Layering and Encapsulation in the Protocol Stack · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

One message, many wrappers

Computing · Networks & Security · ages 18-19
Name ______________________   Date ____________

  1. Your browser sends a request starting with GET /index.html. Which layer chops it into numbered segments?

    • The Internet layer, which adds addresses
    • The transport layer, which adds order numbers
    • The link layer, which adds the local header

  2. Which layer moves raw bits across a wire, a wifi signal or fiber?

    • The physical layer
    • The transport layer
    • The application layer

  3. On the receiving computer, each layer removes only the header it understands.

    Circle one:   True   False

  4. A request is wrapped once by TCP, once by IP, and once by the link layer. How many headers does it carry on the wire?

    Answer: ______________

  5. A cable fails, the router picks another path, and your page arrives a little late. What happened?

    • The application layer rerouted the packets
    • The message was lost because one path broke
    • A lower layer handled it, so the app saw only a delay

  6. You inspect a captured packet and find a header with a source and a destination address. Which layer added it?

    • The application layer
    • The Internet layer
    • The transport layer

  7. A log reads: segment 5 missing, asking the sender to resend it. Which layer speaks here, and why?

    • The transport layer, because it numbers pieces and fills gaps
    • The Internet layer, because it picks routes
    • The application layer, because it shows the page

  8. Engineers replace old copper with fiber, and no app needs rewriting. What earns that freedom?

    • The wire understands web requests
    • Fiber needs no headers at all
    • Each layer trusts only its neighbors, so the bottom can change alone
LightMySky · lightmysky.comW1-mt_D33SEBslXH-s1

Answer key

For grown-ups. Fold this page away before handing over the rest.

One message, many wrappers W1-mt_D33SEBslXH-s1

  1. The transport layer, which adds order numbers · TCP numbers each piece so the far end can reorder and resend.
  2. The physical layer · Raw ones and zeros are the bottom layer's job.
  3. True · Headers peel off in reverse, one layer at a time.
  4. 3 · Three wrapping layers means three headers.
  5. A lower layer handled it, so the app saw only a delay · Extra paths plus resends keep the app whole; it notices at most a delay.
  6. The Internet layer · Addresses for travel between networks are IP's work.
  7. The transport layer, because it numbers pieces and fills gaps · Numbering pieces and resending gaps is TCP's voice.
  8. Each layer trusts only its neighbors, so the bottom can change alone · Neighbors-only talk lets each layer improve without touching the rest.
Worksheet · LightMySky