Communication and Internet Technologies

Question 1

Where/when is circuit switching used?

Answer 1

-It is used when dedicated path needs to be sustained throughout the communication // used where the whole bandwidth is required or a real time communication is used.
-Common applications are voice communications / video streaming / private data networks.

Question 1

How is data transmitted in circuit switching?

Answer 1

-A circuit is established at the start of the communication.
-Between the sender and the receiver.
-This lasts for the duration of the data transfer.
-Then the links that make up the circuit are removed.
-All data is transferred along the same route.

Question 2

Benefits of circuit switching. (min 2 max 10)

Answer 2

-Whole of bandwidth is available.
-No waiting time at switches.
-Data arrives in the same order as it left. No need to reassemble.
-Better for real-time
-Data is transmitted with a fixed rate.
-Dedicated communication channel increases the quality of transmission.
-Suitable for long continuos communication.
-Data can’t get lost.
-Data follows the same route.
-Simple method of data transmission.
-Fast method of data transfer.

Question 3

Drawbacks of circuit switching (min 2 max 6)

Answer 3

-No alternative route in case of failure.
-Can have cost implications in establishing a dedicated path.
-Bandwidth can’t be shared
-Time required to establish physical connection might take too long.
-Not very flexible.
-A dedicated connection makes it mpossible to transmit other data from another person even if the channel is free.

Question 4

Describe packet switching

Answer 4

A large message is divided up into a group of smaller chunks of the same size called packets
* The packet has a header and a payload
* The header contains a source IP address, destination IP address (and sequence number)
* Each packet is dispatched independently
* … and may travel along different routes / paths
* The packets may arrive out of order
r * … and are reassembled into the original message at the destination
* If packets are missing / corrupted a re-transmission request is sent.

Question 5

Advantages Packet switching

Answer 5

• Packets can be rerouted if there are problems// more secure as harder to intercept messages
  -Missing packets can be easily detected and resend requests sent so the message arrives complete.
  -Allows simultaneous use of the channel.
  -Allow accurate delivery of messages

Question 6

Drawbacks packet switching

Answer 6

-– Time taken to reassemble packets at the destination.
-Requires complex protocols
-Unsuitable for real-time applications
-Time delay to correct errors.

Question 7

Why is packet switching used by a company? Include examples.

Answer 7

-Communication is asynchronous
-Allows for error checking
-Real time transmission is not needed
-Smaller amounts of data are sent therefore dedicated line/ higher bandwidth is not required.
-Packet switching is used when it is necessary to overcome faulty lines.
-Packet switching is used for high volume data transmission

-Emails
-Documents
-Text messages

Question 8

What is the role of the router in packet switching?

Answer 8

The router examines the packet’s header
* It reads the IP address of the destination (from the packet header)
* A router has access to a routing table
* …containing information about, e.g., available hops / netmask / gateway used
* … and the status of the routes along the route
* … the router decides on the next hop / best route
* … and sends the packet on its next hop.

Question 9

Packet Switching Vs Circuit Switching. Differences. (min4 max9)

Answer 9

-Circuit switching uses a dedicated channel to make communication, whereas packet switching forms data into packets to transmit over a digital network.
-The dedicated path for circuit switching must be established before the transfer of data can commence, which is not the case with packet switching (as it doesn’t require a dedicated path).
-Data in packet switching is split into packets, in circuit switching the message remains intact.
-All of the transmission in circuit switching follows the same path whereas different packets in packet switching can take different routes.
–The message is received in the same order in which it is sent with circuit switching, but with packet switching, the packets can be received out of order (for assembly at the destination). -Circuit switching is implemented at the physical layer while packet switching is implemented at the network layer.
-Circuit switching uses the whole bandwidth of the channel used, packet switching can share bandwidth.
-Circuit switching communication ends with an error but packet switching allows packets to be re-sent.
-Circuit switching is a simpler process than packet switching.

Question 10

What is a protocol?

Answer 10

-Sets of rules.
-For successful transmission and receipt of data.

Question 11

HTTP(s) is a protocol part of the application layer. Explain its purpose and give a use.

Answer 11

-Purpose: Transfer web pages / hypertext from server to client.

-Use: Browsing website.

Question 12

FTP is a protocol part of the application layer. Explain its use.

Answer 12

Purpose: Used for interactive file transfer; To directly transfer data between two computers over the internet
Use: Upload and download files over the internet

Question 13

SMTP is a protocol part of the application layer. Explain its purpose and give a use.

Answer 13

-Purpose: Protocol for sending email. Push protocol.

-Used: Used by mail servers to forward email messages to another mail server. Email client sends email to email server.

Question 14

POP(3) is a protocol part of the application layer. Explain its purpose and give a use.

Answer 14

-Purpose: Mail is held for you by a remote server until you download it // download email.

-Use: To receive email.

Question 15

IMAP is a protocol part of the application layer. Explain its purpose and give a use.

Answer 15

-Purpose:
-For receiving/downloading emails / pull protocol.
-From a mail server
-Keeps the server and client in sync.

Use: To receive email.

Question 16

BitTorrent is a protocol part of the application layer. How does it work and give it use

Answer 16

-Used in peer-to-peer for file sharing

-BitTorrent client software made available
- A computer joins a swarm by using this to load a Torrent descriptor file
-A server called a tracker that keeps records of all the computers in the swarm …
… and shares their IP addresses allowing them to connect to each other
-One computer in the swarm must have a complete copy of the torrent to be shared
-Torrent is split into small pieces
-Pieces of the torrent are both downloaded and uploaded
-Once a computer has a piece it can become a seed and upload
-Leeches download much more than they upload

Use: Decentralized distribution of data.

Question 17

What are 3 protocols in the application layer.

Answer 17

-http
-ftp
-smtp
-pop3
-imap
-bitTorrent

Question 18

Purpose of the transport layer.

Answer 18

The transport layer handles packets.

-The transport layer breaks the data into packets.
-It then adds a packet header to each packet/ it sequences them
-After that it sends the packets to the internet layer.
-It manages the packet flow
-It handles packet loss/corruption

Question 19

Purpose of the internet layer.

Answer 19

The internet layer handles transmission of data using IP addresses.

-The internet layer identifies the intended network and host.
-IT routes the packets independently through an optimum route.
-It addresses packets with their source and destination IP addresses.
-It then uses an IP address and a port it creates a socket.
-Encapsulates data into datagram.
-Passes datatgram to network access layer.

Question 20

Purpose data Link (Physical) Layer

Answer 20

The data link layer handles how data is physically sent.
-Encapsulates Ip packets into frames for transmission.
-Ensure correct protocol is followed.

Question 21

Why are communication protocols necessary? (decir dos de arriba)

Answer 21

-Provide a set of standards for communication.
… that gives a known set of rules for transmitting and receiving of data.
-This enables communication/compatibility between devices from different manufacturers.
-All data is sent and received using the same rules and format.
-Allows communication between devices operating on different platforms.
-The communication is independent of the software and hardware used.

Question 22

Characteristics of the protocol Stack.

Answer 22

-Each layer can only accept input from adjacent layers.
-There is a defined interface between adjacent layers which constitutes the only interaction allowed between layers.
-A layer is serviced by the actions of lower layers. Except the last that is created and installed by software.
-A layer may comprise sub-layers.
-Any user interaction will take place using protocols associated with the highest level layer in the stack.
-Any direct access to hardware is confined to the lowest layer in the stack.

Question 23

Describe the tcp/ip protocol suite

Answer 23

-A layered model with four layers.
-Uses a set of protocols for transmission of data.
-Transport control protocol with internet protocol.
-Application layer, transport layer, internet layer, network access layer.

Question 24

Describe application layer

Answer 24

-Handless access to services.
-Define protocol used.
-Manages data exchange.

Question 25

Porperties of the bit torrent protocol.

Answer 25

-Based on peer-to-peer networking concept.
-Allow fast sharing of files between computers
-Allow many computers to share files.

Question 26

Define the term swwarm in the context of bit torrent software.

Answer 26

-A group of peers connected togetehr.
-All the connected shared computes
-That have all or other parts of the file to be downloaded.
-Share a torrent.

Question 27

Define the term seed in the context of bit torrent software.

Answer 27

-A peer has downloaded a file and has then made it available to others in the swarm.
-Peer computer that has 100% of the file.
-It uploads the downloaded content.

Question 28

Define the term tracker in the context of bit torrent software.

Answer 28

-Central server that stores details about other computers that make up the swarm.
-It will store details about all the peers uploading/downloading the file.
-Allowing peers to locate each other using the stored IP address.

Question 29

Define the term leech in the context of bit torrent software.

Answer 29

A peer that has negative impact on the swarm by having a poor sharing ratio.

Question 30

Define the term lurker in the context of bit torrent software.

Answer 30

A peer that downloads many files but does not make available any new content for the community as a whole.

Question 31

Why is circuit switching used in voice calls?

Answer 31

-Dedicated circuit is established.
-Can use the whole bandwidth
-Two way real-time conversation
-No delay as no switching
-Data arrives in the order sent.

Question 32

Purpose of packet header

Answer 32

-To store data about the header.
… and its routing // to ensure it reaches the correct destination.
-To ensure the packet can be correctly constructed

Question 33

What are things that may be in the packet header.

Answer 33

-IP address of the sender/receiver-ID of the packet
-Packet length
-Checksum
-Protocol used
-Synchronisation data
-NUmber of packets the message consists of
-Type of service
-IP version number
-Fragmentation flags
-Fragmentation offsets.

Question 34

Contents of a routing table

Answer 34

-Network ID // network destination
-Routing data to decide best route
-IP address of next/hop
-Interface

Question 35

Explain the role of routers in sending an email from one email server to another

Answer 35

-A router is a node in the internet.
-A router will receive a packet that is in the process of transmission.
-A router has data stored regarding the routers that are within its vicinity.
-A router can access this data to make a choice of which router to send the packet to next.
-The destination IP address in the packet also guides this choice.
-Some of the data stored relates to the amount of traffic using a particular network link.
-Different packets heading to the same destination will not necessarily be directed along the same link from the router.