Computer Hardware & Networking

Third Year Diploma Courses in Electronics & Telecommunication Engineering Branch. Computer Hardware & Networking As per MSBTE G Scheme Syllabus Topic 4 Introduction to Networks Total Marks- 10 Specific Objectives: Classify types of networks Plan and design network Install, configure and use networking devices Test and maintain networks Contents: 4.1 Network classification: LAN, WAN, MAN. Peer to peer and client server networks 4.2 Network topology, Benefits of networks 4.3 Network cables- coaxial, UTP, STP, fiber optics their comparison and characteristics 4.4 Network standards- Ethernet, Ring, Token, wireless 4.5 Principle, operation and function of Hubs, Switches, Routers, Bridges, Repeaters, Gateways, firewalls. Prof. Gunwant V. Mankar B.E(IT), M.Tech(CSE), AMIE, MIAEng, MSCI HOD CSE Dept. (Somayya Dip. In Engg, Chandrapur) e-mail:- info@gunwantmankar.com Website-

Topic 4 Introduction to Networks Basic of Networking A computer network consists of a collection of computers, printers and other equipment that is connected together so that they can communicate with each other. Fig 1 gives an example of a network in a school comprising of a local area network or LAN connecting computers with each other, the internet, and various servers. Fig. Representation of Network in School 1. Network classification: LAN, WAN, MAN. Peer to peer and client server networks 1.1 Network classification: [S-16] Computer Networks are classified based on the geographical area into Local Area Network (LAN) Metropolitan Area Network (MAN) Wide Area Network (WAN) Personal Area Network (PAN) Campus Area Network (CAN) 1.1.1 Local Area Network(LAN) A LAN is a network that is used for communicating among computer devices, usually within an office building or home. A LAN permits users to share resources- hardware, software or user-created files. Sharing of resources makes it possible to maximize the investments made in each resource. Ideally, distant resources should appear to be local to the user LANs are capable of very high transmission rates (100s Mb/s to G b/s). LAN s can be either wired or wireless. Twisted pair, coax or fibre optic cable can be used in wired LAN s Page 2

LAN s enable the sharing of resources such as files or hardware devices that may be needed by multiple users LAN is limited in size, typically spanning a few hundred meters, and no more than a mile LAN is fast, with speeds from 10 Mbps to 10 Gbps Requires little wiring, typically a single cable connecting to each device Advantages of LAN Speed Cost Security E-mail Resource Sharing Disadvantages of LAN Expensive To Install Requires Administrative Time File Server May Fail Cables May Break 1.1.2 Metropolitan Area Network (MAN) [W-15] Definition- [W-15] Short for Metropolitan Area Network, a data network designed for a town or city. In terms of geographic breadth, MANs are larger than local-area networks (LANs), but smaller than wide-area networks(wans). MANs are usually characterized by very high-speed connections using fiber optical cable or other digital media. Page 3

A metropolitan area network (MAN) is a large computer network that usually spans a city or a large campus. A MAN is optimized for a larger geographical area than a LAN, ranging from several blocks of buildings to entire cities. A MAN might be owned and operated by a single organization, but it usually will be used by many individuals and organizations. A MAN often acts as a high speed network to allow sharing of regional resources. A MAN typically covers an area of between 5 and 50 km diameter. Examples of MAN: Telephone company network that provides a high speed DSL to customers and cable TV network Fig. MAN Network Advantages of MAN It provides a good backbone for large network It provides greater access to the WAN Best use of bandwidth and resource sharing Improves the quality of service Disadvantages of MAN Costly More cable required Difficult to manage It is difficult to secure MAN network from hackers Page 4

1.1.3 Wide Area Network (WAN) WAN covers a large geographic area such as country, continent or even whole of the world. A WAN is two or more LANs connected together. The LANs can be many miles apart. To cover great distances, WANs may transmit data over leased high-speed phone lines or wireless links such as satellites. Multiple LANs can be connected together using devices such as bridges, routers, or gateways, which enable them to share data. The world's most popular WAN is the Internet. Fig. WAN Internet Network 1.1.4 Personal Area Network(PAN) A PAN is a network that is used for communicating among computers and computer devices (including telephones) in close proximity of around a few meters within a room It can be used for communicating between the devices themselves, or for connecting to a larger network such as the internet. PAN s can be wired or wireless A personal area network (PAN) is a computer network used for communication among computer devices, including telephones and personal digital assistants, in proximity to an individual's body. The devices may or may not belong to the person in question. The reach of a PAN is typically a few meters Page 5

1.1.5 Difference between LAN and WAN. [S-15] Parameters LAN WAN Stands For Local Area Network Wide Area Network Covers Local areas only (e.g., homes, offices, schools) Large geographic areas (e.g., cities, states, nations) Definition LAN (Local Area Network) is a computer network covering a small geographic area, like a home, office, school, or group of buildings. WAN (Wide Area Network) is a computer network that covers a broad area (e.g., any network whose communications links cross metropolitan, regional, or national boundaries over a long distance). Speed High speed (1000 mbps) Less speed (150 mbps) Data transfer rates LANs have a high data transfer rate. The network in an office building can be a LAN WANs have a lower data transfer rate compared to LANs. The Internet is a good example of a WAN WANs tend to use technologies like MPLS, ATM, Frame Relay and X.25 for connectivity over longer distances Computers connected to a wide-area network are often connected through public networks, such as the telephone system. They can also be connected through leased lines or satellites. Example Technology Tend to use certain connectivity technologies, primarily Ethernet and Token Ring Connection One LAN can be connected to other LANs over any distance via telephone lines and radio waves 1.1.6 Comparisons of LAN, WAN, MAN Characteristics LAN MAN Metropolitan area network Within one city or campus WAN Full form Local area network Size Within one kilometer Types of cable Twisted pair cables user Coaxial cables used For connecting two countries fiber optic cables used Speed High speed (1000 mbps) Speeds from 10 Mbps to 10 Gbps Less speed (150 mbps Installation Expensive To Install and Less Expensive To difficult Install and easy Expensive To Install and complex Maintenance Complex troubleshoot but not difficult Easy to troubleshoot Complex and difficult Example Cyber cafes and college network labs Telephone company network that provides a high speed DSL to The world's most popular WAN is the Internet. Wide area network Would wide Page 6

customers and cable TV network. 1.2 Peer to peer and client server networks 1.2.1 Peer to peer (P2P Network) [W-14] Peer-to-peer (P2P) is an alternative network model to that provided by traditional client -server architecture. P2P networks use a decentralized model in which each machine, referred to as a peer, functions as a client with its own layer of server functionality. A peer plays the role of a client and a server at the same time. That is, the peer can initiate requests to other peers, and at the same time respond to incoming requests from other peers on the network. It differs from the traditional client-server model where a client can only send requests to a server and then wait for the server s response. In P2P networks overall network performance actually improves as an increasing number of peers are added to the network. These peers can organize themselves into ad-hoc groups as they communicate, collaborate and share bandwidth with each other to complete the tasks at hand (e.g. file sharing). Each peer can upload and download at the same time, and in a process like this, new peers can join the group while old peers leave at any time. This dynamic re-organization of group peer members is transparent to end-users. Fig. Peer to Peer based network 1.2.1.1 Features of peer to peer network [S-15] Page 7

1. A peer-to-peer (P2P) network is a type of decentralized and distributed network architecture in which individual nodes in the network (called peers ) act as both suppliers and consumers of resources. 2. In Peer-to peer network each computer is responsible for making its own resources available to other computers on the network. 3. Peer to peer network is useful for a small network containing less than 8-10 computers on a single LAN and each computer maintains its own accounts and their security settings. 4. In a peer to peer network, a group of computers is connected together so that user can share resources and information. 1.2.2 Client server network [W-14] There are an almost infinite variety of client/server networks, but all of them have a couple of things in common. All have centralized security databases that control access to shared resources on servers. A client can only send requests to a server and then wait for the server s response. The server contains a list of usernames and passwords. Users can t log on to the network unless they supply valid usernames and passwords to the server. Once logged on, users may access only those resources that the network administrator allows them to access. Thus, client/server networks possess much more security than do peer-to-peer networks. Client/server networks also tend to be much more stable. Fig. client/server network 1.2.3 Comparison of Peer to peer and Client server network Page 8

2. Network topology, Benefits of networks Topology:The physical topology of a network refers to the configuration of cables, computers, and other peripherals. Physical topology should not be confused with logical topology which is the method used to pass information between workstations. 2.1 Network topology [W-14, S-16] Page 9

The topology of a network is the geometric representation of the relationship of all the links and linking devices (usually called nodes) to one another. OR Networks can be laid out in different ways. The physical layout, or shape of network, or the way in which network connections are made is called a topology. It refers especially the locations of computers and how the cable is run between them. It is important to select the right topology for how the network will be used. 2.1.1 Types of Topology with meaning [S-15] 1. Bus topology 2. Star Topology 3. Ring topology 4. Tree Topology 5. Mesh topology 6. Hybrid Topology 1. Bus Topology: In networking a topology that allows all network nodes to receive the same message through the network cable at the same time is called bus topology. 2. Star Topology: Unlike bus topology, where nodes are connected to central cable, here all the hosts or workstations are connected to central device called hub or connector with a point-to-point connection. 3. Ring Topology: A network topology that is setup in circular fashion. In other words all nodes in ring topology are connected in ring structure. 4. Tree Topology: As its names implies in this topology devices make a tree structure. It is also called expanded star topology. 5. Mesh Topology: In a mesh network topology, each of the network node, computer and other devices, are interconnected with one another. 6. Hybrid Topology: A combination of two or more different topologies makes for a hybrid topology 2.1.1.1 Bus Topology: [W-14] Page 10

In a bus topology the computers are connected in a line, the cable is just one or more wires; pass it along from computer to computer. It is a passive topology. When one computer sends a signal up (and down) the wire, all the computers on the network receive the information, but only one (the one with the address that matches the one encoded in the message) accepts the information. The rest disregard the message. Only one computer at a time can send a message; therefore, the number of computers attached to a bus network can significantly affect the speed of the network. A computer must wait until the bus is free before it can transmit. Fig shows Bus network. Figure 1: All computers are connected to common channel (BUS) The important issue in bus networks is termination. Since the bus is a passive topology, the electrical signal from a transmitting computer is free to travel the entire length of the cable. Without termination, when the signal reaches the end of the wire, it bounces back and travels back up the wire. When a signal echoes back and forth along an unterminated bus, it is called ringing. To stop the signals from ringing, you have to attach terminators at either end of the segment. The terminators absorb the electrical energy and stop the reflections. Cables cannot be left un-terminated in a bus network. Advantages Simple, easy to use, and suitable for very small networks Least amount of cable is required to connect the computers together and therefore it is less expensive. Easy to extend a bus, two cables can be joined with a BNC barrel connector, allowing more computers to join the network. Disadvantages Network disruption when computer added or removed. A break in the cable will prevent all system from accessing the network Difficult to troubleshoot 2.1.1.2 Star topology [W-14] Page 11

A star network is one in which all the cables run from the computers to a central location, where they are all connected by a device called a hub. Each computer on a star network communicates with a central hub that resends the message either to all the computers (in a broadcast star network) or only to the destination computer (in a switched star network). The hub in a broadcast star network can be active or passive. Fig: In a star topology the computers are all connected by Cables to a central point Advantages It is easy to modify and add new computers to a star network without disturbing the rest of the network. Hub can accommodate multiple cable types. Fault finding becomes very simple Single computer failure does not bring down the whole network It is more flexible among the remaining topology. Disadvantages Requires more cable A central connecting device allows for a single point of failure More difficult to implement 2.1.1.3 Ring topology Logical ring Meaning that data travels in circular fashion from one computer to another on the network. Typically FDDI, SONET or Token Ring technology are used to implement a ring Network Ring networks are most commonly wired in a star configuration Token Ring has multi-station access unit (MSAU),equivalent to hub or switch. MSAU performs the token circulation internally. Page 12

Fig. Ring Topology 2.1.1.4 Tree topology Fig. Tree topology A tree topology combines characteristics of linear bus and star topologies. It consists of groups of star-configured workstations connected to a linear bus backbone cable. Page 13

Tree topologies allow for the expansion of an existing network, and enable schools to configure a network to meet their needs. Advantages Point-to-point wiring for individual segments. Supported by several hardware and software vender s. Disadvantages Overall length of each segment is limited by the type of cabling used. If the backbone line breaks, the entire segment goes down. More difficult to configure and wire than other topologies. 2.1.1.5 Mesh topology Each computer connects to every other. High level of redundancy. Rarely used. -Wiring is very complicated -Cabling cost is high -Troubleshooting a failed cable is tricky A variation hybrid mesh create point to point connection between specific network devices, often seen in WAN implementation Page 14

2.2 Benefits/Advantages/Features of network: [S-15, S-16] Resource Sharing Reducing cost Application services High Reliability Improved security Centralized management. E-mail Flexible access OR Sharing information: Networks allow users to share information in several different ways. The most common way of sharing information is to share individual files. Communication : Networks allow users to communicate with each other in various ways. For example, messaging applications let network users exchange messages with each other using an e-mail, messaging, conferencing etc. Sharing resources: Certain computer resources, such as printers or hard drives, can be set up so that network users can share them. Sharing these resources can result in significant cost savings. Resource can be network connections (internet) also, where a single connection can be shared among various computers. Sharing applications: One of the most common reasons for networking is that several users can work together on a single application. A single application can be shared and hence the cost of installation, maintenance reduces and also makes it easier to manage these applications. 3. Network cables- Coaxial, UTP, STP, fiber optics their comparison and characteristics Cable is the medium through which information usually moves from one network device to another. There are several types of cable which are commonly used with LANs. In some cases, a network will utilize only one type of cable, other networks will use a variety of cable types. The type of cable chosen for a network is related to the network's topology, protocol, and size The following are types of cables used in networks. 1. 2. 3. 4. Coaxial Cable Unshielded Twisted Pair (UTP) Cable Shielded Twisted Pair (STP) Cable Fiber Optic Cable 3.1 Coaxial Cable Coaxial cabling has a single copper conductor at its center. A plastic layer provides insulation between the center conductor and a braided metal shield (See fig.). Page 15

The metal shield helps to block any outside interference from fluorescent lights, motors, and other computers. Fig. Coaxial cable Although coaxial cabling is difficult to install, it is highly resistant to signal interference. In addition, it can support greater cable lengths between network devices than twisted pair cable. The two types of coaxial cabling are thick coaxial and thin coaxial. 3.1.1 Thin coaxial cable is also referred to as thinnet. 10Base2 refers to the specifications for thin coaxial cable carrying Ethernet signals. The 2 refers to the approximate maximum segment length being 200 meters. In actual fact the maximum segment length is 185 meters. Thin coaxial cable has been popular in school networks, especially linear bus networks. Thick coaxial cable is also referred to as thicknet. 10Base5 refers to the specifications for thick coaxial cable carrying Ethernet signals. The 5 refers to the maximum segment length being 500 meters. Thick coaxial cable has an extra protective plastic cover that helps keep moisture away from the center conductor. This makes thick coaxial a great choice when running longer lengths in a linear bus network. Coaxial Cable Connectors The most common type of connector used with coaxial cables is the Bayone-NeillConcelman (BNC) connector. Different types of adapters are available for BNC connectors, including a T-connector, barrel connector, and terminator. Connectors on the cable are the weakest points in any network. To help avoid problems with your network, always use the BNC connectors that crimp, rather screw, onto the cable. Fig. BNC connector Page 16

3.2 Unshielded Twisted Pair (UTP) Cable Twisted pair cabling comes in two varieties: shielded and unshielded. Unshielded twisted pair (UTP) is the most popular and is generally the best option for school networks Fig. Unshielded twisted pair 3.2.1 The quality of UTP may vary from telephone-grade wire to extremely high-speed cable. The cable has four pairs of wires inside the jacket. Each pair is twisted with a different number of twists per inch to help eliminate interference from adjacent pairs and other electrical devices. The tighter the twisting, the higher the supported transmission rate and the greater the cost per foot. The EIA/TIA (Electronic Industry Association/Telecommunication Industry Association) has established standards of UTP and rated six categories of wire (additional categories are emerging). Unshielded Twisted Pair Connector The standard connector for unshielded twisted pair cabling is an RJ-45 connector. This is a plastic connector that looks like a large telephone-style connector. A slot allows the RJ-45 to be inserted only one way. RJ stands for Registered Jack, implying that the connector follows a standard borrowed from the telephone industry. This standard designates which wire goes with each pin inside the connector Fig. RJ-45 connector 3.3 Shielded Twisted Pair (STP) Cable Although UTP cable is the least expensive cable, it may be susceptible to radio and electrical frequency interference (it should not be too close to electric motors, fluorescent lights, etc.). If you must place cable in environments with lots of potential Page 17

interference, or if you must place cable in extremely sensitive environments that may be susceptible to the electrical current in the UTP, shielded twisted pair may be the solution. Shielded cables can also help to extend the maximum distance of the cables. Shielded twisted pair cable is available in three different configurations: 1. Each pair of wires is individually shielded with foil. 2. There is a foil or braid shield inside the jacket covering all wires (as a group). 3. There is a shield around each individual pair, as well as around the entire group of wires (referred to as double shield twisted pair). 3.4 Fiber Optic Cable Fiber optic cabling consists of a center glass core surrounded by several layers of protective materials. It transmits light rather than electronic signals eliminating the problem of electrical interference. This makes it ideal for certain environments that contain a large amount of electrical interference. It has also made it the standard for connecting networks between buildings, due to its immunity to the effects of moisture and lighting. Fiber optic cable has the ability to transmit signals over much longer distances than coaxial and twisted pair. It also has the capability to carry information at vastly greater speeds. Fig. Fiber optic cable This capacity broadens communication possibilities to include services such as video conferencing and interactive services. The cost of fiber optic cabling is comparable to copper cabling; however, it is more difficult to install and modify. 10BaseF refers to the specifications for fiber optic cable carrying Ethernet signals. Page 18

The center core of fiber cables is made from glass or plastic fibers. A plastic coating then cushions the fiber center, and kevlar fibers help to strengthen the cables and prevent breakage. The outer insulating jacket made of teflon or PVC. 3.4.1 Different modes of Fiber Optic Cable [W-15] STEP-INDEX MULTIMODE FIBER has a large core, up to 100 microns in diameter. As a result, some of the light rays that make up the digital pulse may travel a direct route, whereas others zigzag as they bounce off the cladding. These alternative pathways cause the different groupings of light rays, referred to as modes, to arrive separately at a receiving point. The pulse, an aggregate of different modes, begins to spread out, losing its welldefined shape. The need to leave spacing between pulses to prevent overlapping limits bandwidth that is, the amount of information that can be sent. Consequently, this type of fiber is best suited for transmission over short distances, in an endoscope, for instance. GRADED-INDEX MULTIMODE FIBER contains a core in which the refractive index diminishes gradually from the center axis out toward the cladding. The higher refractive index at the center makes the light rays moving down the axis advance more slowly than those near the cladding. Also, rather than zigzagging off the cladding, light in the core curves helically because of the graded index, reducing its travel distance. The shortened path and the higher speed allow light at the periphery to arrive at a receiver at about the same time as the slow but straight rays in the core axis. The result: a digital pulse suffers less dispersion. Page 19

SINGLE-MODE FIBER has a narrow core (eight microns or less), and the index of refraction between the core and the cladding changes less than it does for multimode fibers. Light thus travels parallel to the axis, creating little pulse dispersion. Telephone and cable television networks install millions of kilometers of this fiber every year. 3.5 Comparison and Characteristics of twisted pair, coaxial and fiber optical cable Characteristics Twisted Pair Cable Coaxial Cable Fiber Optic Cable Use Mostly used in LAN Mostly used in MAN Speed Installation Cost Types of Connectors Used 100 to 1 Gbps Difficult to install High Up to 1 Gbps Easy to install High Mostly used in LAN & WAN 1 Gbps to 100 Gbps Complex and difficult Very High RJ 45, RJ 11 BNC type - Types of cable STP and UTP Thick and Thin Single mode and Multimode Color Coding Signal transmission Complex, crossover and No color coding streight forword In Analog format with Analog format with low frequency high frequency No color coding Light ray signals refers glass cladding 3.5.1 Compare Fiber Optic cable with UTP cable [W-15] Parameters Transmission rate Fiber optic cable It has low transmission rates It is easy to install as compared to fiber cables It has high transmission rates It does take a bit longer to terminate fiber than copper. Security It can be easily eavesdrop. It is very secured Cost UTP is cheaper as compared to fiber optic cables Fiber is more expensive than copper due to the light emitting equipment and cost. Ease of installation 3.5.2 UTP Characteristics of fiber optic cable [S-15] 1. Fiber optic cabling can provide extremely high bandwidths in the range from 100 mbps to 2 gigabits because light has a much higher frequency than electricity. 2. The number of nodes which a fiber optic can support does not depend on its length but on the hub or hubs that connect cables together. 3. Fiber optic cable has much lower attenuation and can carry signal to longer distances without using amplifiers and repeaters in between. 4. Fiber optic cable is not attached by EMI effects and can be used in area where high voltages are passing by. Page 20

5. The cost of fiber optic cable is more compared to twisted pair and co-axial. 6. The installation of fiber optic cables is difficult and tedious. 4. Network standards- Ethernet, Ring, Token, wireless 4.1 Ethernet Ethernet has been a relatively inexpensive, reasonably fast, and very popular LAN technology for several decades. The Ethernet standard has grown to encompass new technologies as computer networking has matured. Specified in a standard, IEEE 802.3, an Ethernet LAN typically uses coaxial cable or special grades of twisted pair wires. Ethernet is also used in wireless LANs. Ethernet uses the CSMA/CD access method to handle simultaneous demands. The most commonly installed Ethernet systems are called 10BASE-T and provide transmission speeds up to 10 Mbps. Devices are connected to the cable and compete for access using a Carrier Sense Multiple Access with Collision Detection (CSMA/CD) protocol. Fast Ethernet or 100BASE-T provides transmission speeds up to 100 megabits per second and is typically used for LAN backbone systems, supporting workstations with 10BASE-T cards. Gigabit Ethernet provides an even higher level of backbone support at 1000 megabits per second (1 gigabit or 1 billion bits per second). 10-Gigabit Ethernet provides up to 10 billion bits per second. This comprehensive tutorial includes a wide range of information on IEEE 802.3 standards, Topologies, CSMA/CD access methods, Wireless-LAN, and transmission speeds. Transmission Speed 10Base-T The most commonly installed Ethernet systems are called 10BASE-T and provide transmission speeds up to 10 Mbps. Devices are connected to the cable and compete for access using a Carrier Sense Multiple Access with Collision Detection (CSMA/CD) protocol. 100BASE-T Fast Ethernet or 100BASE-T provides transmission speeds up to 100 megabits per second and is typically used for LAN backbone systems, supporting workstations with 10BASE-T cards. The 100BASE-T standard consists of five different component specifications. These include the Media Access Control (MAC) layer, the Media Independent Interface (MII), and the three physical layers, (100 BASE-TX, 100BASET4, and 100BASE-FX). 4.2 Token Ring Page 21

IEEE 802.5 is the second of the token passing access control methods. Token-ring is most commonly a logical and physical ring topology used in a network structure following both. The right to transmit is controlled by a token. The method of transmission is as follows: A token indicating the right to transmit is known as a free token. When a station receives a free token it changes the configuration of the token to that of a busy token. The busy token is included as part of each data unit transmitted. The station is allowed to transmit data units until a predetermined time is reached. The data unit travels from station to station around the ring. Each station receiving a data unit checks the address to see if it should process the information. If the data unit is intended for another station, it is passed on to the next station in the ring. The intended destination station, upon receiving and processing the data unit, sets three control bits in the data unit before sending it to the next station: The Address Recognized control bit allows the destination station to indicate that it identified the data unit as being addressed to it. The Packet Copied control bit shows that the destination station sent a copy of the data unit to the LLC sublayer for processing. The Error control bit shows that an error condition was detected. This control bit can be set by any station on the ring, not only by the destination station. Once the data unit returns to the originating station, it is removed from the network. The station then sends a free token to the next station in the ring. 4.3 Token Bus The IEEE 802.4 standard specifies the Token-bus media access control method. It is one of two token passing access methods. IEEE 802.4 is based on a physical bus or tree topology. The Token-bus approach requires a station to have possession of a token in order to transmit. The token is passed from station to station in a logical ring. IEEE 802.4 is the basis for LAN architectures often used in factory automation, such as MAP and ARCnet. 4.4 Wireless 802.11 An 802.11 LAN is based on a cellular architecture where the system is subdivided into cells. Each cell (called Basic Service Set, or BSS, in the 802.11 nomenclature) is controlled by a Base Station (called Access Point or, in short, AP). Although a wireless LAN may be formed by a single cell, with a single Access Point, (and as will be described later, it can also work without an Access Point), most installations will be formed by several cells, where the Access Points are connected Page 22

through some kind of backbone (called Distribution System or DS). This backbone is typically Ethernet and, in some cases, is wireless itself. The whole interconnected Wireless LAN, including the different cells, their respective Access Points and the Distribution System, is seen as a single 802 network to the upper layers of the OSI model and is known in the Standard as Extended Service Set (ESS). The standard also defines the concept of a Portal. A portal is a device that interconnects between an 802.11 and another 802 LAN. This concept is an abstract description of part of the functionality of a translation bridge. Even though the standard does not necessarily request it, typical installations will have the AP and the Portal on a single physical entity. This is also the case with BreezeCOM s AP which provides both functions. 5. Principle, operation and function of Hubs, Switches, Routers, Bridges, Repeaters, Gateways, firewalls. 5.1 List networking devices [S-16] Hubs Switches Router Bridge Repeaters Gateways Modems 5.1.1 Hubs A hub is a small, simple, inexpensive device that joins multiple computers together at a low level network protocol layer. Functions of Hubs: [S-16] It is essentially a multi port repeater (repeater receives digital data, regenerates the signal and then re-transmits the data). Principle operation/working of Hub 1. At the bottom of the networking food chain, so to speak, are hubs. Hubs are used in networks that use twisted-pair cabling to connect devices. 2. Hubs can also be joined together to create larger networks. Hubs are simple devices that direct data packets to all devices connected to the hub, regardless of whether the data package is destined for the device. This makes them inefficient devices and can create a performance bottleneck on busy networks. Page 23

3. In its most basic form, a hub does nothing except provide a pathway for the electrical signals to travel along. Such a device is called a passive hub. Far more common nowadays is an active hub, which, as well as providing a path for the data signals, regenerates the signal before it forwards it to all of the connected devices. 4. A hub does not perform any processing on the data that it forwards, nor does it perform any error checking. 5. Hubs come in a variety of shapes and sizes. Small hubs with five or eight connection ports are commonly referred to as workgroup hubs. Others can accommodate larger numbers of devices (normally up to 32). These are referred to as high-density devices. Because hubs don t perform any processing, they do little except enable communication between connected devices. 5.1.2 Switches A switch is a networking device that joins multiple computers together at a low level network protocol layer. Functions of Switches: [S-16] It is used to transport the data to the specific computer. Principle operation/working of Switches 1. Like hubs, switches are the connectivity points of an Ethernet network. 2. Devices connect to switches via twisted-pair cabling, one cable for each device. 3. The difference between hubs and switches is in how the devices deal with the data that they receive. Whereas a hub forwards the data it receives to all of the ports on the device, a switch forwards it only to the port that connects to the destination device. It does this by learning the MAC address of the devices attached to it, and then by matching the destination MAC address in the data it receives. Fig. How switch works. 4. By forwarding data only to the connection that should receive it, the switch can improve network performance in two ways. First, by creating a direct path between two devices and controlling their communication, it can greatly reduce the number of collisions on the network. As you might recall, collisions occur on Ethernet networks when two devices attempt to transmit at exactly the same time. 5. In addition, the lack of collisions enables switches to communicate with devices in full-duplex mode. In a full-duplex configuration, devices can send and receive data from the switch at the same time. Page 24

6. Contrast this with half-duplex communication, in which communication can occur in only one direction at a time. Full-duplex transmission speeds are double that of a standard, half-duplex, connection. So, a 10Mbps connection becomes 20Mbps, and a 100Mbps connection becomes 200Mbps. 7. The net result of these measures is that switches can offer significant performance improvements over hub-based networks, particularly when network use is high. 8. Irrespective of whether a connection is at full or half duplex, the method of switching dictates how the switch deals with the data it receives. There are three basic types of switch 1. Cut-through In a cut-through switching environment, the packet begins to be forwarded as soon as it is received. This method is very fast, but creates the possibility of errors being propagated through the network, as there is no error checking. 2. Store-and-forward Unlike cut-through, in a store-and-forward switching environment, the entire packet is received and error checked before being forwarded. The upside of this method is that errors are not propagated through the network. The downside is that the error checking process takes a relatively long time, and store-andforward switching is considerably slower as a result. 3. FragmentFree To take advantage of the error checking of store-and forward switching, but still offer performance levels nearing that of cutthrough switching, FragmentFree switching can be used. In a FragmentFree-switching environment, enough of the packet is read so that the switch can determine whether the packet has been involved in a collision. As soon as the collision status has been determined, the packet is forwarded. 5.1.3 Router Router is a physical device that joins multiple networks together. Functions of Router: [S-16] It connects dissimilar networks such as LAN and Internet together. Features of Router:-[S-15] 1) A router is a specialized computer connected to more than one n/w 2) Router operate at the n/w layer 3) The primary function of a router is to connect n/w together & keep layer 2 broadcast traffic under control. 4) A router is typical connected to at least two n/w commonly two LAN OR WAN or LAN and its ISP s n/w or more n/w connects. 5) Routers are located at gateways, the places where two or more n/w connect. Principle operation/working of Router Page 25

1. In a common configuration, routers are used to create larger networks by joining two network segments. Such as a SOHO router used to connect a user to the Internet. 2. A router can be a dedicated hardware device or a computer system with more than one network interface and the appropriate routing software. All modern network operating systems include the functionality to act as a router. 3. Routers will normally create, add, or divide on the Network Layer as they are normally IP-based devices. 4. A router derives its name from the fact that it can route data it receives from one network onto another. When a router receives a packet of data, it reads the header of the packet to determine the destination address. 5. Once it has determined the address, it looks in its routing table to determine whether it knows how to reach the destination and, if it does, it forwards the packet to the next hop on the route. The next hop might be the final destination, or it might be another router. Fig shows, in basic terms, how a router works. 6. As you can see from this example, routing tables play a very important role in the routing process. They are the means by which the router makes its decisions. For this reason, a routing table needs to be two things. It must be up-to-date, and it must be complete There are two tyes of Routers 1) Static Router: This router is hard coded in the routing table The administrative has to configure & setup all router manually. Static routing is the process of predefining router paths across data n/w & can be used to conserve LAN & WAN bandwidth. 2) Dynamic Router: Only the 1st Route has to be manually configured after that additional route are automatically discovered. The route is decided by the router on the basis of traffic & cost. They use specialize protocols to exchange information 5.1.4 Bridge Page 26

A bridge is an electrical device which connects and passes packets between two network segments. Functions: [S-16] It is used to send the data to the concerned segment, thus reducing excess traffic. Principle operation/working of Bridges Bridges are used to divide larger networks into smaller sections. They do this by sitting between two physical network segments and managing the flow of data between the two. By looking at the MAC address of the devices connected to each segment, bridges can elect to forward the data (if they believe that the destination address is on another interface), or block it from crossing (if they can verify that it is on the interface from which it Bridges can also be used to connect two physical LANs into a larger logical LAN. When bridges were introduced, the MAC addresses of the devices on the connected networks had to be entered manually, a time-consuming process that had plenty of opportunity for error. Today, almost all bridges can build a list of the MAC addresses on an interface by watching the traffic on the network. Such devices are called learning bridges because of this functionality. Fig. working of Bridges Types of Bridges Three types of bridges are used in networks: Transparent bridge Derives its name from the fact that the devices on the network are unaware of its existence. A transparent bridge does nothing except block or forward data based on the MAC address. Source route bridge Used in Token Ring networks. The source route bridge derives its name from the fact that the entire path that the packet is to take through the network is embedded within the packet. Translational bridge Used to convert one networking data format to another; for example, from Token Ring to Ethernet and vice versa. 5.1.5 Repeaters Page 27

A repeater is an electronic device that simply regenerates a signal. Functions: [S-16] It recreates the bit pattern of the signal and puts this regenerated signal back to the transmission medium 5.1.6 Gateways Gateway is a device used to connect networks using different protocols. Functions of Gateways: [S-16] A gateway repackages information to match the requirements of the destination system. Principle operation/working of Gatways: 1. Any device that translates one data format to another is called a gateway. Some examples of gateways include a router that translates data from one network protocol to another, a bridge that converts between two networking systems, and a software application that converts between two dissimilar formats. 2. The key point about a gateway is that only the data format is translated, not the data itself. In many cases, the gateway functionality is incorporated into another device 5.1.7 Modems Page 28

Modem is a device that makes it possible for computers to communicate over a telephone line. The word MODEM Stands for MOdulator-DEModulator. Functions: [S-16] It is used to connect telephone lines (which uses analog signals) to computers (which uses digital signals) for data communication. 5.1.8 Firewalls [W-15, S-15] Functions, principle operation and working of Firewall [W-15, S-15] 1. A firewall is a part of computer system or network that is designed to block unauthorized access while permitting authorized communications. 2. It is a device or set of devices configured to permit, deny, encrypt, decrypt, or proxy all (in and out) computer traffic between different security domain based upon a set rules and other criteria. 3. Firewalls can be implemented in either hardware or software, or a combination of both. Firewalls are frequently used to prevent unauthorized internet users from accessing private networks connected to the internet, especially intranets. 4. All messages entering or leaving the intranet pass through the firewall, which examines each messages and block those that do not meet the specified security criteria. 5. A firewall blocks unauthorized connections being made to your computer or LAN,, normal data is allowed through the firewall but all other data is blocked. There are several types of firewall techniques: i. Packet filter ii. Proxy server iii. Circuit-level Gateway iv. Application Gateway. Page 29

Important Questions:1) List two important features of peer to peer network. 2) List any two important benefits of networks. 3) List important features of routers used in computer network 4) What is network topology? List their types with meaning. 5) Explain the working principle of Firewalls. 6) Explain important characteristics of fiber optics cable. 7) Describe peer to peer and client server networks. 8) What is network topology? Explain star and bus topology with its advantages. 9) Define MAN. Give any two differences between LAN and WAN. 10) List classification of network on basis of geographical area. State the benefits of network. 11) List networking devices. State the function of any four devices. 12) Describe the different modes of Fibre Optic Cable with neat diagram. Compare Fibre Optic cable with UTP cable. 13) Describe the function and operation of Firewall with neat diagram. Page 30