OSI and TCP/IP Model

OSI Model

• is a set of rules that explains how different computer systems communicate over a network

• developed by the International Organization for Standardization (ISO)

Physical Layer

• responsible for transmitting individual bits from one node to the next

• contains information in the form of bits

Bit Synchronization

provides the synchronization of the bits by providing a clock, which controls both sender and receiver

Bit Rate Control

defines the transmission rate (number of bits sent per second)

Physical Topologies

specifies how the different, devices/nodes are arranged in a network

Transmission Mode

defines how the data flows between two connected devices

• Simplex

• half-duplex

• full duplex

Data Link Layer

the main function of this layer is to make data transfer error-free from node to another, over the physical layer

Data Link Sublayers

• Logical Link Control

• Media Access Control

Framing

provides a way for a sender to transmit a set of bits that are meaningful to the receiver accomplished by attaching special bit patterns to the beginning and end of the frame

Physical Addressing

adds physical addresses(MAC addresses) of the sender and/or receiver in the header of each frame

Error Control

provides the mechanism of error control in which it detects and retransmits damaged or lost frames

Flow Control

coordinates the amount of data that can be sent before receiving an acknowledgement

Access Control

The MAC sub-layer of the data link helps to determine which devices has control over the channel at a given time

Network Layer

works for the transmission of data from one host to the other located in different network

Packet

segment in the network layer

Routing

protocols determine which route is suitable form source to destination

Logical Addressing

to identify each device inter-network uniquely, the network layer defines an addressing scheme. The sender and receiver's IP addresses are placed in the header by the network layer

Transport Layer

provides services to the application layer and takes services from the network layer

Transport Layer Protocols

• TCP

• UDP

• NetBIOS

• PPTP

Segments

data in the transport layer

Segmentation and Reassembly

accepts the message from the (session) layer and breaks the messages into smaller groups, each segment produced has a header associated with it

Service Point Addressing

the header includes a type of address called service point address or port address, by specifying this, the transport layer makes sure that the message is delivered to the correct process

Services provided by the Transport Layer

• Connection-Oriented Layer

• Connectionless Service

Session Layer

responsible for the establishment of connections, management of connections, terminations of sessions between two devices, it also provides authentication and security

Session Layer Protocols

• NetBIOS

• PPTP

Application Layer

• the very top of the OSI Reference Model

• produce the data to be transferred over the network

• serves as a winder for the application services to access the network and for displaying the received information to the user

Application Layer Protocols

• SMTP

• FTP

• DNS

Why does the OSI Model Matter

although outdated it provides the user a clear structure of "how data moves in the network"

How Data Flows in the OSI model

• Application Layer

  • Applications create the data*

• Presentation Layer

  • Data is formatted and encrypted

• Session Layer

  • Connections are established and managed

• Transport Layer

  • Data is broken into segments for reliable delivery

• Network Layer

  • Segments are framed and sent to the next device

• Physical Layer

  • Frames are converted into bits and transmitted physically

TCP/IP Model

is a framework that is used to model the communication in a network

Role of TCP/IP

makes sure that the data sent by the sender arrives safely and correctly at the receiver's end

TCP/IP Application Layer

acts like a bridge between your software and the lower layers of the network that actually send and receive data

TCP/IP Application Layer

acts like a bridge between your software and the lower layers of the network that actually send and receive data

TCP/IP Transport Layer

responsible for making sure that data is sent reliably and in the correct order between devices

TCP

used when data must be correct and complete

UDP (User Datagram Protocol)

is faster but doesn't guarantee delivery, useful for things like live video or video games where speed matters more than perfect accuracy

TCP/IP Internet Layer

used for finding the best path for data to travel across different networks so it can reach the right destination, takes care of packet forwarding, fragmentation, and addressing

TCP/IP Network Layer

deals with the actual physical connection between devices on the same local network like computer connected by cables or communicating through Wi-Fi, uses MAC addresses to identify devices, creating frames, and checking for basic errors during transmission

Simpler Structure

TCP/IP has only 4 layers, compared to 7 in OSI

Protocol-Driven Design

TCP/IP was designed based on working protocols, while the OSI model is more of a theoretical framework

Flexibility and Robustness

TCP/IP adapts well to different hardware and networks and includes error handling, routing and congestion control

Open Standard

TCP/IP is open, free to use, and not controlled by any single organization helping it gain universal acceptance

Actual Use vs Conceptual Model

The OSI model is great for education and design principles, but TCP/IP is the one actually used in real-world networking

Interoperability

allows different types of computers and networks to communicate with each other, promoting compatibility and cooperation among diverse systems

Scalability

highly scalable, making it suitable for both small and large networks

Standardization

It is based on open standards and protocols, ensuring that different devices and software can work together without compatibility issues

Flexibility

supports various routing protocols, data types, and communication methods, making it adaptable to different networking needs

Reliability

TCP/IP includes error-checking and retransmission features that ensure reliable data transfer, even over long distances and through various network conditions

Security Concerns

was not designed with security in mind

Inefficiency for small networks

the overhead and complexity of the TCP/IP model may be unnecessary and inefficient for smaller networks

Limited by Address Space

although IPv6 addresses this issue, the older IPv4 system has a limited address space, which can lead to issues with address exhaustion in larger networks

Data Overhead

includes a significant amount of overhead to ensure reliable transmission