Chapter 14

Question 1

what is a protocol?

Answer 1

a set of rules for successful transmission and receiving of data, which must be agreed between sender and receiver. enables cross communication between devices functioning on different platforms

Question 2

explain why a protocol is used in communication between computers

Answer 2

• provides a set standard for communication (gives accepted set of rules for transmitting and receiving data)
• enables communication between different platforms
  therefore if two devices were sending messages to each other but using different protocols, they would not be able to communicate properly

Question 3

list the TCP/IP Protocol stack

Answer 3

1. application layer
2. transport layer
3. internet layer
4. data link layer

Question 4

application layer

Answer 4

• sends files to transport layer
• contains all programs that exchange data e.g. web browser
• to allow access to network resources
• presents data to the user, (allows user to communicate with the server?)
  HTTP, SMTP, DNS, FTP, POP3, IMAP

Question 5

transport layer

Answer 5

• handles data packets - data is broken into packets and a packet header is added
• data is sent to the network layer/receives from application
• controls the flow of packets, ensures that packets arrive in sequence without errors
• handles packet loss/corruption
• protocols in this layer: TCP (transmission control protocol - standard for exchanging messages)

Question 6

internet layer

Answer 6

ensures correct routing over the internet // handles the transmission of data using IP addresses
- identifies the intended network and host
- routes packets independently through the optimum route
- transmits packets to the data link layer
- addresses packets with their source and destination IP addresses
- then uses an IP address and port number to form a socket

IP

Question 7

data link layer

Answer 7

• handles how data is physically sent
• ensures network/internet protocols are followed
• delivers data/communicates with other computer
• maps IP addresses to physical/MAC addresses
• formats the data into frames for transmission

ethernet protocol, wifi protocol, bluetooth protocol

Question 8

IMAP

Answer 8

internet message protocol
- a pull protocol
- used to receive/download email messages from the mail server
- allows a copy of the email to be downloaded from the mail server
- same purpose as POP but mail doesn’t get deleted and can be accessed from different devices

Question 9

POP3

Answer 9

post office protocol,
for receiving/downloading emails from the server. pull protocol

Question 10

HTTP(S)

Answer 10

hypertext transfer protocol, for sending and receiving web pages

(every time a user accesses a website using a browser, HTTP is used. browser sends a request for a web page to a web server)

Question 11

FTP

Answer 11

file transfer protocol, for sending and receiving files over a network/between devices

Question 12

SMTP

Answer 12

simple mail transfer protocol, for sending/uploading emails. a push protocol

Question 13

ethernet

Answer 13

a protocol primarily focused on LANs, transmitting data in frames. each frame has a course and a destination address, being the physical or MAC address, uniquely defining one NIC. used in the data-link layer

Question 14

what is stored in a packet header

Answer 14

• source IP address and destination IP address
• checksum
• protocol used
• message data, known as the payload
• ID number of that packet
• packet length

Question 15

purpose of a packet header

Answer 15

• to store data about packet
• …and its routing to ensure that it reaches its destination
• to ensure that messages can be properly reconstructed

Question 16

function of TCP protocol

Answer 16

Transmission Control Protocol and works at the Transport layer.

• allows applications to exchange data
• ensures delivery of data - establishes and maintains connection until exchange of data is completed
• determines how to break application data into packets
• adds packet header
• sends packets to and from the network layer
• manages flow control of data to avoid congestion

Question 17

function of the IP protocol

Answer 17

internet protocol, functions at the internet/network layer.
* provides rules for exchange of packets over the internet
* decides the path for transmission of each packet
* passes packet to the link layer for transmission on the LAN

Question 18

bit torrent

Answer 18

a peer-to-peer file sharing model. peers act as both clients and servers. the swarm shares a torrent

Question 19

swarm

Answer 19

all the connected peer computers
that have all or part of the file to be uploaded/downloaded
they share a torrent

Question 20

tracker

Answer 20

central server
stores details of other computers/swarm
store IP addresses of other peers in swarm allowing them to connect

Question 21

leeches

Answer 21

peers who download much more than they upload

Question 22

seed

Answer 22

a peer computer that has 100% of the file it is uploading

Question 23

BitTorrent downloading/uploading process

Answer 23

torrent file is made available
file to be shared is split into pieces
bit-torrent client software is made available to other peers which allows them to work as seeds or leeches
once a peer has a piece of a file it can become a seed for the parts downloaded
tracker keeps record of all the peers and the parts of the file they have and can pause and restart at any time

Question 24

packet switching

Answer 24

• data is split into same-size packets
• packets have a header and a payload (the message)
• The header contains a source IP address, destination IP address, and serial number
• each packet is given its own independent route that may be different.
• routes determined based on congestion
• packets are reassembled in the correct order at the receiver’s end
• if packets are missing, re-send

used for: high-volume data transmission, more secure, e.g. email, text messages, VOIP
not for: real-time transmission e.g. live streaming

(a circuit does not have to be established at the start of communication)
(packets can travel different routes independently)

Question 25

circuit switching

Answer 25

* a dedicated circuit is established which lasts for the duration of the connection (is released after transmission ends) * between sender and receiver * data is transferred using the whole bandwidth, * all data is transferred over the same route * the link that makes up the circuit is then removed used: real time communication, where a dedicated path needs to be sustained, where the whole bandwidth is required e.g. video streaming, voice calls, private data networks not used:

Question 26

advantages of packet switching

Answer 26

doesn't use whole bandwidth (allows simultaneous use of channel) more secure as packets are sent by different routes and hashed packets can be rerouted if there are problems or take the least congested route transmission error is more easily detected - missing packets can be resent

Question 27

disadvantages of packet switching

Answer 27

unsuitable for real-time transmission time delays to correct errors requires complex protocols

Question 28

advantages of circuit switching

Answer 28

* data arrives in same order * data cant get lost * dedicated communication channel increases the quality of transmission * simple method * data is transmitted with fixed data rate * fast method of data transfer - no waiting time at switches

Question 29

disadvantages of circuit switching

Answer 29

* A dedicated connection doesnt allow other data transmission even if the channel is free//bandwidth is wasted during periods when no data is sent * no alternative route in case of failure (not flexible) * less secure as only one channel is used (easier to intercept) * time required to establish physical link between two stations can be too long * whole bandwidth is required, can't be shared

Question 30

differences between packet switching and circuit switching

Answer 30

* circuit switching transfers data over a dedicated channel, packet transmits its packets over a digital network * dedicated path for circuit switching must be established before the transfer, unlike packet switching * message is split into packets vs message remains itact * packet switching - packets may be sent out of order for reassembly, unlike circuit * circuit switching is implemented at the physical layer whereas packet switching is at the network/internet layer * circuit uses the whole bandwidth * packet switching allows packets to be resent * circuit switching is a simpler process than packet switching

Question 31

router

Answer 31

* examines packet header, * reads the destination IP address, * decides on the next (**optimum**) route to send it on, and sends it * has access to a **routing table** (e.g. gateway used, available hops/routes) * and the status of routes along the way (congestion) * most intelligent

Question 32

hub

Answer 32

ensures that any incoming communication is broadcast to all connected devices

Question 33

switch

Answer 33

has the function of a hub but can also keep track of the addresses of connected devices (more specific). can send communication to specific devices

Question 34

server

Answer 34

central computer that stores all files to be downloaded