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When you send a message from Delhi to a friend in Chennai, it may cross a mobile network, fibre cables and a home Wi-Fi router, each built differently. It arrives because every one of those networks follows the same basic rules, TCP/IP. Those rules were designed by Vint Cerf and Bob Kahn in the 1970s. This post covers the problem they solved, how TCP and IP divide the work, a worked example on addresses and packets, and what students can learn from how they worked.
Who are Vint Cerf and Bob Kahn?
The ACM Turing Award page for Cerf records that he was born on 23 June 1943 in New Haven, Connecticut. He studied mathematics at Stanford and earned his PhD in computer science at UCLA in 1972. He had a hearing impairment from an early age and later said this was part of why computer networking interested him, as another way to communicate.
The ACM page for Kahn records that he was born on 23 December 1938 in Brooklyn, New York, and earned a PhD in electrical engineering at Princeton. At the firm BBN he helped design the ARPANET, an early US research network. In October 1972 he organised its first public demonstration. The two first met in 1969, when Kahn came to UCLA to test the new network.
What problem were they solving?
By 1973 Kahn, now at the US Defense Advanced Research Projects Agency, wanted to connect three networks that could not talk to each other. According to the ACM pages, the ARPANET sent data point to point, the packet radio network broadcast it, and the satellite network had long delays because of the distances involved. The ARPANET tried to deliver every packet reliably; the radio network did not.
In spring 1973 Kahn asked Cerf to work with him on a system for interconnecting networks, what would become an "internet". They set out their design in the May 1974 paper "A Protocol for Packet Network Intercommunication".
How do TCP and IP divide the work?
The 1974 design had two key parts, the ACM page explains: a host protocol, the Transmission Control Protocol, for reliable, ordered delivery between computers, and gateways between networks that pass traffic along and handle addressing. In 1978 Cerf, with Jon Postel and Danny Cohen, split TCP in two:
IP (Internet Protocol) is a stripped-down protocol that moves packets within and between networks. It runs on computers and on the gateways, now called routers.
TCP runs only on the computers at each end and makes the whole exchange reliable.
When did the internet switch to TCP/IP?
RFC 801, the transition plan, set the goal: "to make a complete switch over from the NCP to IP/TCP by 1 January 1983." NCP was the ARPANET's older protocol. Kahn helped guide that changeover.
Worked example: addresses and packets
Part 1: how many IPv4 addresses? RFC 791, the Internet Protocol standard, says addresses are "fixed length of four octets (32 bits)".
Each bit has 2 values, so 32 bits give 2^32 addresses.
2^10 = 1,024, so 2^30 = 1,024³ = 1,073,741,824.
2^32 = 4 × 2^30 = 4,294,967,296, about 4.3 billion.
Another way: each octet holds 0 to 255, which is 256 values, and 256⁴ = 2^32, the same answer.
Part 2: packets (sample numbers). Suppose a 1,000,000-byte file is sent in packets carrying 1,000 bytes of data each. That is 1,000,000 ÷ 1,000 = 1,000 packets. If 3 are lost on the way, TCP notices the gaps and has the missing packets sent again, instead of the whole file.
Common mistakes:
Treating the internet and the web as the same. The web is one service that runs on top of the internet.
Mixing up TCP and IP. IP moves packets; TCP makes delivery reliable.
Writing 2^32 as 32 × 2. That gives 64, not 4.3 billion. Exponents multiply, they do not add.
Our post on computer networks for CBSE covers protocols, devices and topologies in exam form.
How were Cerf and Kahn recognised?
They shared the 2004 ACM Turing Award "for pioneering work on internetworking, including the design and implementation of the Internet's basic communications protocols, TCP/IP, and for inspired leadership in networking." Both received the US Presidential Medal of Freedom in 2005. In 1991 they founded the Internet Society.
What can a student take from how Cerf and Kahn worked?
Define the problem precisely. Listing how the three networks differed pointed straight to the design.
Invite criticism early. The ACM pages note they asked networking experts from around the world to review the design at a June 1973 seminar.
Divide the job sensibly. Splitting TCP from IP kept each part simple.
Plan the switch, not just the idea. RFC 801 set dates years ahead.
If powers of two still slow you down, the Fermi Concept Library covers every concept in physics, chemistry, biology, mathematics and computing, so you can revise exponents before tackling networking questions.
Try it now: IPv6 addresses are 128 bits long. Write how many times larger 2^128 is than 2^32, as a power of 2.
