Topic 5: Communication and the Internet Computer Networks

Communication and the Internet: Computer Networks These days, we are very much a connected civilisation We can easily communicate with anyone Across Earth We can shop online 24 hours a day 7 days a week We can get things delivered right to our door This is all amazing, but how can we do this? It’s thanks to a network called the Internet Communication and the Internet: Computer Networks

Communication and the Internet: Computer Networks Before we look at the Internet, we first need to answer a question What is a network? They are collections of two or more devices Connected together To share resources or data Can be combinations of clients and servers Clients: devices that use the data on the network Servers: devices that host the data on the network Will discuss these later Communication and the Internet: Computer Networks

Communication and the Internet: Computer Networks Types of Network Networks can be created using different mediums, and for different purposes A medium is the way data is sent from one computer to another on a network Wired: ethernet cables, USB cables Wireless: WiFi, Bluetooth The purpose of the network depends on the server used Could be for sending files from one computer to another Could be for backing up data onto one computer Could be for virtually connecting to another computer Communication and the Internet: Computer Networks

Communication and the Internet: Computer Networks Types of Network The overall scale of the network decides the kind of network it is Falls into three categories Local Area Network (LAN) Also has a variant called Wireless Local Area Network (WLAN) Wide Area Network (WAN) Personal Area Network (PAN) We often start small (at a LAN) and build up lots of them into a WAN Communication and the Internet: Computer Networks

Communication and the Internet: Computer Networks Types of Network Local Area Network (LAN) Covers a relatively small geographical area Like a home, or floor in a building Often has many devices (computers, printers, phones) connected to a router Can be connected by physical cables Or wirelessly, making it a Wireless LAN (WLAN) Communication and the Internet: Computer Networks

Communication and the Internet: Computer Networks Types of Network Wide Area Network (WAN) Covers a large geographical area Like a street, province, country, or continent Too large to connect in a single LAN So connects multiple LANs together By connecting their routers together The Internet is an example of a WAN Communication and the Internet: Computer Networks

Communication and the Internet: Computer Networks Types of Network Personal Area Network (PAN) Covers a very small area Typically around a single person Allows multiple small devices to communicate with each other Often wirelessly Like using a smart watch to pay for some items using a contactless pay point Communication and the Internet: Computer Networks

Communication and the Internet: Computer Networks Why Use Networks? Why do we have all these different types of networks? What use do they have? Computer networks were originally created to share research data between laboratories To save researches the trouble of physically sending the data from one location to another The same still holds true today We can use a network to send data to anyone on the same network Without having to give it to them physically Communication and the Internet: Computer Networks

Communication and the Internet: Computer Networks Why Use Networks Here’s a list of just some of the benefits of using a computer network We can save our work externally on a separate computer on the same network (essentially backing up that work). If our computer breaks, we can retrieve that data on the separate computer without worry! One computer may have some work that we want to access. Rather than copying it over, we can share it on the network, allowing both computers to access it at the same time! Printing documents from a computer on a printer requires a network (for the data on the computer to get to the printer). Whereas communication with other people had to be done physically (making inter-country talks difficult), people can freely communicate (via email, phone, or video) on the same network. If we want to access the Internet, we need to connect to its network. Communication and the Internet: Computer Networks

Communication and the Internet: Computer Networks Using Networks A lot of these reasons for using a network rely on two things A server for hosting, or controlling, the data A client for accessing that data This type of network, relying on a server and multiple clients, is known as a Client-Server network The server will always offer a specific service Hosting/backing-up files for clients Hosting websites for clients to browse Hosting virtual computers for clients to use Communication and the Internet: Computer Networks

Communication and the Internet: Computer Networks Using Networks In a Client-Server network, clients will often connect to the server Via a request The server will look at this request, and see If the client is authentic (they are logged in, if needed) What the client’s address is (specifically its Internet Protocol (IP) address) If the server is fine with the client, it will send the requested data to the address it logged Communication and the Internet: Computer Networks

Communication and the Internet: Computer Networks Using Networks There are some networks that don’t have a centralised server Where each client acts as its own server For a specific purpose (like sharing access to a printer, or access to files) These kind of networks are known as Peer-to- Peer networks As the clients (peers) are connected to each other This network won’t fail if a client loses connection As the other clients can ‘fill in’ for the one that was lost Whereas a Client-Server network relies on the server being connected Communication and the Internet: Computer Networks

Communication and the Internet: Computer Networks Using Networks Here is a handy table comparing these two uses of a network Client-Server Peer-to-Peer Uses a centralised server to host/handle requests Each client acts as its own server (no centralised server used) The server often records each request (and where it came from) No records are kept on requests (ensuring privacy) If the server goes down, client’s requests can no longer be handled If a client goes down, other clients can ‘fill in’ (if available) Can often handle larger, more complex tasks (like running applications) for clients Usually handle only small tasks (like sharing files or sharing access to printers) Communication and the Internet: Computer Networks

Communication and the Internet: Computer Networks Network Topologies As well as networks coming in different scales and usages, they can also come in different configurations Known as topologies These determine how devices are connected in the network Are multiple devices connected together? Do devices use the same medium? Is there a device that handles multiple connections? Each topology has its own set of advantages and disadvantages We’ll look at four of them: Bus, Star, Ring, and Mesh Communication and the Internet: Computer Networks

Network Topologies: Bus Involves connecting multiple devices and servers together Along the same medium Includes a terminator at the ends of the medium Absorbs signals that reach it Stops those signals bouncing back to the devices Only one signal can be sent at a time To stop signals from colliding Using Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) Communication and the Internet: Computer Networks

Network Topologies: Bus CSMA/CA works (in a simplified way) like so: Check if the medium is busy If not busy, then send a message, otherwise go back to step 1 Listen to see if the message was received correctly If not, go to step 5, otherwise go back to step 1 Wait a random amount of time and go back to step 1 Communication and the Internet: Computer Networks

Network Topologies: Bus Here are the advantages and disadvantages of this network Advantages Disadvantages Cheaper to install than some of the other topologies (as only one physical medium, like a cable, is needed) If the physical medium is cut, the whole network goes down Easy to add extra devices (as we connect them to the same physical medium) Due to all devices being connected to the same physical medium, it can be difficult working out where a fault on the network is The more devices added to this network, the slower the whole thing runs (as each device has to wait for communications to finish) Data is received by all devices on the network (as they all have access to the physical medium) – making this a security risk Communication and the Internet: Computer Networks

Network Topologies: Star Involves connecting each device independently to a central ‘backbone’ Like a hub, switch, or router Each device has its own medium to send data down Meaning data can’t be ‘listened-in’ by other devices on the network If a medium for one device goes down, it doesn’t affect the other devices Communication and the Internet: Computer Networks

Network Topologies: Star Here are the advantages and disadvantages of this network Advantages Disadvantages A damaged medium for one device will not affect the other devices connectivity If the backbone goes down, the whole network does too As mediums are independent, and only the backbone manages communications, messages are only sent to the devices that need them (making them more secure) More expensive to install (physically) as every device needs its own independent cable It’s easy to locate a fault (as faults typically only affect a certain device) Devices can be added and removed without affecting the other devices on the network Communication and the Internet: Computer Networks

Network Topologies: Ring Connects devices to each other on a closed ring Each device has an input and an output All communications go in the same direction (clockwise or anti-clockwise) No worry about collisions as data can only go in one direction Communication and the Internet: Computer Networks

Network Topologies: Ring Here are the advantages and disadvantages of this network Advantages Disadvantages Extra devices do not affect the performance of the network The whole network will go down if the medium or a device goes down Easy to add extra devices (as we plug the output of one device into it, and it into the input of another) Due to it being a closed loop, the whole network needs to be shut down to add or remove devices Can be difficult to locate faults on the network More expensive than a Bus network (as more cabling is needed to complete the ring) Communication and the Internet: Computer Networks

Network Topologies: Mesh These networks come in two types Fully connected – every device can connect to every other device Partially connected – devices are connected to a few, not all, devices Very fault tolerant (as communications can be routed around different devices) Best example of this network is the Internet Communication and the Internet: Computer Networks

Network Topologies: Mesh Here are the advantages and disadvantages of this network Advantages Disadvantages Very fault tolerant (especially when fully connected) Difficult and expensive to install when physically wired High performance (as each device is likely connected to multiple other devices) Difficult to manage due to the number of connections within the network When used wirelessly, each device extends the range of the network Communication and the Internet: Computer Networks

Communication and the Internet: Computer Networks Wired and Wireless We mentioned that mediums come in wired or wireless forms before Wires connections (using cables) often come in two forms for networks Copper cables (used for transmitting electricity) Fibre-optic cables (used for transmitting light) Fibre-optic cables allow for a much faster rate of transmission than copper cables Communication and the Internet: Computer Networks

Communication and the Internet: Computer Networks Wired and Wireless Wireless connectivity involves using devices to transmit and receive radio waves At different frequencies Need to use a techniques to understand how to read and send these waves Common techniques include WiFi and Bluetooth Wireless mediums allow networks to be constructed through obstacles and over hard-to-wire areas But can leave communications vulnerable to interception Communication and the Internet: Computer Networks

Communication and the Internet: Computer Networks Wired and Wireless Let’s compare these two types of medium Wired Wireless Very fast (especially fibre-optic) over longer distances, and less susceptible to interference Transmission can get slow (especially if obstacles interfere with the transmission) Not easy to intercept data (as it is contained within a physical cable) Easy to intercept data (as it is released ‘out in the open’). Data can be encrypted to help ease this problem Expensive to install and configure (as physical cables are needed) Cheap to install (as no cables are required) A limited range of devices can connect on a wired network (as they need the correct cable type) Allows for more varied devices (like mobile devices) to connect (as they only need to support the wireless technique used) Communication and the Internet: Computer Networks

Communication and the Internet: Computer Networks Network Speeds As data is being sent over a medium on a network, different networks and mediums will have different speeds of transmission These speeds are measured (typically) in bits per second (bps) This is NOT bytes per second (which would be B/s) Transmissions can range from kilo, mega, and giga bits per second This is kbps, Mbps, and Gbps respectively If we want to convert to bytes, we need to divide by 8 Communication and the Internet: Computer Networks

Communication and the Internet: Computer Networks A medium has a transmission speed of 6Mbps. We want to download a 30MB file. How long does it take? How fast is a 0.5Gbps transmission speed in MB? A 650MB file took 2 minutes to download. What is the speed of transmission on the network? Communication and the Internet: Computer Networks