Networking - LAN Terminology and Components.doc

8/9/2019 Networking - LAN Terminology and Components.doc

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LAN Topology

What will be the shape, or topology, that defines the LAN? Topology is a term that refers the shape of the network and the layout of cabling from a bird's eyeview, much as a floor plan identifies the layout of offices and hallways in a building.The topology diagram shown is made up of LAN workstations, also called nodes. The lines betweenthese nodes represent cables. Junction bo es are used to interconnect the cables. !ou will learn moreabout the various types of hardware that support the connectivity function later in the course.Theoretically, any kind of cable medium could be wired together to create an infinite variety ofnetwork layouts. "ut, in fact, certain implementations of topology have become more popular whileother implementations have simply never caught on. #onsider some of the most common types of LANtopology.The Star topology shown above is emerging as the most common network layout in use today. $achworkstation is connected point%to%point to a single central location that is commonly referred to as a

wiring closet .

LAN Bus Topology


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The Bus topology is one of the oldest layout types and remains one of the simplest forms to design andimplement. $ach seat in the network is connected in se&uence along a single network cable using T%shaped network interface connectors, and terminating points are placed at each end.

LAN Mesh Topology

The Mesh topology is a variation of the bus, in which all devices are connected to one another in adaisy%chain fashion, as opposed to connecting in se&uence to a single network cable. $ach node iscapable of transmitting, receiving, and routing data.

LAN Ring Topology

The Ring topology is another simple design that consists of a single cable that forms the main datapath in the shape of a ring. $ach node is connected to a closed loop of cable. ignals travel in onedirection from one node to all other nodes around the loop.


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LAN Tree Topology

The Tree topology is essentially a hybrid of the bus and star layouts. The basic topology is similar tothat of a bus, with nodes connected in se&uence to a linear central cable. "ut tree networks may have(branches( that contain multiple workstations that are connected point%to%point in a star%like pattern.

ignals from a transmitting node travel the length of the medium and are received by all other nodes.

Connection-oriented vs. Connectionless

Will the LAN be connection-oriented or connectionless? )epending on the type of communication technology implemented, LANs can be either connection%oriented *such as an AT+ network or connectionless *broadcast%based, such as $thernet .A connection-oriented LAN re&uires that you establish contact with the receiving party before thee change of information can begin, in the same manner as you would for a telephone call. -f you wantto call someone, you pick up the handset and dial the number. -f, for whatever reason, there is noanswer at the other end, you do not bother to talk-n the same way, a connection%oriented LAN will try to contact the node at the other end of anintended conversation, and will only start sending information if the node at other end is present andavailable. /nce the other side has been contacted, it is not necessary to keep (redialing( the number,


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because the connection to the other party has already been established. -f the other end missessomething during the course of the e change, they can re&uest that the information be retransmitted.

Connection-oriented

uppose you want to talk to two or more people. !ou could arrange a conference call by having theother parties dial into a central place, such as an operator who would then 0oin them together. -f theparties did not know where to call, they could not 0oin. -f the operator had a list of pre%approvedparties, then 0oining may have an element of security in place as well. The difference between a partyline and a conference call is the security element. !ou know when someone 0oins a conference call, butyou may not know who picks up on a party line.#onnection%oriented LANs also support two types of connections1

Point-to-point *private connections refer to a pathway from one location to another *Node Ato Node " .

Point-to- ultipoint *conference connections refer to a pathway from one location to manylocations *Node A to Node ", #, and ) .


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Connectionless!Broadcast

Now, contrast connection%oriented communication with connectionless or broadcast-based communication."roadcast%based communication is connectionless in that it does not re&uire the transmitting party tocontact the receiving party before sending information. 2ith a radio station, the news is "roadcast

whether you are listening or not. -f you were listening, but you missed something, you cannot ask theannouncer to go back and repeat what they 0ust said. -n the same way, a connectionless LAN simplybroadcasts information to all who may or may not be listening.

ome radios offer two%way communication, but you still have the eavesdropping problem associatedwith any broadcast media. The advantage of a two%way broadcast is you can holler, (3eorge, are youout there4( and everyone tuned to the fre&uency will hear the re&uest. -f 3eorge is out there, heanswers and tells you where he is located. 5adio stations also do this with contests, when they say (-fyou are listening and are our seventh caller, you could win...(Nodes in $thernet LANs locate each other in the same way, using what is called an ARP #AddressResolution Protocol$ Broadcast . The originating node broadcasts an A56 re&uest across the networkasking for the location of the target node. The target node responds to the broadcast by sending itsphysical address back to the originating node so that information can be transmitted.-n all cases so far though, the broadcasts are one%way. -magine how much more complicated it gets if

you could be transmitting as well as receiving on a broadcast medium. !ou would need something like a#" or police scanner to check for messages for you on all fre&uencies. -t would be easy to miss a call.

LAN Protocols

Which protocols will be used to define the way in which communication takes place across the LAN? 2hen sending a message from Node A to Node " on the network, there are several additional &uestionsthat may come to mind1

7ow will the message arrive at the destination4 2ill it arrive piece by piece re&uiring anacknowledgement for each or will it arrive all at once whether or not the receiving node isready4

7ow will the message be formatted *frames, packets, cells 4 7ow will Node A communicate with Node "4 2ill the relationship be master8slave, client8server or peer%to%peer4 7ow will the various software programs communicate with each other4


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2ill the same software be re&uired on both systems or can a sending system have one type ofsoftware while the receiving software is of another type4

The answer to all of these &uestions is determined by protocols. Protocols are the rules that hardwareand software follow in order for devices to communicate with each other6rotocols consist of several functional parts. The answers to the &uestions above will become clearer as

you consider each part in detail, beginning with flow control.

Protocol %low Control

7ow will the message arrive at the destination4 2ill it arrive piece by piece re&uiring anacknowledgement for each or will it arrive all at once whether or not the receiving node is ready46rotocols use different methods of &low control to monitor the pace at which data is transferredbetween network nodes. There are three main types of flow control1

The re'uest!reply method mandates that the receiving node acknowledge each data packetbefore the ne t packet is sent.

The sliding window method allows multiple data packets to be transmitted between nodesbefore acknowledgement. "oth ends keep track of what has sent and what has beenacknowledged.

The unrelia"le method is one where there is no guarantee that the packet will arrive at itsdestination. )ata may be discarded at any time without notifying the sender or receiver.


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Protocol Message %or at

How will the message be formatted (frames, packets, cells ? -n communications, the &or at of information sent varies widely. -n addition, the distinction between aframe and packet is not always clear. 2hile some network vendors attempt to differentiate the two,the two terms are often used interchangeably. The term packet will be used throughout this course forpurposes of this training."oth &ra es and pac(ets are parts of a transmitted message that vary in si9e. The actual format ofmay differ depending on the protocol or network specification. "ut in a LAN, environment packetsalways contain both data and addressing information.The graphic shown above represents the standard specification *-$$$ :;


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Protocol Message %or at

Cells are fi ed%si9ed *=> bytes packets of data used to transfer information in an AT+ network. Thefi ed si9e of a cell allows for fast and efficient transfer of information across the network.The cell format consists of two primary parts1

The header contains control information that is used to route and manage cells.

The payload contains the actual user information.

6ackets and cells both rely on network protocols, as well as hardware and software, to determine howthey function in the LAN environment.

Networ( Architecture

How will Node A communicate with Node !? Are network communications based on a master"sla#e, peer-to-peer, or client"ser#er relationship? There are three basic types of architectures that determine how one network node communicates withanother in a LAN1


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Master-slave communications refer to a relationship where a single node *(master( initiatesand controls a session with one or more devices *(slaves( . /riginally designed for mainframecomputer networks where the mainframe was the master and the (dumb( terminals wereslaves. The master8slave architecture is not commonly used in modern networks e cept inisolated cases *?or e ample, terminal emulation .

Peer-to-peer communications refer to a relationship where both nodes share the responsibilityof initiating, maintaining, and terminating a session. )ue to performance limitations asnetwork load increases and a lack of administrative control, peer%to%peer architectures aretypically limited to small, single%platform, and low%traffic LAN environments.

Client!server communications refer to a relationship where dedicated servers support theclients that are attached to them. Also known as two-tier and three-tier architectures,client8server communications are commonly found in large, multi%platform, high performancenetworks where security is an issue.

Protocol Stac(

How will the #arious software programs communicate with each other? Will the same software bere$uired on both systems or can a sending system ha#e one type of software while the recei#ingsoftware is of another type? -n order for two different computers to communicate *e.g. )/ and @N- , the same protocol stac( must be in operation. The protocol stack defines the hierarchy, or ranked order, in which protocols areapplied to a communications network.A widely used model for understanding network communications is the )pen Syste s *nterconnection#)S*$ re&erence odel . This model defines the protocols that allow network hardware and software towork together. The / - model determines how nodes contact each other, transmit data, and ensurethat transmissions are received, as well as, how they are connected. There are seven layers to themodel that define tasks that need to be completed *and protocols that are used to perform them .


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Networ( Manage ent

%nce you ha#e a LAN, how do you manage and troubleshoot the nodes? Networ( anage ent refers to how computer networks monitor and manage active functions,including the following1

%ault anage ent detects, displays, and maintains records of alarm conditions.

Con&iguration anage ent handles additions, deletions, and changes to the network.

Accounting anage ent tracks the measurable use and cost of network resources.

Per&or ance anage ent is designed to optimi9e the speed of the network.

Security anage ent deals with such issues as logging on.

-f you have a si ple network with only three devices, then it might be 0ust as easy to manage eachdevice individually. "ut if your network is larger and more co ple+ , with do9ens *maybe evenhundreds of devices that are logically grouped according to class, then a management tool mightmake sense.Network management tools often re&uire huge workstations to run their software, re&uiring hundredsof +" of 5A+. That workstation is called the Networ( Manage ent Station #NMS$ . The most commontype of N+ in use is 7ewlett 6ackard's /penBiew.At the most basic level, the N+ determines whether or not ob0ects on the LAN are (alive.( -f an ob0ect(dies,( you want to know about it right away. -f a brand new ob0ect appears, you will want to knowabout it right away as well.


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LAN Applications

What types of applications does the LAN support? oftware applications are programs designed for the end user *spreadsheets, games, graphics . haring

applications is why most people install LANs.peciali9ed applications include1

,ertical applications are specific to a particular industry *medical, government, education,etc. .

Strategic applications are vital to business operations, including /racle, A6, and Lotus Notes. ,estigial applications refer to critical business applications that pre%date the LAN, such as

+-N .

Representation o& Networ(ing evices

everal terms have been used to describe networking devices, but there are also graphicalrepresentations of these devices. These icons will appear in some of the graphics in the following


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chapters. 2hen looking at any network diagram, the symbols used are semi%standard. 6lease note thatthe actual representation of network devices on diagrams may vary from vendor to vendor.The following is a guide to the symbols that are used to represent the various kinds of LAN networkingdevices within this course.

u"s , which act as a common connection point for devices in a network, are represented by

small, unmarked rectangular bo es because they are often invisible to the network. 2hile ahub may be visible on the N+ , the hub is always invisible to data passing through it.

Switches , which filter and forward packets between LAN segments, are represented by a bomarked with an .

Routers , which connect any number of LANs, are depicted by a s&uare marked with aunidirectional cross pattern.

%ile Servers , which provide a centrali9ed file repository for LAN users, are depicted by filesoverlaying a server device.

ata"ase Servers , which support LAN database services, are depicted by a database bucketoverlaying a server device.

Networ( Manage ent Stations #NMS$ , which supports LAN management services, is depictedby an N+ terminal overlaying a server device.

Summary This lesson provided an introduction to the basic terminology used to describe the physicallayout of a LAN, the protocol and communication standards that determine how informationis exchanged across the LAN, and various types of transmission media and networkingdevices that are available to construct a LAN.

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Networking - LAN Terminology and Components.doc