Internet
Computer network that interconnects billions of computing devices throughout the world
- Billions of Users
- Billions of Devices
- Millions of Applications
Network Model
To reduce the complexity, networks are organized as a stack of layers.
Each layer offers certain services to the layers above it and abstracts the layers below it.
The header (and footer) and the data together form the PDU for the next layer. The process continues until reaching the lowest-level layer (physical layer or network access layer), from which the data is transmitted to the receiving device. The receiving device reverses the process, de-encapsulating the data at each layer with the header and footer information directing the operations. Then the application finally uses the data. The process is continued until all data is transmitted and received.
Physical Layer
It represents the physical devices that interconnect computers and the technologies that develop them
- Networking Cables
- Wi-Fi and Cellular Hardware
Signals are sent over these media.
Data Link Layer
Data link layer is responsible for defining a common way of interpreting signals.
Network Layer
Network Layer is responsible for getting data delivered across a collection of networks.
- Internet Protocol (IP)
Transport Layer
Transport Layer is responsible for ensuring that data gets to the right process (application).
Application Layer
The protocols in Application Layer are used to allow you to browse the web or send receive email are some common ones.
TCP/IP Network Model
You can think of layers like different aspects of a package being delivered. The physical layer is the delivery truck and the roads. The data link layer is how the delivery trucks get from one intersection to the next over and over. The network layer identifies which roads need to be taken to get from address A to address B. The transport layer ensures that delivery driver knows how to knock on your door and deliver the package to appropriate person. And the application layer is the contents of the package itself.
Protocol
A protocol is a standard set of rules that allow electronic devices to communicate and understand one another.
Format of message
Order of messages
| Layer Name | Protocol |
|---|---|
| Application | HTTP, SMTP,... |
| Transport | TCP, UDP |
| Network | IP |
| Data Link | Ethernet, Wi-Fi |
| Physical | 10 Base T, 802.11 |
Wired Network Cables
Cables are what connect different devices to each other, allowing data to be transmitted over them.
Network Port
Network ports are generally directly attached to the devices that make up a computer network.
Two computers can communicate across the cable connected between them.
How data is transferred If they are more than two devices?
Hub
Transfers data to every other port connected to the hub
The System needs to determine if the incoming data was meant for them or not.
How does the system knows which data is meant for them?
MAC Address
Media Access Control (MAC) address is a globally unique identifier attached to an individual network interface (hardware).
48-bit number
six groupings of two hexadecimal numbers(0-9, A, B, C, D, E, F)
| 00 | 1A | 3F | F1 | 4C | C6 |
|---|---|---|---|---|---|
MAC address are same for your system no matter where you use it.
Data Collisions
When two computers were to send data across the wire at the same time, the data signals can interfere. Collision Domain is a network where collisions can occur.
Carrier Sense Multiple Access
CSMA used to determine when the communications channels are clear and when the device is free to transmit data.
- Listen-Before-Talking
Collision domain
The electrical pulses sent across the cable can interfere with each other.
Systems to have to wait for long time before they try sending their data again.
Network Switch
Switch determine which system the data is intended for and send that data to that one system.
Transmissions in different small networks can happen at once
It store MAC address
Hub Vs Switch
| Hub | Switch |
|---|---|
| They operate in the physical layer | They operate in the data link layer |
| It sends message to all ports. | It sends message to selected destination ports. |
| Collisions occur mostly in setups using hubs. | Less collisions occur in switch. |
| A network hub can't store MAC addresses. | Switch stores the MAC addresses |