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CHAPTER 1 INTRODUCTION TO NETWORKING BASIC CONCEPTS OF COMPUTER NETWORKS NETWORK Computer and devices, connected by some type of media. Two computers to thousands of computers connected across the world via the Internet. Networks may link mainframe computers, desktop computers, printers, plotters, fax machines, and phone systems. NETWORK (CONT.) Manage and administer resources on multiple computer from one location. Networks allow multiple users to share devices and resources such as: - printers - faxes - program and files ADVANTAGES OF NETWORKING • • File Sharing : The major advantage of a computer network is that is allows file sharing and remote file access. A person sitting at one workstation of a network can easily see the files present on the other workstation. Resource Sharing : If there are four people in a family, each having their own computer, they will require four modems (for the Internet connection) and four printers, if they want to use the resources at the same time. A computer network, on the other hand, provides a cheaper alternative by the provision of resource sharing. • • Increased Storage Capacity : As there is more than one computer on a network which can easily share files, the issue of storage capacity gets resolved to a great extent. When many computers are on a network, memory of different computers can be used in such case. One can also design a storage server on the network in order to have a huge storage capacity. Increased Cost Efficiency : There are many software's available in the market which are costly and take time for installation. Computer networks resolve this issue as the software can be stored or installed on a system or a server and can be used by the different workstations. TYPES OF NETWORK Peer-to-Peer Client / Server PEER-TO-PEER NETWORKS Peer-to-peer networks : Resource sharing, processing, and communication controls are fully decentralized often called a workgroup. All clients are given equal importance in using the network resources and users are individually authenticated by workstations. No fixed clients and servers. Common with up to 12 computers Disadvantage – slow transmission 9 Peer-to-Peer Networks CLIENT / SERVER NETWORKS Client/server networks It is a network where the servers provide services to different clients. A centralized server provides client authentication services. Servers play a key role in managing several applications like access to shared files, printers, and hardware. CLIENT-SERVER Usually high-powered servers. The types of servers are: File server (file server) - save the software and data Data server (database server)-store only Print Server (Print Server) - control of one or more printers Fax Server (Fax Server) - manage the fax transmission Mail server (Mail server) - manages e-mail 12 CLIENT-SERVER Advantages Disadvantages Security and data sources are controlled by the server spending more costly for a server All components (client / network / server) work simultaneously need maintenance every time the rates are determined to ensure the effectiveness of the system. Sharing data and software applicatio ns can be done Networking does not work if something went wrong on the server. 13 Client/Server Networks LANS, MANS AND WANS There are three main categories of networks: • Local Area Network (LAN) – is a relatively small network of computers, printers, and other devices in single building or floor. • Metropolitan Area Network (MAN) – is a high-speed internetwork of LANs across a metropolitan area. • Wide Area Network (WAN) – traditionally connects LANs using the PSTN(Public Switched Telephone Network) or more commonly the Internet. To provide connectivity over a large geographic area. LOCAL AREA NETWORK (LAN) LAN characteristics: They are used within small areas ( such as in an office building). They offer high-speed communicationtypically 100Mbps or faster. They provide access for many devices. They use LAN- specific equipment such as hub and NICs-usually no need router. METROPOLITAN AREA NETWORK MAN characteristics: Sites are dispersed across a city/large campus and perhaps the surrounding area as well. With the advent of MANs, historically slow connection (56Kbps-1.5Mbps) have given way to communication at hundreds of megabits per second and even gigabit speeds. They use devices such as routers, telephone switches, and microwave antennas as part of their communication infrastructure A MAN usually interconnects a number of (LANs) using a high-capacity backbone technology, such as fiber-optical links. WIDE AREA NETWORK WAN characteristics : They can cover a very large geographic area even span the world. They usually communicate at slow speed (compared to LANs). They use devices such as routers, modems, and WAN switches, connectivity devices specific to LANs and used to connect to long-haul transmission media. COMMON NETWORK ELEMENT Client A computer on the network that requesting resources or services. Server A computer on the network that manages network access and shared resources. Network Interface Card (NIC) A device inside a computer that connects a computer to the network media. Network Operating System(NOS) Server that enable a computer to control network access and manage resources. The most popular NOS are Microsoft Windows Server, Novell NetWare and UNIX. Host A device that provides resource sharing for other computers on the same network. COMMON NETWORK ELEMENTS (CONT.) • • • • • Node A device such as, client, server, or other network equipment that is identified by a unique network address. Topology The physical layout of a computer network. Network topology can be a ring, bus or star formation, or hybrid combinations. Backbone The backbone of a network (Cable) that combines smaller network into a large network. Transmission Media Media that carrying the network signal (cable/channel) Connectivity Devices Modems, repeaters, bridges, routers, switch, hub and etc. • Segment It is a physical partitioning of network. NETWORK TOPOLOGIES Network topology is the layout pattern of interconnections of the various elements (cable, nodes, etc.) of a computer network. Bus Ring Star Hybrid Mesh Group Activities… Hybrid??? Bus??? Ring??? Star??? Mesh??? BUS Bayonet Neill–Concelman (BNC connector) Connect two or more computer using coaxial cable and BNC connector. Terminator are installed on both ends of the cable. Without the terminator, the electrical signal that represent the data would reached the end of cooper wire and bounce back, causing errors on the network. Advantages : inexpensive to install, can easily add more workstation. Disadvantages : If the cable break down, the network is down, access time and network performance degrade as devices are added to the network. Bus Topology RING Computer are connected in a ring (circle). It has no beginning or end, so there is no need to terminate the cable. Every device have an equal advantage in accessing the media. Advantages : There are no collisions , no terminators are needed, easy to locate and correct problems with devices and cable. Disadvantages : requires more cable than a bus network, a break in the cable brings the entire network down. Ring Topology STAR All computer are connected to a central point such as hub or switch The most common topology used today Data on a star topology passes through the hub or switch before continuing to its destination. Advantages : Cable failure will not disrupt the network. Disadvantages : Single point of failure. Star Topology HYBRID • • • • Combination of any two or more different topologies. The most commonly used topologies are Star-Bus or Star-Ring. Advantages : If a computer fails, it will not affect the rest of the network Disadvantages : If the central component, or hub, that attaches all computers in a star, fails, no computer will be able to communicate. MESH All computer are connected to every other computer on the network Rarely used on a Local Area Network (LAN) The topology of the Internet. Advantages : Very redundant. No disruption when expanded. Disadvantages : Expensive. Requires a lot of cable and network interface cards. ADVANTAGES & DISADVANTAGES OF TOPOLOGIES Topology Advantages Disadvantages Bus Less cable Easy to install Network not working even with 1 PC failed Cable faulty, entire system down Difficult to troubleshoot Least fault tolerance Star Inexpensive Easy to troubleshoot Easy to reconfigure Low data rate Moderately difficult to install Require more cables Ring Almost no loss in signal quality over network Not that easy to install & troubleshoot Failure of single connection can take down entire network Mesh Every PC connected to each other Most fault tolerance Large amount of cables Very expensive & difficult to manage 34 NETWORKING STANDARDS ORGANIZATIONS Organizations that set standards for networking: American National Standards Institute (ANSI) Electronic Industries Alliance (EIA) and Telecommunication Industry Association (TIA) Institute of Electrical and Electronics Engineers (IEEE) International Organization for Standardization (ISO) International Telecommunication Union (ITU) Internet Society (ISOC) Internet Assigned Numbers Authority (IANA) and Internet Corporation for Assigned Names and Numbers (ICANN) ORGANIZATIONS AND ASSOCIATIONS Name Type Standards Established ITU-T ITU Telecommunication Standardization Sector (formerly CCITT) one of the three Sectors of the International Telecommunication Union Standards covering all fields of telecommunications Became ITU-T in 1992 IEEE Institute of Electrical and Electronics Engineers A non-profit, technical professional association Standards for the computer and electronics industry 1884 ISO International Organization for Standardization A network of the national standards institutes of 157 countries Promote the development of international standards agreements 1947 IAB Internet Architecture Board A committee; an advisory body Oversees the technical and engineering development of the Internet 1979; first named ICCB IEC International Electrotechnical Commission Global organization Standards for all electrical, electronic, and related technologies 1906 ANSI American National Standards Institute Private, non-profit organization Seeks to establish consensus among groups 1918 TIA/EIA Telecommunications Industry Association / Electronic Industries Alliance Trade associations Standards for voice and data wiring for LANs After the deregulation of the 36 U.S. telephone industry in 1984 SAFETY STANDARDS OSHA - Occupational Safety and Health Act NEC - National Electrical Code UL - Underwriters Laboratories 37 PRINCIPLES OF NETWORKING Sender • The first of these elements is the message source, or sender. It is the device which sends the data messages. • Message sources are people, or electronic devices, that need to communicate a message to other individuals or devices. Destination •The second element of communication is the destination, or receiver, of the message. •The destination receives the message and interprets it. Source •A third element, called a channel, provides the pathway over which the message can travel from source to destination. RULES OF COMMUNICATION IN NETWORKING Identification of sender and receiver (establish a link) Agreed-upon medium or channel (face-to-face, telephone, letter, photograph)-issue a command and command qualifier Appropriate communication mode (spoken, written, illustrated, interactive or one-way)-acknowledgement of command Common language Grammar and sentence structure - dissection message Error Control and correction Error detecting and recovering is one of the main functions of communication protocol. It ensures that data is transmitted without any error. It also solves the problem if an error is detected. Speed and timing of delivery-termination and transmission Ex:RS232 –handshaking concept Protocols define the details of how the message is transmitted, and delivered. This includes issues of: Message format Message size Timing Encapsulation Encoding Standard message pattern MESSAGE ENCODING •Encoding is the process of converting thoughts into the language, symbols, or sounds, for transmission. Decoding reverses this process in order to interpret the thought. In computer communication Messages sent across the network are first converted into bits by the sending host. Each bit is encoded into a pattern of sounds, light waves, or electrical impulses depending on the network media over which the bits are transmitted. The destination host receives and decodes the signals in order to interpret the message. Message formatting Message formats depend on the type of message and the channel that is used to deliver the message. Ex: The process of placing one message format (the letter) inside another message format (the envelope) is called encapsulation. De-encapsulation occurs when the process is reversed by the recipient and the letter is removed from the envelope. MESSAGE FORMATTING(CONT.) Each computer message is encapsulated in a specific format, called a frame before it is send to network. A frame acts like an envelope; it provides the address of the intended destination and the address of the source host. The format and contents of a frame are determined by the type of message being sent and the channel over which it is communicated. MESSAGE SIZE When long message is sent from one host to another over a network, it is necessary to break the message into smaller pieces. Each piece is encapsulated in a separate frame with the address information, and is sent over the network. At the receiving host, the messages are deencapsulated and put back together to be processed and interpreted. MESSAGE TIMING People use timing to determine when to speak, how fast or slow to talk, and how long to wait for a response. Rules: a) Access Method Access Method determines when someone is able to send a message. If two people talk at the same time, a collision of information occurs. Hosts on a network need an access method to know when to begin sending messages and how to respond when errors occur. MESSAGE TIMING (CONT.) b) Flow Control Timing also effects how much information can be sent and the speed that it can be delivered. In network communication, a sending host can transmit messages at a faster rate than the destination host can receive and process. Source and destination hosts use flow control to negotiate correct timing for successful communication. c) Response Timeout Hosts on the network also have rules that specify how long to wait for responses and what action to take if a response timeout occurs. MESSAGE PATTERN Unicast A one-to-one message pattern Only a single destination for the message. Multicast One-to-many pattern Multicasting is the delivery of the same message to a group of host destinations simultaneously. The most complex type of message because they require a means of identifying a set of specific devices to receive a message. Broadcast If all hosts on the network need to receive the message at the same time, a broadcast is used. One-to-all message pattern. MESSAGE PATTERN(CONT.) Unicast: 1-to-1 Multicast: 1-tomany Broadcast: 1 to all 48 Networking fundamentals LETS TRY NETWORK INTERFACE CARDS Most NICs are internal PCMCIA slot determining the speed and performance of a network The three most common network interface connections are Ethernet cards, LocalTalk connectors, and Token Ring cards. 50 provides the physical connection between the network and the computer workstation. 51 Ethernet card. From top to bottom: RJ-45, AUI (Attachment Unit Interface) , and BNC connectors LOCALTALK Ethernet Cards LocalTalk Fast data transfer (10 to 100 Mbps) Expensive - purchased separately Slow data transfer (23 Mbps) Built into Macintosh computers Requires computer slot No computer slot necessary Available for most computers Works only on Macintosh computers 52 TOKEN RING CARDS One visible difference is the type of connector on the back end of the card. Token Ring cards generally have a nine pin DIN type connector to attach the card to the network cable. 53 Token Ring network cards look similar to Ethernet cards. HARDWARE 54 WORKSTATIONS A typical workstation is a computer that is configured with a network interface card, networking software, and the appropriate cables. Workstations do not necessarily need floppy disk drives or hard drives because files can be saved on the file server. Almost any computer can serve as a network workstation. 55 All of the computers connected to the file server on a network are called workstations. SWITCH In a star topology, twisted-pair wire is run from each workstation to a central switch/hub. Switches are: • Usually configured with 8, 12, or 24 RJ-45 ports • Often used in a star or star-wired ring topology • Sold with specialized software for port management • Also called hubs • Usually installed in a standardized metal rack that also may store net modems, bridges, or routers 56 a central connection point for cables from workstations, servers, and peripherals REPEATERS 57 The repeater electrically amplifies the signal it receives and rebroadcasts it. Repeaters can be separate devices or they can be incorporated into a concentrator. They are used when the total length of your network cable exceeds the standards set for the type of cable being used. BRIDGES A bridge monitors the information traffic on both sides of the network. The bridge manages the traffic to maintain optimum performance on both sides of the network. traffic cop at a busy intersection during rush hour Bridges can be used to connect different types of cabling, or physical topologies. They must, however, be used between networks with the same protocol. 58 A bridge is a device that allows you to segment a large network into two smaller, more efficient networks. ROUTERS routers know the addresses of computers, bridges, and other routers on the network. Routers can: 59 super intelligent bridge Routers select the best path to route a message, based on the destination address and origin. Direct signal traffic efficiently Route messages between any two protocols Route messages between linear bus, star, and star-wired ring topologies Route messages across fiber optic, coaxial, and twistedpair cabling GATEWAYS associated with both a router, which use headers and forwarding tables to determine where packets are sent, and a switch, which provides the actual path for the packet in and out of the gateway. ◘ In homes, the gateway is the ISP that connects the user to the internet. 60 ◘ A node on a network that serves as an entrance to another network. ◘ In enterprises, the gateway is the computer that routes the traffic from a workstation to the outside network that is serving the Web pages. ◘ The gateway node often acts as a proxy server and a firewall