Fundamentals of Digital Communications and Networking

CHAPTER 8 - Communications and Networks Communications Computer communications is the process of sharing data, programs, and information between two or more computers.  Communication Apps :  E-mail—sending and receiving electronic documents.  Texting—short electronic messages.  Videoconferencing—calls using electronic voice and video delivery.  Electronic commerce—buying and selling goods electronically. Connectivity is a concept related to using computer networks to link people and resources.  connectivity means that you can connect your personal computer to other computers and information sources almost anywhere.  With this connection, you are linked to the world of larger computers and the Internet. The Wireless Revolution  Wireless technology allows a wide variety of nearby devices to communicate with one another without any physical connection.  High-speed Internet wireless technology allows individuals to connect to the Internet and share information from almost anywhere in the world Communication Systems Communication systems are electronic systems that transmit data from one location to another. Whether wired or wireless, every communication system has four basic elements: 1. Sending and receiving devices. originate (send) as well as accept (receive) data. 2. Connection devices. These devices act as an interface between the sending and receiving devices and the communication channel. 3. Data transmission specifications. These are rules and procedures that coordinate the sending and receiving devices . 4. Communication channel. This is the actual connecting or transmission medium that carries the message.  This medium can be a physical wire or cable, or it can be wireless. Communication channels These channels actually carry the data from one computer to another. There are two categories of communication channels: 46 1. Physical Connections :use a solid medium to connect sending and receiving devices. These connections include : A. Twisted-pair cable consists of pairs of copper wire that are twisted together.  Both standard telephone lines and Ethernet cables use twisted pair. B. Coaxial cable, a high-frequency transmission cable, replaces the multiple wires of telephone lines with a single solid-copper core. C. Fiber-optic cable transmits data as pulses of light through tiny tubes of glass.  The data transmission speeds of fiber-optic cables are incredible; recently speeds of 1 petabit per second were measured (a petabit is 1 million gigabits).  Compared to coaxial cable, it is lighter, faster, and more reliable at transmitting data.  Fiber-optic cable is rapidly replacing twisted-pair cable telephone lines. 2. Wireless Connections do not use a solid substance to connect sending and receiving devices. Rather, they move data through the air. Primary technologies used for wireless connections are: 1) Bluetooth transmits data over short distances  Bluetooth is widely used for wireless headsets, printer connections, and handheld devices. 2) Wi-Fi (wireless fidelity) uses high-frequency radio signals to transmit data.  Most home and business wireless networks use Wi-Fi. 3) Microwave communication uses high-frequency radio waves./short distance. It is sometimes referred to as line-of-sight communication because microwaves can only travel in a straight line.  Good for sending data between buildings in a city or on a large college campus.  For longer distances, requires microwave stations with microwave dishes or antennas. 4) WiMax (Worldwide Interoperability for Microwave Access) extends the range of WiFi networks using microwave connections.  used by universities. 5) Cellular communication uses multiple antennae (cell towers) to send and receive data within relatively small geographic regions (cells).  Most cell phones and mobile devices use cellular networks. 47 6) Satellite communication  Satellites can be used to send and receive large volumes of data.  Uplink is a term relating to sending data to a satellite.  Downlink refers to receiving data from a satellite.  The bad weather can sometimes interrupt the flow of data. Most interesting satellite communication application is GPS (global positioning system) GPS: A network of satellites owned and managed by the Department of Defense continuously sends location information to earth. 7) Infrared uses infrared light waves to communicate over short distances.  Infrared is a line-of-sight communication. Because light waves can only travel in a straight line.  Sending and receiving devices must be in clear view of one another without any obstructions blocking that view.like TV remote control. Connection Devices  Telephones typically send and receive analog signals.  Computers, send and receive digital signals.  To convert the digital signals to analog signals and vice versa, you need a modem. Modems The word modem is short for modulator-demodulator.  Modulation is the name of the process of converting from digital to analog.  Demodulation is the process of converting from analog to digital. Transfer rate :The speed with which modems transmit data varies (Mbps). There are three commonly used types of modems: DSL, cable, and wireless.    A DSL (digital subscriber line) external devices / uses standard phone lines to create a highspeed connection . A cable uses coaxial cable. A wireless known as a WWAN (wireless wide area network) modem. Connection Service  copper lines, known as T1 lines, that could be combined to form higher-capacity options known as T3 or DS3 lines. These lines have largely been replaced by faster optical carrier (OC) lines.  Dial up service has been replaced by higher-speed connection services including : A. Digital subscriber line (DSL)  ADSL (asymmetric digital subscriber line) is one of the most widely used types of DSL. B. Cable service using existing television cables. These connections are usually faster than DSL. C. Fiber-optic service (FiOS). Current providers of FiOS include Google and Verizon with speeds faster than cable or DSL connections. D. Satellite connection services use satellites to provide wireless connections. 48 E. Cellular service providers,  including Verizon, AT&T, Sprint, and T-Mobile.  support voice and data transmission to wireless devices using cellular networks.  Cellular generations : 1. First-generation (1G) started in the 1980s using analog radio signals to provide analog voice transmission service. 2. Second-generation (2G) started in the 1990s using digital radio signals. 3. Third generation (3G) started in the 2000s and provided services capable of effective connectivity to the Internet, marking the beginning of smartphones. 4. Fourth-generation (4G) has begun to replace 3G networks in some areas with providers using LTE (Long Term Evolution). Data Transmission Bandwidth is a measurement of the width or capacity of the communication channel.  it means how much information can move across the communication channel in a given amount of time . Categories of bandwidth : • Voi e a d, (low bandwidth) is used for standard telephone communication.  Effective for transmitting text documents, too slow for transmitting high-quality audio and video. • Mediu a d used to connect midrange computers and mainframes and to transmit data over long distances.  This bandwidth is capable of very-high-speed data transfer. • Broadband is widely used for DSL, cable, and satellite connections to the Internet.  Single broadband connection used for highspeed data transfer. • Baseband is widely used to connect individual computers that are located close to one another.  Support high-speed transmission  Can only carry a single signal at a time. 49 Protocols Rules for exchanging data between computers . Most widely used protocols : Https. And TCP/IP .  The essential features of this protocol involve : (1) identifying sending and receiving devices . (2) breaking information into small parts, or packets, for transmission across the Internet. • Identification: IP adress(Internet protocol address): a unique numeric address called an IP address the Internet.  Internet uses IP addresses to deliver e-mail and to locate websites.  This system uses a domain name server (DNS) that converts text-based addresses to IP add esses. Be ause it’s diffi ult fo people to e e e a d use . • Pa ketizatio : Packets are small parts of messages)  Before the message is sent, it is reformatted or broken down into small parts called packets.Each packet is then sent separately over the Internet.  At the receiving end, the packets are reassembled into the correct order. Networks a communication system that connects two or more computers so that they can exchange information and share resources. Terms that describe computer networks :        Node—any device connected to a network. Client—node requesting resources. Server—node providing resources. Directory server—specialized node that manages resources. Host—any computer system that provides access to its resources over a network. Router—a node that forwards data packets from one network to another network. Switch—node that coordinates direct flow of data between other nodes. Hub is an older device that directed flow to all nodes.  NIC (network interface card)—LAN adapter card for connecting to a network.  NOS (network operating system)—controls and coordinates network operations.  Network administrator—network specialist responsible for network operations. 50 Network Types Networks can be citywide or even international, using both wired and wireless connections. 1. Local Area Networks : Networks with nodes that are in close physical proximity—within the same building.  LANs span distances less than a mile and are owned and operated by individual organizations. The network gateway : is a device that allows one LAN to be linked to other LANs or to larger networks. Ethernet is a LAN standard. 2. Home Networks 3. Wireless LAN : It uses radio frequencies to connect computers and other devices. Hotspots provide Internet access in public places 4. Personal Area Network (PAN): is a type of wireless network that works within a very small area—your immediate surroundings. PANs connect cell phones to headsets, keyboards to cell phones, and so on. The most popular PAN technology is Bluetooth. 51 5. Metropolitan Area Networks (MAN). These networks are frequently used as links between office buildings that are located throughout a city. 6. Wide Area Networks (WANs) countrywide and worldwide networks. These networks provide access to regional service (MAN) providers and typically span distances greater than 100 miles.  The primary difference between a PAN, LAN, MAN, and WAN is the geographic range. Network Architecture describes how a network is arranged and how resources are coordinated and shared.  It encompasses a variety of different network specifics, including network topologies and strategies. Topologies : topology describes the physical arrangement of the network. The most common topologies are: 1- Bus network—each device is connected to a common cable called a bus or backbone. 2- Ring network—each device is connected to two other devices, forming a ring. 3- Star network—each device is connected directly to a central network switch; most common type today. 4- Tree (hierarchical) network—a central node is connected to subordinate nodes forming a treelike structure. 5- Mesh network—newest; requires that each node have more than one connection to the other nodes. Strategies : define how information and resources are shared. Two of the most common network strategies are client/server and peer-to-peer. Client/server networks —central computers coordinate and supply services to other nodes; based on specialization of nodes;  widely used on the Internet; able to handle very large networks efficiently; powerful network management software available. In a peer-to-peer (P2P) nodes have equal authority and act as both clients and servers;  widely used to share games, movies, and music over the Internet; easy to set up and use; lacks security controls. 52 Organizational Networks Internet Technologies  Internet technologies support effective communication using intranets and extranets  Many organizations use Internet technologies to allow suppliers and others limited access to their networks. • A i tra et is a private network within an organization that resembles the Internet Employees find surfing their organizational intranets to be as easy and as intuitive as surfing the Internet. • A e tra et is a private network that connects more than one organization. Network Security Three technologies commonly used to ensure network security are : A firewall consists of hardware and software that o t ol a ess to a o pa ’s i t a et and other internal networks II. Intrusion detection systems (IDS) work with firewalls to p ote t a o ga izatio ’s et o k.  These systems use sophisticated statistical techniques to analyze all incoming and outgoing network traffic. iii. Virtual private networks (VPN) eate a se u e p i ate o e tio et ee a e ote use a d a o ga izatio ’s i te al network. I. 53