OSI Network Model

Open Systems Interconnection (OSI) model - a conceptual framework that describes the functions of a networking or telecommunication system.

The OSI model has 7 layers. 


Layer 7 - Application Layer

This is what the user communicates with. It is the applications that we used - Google Chrome & Skype are examples. 


Layer 6 - Presentation 

This is where data is converted from the application framework into something that the network understand. The data would be encrypted here for example. 


Layer 5 - Session

Computer need to create a session between the two devices so they can speak to each other. This is done here. The computer communicate telling each other how much time they should wait for a response from each other and what they should do when the task has been completed (end session) etc. 


Layer 4 - Transport 

The Transport Layer deals with the coordination of the data transfer between end systems and hosts. This is where the protocol is decided on. TCP/IP is commonly used here. This is only where a port number will be decided. 


Layer 3 - Network

This layer is responsible for packet forwarding, including routing through different routers. This is where IP addresses are assigned. 


Layer 2 - Data Link

The Data Link Layer provides node-to-node data transfer. This is where MAC addresses are assigned. 


Layer 1 - Physical

This is just the physical hardware that makes all of the above work. Such as NICs, networking cables and the router itself. 

Comments

Post a Comment

Popular posts from this blog

CPU Fetch-Decode-Execute Cycle

Image
A CPU (central processing unit) executes and manages the rest of the hardware inside a computer system - it is the brain of a computer! The CPU is made up of the main memory, the processor and the cache memory. It's job is to process data (by processing we mean searching, sorting, calculating and decision making). The CPU follows the Fetch-Decode-Execute cycle. The Fetch Stage: the CPU use a piece of hardware called the ' address bus ', this is where the CPU asks the RAM for some data. The RAM then responds with this data on the ' Data Bus '.  The Decode Stage: This is where the CPU converts the instructions in to a way in which it understands it. It then gets things ready for the next step.  The Execute Stage: This is where data processing happens. Instructions are carried out on the data, as soon as the command is completed it starts the next one. 
Read more

Scheduling

Image
Scheduling is where a computer prioritises tasks to be carried out in a certain order to maximise the use of the computer and all of its peripherals. The algorithm must be robust so the computer does not freeze and also so every task/user gets a fair response time. Two main types of jobs are I/O bound jobs and processor bound jobs: I/O bound jobs (input/output) examples: Sending a document to the printer. Moving the mouse. Typing on the keyboard. Processor bound jobs examples: Playing Music Watching a video Calculating in Excel. There are different ways a processor can prioritise tasks: FCFS (first come first served) - tasks are started and completed in the order they are received. RR (round robin) – the time slice is 1 minute - each job has a minute spent on it before moving onto the next one. This occurs in a circuit until all jobs are complete. SJF – shortest job first - The job with the shortest completion time is carri
Read more

Utility Software

Image
Computer security Anti-virus - Scans/analysing your system to check for virus’ on a regular basis, if it identifies a virus that it knows of (in its database) it will remove it from the system. Spyware protection - Scans user files, checks for damage caused by installed spyware to the system and analyses domain names that potentially contain spyware. They then remove or warn the user about issues.   Firewall - use to prevent specific network packets making it onto a network. These may be blocking people from accessing certain websites or from certain files from being downloaded/uploaded. Disk organisation Defragmenter - rearranges files stored on the hard drive so related files are stored together. This makes it easier for the CPU to find files easier to find and results in much faster performance. File transfer - software designed to transfer content from one device to another. Either done from one piece of hardware to another using physical cables or done using F
Read more