Data Network and Telecommunications Systems

Transcription

1 1 Department of Computer Science and Information Systems, College of Business and Technology, Morehead State University Lecture 4 CIS 311 Introduction to Management Information Systems (Spring 2017) Data Network and Telecommunications Systems A database is a set of data and physically stored in permanent storage devices (e.g., hard disk drives). It is also managed by a database management system (DBMS, e.g., Oracle s Oracle, IBM DB/2, MySQL, Microsoft SQL Server, etc.). In an enterprise organization, a database is usually stored in a separate computer in a network, and the computer has a database management system that manages the database. A group of databases may also be stored in a separate group of storage devices (e.g., Storage Area Network). A user in an organization can use an application software program (e.g., custom-made software such as Accounting Information System) to complete his/her work. When he or she needs data from a database, the application software program (e.g., Accounting Information System) requests the database management system to provide the necessary data, and the database management system locates the data in the database, retrieves the data set, and returns it to the application software program (e.g., Accounting Information System). In this case, the application software program (e.g., Accounting Information System) is considered a client system, and the database management system is a database server system. Technically, the client program sends a set of requests (SQL and other database code) to the database server, and the server reviews the code and processes the request if it is valid. All these happen in a networking environment. Nowadays, networking systems consist of not just pure computer networking systems but also telecommunication systems. Old telecommunication systems were based on analog technology. In analog technology, signals are captured as the natural form (i.e., continuous quantity), and keeping them electronically is an expensive technology. For instance, many devices are used to keep the original fidelity of analog signals especially when they need to be transmitted to a long distance. For this and other reasons, modern telecommunications systems have moved to digital technology.

2 2 In digital technology, signals are processed as discrete binary code. This technology is so efficient that immense amounts of data can be stored and transported at a lower cost than the analog technology. That s why computer systems (including computer networks) are based on digital technology. The traditional phone lines, however, were based on analog technology. For instance, when the traditional phone line is used to access the Internet (the network of networks), the data from a computer are based on digital technology, and digital signals should be converted into analog signals which can be passed through the analog telephone lines. The device for this conversion is called a MODEM (MOdulator/DEModulator) which is used to convert digital signals into analog and vice versa. A computer network is a set of computers that are connected via networking devices to send and receive data from one computer to other computers. Each computer in a network includes at least one network interface card (NIC). It may use a wired connection adaptor (e.g., Ethernet, Fibre Channel, or Token Ring) or a wireless adaptor (e.g., Wi-Fi). The computers in a network are connected through a network control device (e.g., hub or switch). A network hub is a simple networking device that connects several computers and other devices. It can detect basic network error, but it simply broadcasts all the network data to all other devices in the network. This approach makes hubs cheaper than other networking devices but could lead to a security problem. A network switch is also used to connect computers in a network, but it is more intelligent in that it can filter data and forward the filtered data to selected devices. A router is a special network device that is used to connect networks of the same or different types. A bridge is similar to a router, but the former is used to connect two local area networks (LANs, to be explained later) or two segments of the same local area network. Bridges are protocol-independent and forward packets without analyzing and re-routing messages. There are different types of networks, and they can be classified in different viewpoints. In terms of a geographical scope, a network can be a local area network (LAN) or a wide area network (WAN). A local area network covers a limited geographical area (e.g., an office, a building, closely located buildings, etc. within a half-mile or 500-meter radius). LANs are mostly based on Ethernet technology and process data at higher transfer rates than wide area networks. Wide area networks (WANs) cover large geographic areas (e.g., regions, states, continents, etc.), and use public networks (e.g., the telephone system, private cable system) or leased lines or satellites. The Internet is considered an example of a wide area network. The scope of a metropolitan area network (MAN) is between a local area network and a wide area network. It usually covers a large city as a single larger network (than a local area network). This also allows more efficient connection to a wide area network. Network topology explains what the components of a network are and how they are connected. Among the different types, there are three popular topologies: 1. Bus: A central cable (backbone) is used to connect computers in a network. A signal from a computer (source) travels in both directions to all devices until it finds the intended recipient device.

3 3 2. Star: A central node (a switch or a router) is used to connect computers in a network. Data are sent from one source to others via the central node. The node manages and controls all functions of the network. 3. Ring: Each node handles data transmission in a closed loop. Data passes through each intermediate node in the network until it reaches its destination. The intermediate nodes pass the data to the next node. Network Media In a network, data are transmitted via networking media. Traditionally, networking media was based on physical cables, but wireless media (the atmospheric paths) has become more popular. The first networks were based on thick coaxial cable, but modern wired networks use more of twistedpair cable and fiber-optic cable. Coaxial cable (coax) has a central conducting core (usually made of copper) enclosed by an insulator (PVC or Teflon), a braided metal shielding (braiding or shield), and an outer cover (sheath or jacket). There are different types of coax. The RG-6 (radio guide - 6) type has 75 ohms of impedance and uses an 18 AWG (American Wire Gauge) conducting core (usually made of solid copper). It is used to deliver broadband cable Internet service and cable TV. The RG-59 type also has 75 ohms of impedance and uses a 20 or 22 AWG core (usually made of braided copper). It is frequently used for short connections such as distribution of video signals from a central receiver to multiple monitors in a building. Twisted-pair cable is widely used in networking because it is relatively inexpensive, flexible, and easy to install. It can also cover a significant distance before a repeater should be used to retransmit a digital signal in its original form. In general, twisted-pair cable consists of color-coded pairs of insulated copper wires, each of which is twisted around each other to cancel out electromagnetic interference (EMI). Shielded twisted-pair cable has an additional shielding (made of braided copper or foil) which insulates the twisted pairs of wires. Unshielded twisted-pair cable doesn t have the extra shielding but is frequently used in networking due to its lower cost. The TIS/EIA 568 standard classifies twisted-pair wiring into several categories, and modern LANs use Cat 5e or higher wiring (required to support Gigabit Ethernet). Fiber-optic cable (or fiber) contains a core (consists of one or more glass fibers), a layer of glass (cladding) that surrounds the core, a plastic buffer that protects the cladding and core, strands of Kevlar (a polymeric fiber) that protect the inner core, and a plastic sheath that covers the strands of Kevlar. Some benefits of fiber-optic cable include extremely high throughput (due to the physics of light traveling through glass), very high resistance to noise (unaffected by EMI), excellent security (capturing signals in a light form is difficult), ability to carry signals for longer distances (150 40,000 meters), and industry standard for high-speed networking. It is, however, more expensive and inflexible to manipulate than twisted-pair cable. Due to these characteristics, fiber-optic cable is mostly used in network backbones which requires high-speed transmission of large quantities. Wired media provide reliable data transmission, but sometimes they are neither available nor convenient. For instance, using wired media in a car to access the Internet is not practical; therefore, along with wired media, modern networking environment includes wireless transmission methods. In wireless networks, signals are transmitted through the air (atmosphere) via radio frequency (RF) waves. In other words, all wireless signals are carried through the atmosphere by electromagnetic waves. The

4 4 electromagnetic waves are classified according to frequency and their linked wavelengths of the photons (electromagnetic spectrum). The radio spectrum is a part of the electromagnetic spectrum, and electromagnetic waves in the spectrum from 3 KHz to 300 GHz (radio frequency) are widely used in telecommunication. Specifically, the spectrum between 300 MHz and 300 GHz is called microwave. Source: (accessed on October 15, 2017) Since wireless transmission is open to the air, the Federal Communications Commission (FCC) and the National Telecommunications and Information Administration (NTIA) administer spectrums for non- Federal use and for Federal use, respectfully. Amplitude modulation (AM) broadcasting, for instance, uses frequencies between 535 KHz and 1605 KHz in the United States. The International Telecommunication Union (ITU) is a United Nations agency that sets standards for international telecommunications (e.g., frequency allocation). Wireless media uses the air which has no fixed path for signals to follow, and thus signals are transmitted without guidance. Therefore, wireless transmissions require special devices such as a transmitter, antenna, and receiver. In wireless networks, signals travel from a transmitter to an antenna which emits the signals to the atmospher. The signals propagate through the air until they reach their destination where another antenna accepts the signals. The antenna passes the signals to a receiver which converts them to current. The two antennas should share the same channel or must be tuned to the same frequency. Receivers must also be within the range to receive accurate signals consistently (range is the geographical area that an antenna or wireless system can reach).

5 5 These wireless media are used frequently for data network and telecommunications. Some examples are: Terrestrial microwave transmission Satellite microwave transmission Cellular telephones Wireless Fidelity (Wi-Fi) Bluetooth WiMAX (Worldwide Interoperability for Microwave Access) Radio Frequency Identification (RFID) Wireless Sensor Networks Data processing or transmission speed is measured by Hertz (Hz), or how many cycles per second. For instance, if a device has a potential of 1Hz, it uses one cycle per second. For another example, if you have a 1 GHz CPU, it can handle 1 billion cycles per second. A cycle of an electromagnetic wave may handle (carry) one bit per second (bps or bits/second) or more bits per second. The Internet The Internet is a network of networks, and is also considered a type of wide area network (WAN). It was originated from the ARPANET (by Advanced Research Projects Agency, or ARPA) in the 1960s. In the 1980s, the National Science Foundation expanded it with the NSFNET. Nowadays, the Internet includes multiple backbones by universities and private industries. Many organizations support the Internet, but there is no one central organization that owns it. There are many features of the Internet, but the following three can summarize them: 1. TCP/IP protocol: The Internet is based on the TCP/IP protocol which is the standard network language in modern networks. It includes four layers: application (e.g., http), transport (e.g., TCP, UDP, etc.), Internet (e.g., IP), and network interface (e.g., MAC). 2. Packet switching: This is possible because of digital technology, and is also frequently used in the TCP/IP protocol. It is a way of sending/receiving data (messages) more efficiently. For instance, when an is sent via the Internet, the message is divided into small pieces (i.e., packets), and each packet is transmitted through different routes (networks). The packets later are combined at the receiving party. 3. Client/server architecture: Most applications of the Internet are based on the client/server architecture. In other words, some systems are servers while others are clients. For instance, when a person uses her , she is using an client program to access an server which manages (i.e., sends, receives, and stores) messages. The World Wide Web is also an application of the Internet that is based on the client/server architecture. For instance, an Web browser (e.g., Firefox) is a client program that is used to access a Web server (e.g., a computer with the domain name of moreheadstate.edu).

6 6 Every computer (including computing devices) has an IP address which is like an address of a person s house. It is used to recognize a computer (or a device) on the global network. Web servers also have IP addresses, and Web client programs can access a Web server by its IP address. Using IP addresses, however, sometimes is not convenient because it is not easy to memorize a series of numbers (e.g., ). Therefore, many organizations use domain names (host names) as an alias (e.g., moreheadstate.edu). This way, people can remember the domain name for a Web server much more easily. These domain names are managed by the Domain Name System (DNS) which is a hierarchical distributed database. Internet Protocol version 4 (IPv4) is the core protocols for the current Internet. Since it was introduced in 1983, it has been the main protocol, but it uses only 32-bit integer values for IP addresses. It limits the number of computers on the Internet, and thus a new version has been introduced (Internet Protocol version 6, or IPv6). The new standard uses a 128 bits to represent an IP address, which overcomes the limitations of IPv4. Users of the Internet can subscribe to an Internet Service Provider (ISP) which provides Internet access services such as digital subscriber line (DSL), cable Internet access, or leased/dedicated lines (e.g., T1, T3, etc.) The Internet is an infrastructure of the globally-connected networks which can be utilized by many applications (e.g., the World Wide Web, , etc.). The World Wide Web (WWW) is the most important application of the Internet and has changed many of our lives. The main protocol of the World Wide Web is the hyper-text transfer protocol (http). In other words, the communication on the World Wide Web is based on the http protocol. For instance, a Web server keeps or dynamically generates Web documents (e.g., html documents) which are accessed by Web clients (Web browsers). When a Web browser sends a request to a Web server, the request is sent to the Web server based on the http protocol. The Web server receives the request, locates the Web document, and send it to the client. These processes are also based on the http protocol. The Internet and the World Wide Web have changed the business world, too. In the past, big organizations used private lines to connect their organizational units. The private lines are either purchased or leased, but they are expensive. Nowadays, many organizations use the public network (i.e., the Internet) in a secure and private way. This is called a virtual private network (VPN). The Internet and the World Wide Web are also used exclusively inside an organization, and this use is called an intranet. An organization may be so large that its units may be located in several continents, and can use the Internet technologies to connect the units and people. This is also an example of an intranet. An extranet is similar to an intranet in that both of them use the internet technologies. The former is different from the latter because the former is used to connect external organizations (e.g., suppliers) or individuals (e.g., consumers). The most important outcome of the Internet technologies is e-business, a new business model. E- business is literally electronic business, but the letter e means more than electronic. The magic letter e here means the Internet or digital technology which is useful to manage information. Therefore, e-business means the use of digital or Internet technology to manage business processes.

7 7 A part of e-business is e-commerce. Again, the letter is derived from electronic, but e-commerce is more than electronic commerce. Formally, e-commerce is the use of digital or Internet technology to sell or buy goods or services over the Internet. When a person purchases a product from Amazon, for instance, she is using e-commerce. In the process, the Internet is the main tool for the transaction. The data (e.g., browsing products, selecting a product, making a payment, etc.) are processed in the digital format (e.g., packet switching). All these are about the magic letter e. Other applications of the Internet include, but not limited to, Instant messaging Newsgroups Voice over IP (VoIP) Cloud computing The Internet is not owned by anyone, but there are some organizations who contribute to the development of the Internet. Some of them are: Internet Architecture Board (IAB) Internet Corporation for Assigned Names and Numbers (ICANN) World Wide Web Consortium (W3C)