3.4 Client Server and P2P networks Flashcards
What is the client-server model?
- There is a client computer and a server.
- The server is a powerful computer which provides services or resources required by any of the clients
- A client is a computer or device which requests the services or resources provided by the server
Process of client-server
- Query -> request
- Database
- response
LAN servers
One or more servers may be part of a local area network (same for WAN)
What is a data centre?
A site that contains thousands of servers
What are the 5 typical types of servers in a school (Client server) ?
- File server
- Print server
- Mail server
- Web server
- Database server
File server
Holds all the data files and databases and manages backups
Print server
May organise printing on different printers
Email server
May receive, detect and block spam emails, distributes emails to users
Web server
May host school’s external website
Database server
May hold student records
What is the role of a client
- Clients sends requests to the server
- Waits for a reply
- Receives the reply
What is a server?
A powerful computer that provides service to clients
Role of server
- Server waits for requests from a client
- Performs any processing required to fulfil the request
- The requested data is sent back to the client
Client-server advantages
- With file severs, just one file server needs to be backed up and files can be accessed from any computer
- Email servers provide a central place for email that is then accessed from different devices
- Same for different types of servers
What is Peer-to-peer (P2P) structure?
No central server
Features of P2P networking
- Suitable for small companies with small computers
No central server controls files or security - All computers can easily see files on other computers
- All computers can communicate with each other without going through a server
Advantages of P2P
- Easier to set up - can be cabled together
- No need for dedicated server equipment
- Individual computers can share a printer, router, modem and other hardware
- Users can communicate directly with each other and share each others’ files
Disadvantages of P2P
- Viruses and malware are more easily transferred over this type of network as there is no central firewall
- Data recovery and backup is not done centrally, so each computer has to have its own backup system
- Files are not centrally organised, but stored ion individual computers and may be hard to locate if the computer’s owner does not have a logical filtering system
- If a computer is switched off, data on that machine cannot be retrieved from other machines
Client server vs P2P
Client-Server:
- A central backup server backs up all file severs
- Security is controlled by a central server
- All users are reliant on the central server]Using servers enables businesses to grow to hundreds or thousands of computers and users
P2P:
- Each computer needs to be backed up
- Security is controlled by each individual machine
- There is no central server. If one computer goes down the only it’s services are lost
- P2P networks are difficult to maintain beyond a few computers
P2P on WAN
- P2P can be used for file sharing
- P2P is often used for illegal file sharing of copyright material such as music and films as they are harder to close down
- P2P file sharing allows each user to share parts of a file, rather than all downloads coming from one central server
- This significantly reduces the amount of bandwidth required when trying to share a file
What is web hosting?
A service offered by companies that will host web pages and files for websites. Web hosts will often provide database servers. Companies that provide more general hosting, such as backup servers, are known as hosting service providers
Advantages of web hosting over sharing files from your own computer
- Web hosts have far more bandwidth - can serve more users
- Web hosts are able to monitor their equipment all the time
- Web hosts will automatically backup web sites remotely
What is the cloud?
- The Cloud is the term used to refer to services that are delivered over the internet.
- It enables users connected to any Internet-enabled computer to access these services
Give examples of cloud computing
Google Drive, OneDrive and Dropbox
Software as a Service (SaaS)
Cloud based servers enable access to software on demand. This means the software is used via subscription, doesn’t need to be on a local machine and can be accessed from any Internet-connected computer, including smartphones
Examples of SaaS
- Online accounting packages
- Customer Relationship Management systems (CRMs)
- Share trading applications
Cloud computing advantages
- You can access data and applications from anywhere at any time
- You don’t need a powerful computer with a huge hard drive - everything is stored and run on a remote computer
- Backing up data is no longer crucial - it is done by the service provider
Cloud computing disadvantages
- Personal data will be stored on another company’s servers
- If the Internet connection is lost, often the service becomes unusable
- Slow internet connections may result in a poor quality of service
- It is not easy for people and organisations to see how reliable the service is
Methods of connecting computers
- Copper cable (electricity)
- Fibre optics (uses light)
- Wi-Fi (radio waves)
Copper cable advantages
- Tried and trusted technology
- Relatively inexpensive
Copper cable disadvantages
- signal affected by electric and magnetic fields
- low bandwidth
- heavy cables
Fibre optic advantages
- very fast transmission
- low loss of signal over distance
- not affected by fields
- required very little power
- more difficult to ‘tap into’ than copper cables
Fibre optic disadvatanges
- high investment cost
- need for expensive optical transmitters and receivers
Wireless transmission advantages
- no need for trailing wires (safer)
- allows devices to be used anywhere provided there is a signal
- easier to add devices to a network
Wireless transmission disadvantages
- data transmission rate less than wired systems
- signal can be blocked by objects or walls
- increased security issues
What factors affect network performance
- Bandwidth
- Latency
- Error rate/collisions
Bandwidth
The amount of data that can be carried through a connection at a time
Connection speeds
Measured is Mbps (Megabits per Second)
Latency
- The delay between the client and the server
- The length of time a packet of information takes to travel trough a network
