In practice, the whole Internet functions precisely on the principle of TCP/IP protocol. This is a set of protocols that contains two main protocols, TCP and IP (the standards by which data packets travel from one computer to another and return via a specific route or not).

TCP protocol (Transmission Control Protocol)

TCP protocol provides reliable data transfer in an IP environment. Sequential identification of bytes is in the series without the structure in the TCP protocol transfer. Bytes get the number of sequence in the segments, then the application is assigned a port number, and this is forwarded to the IP protocol. TCP performs the control of data transmission, or more clearly, it regulates the transport layer of the network.

UDP protocol (User Datagram Protocol)

UDP creates mismatched packages. It does not create connections and is used when data needs to be sent fast and when speed is the most crucial factor. It does not think about whether the packages will be destroyed and the order is not important to him. Usually, it is used for video conferences, video telephony (VoIP), computer game servers, DNS, and more. UDP unlike TCP, emphasizes the efficiency (speed) of packet transmission with minimal protocol structure. Due to the lack of checks, it is often misidentified as Unreliable Datagram Protocol. For UDP, different from TCP, it can be said that it is “puritan” with minimal equipment. That gives him speed. It requires very few data from the server and performs all necessary network activities, but it just does not guarantee anything.

IP (Internet protocol)

Among internet protocols, IP is the primary network layer protocol. IP contains address information and some control information that gives the packets the ability to be routed. IP includes addressing information, enabling each network device (computer, server, workstation, router) to be addressed, have a unique address and be easily identified in the network. IP also contains control information so that the packets can be routed based on known IP addresses.


Routing is directing the packet to the IP network on which the computer to which the packet is being sent to is.

OSI Reference Model

Unlike the TCP/IP model (four layers), the OSI model has seven layers. The layers in the TCP/IP model are network access, internet layer, transport layer, and application layer. Layers in the OSI reference model are a physical layer, data link layer, network layer, transitive layer, session layer, presentation layer, and application layer.

OSI Reference Model (Open Systems Interconnection Basic Reference Model) is an abstract description of the network architecture. The OSI reference model consists of seven different levels of abstraction.

  1. A physical layer (signal transmission): unit – bit : Protocols – Token Ring, IEEE 802.11.
  2. Link layer (physical addressing, access to the media): unit – frame : Protocols – PPP, HDLC, Frame relay.
  3. Network (logical addressing and routing): unit – package : Protocols – IP, ICMP, ARP, RARP.
  4. Transport (connection, reliability, transport): unit – segmentdatagram : Protocols – TCP, UDP.
  5. Session (establishing of end user session): unit – data : Protocols – RPC, PAP, SCP.
  6. Presentation (encryption and data encoding): unit – data : Protocols – MIME, SSL, TLS.
  7. Application (application-related network processes): unit – data : Protocols – HTTP, HTTPS, FTP, SSH, DNS, SMTP.

HTTP protocol

HTTP (Hypertext Transfer Protocol) is a network protocol that represents the main and most common method of transmitting information on the web. The primary purpose of this protocol is the distribution of HTML documents, websites. This protocol is used for communication between the server and the client and functions according to the request/response principle. The HTTP client, which is usually a web browser, initiates data transfer after establishing a TCP/IP connection to a remote web server on a particular port. An HTTP server listens to the requests on the communication port (port 80 is default) and waits for the client to send the request. After the server receives a response at the request of the client, the connection is interrupted until next time.

HTTPS protocol

HTTPS (Hypertext Transfer Protocol Secure) is a combination of HTTP and SSL/TSL protocols. HTTPs provide encryption and secure server identification using port 443. The main idea behind the HTTPS protocol is to create a secure channel on an unprotected network. The certificate is issued by a verified and trusted publisher (Certificate Authority), which is a prerequisite for the server to be protected against attacks. When accessing websites that use invalid (non-validated) certificates, newer browsers display a question across the screen. Also, in the address bar, there is a crossed-out https:// in red color indicating that the certificate is not valid.

FTP protocol

FTP (File Transfer Protocol) is the most commonly used protocol for data transfer between two computers on the network. It is suitable for transferring large documents. FTP uses TCP/IP for network communications, which enables it to be reliable and session-oriented. An FTP connection is established on request from a client computer to a server computer. The client computer must use an FTP client (FileZilla, Cyberduck) to send connections to an FTP server. Furthermore, they communicate on the standard FTP communication port 21. Passwords and file content are transmitted without encryption, byte by byte, and traffic can be intercepted and exploited for unauthorized access to the server. SSL and TLS algorithms solve this problem.

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Author: Milutin Gavrilovic (original source: