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What is Networking? A network is a connection between terminals, computers, servers and components which allows for the easy flow of data and use of resources between one another. Sharing is the main purpose of networking. Today, we are going to learn that how a person can communicate through computers viz., Different ways of connecting and Devices used to connect. 2

Network Topology : 

Network Topology The network topology defines the way in which computers, printers, and other devices are connected. A network topology reefers to the layout or the design of the connected devices. It can be physical or logical. The topology of a network is the pattern used to connect the computers and other devices with the cable or other network medium Physical Topology means the physical design of a network including the devices, location and cable installation. Logical Topology refers to the fact that how a data actually transfers in a network as opposed to its design. Topology can be considered as a virtual shape or structure of a network. 3

Main types of Physical Topologies : 

Main types of Physical Topologies The basic topologies you will find in most LANs today include the following: Bus Topology Ring Topology Star Topology Mesh Topology Hybrids 4

Bus Topology : 

Bus Topology A network cabling topology in which each device is connected to the next device, forming a daisy chain with two ends, each of which must be terminated with lots of binary collision. The bus carries the transmitted message along the cable to check the destination address contained in the message to see if it’s matching it's own. If the address does not match, the workstation does nothing more. If it matches that contained in the message , the workstation processes the message. The main features are: All workstations connect to the same cable segment. Commonly used for implementing Ethernet at 10 Mbps. The cable is terminated at each end. Wiring is normally done point to point. A faulty cable or workstation can take the entire LAN down. Two wire, generally implemented using coaxial cable. 5

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A network that uses a bus topology is referred to as a “bus network.” Bus networks were the original form of Ethernet networks, using the 10Base5 cabling standard. Bus topology is used for Small workgroup local area networks (LANs) whose computers are connected using a Thinnet cable Trunk cables connecting hubs or switches of departmental LANs to form a larger LAN Back boning, by joining switches and routers to form campus-wide networks Bus topology is the cheapest way of connecting computers to form a workgroup or departmental LAN, but it has the disadvantage that a single loose connection or cable break can bring down the entire LAN. 6


RING TOPOLOGY The two ends are connected instead of being terminated, thus forming an endless loop. Networks such as Token Ring, which use token passing for their Media Access Control (MAC) mechanism are wired using a ring topology. The most important thing to understand about the ring topology is that, it is strictly a logical construction, not a physical one. The ring exists in the wiring of the network, but not in the cabling. A frame travels around the ring, stopping at each node. If a node wants to transmit data, it adds the data as well as the destination address to the frame. The frame then continues around the ring until it finds the destination node, which takes the data out of the frame. Single ring – All the devices on the network share a single cable. (Collision) Dual ring – The dual ring topology allows data to be sent in both directions. (No collision) 7

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The main features are: Workstations connect to the ring Faulty workstations can be bypassed More cabling required than bus The connectors used tend to cause a lot of problems Commonly used to implement token ring at 4 and 16 Mbps Four wire generally STP or UTP. IEEE 802.5 Token Ring is widely used in ring networks for controlling station access to the ring. Wiring is done in a physical star fashion, with cables wired directly from each workstation back to the MAU. 8

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STAR & TREE TOPOLOGY A network cabling topology in which each device is connected to a central nexus called a hub. Larger networks use the extended star topology also called tree topology. The main features are: All wiring is done from a central point (hub or switch) Each node (file server, workstations and peripherals) connected directly to a central network hub or concentrator. Data on a star network passes through the hub or concentrator before continuing to its destination. The hub or concentrator manages and control all functions of the network. It also acts as a repeater for the data flow. Has the greatest cable lengths of any topology This configuration is common with twisted pair cable: however, it can also be used with coaxial cable or fiber optic cable. Generally STP or UTP. 10

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The protocols used with star configurations are usually Ethernet or Local Talk. STAR TOPOLOGY Star-Wired ring topology: A star-wired ring topology may externally appear to be the same as a star topology. Internally the MAU of a star-wired ring contains that allows information to pass from one device to another in a circle or a ring. Token Ring uses similar topology, called the star- wired ring topology. 11


FDDI TOPOLOGY Fiber Distributed Data Interface (FDDI): Designed for use with fiber optic cable. Typically used for backbone networks, FDDI uses the token passing Media Access Control (MAC) mechanism and supports a double ring topology that provides fault tolerance in the event of a system disconnection or cable failure. FDDI has since largely been replaced by the Fast Ethernet and Gigabit Ethernet fiber optic options. The main features are: Speed : 100 Mbps. Normally implemented over fiber optic (fast Ethernet, UTP may be used). Dual redundancy built in by the use of primary and secondary ring. Automatic bypassing and isolation of faulty nodes. Primary ring is used for data transmission. Secondary ring used for the back up of the primary ring in case of system failure. Types: Class A which attach directly to dual ring rings. Class B which attach to a station. 12


MESH TOPOLOGY The topology in which every device connects to every other device is called Mesh topology. The mesh topology connects all devices (nodes) to each other for redundancy and fault tolerance. It is used in WANs to interconnect LANs and for mission critical networks like those used by banks and financial institutions. Implementing the mesh topology is expensive and difficult. It work on the concept of routes. In Mesh topology, message sent to the destination can take any possible shortest, easiest route to reach its destination. Full mesh topology: Provides a direct link between each pair of nodes (routers) on the backbone network. Full mesh topologies provide the highest level of fault tolerance but increase the computational strain on dynamic routers for calculating their routing tables. Partial mesh topology: Includes some redundant data paths to provide some level of fault tolerance. This is the more usual implementation in large internetworks. 13

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ROUTER A router is a system connected to two or more networks that forwards from one network to another. A device that forwards data packets between computer networks. Routers are most often used in large internetworks that use the TCP/IP protocol suite and for connecting TCP/IP hosts and local area networks (LANs) to the Internet using dedicated leased lines. Routers generally block broadcast traffic and can thus prevent broadcast storms from slowing down the flow of traffic in a network. Routers can also be used to join dissimilar media such as unshielded twisted-pair (UTP) cabling and fiber-optic cabling, and different network architectures such as Token Ring and Ethernet. Routers often provide basic firewall functions by filtering out packets based on their source or destination network address. Such a device is known as a packet-filtering router. 17

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Routers are classified as one of the following: Static routers: These must have their routing tables configured manually with all network addresses and paths in the internetwork. Administrator manually assigns path. Dynamic routers: These automatically create their routing tables by listening to network traffic. Path selection depends on the routers protocols. (RIP, EIGRP & OSPL) Default routers: We don’t know the destination. 18


BRIDGING Bridging is a technique used to connect networks at the data-link layer. A bridge is a physical unit, typically a box with two ports in it, that you use to connect network segments. You can use a bridge to join two existing LANs or to split one LAN into two segments. Bridges operates in called promiscuous mode, meaning that they read and process all of the packets transmitted over the network segments. Bridges operate by sensing the source MAC addresses of the transmitting nodes on the network and automatically building an internal routing table. Bridges come in three basic types: Local bridges: Directly connect local area networks (LANs) Remote bridges: Can be used to create a wide area network (WAN) link between LANs Wireless bridges: Can be used to join LANs or connect remote stations to LANs 19

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The other types are: Transparent Bridging - They build a table of addresses (bridging table) as they receive packets. If the address is not in the bridging table, the packet is forwarded to all segments other than the one it came from. This type of bridge is used on Ethernet networks. Source route bridging - The source computer provides path information inside the packet. This is used on Token Ring networks. 20


BROUTER Any network device having the capabilities of both a bridge and a router is called a brouter. There is a device called a brouter which will function similar to a bridge for network transport protocols that are not routable, and will function as a router for routable protocols. It functions at the network and data link layers of the OSI network model. 21


GATEWAY Gateway is the point where the packets leaves its own area network and enter into another network. A gateway can translate information between different network data formats or network architectures. It can translate TCP/IP to AppleTalk so computers supporting TCP/IP can communicate with Apple brand computers. Most gateways operate at the application layer, but can operate at the network or session layer of the OSI model. Gateways will start at the lower level and strip information until it gets to the required level and repackage the information and work its way back toward the hardware layer of the OSI model. A gateway is usually a dedicated device or a set of services running on a dedicated computer. Gateways are essentially devices that direct network traffic in some fashion and translate that information. 22

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Examples include the following: E-mail gateways—for example, a gateway that receives Simple Mail Transfer Protocol (SMTP) e-mail, translates it into a standard X.400 format, and forwards it to its destination. Gateway Service for NetWare (GSNW), which enables a machine running Microsoft Windows NT Server or Windows 2000 Server to be a gateway for Windows clients so that they can access file and print resources on a NetWare server. Gateways between a Systems Network Architecture (SNA) host and computers on a TCP/IP network, such as the one provided by Microsoft SNA Server. A packet assembler/disassembler (PAD) that provides connectivity between a local area network (LAN) and an X.25 packet-switching network. 23


REPEATER A networking component that extends a network by boosting the signal so that it can travel farther along the cabling. A repeater connects two segments of your network cable. Repeaters work only at the physical layer of the OSI network model. Other uses for repeaters include the following: Joining two 16-Mbps Token Ring networks in different buildings over distances up to 3000 meters over multimode fiber-optic cabling or up to 20 kilometers over single-mode fiber Increasing the lobe length between a Token Ring main ring and a remote node Joining dissimilar 10Base2 and 10Base5 segments to form a single Ethernet LAN Boosting signals from mainframe controllers to 3270 terminals over coaxial or UTP cabling to support distances up to 2500 meters Extending the operating distance of T1 lines by placing G.703 repeaters at 2.2-kilometer intervals Extending backbone fiber-optic cable runs in campus wide LANs or metropolitan area networks (MANs) 24

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Repeaters are also used in fiber-optic networks to amplify and regenerate light signals for long-distance cable runs. Repeaters come in various types for different network architectures and data communication technologies. Repeaters are also used in fiber-optic networks to amplify and regenerate light signals for long-distance cable runs. Repeaters come in various types for different network architectures and data communication technologies. 25


SWITCHES Any device that can control the flow of electrical signals. A number of special-purpose switches are used in networking. For example, the following types of switches are used to control access to computers by printers, keyboards, and monitors: Matrix switches: Have a keypad for mapping input ports to output ports and are typically used to connect several printers to several workstations Code-operated switches: Use a data string sent by the PC to select the printer port to be used Port-contention or scanning switches: Use several input ports but only one output port and monitor the input ports continually for data to route to the output port KVM switches: Allow one keyboard/video-monitor/mouse to be used for several servers 26

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Types of Switches: Cut-through switch: Cut-through switch forwards packets immediately by reading the destination address as they're received and relaying the packets out through the appropriate port with no additional processing. The switch doesn't even wait for the entire packet to arrive before it begins forwarding it. Cut-through switches use a hardware-based mechanism. Store-and-forward switch: A store-and-forward switch waits until an entire packet arrives before forwarding it to its destination. Verify the data by performing a cyclical redundancy check (CRC). 27

HUB : 

HUB A hub or concentrator is a device used to connect all of the computers on a star or ring network. A hub is generally termed a workgroup hub if it supports up to 50 stations, a departmental hub if it supports up to 250 stations, and an enterprise hub if it supports more than 250 stations. Stackable hubs can be used to provide these various capabilities. Types of hubs: Passive hubs: A hub which does not need an external power source. Passive hubs do not amplify the electrical signal of incoming packets before broadcasting them out to the network. Active hubs: Active hubs which regenerates the signal and therefore needs an external power supply. Intelligent hubs: Intelligent hubs add extra features to an active hub that are of particular importance to businesses. A hub which provides error detection (e.g. excessive collisions) and also does what an active hub does. 28

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There are numerous types of hubs for various specialized uses. These include the following: Minihubs: Which have only 4 to 8 ports and are used for quick or temporary LAN extensions. Minihubs can be as small as a cigarette packet. Workgroup hubs: which are the basic building blocks of small workgroup LANs. These typically have 8 or 16 ports on them. Stackable hubs: which are modular in design and can be mounted in racks and cabinets within the wiring closet and can be connected using special ribbon or DB-50 cables. Stackable hubs are available in configurations of 8, 16, and 24 ports and can be stacked to effectively form a single hub with 48, 72, 144, or more ports. Stackable hubs take less space and are easier to manage than regular workgroup hubs. Dual-speed hubs: Which have autosensing ports that support combinations of both 100-Mbps Fast Ethernet connections and 10-Mbps traditional Ethernet connections. Dual-speed hubs are typically stackable hubs with 8 or 16 ports that can be stacked to support a total of 32 or 48 ports. Fast hubs: Which have 100-Mbps ports only for forming 100BaseTX Fast Ethernet LANs. Supports up to 144 stations, and they might include fiber-optic ports for connecting to a high-speed fiber-optic backbone. Modular hubs: Which are more expensive hubs that provide a backplane or chassis in which cards can be inserted to create custom hub configurations. They are more common in Token Ring or Fiber Distributed Data Interface (FDDI) environments 29


MODEM MODEM: The term “modem” (which actually stands for “modulator/demodulator”). a hardware device that converts the digital signals generated by computers into analog signals suitable for transmission over a telephone line, and back again. A dial-up connection between two computers requires a modem at each end, both of which support the same communication protocols. Modems take the form of internal devices that plug into one of a computer's expansion slots, or external devices that connect to one of the computer's serial ports. The term modem is also used incorrectly, in many cases, to describe any device that provides a connection to a wide area communications service, such as a cable television or DSL connection. These devices are not actually modems, because the service is digital, and no analog/digital conversion takes place. 30

Modem types include the following : 

Modem types include the following Internal modems: which are installed as interface cards inside the computer and functions such as encoding and data compression. External modems: which are generally more expensive and connect to the serial port on the computer using a DB9 or DB25 connector. External modems are useful when several users need to share a modem. PCMCIA modems: which are credit-card-sized modems for laptop computers used by mobile workers. Voice/data/fax modems: which can be used for file transfer, sending and receiving faxes, and voice mail using associated software. 31

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Analog modem: A modem used for asynchronous transmission of data over Plain Old Telephone Service (POTS) lines. Analog modems are still a popular component for remote communication between users and remote networks. this basic process can transmit data only at speeds of about 1200 bps. Digital modem: Any type of modem used for synchronous transmission of data over circuit-switched digital lines. Digital modems are not used for changing analog signals into digital signals because they operate on end-to-end digital services. They are basically data framing devices, rather than signal modulators. V series: A series of communication standards developed by the International Telecommunication Union (ITU). V series protocols define methodologies for exchanging data over the public telephone system by using telecommunications devices such as modems and multiplexers. 32

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