networking 2011.pdf

7/27/2019 Networking 2011.pdf

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BLY / May - 2010 Module 7

ADCPM NETWORKING Page - 1

INTRODUCTION TO NETWORKING

Networking is a concept, where two or more computers are joined together toshare information. This can be in the form of data or programs. Thesecomputers can be within a walking distance or in the same building of the officeor in the same city or even across the cities.

Why is this needed? Have you ever found yourself rushing from one computer to

another in your office or home, attending to several different jobs at variouslocations? Or do you often find yourself moving files that need printing form a PCthat you happen to be working on the PC that is connected to the printer? All ofthese situations can be made easier by allowing the various machines tocommunicate with each other by networking the PCs.

The distance between the computers is narrowed down by the telephone lines.The information from the computer is converted to the media understandable bythe communication lines and then transferred from one place to another.

With networking you can not only share data and programs, but can also share

the resources like printers, scanners, etc. In PC technology, such a collection ofcomputers, all located within a few thousand feet of each other, is called LocalArea Networking.

Netwo rking Basics

Networking several computers together allows data to be transmitted form onemachine to another in rapid and easily managed data streams. This sharing ofdata allows many of the resources that are located on a single machine toeffectively become available to all other machines on the network.

These resources can be physically located on the machine, e.g., as files on the

hard disk, or connected logically to the machine. An example of a logicallyconnected resource would be a printer that is connected to a PC, but which isthen available over the network to other machines on that network.

An alternative situation would be where access to the Internet is available to allthe PCs on a network through a special communication device attached to thenetwork. Access to all external and internal resources are thus made available toPC users on the network.

A network server provides network services to a user workstation (server) on thenetwork. Services can range from sharing database and files, printers,

communications or other network resources. Thus, the network servers are alsocalled file servers, print servers, communication servers, etc. They can bededicated to the task of providing network services.

They are then called dedicated network servers. Otherwise, they may be callednon-dedicated servers. A typical networking is shown on the last page.

Another factor, which also favours the networking, is the cost factor.

Cost Reduct io n

If you have two or three computers attached in a single networking system, youmay go in for a single printer, which can be used, by all of them. The same goes

for other devices like Scanner, Plotter, etc. This results in lots of costs savings.The main advantages of Networking can be clubbed as follows:

Resou rce Sharing


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Module7 May - 2010 / BLY

Page - 2 NETWORKING ADCPM

There are two main types of networking systems. The type used for largernetworks is known as the Client/Server model. This model involves using apowerful computer that runs a Network Operating System and acts as theserver. The Network Operating System then runs the server, supplying networkservices to the other client computers.

These services might include the management of file transfers, running printingjobs, or even running applications across the network. For example, a wordprocessing software package running on a PC is actually being served as theserver across the network, rather than installed onto the PCs local hard disk.

The problem with the Client/Servermodel is that it requires specializedhardware, software and to a largeextent skilled networking techniques toconfigure and maintain the network. Allof this can become expensive.

The second model, the Peer-to Peersystem or resource Sharing isfortunately a lot easier to implementand maintain and it is the model thatwe will use in this book. ResourceSharing is incorporated into Windows98 & XP.

Netwo rk Commun ications

When you connect two or more

computers so they can communicatewith each other, you have to create adata network. This is true, whether you connect the computers using a cable, awireless technology such as infrared or radio waves, or even modems andtelephone lines. The technology that connects the computers together is calledthe network medium. Copper-based cables are the most common form ofnetwork medium, and for this reason, the term network cable is often used torefer to any kind of network medium. Figure 1.1 The networking protocolsrunning on a computer form a layered stack, with each protocol providingservices to the protocoloperating at the layerabove or below it,depending on thedirection of data flow.

When the data arrives atits destination, thereceiving computerperforms the sameprocedure as the

transmitting computer,except in reverse. Thedata is passed up

Figure 1.1


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through the layers to the receiving application, with each protocol providing anequivalent service to the protocol in the layer above it.

For example, if a protocol at layer three on the transmitting computer isresponsible for encrypting data, the same protocol at layer three of the receivingsystem is responsible for decrypting it. In this way, protocols at the various layersin the transmitting system communicate with their equivalent protocols operating

at the same layer in the receiving system, as illustrated in Figure 1.2.Lo cal Area Network s and Wide Area Netwo rks

A LAN is a group of computers located in a relatively small area and connectedby a common medium. Each of the computers and other communicating deviceson the LAN is called a node. A LAN is characterized by three primary attributes:its topology, its medium, and its protocols. The topology is the pattern used toconnect the computers together. With a bus topology, a network cable connectseach computer to the next one, forming a chain. With a star topology, each ofthe computers is connected to a central nexus called a hub or switch. A ring

topology is essentially a bus network with the two ends joined together.

In many cases, an internetwork is composed of LANs in distant locations. Toconnect remote LANs, you use a different type of network connection: a WANconnection. WAN connections can use telephone lines, radio waves, or any oneof many other technologies. WAN connections are usually point-to-point

connections, meaning that they connect only two systems. They are unlikeLANs, which can connect many systems. An example of a WAN connectionwould be a company with two offices in distant cities, each with its own LAN andconnected by a leased telephone line. This type of WAN is illustrated in Figure1.3. Each end of the leased line is connected to a router and the routers areconnected to individual LANs. Any computer on either of the LANs cancommunicate with any one of the other computers at the other end of the WANlink or with a computer on its own LAN.

Netwo rk Topologies

The topology of a network is the pattern used to connect the computers andother devices with the cable or other network medium. The Network+ examalways contains questions about the basic network topologies and their

Figure 1.3


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properties. The topology of your network is directly related to the type of cableyou use. You cannot select a particular type of cable and install it using just anytopology. However, you can create individual LANs using a different cable andtopology for each LAN and connect them together using devices such asbridges, switches, and routers. When choosing the components with which tobuild a LAN, the topology should be one of the most important criteria you use toselect a cable type. The three primary topologies used to build LANs are asfollows:

Bus

Star

Ring

You should also be familiar with the following additional topologies:

Tree

Hierarchical star

Mesh

Wireless Bus Topology

A network that uses the bus topology is one in which the computers areconnected in a single line, with each system cabled to the next system. Busnetworks are illustrated in Figure. Early Ethernet systems used the bus topologywith coaxial cable, a type of network that is rarely seen today. The cabling of abus network can take two forms: thick and thin. Thick Ethernet networks use asingle length of coaxial cable with computers connected to it using smallerindividual cables called Attachment Unit Interface (AUI) cables (sometimes

called transceiver cables), as shown on the top half of Figure 2.1. Thin Ethernetnetworks use separate lengths of a narrower type of coaxial cable, and eachlength of cable connects one computer to the next, as shown in the bottom halfof Figure 2.1.

When any one of the computers on the network transmits data, the signals traveldown the cable in both directions, reaching all of the other systems. A busnetwork always has two open ends, which must be terminated. Termination isthe process of installing a resistor pack at each end of the bus to negate thesignals that arrive there. Without terminators, the signals reaching the end of the

bus would reflect back in the other direction and interfere with the newer signalsbeing transmitted.

Figure 2.1


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The main problem with the bus topology is that a single faulty connector, faultyterminator, or break in the cable affects the functionality of the entire network.Signals that cannot pass beyond a certain point on the cable cannot reach all ofthe computers beyond that point. In addition, when a component failure splits thenetwork into two segments, each half of the cable is also unterminated. On thehalf of the network that does receive the signals transmitted by each computer,signal reflection garbles the data. This is one of the primary reasons that busnetworks are rarely used now.

Star Topolog y

Whereas the bus topology hasthe computers in a networkconnected directly to eachother, the star topology uses acentral cabling nexus called ahub or concentrator. In a starnetwork, each computer isconnected to the hub using aseparate cable, as shown inFigure 2.2. Most of theEthernet LANs installed today,and many LANs using otherprotocols as well, use the startopology. Star LANs can useseveral different cable types,including various types of twisted-pair and fiber optic cable.

The unshielded twisted pair (UTP) cables used on most Ethernet LAN is usuallyinstalled using a star topology. Functionally, a star network uses a sharednetwork medium, just as a bus network does. Despite the fact that eachcomputer connects to the hub with its own cable, the hub propagates all signalsentering through its ports out through all of its other ports. Signals transmitted byone computer are therefore received by all other computers on the LAN.

The main advantage of the star topology is that each computer has its owndedicated connection to the hub, providing the network with a measure of faulttolerance. If a single cable or connector should fail, only the computer connected

to the hub by that cable is affected. The disadvantage of the star topology is thatan additional piece of hardware, the hub, is required to implement it. If the hubshould fail, the entire network goes down. However, this is a relatively rareoccurrence because hubs are relatively simple devices that are usually found ina protected environment, such as a data center or server closet.

Ring Topology

In terms of signal transmissions, a ring network is like a bus in that eachcomputer is logically connected to the next. However, in a ring network, the twoends are connected instead of being terminated, thus forming an endless loop.

This enables a signal originating on one computer to travel around the ring to allof the other computers and eventually back to its point of origin. Networks suchas Token Ring, which use token passing for their Media Access Control (MAC)

Figure 2.2


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mechanism: The OSI Reference Model, in "Networking Basics"), are wired usinga ring topology. The most important thing to understand about the ring topologyis that, in most cases, it is strictly a logical construction, not a physical one. Tobe more precise, the ring exists in the wiring of the network, but not in thecabling.

When you look at a networkthat uses the ring topology, youmay be puzzled to see whatlooks like a star. In fact, thecables for a ring networkconnect to a hub and take theform of a star. The ringtopology is actuallyimplemented logically, usingthe wiring inside the cables(Figure 2.3). Ring networksuse a special type of hub,called a Multi-station AccessUnit (MAU), which receivesdata through one port and transmits it out through each of the others in turn (notsimultaneously, as with an Ethernet hub). For example, when the computerconnected to port number 3 in an eight-port MAU transmits a data packet, theMAU receives the packet and transmits it out through port number 4 only. Whenthe computer connected to port number 4 receives the packet, it immediatelyreturns it to the MAU, which then transmits it out through port number 5, and so

on. This process continues until the MAU has transmitted the packet to eachcomputer on the ring. Finally, the computer that generated the packet receives itback again and is then responsible for removing it from the ring. If you were toremove the wire pairs from the sheaths of the cables that make up a ringnetwork, you would have a circuit that runs from the MAU to each computer andback to the MAU.

The design of the physical star topology used by the ring makes it possible forthe network to function even when a cable or connector fails. The MAU containsspecial circuitry that removes a malfunctioning workstation from the ring, but still

preserves the logical topology. By comparison, a network that is literally cabledas a ring would have no MAU, but a cable break or connector failure wouldcause the network to stop functioning completely. The one commonly usedprotocol that does include an option for a physical ring topology, FiberDistributed Data Interface (FDDI), defines the use of a double ring, whichconsists of two separate physical rings with traffic flowing in opposite directions.When computers are connected to both rings, the network can still functiondespite a cable failure.

Mesh Topology

The mesh topology, in the context of local area networking, is more of atheoretical concept than an actual real-world solution. On a mesh LAN, eachcomputer has a dedicated connection to every computer, as shown in Figure 2.4.

Figure 2.3


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In reality, thistopology onlyexists on a two-node network. Fora mesh networkwith threecomputers or more,it would benecessary to equipeach computer witha separate networkinterface for everyother computer onthe network. Thus, for a five-node network, each computer would require fournetwork interface adapters, which is certainly not practical. A mesh LANprovides excellent fault tolerance, however, as there is no single point of failure

that can affect more than one computer.In internetworking, the mesh topology is a cabling arrangement that you canactually use. A mesh internetwork has multiple paths between two destinations,made possible by the use of redundant routers, as shown in Figure 2.5.

This topology is very common on large enterprise networks because it enablesthe network to tolerate numerous possible malfunctions, including router, hub,and cable failures. In most cases, when you see a reference to a mesh topology,this is the application being cited.

Wireless TopologiesThe term topology usually refers to

the arrangement of cables that formsa network, but it does not have to.Although wireless networks use whatare called unbounded media, thecomputers still have specific patternsthey use to communicate with eachother. Wireless LANs have two basictopologies: the adhoc topology, andthe infrastructure topology. In theadhoc topology, a group of computersis all equipped with wireless network

Figure 2.4

Figure 2.5

Figure 2.6


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interface adapters and are able tocommunicate freely with each other.This provides complete freedom ofmovement for all of the computers onthe network, as long as they remaininside the communication range ofthe wireless technology. Thistopology is useful for a home or smallbusiness network that consists ofonly a handful of computers, and forwhich the installation of cables is inconvenient, impractical, or impossible.

An infrastructure network consists of wireless-equipped computers thatcommunicate with a network using wireless transceivers connected to the LANby standard cables. These transceivers are called network access points. In thisarrangement, the wireless computers do not communicate directly with eachother. Instead, they communicate only with the cabled network via the networkaccess points. This topology is better suited to a larger network that has only afew wireless computers, such as laptops belonging to traveling users. Theseusers have no need to communicate with each other; instead, they use thewireless connection to access servers and other resources on the corporatenetwork.

Ad vantages and Disadvantages of Dif ferent Networkin g Topo logies

BUS Topolog y

In this case all the server/nodes share a common bus of connecting cables.Every computer can communicate directly with ever other computer or device inthe network. Each node is given an address. To access a particular, a user justneeds to know its address. This topology is frequently used with local areanetworks. Going through a hierarchy of nodes is not necessary.

Advantages of the Bus Netwo rk

Short Cable Length and Simple Wiring L ayout: Because there is a singlecommon data path connecting all nodes, the bus topology allows a very shortcable length to be used. This decreases the installation cost and also leads to asimple, easy to maintain, wiring layout.

Resi l ient Arch i tecture: The bus architecture has an inherent simplicity thatmakes it very reliable from a hardware point of view. There is a single cablethrough which all data passes and to which all nodes are connected.

East to Extend: Additional nodes can be connected to an existing bus network

at any point along its length. More extensive additions can be achieved byadding extra segments connected by a type of signal amplifier known as arepeater.

Disadvantages of th e Bus Netwo rk

Fault Diagnosis is di f f ic ul t: Fault detention in the bus topology is not a simple

task. In most LANs based on a bus, control of the network is not centralized inany particular node. This means that detection of a fault may be performed frommany points in the network.

Fault Isolat ion is di f f icul t: If a node is faulty on a bus, it must be rectified at the

Figure 2.7


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point where the node is connected to the network. Once the fault has beenlocated the node can simply be removed. In the case where the fault is thenetwork medium itself, an entire segment of the bus must be disconnected.

Repeater Con figu ration: When a bus-type network has its backbone extendedusing repeaters, reconfiguration may be necessary. This may involve tailoringcable lengths adjusting terminators, etc.

Nodes mu st be Intel l igent: Each node on the network is directly connected tothe central bus. This means that some way of deciding who can use the networkat any given time must be performed in each node. It tends to increase the costof the nodes irrespective of whether this is performed in hardware of software.

RING Topolo gy

As the name suggests all the server/nodes are joined together to form a ring.There is no central server in this case. A ring may be unidirectional or bi-directional. A unidirectional ring moves data in one direction only; a bi-directionalring moves data in both directions, but only one direction at a time. In a

unidirectional ring, if one computer breaks down, special software is required tokeep the network functional. When one node malfunctions in a bi-directionalring, a message can usually be sent in the opposite direction still allowing thenode to communicate with all the other active nodes in the network.

Advantages of the Ring Network

Short Cable Length: The amount of cabling involved in a ring topology iscomparable to that of a bus and is small relative to that of a star. This meansthat less connections will be needed, which will in turn increase networkreliability.

No wiring closet space requ ired: Since there is only one cable connectingeach node to its immediate neighbors, it is not necessary to allocate space in thebuilding for wiring closets.

Suitable fo r Op tical Fibers: Optical fibers offer the possibility of very highspeed transmission. Because traffic on a ring travels in one direction, it is easyto use optical fibers as a medium of transmission. Also, since a ring is made upof nodes connected by short segments of transmission medium, there is apossibility of mixing the types used for different parts of the network. Thus, amanufacturing companys network could use copper cables in the office area

and optical fibers in the factory areas, where electrical interference is higher.Disadvantages of th e Ring Netwo rk

Node Fai lure causes Network Failure: The transmission of data on a ring goesthrough every connected node on the ring before returning to the sender. If onenode fails to pass data through itself, the entire network has failed and no trafficcan flow until the defective node has been removed from the ring.

Diff icul t to Diagno se Faults: The fact that failure of one node will affect allother has serious implications for fault diagnosis. It may be necessary toexamine a series of adjacent nodes to determine the faulty one. This operation

may also require diagnostic facilities to be built into each node.Netwo rk recon f igurat ion is di f f icu l t: The all or nothing nature of the ringtopology can cause problems when one decides to extend or modify thegeographical scope of the network. It is not possible to shut down a small section


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of the ring while keeping the majority of it working normally.

Topology af fects the Access Protocol: Each node on a ring has aresponsibility to pass on data that it receives. This means that the accessprotocol must take this into account. Before a node can transmit its own data, itmust ensure that the medium is available for use.

STAR Topolog y

In this case all the computers and the main server form a star like shape. All thecomputers are connected to a single main host. All communication first goesthrough the centralized computer allowing it to control the operation, work load,and resource allocation of the other computers in the network.

The advantage is relative simplicity, but a problem exists with the single-pointvulnerability of the network. If the central computer (server) breaks down, noneof the other computers can communicate with each other.

Ad vantages of the Star Network

Ease of Servic e: The star topology has a concentration points, the central node

and intermediate wiring closets. These provide easy service of the network.One Device per Connect ion: Connection points in any network are inherentlyprone to failure. In the star topology, failure of a single, connection typicallyinvolves disconnecting one node from an otherwise fully functional network.

Central ized Control / Problem Diagno sis: The fact is that the central node isconnected directly to every other node in the network. It means that faults areeasily detected and isolated. It is a simple matter to disconnect tailing nods fromthe system. In the star topology, a defective node can easily be isolated from thenetwork by removing its connection at the central Hub.

Simple Access Protoco ls: Any given connection is a star network involves onlythe central node and one peripheral node. In this situation, contention for whohas control of the medium for transmission purposes is easily solved. Thus in astar network, access protocols are very simple.

Disadvantages of th e Star Network

Lon g Cable Length: Because each node is directly connected to the center, thestar topology necessitates a large quantity of cable. While the cost of the cableis often small, congestion in cable ducts and maintenance and installationproblems can increase costs considerably.

Diff icul t to Expand: The addition of a new node to a star network involves aconnection all the way to the central node. Expansion is usually catered for byproviding large numbers of redundant cables during the initial wiring. However,problems can arise if a longer cable length is needed or an unanticipatedconcentration of nodes is required.

Central Node Dependency: If the central node in a star network fails, the entirenetwork is rendered inoperable. This introduces heavy reliability and redundancyconstraints on this node.

MESH Topolog y

A network topology featuring a direct path between two nodes. The backbone ofthis topology looks like this, where most major cities have a direct connection toother major cities.


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Advantages and Disadvantages of th e Mesh Network

Units affected by Media Fai lure: Mesh topologies resist media failure betterthan other topologies. Implementations that include more than two devices willalways have multiple paths to send signals from one device to another. If onepath fails, the transmission signals can be routed around the failed link.Theoretically, no units are affected by media failure. However, if all pathsnormally use the maximum capacity of each link, some performance degradationwill occur are signals are routed around a failed link.

Ease of Inst al lation: Mesh networks are relatively difficult to install becauseeach device must be linked directly to all other devices. As the number ofdevices increases, the difficulty of installation increases geometrically.

Ease of Troub leshooting: Mesh topologies are easy to troubleshoot becauseeach medium link is independent of all others. You can easily identify faults andcan isolate the affected link.

Ease of Recon figurat ion: Mesh topologies are difficult to reconfigure for the

same reasons that they are difficult to install.HYBRID Topo logy

It is a combination of two or more network topologies. The backbone is mostly amesh network; each local loop is a star network with a central office at each hub.

Advantages of the Hybrid Network

Fault Diagno ses and Isolat ion: The presence of concentration points in thenetwork greatly eases fault diagnosis. If a fault is detected on the network, theinitial problem is to find out which concentration point in the ring is to blame. Thefact that this ring is quite small in relation to the total size of the network makes

this problem more manageable. The offending concentration point can beisolated easily, leaving the network in a fully functional state while further faultdiagnosis is carried out.

Ease of Expansio n: The modular construction of a star-ring network means thatnew sections may be easily added. When designing the network originally, eachconcentration can have extra, unused lobes which can be called upon later, ifneeded. The next growth step involved adding a new concentration point andwiring it into the ring.

Cabl ing: The concentration points in a star-ring are connected by a single cable.

This simplifies wiring between areas in an installation and cuts down on thecongestion of cable ducts. Also, the wiring practices involved are very similar tothat of telephone system installation. These techniques are well understood by

building engineers and lend themselves well to the pre-wiring of buildings.

Disadvantages of th e Hybrid Netwo rk

Intel l igent Concentrat ion Points required: Depending on the implementationused, the concentration points may need to have built in intelligence/processingability. This will be necessary if it is to assist in network fault diagnosis, nodeisolation or conversion from one form of transmission medium to another.

Cabl ing: The intercloset cabling in a star ring is critical to its operation. This maymean that redundant cabling in the form of one or more back up rings may benecessary to meet reliability requirements. The largest section of the network


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(i.e. between the concentration points and the nodes) is laid out in a star. Thismeans that a considerable amount of cable may be required.

TREE Topolog y

From a purely topological viewpoint, this network resembles an interconnectionof star networks. Individual peripheral nodes must transmit to and receive fromone other node only, toward a central node. An advantage of a tree structure is

that functional groupings can be created. For example, one branch could containall the general ledger terminals, another branch all the accounts receivableterminals, and so on. If one branch stops functioning, the other branches in atree network are not affected. However, data movement through this networkcan be slow.

Ad vantages of the Tree Netwo rk

Easy to Extend: Because the tree is of its very nature, divided into subunits, it iseasier to add new nodes or branches to it.

Fault Isolatio n: It is possible to disconnect whole branches of the network from

the main structure. This makes it easier to isolate a defective node.Disadvantages of th e Tree Netwo rk

Depend ant on the Roo t: If the head-end device fails to operate, the entirenetwork is rendered inoperable. In this respect, the tree suffers from the samereliability problems as the star.

Cable Types

There are three primary types ofcable used to build LANs: coaxial,twisted-pair, and fiber optic. Coaxial

and twisted-pair cables are copper-based and carry electrical signalsand fiber optic cables use glass orplastic fibers to carry light signals.

Coaxial Cable

Coaxial cable is so named becauseit contains two conductors withinthe sheath. Unlike other two-conductor cables, however, coaxial cable has one conductor inside the other, as

illustrated in Figure. At the center of the cable is the copper core that actuallycarries the electrical signals. The core can be solid copper or braided strands ofcopper. Surrounding the core is a layer of insulation, and surrounding that is thesecond conductor, which is typically made of braided copper mesh. This secondconductor functions as the cable's ground. Finally, the entire assembly isencased in an insulating sheath made of PVC or Teflon.

There are two types of coaxial cables, which have been used in local areanetworking.

RG-8, also known as thick Ethernet,

RG-58, which is known as thin Ethernet,These two cables are similar in construction but differ primarily in thickness(0.405 inches for RG-8 versus 0.195 inches for RG-58) and in the types of

Figure 3.1


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connectors they use (N connectors for RG-8 and Bayonet-Neill-Concelman[BNC] connectors for RG-58). Both cable types are wired using the bus

topology.

Because of their differences in size and flexibility, thick and thin Ethernet cablesare installed differently. On a thick Ethernet network, the RG-8 cable usuallyruns along a floor, and separate AUI cables run from the RG-8 trunk to thenetwork interface adapter in the computer. The RG-58 cable used for thinEthernet networks is thinner and much more flexible, so it is possible to run itright up to the computer's network interface, where it attaches using a T fittingwith a BNC connector to preserve the bus topology.

Twist ed-Pair Cabl e

Twisted-pair cable wired in a startopology is the most commontype of network medium used inLANs today. Most new LANs useUTP cable, but there is also ashielded twisted pair (STP)variety for use in environmentsmore prone to electromagneticinterference. Unshielded twisted pair cable contains eight separate copperconductors, as opposed to the two used in coaxial cable.

Each conductor is a separate insulated wire, and the eight wires are arranged infour pairs, twisted at different rates. The twists prevent the signals on thedifferent wire pairs from interfering with each other (called crosstalk) and alsoprovide resistance to outside interference. The four wire pairs are then encasedin a single sheath, as shown in Figure 3.3. The connectors used for twisted-paircables are called RJ45s; they are the same as the RJ11 connectors used onstandard telephone cables, except that they have eight electrical contactsinstead of four or six.

Twisted-pair cable has been used for telephone installations for decades; itsadaptation to LAN use is relatively recent. Twisted-pair cable has replacedcoaxial cable in the data-networking world because it has several distinctadvantages. First,because it containseight separate wires,the cable is moreflexible than the moresolidly constructedcoaxial cable. Thismakes it easier tobend, which simplifiesinstallation. Thesecond major

advantage is that thereare thousands ofqualified telephone

Figure 3.2

Figure 3.3


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cable installers, who can easily adapt to installing LAN cables as well. In newconstruction, the same contractor often installs telephone and LAN cablessimultaneously.

UTP Cable Grades

Unshielded twisted pair cable comes in a variety of different grades, calledcategories by the Electronics Industry Association (EIA) and the

Telecommunications Industry Association (TIA), the combination being referredto as EIA/TIA. These categories are listed in Table. The two most significantUTP grades for LAN use are Category 3 and Category 5. Category 3 cable wasdesigned for voice-grade telephone networks and eventually came to be usedfor Ethernet. Category 3 cable is sufficient for 10-Mbps Ethernet networks(where it is called 10Base-T), but it is generally not used for Fast Ethernet(except with special equipment). If you have an existing Category 3 cableinstallation, you can use it to build a standard Ethernet network, but virtually allnew UTP cable installations today use at least Category 5 cable.

Category Used for1 Voice-grade telephone networks only; not for data transmissions

2Voice-grade telephone networks, as well as IBM dumb-terminalconnections to mainframe computers

3Voice-grade telephone networks, 10-Mbps Ethernet, 4-Mbps TokenRing, 100Base-T4 Fast Ethernet, and 100Base-VG-AnyLAN

4 16-Mbps Token Ring networks

5100Base-TX Fast Ethernet, Synchronous Optical Network (SONET),and Optical Carrier (OC3) Asynchronous Transfer Mode (ATM)

5e 1000Base-T (Gigabit Ethernet) networks

Fiber Optic Cable

Fiber optic cable is a completelydifferent type of network medium thantwisted-pair or coaxial cable. Instead ofcarrying signals over copper conductorsin the form of electrical voltages, fiber

optic cables transmit pulses of light overa glass or plastic filament. Fiber opticcable is completely resistant to theelectromagnetic interference that soeasily affects copper-based cables.

Fiber optic cables are also much lesssubject to attenuationthe tendency ofa signal to weaken as it travels over acablethan are copper cables. On copper cables, signals weaken to the point of

unread ability after 100 to 500 meters (depending on the type of cable). Somefiber optic cables, by contrast, can span distances up to 120 kilometers withoutexcessive signal degradation. Fiber optic cable is thus the medium of choice for

Figure 3.4


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installations that span long distances or connect buildings on a campus. Fiberoptic cable is also inherently more secure than copper because it is impossibleto tap into a fiber optic link without affecting normal communication over that link.

A fiber optic cable, illustrated in Figure, consists of a clear glass or a clear plasticcore that actually carries the light pulses, surrounded by a reflective layer calledthe cladding. Surrounding the cladding is a plastic spacer layer, a protective

layer of woven Kevlar fibers, and an outer sheath.SETTING UP THE CABLES

We have theoretically learned about the networking and how the computers areconnected to each other in different type of networking. In this chapter, you willread about the various types of cables used in connecting the computers andlook at the various types of conduits, and wall boxes used in networking.

Let us understand about the type of cables that are used for networking.

Unsh ielded Tw isted Pair (UTP)

It is made up of copper. Data cabling systems are now based around the

Twisted Pair model. This type of cables are available as two types, referred to asCategory 3 (Cat3) UTP and Category 5 (Cat5) UTP where the UTP standing forUnshielded Twisted Pair. Both types consist of eight copper cores arranged asfour pairs twisted together and surrounded by a protective sheath.

The twisting of the pairs is carefully controlled during the manufacturing processto give the high-speed data carrying capacities associated with this kind ofcable. The Cat 3 cable is rated to carry up to 10MHz and the Cat 5 to 100 MHz.As most new installations need to be future proofed for new data technologies,the Cat 5 cable is generally the most popular and as such is more widely

available at little additional cost.Shielded Tw isted Pair (STP)

Twisted Pair cable is also available with Shield, called STP. This type of cablehas an additional metal shield around the four pairs of wires. It is used forcabling, where protection from excessive electrical noise is required. As in heavyengineering establishments. Generally this additional protection is unnecessary.

Twisted Pair cables use RJ-45 plugs. You have seen a modular phone plug, anRJ-45 plug looks same, but it has eight connectors instead of the 4 connectorsthat phone wires use. The steps and requirements for making these cables are:

Category 5 Unshielded Twisted Pair (UTP) cable, easily available at allcomputer stores and electrical goods shops.

RJ-45 ends (jacks), which are also available at computer hardware shops. An RJ-45 Terminating Tool, which is used to fix the RJ-45 ends of the UTP

cable. Some terminating tools will work for both 4-wire and 8-wire plugs.These may expensive but very useful, if you are working on lots of cables.

Inexpensive cable continuity tester. Start with the cable. Strip the outer insulation back about an inch, very

carefully, do not damage the wires inside. Notice that you have 4 pairs of

wire inside, one is white/orange and orange, one is white/green and green,one is white/blue and blue, and one is white brown and brown. Separate the wires so they will line up in the following order from left to right. Trim all the ends equally so that they are of the same length. You can use


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the wire cutters or the cutter edge of your terminating tool for trimming. Now comes the tricky part, insert all 8 wires into the RJ-45 end so that they

are inserted as far as possible. Then push the cable jacket up under thenotch in the end.

Carefully insert the end in the terminating tool to its full depth and squeezethe terminating tool tightly. This will crimp the end onto the cable andconnect the pins on the RJ-45 jack to the wires in the cable. Now do thesame at other end.

Straight Cable

Most 1OBASE-T and 100BASE-T patch cords are straight through, which meansthat the colours are lined up the same at both ends. You can make a standard1OBASE-T cable using colour sequences as given below (568B cablingspecifications), the most common wiring used for networking.

Pin No. End 1 colou r End 2 colou r

1 White/Orange White/Orange

2 Orange Orange3 White/Green White/Green

4 Blue Blue

5 White/Blue White/Blue

6 Green Green

7 White/Brown White/Brown

8 Brown Brown

Crosso ver Cables

If you have got Ethernet hubs or switches to interconnect it is necessary in manycases to use a specially made cable a crossover cable. Essentially, it looks likea standard 1OBASE-T patch cable except that it is wired differently.

In a crossover cable, the difference is that the wire on pin 1 at each end mustconnect to pin 2 at the other end, and pin 3 on each end must terminate at pin 6at the other end. Therefore, the wiring scheme is as follows:

Pin No. End 1 colou r End 2 colou r

1 White/Orange Orange

2 Orange White/Orange3 White/Green Green

4 Blue Blue

5 White/Blue White/Blue

6 Green White/Green

7 White/Brown White/Brown

8 Brown Brown

This works because Ethernet only uses pins 1, 2, 3, and 6. A crossover cableconnects pin 1 at one end to pin 2 at the other and pin 3 to 6. It is useful and it iseasy to make. If you have followed the above instructions, you should be able toplug the cable you have made into a cable continuity tester and see that pin 1 at


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Figure 3.6

one end connects to pin 1 at the other end, followed same up to the pin 8. Donot get discouraged if your first cable does not work.

Thinn et Cables

It uses a special kind of coaxial cable. It is referred to by the coaxial cablingstandards as type RG58 C/U. The main characteristics of this cable are animpedance rating of 50 ohms and an outside diameter of 4.95mm. Various cable

manufacturers refer to this cable generically as Thinnet, the specifications andcharacteristics may vary slightly from vendor to vendor. It must meet out theEthernet standard, which is technically referred to as the IEEE 802.3 standard.

Advantages & Disadvantages of Thinnet Cables

Advantages:

Inexpensive

Disadvantages:

10MHz Ethernet only More vulnerable to network failure

Advantages & Disadvantages of Tw isted Pair CablesTwisted Pair generally used in Star System

Advantages:

More compliant to International Standards 10 MHz and 100 MHz Ethernet capability Less vulnerable to network failure

Disadvantages:

Requires a distribution hub More cabling required

Netwo rk Interface Adapters

The network interface adapter(NIC, which installed in anexpansion slot) is thecomponent that provides the linkbetween a computer and thenetwork of which it is a part.Every computer must have anadapter that connects to the system's expansion bus and provides an interface

to the network medium.Some computers havethe network interfaceadapter integrated intothe motherboard, but inmost cases, the adaptertakes the form of an expansion card that plugs into the system'sIndustry Standard Architecture (ISA), Peripheral Component Interconnect (PCI),or PC Card bus. An ISA-bus NIC is illustrated in Figure 3.5. The network

interface itself is, in most cases, a cable jack such as an RJ45 for UTP cables ora BNC or AUI connector for a coaxial cable connection, but it can also be awireless transmitter of some sort.

Figure 3.5


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Module7 May - 2010 / BLYREPEATERS

Repeaters, located within the physical layer of a network, regenerate andpropagate signals from one to another. They do not change any informationbeing transmitted, and they cannot filter any information. Repeaters help toextend the distances of networks by boosting weak signals.

HUB

Hubs and switches both receive data packets from the computers on thenetwork, but they process them differently. Hub operates at the physical layeronly. Hubs connect all computer LAN connections into one device. When a hubreceives signals through one of its port, it amplifies the signal and immediatelytransmits them out through the other ports of hub. Hubs cannot determinedestinations; they merely transmit to every line attached in a half-duplex mode.

It works as a repeater having multiport.

SWITCH

Switches operate at the data link layer. When a switch receives signal through

one of its ports, it interprets those signals as a data packet and read thedestination address from the data link layer protocol header. The switch thentransmits the packet through the only port that is connected to the computerusing that address. Switches connect all computer LAN connections, same ashubs. The difference is that switches can run in full-duplex mode and are ableto direct and filter information to and from specific destinations. Thus switchesreduce the amount of traffic on the network and the number of collisions.

BRIDGE

Bridges and Routes are both devices connect network cable segments together,

but they process these packets arriving from the segments in different ways.Bridges operates at data link layer and connect segment together. When abridge receives a packet through one of its port, it reads the destinationaddress in the data link layer protocol header and consults its internal addresstables to determine the destination computer segment. If the destinationcomputer is on the same segment as the source computes, the bridge discardsthe packet, because it already reached its destination. But if the destination is onthe other segment, the bridge transmits the packet out through its other ports.Bridges are intelligent, they regenerate transmitted signals, but unlike repeaters,

they can also determine destinations. Bridges relay all broadcast messagesbetween the segments.

ROUTER

Router operates at the network layerand connects networks together. When apacket arrives at a route through one of its ports, the routerstrips offthe datalink layer protocol frame and uses the destination address in the network layerprotocol header to determine where to send the packet next. The router thenencapsulates the network layer data in a new data link layer frame beforetransmitting it. Routers are a step up from bridges, they are able to route and

filter information to different networks. The routes may send the packet directlyto the destination (if the destination computer is on one of the networks to whichthe router is connected) or another router, which relay the packet in the sameway. Routers do not forward broadcast packets.

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