficiently through the transmission medium.
- Interfacing with the network adapter hardware.
- Addressing:
The sending computer must be capable of targeting data to a receiving computer. The receiving computer must be capable of recognizing a message that it is supposed to receive.
- Routing data to the subnet of the destination computer, even if the source subnet and the destination subnet are dissimilar physical networks.
- Performing error control, flow control, and acknowledgment: For reliable communication, the sending and receiving computers must be able to identify and correct faulty transmissions and control the flow of data.
- Accepting data from an application and passing it to the network.
- Receiving data from the network and passing it to an application.
