Home · A-Level Computer Science 9618 · Communication and internet technologies · HTTP, FTP, POP3, IMAP, SMTP and BitTorrent · Practice
A2 · Practice questions · HTTP, FTP, POP3, IMAP, SMTP and BitTorrent

Name the protocol.

Six original Cambridge-style questions on Application layer protocols and BitTorrent, with mark-scheme style solutions.

Original questions All questions on this page are original work, written in the Cambridge AS & A Level style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
Keep these straight

Push, pull or share.

01
Recall
[3 marks]

State the purpose of each protocol: (a) HTTP (b) FTP (c) SMTP.

  • (a) To request and transfer web pages / web resources between a web server and a browser. ✓
  • (b) To transfer files between a client and a server (upload and download). ✓
  • (c) To send email from a client to a mail server / between mail servers. ✓
02
Explain
[4 marks]

Describe two differences between POP3 and IMAP.

  • POP3 downloads email to the client device ... ✓
  • ... and usually deletes it from the server, whereas IMAP leaves the email on the server. ✓
  • With IMAP, changes made on one device (read, deleted, moved to a folder) are synchronised across all devices ... ✓
  • ... whereas with POP3 each device has its own separate copy / email can be read offline once downloaded. ✓
03
Apply
[4 marks]

Ali sends an email from his laptop to Bea, who reads it on her phone. Describe the protocols used as the email travels from Ali to Bea.

  • Ali's email client uses SMTP to send the email to Ali's mail server. ✓
  • Ali's mail server uses SMTP to send the email to Bea's mail server. ✓
  • The email is stored on Bea's mail server (in her mailbox). ✓
  • Bea's phone uses POP3 or IMAP to retrieve the email from her mail server. ✓
04
Explain
[5 marks]

Explain how the BitTorrent protocol allows a large file to be shared between many users.

  • The file is split into small pieces of equal size, each with a hash value. ✓
  • A user obtains a torrent file containing metadata, including the tracker's address and the piece hashes. ✓
  • The tracker provides a list of peers in the swarm that have pieces of the file. ✓
  • The user's client downloads different pieces from many peers at the same time, and checks each one against its hash. ✓
  • As soon as it has a piece, the user's client uploads it to other peers; seeds have the complete file. ✓
05
Calculate
[2 marks]

A 1.5 GiB file is shared using BitTorrent with a piece size of 512 KiB. Calculate the number of pieces. Show your working.

  • 1.5 GiB = 1.5 x 1024 x 1024 KiB = 1 572 864 KiB. ✓
  • 1 572 864 / 512 = 3072 pieces. ✓
06
Analysis
[4 marks]

A games company must distribute a 40 GiB update to millions of players on the day it is released. Discuss the benefits and drawbacks of using a peer-to-peer protocol such as BitTorrent instead of downloads from the company's own servers.

  • Benefit: each player who downloads pieces also uploads them, so capacity grows with demand and the company's servers are not overloaded. ✓
  • Benefit: lower bandwidth and server costs for the company; no single point of failure. ✓
  • Drawback: players' upload bandwidth is used, and some may block it or have slow connections. ✓
  • Drawback: the company has less control; pieces come from unknown peers (security/integrity must rely on hashes), and early on there may be few seeds. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.