A108 Computer Networks

Question 1

What does ISP stand for?

Answer 1

Internet Service Provider

Question 2

What is a packet and what are the main items in the item header?

Answer 2

A packet is what data being transported across the internet is split into.

A packet is made up of the header and the payload.

Question 3

What is an NIC?

Answer 3

A Network Interface Card is hardwired with a unique MAC address and allows a computer to connect to a network.

Question 4

What are the steps in packet switching?

Answer 4

1. Data is split into packets.
2. Header is added to packet
3. Packets are sent along the network, not necessarily along the same route
4. Once packets arrived, they are re-ordered using their sequence number
5. Receipt message sent from recipient to sender
6. Transmission happens again if no confirmation message is received

Question 5

What is a protocol?

Answer 5

tbc

Question 6

What does TCP/IP stand for?

Answer 6

Transmission Control Protocol / Internet Protocol

Question 7

What are the four layers of the TCP/IP protocol and what does each layer do?

Answer 7

1. Application Layer -
   The application layer uses an appropriate protocol relating to whatever application is being used to transmit data
2. Transport Layer -
   (uses TCP)
   The transport layer is responsible for establishing the “end-to-end” connection and splitting the data into packets once the connection is made.
   To each packet, the transport layer adds:
   
   1. The sequence number
   2. The total number of packets
   3. The port number the packet should use
3. Network Layer (aka internet layer)-
   (uses IP)
   Adds:
   
   1. Source IP address
   2. Destination IP address
      (used by routers)
4. Link layer
   The link layer is responsible for adding the MAC addresses of the source and destination device.
   This MAC address is changed at each hop on the route

Question 8

What is a MAC address?

Answer 8

The Media Access Control address is a unique 12-digit hexadecimal address hardcoded on each NIC for use as an address in network communications to uniquely identify any device.

Question 9

What is a socket in the context of TCP/IP and routing packets?

Answer 9

A socket is the IP address (provided by the IP protocol) combined with the port (provided by the TCP protocol)

Question 10

What is a port in the context of TCP/IP and routing packets?

Answer 10

The port determines what application on the device needs the packet

Question 11

What does FTP stand for and what is its purpose?

Answer 11

File Transfer Protocol

Used to move files between two devices. (commonly used to transfer data and programs as opposed viewable content)

Question 12

What does HTTP stand for and what is its purpose?

Answer 12

Hypertext Transfer Protocol

HTTP is used for accessing a webpage from a web server

Question 13

What does HTTPS stand for and what is its purpose?

Answer 13

Hypertext Transfer Protocol Secure

HTTPS is used for accessing a webpage from a web server securely. HTTPS encrypts data between the client and server.

Question 14

What does POP3 stand for and what is its purpose?

Answer 14

Post Office Protocol (v3)

Used to retrieve emails from an email server.

Question 15

What does SMTP stand for and what is its purpose?

Answer 15

Simple Mail Transfer Protocol

Used to send emails from client device to the linked mail server or to forward the email to the recipient’s mail server.

Question 16

What does SSH stand for and what is its purpose?

Answer 16

Secure Shell

Used to provide an encrypted connection for remove access to another computer.

Question 17

How does FTP work?

Answer 17

FTP commands can be issued from a command line interface, but more commonly a user interacts with an FTP client, which sits on top of the actual FTP protocol.

Once logged in, the user can access directories on the FTP server and can download and upload files.

FTP sites which are publicly available are known as anonymous FTP.

Question 18

How does HTTP work?

Answer 18

The web client sends a request message to a web server and the web server sends back a response message containing the data needed to display the webpage.

Question 19

How does HTTPS work?

Answer 19

HTTPS uses encryption to secure the data being transferred, and authenticates the web server through certificates.

Question 20

How does POP3 work?

Answer 20

POP3 retrieves emails from a mail server, removes it from the server and transfers in to your device.

Question 21

How does SMTP work?

Answer 21

SMTP sends the email from the client device to the linked mail server or forwards the email to the recipient’s mail server.

Question 22

How does SSH work?

Answer 22

SSH uses for port 22. It uses public key encryption to authenticate the user and prevent unauthorised access.

1. The client initiates the connection by contacting the server.
2. The server sends a public key to the client
3. The server and client agree communication rules and open a secure channel.
4. The user can now login to the remote server host OS and can issue commands

SSH can be used to tunnel through firewalls on port 22 to use other application level protocols.