NETWORKS

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Networks

A network is two or more computers - or other electronic devices - that are connected together for the purpose of communication. They are connected by a wired medium such as cables, or by a wireless medium such as Wi-Fi.

A computer or device that is not connected to a network is called a stand-alone.

Many different types of computer are connected to some form of network. As well as desktop computers and laptops, other devices such as smartphones, smartwatches, fitness trackers, car engine management systems, internet-enabled fridges, intelligent personal assistants and media boxes can all be connected.

Advantages of using networks

Networking computers together brings several benefits:

software and file sharing - users can share software and files with other users

hardware sharing - users can share hardware, such as a printer

communication - users can communicate via email, chat, or by video

roaming access - users can sign in to any computer on the network and access their files

On larger networks, such as those used by businesses and schools, there are additional benefits:

centralised maintenance and updates - network managers can apply software updates across a network, removing the need for users to have to do so

centralised security - anti-virus software and firewalls can be implemented across a network, helping to protect user files from risks

user monitoring - network managers can monitor what users do on a network

levels of access - different users can be given different access rights, giving network managers the ability to restrict groups of users access to certain files while granting permission to specific users

Disadvantages of networks

Networking computers together also brings several problems:

cost - additional equipment is needed to allow computers to communicate

management - larger networks require management by specialist staff such as a network manager

spread of malware - viruses and other forms of malware can easily spread across an improperly secured network

hacking - once a device is connected to another device, it is possible that data may be accessed without the device owner's permission

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Local area networks and wide area networks

There are two classifications of network:

local area networks - LANs

wide area networks - WANs

Key fact

A LAN is geographically confined to a single site. A WAN is spread over a wide geographical area.

LANs

A LAN is a network that is geographically confined to a single site. Examples include networks employed by small businesses, small organisations, schools, colleges, universities and in homes. LANs are connected by a wired medium such as cables, or by a wireless medium such as Wi-Fi.

LANs are owned and maintained by the organisation.

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WANs

A wide area network (WAN) is a network that is spread over a wide geographical area. It can cover more than one site, or be spread across a country, or even the world. WANs are usually made up of two or more LANs.

Organisations that have more than one office or branch, such as banks, tend to use a WAN. The WAN allows the head office to communicate and share data with the sub-offices and branches. Communication is done through national telephone infrastructures or via wireless transmission. Each office or branch has its own LAN that is connected to others using the WAN.

The internet is essentially a huge, international WAN.

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Wired and wireless connectivity

Networks can be classified as wired or wireless. A wired network uses copper cable or fibre optic cable to form the connections between the networked devices (nodes). Fibre optic cables have a greater bandwidth so transfer speeds are faster. Wireless networks tend to use radio signals as their communication medium but could use other wireless methods such as infrared light.

Key fact

A wireless network usually uses radio signals to connect nodes. A wired network uses copper cables or fibre optic cable.

Advantages and disadvantages of using wireless networks

Using a wireless network brings many benefits to a user:

new nodes can easily be added without interruption to the network

users can move around freely and still stay connected

However, there are disadvantages to using a wireless network:

Radio signals have a limited range.

Radio signals can suffer from electromagnetic interference from other devices and even other radio signals. They can also be blocked by walls, leading to dead spots where no signal can be found.

Each wireless access point (WAP) only has so much bandwidth to share among connected nodes. The greater the number of nodes that are connected, the less bandwidth each receives and the slower communication becomes.

Radio signals pose a security risk as they can be intercepted by unauthorised users. To overcome this problem, messages need to be encrypted.

Wireless networks in use

Wireless networking has seen an increase in popularity because it is easy to connect a node to a network. Many different types of device, such as laptops, tablets, smartphones, interactive TVs, media centres, games consoles and security cameras, can easily connect to a network when needed, without having to run a cable to each device.

Wireless networks give freedom of movement. They are therefore popular in homes, schools and any organisation that has a constantly changing number of connected nodes.

Advantages and disadvantages of using wired networks

Using a wired network has a number of advantages:

generally faster data transfer compared to wireless networks

much less likely to suffer from interference than wireless networks

more difficult for unauthorised users to intercept data

However, there are disadvantages to using a wired network:

they are expensive to install or reconfigure

users can’t instantly move a device from one location to another as there may not be a network connection available

Wired networks in use

Wired networking is still widely used in businesses or schools where devices such as desktop computers are unlikely to need to be relocated very often. Tasks that require large amounts of data to be accessed from servers - such as commercial video editing - are likely to be quicker using a wired network as the bandwidth available to each connected device is much larger.

Many organisations run both a wired and wireless network, allowing flexibility on the types of device used depending on the need of the user.

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Network data speeds

Network data speeds are measured in bits per second. These numbers are huge so they are measured in millions of bits per second - Mbps - and billions of bits per second - Gbps:

1 Mbps = 1,000,000 bits per second

1 Gbps = 1,000,000,000 bits per second

Calculate how long it would take to transmit a file. Use the formula:

time = size of file (in bits) / network speed (in bits)

So, for a 4 kilobytes (KB) file and a network transmission speed of 10 Mbps:

Size of file:

1 KB = 1,024

4 KB = 1,024 x 8 x 4 = 32,768 bits

Speed of network:

10 Mbps = 10 x 1,000,000 = 10,000,000 bits per second

Time to transmit:

32,768 / 10,000,000 = 0.0032768 seconds

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Network data speeds

Network data speeds are measured in bits per second. These numbers are huge so they are measured in millions of bits per second - Mbps - and billions of bits per second - Gbps:

1 Mbps = 1,000,000 bits per second

1 Gbps = 1,000,000,000 bits per second

Calculate how long it would take to transmit a file. Use the formula:

time = size of file (in bits) / network speed (in bits)

So, for a 4 kilobytes (KB) file and a network transmission speed of 10 Mbps:

Size of file:

1 KB = 1,024

4 KB = 1,024 x 8 x 4 = 32,768 bits

Speed of network:

10 Mbps = 10 x 1,000,000 = 10,000,000 bits per second

Time to transmit:

32,768 / 10,000,000 = 0.0032768 seconds

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Network layering

In networking, layering means to break up the sending of messages into separate components and activities. Each component handles a different part of the communication. This can be referred to as a protocol stack. The Transmission Control Protocol/Internet Protocol (TCP/IP) is a protocol stack used when connecting a device to the internet.

There are four layers to be considered:

Application layer - encodes/decodes the message into a form that is understood by the sender and the recipient devices using protocols like HTTP, file transfer protocol (FTP) and SMTP.

Transport layer - breaks down the message into small pieces called packets. Each packet is given a packet number and the total number of packets. The recipient uses this information to assemble the packets in the correct order. It also allows the recipient to see if there are any missing packets.

Internet layer - adds the sender’s IP address and that of the recipient. The network then knows where to send the message, and where it came from. This is sometimes called the network layer.

Link layer - enables the physical transfer of packets between nodes on a network, and between one network and another.

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Layering enables standards to be developed, but also to be adapted to new hardware and software over time. For example, different software packages (applications) may use the same transport, internet and link layers but may each use their own application layer. The way the program encodes the message changes - the rest of the communication method remains the same.

Key fact

Layering allows standards to be put in place and adapted as new hardware and software is developed.

IP addressing

At the internet layer, the IP - Internet Protocol - part of the TCP/IP protocol stack needs each node to have an IP address assigned to it. This address consists of four sets of up to three digits, each with a maximum value of 255. Each set is separated by dots. An example is:

192.168.0.254

When a node wants to send a message to another node, it uses the recipient node's IP address as the destination.

The method of addressing using four sets of digits held in 32 bits is called IPv4. When IPv4 was devised, the range of addresses it allowed was deemed to be sufficient. However, the huge increase in internet-enabled devices led to IPv4 running out of addresses. A new version - IPv6 - has been introduced, significantly increasing the number of possible addresses to trillions. IPv6 addresses are held in 128 bits.

Transmissions over a network can be extremely large. To send a large message in one go can be impractical, as both the sending and receiving node are tied up with one communication.

Layering enables standards to be developed, but also to be adapted to new hardware and software over time. For example, different software packages (applications) may use the same transport, internet and link layers but may each use their own application layer. The way the program encodes the message changes - the rest of the communication method remains the same.

Key fact

Layering allows standards to be put in place and adapted as new hardware and software is developed.

IP addressing

At the internet layer, the IP - Internet Protocol - part of the TCP/IP protocol stack needs each node to have an IP address assigned to it. This address consists of four sets of up to three digits, each with a maximum value of 255. Each set is separated by dots. An example is:

192.168.0.254

When a node wants to send a message to another node, it uses the recipient node's IP address as the destination.

The method of addressing using four sets of digits held in 32 bits is called IPv4. When IPv4 was devised, the range of addresses it allowed was deemed to be sufficient. However, the huge increase in internet-enabled devices led to IPv4 running out of addresses. A new version - IPv6 - has been introduced, significantly increasing the number of possible addresses to trillions. IPv6 addresses are held in 128 bits.

Transmissions over a network can be extremely large. To send a large message in one go can be impractical, as both the sending and receiving node are tied up with one communication.

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Network topologies

Any device connected to a network is referred to as a node. All nodes are connected to the network either by cables or wirelessly.

A network's topology is the arrangement, or pattern, in which all nodes on a network are connected together. The major network topologies are:

bus

ring

star

mesh

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Bus networks

In a bus network all the nodes are joined to one cable - the bus. At each end of the cable, a terminator is fitted to stop signals reflecting back down the bus.

Advantages and disadvantages of using a bus topology

The advantages of a bus topology are:

it is easy to install extra network devices

it is cheap to install as it doesn't require much cable

The disadvantages of a bus topology are:

if the main cable fails or gets damaged, the whole network will fail

as more nodes are connected, the performance of the network will become slower because of data collisions

every node on the network receives all of the data sent on the network - this is a security risk

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Star networks

In astar topology all nodes indirectly connect to each other through one or more switches or hubs. A hub broadcasts a message across the whole network, whereas a switch sends the message to the intended recipient only. The switch or hub acts as a central point through which all communications are passed. Star topologies are used in many networks, large and small.

Large networks using a star topology are usually controlled by one or more servers. Hence, the client-server model usually uses a star topology. However, peer-to-peer networks can also have a star topology. Even though no single computer controls the network, all communications still pass through the central switch.

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Advantages and disadvantages of using a star topology

The advantages of a star topology are:

Each node is separately connected. Therefore, the failure of one node or its link, also known as transmission media, does not affect any other nodes.

New nodes can be added to the network simply by connecting them to the switch.

Star networks tend to have higher performance, since a message is passed on only to its intended recipient.

The disadvantages of a star topology are:

the whole network fails if the switch fails, since no node can communicate

a wired star topology requires a lot of cable - in a large network this can be expensive

Star topologies in use

Star topologies tend to be found in large organisations, such as educational establishments and businesses, where high performance is a must.

They are also found in home networks, especially those that are wireless. In this case, a router with a wireless access point (WAP) provides the central connection for all nodes.

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Mesh networks

In a mesh topology there is no central connection point. Instead, each node is connected to at least one other node and usually to more than one. Each node is capable of sending messages to and receiving messages from other nodes. The nodes act as relays, passing on a message towards its final destination.

There are two types of mesh topology:

fully connected mesh topology

partial mesh topology

In a fully connected mesh, each node is directly connected to every other node. This enables a message to be sent along many individual routes.

In a partially connected mesh, not all nodes are connected directly to each other. A partially connected mesh therefore has fewer routes for a message to travel along than a fully connected mesh but is simpler to implement.

Wired mesh networks tend to be uncommon, mainly because connecting all nodes to all other nodes is expensive and impractical. However, wireless mesh networks are increasingly being used since it is far simpler and cheaper to connect using radio signals.

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Advantages and disadvantages of using a mesh topology

The advantages of a mesh topology are:

messages can be received more quickly if the route to the intended recipient is short

messages should always get through as they have many possible routes they can travel along

multiple connections mean - in theory - that no node should be isolated

multiple connections mean each node can transmit to and receive from more than one node at the same time

new nodes can be added without interruption or interfering with other nodes

The disadvantages of a mesh topology are:

fully connected mesh networks can be impractical to set up because of the high number of connections needed

many connections require a lot of maintenance

Mesh topologies in use

Mesh topologies are used where the reliability of network communication is very important:

military organisations often use mesh topologies to avoid breakdowns in communication

cities are increasingly using wireless mesh networks to help monitor traffic flow, sewage treatment and to help control street lighting

emergency services, such as police and fire services, also use wireless mesh networks to ensure that communication is reliable

some utility companies who provide gas and electric use mesh networks to enable smart meters to send readings automatically

the internet is a huge partially connected mesh network