Chapter 2 Flashcards
What are the 3 groups networks are classified into?
- LAN
- WAN
- MAN
What is a LAN?
• A network covering a small geographical area
(e.g. a building) connecting computers & shared devices
• Uses dedicated infrastructure
What are devices connected to in a LAN?
• Computers and devices connected to hubs or switches
What is a hub?
• Hardware used to connect together a number of
devices to form a LAN that directs incoming data
packets to all devices on the LAN
All packets will be sent to every device
• If the address in packet matches the deviced address ➔ packet is accepted; otherwise it is rejected
What is a switch?
• Hardware used to connect together a number of
devices to form a LAN that directs incoming data
packets to a specific destination address only.
- It stores the MAC addresses of devices on a
network and filters data packets to see which
devices have asked for them.
- This makes a switch more efficient when demand
is high.
• More powerful/secure
• Packets will only be sent to devices where the address matches the recipient address
What is the hub/switch connected to and for what reason?
• One of the hub/switch is connected to a router and/or modem to allow the network to connect to the Internet
What is a router?
- Connects devices to form a LAN
- Connects different networks together
- Homes and businesses use it to connect to the Internet
- Can often incorporate a modem within the hardware
What is a modem (Modulator/Demodulator)?
- Enables a computer to connect to the Internet over a telephone line
- Converts digital signals from a computer to analogue signals that are then sent down the telephone line
- A modem on the other end converts the analogue signal back to a digital signal which another computer can understand
What is a WLAN (Wireless Local Area Network)?
- Wireless network communications over short distances
* Uses: Infrared/Radio signals
WAP – Wireless Access Point
- Connects the devices to the wired network
- Uses
- Spread spectrum technology – wideband radio frequency
- Infrared – very short range & easily blocked
Where can a LAN be applied?
- Sending and receiving email
- A company or school centrally storing files
- Using a print server
- Using a file server
What is a WAN (Wide Area Network)?
• Network covering a very large geographical area
(worldwide)
• Multiple LANs are joined together using a router/modem to form a WAN
• Consists of LANs connected via:
-Telephone lines
- Satellites
What do WANs use to connect to each other?
• Public communication networks (Broadband & Fibre)
OR
• Dedicated/leased lines
+ Faster connection / transmission of data
+ Usually more consistent transmission speed
+ More secure (less risk of hacking)
- More expensive to set up/maintain
- Disruption will leave no alternative
What are the characteristics of telephone lines used to transmit data?
- Transmission of data using telephone lines (PSTN)
- The PSTN consists of many different types of communication lines
- Data is transmitted in both directions at the same time // (full) duplex data transmission
- The communication passes through different switching centres
What is a MAN (Metropolitan Area Network)?
- Network which is larger than a LAN but smaller than a WAN, which can cover several buildings in a single city, such as a university campus
- Size restriction – a single city
+ of networking computers?
+ Devices can be shared (e.g.: printers) ➔ costs are reduced
+ Data and files can be shared
+ Licences for software on network are cheaper than buying licences for the same number of individual stand alone computers
+ Access to reliable data from a central source (e.g.: file server)
+ Data & files can be backed up centrally at the end of the day
+ Users can communicate using email and instant messaging
+ Apply/restrict access to certain files and/or networks (e.g. Internet)
- of networking computers?
- Cabling and servers can be an expensive initial cost
- Managing a large network can be complex and difficult
- Malfunction of devices (e.g.: file servers) can affect the whole network
- Malware and hacking can affect entire networks (although afford some protection)
Characteristics of public networks?
- Owned by a communications carrier company
- Many organisations use it
- Usually no specific password requirements to enter it
- Sub-networks may be under security management
Characteristics of private networks?
- Owned by a company/organisation
- LANs/intranets
- With restricted user access, passwords are required to enter
What are the two types of Networking Models?
- Client-Server
* Peer-to-peer
How does a client-server model work?
• Uses separate dedicated servers and client computers connected to the servers
• A server:
- provides services to other computers on the network (e.g.: sending and receiving of email - to a number of “client” computers on the network)
- provides a resource to the other machines on the network (e.g.: File server, Print server)
• A client is a computer that relies on servers to provide and manage data
What do typical servers include?
- file servers - hold and maintain user files
- applications servers - allow programs to be run over a network
- web servers - hold and share web pages
- print servers - manage printing across a network
- mail servers - handle emails between users
Characteristics of a client-server model?
• Users can access files stored on dedicated servers
• Server dictates which users can access which files
• Allows installation of software onto a client’s computer
• Server is responsible for the authentication of user log-ons
• More secure as clients have access to only those resources and files assigned by the network
administrator
• Can be as large as you want – easier to scale up
• If a shared resource is deleted form the server, the back-up would restore it
• Can become bottlenecked if there are several requests at the same time
Where can client-server models be used?
- A web browser is the client software which makes a request to the server, the server finds the website on a webserver and it sends the website to the browser
- An email client is another client program (Client is the front end of an application): provides the interface between the user and the application
• Bank:
When checking your bank account from your computer: your client computer forwards a request to a server program at the bank, the program may then turn forward a request to its own client program, which then sends a request to a database server at another bank computer and once your account balance has been retrieved from the database, it is returned back to the bank data client, which in turn serves it back to your personal computer, which then displays the information to you
How does a peer-to-peer model work?
- All computers have equal status - no computer (node) has control over the network
- There are no servers or clients. Instead, each computer is known as a peer: peers are both a client and a server
- Peers store their own files, which can be accessed by all other peers on the network – no central storage
- No requirement to authenticate users
- It is best suited to smaller organisations that have fewer computers, or where fewer computers need access to the same data
- No more than 10 computers
Where can a peer-to-peer model be used?
- Fairly small network of users
- Ideal for sharing files
- When no need for robust security
- When they need workstation-based applications rather
- Unsuitable for a service such as booking tickets, as one server needs to keep track of how many tickets are left
Client-server VS P2P:
Client server:
The server controls the security of the network
The server manages the network: needs a dedicated team of people to manage the server
Clients are dependent on the server
The server can be upgraded to be made more powerful to cope with high demand
Data is all backed up on the main server
P2P
No central control over security
No central control over network: anyone can set up
Clients are independent
If machines on the network are slow they will slow down other machines
Each computer has to be backed up: data can be easily deleted by users
What is a thick client?
• A full computer that can work online & offline and does not require processing from the server
What is a thin client?
• Connect to and interact with a server.
The device often has a small hard drive or none at all, as data and programs are primarily stored in cloud / on the network’s main servers
• Thin clients have limited functionality and most features do not function when connected to the network
Thick VS Thin Client:
Thin client software:
• Always relies on a connection to a remote server or computer for it to work
• Requires very few local resources (such as
SSD, RAM memory or computer processing time)
• Relies on a good, stable and fast network connection for it to work
• Data is stored on a remote server computer
Thick client software
• Can run some of the features of the software even when not connected to a server
• Relies heavily on local resources
• More tolerant of a slow network connection
• Can store data on local resources such as HDD or SSD
+ of thick clients:
- More robust (device can carry out processing even when not connected to server)
- Clients have more control (they can store their own programs and data)
- of thick clients:
• Less secure (relies on clients to keep their own data secure)
• Each client needs to update data & software individually
• Data integrity issues, since many clients access
the same data which can lead to inconsistencies
+ of thin clients:
• Less expensive to expand (low-powered and
cheap devices can be used)
• All devices are linked to a server (data updates and new software installation done centrally)
• Server can offer protection against hacking and malware
- of thin clients:
• High reliance on the server; if the server goes
down or there is a break in the communication
link then the device cannot work
• Despite cheaper hardware, the start-up costs
are generally higher than for thick clients
What are the 4 ways of connecting computers (network topologies)?
✓ Bus
✓ Star
✓ Mesh
✓ Hybrid
Characteristics of a Bus Network Topology:
!P2P – for small number of devices: company/office!
• Use of a central cable – all devices are connected
to the cable
• Easy to expand
• Requires little cabling
• Data travels in one direction
• While data is sent between devices then other
devices cannot transmit
• Terminators at each end to prevent signal reflection
• Each node looks at each packet and compares the
address – if the recipient’s address matches the
node address packet is accepted
+ of a bus network topology:
- If one node fails, the other nodes continue to function
* Easy to increase the size of the network (adding nodes on the cable)
- of a bus network topology:
- If main cable fails, then the whole network goes down
- Heavy loading lowers the performance
- Each packet passes through every node ➔ not secured network
Characteristics of a Star Network Topology:
!Client-server!
• Each computer/device is connected to a central hub/switch
• Data going from host to host is directed through the central hub/switch
• Useful for networks where
• Devices are frequently added/removed
• There is heavy data traffic
+ of a star network topology:
- Reduced data collision
- More secure b/c packets can only travel to nodes with the correct address (switch)
- Easy to improve – upgrade the hub
- If one connection fails, it only affects one node
- of a star network topology:
- High initial installation costs
* If central hub/switch fails, whole network goes down
What are the 2 types of Mesh Network Topology:
• Type of P2P
- Routing
- Data is directed to its destination by the shortest route; it is re-routed if one node has failed - Flooding
- Data is sent via all nodes
What are the applications of a mesh network topology?
• Internet, MANs/WANs
• Industrial monitor & control (use of sensors)
✓ Medical monitoring of hospitalised patients
✓ Electronics interconnectivity
✓ Modern vehicles use wireless mesh topology to control/monitor all the components of the vehicle
+ of a mesh network topology:
- Easy to identify where faults on the network have occurred
- Broken links do not affect the other nodes
- Good privacy and security, since packets travel along dedicated routes
- Relatively easy to expand
- of a mesh network topology:
- Large amount of cabling is needed ➔ expensive, time consuming
- Set-up & maintenance is difficult and complex
What is a Hybrid Network Topology?
- Mixture of two or more different topologies
- Packets handling depends on which of the topologies are used to make up the hybrid structures
• Application example
- 3 hotel chains, having different topologies
- If all 3 chains are taken over by another company
Hybrid topology can be used to connect all 3 chains
+ of a hybrid network topology:
- Depends on the topologies used
- They can handle large volumes of traffic
- It is easy to identify where a network fault has occurred
- Ideal for creating larger networks
- of a hybrid network topology:
- Can be very complex to install, configure and maintain
* Depends on the topologies used
What is cloud computing?
• Cloud computing is the on-demand availability of computer system resources, without direct active management by the user • Data centers available to many users over the Internet • Covers: - Storage - Databases - Networking - Software - Analytical services using the Internet
What is cloud storage?
• A method of data storage where data is stored on off-site servers
- Same data stored on many servers → access data in case of maintenance/repair
• Owned & managed by a hosting company
