2.1 Application Layer Principles

Question 1

P2P architecture meaning

Answer 1

there is no server;
instead, end systems (peers) DIRECTLY communicate with each other

no permanent IP

Question 2

TCP vs UDP

Answer 2

both are transport-layer protocols:

TCP - reliable, makes sure all data packets arrive and are in the correct order
- requires handshake between client & server before sending data
- used for web browsing (HTTP), email (SMTP), file transfer

UDP - faster but unreliable data transfer
- for video streams, live gaming

Question 3

What type of architecture does file-sharing use? (e.g. BitTorrent)

Answer 3

Peer-to-peer (P2P)

Question 4

client-server architecture meaning

Answer 4

client: sends request
server: processes and sends back data

server:
- host is always ON
- has a well-known permanent IP address

client:
- not always connected to the internet
- no permanent IP
- clients do NOT communicate directly with each other

HTTP, IMAP, FTP

Question 5

API meaning

Answer 5

application-layer interface

Question 6

application definition

Answer 6

multiple programs (processes) interacting, exchanging messages

Question 7

socket definition

Answer 7

abstraction that sends messages between API and transport layers

like a door; the sending process shoves the message out the door

relies on underlying structure (application, transport, network, link)

Question 8

object definition

Answer 8

a structured data unit
- e.g. HTML files, JPEG images, Java applets

Question 9

identifier definition

Answer 9

information attached to a process that enables it to receive messages

like an address
every host device has a unique 32-bit IP address

2 important pieces of info:
1. IP address
2. port numbers

Question 10

open vs proprietary protocol

Answer 10

open: allows for interoperability, message syntax is public info (RFCs are publicly available)
e.g. WiFi, HTTP, STMP

proprietary: owned by a company, operation isn’t publicly known
e.g. Skype, Zoom

Question 11

TCP

Answer 11

Transmission Control Protocol - communication protocol that operates on the transport layer

reliable, makes sure all data packets arrive and are in the correct order

requires handshake between client & server before sending data

used for web browsing (HTTP), email (SMTP), file transfer

Question 12

UDP

Answer 12

communication protocol that operates on the transport layer

faster but unreliable data transfer

for video streams, live gaming

Question 13

datagram definition

Answer 13

packets of information that are exchanged at the application layer