The OSI model (Open Systems Interconnection Model) is a critical model, providing a framework on how all networked devices send, receive and interpret data.
The OSI model is made up of 7 layers, each with their own set of responsibilities and is arranged from Layer 7 (Application) to Layer 1 (Physical).
At each layer data passes through, various processes occur, and additional information is appended. This phenomenon is called encapsulation
The application layer of the OSI model facilitates user interaction with data through protocols and rules. This layer is familiar due to everyday applications like email clients, browsers, and file server browsing software (e.g., FileZilla) offering a GUI (Graphical User Interface). Protocols such as DNS (Domain Name System) translate website addresses into IP addresses.
This layer initiates standardization, ensuring consistent data handling regardless of software variations. Serving as a translator between the application layer (layer 7) and lower layers, it ensures data compatibility even if received by different applications. Security measures like data encryption (e.g., HTTPS) are implemented at this layer.
The session layer (layer 5) establishes and manages connections between computers, creating sessions for data exchange. It ensures synchronization and breaks data into smaller packets for transmission, reducing data loss risks. Sessions are unique, restricting data transmission to within each session.
Layer 4 of the OSI model is crucial for data transmission in networks, involving protocols like TCP and UDP.
or Transmission Control Protocol ( [[Study notes/Networks/Networking#TCP/IP Model|TCP/IP Notes]] ), prioritizes reliability and ensures a continuous connection between devices until data transmission is complete. It incorporates error checking to guarantee the accurate reception and reassembly of data sent in small chunks.
| Advantages of TCP | Disadvantages of TCP |
|---|---|
| Accuracy of data | Requires a reliable connection; if one data chunk is lost, the entire data set becomes unusable. |
| Capable of synchronizing (2) devices to prevent data overload. | A slow connection can bottleneck other devices as it reserves the connection on the receiving end continuously. |
| More reliable | Significantly slower than UDP |
| Used for things where data has to be accurate and complete (e.g. file transfer, browsing pages, sending emails |
or User Datagram Protocol, doesn't provide the features TCP does, there is no error checking, reliability or synchronization, while this sounds bad, it does have its merits.
| Advantages of UDP | Disadvantages of UDP |
|---|---|
| Much faster than TCP. | UDP doesn't care if the data is received. |
| UDP leaves the application layer (user software) to decide if there is any control over how quickly packets are sent. | It is quite flexible to software developers in this sense. |
| UDP does not reserve a continuous connection on a device as TCP does. | This means that unstable connections result in a terrible experience for the user. |
UDP is widely used where speed is required, such as video streaming (If the view is pixelated it simply shows lost data). It is also used in protocols such as ARP and DHCP for discovering devices.
The network layer, handles routing and reassembly of data from small to larger chunks. Routing determines the optimal path for data transmission, involving protocols like OSPF (Open Shortest Path First) and RIP (Routing Information Protocol).
Factors include
- shortest path
- reliability
- speed of physical connection.
We work with IP addresses here, Devices like routers also operate at this layer (Known as Layer 3 Devices)
The data link layer handles physical addressing by adding the MAC (Media Access Control) address to packets received from the network layer. MAC addresses are unique identifiers burned into Network Interface Cards (NICs). They can't be changed but can be spoofed. The data link layer ensures data is formatted appropriately for transmission.
This layer deals with the physical components of networking hardware, operating at the lowest level. It involves transferring data between devices using electrical signals in a binary numbering system (1's and 0's).
e.g. an Ethernet cable
