Network Basics: Chapter One: Explaining the Network
Networks and the impact on daily life
It is hard to imagine a time when there was no access to the Internet. We use Google for research purposes without a second thought, online shopping, video communications (in both a business and personal use). Yet this process only came into being in 1989 when Tim Berners-Lee invented the World Wide Web (www). Networks, however, date back a lot further than 1989 (I do not intend to do a ‘timeline’ of networking but may mention some of the more relevant dates).
The availability of information and the resources that can be accessed over the Internet is increasing every day, these are just a few examples of what you can do;
• Share information, photographs, videos with friends, family, or business partners.
• Schoolchildren, who live in remote areas, can get access to their schoolwork by using virtual classrooms.
• Watch films or missed television programmes at your convenience.
• Use instant Messaging (IM), email or video to keep in touch with friends or family.
• Play online games with friends who might live in different countries.
• Use the online weather services to help in planning a day out.
• Plan a journey using online maps and find out where the worst congested areas are.
• Pay bills or view your bank balance.
The range of activities that can be utilised over the Internet is only limited by the imagination of the many trendsetters that are constantly coming up with new innovations.
Developments in technology has the power to transcend the physical boundaries that were once an almost impossible obstacle to overcome. For example, video conferencing means you can hold business meetings at any time with partners or customers in different countries, which means time zones or the need to travel vast distances is no longer an issue. Networks are also changing the way we go about our life, they affect the way we learn, communicate, work and even the way we spend our leisure time.
Learning
To provide a good education you must be able to engage the student in such a way that makes potentially ‘dry’ and dull subjects more interesting. In the past, there was only the teacher and a series of text books to learn from and sitting through one of these classes, where you write everything down from a board at the front of a classroom, is one of the most tedious experiences you can imagine, which results in many, if not all, of the students quickly losing all interest. However, a dependable network can deliver the kind of education that will enliven the dullest of subjects. This type of teaching can;
• Provide a virtual classroom
• Deliver video content when needed
• Allow Collaborative learning
• Support mobile learning
Students who cannot get to their place of education, because of adverse weather conditions or perhaps they live in a remote location can now gain access to their course material. Online learning, which is also known as e-learning, has overcome geographical obstacles, and greatly improved the opportunity for everyone to have access to a decent education.
The e-learning course can be delivered through text (e.g. downloading .pdf documents), they can click on links to material stored on a server. They can get audio (podcasts) or video at any time. The student can also use online forums and message boards to discuss any problems with the teacher or classmates, they can even talk to students in different countries.
You can combine both the traditional ‘go-to-school’ style of learning with the ‘at home’ e-learning model, which is known as Blended Learning. This allows the student to do the curriculum schoolwork at home and do the projects (or homework) in the class, which allows for more one-on-one help for students who need it. All this is possible due to network delivered course materials.
Communications
The true power of the Internet is the way it has shaped our methods of communications. It has made the world seem a smaller place within the context of the way we communicate with each other. These are just a few of the forms of communications to make use of the Internet;
• Instant messaging (IM) and texting: both IM and texting provide instantaneous or real-time communication between two or more parties. Numerous IM and texting programs include elements like file-transfer for instance. Whereas texting offers only a text-based method of communication IM applications can include audio and video as well as text-based.
• Social media: known as social networking these types of sites, the most obvious one being Facebook, are for people to share their personal lives with friends, family, or the global community at large. You can create your own page and invite people to share their experiences or thoughts with you. It is also a way for businesses to get their message across, although many people view companies as unethical that use social media to promote their business interests.
• Collaboration tools: known as groupware collaboration tools allow two or more individuals access to projects, which they can edit. Google docs, Microsoft’s OneDrive are examples of ‘cloud storage’ where files can be stored and then synchronised for easy access. Wikis, a Hawaiian word meaning fast, is another example with Wikipedia being one of the most popular.
• Podcasting: a podcast is an audio-based medium. People record their information and store it on a website, a Wiki-page for instance, then other people can then access or download it to their device.
• Peer-to-peer (P2P) file sharing: this means that people can share files by downloading a P2P application, such as Gnutella, which means that each end-user (client) can share files directly instead of the files being stored and accessed on a centralised server.
Work
Probably the most significant change that networks have impacted on our daily lives is the way we
go about our work. Many employees now work from home or people who used to have to report to their place of work to receive their work orders can now receive them online. When engineers are onsite and require parts, they can order them using a mobile device, directly from their suppliers and pick them up immediately. This eliminates the need for an engineer to return the next day.
Employers can utilise networks for training and skills updating for their employees. This means that an accurately targeted training regime can be used to train/retrain specific employees. This leads to a huge financial saving, because the employees can be trained in-house rather than expensive conventions.
Leisure
The evolution of the Internet has revolutionised the way we spend our leisure time. The original game consoles, connected directly to the television or monitor, was a stand-alone device, but with the advancements in the Internet the game console has become a gateway for players to sign up to worldwide gaming sites and compete with other online players all over the world.
Music and film streaming means that you can download your songs, films, and TV programmes to watch when it is convenient. If you prefer reading then you can purchase an e-reader, such as a kindle, and download hundreds, if not thousands of books to take with you on holiday thus eliminating the need to carry bulky paperback/hardback books with you.
Supporting Communication
There are many ways to communicate and in many different situations. We create a set of rules, which in the world of networking are called protocols, which are agreed upon before the communication begins. In the case of people communicating with each other a set of rules or protocols must be established to complete a successful session. Amongst these protocols are the following;
• Identification of the caller and the recipient
• A mutually pre-arranged communication method, e.g. person-to-person, telephone, a letter or the use of images.
• A language shared by both parties
• An agreed time to initiate contact and sometimes even the duration
• Affirmation or acknowledgement needs
The rules of communication may differ in different scenarios. If the communication considered to be important then an acknowledge that the message has been received might be required, while other, less important communications may not necessitate an acknowledge. These very same practises are followed in communicating over a network.
Quality of Communication
A successful communication session is defined when the context of the message sent has been received and understood by the recipient. In sending the data over a network the same conditions are met for a successful communication, known as a session. Data that travels over the network, however, can be adversely affected by factors that can either internal or external.
External QoS Factors
External quality of service (QoS) factors that impinge on the data moving across the network relate to the intricacy of the network and with the number of devices connected to the network that the data must go through from start to finish. Examples of some of the factors include;
• The quality of the path from the source to the destination
• The number of times the data is transformed from one form into another
• The number of times the data must be rerouted or readdressed
• The amount of traffic (data/messages) transmitted across the network at the same time
• The length of time permitted for successfully completed transmission
Internal QoS Factors
Internal QoS factors that affect the integrity of the data message relate to the character of the message. The actual type of message may differ in its intricacy and its importance. Simple and uncomplicated messages are easier to comprehend than more complex ones. Sensitive data need more attention to guarantee the integrity of the message by the recipient. Internal factors include;
• The size of the message
• The intricacy of the message
• The importance of the message
Messages carrying a lot of data may be held up at various sections of the network. A message that is less sensitive in nature could be discarded altogether if the network traffic is too high. For the network to be able to operate smoothly and efficiently these internal and external factors must be managed properly. Network hardware and software is being constantly improved to ensure the network can meet the needs of the modern world.
Converged Networks
Networks need to constantly evolve to meet the requirements of the modern world. In the early days, the network’s major role was to exchanged data between computer systems. Telephone and television worked independently of the data network. This required that these separate services required a network dedicated to delivering them. This also meant different technology, channels to convey their own signal. The networks also had their own set of protocols or rules and standards for the services to function properly.
As an example, if we take a hospital, built in the ‘70s, then look at how the services were then compared to how they are now, it will illustrate just how far networking has advanced. A room in this hospital would have had separate networks for data, telephone, and video. These networks were disparate, which is to say that they were unrelated and unable to communicate with each other.
Developments in network technology now means that we can merge these disparate networks onto a single platform, which is known as the converged network. The converged network, unlike the example we used here, can distribute voice, video, text, and graphics using to many diverse kinds of devices over the same network. The converged network platform enables access to a variety of different ways for people to interconnect. A converged network has many kinds of devices connected to it, such as;
• PCs
• Smart phones
• Televisions
• Tablets
Even with these devices connected, the network operates with the same set of protocols for all these devices.
Reliable Network
The Supporting Network Architecture
A network’s infrastructure is comprised of an extensive range of applications, services as well as supporting different kinds of cabling and devices. There is a term called network architecture which describes the technology that supports the infrastructure including the services and protocols that transport the data across the network.
There are four fundamental features that underpin the architecture needs to address in order to satisfy end-user expectations;
• Fault tolerance
• Scalability
• QoS
• Security
Fault Tolerance
For the millions of users who rely on the Internet there is an expectancy that it will always be available whenever they need it. This would necessitate that the network architecture be fault tolerant. A network that incorporates fault-tolerance is one that reduces the adverse effects of a failure would have on the least number of the devices attached to the network. It is also constructed in such a way that a fast recovery is at hand if a failure occurs. A fault-tolerant network relies upon multiple paths from the source to the destination. This means that if one path fails the data can then be rerouted through an alternative path, this is known as redundancy.
Circuit-Switched, Connection-Orientated Networks
To demonstrate redundancy, and why it is needed, an example on how an old-fashioned telephone system functioned will be used.
When a call is made the first step is called the setup. This procedure identifies the switching location of both the source and the destination. A circuit or temporary path is created, which lasts for the length of time of the call. If the link or the device failed then the call would be dropped. If the call was to be reconnected then the whole process would have to be repeated. This process is known as a circuit-switched process.
A lot of circuit-switched networks prioritise to connected circuits sacrificing requests for new circuits. A newly created circuit is launched then this circuit will remain intact even if communication has stopped. It will stay connected until disconnected by either the source or destination device. As there a finite amount of available circuits then it is possible that all circuits are in use and other communications cannot be setup. The cost and resources needed to add enough circuits to meet demand are the main reason circuit-switched technology was not suited to the Internet.
Packet-Switched Network
In pursuit of a network that is a better fault tolerant Internet the Internet designers explored Packet-Switched Networks. The idea behind this is that a message can be split into several blocks. Each block would contain the information required to identify the source and destination. This information inside these blocks, called Packets, can be transported through the network, along different paths or circuits, then be re-built at the destination.
The nodes (a node is any device connected to the internet) on the network do not know what kind of content these packets contain. The only information in the packet that an intermediate device (intermediate devices help the data travel through the network, e.g. a switch or a router) uses is the source and destination address, which is called an IP Address (Internet Protocol address). An example of such an address would be 192.168.90.1 and the format of this address is known as a dotted-decimal.
When a packet is transported over the network it passes through intermediary devices, such as a switch or a router, in which a choice is made concerning which path the packet should take on its way to its destination. If a path, which has been used before, is not obtainable then the intermediate device can find the packet an alternative path. The complete message is broken up into several different packets, so if any of the packets are lost or dropped, then they can be re-sent and usually, the destination device won’t even be aware that any of the packets have been re-addressed or re-routed.
Summary
• Connection-oriented – needs a connection to be established before any messages can be sent. This process is frequently called a "reliable" network. It can guarantee that the message will be received in the correct order.
• Connectionless – does not need a connection between the source and the destination. The source just starts sending the packets (also called datagrams) to the destination. This service does not provide the reliability that the connection-oriented service does.
Scalability
There are thousands of new users connecting to the Internet every week. So that the Internet can support this growth it must be scalable. A scalable network needs to be able to grow and develop to meet the needs of these new users in such a way that the expansion does not has a detrimental effect on the performance of the Internet. The Internet is designed with a structured, hierarchical format. This design means that network traffic that is bound for local or regional services can avoid being routed through a centralised area for distribution. Shared services can be replicated in different regions and so keep traffic away from the higher-level backbone networks.
Scalability can refer to the capability to take new products and applications. The protocols and standards used by the Internet are not governed by a single institution, but the various network provides collaborate to follow these standards and protocols. By observing to the standards means that the companies who develop the hardware and software are left free to focus on the development of their products and can be assured that there will not be a problem with combability issues on the network infrastructure.
New Protocols and standards are being constantly developed to keep up with the rapidly expanding pace at which Internet applications and services are being implemented. This means that the existing Internet structure might not match the leaps and bounds in demands placed on it by the ever-increasing number of users.
Quality of Service
Quality of Service
An important necessity for the modern network is a service called Quality of Service or QoS. The advent of new applications, offered to users, such as voice and instant live streaming video put higher expectations for the reliability and quality of the network for these services.
Although packet-switched networks cannot ensure that the data will arrive on time, in the right order or even arrive at all, networks must deliver an expected, gaugeable, and failsafe service.
There is also a need to be able to manage the vast amount of data, travelling over the network, efficiently, and avoid log-jams or congestion on the network. This can happen when the amount of data transmitted over the network, within a limited period, which is measured in ‘bits-per-second’ or bps, (this measure is called the network’s bandwidth) outstrips the available bandwidth.
When this type of problem happens the devices on the network ‘queue’ or hold the data packets in the memory until there are enough resources available to begin re-transmission of that data. However, the problem is magnified by the packets that are being held in the memory, because new packets cannot start to be delivered until this backlog is cleared. This results in some packets being dropped’ or discarded when the memory becomes full.
One of the ways to run and maintain an efficient network to a high standard is by the implementation of QoS. The organisation of how packets are managed is fundamental in achieving this high standard. One way of achieving this is through a process called classification.
A combination of communication features and the importance allocated to the application would aid the successful transmission of data. Data, which has the same classification has the same rules applied to them, e.g. voice communication, which is time-sensitive, would have a different classification applied to it rather than non-time-sensitive data, such as file transfers. Here are some examples of the type of communications that would require some form of classification;
• Time-sensitive communications: VoIP (Voice over Internet Protocol) and video communication would require priority.
• Non-time-sensitive: the retrieval of web pages or email would not require priority.
• High-importance to organisation: business transactions, control of production would need priority.
• Undesirable communication: block completely or lessen priority to activities like peer-to-peer file sharing or unnecessary live-streaming video.
Network Security
The evolution of the Internet, from its beginning as a distribution hub for mostly education and governmental organisations to today’s provider for the means for the transmission of sensitive personal and business communications, requires the complete overhaul of the networks’ security. The network’s structure, services, and data, within the various network devices, are essential to both individual or business ventures. Should the integrity of the network infrastructure be compromised then the consequences could be catastrophic, such as;
• Network breakdowns could be costly to businesses if they cannot complete their transactions across the internet.
• Theft of what is known as intellectual property, which could be new technology or research, and used by a rival company.
• Somebody’s’ personal details, e.g. bank or credit card details, login details such as passwords.
• Irretrievable loss of data, which could lead to a damaged reputation for the company whose job it is to ensure the safe storage of other people’s data.
There are two fundamental types of network security. They are known as network infrastructure security and information security.
Network Infrastructure Security
This comprises of two factors, the first is the strictly controlled access to the hardware devices that provides the connection to the network and the prevention of unauthorised access to the network operating system on those devices.
Information Security
This is the protection for the data and information that is stored in the packets that travel across the network and the data kept on those network devices. The procedures adopted in securing a network should avoid the following from occurring;
• Unauthorised disclosure
• Theft of information
• Unauthorised modification of information
• Denial of service (DoS)
To attain the aims of network security, there are three prime necessities;
Ensuring Confidentiality: Data privacy means that only the planned and approved receivers – individuals, processes, or devices – can access and read data. This is realised by having a robust system for user authorisation, imposing passwords that are hard to guess, and needing users to change their passwords regularly. Encoding or encrypting data, so that only the intended recipient can read it, is also part of confidentiality.
Maintaining communication integrity: To ensure data integrity gives the client confidence that the data has not been changed in transmission. Compromised integrity can occur when, accidentally or deliberately, the data has become corrupted. Data integrity can be achieved by authenticating the sender and by using techniques to ensure that the packet has not altered during transmission.
Ensuring availability: This means having dependable access for legitimate users to gain access to the resources they require over the network. Network devices such as firewalls, which can be either hardware or software, combined with anti-malware software can safeguard the system against possible security breaches. Installing redundant features on the network, with the fewest individual points of failure, can lessen the effect of possible threats.
LANs, WANS, and the Internet
Components of the Network
The data that travels across the network, from the source device to the destination, can use a pathway as basic as a single cable connecting the two devices together directly. Alternatively, the pathway could be a complicated and huge network, such as the Internet, which literally covers the entire planet. The infrastructure that carries the data can be broken down into three separate parts;
• End devices
• Intermediary devices
• Network media
The devices and media, or the hardware, of the network consists of components such as, PCs, laptops, switch, router, wireless access point, and including the cabling that connects the network and the devices together. Network services and procedures are used by components on the network and are the programs which make communication on the network possible.
Network services and processes
A network service responds to a request, from a user, for information. These services include routine, every-day applications such as email and web hosting services. A network process provides the functionality that directs and moves the messages or information across the network.
End devices
End devices are the most common and recognisable hardware items on the network. Any device on the network is commonly known as a node. End devices are usually known as hosts. These hosts provide the user with the means to communicate with the network, referred to as an interface. This is a few examples of end-devices;
• Computers (work stations, laptops, file-servers, web-servers).
• Network printers.
• VoIP phones.
• Telepresence endpoints (video conferencing).
• Security cameras
• Mobile handheld devices (smartphones, tablets, PDAs, credit card readers, barcode readers).
A host device can be either the source or destination device for the message over the network. Each of these host devices is identified by a different address. A host will use the address to identify destination counterpart.
On more modern networks a host can act as a client, a server, or a combination of both. The software installed on the host will define its purpose on the network. Servers are hosts which have software on them and this software provides the data and services requested by the source host, such as mail or web pages. Clients are the hosts that make the requests from the server.
Intermediary devices
Intermediary devices provide the connect for the client and the server to communicate with each other. These devices could be described as ‘behind-the-scenes’ devices, because they work in the background and their job is to guarantee connectivity across the network. They are also responsible for the connection of the hosts to the network. They can also connect a number of networks, which would form an internetwork, and the biggest example of this is the Internet.
Intermediary devices consist of;
• Network access devices (switches and wireless access points).
• Internetwork devices (routers).
• Security devices (firewalls)