2.1 Networking

## Networking
- Networking devices are interconnected devices that allow a fast means of data transmission within the network.
### Networking benefits:
- File sharing - you can easily share data between different interconnected devices
- Resource sharing - using network-connected output devices like printers, or can share the same software within the network
- Higher storage - can store files in network-connected storage mediums.
- Communication – user can send mail or chat
### Networking Drawbacks
- Cost: Cabling and servers can be an expensive initial outlay.
- Management: Network requires management from technical stuff
- Malware: Virus can easily spread through improperly secured network
- Hacking: Once a device is connected to another device, it is easy to hack
- A breakdown of devices, such as the file servers, can affect the whole network.
### LAN(Local Area Network) vs. WAN(Wide Area Network)

| LAN                                                             | WAN                                                                    |
| --------------------------------------------------------------- | ---------------------------------------------------------------------- |
| Network that connects devices within a small geographical area  | Network that connects devices within a larger geographical area        |
| Higher data transfer rate                                       | Lower data transfer rate                                               |
| Transmission medium: twisted pair cable, coaxial cable or Wi-Fi | Transmission medium: Leased telecommunications, PSTN or satellite link |
| Only private ownership                                          | Private or public ownership                                            |
| Lesser congestion                                               | Higher congestion                                                      |
| Secure                                                          | Less secure                                                            |

### Client-server Model

![](/media/202609/a4c6cfbedccd4b9ba5b9866a473d2b994325.png)
- Server based network: dedicated server provides an application (administration of users, security and resources) for the client computer to utilize
- At least one computer used to “serve” other computers are referred to as “clients”
- Server provides services which may be requested by clients
#### Roles of the different computers within the network and subnetwork models
##### Client:
- End-user device that requests and utilizes the services or resources provided by the server.
- eg. desktop computers, laptops, smartphones
##### Server:
- hosts and provides the services, data, or resources requested by the clients
- centralized system that manages and controls the network resources.
- high-performance machines with specialized hardware and software configurations
#### Client-server Applications
- Printer server: manages print jobs from client computers 
- File Sharing: the client accesses software and user's data files stored on the server 
- Web server: manages pages available from a website
- Email server: for sending, receiving & storing emails 
- Database server: manages DBMs(Data Base Management System)
- Domain controller server
  - Management of user accounts (IDs & passwords)
  - Client sends login request to server which processes and grants request if user ID & password recognized
##### Benefits of Client-server
- Centralized management -by central server
- Scalability可扩展性 - can add or upgrade
- Specialized functionality
- Robustness坚固性- fault-tolerant容错 i.e if one server fails, other servers can continue to- serve clients without significant interruption
##### Drawbacks of Client-server
- single point of failure - If the server goes down, clients lose access to the resources and services provided by the server.
- Cost -setting up and maintaining servers can be expensive 
- Network congestion - especially when there are many clients accessing the server simultaneously.
#### Thin-client(a client that only provides input and receives output from the application)
- A client that solely runs on the resources provided by the server 
- Only provides input and receives output processing done by server 
- Less purchase cost, expensive & demanding hardware is not required 
- 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 or computer
#### Thick-Client(a client that carries out at least some of the processing itself)
- An independent client that does not require the server to run
- The server performs only some processing for the client
- Thick client process most of the application
- Can Function even if no server is connected (works offline)
- No lag related to network problems, more tolerant of a slow network connection
- relies heavily on local resources
- can sore data on local resources sch as HDD or SSD
### Peer-to-peer network model (P2P)

![](/media/202609/595add6633e846a08b670a9e0bf1eddc6145.png)
- Decentralised network where each connected computer stores data and operates independently as a ‘peer’, and can act as both a client & server.
- Roles of the different computers within the network and subnetwork models
#### Peer
- All computers are of equal status/all computers within the network are considered peers
- each peer acts as both a client and a server
- having the ability to request and provide resources or services
- is responsible for its own security
#### Applications:
- Internet and Ad hoc networks临时网络
#### Benefits of peer-to-peer
- Decentralization
- Scalability-can add or delete nodes
- Cost-effectiveness
- Flexibility - peers can join and leave the network dynamically
#### Drawbacks of peer-to-peer
- Reduced security // no central management of security
  -  … only as secure as the weakest computer on the network
  -  … each computer is at risk from viruses from other computers
- No central management of backup
  -  ... if the data from one computer is not backed up it is lost to all of them
- No central management of files/software
  -  … consistency may be difficult to maintain
  -  … each computer may have different software from the others
- Individual computers may respond slower
  -  … because they are being accessed by other computers
- In order to share files etc. all the computers involved need to be switched on
  -   ... so the files etc. may not be always available
### justify use of each network model in the given scenario
#### Client Server Model is suggested if
- Large user-base
- Access to network resources needs to be properly controlled.
- Need for good network security
- Data needs to be backed up at a central location
#### Peer to Peer(P2P) Model is suggested if
- The network of users is fairly small
- No need for robust security
- Require workstation-based applications rather than being server-based
## Network Topologies
- Ways to connect computers to make complex networks
- The configuration of a network that defines how the various devices on the network are connected
### Bus networks

![](/media/202609/c90b691d29ec4a269c0c3c8797a507df4096.png)

- Single line (bus) connecting all devices with terminators at each end.
- Other computers can read the data being sent from one to another computer.
- Unsuitable for heavy traffic since collisions occur.
#### How data packets are transferred between two hosts in Bus topology
- Each node examines packet addresses
- Accepts if address matches node, ignores if not
#### Benefits
- Simple and easy to implement
- Requires less cabling compared to other topologies
- Cost-effective for small networks
- Requires less hardware compared to other topologies
- It is easy to increase the size of the network by adding additional nodes
- Even if one node fails, the remainder of the network continues to function
#### Drawbacks
- If the main cable fails, the whole network goes downs 
- The performance of the network deteriorates under heavy loading 
- The network is not secure since each packet passes through every nodes
- Susceptible to collisions, especially as the number of nodes increases
- Difficult to troubleshoot and isolate faults
- Limited scalability and bandwidth as all devices share the same communication medium
### Star networks

![](/media/202609/5588db0c9ae14122bf235a620b5a73562163.png)
- uses a central hub/switch
- each computer/device is connected to the hub/switch.
- Data going from host to host is directed through the central hub/switch. 
- Each computer/device has its own dedicated connection to the central node
#### How data packets are transferred between two hosts in Star topology
- A packet has a header which gives the recipient's address.
- These packets are transmitted directly to the relevant server.
- Hub as Central Node
  - Broadcasts packets to all nodes
  - Node matching address accepts, others ignore
- Switch as Central Node
  - Server identifies the recipient's location and delivers directly to the correct destination.
  - Switch provides more secure communication
#### Benefits
- Data collisions are greatly reduced due to the topology.
- It is a more secure network since security methods can be applied to the central node and packets only travel to nodes with the correct address.
- It is easy to improve by simply installing an upgraded hub.
- If one of the connections is broken it only affects one of the nodes.
- Suited to applications where there is heavy data traffic.
#### Drawbacks
- The initial installation costs are high.
- If the central hub/switch fails, then the whole network goes down.
### Mesh networks

![](/media/202609/c9f6742a661244489b9bc193a9347aac1488.png)
- All computers are connected to at least one other device
- There are multiple routes between devices
- The computers can act as relays, passing packets on towards the final destination
#### How data packets are transferred between two hosts in Mesh topology
- In a mesh network, a data packet is transmitted in either of these two ways:
  - i.Flooding: Sending to all the devices and the intended receiver will pick-up the data packet.
  - ii.Routing:Routing the data packet to a particular device.
- In case a particular route is blocked due to failure, the data packet is then re-routed by algorithms. 
- This characteristic of a mesh network is referred to as ‘self-healing’. As a result, mesh networks are comparatively reliable.
#### Benefits
- If one line goes down there are more routes available
- No/fewer collisions
- New nodes can be added without interruption or interfering with other nodes
- More secure because data is sent over a dedicated connection
- It is easy to identify where faults on the network have occurred.
#### Drawbacks
- A large amount of cabling is needed, which is expensive and time consuming.
- Set-up and maintenance is difficult and complex.
### Hybrid networks
- Combination of two or more topologies.
#### Benefits & Drawbacks
- The main advantages and disadvantages depend on which types of network are used to make up the hybrid network, but an additional disadvantage is that they can be very complex to install, configure and maintain
- Additional advantages include:
  - They can handle large volumes of traffic.
  - It is easy to identify where a network fault has occurred.
  - They are very well suited to the creation of larger networks.
### Cloud computing
- Accessing a service/files/software on a remote server
- Refers to the on-demand provision of computing services through the internet
- Services provided include
  - Infrastructure: Storage capacity and higher processing power
  - Platform: Software, testing & debugging resources
#### Benefits of cloud computing
- Can be accessed anywhere with Internet access
- Do not need to buy specific software/hardware(No need for a client to carry an external storage device with them)
- Do not need to install security / security could be better
- Most cloud data service will have in-built backup/disaster recovery
- Can easily increase capacity
- Data can be shared easily
#### Drawbacks of cloud computing
- Can only access (the cloud) with internet access
- There could be a limit to the amount of storage unless paid for
- Reliant on someone else to backup // no control over backups
- Reliant on someone else for security // can have poorer security
- Cannot access if server goes down
- It make take a long time to upload/download the data

| **Public cloud**                                                                       | **Private cloud**                                                                                                                               | **Hybrid cloud**                                                                                                                    |
| -------------------------------------------------------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------- |
| Computing services offered by 3rd party provider over the public Internet              | Computing  services offered either over the Internet or a private internal network       Only  available to select users not the general public | Combination of private and public  clouds.                                                                                          |
| Public is open/available to anyone with the appropriate equipment/software/credentials | Private  is a dedicated/bespoke system only accessible for/from the organisation                                                                | Some data sits in the private cloud and  less sensitive/less commercial data can be accessed from a public cloud  storage provider. |