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An enterprise WAN connects an entire organization including all LANs at various sites. This term is used for large, widespread organizations such as corporations, universities and governments. Global WANs also span the world but they do not have to connect LANS within a single organization. The Internet is an example of a global WAN. It connects diverse locations, organizations and institutions throughout the world. Global WANS can be public or private. Private WANs are called Intranet which belongs to an organization. Public WANs are open to everybody so that anybody can connect and use the resources and services available.
Bound transmission media are the cables that are tangible or have physical existence and are limited by the physical geography. Popular bound transmission media in use are twisted pair cable, co-axial cable and fiber optical cable. Unbound transmission media are the ways of transmitting data without using any cables. These media are not bounded by physical geography. Microwave, Radio wave, Infra red are some of popular unbound transmission media.Unbound transmission media extend beyond the limiting confines of cabling. They provide an excellent communication alternative for WANS. The lack of physical restrictions provides larger bandwidth as well as wide area capabilities. Unbound media typically operate at very high frequencies. The three types of unbound transmission media are: Radio wave, Micro wave, Infrared
Infrared offers a great unbound photonic solution. Like fiber-optic cabling, infrared communications use light, so they are not bound by the limitations of electricity.
Types of Networks: LANs (Local Area Networks) A network is any collection of independent computers that communicate with one another over a shared network medium. LANs are networks usually confined to a geographic area, such as a single building or a college campus. LANs can be small, linking as few as three computers, but often link hundreds of computers used by thousands of people. The development of standard networking protocols and media has resulted in worldwide proliferation of LANs throughout business and educational organizations. WANs (Wide Area Networks) Wide area networking combines multiple LANs that are geographically separate. This is accomplished by connecting the different LANs using services such as dedicated leased phone lines, dial-up phone lines (both synchronous and asynchronous), satellite links, and data packet carrier services. Wide area networking can be as simple as a modem and remote access server for employees to dial into, or it can be as complex as hundreds of branch offices globally linked using special routing protocols and filters to minimize the expense of sending data sent over vast distances. Internet The Internet is a system of linked networks that are worldwide in scope and facilitate data communication services such as remote login, file transfer, electronic mail, the World Wide Web and newsgroups. With the meteoric rise in demand for connectivity, the Internet has become a communications highway for millions of users. The Internet was initially restricted to military and academic institutions, but now it is a full-fledged conduit for any and all forms of information and commerce. Internet websites now provide personal, educational, political and economic resources to every corner of the planet. Intranet With the advancements made in browser-based software for the Internet, many private organizations are implementing intranets. An intranet is a private network utilizing Internet-type tools, but available only within that organization. For large organizations, an intranet provides an easy access mode to corporate information for employees. MANs (Metropolitan area Networks) The refers to a network of computers with in a City. VPN (Virtual Private Network) VPN uses a technique known as tunneling to transfer data securely on the Internet to a remote access server on your workplace network. Using a VPN helps you save money by using the public Internet instead of making long–distance phone calls to connect securely with your private network. There are two ways to create a VPN connection, by dialing an Internet service provider (ISP), or connecting directly to Internet.
The physical Bus topology is the simplest and most widely used of the network designs. It consists of one continuous length of cable (trunk) and a terminating resistor (terminator) at each end. Data communication message travels along the bus in both directions until it is picked up by a workstation or server NIC. If the message is missed or not recognized, it reaches the end of the cabling and dissipates at the terminator. All nodes on the bus topology have equal access to the trunk. This is accomplished using short drop cables or direct T-connectors. The number of devices and the length of the trunk can be easily expanded. The advantages of physical bus topology are: a. It uses established standards and it is relatively easy to install. b. It requires less media than other topologies. The disadvantages of bus topology are: a. The bus networks are difficult to reconfigure, especially when the acceptable number of connections or maximum distances have been reached. b. They are also difficult to troubleshoot because everything happens on a single media segment. This can have dangerous consequences because any break in the cabling brings the network to its knee.
A networking model where one or more powerful computers (servers) provide the different network services and all other user's computers (clients) access those services to perform user's tasks is known as client/server networking model. Client-server networking model became popular in the late 1980s and early 1990s as many applications were migrated from centralized minicomputers and mainframes to networks of persona computers. The design of applications for a distributed computing environment required that they effetely be divided into two parts: client (front end) and server (back end). The network model on which they were implemented mirrored this client-server model with a user's PC (the client) typically acting as the requesting machine and a more powerful server machine to which it was connected via either a LAN or a WAN acting as the supplying machine. It requires special networking operating system. It provides user level security and it is more expensive.
A solid central conductor surrounded by insulating material and then by a cylindrical shield woven from fine wires is known as co-axial cable. The shield is usually connected to electrical ground to reduce electrical interference. Co-axial cables have broader bandwidth and thus suitable for audio, video data transmission.
The heart of Ethernet system is the Ethernet Frame, which is used to deliver information between the computers. The frame consists of a set of bits organized into several fields. These fields include address fields, a data field and an error checking field that checks the integrity of the bits in the frame to make sure that the frame has arrived intact. Ethernet's major advantages are: 1. It is an inexpensive way to achieve high speed LAN transmissions (10 to 100 MB/s) 2. It is a proven technology that supports various writing configurations. 3. It works well with a large number of LAN and micro-to-mainframe applications. 4. It is easy to install.
A cable with central glass tube covered with protective shield which transmit data using photons is fiber optics cable. These cables transmit data via concentrated bursts of laser beams which are carried through bundles of hair thin glass fibers. They have advantages over electronic cables in transmission speed and volume. This technology has revolutionized telecommunication applications which used electronic cables. Fiber optics cables as free from electro-magnetic interference as well as wire tapping.
The Open System Interconnection (OSI) is a standard reference model for communication between two end users in a network. It is used in developing products and understanding networks which means commonly used Internet product and services fit within the model. The OSI model describes seven layers of related functions that needed at each end, when a message is sent from one party to another party in a network. Each layer has its own set of special related function as follows: Layer 6 – Presentation Layer: Standardize data presented to the application. Layer 5 – Session Layer: Manages sessions between applications Layer 4 – Transport Layer: Provides error detection and correction Layer 3 – Network Layer: Provides data delivery across the physical connection Layer 2 – Data Link Layer: Provides data delivery across the physical connection Layer 1 – Physical Layer: Defines the physical network media.
Network services are the thing that a network can do. The major networking services are File Services: This includes file transfer, storage, data migration, file update, synchronization and achieving. Printing Services: This service produces shared access to valuable printing devices. Message Services: This service facilitates email, voice mails and coordinate object oriented applications. Application Services: This services allows to centralize high profile applications to increase performance and scalability Database Services: This involves coordination of distributed data and replication. Major Network Services are: a. File Services b. Print Services c. Message Services d. Application Services e. Database Services
A networking model where each workstation has equivalent capabilities and responsibilities is known as peer-to-peer model. There is no central server in this network and computers join hands to share files, printers and Internet access. It is practical for workgroups of a dozen or less computers making it common environments, where each PC acts as an independent workstation that stores data on its own disk but which can share it with all other PCs on the network. Software for peer-to-peer network is included with most modern desktop operating systems such as Windows and Mac OS.
A point-to-point connection is a direct link between two devices such as a computer and a printer. Most of today's point-to-point connections are associated with modems and PSTN (Public Switched Telephone Network) communications.
Although Radio waves are prevalent and well understood, we are just beginning to realize their enormous potential as a networking medium. Radio waves can operate on a single or multiple frequency bands.
The physical star topology uses a central controlling hub with dedicated legs pointing in all directions – like points of a star. Each network device has a dedicated point-to-point link to the central hub. This strategy prevents troublesome collisions and keeps the lines of communications open and free of traffic. This topology, obviously, require a great deal of cabling. This design provides an excellent platform for reconfiguration and trouble-shooting. Changes to the network are as simple as plugging another segment into the hub and a break in the LAN is easy to isolate and doesn't affect the rest of the network. The benefits of star topology are: a. Relatively easy to configure. b. Easy to troubleshoot c. Media faults are automatically isolated to the failed segment. The disadvantages are considered as follows: a. Requires more cable than most topologies. b. Moderately difficult to install.
A pair of wires twisted with each other is known as twisted pair cable. A set of four pairs of twisted wires are bundled to form cable. These are the most common medium for LAN. Wires are twisted with each other so as to reduce the interference. We can find two types of twisted pair cables, namely: Unshielded Twisted Pair Cable (UTP) and Shielded Twisted Pair Cable (STP). The twisted pair cable that is protected against electro-magnetic interference (EMI) is known as STP and the one which is not shielded against EMI is called Unshielded Twisted Pair.
Here are Token ring's most useful advantages: a. It offers excellent throughput under high-load conditions. b. Token Ring facilitates LAN-to-LAN mainframe connections especially for interfacing with IBM's broader connectivity strategies. c. It has built-in troubleshooting mechanisms such as beaconing and auto-reconfiguration and may now be used with UTP cabling. d. It has the most reliable protocol (token-passing), the most trouble-free configuration (physical star) and the fastest connectivity scheme (r or 16 mb/s). Few of the disadvantages of Token Ring are: a. Token Ring is very expensive. All topology components cost much more than other more popular standards. b. It is relatively proprietary. Token Ring's complexity is built into the hardware components. This means hat you need to choose a manufacturer and stick with it. c. Engineers must have considerable expertise to manage and troubleshoot token ring components.
The advantages of ring topologies are: a. They are very easy to troubleshoot because each device incorporates a repeater. b. A special internal feature called beaconing allows troubled workstations to identify themselves quickly. The disadvantages of ring topologies are: a. It is considerably difficult to install and reconfigure ring topology b. Media failure on unidirectional or single loop causes complete network failure.
Computer networks fall into three classes regarding the size, distance and the structure namely: LAN (Local Area Network), MAN (Metropolitan Area Network), WAN (Wide Area Network). A LAN links a small group of functionally similar workstations within a local geographic area such as a series of adjacent cubicles or offices on the same floor. Once the network expands to include other floors or divers office within a metropolitan area, it becomes a MAN. Finally, a WAN is simply a LAN of LANs. WANs expand the boundaries of networking to a global or even galactic scale.
10Base2—An Ethernet term meaning a maximum transfer rate of 10 Megabits per second that uses baseband signaling, with a contiguous cable segment length of 100 meters and a maximum of 2 segments. 10Base5—An Ethernet term meaning a maximum transfer rate of 10 Megabits per second that uses baseband signaling, with 5 continuous segments not exceeding 100 meters per segment. 10BaseT—An Ethernet term meaning a maximum transfer rate of 10 Megabits per second that uses baseband signaling and twisted pair cabling.
Those Workstations that have no disk drive of their own and rely completely on LAN for their access are called dumb terminals. The network operating system lets these terminals work as if all the resources at the server belong to the workstation itself.
Repeater: Also called a regenerator, it is an electronic device that operates only at physical layer. It receives the signal in the network before it becomes weak, regenerates the original bit pattern and puts the refreshed copy back in to the link. Bridges: These operate both in the physical and data link layers of LANs of same type. They divide a larger network in to smaller segments. They contain logic that allow them to keep the traffic for each segment separate and thus are repeaters that relay a frame only the side of the segment containing the intended recipent and control congestion. Routers: They relay packets among multiple interconnected networks (i.e. LANs of different type). They operate in the physical, data link and network layers. They contain software that enable them to determine which of the several possible paths is the best for a particular transmission. Gateways: They relay packets among networks that have different protocols (e.g. between a LAN and a WAN). They accept a packet formatted for one protocol and convert it to a packet formatted for another protocol before forwarding it. They operate in all seven layers of the OSI model.
a. Attenuation by solid objects: birds, rain, snow and fog. b. Reflected from flat surfaces like water and metal. c. Diffracted (split) around solid objects. d. Refracted by atmosphere, thus causing beam to be projected away from receiver.
A network is any collection of independent computers that communicate with one another over a shared network medium. A computer network is a collection of two or more connected computers. When these computers are joined in a network, people can share files and peripherals such as modems, printers, tape backup drives, or CD-ROM drives. When networks at multiple locations are connected using services available from phone companies, people can send e-mail, share links to the global Internet, or conduct video conferences in real time with other remote users. When a network becomes open sourced it can be managed properly with online collaboration software. As companies rely on applications like electronic mail and database management for core business operations, computer networking becomes increasingly more important. Every network includes: At least two computers Server or Client workstation. Networking Interface Card's (NIC) A connection medium, usually a wire or cable, although wireless communication between networked computers and peripherals is also possible. Network Operating system software, such as Microsoft Windows NT or 2000, Novell NetWare, Unix and Linux.
Computer Network is a collection of distributed intelligent machines that are connected with each other with transmission media for the purpose of data sharing, communication and sharing of computer resources. The following are the distinct notes in favor of computer networking. a. The computers, staff and information can be well managed b. A network provides the means to exchange data among the computers and to make programs and data available to people c. It permits the sharing of the resources of the machine d. Networking also provides the function of back-up. e. Networking provides a flexible networking environment. Employees can work at home by using through networks ties through networks into the computer at office.
A network server designated to provide one particular service is known as dedicated server. For example if a computer is assigned for database service only then that computer is known as dedicated database server.
A LAN is a Local Area Network, within a single building or a specific confined space. LANs typically comprise only one transmission media type such as coaxial cable or twisted pair. LANs are characterized by comparatively high-speed communications. These high speeds are possible because LANs use one kind of cable which generally is limited to 5 km or less.
A firewall is a system or group of systems that enforces an access control policy between two networks. The actual means by which this is accomplished varies widely, but in principle, the firewall can be thought of as a pair of mechanisms: one which exists to block traffic, and the other which exists to permit traffic. Some firewalls place a greater emphasis on blocking traffic, while others emphasize permitting traffic. Probably the most important thing to recognize about a firewall is that it implements an access control policy. If you don't have a good idea of what kind of access you want to allow or to deny, a firewall really won't help you. It's also important to recognize that the firewall's configuration, because it is a mechanism for enforcing policy, imposes its policy on everything behind it. Administrators for firewalls managing the connectivity for a large number of hosts therefore have a heavy responsibility.
Protocol (the logical component) and Topology (the physical component) is combined together to create a networking standard. These standards are developed and controlled by the Institute of Electrical and Electronics Engineers (IEEE). The four major industry standards are (a) Ethernet, Token Ring, ARCNet and FDDI (Fiber Distributed Data Interface).
The term protocol refers to a set of rules and procedures that govern the transmission of messages over a physical networking medium. The most common network protocols are: (a) TCP/IP, (b) IPX/SPX and (c) NetBEUE The three major network protocols are: 1. TCP/IP 2. IPX/SPX (Used in Novell Netware) 3. NetBEUE (Product of Microsoft Co.)
The Ethernet topology was developed at the University of Hawaii to connect computers on the various Islands. It was radio based design. Later, Robert Metacalfe went to Xeros's Palo Alto Research Center (PARC) laboratories and eliminated the radio portion and changed to co-axial cabling. Ethernet is one of the most popular LAN technologies in use today covering more than 85% of the networks. Ethernet system consists of three basic elements: 4. The physical medium use to carry Ethernet signals between computers on the network 5. A set of rules (protocols) embedded in each Ethernet interface that will decide how multiple computers on the network will have access to the data on the medium. 6. An Ethernet frame that consists of a standardized set of bits used to carry data over the system. The operation of Ethernet can be described in simple terms as follows: Each computer on the Ethernet Network, also known as a node, operates independently of all other nodes. All nodes attached to an Ethernet are connected to a shared medium over which the Ethernet signals travel serially, one data bit at a time. To send data a station first listens to the channel and when the channel is idle the station transmits its information in the form of an Ethernet frame, or packet. The Ethernet rules (protocol) are defined in such a way that every node gets a fair amount of frame transmission opportunity. As each Ethernet frame is sent out on the shared medium, the Ethernet interfaces inside the node look at the destination address. The interfaces compare the destination address of the frame with their own address. The Ethernet interface with the same address as the destination address in the frame will read the entire frame and all other network interfaces will ignore the information.
The Attached Resource Computer Network (ARCNet) standard was created in 1977 at the Data Point Corporation by a scientist – John Murphy. ARCNet uses the token-passing protocol over a star and bus topology. The star and bus topology combines the flexibility of a star with the simplicity and throughput of a bus. Thus, ARCNet standard has a unique protocol/topology combination: token-passing protocol and Distributed star/bus topology. Here are some of the ARCNet's advantages: 1. It is extremely reliable. 2. ARCNet is easy to install and troubleshoot. 3. It has an excellent track record of interoperability for those using ARCNet components from various manufacturers. 4. ARCNet supports a variety of cable types including coaxial, UTP and Fiber Optics. 5. It is inexpensive and built to stay that way. Here are some disadvantages of ARCNet: 1. Standard ARCNet is very slow (2.5 Mb/s). It is almost seven times slower than Token Ring. 2. ARCNet was not designed with interconnectivity in mind. For many installations, it's difficult to go beyond the confines of single LAN.
The term topology defines the geographic arrangement of networking devices. It describes the actual layout of the network hardware. Given the location of workstations and peripherals, the goal of topology is to find the most economical and efficient way to connect all the users to the network resources while providing adequate capacity to handle user demands, maintain system reliability and minimize delay. The selection of a topology for a network can not be done in isolation as it affects the choice of media and the access method used. Because it determines the strategy used in wiring a building for a network and deserves some careful study.
MAN stands for Metropolitan Area Networks. MAN is larger than a LAN and as its name implies, covers the area of a single city. MANs rarely extend beyond 100 KM and frequently comprise a combination of different hardware and transmission media. The two most important components of MANs are security and standardization. Security is important because information is being shared between dissimilar systems. Standardization is necessary to ensure reliable data communication.
Microwaves have been used in data communications for a long time. They have a higher frequency than radio waves and therefore can handle larger amounts of data. Microwave transmission is line of sight transmission. The transmit station must be in visible contact with the receive station. This sets a limit on the distance between stations depending on the local geography. Typically the line of sight due to the Earth's curvature is only 50 km to the horizon! Repeater stations must be placed so the data signal can hop, skip and jump across the country. Microwaves operate at high operating frequencies of 3 to 10 GHz. This allows them to carry large quantities of data due to their large bandwidth. List the Advantages of microwaves. a. They require no right of way acquisition between towers. b. They can carry high quantities of information due to their high operating frequencies. c. Low cost land purchase: each tower occupies only a small area. d. High frequency/short wavelength signals require small antennae.
When two or more computer are connected with one another for the purpose of communicating data electronically, besides physical connection of computers, communication devices and system servers, a well defined standard known as architecture is required to establish cohesive communication between devices in Network. The most popular architectures are: a. ISO Open System Architecture (OSI) b. IBM's System Network Architecture (SNA)
Network Server is a computer in Network that is designated to provide one or more network service. For example file server, database server etc. A computer in network that connects to the server and uses the network services to perform user's tasks is a client.
Physical media: • Twisted pair cable – consists of two independently insulated wires twisted around each other • Coaxial cable – consists of an insulated center wire grounded by a shield of braidedwire Fiber optic cable – contains hundreds of clear fiberglass or plastic fibers • ISDN line – a special digital telephone line that transmits and receives information at very high speeds Wireless media: • Microwave system – transmits data via high-frequency radio signals through the atmosphere • Satellite system – receive signals from the earth, amplify them, and then transmit back these signals to the appropriate locations on the earth. • Cellular technology – uses antennae resembling telephone towers to pick up radio signals within a specific area
The physical ring topology is a circular loop of point-to-point links. Each device connects directly to the ring or indirectly through and interface device or drop cable. Message travel around the ring from node to node in a very organized manner. Each workstation checks the message for a matching destination address. If the address doesn't match the node simply regenerates the message and sends it on its way. If the address matches, the node accepts the message and sends a reply to the originating sender.
The Trivial File Transfer Protocol (TFTP) allows a local host to obtain files from a remote host but does not provide reliability or security. It uses the fundamental packet delivery services offered by UDP. The File Transfer Protocol (FTP) is the standard mechanism provided by TCP / IP for copying a file from one host to another. It uses the services offered by TCP and so is reliable and secure. It establishes two connections (virtual circuits) between the hosts, one for data transfer and another for control information.
Transmission media is a pathway through which data are transmitted in network. We use different types of cables or waves to transmit data. types: There are two types of transmission media namely: bound transmission media and unbound transmission media.
A wide area network is simply a LAN of LANs. WANs connect LANs that may be on opposite sides of a building, across the country or around the world. WANS are characterized by the slowest data communication rates and the largest distances. WANs can be of two types: an enterprise WAN and Global WAN.
A workstation is a node in network that is more powerful and can handle local information processing or graphics processing. A workstation usually has an inexpensive, small hard disk to carry out local tasks. Some workstations that have no disk drive of their own is known as diskless-workstation or dumb terminals. They terminals completely rely on LAN for their access. Network operating system lets the node work as if all the resources at the server belong to the node itself.