TCP/IP

🎬 This chapter has a 10:53 video: Network Protocols →

A web page, an email, a video call — on the Internet, all of them travel the same way: cut into small packets, each with an address on it. The rules for that are TCP/IP, the protocols underneath every other protocol in this chapter.

1What TCP/IP is

TCP/IP

TCP/IP stands for Transmission Control Protocol / Internet Protocol. It is a set of standard rules for communication over the Internet. It is two protocols working as a team:
IP gives every device an IP address and gets each packet to that address.
TCP breaks the message into packets, makes sure every packet arrives, and puts them back in order.

One message, four packets

Play the story, then lose a packet on the way and play it again. Drag sideways to turn.

Press ▶ Play to watch TCP and IP carry one message across the Internet.

2Two protocols, two jobs

	TCP	IP
Stands for	Transmission Control Protocol	Internet Protocol
Its job	Breaks the message into packets, numbers them, puts them back in order	Gives each device an IP address and routes each packet to it
Checks	That every packet arrived; asks again for a lost one	Nothing — it just delivers packets as best it can
Works at	The two ends: sender and receiver	Every router along the way

IP is what holds the whole Internet together: every computer connected to it has an IP address, and every router uses those addresses to pass packets on. There are many paths between two computers, so two packets of the same message can take different routes and arrive out of order. That is exactly the packet switching you learnt earlier — TCP/IP is the set of rules that makes it work on the Internet.

Who cuts and addresses the packets — the computer or the router?

The sender’s own computer. The TCP/IP software built into its operating system splits the data into numbered packets and writes the IP addresses on them before anything leaves the computer. Routers, including the first one at home or school, do not cut up or number anything: they read each packet’s destination IP address and pass it on. (A home router does one more thing, swapping the private source address for its public one — the NAT lesson.) At the far end, it is the receiving computer, not a router, that puts the packets back in order.

Think of posting a book, chapter by chapter

You tear a book into chapters, number each envelope 1, 2, 3, 4 and write the same address on every one (that is IP). The postal service may send them by different trucks. Your friend waits until all four have come, puts them in order by number, and phones you if chapter 3 is missing (that is TCP).

Why HTTP, FTP and email need it

HTTP, FTP, SMTP and POP3 decide what the two programs say to each other. TCP/IP is what actually carries it, in packets. So every one of them runs on top of TCP/IP.

3From the board papers

Write the full form of TCP.CBSE board exam 2023 (with HTML) · compartment exam 2025 (with POP)

1 mark

▶Show the answer

Transmission Control Protocol.

What does TCP do, and what does IP do? (Practice)

2 marks

▶Show the answer

TCP breaks the data into packets at the sender, makes sure all of them reach the receiver, and puts them back in order there. IP gives each device an IP address and routes every packet across the network to the right address.

4Check yourself

Quick Check

Packets of one message reach the receiver in the order 2, 1, 4, 3. Which protocol puts them back in order?

Quick Check

Which part of TCP/IP makes sure each packet can find the right computer?

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🤝 What is a Protocol?

PPP — Point to Point Protocol ↔️