The Speed of Light in Glass: teacher key

The Internet, grade 11 edition, written for 11th grade. Delay on the internet comes from distance, handshakes and heavy pages. See how much slower light is in glass fiber than in a vacuum, how a first connection costs extra trips, and who runs out of addresses first.

Read the book. Print this page for the key.

Questions and answers

1. What is latency?
   • The time it takes a packet to travel from its source to its destination (answer)
   • The size of a web page
   • The number of servers a site has
2. How fast does light travel through glass fiber, compared with a vacuum?
   • About 68 percent of its speed in a vacuum (answer)
   • Faster than in a vacuum
   • About half as fast
3. Why does TLS start only after TCP has set up a connection?
   • TLS needs a reliable, in-order connection underneath it (answer)
   • TCP is faster
   • DNS is slower
4. Which registry was first to reach its final block of IPv4 addresses?
   • RIPE NCC
   • APNIC (answer)
   • The central pool
5. What is a cost of using a content delivery network?
   • The website depends on another service (answer)
   • The site always loads slower
   • The site loses its domain name

Words

• latency: travel delay
• vacuum: empty space
• autonomous: self-governing
• registries: address managers
• grapnel: hook-like tool