How are all computers connected?

I am reading computer networks from Computer Networks: A Top-Down Approach and the following are my notes (raw). I write in easy, no-jargon words that are easier to grasp different topics.

The Internet

1. What is the internet?
   • Nuts and Bolts of Internet
   • network of infrastructure that provides internet

Key Terminologies

1. End Systems (Hosts) : laptops, smartphones, TV, smart watches are called End-system or Hosts in a network.
2. Communication Links : End systems are connected together by commnuication links and Packet switches.
3. Transmission Rate : The rate at with data is transfered. Measured in bits/second.
4. Packets : Packages of information transfered over the network. Chunks of data transported in small bundles (packets).
   • Example : A cargo(data) shipment in divided in multiple trucks(packets) via highways (network).
5. Packet Switches: To route packet from source to destination.
   1. Routers
   2. Link-layer switches
6. Route (Path) : The sequence of communication links and packet switches traversed by a packet from the sending end system to the receiving end system is known as a route or path.
7. Internet Service Provider (ISP) : Players like Jio, Airtel, AT&T, BSNL who set up infrastructure, both software and hardware, to provide internet services (connectivity to the network) are called ISPs.
8. Protocols : The set of rules followed at each stage of data transmission on the network.
   1. Transmission Control Protocol (TCP)
   2. Internet Protocol (IP)
9. Request for Comments (RFCs) : To resolve network and protocol design problems that faced the precursor to the Internet
10. Socket Interface : End systems attached to the Internet provide a socket interface that specifies how a program running on one end system asks the Internet infrastructure to deliver data to a specific destination program running on another end system

Analogy with post office

From the above example, the following analogy can be established:

• Sender -> Alice
• Receiver -> Bob
• Data -> Letter
• Socket interface -> destination on letter, stamp in center (post-office interface)

Protocols

A protocol defines the format and the order of messages exchanged between two or more communicating entities, as well as the actions taken on the transmission and/or receipt of a message or other event.

More than A set of rules that govern that transmission of data on the internet

Analogy : Human Protocols

After a lecture on, teacher stops to ask,

• "Are there any questions" (message transmitted to, and received by all students in class who are not sleeping)
• You raise your hand (transmitting an implicit message to the teacher that you want to ask question)
• Teacher says "Yes" (transmitting message to you to ask question)
• You then ask your question (transmitting your message to the teacher)
• Your teacher hears your question (receiving your message) and the answers (transmitting reply to question).

NOTE : If you don't understand teacher's language (can't receive teacher's message), or no one asks a question (no reply/action from receive) are also probable cases.

we see that the transmission and receipt of messages, and a set of conventional actions taken when these messages are sent and received, are at the heart of this question-and-answer protocol

Network Protocols

A network protocol is similar to a human protocol, except that the entities exchanging messages and taking actions are hardware or software components of some device (for example, computer, smartphone, tablet, router, or other network-capable device).

All activity in the Internet that involves two or more communicating remote entities is governed by a protocol. Examples:

1. For hardware implemented protocols govern flow of bits in a wire.
2. Congestion-control protocols in end systems control the rate at which packets are transmitted between sender and receiver
3. Protocols in routers determine a packet's path from source to destination

Example : Requesting a web page on the browser