1.3.3

Question 1

Layers of TCP/IP stack

Answer 1

Application
Transport
Internet
Link

Question 2

Application layer

Answer 2

The application layer collects / delivers data.
It is only concerned with the format and content of the requests and responses that are exchanged and not how the data will be transmitted.

It provides an interface between user applications and the network. For example, the browser translated the URL http://www.example.com/doc/index.html into the following request message (default port: 80)

Question 3

Transport layer

Answer 3

The transport layer establishes an end-to-end connection
Splits data into packets.
Adds a TCP header with the packet sequence number, source and destination port (so it is handled by the correct application).
Requests transmission of lost packets.
Receipt of packets are acknowledged.

UDP does not do the last two. It is not concerned with reliability.

Question 4

Internet layer

Answer 4

The Internet layer is concerned with the transmission of the packets. It adds the source and destination IP address to the header. “Time to live” is also added to prevent bouncing packets. Protocols that operate at this layer are IPv4 and IPv6

Question 5

Link

Answer 5

The data link layer is concerned with the physical transmission of data on the network media. It adds the MAC address from the devices (NICs) of the source and destination devices. Protocols that operates at this layer are Ethernet and ARP (maps IP addresses and MAC addresses).

Question 6

The Domain Name System

Answer 6

• Humans use memorable names, rather than numeric IP addresses, to request data on a network.
• A Domain Name System (DNS) is used to translate the names into IP addresses.
• This happens in the application layer.
• A domain name identifies the area or domain where an internet resource resides.
• These are structured into a hierarchy of smaller domains and written as a string separated by full stops. For example: mail.google.com
• Each different part of the domain name is separated by a dot.
  “com” is the top level domain (TLD), “google” is the second level domain and “mail” is the third level domain or host.

Question 7

Advantages of DNS

Answer 7

Allows the IP address to change but the domain name to remain the same. The new address is linked to the existing domain name and connectivity is maintained.
DNS allows for unique names. ICANN holds records of all registered domain names.

Question 8

Steps involved in DNS Resolution

Answer 8

1. Client requests the IP address of www.google.co.uk from the DNS resolver (ISP).
2. Request is sent to the root server. These hold the locations of all of the top level domains (TLDs) such as .com, .uk, .io, etc.
3. Returns the location of the .uk servers.
4. Request sent to the TLD for .uk. Each TLD server holds a list of all of the authoritative name servers for each domain in the TLD.
5. Responds with a list of .co.uk name servers (2LD).
6. Queries one of the .co.uk name servers for the IP address of google.co.uk (3LD).
7. Responds with the IP address for google.co.uk. At this stage the google name server will most likely know the IP address of all its hosts but it may also have to query more name servers to find the IP address of www.google.co.uk (the host or 4LD).
8. The resolver responds with the IP address of www.google.co.uk to the client.
9. The client makes a request using the IP address.

Question 9

What is a protocol?

Answer 9

A protocol is a set of rules (an agreed-upon format) for transmitting data between two devices. For example IPv4 (Internet Protocol) which used to transfer all packets between routers on the Internet. IPv4 uses 32-bit addresses for Ethernet communication in five classes, named A, B, C, D and E.

Question 10

What does a TCP protocol determine?

Answer 10

• the type of error checking to be used
• data compression method, if any
• how the sending device will indicate that it has finished sending a message
• how the receiving device will indicate that it has received a message
• type of encryption used
• packet size

Question 11

What are standards?

Answer 11

A standard is a definition or specification that is an agreed way of doing things. Standards make it easier to build software or hardware that will run (is compatible) on different systems (in different countries). Without standards most devices would not be able to communicate with each other.

Question 12

De jure (by force of law) standards

Answer 12

These are regulated by official bodies. For example, ICANN provides effective regulation of the names and numbers that are used across the internet. The term JPEG is an acronym for the Joint Photographic Experts Group, which created the image compression standard in 1992 and continues to update and maintain it.

Question 13

De facto standards

Answer 13

De facto standards are ones that arise through popular use but are not managed or regulated. For example, it may be standard to use sans serif fonts for web pages but no one will stop you if you go wild with Garamond.

Question 14

Why are standards important?

Answer 14

• Standards form the fundamental building blocks for product development by establishing consistent protocols that can be universally understood and adopted.
• Standards are important in the computer industry because they allow the combination of products from different manufacturers to create a customized system.
• Without standards, only hardware and software from the same company could be used
• For example, ASCII A (01000001) is recognised on all devices using the ASCII standard. HTML is a WWW standard recognised by all browsers.

Question 15

Why are protocols important?

Answer 15

• Set of rules that allow transmission between devices.
• Allowing devices to communicate
• By ensuring all devices follow the same rules
• So they interpret data/signals in the same way

Question 16

Local Area Network (LAN)

Answer 16

Geographically small area e.g. buildings or several buildings on the same site (schools, universities, offices etc)

Equipment is generally owned by the company using it

Question 17

Wide Area Network (WAN)

Answer 17

Geographically remote area e.g. across a country, between continents

Connects LANs together using third party telecommunications equipment (the servers owned by ISPs, he telephone/cable/satellite connections owned by telecommunications
companies such as BT, China Mobile, Vodafone, AT&T etc).

Question 18

What is packet switching?

Answer 18

A packet takes the best route through the network which may not be the same for every packet.

Question 19

What happens during packet switching?

Answer 19

• Data to be sent is split into packets (usually between 500 and 1500 bytes)
• Each packet includes a header (see right) including source and destination IP address and sequence number
• The packets are transmitted in order.
• The packets may take different routes across the network as each node determines the best path, eg routing around link failures
• Packets are reordered using the sequence number in the packet header at the destination.

Question 20

Advantages of packet switching

Answer 20

• It makes very efficient use of the network - no tied-up lines which is particularly good for internet traffic which is bursty (ie lots and then nothing)
• It can easily get around broken bits of the network. The node will simply send the packet a different route.
• Transmission is safer from interception since it is impossible to intercept all packets as they use different routes

Question 21

Disadvantages of Packet Switching

Answer 21

• The time it takes to put back the data package changes each time, which can be a problem for time-critical information such as an emergency signal. The fancy name is for this is ‘latency’.
• Not very good for small data packages - packet header becomes a considerable overhead.

Question 22

What is circuit switching?

Answer 22

The participants in a circuit-switching network are electrically connected and remain so until the conversation of data exchange is terminated. Example plain old telephone service (POTS)

Question 23

Advantages of circuit switching

Answer 23

• Frames will arrive in the order in which they were sent and no data will get lost
• No additional header information needed.
• Dedicated path and guaranteed performance as all bandwidth is reserved

Question 24

Disadvantages of Circuit Switching

Answer 24

• A portion of the network is made unavailable for the time the connection is made.
• Data may be more easily intercepted if the path used is known
• When resources are not sufficient, the connection will not be made.
• Connection even if no data is sent.

Question 25

What are threats to a network?

Answer 25

Malware, Pharming, Spyware, Ransomware, SQL Injection, Hacking, Phishing, Shoulder Surfing, DDoS, Packet Sniffing, MMA, physical damage, power failure, etc.

Question 26

How are threats classified?

Answer 26

Confidentiality - Keeping data private (hacking, phishing…) Integrity - Preventing data modification (SQL Injection, MMA..) Availability - Keeping your network services up and running (ransomware, DDoS, malware, power failure…)

Question 27

What measures can be put in place to stop Malware, Pharming, Spyware?

Answer 27

anti-virus, anti-spyware, Firewall/Proxy (packet filter), train staff, spamware, patching

Question 28

What measures can be put in place to stop Ransomware?

Answer 28

backup data, anti-virus, Firewall/Proxy (packet filter), patching

Question 29

What measures can be put in place to stop SQL Injection?

Answer 29

use prepared statements, form validation.

Question 30

What measures can be put in place to stop Hacking?

Answer 30

secure passwords, biometrics, change passwords, 3 attempts only, hash passwords, Captcha, 2-factor authentication, VPN (encryption), restrict access rights.

Question 31

What measures can be put in place to stop Phishing, Shoulder Surfing?

Answer 31

spam filter, proxy server (checks emails), train staff to recognise suspicious emails, websites or links.

Question 32

What measures can be put in place to stop DDoS?

Answer 32

Firewall (packet filter), Proxy Server (privacy - hide client/server IP address - prevent access)

Question 33

What measures can be put in place to stop Packet sniffing, MMA?

Answer 33

VPN (encryption), HTTPS (encryption), hashed passwords.

Question 34

What measures can be put in place to stop Power Failure, physical damage?

Answer 34

UPS, lock server rooms, log all access, backups. CCTV.

Question 35

What is a firewall?

Answer 35

- Prevent unauthorised access to the network. - Has two NICs. - Data enters one NIC and is compared to a set of rules. - Traffic which matches the rules is passed out the other NIC.

Question 36

What is Proxy Server?

Answer 36

- Sits between a user and the resource they are accessing. - Protects users’ privacy. - Caches frequently accessed websites to increase performance. - Reduces web traffic. - Uses rules to block access to sensitive information

Question 37

NIC

Answer 37

- Network Interface Card - May be wired or wireless. - Allows a device to connect to a network. - Has a unique MAC (Media Access Control) address assigned to it.

Question 38

Switches

Answer 38

- Controls the flow of data through the network. - Used in star topologies.

Question 39

Wireless Access Points (WAPs)

Answer 39

- Allows devices to connect wirelessly to a network. - Used in mesh networks. - Often used with a router to allow devices Internet access.

Question 40

Routers

Answer 40

- Used to connect two or more networks together. - Often used between a home/office network and an ISP to allow Internet access.

Question 41

Repeater

Answer 41

- With copper cable (like Cat5/5e/6) the maximum distance that data can be transmitted is approximately 100m. - Each time the signal is regenerated it is never quite restored to its previous strength. - Eventually the signal becomes to distorted for devices to read and therefore there is a limit on how many times a signal can be boosted. - In copper cable LANs this is typically no more than four times over a 500m distance. - Wireless signals can also be strengthened using a wireless repeater. - Repeaters take the weakened signal and try to refresh it as much as it can so that it can be re-sent along another length of cable

Question 42

Hub

Answer 42

- If a device on a LAN wants to send data to another device via a hub, the hub broadcasts all of the information to all devices it is connected to. - It is up to the recipient devices to ignore the data and only the intended device to accept it. This creates what we refer to as a ‘collision domain’ which is an area of the network where a number of devices (nodes) are trying to access the network at the same time. - A hub also boosts the strength of a signal received and therefore acts as a repeater as well. - Hubs are mostly used in situations where the performance of a network is unlikely to be unduly affected by the number of collisions e.g. at home.

Question 43

Bus Network

Answer 43

All devices are connected to a single cable (called the bus) A terminator is at each end of the cable.

Question 44

Bus network advantages

Answer 44

Easy to install extra devices. Cheap to install as it doesn't require much cable.

Question 45

Bus network disadvantages

Answer 45

If the cable fails or is damaged the whole network will fail. Performance becomes slower ad additional devices are connected due to data collisions. Each device receives all data, a security risk

Question 46

Star Network

Answer 46

All nodes are connected to one or more central switches. Often used with wireless networks.

Question 47

Star Network advantages

Answer 47

▪ Every device has its own connection so failure of one node will not affect others. ▪ New devices can be added by simply connecting them to the switch. ▪ Usually have higher performance as a message is passed only to its intended recipient.

Question 48

Star Network disadvantages

Answer 48

▪ If the switch fails it takes out the whole network. ▪ Requires a lot of cable so can be expensive.

Question 49

Mesh Networks

Answer 49

No central connection point, with each device connecting directly to others. Full mesh networks have every device connected to every other device. Partial mesh networks have each device connected to several others but not necessarily every other device.

Question 50

Mesh Networks advantages

Answer 50

▪ Messages can be received more quickly. ▪ Messages have many possible routes they can take. ▪ Multiple connections mean that no device should be isolated ▪ Each device can talk to more than one node at the same time. ▪ Devices can be added without interruption.

Question 51

Mesh Networks disadvantages

Answer 51

▪ Can be impractical and expensive to setup. ▪ Require a lot of maintenance

Question 52

Client server

Answer 52

In a Client-server model, one entity (the client) requests services from another (server) eg file server Server stores security information eg logins and permissions

Question 53

Peer-to-Peer (P2P) Networks

Answer 53

In a P2P network, there is no central server. Peers make a portion of their resources, such as processing power, disk storage or network bandwidth, directly available to other network participants. Each computer acts as both client and server. Devices on the network have equal status. Might be used in small offices or within a single department of a larger organization.

Question 54

Client server advantages

Answer 54

- Centralized control. For files for example, all files are stored at the same place. In this way, management of files becomes easy. - As all the data is stored on the server, it's easy to backup and restore. - Changes can be made easily by just upgrading the server. Also new resources and systems can be added by making necessary changes in server. Each workstation does not have to be upgraded. - Servers can be accessed remotely. - Security and access rights can be defined at the time of set-up of server and these are then centrally managed. - Easier to monitor traffic and resource usage

Question 55

Client server disadvantages

Answer 55

- Centralized control. For files for example, all files are stored at the same place. In this way, management of files becomes easy. - As all the data is stored on the server, it's easy to backup and restore. - Changes can be made easily by just upgrading the server. Also new resources and systems can be added by making necessary changes in server. Each workstation does not have to be upgraded. - Servers can be accessed remotely. - Security and access rights can be defined at the time of set-up of server and these are then centrally managed. - Easier to monitor traffic and resource usage

Question 56

Peer to peer advantages

Answer 56

- Easy to set up - P2P is more reliable as central dependency is eliminated. Failure of one peer doesn’t affect the functioning of other peers. - There is no need for full-time System Administrator. Every user is the administrator of his machine. User can control their shared resources. - The overall cost of building and maintaining this type of network is comparatively very less. - As more peers are added, both demand and capacity of the network increases

Question 57

Peer to peer disadvantages

Answer 57

- In this network, the whole system is decentralized thus it is difficult to administer and keep stable and fully accessible. - Security in this system is less strong therefore viruses, spywares,trojans, etc malwares can easily transmitted over this P2P architecture. - Data recovery or backup is very difficult. Each computer should have its own backup system - Lot of movies, music and other copyrighted files are transferred using this type of file transfer. P2P is the technology used in torrents. - Finding peers on the network can be difficult