By the end of this unit, you will be able to complete the following tasks:
- Describe the basic structure of a network.
- Identify network types.
- Describe the role of protocols in communication over networks.
- Delineate the methods of process communication between client/server and the peer-to-peer model.
- Discuss the features of cluster, grid, and cloud computing.
- Identify types of network hardware.
- Describe the tiered internet architecture.
- Explain internet addressing.
- Identify types of malicious software.
- List tools supporting protection and risk management.
Sharing information and resources through linked computer systems is called networking. Networks enable users to exchange messages and share resources, such as printers, software packages, and data storage devices. Network software and its configurations manage the operations of the network interfaces. Networks are deployed using different paradigms, hardware, and software, and they are susceptible to malicious attacks.
In this section, you will survey the types of networks and their applications, the communication protocols, and the architectures and their applications. You will learn about common protection and risk management strategies to protect against malicious attacks. You will explore how to effectively design, manage, and secure networks.
Network Types
Networks are commonly classified based on the physical distance between components (geographic scope). According to this classification, there are three major categories of networks: personal area network (PAN), local area network (LAN), and wide area network (WAN).
Figure. Example of a PAN.PAN
A PAN is normally used for short-range communications, within a few feet, such as wireless headphones to a smartphone or a wireless mouse to a PC.
Figure. Example of a LAN.
LAN
LANs consist of a collection of computers in a single building or building complex. For example, the computers in a manufacturing building may be connected via a LAN.
Figure. Example of a WAN.
WAN
WANs link systems over a greater distance, including machines on the opposite sides of the world.
Other Classifications
Other classifications of networks consider whether the network’s internal workings are based on designs that are in the public domain (open network) or on designs owned or controlled by third parties (closed or proprietary networks). Open network designs are freely circulated and are often more popular than proprietary designs that are restricted by license fees and contracts. The internet is an example of an open network. Communication over the internet is governed by an open collection of standards known as the TCP/IP protocol. Anyone is free to use these protocols without paying fees or signing license agreements. In contrast, an IT company might develop proprietary systems for which it chooses to maintain ownership rights, allowing the company to draw income from selling or leasing its system.
Figure. Example of a bus network.
Bus
Yet another classification of networks considers the topology of the network or the pattern in which the machines are connected. Four common topologies are bus, star, ring, and mesh. Bus and star network topologies are the most common. In a bus network, the machines are connected to a common communication line called a bus.
Star
Figure. Example of a star network.Star networks have a single machine serving as a central point to which all others are connected.
Figure. Example of a ring network.
Ring
Ring topologies connect directly to each other as a peer.
Mesh
Figure. Example of a mesh network.Mesh connects every device in a network to every other device; mesh networks enable redundancy while also introducing significantly more network traffic.
Alternatively, a network could use a hybrid of these topologies.
The bus topology became popular in the 1990s when it was implemented under a set of standards/protocols known as the Ethernet. The star topology has roots as far back as the 1970s when it evolved from the idea of a large central computer system servicing many users at once. The star topology is used today in wireless networks where communication is carried out via radio broadcast to a central machine called the access point (AP).
Protocols
Networks rely on protocols to govern communication. Without protocols, the computers in a network might try to transmit messages at the same time or fail to provide needed assistance to other machines. Using protocols, vendors are able to build products for network applications that are compatible with products from other vendors.
Methods of Process Communication
Interprocess communication allows the activities or processes on different computers within a network to coordinate actions and complete tasks.
Client/Server Model
Figure. Example of communication in client/server networking model.The client/server model is a popular convention used for interprocess communication. The basic roles played by the processes are categorized as either a client making requests or a server satisfying client requests. An early application of the client/server model appeared in networks connecting clusters of offices with a single printer available to all computers. The printer (also known as the print server) is the server, and the machines are clients requesting printed documents. Early networking systems also used file servers that accepted requests for company data that were centrally stored.
Peer-to-Peer (P2P)
Figure. Example of communication in peer-to-peer networking model.Peer-to-peer (P2P) is another model for interprocess communication. In this model, processers both request and provide service to each other. Instant messaging and interactive games played by users on multiple machines are both examples of the P2P model.
A new generation of P2P services arose to fill the void, expanding the range of sharable file types and further decentralizing networks. The Gnutella protocol operates without any centralized server and allows for numerous software clients to be used for access, which makes it nearly impossible to shut down. BitTorrent, used commonly for distributing large video files, employs a “swarm” model, whereby files are downloaded in simultaneous pieces from multiple host computers. Newer services have established degrees of encryption and anonymity to protect users from legal action by copyright holders.
Distributed Systems
Interactions between computers via networks have become commonplace and multifaceted. Many modern systems, such as global information retrieval systems or computer games, are designed as distributed systems. Distributed systems execute software as processes on more than one computer.
There are several types of distributed systems.
- Cluster computing uses many independent computers to provide computation or services comparable to those of a larger machine. The cost of several individual machines can be less than a higher-priced supercomputer, with comparable performance. Cluster computing provides high availability as it is likely that at least one computer in the cluster will be able to answer a request even when others in the cluster are unavailable or broken down. In addition, clusters can balance loads by automatically shifting requests among the cluster members.
- Grid computing is a type of distributed system that is more loosely coupled than clusters but still works together as a system to complete large tasks. Grid computing typically includes specialized software to make it easier to distribute the workload and data among the machines in the grid.
- Cloud computing provides large pools of shared computers that can be allocated to clients as needed. Services such as Amazon’s Elastic Compute Cloud allow clients to rent virtual computers by the hour no matter where the associated computer hardware is located. Services such as Google Cloud and Google Apps allow users to collaborate or build web services without needing to know how many computers are working on the problem or where the relevant data is stored. Cloud computing provides reasonable guarantees for reliability and scalability while raising concerns about security and privacy.
Network Hardware
A network is a collection of two or more connected devices that can communicate with one another. Before we talk about the hardware that processes messages on a network, let’s start with the lowest level of components in a network: the transmission media. A transmission medium (the singular form of the word “media”) is simply a component that carries data from one network device to another. There are two types of transmission media: wired and wireless.
Transmission Media
Figure. Twisted pair cable.Data travels through a network using communication channels that connect the network components. Both wired and wireless networks require network media to transfer data. Twisted pair cables, coaxial cable, and optical fiber cables are common network media used in wired networks, while wireless networks use radio waves, microwaves, and infrared waves.
Twisted pair cables are the most widely used type of transmission media. Two common types of twisted pair cables are unshielded twisted pair (UTP) and shielded twisted pair (STP). STP cables consist of two separately insulated copper wires wound around each other, making them more expensive than UTP cables. The insulating sheath on STP cables protects the wires from things like neighboring unshielded cables and electromagnetic interference from fluorescent lights. Twisted pair cables come in various bandwidth capacities with a maximum segment length of 100 meters (328 feet).
Network Bandwidth
Network bandwidth is typically measured in megabits per second (Mbps) and gigabits (Gbps) per second. (Note the distinction between Mbps and MB. One megabit is equivalent to 1,000 kilobits, whereas one megabyte is equivalent to 1,024 kilobytes.).
| Category | Maximum Bandwidth |
| CAT1 | 1 Mbps |
| CAT2 | 4 Mbps |
| CAT3 | 10 Mbps |
| CAT4 | 16Mbps |
| CAT5 | 100Mbps |
| CAT5e | 1 Gbps |
| CAT6 | 10Gbps |
| CAT6a | 10Gbps |
| CAT7 | 10Gbps |
Table. Cable category and bandwidth
Coaxial Cables
Figure. Coaxial cables.
Coaxial cable is a shielded and insulated copper cable that is used in computer networks and to deliver cable TV services. First used commercially used in the 1940s, it is used for both baseband and broadband data communication services. The bandwidth of coaxial cables is about 80 times the bandwidth of twisted wires. Cable modems and televisions typically use coaxial cables.
Baseband is a signal at a very narrow frequency range on which data or information is superimposed and then transmitted. Examples include Ethernet LANs and serial cables.
Broadband is considered high-capacity transmission technologies that are used to transmit data, voice, and video across long distances and at high speeds. Examples include coaxial cable, fiber optic cable, and radio waves.
Fiber-Optic Cable
Figure. Fiber-optic cable.Fiber-optic cable uses the concept of reflection of light through a core made up of glass or plastic. The core is surrounded by a less dense glass or plastic covering called the cladding. Fiber-optic cables are able to transmit large volumes of data. Their bandwidth can provide up to 26,000 times the bandwidth of the twisted pair wires, at the time of this writing.
Wireless Transmission
The use of wireless transmission media is sometimes more convenient and practical than installing cables. Electromagnetic waves of different frequencies, such as infrared or radio waves, can be used to transmit data within a network with the use of Wi-Fi, Bluetooth, or even near field communication. These radio waves are what is used to carry radio signals far distances to other networked devices.
Many believe Wi-Fi stands for wireless fidelity. However, it is just a play on words according to the Institute of Electrical and Electronics Engineers (IEEE), and it was created by a marketing team. Wi-Fi adapters are commonly installed on mobile computer devices such as laptops, tablets, and smartphones. Wi-Fi adapters enable devices to connect to each other or to the internet. Each of these wireless transmission methods has its own protocols to identify how to connect and transmit or receive data. Each uses different frequencies, which makes it possible for data to travel over small and large distances. These wireless technologies are examples of wireless media that can exchange data, such as sending audio to a Bluetooth speaker, sending files from one PC to another, or making a payment with your smartphone at the grocery store through near field communication (NFC). Bluetooth supports distances shorter than 30 feet, while Wi-Fi devices can be accessed up to 300 feet away.
Combining Networks
Local Area Networks (LAN) can be connected to create a larger network and sometimes become Wide Area Networks (WAN. These connected networks can expand and increase communication and effectiveness of the organization. The following devices can be used to connect networks:
- Repeaters extend the range of cabling types so connections can be made by increasing the strength of the network signal. For example, if two twisted pair cabling networks are 500 feet apart, a repeater can be used to extend the 300 feet range of twisted pair cabling to 500 feet. Repeaters can be used on fiber and coaxial also.
- Bridges are used to connect to different types of network and provide management of the message. For example, a bridge can connect a twisted pair and coaxial network. The bridge analyzes the network message and will only bridge the network if a message is addressed to a device on the other side.
- Switches are used on LANs to reduce network traffic by management of network messages. Older devices would broadcast all messages to all devices on the LAN. For example, on a 100-device network a switch would only send one message to the destination device. This management example would create 99% less traffic.
- Routers are the device that makes the internet possible. A router connected to your LAN acts as gateway to the internet. (This device on your LAN can be also be called a Gateway.) Router manage network traffic by having a routing table of know devices. If a destination address is unknown to the Router, it will forward the message to another router. This analyze and forward process continues until the message reaches the correct address.
The Architecture of the Internet
The internet began as a research project in the early 1960s funded by DARPA (Defense Advanced Research Projects Agency). DARPA hoped to develop a method for linking multiple computer networks, allowing them to function as a single system unaffected by disasters degrading the performance of local components.
The Three Tiers of ISPs
Figure. The three tiers of ISPs.The individual networks comprising the internet are constructed and maintained by internet service providers (ISPs). ISPs are classified in tiers depending on the role they play in the overall internet structure.
Tier 1, at the top of the ISP hierarchy, is the least common type of ISP and serves as the backbone of the internet. Tier 1 ISPs consist of high-speed, high-capacity, international WANs that are typically operated by large communication companies.
Tier 2 ISPs are more common and regional in scope. Tier 1 and Tier 2 ISPs are essentially networks of routers that collectively provide the internet’s communication infrastructure.
Tier 3 ISPs (access ISPs) are typically independent internets, sometimes called intranets, operated by a single organization that supplies internet access to homes and businesses. The devices used to connect to the access ISP are called end systems or hosts. These include common internet devices such as PCs, laptops, and smartphones, but also devices such as cameras, automobiles, and home appliances. A variety of technologies are used to connect end systems to larger networks. Common connecting technologies are telephone lines, cables, and satellites.
Internet Addressing and Applications
Internet networking systems use addressing systems to assign a unique identifier to each computer in the network. The internet uses IP (internet protocol) addresses as unique identifiers. The internet used a 32-bit address pattern (IP version 4 or IPv4) to uniquely identify all of the internet components until we ran out of unique identifiers. Today we use 128-bit addresses (IP version 6 or IPv6) in addition to legacy IPv4 addresses.
The ICANN (Internet Corporation for Assigned Names and Numbers), a nonprofit organization that coordinates the internet’s operations, awards blocks of consecutively numbered IP addresses to ISPs. ISPs then assign a unique IP address to each machine within their region of authority.
IPv4 addresses are traditionally written in dotted decimal notation, with the bytes of the address separated by periods. An IPv4 address might look something like this: 192.207.177.103. IPv6 addresses are written in hexadecimal; an IPv6 address could look like this: 2001:DB8:12:34::1111.
While the dotted decimal notation works well for computers, people needed a different method of identification. An alternative system accesses machines using mnemonic names. This system is based on domains, a section of the internet operated by a single authority, such as a university or a business. The domain name of Western Governors University is wgu.edu. The suffix edu is a top-level domain (TLD) denoting an educational institution. Other top-level domains include com for commercial institutions, gov for government agencies, org for nonprofit organizations, tv for television stations, and so on. TLDs include two-letter country codes such as au for Australia and kr for Korea.
Just as the ICANN assigns batches of IP addresses to ISPs, every domain must be registered with the ICANN.
Internet Applications
In the earlier days of the internet, most applications were simple programs that followed a network protocol. Network protocols are rules, procedures, and formats that govern the communication of multiple devices over a network. This ensures timely, secure, and managed network communication. As web servers and browsers became more sophisticated, traditional networks became handled by web pages using the powerful hypertext transfer protocol (HTTP).
Multiple applications are used for exchanging messages between end users over a network, including instant messaging (IM), browser-based online chatting, tweets on Twitter, Facebook walls, and email (electronic mail system).
While most users rely on sophisticated applications to send and receive an email, the actual email transmission is supported by basic network protocols such as Simple Mail Transfer Protocol (SMTP). SMTP uses Domain Name System (DNS) lookups to identify the recipient of the email and send the message over the internet to a mail server where it can be retrieved using protocols such as POP3 (Post Office Protocol version 3) and IMAP (Internet Message Access Protocol).
VoIP (Voice over Internet Protocol) is used for voice communication over the Internet. VoIP operates by establishing a connection between two devices and then performing real-time, two-way transmission of audio data. Softphones allow two or more computers to share a call without any additional hardware. Analog telephone adapters allow users to connect their physical phones to a port that digitizes and then transmits real-time audio data.
Transporting audio and video data across the Internet in near real-time is referred to as streaming. Most applications in this category are now on-demand streaming in which the end user expects to view or listen to media at an arbitrary time of their choosing, unlike broadcasting where a server transmits content to several users simultaneously like traditional radio and TV stations. Large-scale streaming services use content delivery networks (CDNs), which are groups of servers distributed strategically over the internet that stream copies of content to nearby end users. A networking technology called anycast enables an end user to connect to the closest server automatically.
Explore: Determine Your IP Address
Using this site (or another tool), determine the IPv4 and IPv6 address of the computer you are using. Knowing your IP address is crucial for online gaming, tech support, using remote desktop connections, connecting to a security camera DVR, retaining anonymity, or even running an email server. Always keep your IP address secret. Do not share it with anyone.
The World Wide Web
In the late 1980s, Tim Berners-Lee realized the potential of combining internet technology with hypertext (linked documents), leading to the World Wide Web, which quickly became the dominant application of the internet. The World Wide Web (WWW) is composed of a hypertext document format for embedding hyperlinks to other documents, a protocol for transferring hypertext over the network, and a server process that supplies hypertext pages upon request. Today, the WWW also supports images, audio, and video.
Software packages that allow users to access hypertext are either browsers or web servers. A browser resides on the user’s machine to obtain the requested materials and present them to the end user in an organized way. The web server resides on the computer containing the hypertext documents. HTTP protocol or similar protocols are used to transfer data between web servers and browsers.
Each hypertext document available through the World Wide Web is given a unique address called a uniform resource locator (URL). The URL includes the protocol, domain, and all subdomains, as well as the resource path ID and name of the document. This information collectively indicates the location of the document on the server. The following is a commonly structured model of a URL: http://subdomain.domain.top-level-domain/directory-path/document_name.html
HTML (HyperText Markup Language) is a way of encoding a document. Special symbols called tags describe how the document should appear on a display screen, what multimedia resources (audio, video, images) should accompany the document, and which elements within the document are linked to other documents. A generalized language, the extensible markup language (XML), provides a standardized style for designing notational systems for representing data as text files. XML emphasizes semantics, while HTML focuses on appearance.
Network Security
A computer connected to a network is at risk for unauthorized access and vandalism. There are numerous ways that a computer system and its contents can be attacked via network connections. Many of those incorporate the use of malicious software or malware. Malware might be transferred to and executed on the computer itself or might attack the computer from a distance.
Malware
Malware (malicious software) is any software intentionally designed to cause damage to a computer, server, client, or computer network (by contrast, software that causes unintentional harm due to some deficiency is typically described as a software bug). A wide variety of types of malware exist, including computer viruses, worms, spyware, and phishing to name a few.
A virus is a software program that infects a computer by inserting itself into programs that already reside in the machine. When the “host” program is executed, the virus is also executed, possibly performing degradations of portions of the operating system, erasing large amounts of data, or corrupting data and other programs.
A worm is an autonomous program that forwards copies of itself to other machines in a network and could result in detriment of individual machines or the operations of the network.
Spyware is another form of malicious software. Spyware resides on a computer, collecting information about the computer’s activities and reporting back to the spyware’s instigator. Passwords or credit card numbers can be exposed via spyware.
Phishing is another technique used to obtain private information by simply asking for it. The perpetrator sends emails posing as a legitimate business asking for information.
Other Attacks
In contrast to internal infections that affect a computer system from the inside, a computer system can be attacked from other computers in a network. An example is the denial-of-service (DoS) attack, which is the process of overloading a computer with messages and results in suffocating the network resources. Packet sniffing is another form of attack, also referred to as a man-in-the-middle (MITM) attack, where the attacker intercepts the data as it is traveling to or from the victim’s device, including authentication credentials. MITM is just one way an attacker can get unauthorized access to resources and systems. Another method could be through a brute force attack. This is where the attacker uses all possible combinations of characters to learn a user’s password. There are multiple variations of the brute force attack, such as rainbow table attack and dictionary attack.
Dictionary attacks are performed by the attacker by using an application and a large dictionary text file with just words. When the attacker runs the application it tries identifying the password by trying hundreds or thousands of words per minute from that dictionary file.
In most applications, passwords are not stored in plain text like “PassW0rd” and often stored as scrambled text, or hash values, similar to “298cde70c32a57b84d0a546fedbb2596.” Rainbow tables try to identify the hash value of the password, then convert it back to plain text.
Protection and Risk Managements
The saying, “An ounce of prevention is worth a pound of cure” certainly holds for keeping network connections secure. One primary prevention technique is to filter the traffic passing through a point in the network using a program called a firewall. Firewalls block outgoing messages with certain destination addresses or block incoming messages from untrustworthy sources.
Another preventative tool is the proxy server, a software that acts as an intermediary between a client and a server to shield the client from adverse actions of the server.
Network auditing software monitors network behaviors such as the origin and volume of traffic, looking for anomalies to proactively or reactively mitigate unwanted occurrences.
Antivirus software detects and removes known viruses from the network.
In some cases, the purpose of network vandalism is to disrupt the system. In other cases, the goal is to gain information. Traditional means of protecting information is to control access through the use of passwords. However, passwords can be compromised and are of little value when data is transferred over a network. Encryption encodes information to keep it confidential even if the data is stolen.
Data Breach in the News
Data breaches occur frequently. Malicious actors try various techniques to gain unauthorized access to data. Mei tries to keep current of these trends since the network and data in her office are not immune to such attacks. She is constantly tasked with applying security patches, scanning through suspicious email, and taking other precautions to prevent such attacks, and she must have a plan for mitigating the impact of potential attacks should they affect her medical office.
Data can be compromised at any time, and companies must be diligent about protecting secure data. It is not uncommon for time to pass before a data breach is even discovered and actions are taken. In addition, companies do not like to publicize malicious data attacks and data breach events that could negatively impact their reputation and revenue, so it is often difficult to obtain much information about such occurrences. However, there have been many widely known attacks that have come to light simply as a result of the size of their impact (sometimes affecting millions of unsuspecting individuals), such as the attack on Equifax in 2017, the attack on Marriott International in 2014, and the attack on the game developer Zynga in 2019.
In May 2017, personally identified data from millions of consumers were stolen from Equifax when the company’s web portal was hacked. The hackers exploited the credit bureau’s unpatched system, gaining access to username and password combinations. In July of the same year, the company finally announced the discovery of the data breach and estimated a direct impact of 147 million people.
Now, hackers are able to successfully gain access to systems and data through more complex and sophisticated social engineering attacks. In 2018, a U.S. school district in the process of having a new school built was contacted via email requesting that they update their banking information, including completing a new electronic funds transfer (EFT) form. The school district confirmed the request was legitimate and provided the updated information before making a $2.5 million payment to the contractor. As you might have guessed, the contractor never received this payment. Instead, the school district had become the victim of a type of social engineering scam called a business email compromise (BEC). A small portion of the $2.5 million payment was recovered, but the perpetrators of the BEC have never been caught.
In September 2019, Zynga experienced a breach that affected 200 million players of its popular games Draw Something and Words with Friends. Hackers gained access to email addresses, usernames, passwords, and more.
In 2014, hackers accessed Marriott International’s reservation system and exposed the private details of up to 500 million customers, including names, addresses, credit card numbers, phone numbers, passport numbers, travel locations, and arrival and departure dates.