Introduction
I use this page as a space to remind myself on concepts that I found difficult while learning networking.
OSI Model
Application Layer
Purpose: Provides network services directly to end-users and applications.
Examples: HTTP, FTP, SMTP, and other application protocols.
Presentation Layer
Purpose: Translates, encrypts, or compresses data for the Application layer.
Examples: Data encryption, character encoding, data compression.
Session Layer
Purpose: Manages sessions or connections between applications.
Examples: APIs, session establishment and management.
Transport Layer
Purpose: Ensures complete data transfer and error recovery.
Examples: TCP (Transmission Control Protocol), UDP (User Datagram Protocol).
Network Layer
Purpose: Manages logical addressing and routing of data across the network.
Examples: IP addresses, routers.
Data Link Layer
Purpose: Provides node-to-node data transfer and handles error correction from the Physical layer.
Examples: Ethernet, MAC addresses, and switches.
Physical Layer
Purpose: Transmits raw bitstreams over a physical medium.
Examples: Cables, switches, and the physical aspects of network devices.
Data Encapsulation
As data is being sent from on computer to another it undergoes a process called Encapsulation.
The Application, Presentation and Session layer provide data for the Transport layer where headers and trailers are added to the data.
Segmentation
Once the data is received, the transport layer breaks the data into smaller pieces and creates and attaches a header for each piece with information about reassembly. This is known as a segment and is then sent to the Network Layer.
Packet
A header is then created for the segment with addressing and routing information and once attached this becomes packet.
Frame
Packets are then given a header and a trailer by the data link layer called a frame. Headers have information regarding switching requirements while the trailer is used to detect and drop corrupt data during de-encapsulation
Bits
Frames are then converted into required medium for physical layer to send such as signals or voltage.
De-Capsulation
At the receiving computer the process is reversed as each layer uses the attached header/trailer to move the data through each layer.
TCP/IP Model
Similar to the OSI Model, the TCP/IP Model consists of four layers, Application, Transport, Internet and Link.
This is done by combining layers together to be simpler and more practical when reflecting protocols such as TCP and IP, emphasising end-to-end communication.
Subnetting
Subnetting is the process of dividing a larger network into smaller, more manageable sub-networks (subnets). This improves performance and security by isolating network segments.
Steps for Subnetting:
- Determine the Number of Required Subnets: Decide how many subnets you need.
- Calculate the Subnet Mask: Adjust the subnet mask to create the necessary number of subnets.
- Divide the IP Address Range: Allocate the IP ranges for each subnet.
- Assign IP Ranges: Assign ranges to devices within each subnet.