In this article, we are going to discuss the OSI Model and TCP Model. The OSI model has seven layers: application, presentation, session, transport, network, data link, and physical. We use TCP/IP in real-world networks. TCP/IP combines the application, presentation, and session layers into the application layer. Transport and network layers remain the same, and the combination of the data link and physical layers is known as the network interface. In the updated version of TCP/IP, we have five layers: application, transport, network, data link, and physical.
OSI Model: OSI Model and TCP Model
We learn the OSI model to understand how packets travel from one source to destination. Protocols are a set of rules that we follow over the internet.
We learn the OSI model to understand how packets travel from one source to destination. Protocols are a set of rules that we follow over the internet. The application layer is responsible for any software that interacts with humans. The presentation layer converts data into a format that is understandable to humans and is responsible for encryption and decryption. The session layer creates and maintains sessions.
Introduction to Data Communication and Networking Fundamentals 7 Layer of OSI
The Application Layer
The application layer is where any software that interacts with humans falls. In the Application layer, these protocols are used HTTP, HTTPS, email protocols, FTP, telnet, and SSH. The layer is responsible for sharing data, accessing websites, sending emails, sending files, and accessing devices remotely.
The Presentation Layer
The presentation layer is responsible for converting data into a format that is understandable to humans. It also handles encryption and decryption and compression and decompression.
The Session Layer
The session layer creates and maintains sessions. Establishes, manages, and terminates sessions between applications on different network devices.
Transport Layer
The transport layer is responsible for managing the data transmission between devices. It is divided into two protocols: TCP and UDP. TCP is connection-oriented and reliable, meaning it always ensures that data is delivered and acknowledged by the recipient. UDP, on the other hand, is connectionless and unreliable, meaning it does not guarantee delivery or acknowledgment of data.
TCP vs. UDP
TCP and UDP differ in several ways
- TCP is connection-oriented, while UDP is connectionless.
- TCP is reliable and guarantees delivery and acknowledgment, while UDP is not reliable and does not provide acknowledgment.
- TCP has a higher overhead due to its need for acknowledgment and sequencing, while UDP has a lower overhead due to its lack of acknowledgment and sequencing.
- TCP uses 20 bytes of information to add addresses and port numbers, while UDP uses only 8 bytes for the same purpose.
- The TCP protocol number is 6, while the UDP protocol number is 17. Both protocols fall under the IP protocol.
Session Layer
The session layer controls the time frame for sessions, meaning it logs out users after a certain period of inactivity. This is done through algorithms integrated into websites and applications. The session layer creates and maintains sessions with time frames.
Application Layer
The application layer takes care of the format of data. In real-world scenarios, all three layers (presentation, session, and application) are often combined into one layer known as the application layer.
Transport Layer
The transport layer converts data into segments and adds sequencing and acknowledgment. TCP is more reliable due to its connection-oriented nature, while UDP has lower overhead and is faster.
TCP/IP Model: The Reliable Protocol
TCP, or Transmission Control Protocol, is the main protocol of the Internet protocol suite. It operates at the transport layer of the OSI model and ensures reliable and ordered delivery of data between network devices.
Connection Establishment
TCP establishes a connection between a sender and a receiver before data transmission. This process involves a three-way handshake, where both parties exchange control packets to synchronize sequence numbers and establish communication parameters.
Reliable Data Transfer
TCP is a connection-oriented network protocol. That is why data packets arrive at the destination in the correct order and without errors. It uses sequence numbers and acknowledgment mechanisms to detect missing or corrupted packets and retransmits them if necessary.
Flow Control
To prevent overwhelming the receiver with more data than it can process, TCP employs flow control. It uses a sliding window mechanism to regulate the amount of data sent at a time, optimizing the network’s overall performance.
Congestion Control
TCP actively monitors the network for signs of congestion and adjusts its transmission rate accordingly. It employs algorithms like TCP Reno and TCP Vegas to manage congestion and prevent network collapse.
Connection Termination
When the data transmission is complete. The TCP terminates the connection between the sender and the receiver. This ensures efficient resource allocation and frees up network resources for other connections.
OSI Model and TCP/IP Model in Brief
OSI Model
Application Layer
- Description: The top layer of the OSI Model enables communication between user applications and the network.
- Key Protocols: HTTP, FTP, SMTP, DNS
Presentation Layer
- Description: Responsible for data translation and encryption to ensure compatibility between different systems.
- Key Protocols: SSL, TLS
Session Layer
- Description: Manages the establishment, maintenance, and termination of sessions between devices.
- Key Protocols: NetBIOS, SSH
Transport Layer
- Description: Provides reliable data delivery and error-checking mechanisms.
- Key Protocols: TCP, UDP
Network Layer
- Description: Handles logical addressing and routing of data packets across different networks.
- Key Protocols: IP, ICMP, ARP
Data Link Layer
- Description: Ensures error-free transmission of data frames between adjacent network nodes.
- Key Protocols: Ethernet, MAC, PPP
Physical Layer
- Description: Deals with the physical transmission of data bits over the network medium.
- Key Protocols: Ethernet, USB, DSL
TCP/IP Model
Application Layer
- Description: Corresponds to the application layer of the OSI Model, providing network services to user applications.
- Key Protocols: HTTP, FTP, SMTP, DNS
Transport Layer
- Description: Equivalent to the transport layer of the OSI Model, responsible for reliable data delivery.
- Key Protocols: TCP, UDP
Internet Layer
- Description: Equivalent to the network layer of the OSI Model, handles the addressing and routing of packets.
- Key Protocols: IP, ICMP, ARP
Network Interface Layer
- Description: Equivalent to the data link and physical layers of the OSI Model, manages the connection to the physical network.
- Key Protocols: Ethernet, MAC, PPP
Conclusion
The knowledge of OSI model and TCP is essential for a network engineer. The OSI model gives a complete picture of the message from one layer to another layer. TCP ensures reliable data transmission, guaranteeing the integrity and order of information exchange.
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