1.4 Wired and wireless networks
What is a LAN?
- A LAN is a Local Area Network - The computers and connections are located on one site such as a school or small business - Lots of homes have a LAN to connect various devices, such as PCs, tablets, smart TVs and printers - All the hardware for a LAN is owned by the organisation that uses it
What are the features of a client-server network?
- A client-server network is managed by a server. The devices connected to the server are clients - Files and software are usually stored centrally on the server rather than on individual client devices - Clients send requests to the server, e.g. asking for data or for services such as email, file storage, backup and printing. The server processes the request and responds - The server stores user profiles, passwords and access information - it may request a password before fulfilling certain requests or deny requests to users without the right access level - Most uses of the Internet work on a client-server relationship e.g. web browsers are client programs which send requests to web servers
What are the advantages of a client-server network?
- All data can be backed up centrally rather than on each individual computer so it is easier to keep track of files - Easier to perform back-ups - Easier to install and update software - Servers are very reliable and are always on - Security is better because data is held in one location rather than all over the organisation - Users can log in from any computer on the network and access their data
What are the advantages of a peer-to-peer network?
- Easier to set up - computers can simply be cabled together - No special software is required to run the network - Individual computers can share a printer, router, modem and other hardware - Users can communicate directly with each other and share each other's files - No dependence on server - if one device fails the whole network isn't lost
What are the disadvantages of a client-server network?
- Expensive to set up and needs IT specialists to maintain the network and server - Server dependence - if the server goes down all clients lose access to their work - The server may become overloaded if too many clients are accessing it at once
What are the advantages of the cloud?
- Users can access files from any connected device, anywhere in the world and at any time - Easy to increase how much storage is available - No need to buy expensive hardware to store data - No need to pay IT staff to manage hardware - Cloud host provides security and back ups for you - Cloud software will be updated automatically
State and describe the different types of transmission media
1) Copper wire: - Most LANs have traditionally been connected by means of copper wire. This allows fast and reliable data transmission. The wire is usually in 'twisted pair' cables, containing four pairs of copper wires which are twisted together to reduce internal interference 2) Coaxial cable: - Coaxial cables are made from a single copper wire surrounded by a plastic layer for insulation and a metallic mesh which provides shielding from outside interference. This means they are bulkier and less convenient to install 3) Fibre optic cables: - Fibre optic cable is used for long distances. Light is transmitted along glass fibres and total internal reflection keeps losses to a minimum - They are high performance and are not subject to interference from neighbouring cables and does not deteriorate in exposed locations
Network hardware - what is an NIC (Network Interface Controller/Card)?
A NIC (Network Interface Controller/Card) is an internal piece of hardware that allows a device to connect to a network These used to be on separate cards, but nowadays they're built into the motherboard of every networked device capable of connecting to a wireless network, for example PCs, smart phones and wireless speakers The NIC provides the electrical signals for sending messages on the network and also for receiving incoming signals
What is a VPN?
A VPN (Virtual Private Network) is a type of virtual network that can be used to send data securely over a large network, like a WAN or the Internet
What is a client? What is the role of the client?
A client is a computer which requests the services or resources provided by the server The client sends requests to the server, waits for a reply and then receives the reply
What is a hardware client in the context of the internet?
A hardware client can be any of a wide variety of micro-processor controlled devices such as a desktop or laptop computer, a tablet or a mobile phone
Define the term client in the context of the internet
A typical user on the internet uses a computer of some sort as a client in order to access data from a server. Clients can be hardware or software
How does bandwidth affect the performance of networks?
Bandwidth is the amount of data that can be transferred in a given time, e.g. 500Mbps. The greater the bandwidth, the more data can be transferred in a given time and the better the network can perform Available bandwidth is shared between users of a network - too many users or heavy use (e.g. streaming video) may cause congestion and slow the network. You can limit the bandwidth available to individual users to address thus
What factors affect the performance of networks?
Bandwidth, latency, error rate/collisions and retransmission rate, the type of transmission media
What are the two ways in which networks are organised?
Client-server and peer-to-peer
What is a software client in the context of the internet?
Clients can also be software, for example a web browser is client software and so is an email program. Many apps on phones and tablets such as those that look up rail timetables are examples of client software. Other common examples are chat applications, ebook readers and online learning resources
What are some of the suffixes for domain names?
gov: government address org: non-profit organisations com: commercial businesses uk: based in the United Kingdom
How do errors, collisions and retransmission affect the performance of networks?
Errors and high network traffic may result in data collisions between packets When packets collide, they are corrupted or lost Lost packets are retransmitted, and this process takes longer owing to the bandwidth and latency of the network
What is the host?
Hosting is when a business uses its servers to store files of another organisation. The traditional use for this on the Internet is the hosting of websites An Internet host is a company that is able to store your files and make them available to you or others from other Internet-connected computers
Network hardware - what is a hub?
Hubs and switches connect devices to a LAN. Hubs are less common these days on large enterprise networks. Home users sometimes get small hubs to connect a few devices because they are cheaper than switches or routers and require no setting up
How does latency affect the performance of networks?
Latency is determined by the speed of delivery, or time delay between the moment the first data packet of a communication starts and when it is received at its destination. The lower the latency, the less delay and the better network performance
What is a DNS?
Resources on the internet are given domain names to make them easier to remember - you don't need to remember IP addresses A DNS (Domain Name System/Server, depending on whether it is the overall facility of one of the computers) translates a website's domain name into its IP address The internet has a network of Domain Name Servers. When you type in a domain name or the complete reference for a resource into the URL box in a browser, the name is forwarded to a domain name server
Network hardware - what are routers?
Routers are devices that send data packets in the best direction between networks. In a small home network, they connect individual computers to each to other and also to the internet Routers are extensively used on the internet and provide the connection between nodes, making decisions about where to send data and by what route
What is the cloud?
The 'cloud' is a term that denotes the remote provision of storage and increasingly software resources that we can access from our own devices. In physical terms, it refers to servers and data centres that can be anywhere in the world and are connected to the internet. It enables users connected to any internet-enabled computer to access these files or services
What is the World Wide Web?
The Word Wide Web is a collection of websites that are hosted on web servers and accessed through the http protocol
Network hardware - what is transmission media?
The cables that carry data - copper wires, coaxial cable or fibre-optic cable
What is the internet?
The internet is a network of networks - it is a WAN which connects devices and networks from all over the world. It's based around the protocol TCP/IP. It is an infrastructure The internet hosts a wide variety of services Many phone and other apps work through the internet
Network hardware - what are wireless access points?
The point at which a wireless-enabled device such as a laptop connects with a network, using WiFi, is a hardware device called a wireless access point. The AP (Access Point) usually connects to a router (via a wired network) as a standalone device, but it can also be an integral component of the router itself
What is a server? What is the role of the server?
The server is a powerful computer that provides services or resources required by any of the clients The server typically looks after: - logins and security - file handling - printing - Internet access There are often many servers in a network, with some specialised to do particular functions, for example there may be an email server where the corporate emails are stored A file server holds all the data files and databases and manages backups A print server may organise printing on different levels A web server interacts with remote users who access them via their browsers The server waits for requests from a client, acknowledges the request, the server may need to pads the request to another server (in which case the server becomes the client), then the requested data is sent back to the client
Define the term server in the context of the internet
The word server can refer to an item of hardware or the software residing on it that responds to client requests
What are URLs?
URLs are addresses used to access web servers and resources on them
What is Wi-Fi?
Wi-Fi is the standard used for wireless networks. Wi-Fi uses two radio frequency bands - 2.4 GHz and 5 GHz The bands are split into numbered channels that each cover a small frequency range and has a certain bandwidth. The channels overlap Wi-Fi performance is affected by interference between networks using adjacent channels. To avoid problems, certain channels that are spaced apart tend to be used
How does the type of transmission media affect the performance of networks?
Wired connections are generally faster and more reliable than wireless Fibre optic cables can give much better performance than copper cables Wireless performance depends on signal quality so is affected by the range of the device, the amount of interference from other devices and physical obstructions like thick walls and buildings
How do wireless networks transmit data?
Wireless networks use radio waves to transmit data. They are susceptible to interference from objects and other nearby electronic or radio devices
What is a WAN?
- A WAN is a Wide Area Network - WANs typically cover a large geographical area, often worldwide. For example a business with offices in three different countries would need a WAN for all their devices to connect together - Unlike a LAN, organisations hire infrastructure from telecommunications companies, who own and manage the WAN. This is because a WAN is much more expensive to set up than a LAN - communication resources are provided by a third party carrier - WANs may be connected using fibre or copper telephone lines, satellite links or radio links - The Internet is the biggest WAN
What are the features of a peer-to-peer network?
- A peer-to-peer network is a distributed system, where functionality can be divided among the network nodes - All computers have equal status and are connected directly to each other without a server - Each computer can potentially act as a server and supply services and/or data to the others. You store files on individual devices and share them with others - The administration of a peer-to-peer is entirely up to the owner to decide - You may use a P2P network at home to share files between devices, or connect devices to a printer. They are suitable to small companies with fewer computers - All computers can communicate with each other without going through a server
What are virtual networks?
- A virtual network is a network that is entirely software-based. Virtual networks are created by partitioning off some of a physical network's bandwidth to form a separate network - Several virtual networks can exist on the same physical network. These networks all share the same hardware, making virtual networks more efficient than standard physical networks - Each virtual network has its own security, including its own firewall. This means virtual networks can only be accessed by using certain software or login information so that other people using the same physical network do not have access to the virtual network
What protective measures are put in place for wireless networks?
- Hiding the wireless server set identifier (SSID). This can make it less obvious that there is a network in the area - Restricting access to authorised MAC addresses only - Using WiFi protected access (WPA) encryption so that the signals are meaningless to outsiders
What are the disadvantages of the cloud?
- Need connection to the Internet to access files - Dependent on host for security and back-up - Data in the cloud can be vulnerable to hackers - Unclear who has ownership over cloud data - Subscription fees for using cloud storage and software may be expensive
What are the disadvantages of a peer-to-peer network?
- Security is hard to implement as there is no centralised management (devices need their updates and security installed individually) and network performance can become unpredictable and slow - Keeping track of data and its updates can become difficult and maintenance routines such as backup are also difficult to keep track of - It is generally only useful for small or domestic installations - The P2P configuration can be used for file-sharing websites. Because of the lack of server involvement, peer-to-peer activity on the internet has led to much illegal file sharing and copyright infringements
What are the advantages of a LAN?
- Sharing files is easier - network users can access the same files from any computer in the network - You can share the same hardware (like printers) on a LAN. This saves money - The Internet connection can be shared between every device connected to the LAN - You can install and update software on all computers at once, rather than one-by-one - You can communicate with other LAN users cheaply and easily, e.g. with instant messaging - User accounts can be stored centrally, so users can log in from any device on the network - However, purchasing the network hardware is expensive and viruses may be able to infiltrate the network and infect every computer
What do hubs do?
Hubs receive signals from a device and rebroadcast them indiscriminately to all connected nodes. They do not have any routing tables and they have no means of deciding where to send data. Hubs also switch the available bandwidth between any connected computers so they slow down network traffic
Why are switches more efficient than hubs?
Switched are usually self-learning so that they build up a table of connected devices and use this to route data packets to their correct destination. They do not send data uselessly to unintended nodes. Switches do not share bandwidth so they are more efficient than hubs and are preferred in most medium to large installations Switches are more expensive than hubs, however Switches usually work at a higher capacity than the ethernet transmission medium
Network hardware - what are switches?
Switches also connect computers together but a switch sends packets of data only to the correct MAC address, not to every connected node