Networks Flashcards
What is a network?
A computer network is two or more computing devices (such as a computer) connected together in order to share resources and exchange information.
What is a device that is able to join a network?
A device is said to be ‘network enabled’ when it is capable of joining a network.
Example of a network enable devices?
Network enabled devices include
Network servers
Personal computers
Tablets
Smart phones
E-readers
Smart televisions
Printers
What are the two types of networks?
There are two types of networks that you need to understand, Local Area Networks (LANs) and Wide Area Networks (WANs).
What is a LAN?
A Local Area Network is one that has two or more network-enabled devices connected within a fairly close geographical area.
What are some examples of places you will find LANs?
For example the LAN may be located within a single building such as a home or business office or it may cover a few nearby buildings as well, such as an University campus, hospital, library or school.
How can devices be connected on a LAN?
Computers and devices can be connected by physical Ethernet cables, which are usually owned by the organisation. They can also be connected wirelessly by using Wi-Fi connections.
What are advantages of using a LAN?
- A user can log on from any workstation and still access all of their files.
- Peripherals such as printers and photocopiers can be shared between many users, thus reducing costs
- Resources and files can be shared by users, this means that they can collaborate on a project.
- Backups of files and documents can be done centrally rather than needing to do it from each machine
- When software needs to be installed it can be done centrally rather than having to go to each individual workstation.
- An anti-virus and malware check can be carried out from the server to all workstations.
- Data can be transmitted very quickly between networked computers
- A LAN at home allows many devices to connect to one another, such as a smart TV or a media server
What are the disadvantages of using a LAN?
- Network failure. If there is a problem with the file server then no one will be able to access their files. If the internet server has an issue no one will be able to get onto the internet.
- Slow service. If there are a lot of users logged into the network requesting files and jobs then the network can start to slow down. There is only a limited amount of bandwidth in any network and the more data that is being used the slower things will become.
- Viruses and malware. Although these are dealt with centrally, if someone does install a virus on the local workstation it could easily spread
around the network - Cost - large business networks can be expensive to set up and keep running. The cost
of the physical components can be very high.
-Expert support required. Many business networks will require specialist staff such as network managers or technicians who can deal with problems as they arise and keep the network running smoothly.
- Security. Although users have their own user names, giving them access to just their files, users can be careless and not log out when they leave their workstation. This could give an unauthorised person access to their files or to sensitive documents stored centrally on the network.
How to improve the security on a LAN?
- Passwords. Strong passwords should be required and users encouraged to change their passwords frequently - at least once per month.
Access rights. Each user is assigned to a group e.g. students, teachers, admin etc. This is done via the user name. Each group is given different permissions to view folders and files. For example, when students log in they cannot see all of the admin and finance documents whereas office staff cannot view students’ work. - Access rights can also govern what you can do on a network, for example, install software, delete files etc.
- Audit log. This means the computer will record every important event in an ‘audit file. It records who saved what and when. Who deleted records or changed them.
- Backups. Central backups should be made regularly, at a minimum once a day. This way a rollback or restore of files can be made if an issue occurs.
- Encryption. Data travelling around the network should be encrypted, especially if hubs and Wi-Fi are being used. This is because data is broadcast to all devices on the network.
- Installing software. Users should not be able to install software or run .exe files because of the risk of introducing malware and viruses into the network.
What is WAN?
A wide area network (WAN) connects two or more local area networks (LAN) that are in different geographical locations.
What are some examples of WANs?
For example, a company might have offices in London and also New York, but they want to share a common work area so they can collaborate. In this case the LAN in London is connected to the LAN in New York by a Wide Area Network.
A WAN can also connect offices that are a bit closer together, such as estate agent offices in different towns. In this case a ‘leased line’ from a telecom company can be used.
How are WANs usually set up?
A company normally hires the WAN from a major telecom company because it is so expensive and complicated to set up and maintain.
How may WANs be connected?
The WAN involves long distance communications and this can be achieved using
- Fibre optic lines, including laying undersea cables
- Satellite communication links
- Leased telephone lines
- Microwave links
What is largest WAN that exists?
The largest WAN of all is of course the internet. No single organisation owns the internet itself.
What are the pros to using a WAN?
- Allows LANs to connect to one another.
- Allows workers to collaborate over a wide area, even across continents..
- Allows files and data to be shared between LANs. A WAN also allows direct person-to-person contact by methods such video conference virtually anywhere across the planet.
What are the cons of using a WAN?
-Can be expensive to hire a WAN service from the telecom operator.
- With a LAN, a company often has its own experts to maintain the network so any problems which arise can be addressed quickly. However with a WAN, it is owned by a number of external suppliers and so a failure of the WAN is usually beyond the control of the company to fix. For example, when an external DNS server fails, this immediately affects web access in the company.
What is bandwidth?
Any network has a limit in how much data can be moved across it in a given time. This quantity is called the bandwidth of the network.
What is bandwidth measured?
Bandwidth is measured in bits per second also called the bit rate.
Typical bit rates are:
Kilobits per second (Kbps), a thousand bits per second.
Megabits per second (Mbps), a million bits per second.
Gigabits per second (Gbps), a thousand million bits per second.
What happens as the bandwidth becomes higher?
The higher the bandwidth the more expensive the network becomes to put together because of the cost of the cables and equipment.
What happens if there are more users of the network?
Even the most impressive network can be slowed down if too many people are using it at the same time because the bandwidth has to be shared between all users. The more bandwidth each person uses, the less is available for everyone else.
What is the limit of users in a network?
In a wired network the maximum number of people that can connect is simply the number of workstations connected to the network. However, this does not mean that bandwidth is shared equally amongst them.
In a Wifi network what is the limit of users in a network?
In a Wi-Fi network the same thing applies - the more people or devices connecting to the network the slower the performance becomes.
There is also a limit in how many connections a Wi-Fi WAP accepts at any given time.
What are transmission media?
These are the physical cables used within the network. They too have a performance limit in terms of bandwidth and allowed cable lengths.
What is a popular choice for a wired network?
A very popular choice for a wired network is copper Ethernet cables to carry data.
They have a length limit because the signal gets weaker and weaker the more it has to travel along the cable. Eventually it becomes too weak to be useful.
What are the two main performance categories for ethernet cables?
Ethernet cables come in two main performance categories called Cat-5 (slower) and Cat-6 (faster).
Why would pick the Cat-5 cable or Cat-6 cable?
Cat-5 cable is cheaper per metre and is an excellent choice for a 100Mbps network. However, if a 1Gbps network or higher is required then the more expensive Cat-6 cable is recommended.
How do fibre optic cables transmit data?
Fibre optic cables transfer data using light which is reflected along the inside of the cable. Fibre optic offers extremely high bandwidth - in fact the bandwidth is actually limited by the equipment connected to it rather than the cable itself. But fibre optic is expensive compared to standard ethernet copper cable.
When is copper cable or fibre optic cable used?
Many of the larger networks use both types - copper cable for local connections and a high-bandwidth fibre optic cable to handle the heaviest traffic such as between two LANS
What the four different ways Wi-Fi performance can be affected?
- Range
- Radio interference
- Blocked by walls and floors
- Limited connections
How do errors in a network effect performance?
A factor in measuring network performance is how many data errors happen over a given time.
An ‘error’ happens when a binary 1 was sent, but a binary 0 was actually received or the other way around.
How do errors happen?
There are two main reasons for errors happening:
- Interference
- Signal is too weak
If a cable or switch is too near heavy equipment such as electric motors or other power equipment then interference may cause bits to flip randomly. This is why shielded cables are used to try and reduce this problem, and network cable run layouts are thought through carefully to avoid problems.
The other factor is length of cable - the longer the cable, the weaker the signal. For example the longest recommended length of Cat-5 cable is 100 meters. If the signal gets too weak, then errors begin to creep in.
On a wireless network, radio interference can introduce errors. And if the Wi-Fi signal is too weak, then again errors creep in.
What is another factor of network performance?
On a small local area network, latency is not much of a problem as everything is quite close to one another.
But on large networks such as a WAN (e.g the Internet), latency becomes much more important.
How does latency happen?
Every switch, cable and router is adding delay (latency) to the connection. And to make it worse, the actual connection changes second by second as the routers decide which path to use at that instant. This will cause bits to arrive in a different order to what was sent.
A high performance network should have low latency.
What are wired networks affected by?
Performance of wired networks is affected by:
Type of cable connection (Ethernet or fibre optic)
Bandwidth available
Number of users
Error rates
Latency
What are wireless networks affected by?
Performance of wireless (wi-fi) networks is affected by:
The number of connections available
Range from WAP
Radio interference
Physical layout; solid walls and floors block signals
What are some pros of a wired network?
- Allows hundreds of people to log in at the same time.
- It is immune to radio interference
- High bandwidth, more than 10 Gbps is common
- Excellent security as a computer needs to be physically connected to the network
- Not affected by building layout
What are some cons of using a wired network?
- It is more costly than Wi-Fi to install in a building.
- Not portable as each computer needs to have a network socket available.
What are some pros of using a wireless network?
- Only needs a Wireless Access Point to set up, so is cheaper.
- Very mobile, an user can carry their laptop from office to office and not lose a connection.
What are some cons of using a wireless network?
- Can only allow a limited number of people to connect at any one time
- Affected by radio interference
- Lower bandwidth
- Not so secure as connection is by radio. So the WAP needs a strong password and encryption to disguise data being transmitted
- Signal is affected by walls and floors
What are the two main ways a LAN can connect nodes?
Client-Server
Peer-to-Peer
What is a Client Server network?
In a Client-Server LAN arrangement, most files and data are stored on a server. All computers on the network connect to this server through a central hub or switch.
The other computers on the network are called ‘workstations’ or ‘clients’.
Users can access files and data from the server using any workstation. They just need to log into their account using their username and password. These accounts are managed by the server. Once they log in, they will see their work area or ‘desktop’ appear on the workstation screen.
Workstations cannot normally ‘see’ or share data with each other directly over the network. If people need to share data then a ‘shared network folder’ is created on the server by the network manager in order to share files.
There may be multiple shared folders on a server with different access rights.
In a Client-Server LAN what special features are there?
Users will have their own private area on the network where they can save their files and documents. No one else can access this area (except the network manager and staff).`
A client server network requires a specialist network operating system.
As files are stored on the server and they can be backed up centrally.
What is a Peer-to-Peer (P2P) network?
Peer to peer networks are very common in small offices or at home where there are only a few computers connected together.
With a peer-to-peer network a central server is not required because the files are stored on the hard disks of individual network machines.
Each computer on the network has equal importance and no more privileges than any other.
Each computer is both a client and a server - it acts as a ‘host’. And users can access files and peripherals directly from all the other peers on the network.
Each peer computer can be set up to share folders with other peers.
What are the differences between a Client-Server and a P2P network?
[CS] = It has one or more servers
[P2P] = There is no central server
[CS] = A workstation computer or ‘client’ is used to log in to the server
[P2P] = Each peer may have its own local user accounts (or just a single account)
[CS] = The network administrator sets up shared folders on the server
[P2P] = Each peer can be set to share folders (or no folders at all)
[CS] = Needs technical skill to maintain a client-server network
[P2P] = Needs little technical skill as operating systems such as Windows and Linux have built-in support of network sharing
What are the differences between a Client-Server and a P2P network?
[CS] = Files and data are stored centrally on the server
[P2P] = Files and data are stored locally or in a shared folder hosted by a specific peer computer
[CS] = A broken workstation has no effect on the overall network. You just log in to a different workstation. A broken server, though, takes down the entire network.
[P2P] = A broken or disconnected peer computer has an effect on all peers because their shared folder(s) are no longer available.
[CS] = Commonly used in organisations that need to connect many workstations / computers together e.g. school network.
[P2P] = Commonly used in small LANs such as at home or a small office with few computers
[CS] = Requires a network operating system
[P2P] = Can use a standard operating system
