Fundamentals of computer networks Flashcards
Define what a computer network is
Connections between nodes to share resources
Discuss the benefits and risks of computer networks
Advantages of networks;
- People can communicate with one another more easily. E-Mail and instant messenger applications are much more versatile than sending letters through the post. Offices that are half-way across the world from one another can keep in constant up-to-date contact. And these functions rely on connections between computers i.e. a network.
- As well as communicating more easily, people can share resources easily. One printer can serve an entire office. One database can hold information gathered by hundreds of people, and be accessed by just as many.
- Data can be backed up more easily. By keeping data on a central server, there is only one set of files to back up or archive, in case of damage or theft.
Disadvantages of networks
- Security has become ever more important for computer networks. While it would be annoying if data was compromised on a single workstation, the prospect of an entire company network being breached requires a lot of attention to prevent.
- Network hardware can be expensive. Central file servers need a lot of storage space and a lot of processing power. Computers have to be connected through cables, which get more expensive as they get longer. Even wireless networks need regular hardware updates and maintenance.
- Networks are also difficult to manage. You need a very specialised skill set to handle complex networks, to keep all of the devices connected to the network secure and the software up to date.
Describe what a Personal Area Network (PAN) is
It consists of connected devices that are in close proximity to an individual, usually within a few meters. In order to be classified as a PAN, these devices must be able to communicate with one another.
The main technology used in a PAN is Bluetooth. Bluetooth was designed specifically to handle these kinds of in-close connections, but its range is very limited.
Describe what a Local Area Network (LAN) is
Usually cover relatively small geographical areas, these are often owned and controlled/managed by a single person or organisation
Describe what a Wide Area Network (WAN) is
The Internet is the biggest example of a WAN, these usually cover a wide geographic area and these are often under collective or distributed ownership.
Discuss the benefits and risks of wireless networks as opposed to wired networks
Wireless networks are cheaper as Only needs a Wireless Access Point to set up. However they can only allow a limited number of people to connect at a time and they are affected by radio interference, they have a lower bandwidth of 54mbps. Not so secure as radio waves can be picked up by anyone. So the WAP needs a strong password and encryption to disguise data being transmitted. They are very portable.
Wired networks are more costly than Wi-Fi but allows hundreds of people to log in at the same time and they have a higher bandwidth of 10gbps. They have excellent security as a computer needs to be physically connected to the network.
Explain a star topology
All the devices are connected to a central switch that controls the server which allows many devices to access the server simultaneously. It can be wired or wireless. The advantages are: if a device fails, the rest of the network is unaffected. They have better performance than other setups as data goes straight to the central device so all devices can transmit data at once and there are very few data collisions. It’s also simple to add more devices.
However, in wired networks every device needs a cable to connect to the central switch which can be expensive. If there is a problem with the switch or server then the whole network is affected.
Explain a bus topology
All the devices are arranged in a line, connected to a single backbone cable. Devices send data in both directions which causes data collisions and slows the network. If there is a problem with the backbone cable, the whole network is affected and there is low security as every device can see the data in the network. However they are easy to install and require less cable than star, making it cheaper
Define the term “network protocol”
A set of rules for how devices communicate and how data is transmitted across a network.
Explain the following methods of network security: • authentication • encryption • firewall • MAC address filtering
Authentication - once the user has entered their login details, they are sent either an e-mail, a text message or automated phone call. The message contains a one-time code that the user must enter before they are allowed access. This is a much more secure method, as anyone attempting to impersonate you needs not only to have your username/password, but also access to your phone or e-mail account. Two-factor authentication is commonly used by banks or secure online shops. Some even provide their customers with specially-made hardware. It is slow and requires user to have email or phone everywhere
Encryption - scrambling data so that only legitimate users can read it. Even if someone gets hold of the file, they cannot read it without knowing the digital decryption key. However, if key is gone - data is lost and can be time consuming.
Firewall - Firewalls limit how data can enter or leave a system. The rules that determine which pieces of data can go where is called ‘packet filtering’. The firewall also has rules in place to block access to certain IP addresses. For example, many schools use their firewalls to block student access to YouTube and Facebook.
MAC - Networks can be configured to only accept connections from devices with a MAC address from an approved list. This prevents unknown devices from getting into the network. E.g. in a shop, credit card machine makes contact with company to record transaction
Explain the purpose of HTTP (Hypertext Transfer Protocol), HTTPS (Hypertext Transfer Protocol Secure) and FTP (Fire Transfer Protocol)
FTP - used to transfer (i.e. upload and download) files between a regular computer and a server on a computer network.
HTTPS - encrypts web page data before it is sent out of the browser or server, to make sure that nobody can intercept the data and read it themselves
HTTP - the protocol underlying the World Wide Web.
Web pages are sent and received using the http protocol. Allows a browser to request individual files from a web server in an orderly way. Once received, they are rendered into a web page.
Explain the purpose of SMTP (Simple Mail Transfer Protocol) and IMAP (Internet Message Access Protocol)
STMP - used by the mail server itself to send and receive emails from all other mail servers across the internet.
IMAP - you can use multiple devices: view your emails using your laptop and then access them from elsewhere on your smartphone and they will still look exactly the same. Set flags on emails showing whether they have been viewed (read), replied to, deleted etc. It allows complex searches to be carried out based on subject, headers and so on
Explain the purpose TCP (Transmission Control Protocol) and UDP (User Datagram Protocol)
TCP - governs how messages are prepared for transmission, and how computers that receive a message from the Internet will put the message back together.
UDP - alternative to TCP. Messages sent using UDP are sent without any error correction bits. The sender just assumes that they will all arrive error-free. The advantage of UDP is that since it doesn’t have this back-and-forth of asking for corrupted packages to be re-sent (a process called ‘handshaking’), it transfers messages much faster. if errors happen, they aren’t fixed.
Describe the 4 layer TCP/IP model: • application layer • transport layer • internet layer • link layer.
Application layer: this is where the network applications, such as web browsers or email programs, operate.
Transport layer: this layer sets up the communication between the two hosts and they agree settings such as ‘language’ and size of packets.
Internet layer: addresses and packages data for transmission. Routes the packets across the network.
Link layer: this is where the network hardware such as the NIC (network interface card) is located. OS device drivers also sit here.
The HTTP, HTTPS, SMTP, IMAP and FTP protocols operate at the application layer.
The TCP and UDP protocols operate at the transport layer.
The IP protocol operates at the internet layer.
