PC Networking Level 5

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PC Networking Level 5.doc 1

PC NETWORKING Level 5

- An Introduction to PC Networking.

Copyright by CTF Services Limited 2005All rights reserved worldwide. No part of this book may be reproduced or transmitted inany form, or by any means, electronic or mechanical, including photocopying, recording,or by any information storage and retrieval system, without the written permission of thepublisher, except where permitted by law.

Published byCTF Services Limited, 19 Regent St, Timaru 8601, New Zealand

Distributed bywww.ebooksctf.co.nz


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PC NETWORKING Level 5

An Introduction to PC Networking.

PREFACE.

Welcome to the exciting world of PC Networking. This is a huge growth areaworldwide.

I hope you enjoy doing this course, and will want to learn more after you finish.This course is arranged as follows:

Four Theory Chapters

USE the Bookmarks and Thumbnails to help you to navigate this pdf document.

Please E-Mail us if you have any questions or comments.Our E-Mail address is [email protected] include (where possible) the Course Name and the Page Number (thesecan be found on the footer of each page)

Enjoy the journey. We look forward to your continual success.


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CONTENTS.

CHAPTER ONE INTRODUCTION to LANs Why Network? Definitions Types of Network Cabling and Topologies Media Access Control

CHAPTER TWO LAN STANDARDS A Network Model Network Operating Systems Hardware and Peripherals The Network Interface Card

Interconnection Class Exercise

CHAPTER THREE LAN STRATEGIES Server Based LANs Peer-to-Peer Networking Client / Server Computing Overview of Network Management

E-Mail

CHAPTER FOUR. PROTOCOLS, STANDARDS and INTERCONNECTION Protocols

IEEE 802 Standards Links between LANs

Repeaters, Bridges and Routers

THIS COURSE SHOULD BE COMBINED WITH:a) PC NETWORKING PRACTICAL EXERCISES andb) Network + (2005)


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Majestic Mt Aoraki is an awe inspiring site.

My pledge to my students:To help you with your Learning Climb which is like scaling the heights ofMt Aoraki.There are times when you will be stretched beyond your comfort zone,and there will be other days when the upward journey seems difficult (justlike bad weather on the mountain).

Aoraki is not the easiest challenge.There are many easier, but less rewarding climbs.

Remember the words of Winston Churchill "Never, ever give up."

If you are willing to learn, and willing to work, then I am willing tobe your guide in your learning climb.

The view from the peak is even more awe inspiring than the view from the lake.One day, you will reach the top, if you follow the right path, and have the rightself belief.

Nick ThorneDirector of CTF Services


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CHAPTER ONE.

INTRODUCTION to LANs.

A. WHY NETWORK?B. DEFINITIONS.C. TYPES of NETWORK.

D. CABLING and TOPOLOGIES.E. MEDIA ACCESS CONTROL.


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A. WHY NETWORK?Networking is one of the biggest growth areas in the computing world -there is a real shortage of experts in the area.

A network is a system of interconnection between computers that allows them toshare facilities. Typically, these facilities might be printers, disk space andsoftware. A Network allows different users to communicate, and to pass datafrom one Network Resource to another.

It makes sense for a group of users to share an expensive item, such as a colourLaser Printer. Even to share a colour laser between a group could mean that thetotal printing cost is less than if each individual had a colour dot matrix -- and the

quality of the output would be a lot better.

Typically, a Network will consist of any number of terminal devices (intelligentwork stations such as IBM compatible PCs, or dumb terminals) connected to alarge processor, which contains most of the software needed for operation. Thelarge processor containing most of the software is called the File Server. Thedevices attached to the file server are called Workstations.

Networking allows us to get good use out of our resources for all our users.When you have just one computer, what you have loaded on that computer is allyou have access to. To transfer data from one computer to another, data must

be copied to a backup device, and then copied from the backup device to thesecond computer. This can be cumbersome and time consuming.

If the computers were linked, transfer of data would be easier.

The basic reasons why computers are networked are: To share resources such as files, printers, modems and fax machines To share application software e.g. 10 Workstations share MS Office, rather

than have 10 individual licences To increase productivity (make it easier to share data among users)


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Imagine a Small Business office in which a number of users all require access tocommon information. If the users computers are connected via a network, theycan share files, exchange mail, schedule meetings, send faxes and printdocuments all from any point in the network.

It would not be necessary for users to transfer files via floppy disk, electronic

mail, hard copy or any other format. Each user could access the information theyneeded. Less time would be wasted, and productivity would be improved.


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B. DEFINITIONS.

A computer network is a communications system connecting two or morecomputers together to exchange information and share resources.

Reasons to network may include: Internal electronic mail centralized file storage sharing files (you can get access

(if permitted!) to other's fileswithout having to use floppy disksfor transfer)

sharing applications (you may

have access to a larger range ofsoftware than you would have onyour own hard disk)

relative ease in adding newsoftware

sharing printers and otherhardware such as DVD drives,modems and disk drives

central management includingsecurity and backups

to provide a gateway to the

internet

GROUP ACTIVITY.

Discuss the listed "Reasons to Network". Explain what they mean. Can you think of any other reasons why you might network computer

resources?


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OTHER ADVANTAGES OF NETWORKING PCS.

Lower Software Costs. No need to purchase multiple copies of the same Application Software.

One copy held on the Server (Network Version of the Software) and thecorrect Software Licence Agreement (or Site Licence) to cover themaximum number of concurrent users (Network Operating System egNetware is also required)

Ability to share software eg databases among several userssimultaneously

Group access to external services and other file servers

Lower Hardware Costs.

Perhaps one printer is shared between 6 PCs i.e. Print Sharing No need for the Workstations to have a Hard Disk drive (depending on the

Network Operating System used) (if a Windows Workgroup, smaller HardDisk required than for a Stand Alone).

However, each PC must have a Network Card and a Network Link, suchas co-axial cable.

Ability to use less expensive PCs (essentially, you need a processor andRAM, plus input and output devices)

Lower cost that a Mini Computer, and probably more versatile

Data Integrity/Data Security/Reliability.

All users have access to the same Database. There is only one copy,therefore the data is consistent (called better integrity)

Centralised control of data, for better security Files can be password protected at all levels. Backups from server (easier)

ADVANTAGES OF USING STAND-ALONE PCs instead of LANs

Less complex A breakdown only impacts the one PC


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C. TYPES OF NETWORK.

Traditionally computing has moved from batch processing to time sharing(possibly from dumb terminals) to file servers to client/servers and possibly toThin Client (i.e. back to dumb terminals!)

Mainframe centralised large computer "dumb" workstations

Peer to Peer workstations can make available their resources

no central server running a network operating system (NOS) security is the responsibility of each workstation each station runs compatible operating system can still have centralised storage of data

Workstation OSs (operating systems) that support peer to peer networkinginclude Windows 3.11 and Windows 9x (95 and 98).

Fileserver workstations communicate with a central server (a high end computer) security is enforced by a network administrator from the server

resources in the workstation disk are not normally made available to thenetwork

server runs special networking software which may allow computers to beconnected across different platforms

NOS (Network Operating Systems) that reside on the server include NovellNetWare, Windows NT Server (soon to become Windows 2000 Server), Unix (orLinux) and AppleTalk.


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Client/Server

In a file server environment, when you load a database file, the whole of the file

will transfer from the fileserver hard disk (HDD) to the RAM of the workstation.When this happens, there are a number of issues that need to be addressed todo with file, table or record locking so that more than one person is not updatingdata at the same time.

Limitations of using the file server technology on a LAN:

excessive data movement need for powerful workstations decentralized data control

Server does not need to be as powerful as a thin client server but needs morepower than file server.

In a client/server environment, only the data required is transferred to the client.Additional software is run on the server to manage this (e.g. SQL Server). Thissystem is like a combination of the mainframe/dumb Concurrent access ismanaged from the server. Processes like queries are performed on the server.However the application program is still run on the client (unlike the mainframesituation)

Note that the word server can refer to hardware, software or both terminal andfile server environments.


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Thin Client

This relatively recent development (or maybe it's old ideas being readapted)

allows modern software to be run on aging PC workstations - the workstationacts as a dumb terminal with all applications and processing being achieved onthe server. An example of this technology is Windows NT Terminal Server.

All of the above categories of network are either examples of central processing(all processing done on the central computer) or distributed processing (some orall processing done on the workstations).

MainframeMainframe Terminal

Application

Data Presentation

Processing File Server

Server ClientApplication * Data

Presentation

PPrroocceessssiinngg

Client/ServerServer Client

Application Data

Presentation

Processing

* Some applications run are loaded off the file server (e.g. MYOB) but theprocessing still happens in the client.


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Local Area Networks (LAN)

Used for small localised clusters of computers. High data speeds over shortdistances are provided - up to 100Mb/sec for (say) 2km. Inexpensive cableowned by the user, baseband (often not multiplexed).

Wide Area Networks (WAN)

Operate over a much wider area (even globally). Speed is limited by thecapability of the telecommunications network and the cost involved in leasinghigh speed lines (digital or analogue).

Some texts add a definition in between the LAN and WAN - that of the MAN

(Metropolitian Area Network). This network goes beyond the 2km limit but is notinter-city.

A WAN can be a number of LANs inter-connected together.

The main distinction between WANs and LANs is mainly the physical linksbetween Network resources. In general, LANs: extend over a much shorter distance

carry a very high volume of traffic over this short distance Equipment and circuitry is locally owned. Although a LAN can have

gateways to other Networks, processing is done independently of any other

Computer other than the workstation being used.


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D. CABLING and TOPOLOGIES.

Like any computer system, a network includes hardware and software.The transmission medium used is also important. Examples of transmissionmedium are:

Cable (Unshielded Twisted Pair (UTP), Shielded Twisted Pair (STP), ThinCo-axial, Thick Co-axial and Fibre Optic

High Frequency Carrier (Radio W aves, Infra Red, Microwave)

A Topology is the pattern by which network resources are interconnected. Thereare a variety of methods for connecting LANs and WANs, and the topologychosen depends very much on the amount of functionality you require, and thecost you are prepared to pay. Some topologies are listed below:

StarOriginally used for relatively dumb terminals connected to a central server. Theterminals had little processing power in themselves.

Each station is attached to a common central switch whose job it is toroute traffic to specific stations depending on addresses. Thisconfiguration provides a convenient central point for network maintenanceand testing but does require a separate cable pathway to eachworkstation.

The star is also used today with twisted pair cabling and hubs. A popular

topology that is easy to fault find.

STAR Where resources are independently linked to a central node If one link breaks, the rest of the network is intact Higher cost of cabling


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Bus Used for PC networks - e.g. Xerox's "Ethernet" topology.

Coaxial cable in a bus system has two ends (terminated with resistors to stop thesignal from reflecting i.e. the signal is absorbed). When a signal is transmitted, ittravels in both directions (full duplex system) from the station until it reaches theresistors. Every station receives the signal but only the station that the data isaddressed to copies the data.

A station listens to see if the bus is busy (called contention)- if some other stationis using the bus then it waits a predetermined length of time and listens again.When the bus is not busy, the station transmits. If two stations transmit at thesame time, there is a collision - each station waits a random period of time beforetrying again.

This access method is called CSMA/CD - Carrier Sense Multiple Access withCollision Detection.

BUS Several resources connected in a line, and hang off that main feeder (Bus)

A bad link can be bypassed


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LOOP or RINGCheap cost (dont confuse with IBM Token Ring, which is really a Star topology)If a link is broken, the entire loop is lost

MeshUsed often for WANs to give extra reliability - there are multiple routes betweencomputers in case of telecommunications failure - you can't afford the wholenetwork to go down if a cable across the Tasman Sea is cut.

Real networks are usually combinations of topologies - e.g. a network with somecoax (bus system) and some TP (star system). In this case the network will stillbe CSMA/CD with the star portion acting as a logical bus. Every workstation is interconnected Complex and expensive


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IBM Token Ring.

Used for PC networks - e.g. IBM's "Token Ring" topology.

The signal is transmitted around the ring in one direction - each station receives

the signal from the station before it and repeats it to the next station. When astation transmits, it gives the data the address of some other station in the ring -it passes from station to station and is copied by the one it is addressed to. Whenthe signal returns to the originating station, it is removed from the ring. Thesystem can check to see if the data has been received by using a status bit.

A station can only transmit when it is in possession of the token (which it canhave only for a limited period of time).

Technically the token ring MAC is a logical ring - in reality token ring calls for acentral hub. Token ring is a lot more technically sophisticated than the Ethernet

bus but handles heavy traffic better. Everything is more expensive than Ethernet- cable, NICs, etc.


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TRANSMISSION MEDIA (CABLING).

Essentially, there is CABLE and HIGH FREQUENCY CARRIER WAVE

Your choice of which transmission medium depends on: Distance of transmission Susceptibility of interference

Cost Bandwidth required Volume of Traffic

Twisted Pair cable (UTP and STP) has the following characteristics: The most economical wiring system

It may already be installed in the form of the telephone system It is susceptible to some outside interference

Coaxial cable has the following characteristics:

It may be effected by outside interference Harder to bend and terminate than UTP It has grounding problems It is more expensive than twisted pair, but it has a greater bandwidth.

Fibre Optic cable has the following characteristics: It is the most expensive

It has the best potential It does not emit an electromagnetic signal, and therefore can be used in

high security areas

Price approx $5 per metre (single strand) Termination not easy


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E. MEDIA ACCESS CONTROL ACCESS METHODS.

CSMA / CD (Carrier Sense Multiple Access / Collision Detect)

Used on Bus Topology Networks, typically with Ethernet All Work Stations haveseparate Ids. Before transmitting, a Work Station listens to see if the Bus is busy.If not, a message is sent. If 2 work stations transmit simultaneously, a collisionis detected, and both terminals must wait a random time before re-transmitting.If traffic usage (throughput) is high, severe performance fall off

Token Passing.

Used mainly with IBM Token Ring Networks. A token, consisting of an ALLCLEAR message, is circulated continuously on the ring. A Work Station wishing

to send a message will use the circulating token. The tokens message codechanges to IN USE, and attaches the message, along with the address (to andfrom) and an error checking code.

Only one message can be circulated at a time. Each node (network resource or junction point, capable of communicating with the other network devices)includes a Repeater, which regenerates the Token to maintain its signalstrength.

Each node will inspect the IN USE token, to see if the token contains the nodesaddress. The intended node will copy the message, and return the message tothe originating node. The message is cleared, and the ALL CLEAR signal is

restored.

Polling.

Ideally suited to a Star Topology. The server continually polls each workstation inturn, asking if it wishes to use the network. In a Star Network, the message isthen directed (via the server, if Star) to the address required.

If a Workstation is monopolizing the network, the messages will be broken upinto smaller pieces. Only so many pieces (bytes) will be accepted with each poll.

FDDI.

Fibre Distributed Data interface - a MAC that employs a pair of fibre optic ringsand tokens. Can support very high data transfer rates over long distances.


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IEEE 802 STANDARDS.

A set of standards developed by IEEE (Institute of Electrical and ElectronicsEngineers) to define methods of access and control on Local Area Networks(LANs).

The IEEE 802 standards correspond to the Physical and Data-Link layers of thewidely accepted ISO Open System Interconnection (OSI) Model, but they dividethe Data-Link layer into 2 sublayers (Logical Link Control and Media AccessControl).

Three primary IEEE 802 standards exist: 802.3 for Bus Networks that use Carrier Sense Multiple Access with

Collision Detection (CSMA / CD). Based on the Ethernet networkdeveloped by Xerox Corporation.

802.4 for Bus Networks that use Token Passing to regulate networkaccess and traffic control

802.5 for Ring Networks that use Token Passing (token ring networks)


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For each of the networks shown below: Identify the typology of the network and Describe how the signal is transmitted around the network.


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Questions on Network Topologies:

1. Topology means:

2. What is the terminating resistor for in the bus system?

3. What piece of hardware is required in a 10BaseT network that is not

needed in a physical bus system?

4. What intelligence is built into a physical star wired ring typology?

5. What makes a typology "logical bus"? What frame transmission method isused?

6. Describe the media access method for the logical ring topology.

7. Some switches are designed to support multiple .

8. Some networks can support IBM compatibles and Apple Mac PCs - true orfalse? How can this happen?


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CHAPTER TWO.LAN MODEL.

A. A NETWORK MODEL.B. NETWORK OPERATING SYSTEMS.C. HARDWARE and PERIPHERALS.D. The NETWORK INTERFACE CARD.E. INTERCONNECTION.F. CLASS EXERCISE.


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A. A NETWORK MODEL.

Networks are for sharingresources.The Computers interoperate.

Every sharing activity has its rules of operation.In Networking, we call these rules standards and protocols.

STANDARDS describe how things should be. Typically, they outline theminimum level of performance.PROTOCOLS are sets of rules and agreements, that describe how variouselements interact.

The ETHERNET set of standards and protocols was developed by XeroxCorporation.The ARCNET set of standards and protocols was developed by DatapointCorporation quite independent of Xeroxs Ethernet. Datapoint kept ARCnet as aproprietary set of specifications, and it didnt have the commercial success ofEthernet.The TOKEN-RING set of standards and protocols was developed by IBMCorporation later on in the 1980s.

These early Local Area Network (LAN) architectures tended to combine inflexiblehardware specifications with strict protocol descriptions. Specific types of cable,

cable connectors, topologies and software were required to satisfy each LANdefinition. Interoperability was not easy, and to be successful at installation, itpaid to stick to consistent equipment throughout the LAN.

Due to Industry and Market demand, standards today are a lot more flexible, anddo allow more mixing and matching. While the move to purely Open Protocols(protocols that do not favour a single manufacturer) has lost some momentumcompared with the 1980s, the idea was good. Today (the 1990s), the emphasisis more on the tried and proven protocols, but with the development of more toolsand programs to enable different computers eg IBM PC and Apple MacIntosh tolink effectively and interoperate.

Also, there has been considerable development with Software, as well as withHardware, and with the above mentioned development of interoperability withstandards and protocols. Workgroup productivity programs, and Workflowsoftwarehave come to be. This makes it easier to search for data, organise dataand link data (and even embed it). Sharing now means more than queuing up fora file or a printer.


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THE NETWORK MODEL.

Here are the major components of a network:Network Operating System.

The NOS consists of a family of programs that control the operation of thenetwork. Some of these programs provide the ability to share files and hardwaredevices.

Servers are computers that share their resources. This is software controlled.Clients are programs that give a user the ability to use the shared resourcesprovided by the server.

It is quite common today to have client and server software running in the sameComputer. This enables you to use resources on another Computer, and forother users to use resources on your Computer.

Network Hardware and Peripherals.

These are Hardware peripherals, such as printers and modems, which havespecial internal processors that run networking server software. They dont haveto be directly attached to a computer. Different computers eg IBM and Apple,providing they have the appropriate client application program can use thesenetworked peripherals, and the effect is that it looks as though they are locally

attached (even though they arent).

Network Interface Card (LAN Adapter).

The low-powered digital signals inside a computer are not powerful enough totravel long distances, without fading.The Network Interface Card: Changes the signals that come from inside the computer into more powerful

signals that can be transmitted down a network cable ie Amplification. Packages the data for transmission.

Controls access to the shared network cable (the cable is shared by the

linked workstations).

Network Interconnection eg Cabling.

Computers can send messages using: Electrical pulses over Copper Cable (UTP, STP, Co-axial). Pulses of light over fibre optic cable. Radio or light waves through air.and even combinations of all of these.


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B. NETWORK OPERATING SYSTEMS.

The function of the network software is to: ensure that information is transmitted and received reliably - the network

protocol defines a set of rules for this make the system transparent to the user

provide security enable resources to be shared.

Examples of network software include Novell NetWare, Apple Appletalk,Microsoft Windows NT, Unix and Linux.

Just as a PC requires an Operating System such as DOS to control it, so a

Network needs to have a Network Operating System (NOS) to control it.

Special software enables the workstations to share peripherals. Most of thesoftware is located in the network server, but some is located in eachworkstation. One of the most popular LAN software systems (NOS) is NetWare,marketed by Novell Incorporated. In a Novell network, the network servercontains the NetWare operating system and each workstation contains aNetWare Shell. It is called a shell because it fits around the micros operatingsystem.

The software allows you to connect various machines with different operating

systems within a building or over a wide area. The technology involved innetworking is improving and expanding every day leading toward intelligenthouses and buildings. It is estimated that within the next twenty years, only onefibre optic communication cable will enter your house. Your TV, computer andtelephone will all run off the same system.

Network Operating Systems are a combination of programs that give somecomputers and peripherals the ability to accept requests for service across thenetwork, and give other computers the ability to correctly use those services.

Servers are computers that share their hard-disk drives, attached peripherals

such as printers and CD-ROM drives and communication circuits. A request for aservice is made to the server. The server will inspect the request for properauthorisation, check for any conflicts and then, providing the checks are passed,provide the requested service.

File Servers store files created by application programs, or may store theapplication program itself. The file server must have a large enough hard-disk tostore enough to store the data. File servers also allow more than one workstationsimultaneous access to the same file. Access can be controlled ie who canaccess what, and when. Excellent system for shared Databases eg an AirlineBooking System.


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Print Servers accept print jobs sent by anyone across the network. Spooling(Spool = Simultaneous Print Operations On Line) print jobs is a critical function ofprint-server software. Why?The print-server can also report on status of jobs waiting for printing, and sortsout priorities.Practically any number of printers can be shared on a single network in a varietyof ways.

Client Software works with the internal operating system of a computer, so itcan route requests from application programs and user request via input devicessuch as keyboard and mouse to the File Server and Print Servers on thenetwork.

The principal element of the Client Software is called a redirector.

The redirector captures service requests that it has been programmed torecognise, and routes these requests to the appropriate place in the network forservice.

Network Communications Software packages requests from the ClientComputer and sends the request across the network. This software mustconform to specific protocols for addressing, ensuring deliver, and ensuringaccuracy.

Typical suites of network communications protocols include: Apples Apple File Protocol (AFP). Artisofts (Lantastic) Network Basic Input Output System (NETBIOS). Microsofts NetBIOS Extended User Interface (NETBEUI) ) (net-boo-ee).

Novells Sequential Packet Exchange (SPX) and Internetwork PacketExchange (IPX).

Driver (regulates or drives a device) Software works between the NetworkInterface Card and the Network Communications Software. At one time, youneeded to generate a special configuration of the Network Operating System forevery make of LAN adapter. Today, adapter (NIC) manufacturers supply driversthat conform to Microsofts Network Driver Interface Standard (NDIS) (N-diss)or Novells Open Data-Link Interface (ODI). This enables you to choose whichNetwork Operating System you use.


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C. HARDWARE and PERIPHERALS.

ServerYour network may have a file server, application server or both installed.

WorkstationsDepending on your network, these may be of one or more platforms.

HubsNot needed with thinnet. Also known as concentrators. Provides good faulttolerance because all workstations are attached separately to the hub. Able toconnect four, eight, sixteen or twenty four PCs.

SwitchesUsed to reduce congestion on the network. The network is broken up intosections so that traffic that has no business on parts of the network are not sentthere.

PrintersNetwork or personal. Network printers are more robust, print faster and hencecost more than personal printers. Printers can be connected in the followingmanners:

On a workstation for local use only. On a workstation shared with the network.

On a dedicated workstation set up as a print server (old XT or 286). On a print server box.

On the file server. Direct onto the network (if printer is capable).

Uninterruptible Power SupplyProvides uninterruptible power source for servers so time as available to shutdown properly in the event of a prolonged power cut.


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INTERCONNECTION BETWEEN NETWORKS.

BridgeUsed to connect together LANs of the same type. The bridge reads all themessages and addresses, and only passes on the messages that are intendedfor the other LAN. Messages are either blocked or redirected. This avoidsoverloading on either network.

Bridges filter and forward packets by using the physical address of the networkcards on the nodes - they operate at the OSI Data Link Layer.

RouterDevice to connect physically separate networks of different types (e.g. a bus to atoken ring network). Has software and a processor to enable it to connectdifferent protocols and topologies; is able to find all other hardware on thenetwork and route according to use and traffic. Can be simply a computer withseveral NICs and software to enable routing.

Routers are able to interconnect between different network types since they filtertraffic by logical address rather than physical address.

BrouterA brouter is a device that can function both as a bridge and a router.Not many around these days switches or routers are more the norm.

GatewayUsed to connect a LAN to a WAN (e.g. a Novell network to the internet)

Tape Backup DriveOr alternative device is needed to enable easy backup and restoration of lostdata.

DISCUSSION:

Discuss other types of Hardware that could be used in a LAN

How would your choice of hardware and peripherals be dictated by the User'sneed?


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D. THE NETWORK INTERFACE CARD.

The Network Interface Card, or LAN adapter, functions as an interface betweenthe computer and the network cabling. Inside the Computer, the NIC must beable to move data to and from RAM (over the parallel bus). Outside thecomputer, the NIC controls the flow of data in and out of the network cablesystem. The NIC has a specialised port that matches the electrical signallingstandards used on the cable and the specific type of cable connector.

The NIC must also buffer the data between the computer and the cable. Thecomputer is typically a lot faster than the network. The NIC must also change theform of the data from a wide parallel stream (within the computer) to a narrow,

one bit at a time, serial data stream (outside the NIC).

The jobs that the NIC performs means that it needs special on board processors.These processors can have their own RAM added, and can also include aspecial transceiver to handle the electrical interface to the cable.

Some NICs have a socket for a special Boot ROM. This allows a PC to startDOS from a file on a server, eliminating the need for an Internal Hard Disk Drive.

You must choose a NIC that matches your computers data bus and the networkcable. EISA or PCI adapters prove their worth in servers. Most workstations still

use the ISA adapters. If you use adapters that use EISA, IBM PS/2s MCA or PCIbuses, you can also choose products that use bus-mastering. Bus Mastering canmove data to and from RAM without interrupting the computers processor,hence lightening the load.

On the Network Cable side, the LAN adapter performs 3 important functions: Generates the electrical signals that travel over the network cable.

Follows the rules controlling access to the cable. Makes the physical connection to the cable.

Adapters for Ethernet and Token-Ring use the same basic system of electrical

signalling over the cable. A technique called MANCHESTER ENCODINGprovides a way to transmit 0s and 1s using DC (Direct Current) Voltage pulsesranging from -15 Volts to +15 Volts. The LAN adapters translate each change involtage level as a character in the ASCII data alphabet.


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An interface card is the interface between the Local Area Network (LAN) cablingand the Computer itself. The Network Interface Card (Network Adapter) doesmany things, such as: Converts data that is sent down the Computers Bus in parallel form into the

serial form required for the LAN cabling. Provides buffering. Amplifies signals. Provides addresses for each work station. Obeys the rules of the Network Operating System and the Media Access

Control method being used.

Try to find some examples of Network Interface Card, and (if possible) LANCabling (especially for the Practical Exercises)

NIC or network adaptor. Connector required for thinnet is BNC; for 10BaseT, RJ-45. A combo card has both connectors installed. If you have a Pentium PC with aPCI bus, then it is advantageous to use a 32 bit PCI NIC. Some of the functionsof the NIC include:

Converts data that is sent down the Computers Bus in parallel form into theserial form required for the LAN cabling.

Provides buffering. Amplifies signals.

Provides addresses for each work station. Obeys the rules of the Network Operating System and the Media Access

Control method being used. Forms the data into frames.

Deciding factors for NICs: Access method and protocol.

Transmission speed. Amount of an-board memory for buffering frames of data. Bus design - ISA, PCI. Compatibility with motherboard chipsets.

DMA usage. IRQ and I/O addressing. Connector design.


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E. INTERCONNECTION.

MediaTransmission media for LANs fall into two general categories - guided andunguided (radio).

Media suitable for LANs fall into five categories: Broadcast radio (wireless )

twisted pair wiring baseband coaxial cable broadband coaxial cable optical fibre

microwave radioFor WANs we can add satellite to the list.

Cable

Thick coax was the original Ethernet cable - too inflexible and expensive.Needs a drop cable to interconnect the network cable and the workstation.

Thinnet with T- connector at each computer is common. Max. length ofsection is 185m and 30 computers or a repeater is needed.

Twisted pair (unshielded twisted pair, UTP, 10baseT). Cheapest method -same as used for the phone system - convenient. Twisted pair can beshielded for noisy environments (STP). Comes in various standards, suchas:

category 3 which is normal telephone cable - good to 16Mbps

category 5 - 100Mbps Fibre optic - used for high speed connection between parts of the network.

Examples of abbreviations for ethernet cabling (distances are without signalregeneration) are:

10base2 (10Mbps baseband ethernet over coaxial cable to a maximumdistance of 185m - known as thin ethernet).

10base5 (10Mbps baseband ethernet over coaxial cable to a maximun of500m - known as thick Ethernet).

10baseT (10Mbps baseband transmission on twisted pair (cat 3 or 5 UTP)

to 100m using a star configuration with hub(s)). 100baseTX (100Mbps to 100 meters using cat 5 UTP or STP). 100baseFX (100Mbps baseband on fibre to 2000m).

Question?Which cabling system would you use for a small network say at home?


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Coaxial cable

A type of wire that consists of a center copper conductor surrounded by

insulation and then a grounded shield of braided wire. The shield minimizeselectrical and radio frequency interference.

Coaxial cabling is the primary type of cabling used by the cable televisionindustry and is also widely used for computer networks. Although moreexpensive than standard telephone wire, it is much less susceptible tointerference and can carry much more data. Because the cable televisionindustry has already connected millions of homes with coaxial cable, manyanalysts believe that they are the best positioned to capitalize on the much-heralded Information highway.

Coaxial cable can provide both baseband and broadband communications.Broadband coax could allow the media to be shared with other services such asCCTV. However the cost is higher and often it is easier and cheaper to installmultiple baseband cables instead.

Fibre optic cable

A technology that uses glass threads (fibres) of about 50m in diameter totransmit data. A fiber optic cable consists of a bundle of glass threads coated inplastic, each of which is capable of transmitting messages modulated onto lightwaves.

Fibre can either be: single mode

Or multi-mode

Fibre optics has several advantages over traditional metal communication lines: Fibre optic cables have a much greater bandwidth than metal cables including

coax). This means that they can carry more data (at speeds of about 1Gbps). Fibre optic cables are less susceptible than metal cables to interference. Fibre optic cables are much thinner and lighter than metal wires. Data can be transmitted digitally (the natural form for computer data) rather

than analogically.


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The main disadvantage of fibre optics is that the cables are expensive to install.In addition, they are more fragile than wire and are difficult to join. Terminalequipment is usually quite expensive.

Fibre optics is a particularly popular technology for Local Area Networks. Inaddition, telephone companies are steadily replacing traditional telephone lineswith fiber optic cables. In the future, almost all communications will employ fibreoptics.

Twisted Pair Cable

A type of cable that consists of two independently insulated wires twisted around

one another to reduce "crosstalk". The cable pair (or pairs) is then covered in aPVC sheath. Twisted-pair cable is used by telephone networks, and is the leastexpensive type of LAN cable.

Wireless

Can be radio waves or light - generally used for slower speeds (


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F. CLASS EXERCISE.

Remembering the Network Model, ie: NOS NIC CABLING HARDWARE and PERIPHERALS

In your groups (in the time allowed), produce a design for the following situations:

A. A Tertiary School Class using a Server Based Network and 20Workstations.

B. A Small Business with five staff.

Consider exactly what you need to have in each Network (Price is not a problem)and how you would go about things.Appoint a spokesperson (you will be required to do a Group Presentation to theclass).Appoint a recorder.


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CHAPTER THREE.LAN STRATEGIES.

A. SERVER BASED LANs.B. PEER-to-PEER NETWORKING.C. CLIENT/SERVER COMPUTING.D. OVERVIEW of NETWORK MANAGEMENT.E. E-MAIL.


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A. SERVER-BASED LANs.

There are four types of servers: File Servers. Application Servers (see C. Client / Serving Computing).

Print Servers. Communications Servers (sometimes called Web Servers).

However, under different strategies, various devices on the network can alsoperform the functions that the server does.

Server-based networking relies on a single, powerful computer dedicated toproviding all server functions for many (perhaps 500 or more) client computerson the network.

Peer-to-Peer networking is where the server functions are distributed amongmany computers. They act as file or print servers, and can also run applicationprograms at the same time.

Server-based networks, compared to Peer-to-Peer networks, have: Higher start-up cost (but there is an economy of scale as more client

computers that share the Servers resources are added). More technical expertise needed to install and manage (in general).

Features of a dedicated file server are:

Large amount of cabinet space for drives and other components. Large Power Supply Unit to handle the load. Fast interface bus.

Ability to expand RAM capacity considerably. Fast processor. Several Network Interface Cards, each with separate segments of cabling.

Benefits of Server-based systems are: Better Data Integrity and Data Management (important records and files are

in one place, making management and control of data easier, and allowingeasier backups).

Multitasking Operating system so that several programs can run at the sametime.

Good Network Administration from special Network Management software(even includes Client invoicing for access time).

Security. Fast response. Room for expansion. Ease of backup.


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B. PEER-to-PEER NETWORKING.

The processing power and storage capacity is shared between the networkedcomputers. Peer-to-Peer networking provides cost economy, because thecomputers are probably already available as Stand Alones, and are no doubtnot utilized to the maximum potential. This means there are resources that canbe shared.

Some Peer-to-Peer networks run file server networking software as well as ClientNetworking Software, Application Programs and, of course, an underlyingOperating System consistent across the network. This type of peer-to-peernetworking software is part of MS Windows 95, MS Windows for WorkgroupsVersion 3.11 and the Apple Macintosh Operating Environment.

Not all of the Computer Resources are automatically available to every user onthe network. The person using a particular PC can decide what files, directories,drives and peripheral devices (such as printers) can be shared with othernetworked computers. It is also possible to combine Peer-to-Peer Networkingwith a Server-based architecture.

Peer-to-Peer networking typically doesnt have the powerful management andauditing features found in server-based software. This is because the processingpower is used by local applications. Also the power (at a $ cost) and specialistsoftware of a dedicated server is probably not available in any of the Peer-to-Peer networked computers. With the power of modern PCs increasing rapidly,

and costs falling, the performance of Peer-to-Peer networking is improving.

Benefits of Peer-to-Peer networking are: Ease of installation. Ease of maintenance. Low Start-up costs.

Simplicity. Sufficient power to satisfy many organizational needs.


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C. USE of CLIENT/SERVER COMPUTING.

We have previously described several types of SERVER and CLIENTS(workstations). However, the term CLIENT/SERVER COMPUTING does have aspecial meaning. CLIENT/SERVER COMPUTING is where work is sharedbetween the client and the server, so that each device performs the task that itcan do the most efficiently.

The best example of client/server computing is in Database ManagementSystems. In older Database technology, each workstation runs a DatabaseProgram. Large Data Files are called from the File Server, processed at theWorkstation, and a Report is generated with the desired information. The newerClient/Server model distributes the task.

The client computer sends a request to a special program called a databaseengine (also known as Database Server), which runs in the File Server. TheDatabase Engine indexes, sorts, and searches the shared files, without sendingthem over the network. The Database Engine will only respond to what isspecifically requested, meaning no waste of resource. It also means that theclient computer (workstation) can allocate its resources to running otherapplications.

Resources can be allocated anywhere. A Workgroup is a good example of aClient / Server application --- especially for things such as Personal Management

and Scheduling, Project Management and general workflow. Such automationand integration of tasks produces better productivity.

SQL = Structured Query Language

Discuss what the Redirector does

In a LAN, software that routes workstation (client) requests for data to the server.In an MS Windows network, the redirector program is added to the PC tointercept requests for files and printers and direct them to the appropriate remotedevice if applicable. Starting with Windows 95 and Windows NT 4.0, the

redirector recognizes UNC names as well as drive letters that have been mappedto remote servers. The counterpart in NetWare is known as the Requester.


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D. OVERVIEW of NETWORK MANAGEMENT.

Computers have become an essential part of Business Operation andManufacturing Operations, and their role is becoming more and more important.Computer Networking has enabled Computer users to share resources. NetworkManagement is extremely important.

Network Management Programs run in Servers, Wiring hubs and even onNetwork Interface Cards and Uninterruptable Power Supplies. They gatherstatistics on data movement, and watch for conditions that exceed thresholds(safe limits that are programmed in). If a problem is detected (or evensuspected), the Network Management Program will take action. Actions mightinclude restarts, rerouting of data, call for human assistance or reallocation of aresource (such as extra loading on a load balanced power supply).

Manufacturers of Network equipment have adopted several sets of standards foroperating Network Management Software. SNMP (Simple Network ManagementProtocols) is a popular set of standards, and a set of standards that manysystems will either directly follow, or run to a similar style.

Under the SNMP Architecture, small management programs (in all sorts ofnetworked devices) monitor network devices and gather data. These smallmanagement programs are called AGENTS.

The data collected by the agents comes in a special format, known as MIB

(rhymes with rib). MIB = Management Information Base. A central program(MANAGEMENT CONSOLE PROGRAM) polls the agents regularly, and thecontents of their MIBs are downloaded. These Management Console Programstypically displayed detailed graphical information (e.g. green / orange / red bargraphs to indicate performance compared to thresholds) to a display screen(console). They can also send detailed statistical data to specialized analyticaldatabase programs.

Network Managers can use the Management Console to command changes tothe network eg status of a resource, activation of a link.

Good Network Management can dramatically enhance the performance of aNetwork, and ensure successful operation. It is a very effective insurance policy,even though the initial investment might be considered costly.


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RMON

(Remote MONitoring) Extensions to the Simple Network Management Protocol(SNMP) that provide comprehensive network monitoring capabilities. In standardSNMP, the device has to be queried to obtain information. RMON is proactiveand can set alarms on a variety of traffic conditions, including specific types oferrors. RMON2 can also monitor the kinds of application traffic that flow throughthe network. The full RMON capabilities are very comprehensive, and generallyonly portions of it are placed into routers and other network devices.

REMOTE ACCESS.

The ability to log on to a computer or network within an organization from anexternal location. Remote access is typically accomplished by directly dialing upanalog or ISDN modems or via a connection to the Internet.

REMOTE CONTROL SOFTWARE

Software that lets a user control a local computer from a remote location via anetwork connection. The software is installed at both ends, and both local andremote users can control the machine. Each user sees the same screen displayas if they were both looking at the same machine.

Also known as "desktop sharing," "remote desktop sharing" and "applicationsharing," remote control software is used to provide instruction and technical

support to remote users at their computers as well as take control of anunattended computer from a remote location.

REMOTE CONTROL VS. REMOTE NODE

In remote control, only keystrokes and mouse movement are sent from theremote machine, and only screen changes are sent back to the remote. Allapplication processing takes place in the local computer.

In contrast, a remote node setup is the normal way remote users log onto thecompany network. All data flows to the remote machine as if it were a local PC.

With high-speed connections, remote node is the preferred method; however, ifan enormous amount of data on the network must be processed by a remoteuser who has only a dial-up connection or perhaps a slow computer, the remotecontrol method can be used. Instead of passing all the data to the remote PC, theuser's unattended local PC performs the processing under the control of theremote PC. The remote user will not have the actual data files, but will have theresults of the processing on the remote screen, which can be captured andsaved.


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E. ELECTRONIC-MAIL (E-MAIL).

Electronic Mail Systems (E-Mail) store messages, and deliver these messageswhen the addresses are ready to receive them. These store are forward servicescan partially replace phone calls and meetings, overcome any limitations of timeand work hours, and have the advantage of Written Copy.

In an electronic-mail system, software in each computer reads and writes to ashared set of sub-directories in the network file server (or Workgroup PostMaster). Each electronic-mail subscriber runs a program that checks the files inthe subdirectories for any waiting mail. In larger networks, each LAN has its ownset of electronic-mail message files (generally called a Post Office). Onecomputer on each LAN, called the Postmaster, runs a program on a regular basisthat identifies messages identified for other Post Offices, collects them andforwards them.

In many ways, this process is similar to NZ Post Snail Mail, except it is all doneelectronically. If messages are destined for other electronic mail systems that usedifferent message formats or different address structures, a GATEWAY functionis required.

A good electronic Mail System is a superb (and cheap) method for disseminatinginformation between Business and other users.


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CHAPTER FOUR.PROTOCOLS, STANDARDS and

INTERCONNECTION.

A. PROTOCOLS.B. IEEE 802 STANDARDS.C. LINKS BETWEEN LANs.D. REPEATERS, BRIDGES and ROUTERS.


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A. PROTOCOLS.

A protocol is a set of rules for communicating between computers. Protocolsgovern format, timing, sequencing, and error control. Without these rules, thecomputer will not make sense of the stream of incoming bits.

Communicating data from computer to computer takes many steps. Suppose youare sending a file from one computer to another. The file must be broken intopieces. The pieces have to be grouped in a certain fashion. Information must beadded to tell the receiver where each group belongs in relation to others. Timinginformation and error correcting information must be added.

Because of this complexity, computer communication is broken down into steps.

Each step has its own rules of operation and, consequently, its own protocol.These steps must be executed in a certain order, from the top down ontransmission and from the bottom up on reception. Because of this hierarchicalarrangement, the term protocol stack is often used to describe the steps incomputer communication. A protocol stack is a set of rules for communication,and each step in the sequence has its own subset of rules.

What is a protocol, really? It is software that resides either in a computer'smemory or in the memory of a transmission device like a network interface card.When data is ready for transmission, this software is executed. The softwareprepares data for transmission and sets the transmission in motion. At the

receiving end, the software takes the data off the wire and prepares it for thecomputer by taking off all the information added by the transmitting end.

The existence of many protocols often causes confusion. Novell does it one way.3Com does it another. DEC does it a third way. IBM does it another way. Andsince the transmitter and the receiver have to 'speak' the same protocol, thesefour can't talk directly to each other. That's where protocol standards and the OSImodel fit in.

A protocol standard is a set of rules for computer communication that has beenwidely agreed upon and implemented by many vendors, users, and standards

bodies. Ideally, a protocol standard should allow computers to talk to each other,even if they are from different vendors. Computers don't have to use an industry-standard protocol to communicate, but if they use a proprietary protocol then theycan only communicate with equipment of their own kind.

There are many standard protocols, none of which could be called universal.

The idea of a layered protocol is a little difficult to grasp so an example fromsomething that we are used to might help - writing a letter! An important part ofthe layered protocol model is that each layer provides a service to the layersabove it.


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Protocol for what is said and in what order (i.e. acknowledge previouscorrespondence, discuss your topic).

Protocol for formatting a letter (i.e. precede with address, date, then greeting.Break into sentences - capitals and full stops).

Protocol for receiving/sending a letter to/from the PO (i.e. packaged according toPO regulations (envelope size, stamp denomination, etc).

Going back up is like stripping off the lower level protocols.

Protocol forwhat is said and

in what order

Protocol forwhat is said and

in what order

Protocol forformatting a

letter

Protocol forformatting a

letter

Protocol for

receiving/sending a letter

to/from the PO

Protocol for

receiving/sending a letter

to/from the PO


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THE OSI MODEL

The Open System Interconnection (OSI) model is a set of protocols thatattempt to define and standardize the data communications process. The OSImodel is set by the International Standards Organization (ISO). The OSImodel has the support of most major computer and network vendors, many largecustomers, and most governments, including the United States.

The OSI model is a concept that describes how data communications shouldtake place. It divides the process into seven layers. Into these layers fit protocolstandards developed by the ISO and other standards bodies, including theInstitute of Electrical and Electronic Engineers (IEEE), American NationalStandards Institute (ANSI), and the Comittee Consultatif Internationale deTelgraphique et Telephone (CCITT) (now called ITU-T)

The OSI model is not a single definition of how data communications actuallytakes place in the real world. Numerous protocols may exist at each layer. TheOSI model states how the process should be divided and what protocols shouldbe used at each layer. If a network vendor implements one of the protocols ateach layer, its network components should work with other vendors' offerings.

The OSI model is modular. Each successive layer of the OSI model works withthe one below it. At least in theory, you may substitute one protocol with anotherat the same layer without affecting the operation of layers above and below. Forexample, Token Ring or Ethernet hardware should operate with multiple upper-layer services, including the transport protocols, network operating system, internetwork protocols, and applications interfaces. However, for this interoperabilityto work, vendors must create products to meet the OSI model's specifications.


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Each layer of the OSI model performs an essential function. Here's a look at whateach layer does.

ApplicationLayer

The final layer is the interface between the software runningin the computer and the network. It supplies functions to thesoftware in the computer, such as electronic mail or filetransfer. Note that this layer is not the applicationsthemselves! Protocols here include FTP, POP, SMTP, HTTPand SHTTP.

PresentationLayer

The sixth or presentation layer is concerned with thepresentation of data while in transit and performs codeconversion. It is the translator of the network, making sure thecomputer is talking in the right language for the network (e.g.EBCIDIC to ASCII conversion).

Session Layer The session layer decides when to turn communication onand off between two computers. It coordinates the interactionbetween them. Unlike the network layer, it deals with theprocesses running in each machine to establishconversations between them. Can provide for full or halfduplex operation.

TransportLayer

The fourth layer ensures data is sent successfully betweenthe two computers in an orderly manner. If data is sentincorrectly, this layer has the responsibility to ask forretransmission of the data.

Network Layer The third layer establishes, maintains, and terminatesconnections. The network layer is responsible for translatinglogical addresses, or names, into physical addresses andproviding network routing. Makes sure a packet gets to it'sdestination in a reasonable period of time. Is concerned withrouting.

Data-LinkLayer

The second, or data-link, layer of the OSI model isresponsible for getting data packaged and onto the networkcable. It manages the physical transfer, providing the blocksof data, synchronization, error control, and flow control. Thedata-link layer is often subdivided into two parts. These arethe Logical Link Control (LLC), which is designed to providea consistent level of service to the network layer regardless ofwhich MAC is used, and the Medium Access Control(MAC), which is media dependent, and checks that the mediais free, encapsulates data into frames and checks for dataintegrity using CRC.

Physical Layer The first, or physical layer, of the OSI model conveys the bitsthat move along the cable (or media which can include radio).It is responsible for making sure that the raw bits get from oneplace to another, no matter what shape they are in. It dealswith the mechanical and electrical characteristics of the cableand connectors. Signaling specifications are defined at thislevel.


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Unfortunately, protocols in the real world do not conform precisely to these neatdefinitions. Some network products and architectures combine layers. Othersleave out layers. Still others break apart layers. But no matter what, all workingnetwork products achieve the same result, getting data from here to there. Thequestion is, do they do it in a way that is compatible with the rest of the world'snetworks?

Interestingly not all protocols fit the OSI model - for example, Internet Protocols(TCP/IP) does not.


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B. IEEE 802 STANDARDS.

In 1980, the IEEE (Institute of Electrical and Electronic Engineers) began work onProject 802 - the formulation of standards for LANs. The 802 committee isdivided into a number of sub-committees:

IEEE 802.1: Standards related to Network Management. IEEE 802.2: General standard for the data link layer in the Data Link

Layer in the OSI Reference Model. . The IEEE divides this layer into two

sublayers (the Data Link Control (DLC) Layer, and the media accesscontrol (MAC) layer). The MAC layer varies for different network types

and is defined by standards IEEE 802.3 through IEEE 802.5.

IEEE 802.3: Defines the MAC layer for Bus Networks that useCSMA/CD (contention). This is the basis of the Ethernet standard.

IEEE 802.4: Defines the MAC layer for bus networks that use a

token-passing mechanism (Token Bus networks). IEEE 802.5: Defines the MAC layer for Token Ring networks.

IEEE 802.6: Standard for Metropolitan Area Networks (MANs).

IEEE 802.7: Broadband networks. IEEE 802.8: Fibre optic networks.

IEEE 802.9: Integrated Data and Voice networks (e.g. ISDN).

IEEE 802.10: Interoperable LAN/MAN security.

IEEE 802.11: Wireless LAN media access control. IEEE 802.12: Demand priority access method for the 100VG-anyLAN

system developed by HP. IEEE 802.14: Standard protocol for cable TV broadband

communication networks.


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COMMON NETWORK PROTOCOLS.

NetBIOS (Network Basic Input/Output System) is not really a protocol, ratheran interface running on top of a common protocol on computers networked.

NetBEUI (NetBIOS Extended User Interface) is used on small networks, mainlypeer to peer. Was used on the first version of Windows NT.

Appletalk is a suite of protocols developed by Apple Computer for computernetworking. It was included in the original Macintosh (1984) and is nowdeprecated by Apple in favor of TCP/IP networking.

DECnet is used for very large networks. DECnet is a proprietary suite ofnetwork protocols created by Digital Equipment Corporation, originally releasedin 1975 in order to connect two PDP-11 minicomputers. It evolved into one of thefirst peer-to-peer network architectures, thus making DEC into a networkingpowerhouse in the 1980s.

NetWare (IPX (Internet Packet Exchange), SPX (Sequenced PacketInterchange), SAP (Service Access Protocol), RIP (Routing InformationProtocol), AFP (Apple Filing Protocol). Netware IPX/SPX is a variation of TCP/IPthat Novell developed.

OSI is designed to follow the 7 layer model.

TCP/IP was developed in the late 1970s for the Dept of Defense's ARPAnetwork. It is becoming even more common. Originally with UNIX, and Microsoft,Apple and Novell use it as their native protocol now.


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C. LINKS between LANs.

In todays Information Age, Computers are the Productivity Areas (WorkStations). The Computer Network is like the Production Line and the DistributionCentre, and even the Point of Sale. If Local Area Networks (LANs) are the In-House production lines, the middle and long distance networks (MANs andWANs) are the Transportation Links.

Due to a need to move data over greater distances than, say, 1 km, severaltechniques have been developed for linking and extending LANs. The techniquesused to link LAN segments depend on:

Distance and speed needed. Network Communication Protocols being used. Cost.

Signal degradation and accumulated interference (eg noise) limit the distancethat a high transmission speed cable can extend. LAN to LAN connections movedata more slowly than Local Area Connections, and more technical equipmentand more quality checks are required.

When connections extend beyond a metropolitan area (MAN), it is typical tolease circuits from suppliers such as Telecom for WAN links. The 3 generalcategories for leased services are: Circuit-switched (Equipment dials a connection, transfers data, and hangs

up when finished). Full-Period (where a circuit is dedicated to your use all the time). Packet-Switched (allow multi-point connections for bursts of short packets.

Follow ITU-T X.25 protocol or the newer frame relay standard).There can also be Dial-Up services.

To lease a circuit to link LAN segments is costly. It makes sense to have goodNetwork Portal Devices for both ends of the link, so that the expensive circuitscan be used to maximum efficiency.

A PORTAL is the point where networks meet or connect. If you like, they are like

a shipping port (or dock). Portal devices (REPEATERS, BRIDGES andROUTERS) extend and segment the Local Area Networks high-speed link. Eachdevice offers a different degree of data handling capability, discrimination anddirecting capability.

Network Traffic typically follows specific paths, and travels within a group ofcomputers with common interests (a Workgroup). However, some traffic mustflow between Workgroups. If all Workgroups were linked on the same cable, andallowed to communicate with each other without restrictions, the resources of thecable would be severely extended.


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D. REPEATERS, BRIDGES and ROUTERS.

A PORTAL is the point where networks meet or connect. If you like, they are likea shipping port (or dock). Portal devices (REPEATERS, BRIDGES andROUTERS) extend and segment the Local Area Networks high-speed link. Eachdevice offers a different degree of data handling capability, discrimination anddirecting capabilty.

A REPEATER can typically fit in your hand. It connects 2 segments of yournetwork cabling, retimes and boosts the digital signals, and sends the signals on.Repeaters are relatively inexpensive, and are easy to install. However, the rangeof a high-speed LAN is still very restricted (a couple of km), no matter how manyrepeaters you have.

Bridges are more complex than repeaters. A BRIDGE will read the StationAddress of each Ethernet Packet, or of each Token-Ring frame. This is theoutermost envelope around the data. You might recall the HDLC frame fromDC100:Data Communications lessons:

FF FCS DATA AC

This determines the destination of the message. The bridge does not look insidethe package or frame to read NetBIOS, IPX or TCP/IP addresses (i.e. lowerlayers of the Data Communications model).

A BRIDGE is a network portal device used to link Workgroup LANs. The bridgecan control what traffic is passed between LAN cable segments --- unlike aREPEATER which passes all data between cable segments. The 2 purposes of aBRIDGE are to extend the network, and to isolate network traffic.

A ROUTER is a more complex portal device than a bridge. They are moreexpensive, and require more attention than a bridge. However, they are a lot

more efficient in examining and directing traffic, and also in doing Protocolconversion between different types of LAN.

It digs deeper into the envelopes that surround the data, to find the destinationfor the data packet. The router will read the information in each packet or frame,and by a complex process will determine the appropriate network destination.The outer envelopes are discarded, and the data is repackaged andretransmitted. Accordingly, it doesnt matter too much what type of hardware orprotocols are being used in each LAN segment, because the router handles theconversion process in its repackaging.


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Routers also act as a safety barrier between segments. Data packets with errors just dont get through. Routers also (because they strip off the outer layers of

data) send information across the interLAN circuit more efficiently than bridgesdo (less redundancy). Routers (because of their complex stripping of outerlayers, and network addressing processes) are generally slower than bridges.They are also more costly.

In recent times, the differences between the capabilities of switches and routershave narrowed. Routers are also becoming a lot more capable, and can handleLAN to MAN, and even LAN to WAN that previously required a specialisedGATEWAY connection.

A GATEWAY performs efficient WAN protocol conversion (more about this in

Data Communications - WANs). Routers make very smart connections betweenthe elements of complex networks.


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CONCLUSION.

THANK YOU.I hope you have enjoyed your journey with this course PC Networking Level 5.May this be a significant step in your journey of success? Success might bedefined as the progressive realization of worthwhile goals. We are very pleasedto be able to work with you.

Please refer to our Web Page at www.ebooksctf.co.nz under the section PCNetworks and Data Communications for other relevant Courses.

Please continue to E-Mail us if you have any questions or comments.Our E-Mail address is [email protected] Please also feel free to seek our advice about any area where you think

we can help.

Please include (where possible) the Course Name and the Page Number(these can be found on the footer of each page) if it is a question about aCourse.

Please share your success stories with us. We are delighted to hear from you.

We look forward to your continual success.


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PC NETWORKING Level 5.

Copyright by CTF Services Limited 2005All rights reserved worldwide. No part of this book may be reproduced or transmitted inany form, or by any means, electronic or mechanical, including photocopying, recording,or by any information storage and retrieval system, without the written permission of the

publisher, except where permitted by law.

Published byCTF Services Limited, 19 Regent St, Timaru 8601, New Zealand

Distributed bywww.ebooksctf.co.nz

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