Internet History part 2: Vint Cerf & Bob Kahn Invent Code of Internet (TCP explained)

Summary

The script provides a creative analogy comparing internet packets to postcards sent through the postal service. It explains that, like postcards, internet packets are not guaranteed to arrive in order or at all, simulating a best-effort delivery system. The analogy continues with the concept of numbering each postcard to track them and using acknowledgments, like receiving a postcard back, to ensure data integrity and retransmission of lost packets, effectively illustrating the workings of error control protocols.

Takeaways

• 📚 To send a book via a postal service that only delivers postcards, you have to physically manipulate the book's pages.
• ✂️ Pages must be cut and glued onto postcards, which disrupts the original order and numbering.
• 🔢 Pages may lose their original page numbers due to cutting, so they need to be renumbered on postcards.
• 💌 Postcards, like internet packets, are sent without guarantees of delivery or order.
• 🚫 The postal system is a best-effort service, meaning there's no assurance of successful delivery.
• 🔄 There's no guarantee that postcards will arrive in the order they were sent.
• 🗂 Some postcards may be lost, necessitating the keeping of copies for potential retransmission.
• 🔄 Retransmission of postcards is based on confirmation from the recipient or a timeout period.
• 📬 The recipient can send back postcards to indicate which ones they've received up to a certain number.
• 🔁 If no confirmation is received within a certain time, the sender retransmits postcards starting from the last acknowledged number.

Q & A

What is the main challenge when sending a book through a postal service that only delivers postcards?

The main challenge is that you have to physically alter the book by tearing out the pages, cutting them up, and gluing them onto postcards to fit the service's delivery format.

Why might pages lose their order when sent as postcards?

Pages might lose their order because the postal service does not guarantee that postcards will be delivered in the order they were sent.

How does cutting up the pages of a book relate to the concept of internet packets?

Cutting up the pages of a book and sending them as postcards is analogous to how data is divided into packets and sent over the internet, where the order and delivery of these packets are not guaranteed.

What is the best-effort system mentioned in the script?

The best-effort system refers to the nature of both postal services and internet packet delivery, where there is no guarantee of delivery or order.

Why might some postcards get lost in the postal system?

Postcards might get lost due to various reasons such as mishandling, damage, or logistical errors within the postal service.

What strategy is suggested to ensure that all postcards are received?

The strategy suggested is to keep a copy of each postcard and retransmit them if acknowledgment of receipt is not received within a reasonable time.

How does the receiving end confirm the receipt of postcards?

The receiving end confirms receipt by sending a postcard stating the highest numbered postcard they have received, up to that point.

What is the purpose of numbering every postcard?

Numbering every postcard helps in tracking the sequence of delivery and ensures that the sender knows which postcards have been received and which ones might need to be resent.

Why might the postcard confirming receipt also get lost?

The postcard confirming receipt might get lost for the same reasons as any other postcard, due to the inherent unreliability of the postal system.

How does the sender know when to stop sending postcards?

The sender stops sending postcards when they receive a confirmation postcard from the receiver stating that all postcards up to a certain number have been received.

What is the role of timing in the process of sending and receiving postcards?

Timing plays a crucial role as the sender uses it to determine if they should retransmit postcards that have not been acknowledged within a certain period.