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Day 1-4 Introduction on Networking

Types of networks

Protocols

Networking hardware Topologies

Network operating system

Day 5 OSI model

Day 6-8 Networking media (Cabling)

Unshielded Twisted Pair (UTP)

Cable Shielded Twisted Pair (STP)

Cable Coaxial Cable

Fiber Optic Cable Wireless

LANs Cable Installation Guides

Day 9- How to make a CAT5 Cable

Day 10-13 IP Addressing

Day 14 Installation of NIC

Day 15, 16 Peer to Peer NetworkingUsing windows 98 peer to peer

networking

Day 17, 18 DNS (Domain name system)

DNS troubleshooting

Installing windows server 2003

Joining a domain in windows XP pro

Day 19- Creating & Implementing FTP server

Day 20-Remote Installation Services (RIS) Working with RIS using windows 2000 RIS

Day 21-RAID

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What is a Network

A network consists of two or more computers that are linked in order to share resources (such asprinters and CD-ROMs), exchange files, or allow electronic communications. The computers on

a network may be linked through cables, telephone lines, radio waves, satellites, or infrared light

beams.

The two basic types of networks include:

Local Area Network (LAN)

Wide Area Network (WAN)

Local Area Network

A Local Area Network (LAN) is a network that is confined to a relatively small area. It isgenerally limited to a geographic area such as a writing lab, school, or building. Rarely are LAN

computers more than a mile apart. In a typical LAN configuration, one computer is designated as

the file server. It stores all of the software that controls the network, as well as the software that

can be shared by the computers attached to the network.

Wide Area Network

Wide Area Networks (WANs) connect larger geographic areas, such as Florida, the United

States, or the world. Dedicated transoceanic cabling or satellite uplinks may be used to connect

this type of network.

What is a Protocol

A protocol is a set of rules that governs the communications between computers on a network.

These rules include guidelines that regulate the following characteristics of a network: access

method, allowed physical topologies, types of cabling, and speed of data transfer.

The most common protocols are:

Ethernet

Local Talk Token Ring

FDDI

ATM

Ethernet

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The Ethernet protocol is by far the most widely used. Ethernet uses an access method called

CSMA/CD (Carrier Sense Multiple Access/Collision Detection). This is a system where each

computer listens to the cable before sending anything through the network. If the network isclear, the computer will transmit. If some other node is already transmitting on the cable, the

computer will wait and try again when the line is clear. Sometimes, two computers attempt to

transmit at the same instant. When this happens a collision occurs. Each computer then backs offand waits a random amount of time before attempting to retransmit. With this access method, it

is normal to have collisions. However, the delay caused by collisions and retransmitting is very

small and does not normally effect the speed of transmission on the network.

The Ethernet protocol allows for linear bus, star, or tree topologies. Data can be transmitted overwireless access points, twisted pair, coaxial, or fiber optic cable at a speed of 10 Mbps up to

1000 Mbps.

LocalTalk

LocalTalk is a network protocol that was developed by Apple Computer, Inc. for Macintoshcomputers. The method used by LocalTalk is called CSMA/CA (Carrier Sense Multiple Access

with Collision Avoidance). It is similar to CSMA/CD except that a computer signals its intent to

transmit before it actually does so. LocalTalk adapters and special twisted pair cable can be used

to connect a series of computers through the serial port. The Macintosh operating system allowsthe establishment of a peer-to-peer network without the need for additional software.

Token Ring

The Token Ring protocol was developed by IBM in the mid-1980s. The access method used

involves token-passing. In Token Ring, the computers are connected so that the signal travels

around the network from one computer to another in a logical ring. A single electronic tokenmoves around the ring from one computer to the next. If a computer does not have information to

transmit, it simply passes the token on to the next workstation. If a computer wishes to transmitand receives an empty token, it attaches data to the token. The token then proceeds around the

ring until it comes to the computer for which the data is meant. At this point, the data is captured

by the receiving computer. The Token Ring protocol requires a star-wired ring using twisted pairor fiber optic cable. It can operate at transmission speeds of 4 Mbps or 16 Mbps.

FDDI

Fiber Distributed Data Interface (FDDI) is a network protocol that is used primarily to

interconnect two or more local area networks, often over large distances. The access methodused by FDDI involves token-passing. FDDI uses a dual ring physical topology. Transmissionnormally occurs on one of the rings; however, if a break occurs, the system keeps information

moving by automatically using portions of the second ring to create a new complete ring. A

major advantage of FDDI is speed. It operates over fiber optic cable at 100 Mbps.

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ATM

Asynchronous Transfer Mode (ATM) is a network protocol that transmits data at a speed of 155

Mbps and higher. ATM works by transmitting all data in small packets of a fixed size; whereas,other protocols transfer variable length packets. ATM supports a variety of media such as video,

CD-quality audio, and imaging. ATM employs a star topology, which can work with fiber optic

as well as twisted pair cable.

What is Networking Hardware

Networking hardware includes all computers, peripherals, interface cards and other equipment

needed to perform data-processing and communications within the network.

This section provides information on the following components:

File Servers

Workstations

Network Interface Cards

Switches

Repeaters

Bridges

Routers

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File Servers

A file server stands at the heart of most networks. It is a very fast computer with a large amount

of RAM and storage space, along with a fast network interface card. The network operatingsystem software resides on this computer, along with any software applications and data files

that need to be shared.

Workstations

All of the user computers connected to a network are called workstations. A typical workstationis a computer that is configured with a network interface card, networking software, and the

appropriate cables. Workstations do not necessarily need floppy disk drives because files can be

saved on the file server. Almost any computer can serve as a network workstation.

Network Interface Cards

The network interface card (NIC) provides the physical connection between the network and the

computer workstation.

Switch

A concentrator is a device that provides a central connection point for cables from workstations,

servers, and peripherals.

Repeaters

Since a signal loses strength as it passes along a cable, it is often necessary to boost the signal

with a device called a repeater.

Bridges

A bridge is a device that allows you to segment a large network into two smaller, more efficientnetworks. If you are adding to an older wiring scheme and want the new network to be up-to-

date, a bridge can connect the two.

Routers

A router translates information from one network to another; it is similar to a superintelligentbridge. Routers select the best path to route a message, based on the destination address and

origin.

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What is a Topology?

The physical topology of a network refers to the configuration of cables, computers, and other

peripherals. Physical topology should not be confused with logical topology which is the methodused to pass information between workstations. Logical topology was discussed in the Protocolchapter.

Main Types of Physical Topologies

The following sections discuss the physical topologies used in networks and other related topics.

Linear Bus

Star

Star-Wired Ring

Tree

Linear Bus

A linear bus topology consists of a main run of cable with a terminator at each end .

Fig. 1. Linear Bus topology

Star

A star topology is designed with each node connected directly to a central network hub or

concentrator.

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Fig. 2. Star topology

Tree

A tree topology combines characteristics of linear bus and star topologies.

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7-layer OSI MODEL

The OSI (Open System Interconnection) model is developed by ISO in 1984 to provide a

reference model for the complex aspects related to network communication. It divides the

different functions and services provided by network hardware and software in 7 layers. This

facilitates modular engineering, simplifies teaching and learning network technologies, helps toisolate problems and allows vendors to focus on just the layer(s) in which their hardware or

software is implemented and be able to create products that are compatible, standardized and

interoperable.

The diagram below shows the 7 layers of the OSI Model, to remember them in the correct order

a common mnemonic is often used: All People Seem To Need Data Processing.

Host A Host B

A more detailed description of each layer follows below, but here's what basically happens whendata passes from Host A to Host B:

1. the Application, Presentation and Session layer take user input and converts it into data

2. the Transport layer adds a segment header converting the data into segments,

3. the Network layer adds a network header and converts the segments into packets ,4. the Data Link layer adds a frame header converting the packets into frames,

5. the MAC sublayer layer converts the frames into a bits which the Physical layer can put on the

wire.The steps are known as the 5 steps ofdata encapsulation.

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What is Network Cabling

Cable is the medium through which information usually moves from one network device toanother. There are several types of cable which are commonly used with LANs. In some cases, a

network will utilize only one type of cable, other networks will use a variety of cable types. The

type of cable chosen for a network is related to the network's topology, protocol, and size.Understanding the characteristics of different types of cable and how they relate to other aspects

of a network is necessary for the development of a successful network.

The following sections discuss the types of cables used in networks and other related topics.

Unshielded Twisted Pair (UTP) Cable

Shielded Twisted Pair (STP) Cable

Coaxial Cable

Fiber Optic Cable

Wireless LANs Cable Installation Guides

Unshielded Twisted Pair (UTP) Cable

Twisted pair cabling comes in two varieties: shielded and unshielded. Unshielded twisted pair

(UTP) is the most popular and is generally the best option for school networks

Shielded Twisted Pair (STP) Cable

A disadvantage of UTP is that it may be susceptible to radio and electrical frequency

interference. Shielded twisted pair (STP) is suitable for environments with electrical interference;

however, the extra shielding can make the cables quite bulky

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Coaxial Cable Connectors

The most common type of connector used with coaxial cables is the Bayone-Neill-Concelman

(BNC) connector.

BNC connector

Category 5 Cable

Category 5 cable, commonly known as Cat 5, is an unshielded twisted pair type cable designed

for high signal integrity. The actual standard defines specific electrical properties of the wire, but

it is most commonly known as being rated for its Ethernet capability of 100 Mbit/s. Its specificstandard designation is EIA/TIA-568. Cat 5 cable typically has three twists per inch of each

twisted pair of 24 gauge copper wires within the cable. Another important characteristic is that

the wires are insulated with a plastic (FEP) that has low dispersion, that is, the dielectric constantof the plastic does not depend greatly on frequency. Special attention also has to be paid to

minimizing impedance mismatches at connection points.

It is often used in structured cabling for computer networks such as fast Ethernet, although it is

often used to carry many other signals such as basic voice services, token ring, and ATM (at upto 155 Mbits/s, over short distances).

The other well known flavour of this type of cable is the 10 Mbit/s Category 3 cable. Less wellknown is the 20 Mbit/s Cat 4. Cat 4 offered only a small advance in speed over Cat3, and was

generally ignored in favour of Cat 5. Cat 1 and Cat 2 are 1 Mbit/s systems for voice and low-speed data.

Patch leads created from Cat 5 are often terminated with RJ-45 electrical connectors. Normal Cat

5 cables are wired "straight through" and connect a computer to a hub. In other words, pin 1 is

connected to pin 1, pin 2 to pin 2, etc. The RJ-45 pinout for a Cat 5 cable can either be TIA-568A or TIA-568B. TIA-568A is used by some phone systems and Token Ring. Most everything

else, such as the Ethernet standards 10BASE-T and 100BASE-TX, use TIA-568B.

In Ethernet, "crossover" Cat-5 cables are used to connect two hubs together, in which pairs twoand three are reversed. Crossover cables can also be used to connect two PC's NICs directly

(with no intervening hub). See the TIA-568B article for a pinout diagram.

Cat 5e cable is an enhanced version of Cat 5 for use with 1000 Base-T networks, or for long-

distance 100 Base-T links (350 m, compared with 100 m for Cat5). It must meet the EIA/TIA568A-5 specification.

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Cat 6 cable is defined by the ANSI TIA/EIA 568B-2.1. It is suitable for 1000 Base-T (gigabit)

Ethernet up to 100 m.

Cat 7 cable, with four individually-shielded pairs (ScTP) inside an overall shield, has beenproposed but is not in common use. It is designed for transmission frequencies up to 600MHz,

which should enable it to carry 10-Gigabit Ethernet (10GBaseT), but requires a redesigned RJ-45connector (called a GG45) to achieve this speed. 10GBaseT networks are not yet widely

available, and may not be able to compete with fibre optic networks.

The Anatomy of CAT5 Cable

What CAT5 Cable is

CAT5, which is short for Category 5 and indicates the fifth generation, is a standard for twisted

pair Ethernet cable as defined by the EIA/TIA (Electronic Industries Association and

Telecommunications Industry Association).

CAT5 is the most common cabling system used for networks today. CAT5 cable runs are limitedto a maximum recommended length of 100m (328 feet).

How CAT5 Cable Works

CAT5 cables contain eight wires--usually 24-gauge copper. The wires are divided into four pairsand each pair is twisted together, thus the moniker twisted pair.

Pair 1: White/Blue - Blue

Pair 2: White/Orange - OrangePair 3: White/Green - Green

Pair 4: White/Brown - Brown

Fast Ethernet (100 Mbps) communications utilize two pairs--Pair 2 and Pair 3 are used whilePair 1 and Pair 4 are not.

CAT5 cable pairs are twisted together to promote signal balance. Both wires in a pair carry the

same information and the electromagnetic fields generated by the individual wires cancel eachother out by virtue of being twisted together. Thus, each balanced pair poses less risk of

interference with the other pairs. Because each pair carries two copies of the same information,

less power is required to send the signal, further reducing electromagnetic interference.

CAT5 cables have more twists per inch than earlier CAT cable versions allowing CAT5 cable torun at higher speeds and span greater lengths.

CAT5 cables are terminated by RJ45 connectors. There are two standards for wiring RJ45 plugs

and jacksEIA/TIA T568A and T568B. These standards dictate the color code pattern used toconnect the cable wires to the RJ45 plugs and jacks. Most pre-made patch cables use T568B.

CAT5 Cable Type

Unshielded Twisted Pair (UTP) is the most common and is simply made up of the twisted pairsenclosed in the vinyl jacket.

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All About IP Addresses

IP addresses are 32 bit numbers, most commonly represented in dotted decimal notation

(xxx.xxx.xxx.xxx). Each decimal number represents eight bits of binary data, and therefore can

have a decimal value between 0 and 255. IP addresses most commonly come as class A, B, or C.

It's the value of the first number of the IP address that determines the class to which a given IP

address belongs. ClassD addresses are used for multi-cast applications.

The range of values for these classes are given below.

Class Range Allocation

A 1-126 N.H.H.HB 128-191 N.N.H.H

C 192-223 N.N.N.H

D 224-239 Not applicable

N=Network

H=Host

Note 1: 127.0.0.0 is a class A network, but is reserved for use as a loopback address(typically

127.0.0.1).

Note 2: The 0.0.0.0 network is reserved for use as the default route.

Note 3: Class D addresses are used by groups of hosts or routers that share a common

characteristic: e.g. all OSPF devices respond to packets sent to address 224.0.0.2

Note 4: Class E addresses exist (240-248),but are reserved for future use.

The class of an address defines which portion of the address identifies the Network number and

which portion identifies the Host, as illustrated above, as N and H.

Subnet Masks

Subnet masks are essential tools in network design, but can make things more difficult tounderstand. Subnet masks are used to split a network into a collection of smaller subnetworks.

This may be done to reduce network traffic on each subnetwork, or to make the internetwork

more manageable as a whole. To all intents and purposes, each subnetwork functions as if it werean independent network, as far as entries in the routing table are concerned.

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Interface configuration for router 1

Interface IP Address Subnet mask

E0 150.4.2.1 255.255.255.0E1 150.4.3.1 255.255.255.0

E2 150.4.1.1 255.255.255.0

Network card

A transitional network card with both BNC "Thin net" (left) and Twisted pair (right) connectors.

A network card (also called network adapter, network interface card, NIC, etc.) is a piece of

computer hardware designed to provide for computer communication over a computer network.other type of network is used.

The card implements the electronic circuitry required to communicate using a specific physical

layer and data link layer standard such as ethernet or token ring. This provides a base for a fullnetwork protocol stack, allowing communication among small groups of computers on the sameLAN and large-scale network communications through routable protocols, such as IP.

Installation of NIC

Installation of Network Interface Hardware

Your system will require an Ethernet 10BaseT network interface (also called a network card,

NIC or Ethernet adapter) to be installed in your system. If your system does not have one, you

must purchase one and have it installed and working properly to continue.

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The Windows operating system has the ability to automatically detect the presence of the

Ethernet adapter. After the first restart following the installation of an Ethernet adapter,

Windows will attempt to select and load the Ethernet card drivers. This step may require theoriginal Windows CD or diskettes, or it may require a diskette that came with your Ethernet card.

Windows 98 Peer to Peer Networking

Step 1. Install protocol:

Windows 98:

Right click Network Neighbor hood on your desktop.

Select "properties" Click the ADD button.

Select protocol and then ADD.

From the left panel select Microsoft and then select TCP/IP or Netbeui from the rightpanel then click OK. (you will need the windows98 cd). if you selected netbeui skip this

step. If you selected TCP/IP you will need to decide if u you want to assign ip addresses

manually or dynamically.

If you decide to assign ip addresses with a DHCP server skip this step.

To assign ip addresses manually.

Right click networking neighborhood on the desktop go to properties. Select TCP\IP from the list, and click properties button.

Check the "Specify an ip address" radio button and enter a private ip address.( e.g. ip

192.168.2.* ---- subnet 255.255.255.0).

Step 2. Install client services:

This should also already be present, but if its not then:

Right click network neighborhood and go to properties.

Click the ADD button.

Select Client and then click ADD.

Select Microsoft from the left and "Client for Microsoft" from the right panel and click

OK.

Step 3. Install File & print sharing services:

This should already be present, but if its not then:

Right click network neighborhood and go to properties. Click the ADD button.

Select Services and then click ADD.

Select file & print sharing for Microsoft and click OK.

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Step 4. Test TCP\IP

Go Start >>Command Prompt. at the dos prompt type ping 127.0.0.1 your result should look like

this:

If you don't see this screen then try the steps again. If it works then ping the ip you assigned (e.g.ping 192.168.2.2) if you get the same results then tcp/ip is setup correctly.

Step 5. Setup workgroup.

Right click network neighborhood and go to properties.

Click the "Identification tab".

Enter "computer name". (select a unique name)

Enter "workgroup name". (make sure you have the same workgroup name on allcomputers)

You may need to restart.

Step 6. Create a User account

(make sure you create the same user account on the other machines).

Go to Start>> Settings>> Control Panel.

Double click the Users Icon.

Click the new user button.

Then click Next, enter a username.

Enter a password and click next.

Select "Create new item to save disk space", and click next.

Click Finish.

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DNS

Definitions of DNS

Domain Name Server (or system) An Internet service that translates domain names intoIP addresses.

(Domain Name System) The Domain Name System is the system that translates Internet

domain names into IP numbers. A "DNS Server" is a server that performs this kind of

translation.

DNS stands for Domain Name System. This System translates a domain name such as

rshweb.com into the Internet Protocol (IP) numbers (209.203.234.42) to find the correct

web site - in this case the site for Domain Bank. The network of computers that constitutethe Internet map domain names to their corresponding IP numbers. The data is then made

available to all computers and users on the Internet.

How Domain Name Servers WorkIf you spend any time on the Internet sending e-mail or browsing the Web, then you use

domain name servers without even realizing it. Domain name servers, or DNS, are an

incredibly important but completely hidden part of the Internet, and they are fascinating! The

DNS system forms one of the largest and most active distributed databases on the planet.Without DNS, the Internet would shut down very quickly.

How Domain Name Servers Work

If you spend any time on the Internet sending e-mail or browsing the Web, then you use

domain name servers without even realizing it. Domain name servers, or DNS, are an

incredibly important but completely hidden part of the Internet, and they are fascinating! The

DNS system forms one of the largest and most active distributed databases on the planet.Without DNS, the Internet would shut down very quickly.

The Basics

When you use the Web or send an e-mail message, you use a domain name to do it. Forexample, the URL "http://www.crispindia.com" contains the domain name crispindia.com. So

does the e-mail address "devesh@crispindia.com."

Human-readable names like "crispindia.com" are easy for people to remember, but they don't do

machines any good. All of the machines use names called IP addresses to refer to one another.

For example, the machine that humans refer to as "www.crispindia.com" has the IP address

64.14.119.232. Every time you use a domain name, you use the Internet's domain name servers

(DNS) to translate the human-readable domain name into the machine-readable IP address.

During a day of browsing and e-mailing, you might access the domain name servers hundreds oftimes!

Domain name servers translate domain names to IP addresses. That sounds like a simple task,and it would be -- except for five things:

There are billions of IP addresses currently in use, and most machines have a human-readable name as well.

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There are many billions of DNS requests made every day. A single person can easily

make a hundred or more DNS requests a day, and there are hundreds of millions of

people and machines using the Internet daily.

Domain names and IP addresses change daily.

New domain names get created daily.

DNS Troubleshooting

Some common issues that you may encounter with Active Directory installation andconfiguration can cause a partial or complete loss of functionality in Active Directory.

These issues may include, but not be limited to:

Domain Name System (DNS) configuration errors.

Network configuration problemsDifficulties when you upgrade from Microsoft Windows NT.

You must configure DNS correctly to ensure that Active Directory will function properly.

Review the following configuration items to ensure that DNS is healthy and that the

Active Directory DNS entries will be registered correctly:

DNS IP configuration

Active Directory DNS registration

Dynamic zone updates

DNS forwarders

DNS IP Configuration

An Active Directory server that is hosting DNS must have its TCP/IP settings configuredproperly. TCP/IP on an Active Directory DNS server must be configured to point to itself

to allow the server to register with its own DNS server.

To view the current IP configuration

Open a command window and type

ipconfig /all

to display the details. You can modify the DNS configuration by following these steps:

1. Right-click My Network Places, and then click Properties.

2. Right-click Local Area Connection, and then click Properties.3. Click Internet Protocol (TCP/IP), and then click Properties.

4. Click Advanced, and then click the DNS tab. Configure the DNS information as

follows: Configure the DNS server addresses to point to the DNS server. This should bethe computer's own IP address if it is the first server or if no dedicated DNS server will be

configured.

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5. If the resolution of unqualified names setting is set to Append these DNS suffixes

(in order), the Active Directory DNS domain name should be listed first (at the top of the

list).

Remote Installation Services

What Is Remote Installation Services?

In this section

Remote Installation Services (RIS) is an automated installation technology that you can use to

create installation images of operating systems or of complete computer configurations,including desktop settings and applications. These installation images can then be made availableto users at client computers. RIS is typically used during large-scale deployments when it would

be too slow and costly to have administrators or end users interactively install the operating

system on individual computers.

Compared to a standard interactive installation, RIS decreases installation time, eliminates the

need to use CDs during installation, and minimizes end user and administrator interaction during

installations. To accomplish this, RIS relies on Pre-Boot eXecution Environment (PXE)

technology. PXE technology enables computers without an operating system to start up andconnect remotely over a TCP/IP network connection to a RIS server, which then installs an

operating system. The client computers must support remote booting with the PXE ROM, or theymust be started with a remote-startup floppy disk and have a network adapter that is supported bythat disk.

To perform a RIS installation, an administrator or end user typically boots a client computer

from a PXE-capable network adapter by pressing F12 early in the startup process. This instructs

the computer to acquire an IP address and connect to a RIS server. The client computer thendownloads a small version of the Windows Setup program from the RIS server. You can

configure a RIS installation so that the Windows Setup program interactively steps the

administrator or end user through a shortened setup process, or you can configure it so that theentire setup process is automated after the end user or administrator presses F12. Also, you can

configure a RIS installation so the installation is image-based or setup-based. By using image-

based installations, you can deploy applications with an operating system. By using setup-basedinstallations, you have more flexibility in terms of handling hardware differences among the

computers in your organization.

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Comparison of RIS and Interactive Installations

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FDDI

FDDI stands for Fiber Distributed Data Interface. The FDDI standard is ANSI X3T9.5 . The

FDDI topology is ring with two counter rotating rings for reliability with no hubs. Cable typeis fiber-optic. Connectors are specialized. The media access method is token passing. Multipletokens may be used by the system. The maximum length is 100 kilometers. The maximum

number of nodes on the network is 500. Speed is 100 Mbps. FDDI is normally used as a

backbone to link other networks. A typical FDDI network can include servers, concentrators,

and links to other networks. CDDI is a copper version of FDDI which uses category 5 cable.

Obviously the distance is more limited than FDDI.

Devices called concentrators provide functions similar to hubs. Most concentrators use dual

attachment station network cards but single attachment concentrators may be used to attach moreworkstations to the network.

FDDI token passing allows multiple frames to circulate around the ring at the same time. Priority

levels of a data frame and token can be set to allow servers to send more data frames. Time

sensitive data may also be given higher priority. The second ring in a FDDI network is a methodof adjusting when there are breaks in the cable. The primary ring is normally used, but if the

nearest downstream neighbor stops responding the data is sent on the secondary ring in attempt

to reach the computer. Therefore a break in the cable will result in the secondary ring beingused.There are two network cards which are:

1. Dual attachment stations (DAS) used for servers and concentrators are attached to both

rings.

2. Single Attachment stations (SAS) attached to one ring and used to attach workstations toconcentrators.

A router or switch can link an FDDI network to a local area network (LAN). Normally FDDI is

used to link LANs together since it covers long distances.

Characteristics Summary

Topology - Double ring.

Cable - Fiber.

Speed - 100Mbps.

Maximum segment length - 2000 meters.

Media access - Token passing.

Maximum nodes on the network - 500.

Troubleshooting

Plastic fiber is only useful to 50 meters. Multimode glass is good to 2 kilometers. A tool called

an Optical time domain reflectometer (OTDR) may be used to debug this network

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RAID(redundant array of independent disks)

RAID (redundant array of independent disks; originally redundant array of inexpensive disks) isa way of storing the same data in different places (thus, redundantly) on multiple hard disks. By

placing data on multiple disks, I/O (input/output) operations can overlap in a balanced way,

improving performance. Since multiple disks increases the mean time between failures (MTBF),storing data redundantly also increases fault tolerance.

A RAID appears to the operating system to be a single logical hard disk. RAID employs the

technique of disk striping, which involves partitioning each drive's storage space into units

ranging from a sector (512 bytes) up to several megabytes. The stripes of all the disks areinterleaved and addressed in order.

In a single-user system where large records, such as medical or other scientific images, are

stored, the stripes are typically set up to be small (perhaps 512 bytes) so that a single record

spans all disks and can be accessed quickly by reading all disks at the same time.

In a multi-user system, better performance requires establishing a stripe wide enough to hold the

typical or maximum size record. This allows overlapped disk I/O across drives.

There are at least nine types of RAID plus a non-redundant array (RAID-0):

RAID-0: This technique has striping but no redundancy of data. It offers the best

performance but no fault-tolerance. RAID-1: This type is also known as disk mirroringand consists of at least two drives that

duplicate the storage of data. There is no striping. Read performance is improved since

either disk can be read at the same time. Write performance is the same as for single diskstorage. RAID-1 provides the best performance and the best fault-tolerance in a multi-

user system.

RAID-2: This type uses striping across disks with some disks storing error checking andcorrecting (ECC) information. It has no advantage over RAID-3.

RAID-3: This type uses striping and dedicates one drive to storing parity information.

The embedded error checking (ECC) information is used to detect errors. Data recoveryis accomplished by calculating the exclusive OR (XOR) of the information recorded on

the other drives. Since an I/O operation addresses all drives at the same time, RAID-3

cannot overlap I/O. For this reason, RAID-3 is best for single-user systems with long

record applications. RAID-4: This type uses large stripes, which means you can read records from any single

drive. This allows you to take advantage of overlapped I/O for read operations. Since allwrite operations have to update the parity drive, no I/O overlapping is possible. RAID-4offers no advantage over RAID-5.

RAID-5: This type includes a rotating parity array, thus addressing the write limitation in

RAID-4. Thus, all read and write operations can be overlapped. RAID-5 stores parityinformation but not redundant data (but parity information can be used to reconstruct

data). RAID-5 requires at least three and usually five disks for the array. It's best for

multi-user systems in which performance is not critical or which do few write operations.

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