Computer networks: broad overview
What is the internet ?
The Internet is a network that interconnects hundreds of millions of computing devices throughout the world.
Components
- hots (devices on internet: computers, laptops, routers)
- connection links (wired or not wired)
- routers (special type of host: there job is to create a path for data)
- protocols (rules/contracts for communication on internet)
Internet provides communication infrastructure for devices on internet and different services for application at these devices such as reliable data delivery between two devices.
The user devices
The user devices are devices that are accessible to users (smartphones, laptops, computers and similar). They are connected to computer network by communication links.
Communication links can be
- coaxial cables
- copper wire
- optical fiber
- mobile access networks (4G, 5G)
- LAN — wifi
- satellites
Inside the Network
Internet Service Provider (ISP) provides communication links to user devices, in most cases local cable or telephone companies have a role of ISP.
When user device want’s to send data to another one, it’s data is divided into several parts where each data part gets header. The result is know as packets and then they are sent through the network. Each header contains description of data and receiver address.
Internet Structure
The Internet is all about connecting user devices to each other. This means that ISPs that provide access to end systems must also be interconnected. These lower-tire IPSs are interconnected through national and international upper tiers ISP.
An upper tier ISP (global ISP) consists of high speed routers interconnected with high-speed fiber optic links. Each ISP network is managed independent.
To conclude Internet is hierarchical network of networks consisting of global ISP and hundreds of thousands of lower ISPs. The lower-tier ISPs connect to the higher-tier ISPs, and the higher-tier ISPs interconnect with one another. Users and content providers are customers of lower-tier ISPs, and lower-tier ISPs are customers of higher-tier ISPs.
To have complete picture of computer network I have to mention
- points of presence (PoP — group of routes at the same location where ISP can connect )
- peering (pair of nearby ISPs at the same level that are directly connected)
- Internet exchange points (IXP — is a meeting point where multiple ISP can peer together)
- content provider networks (big companies like Google create they own network and then connect it to some ISP)
Summary
Physically connect each user device with each other it is to expensive and practically impossible, because of this Internet is created as hierarchical structure, consisting of a large number user devices connected to lower-tier ISPs who are connected to higher ISP or interconnected with each other.
When two or more user devices want to communicate first lower-tier ISP checks if they are in its network. If yes, they are connected otherwise request is forwarded to higher ISP and so on until targeted device is not found.
Resources: Computer Networking A Top-Down Approach: Kurose,Ross
