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comptia® network+ certification prep: Lesson 1

comptia® network+ certification prep: Lesson 1 (printer-friendly version)
Your Instructor: Scott Jernigan

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Chapter 1

Introduction

Are you ready to take the plunge into the wild, woolly, and well-paid world of network technicians? Do you already work in the field, but need some credentials to prove your skill levels to potential employers? If so, this is the course?and the certification?for you.

CompTIA Network+ provides a vendor-neutral certification for network technicians. Okay, so what does that mean?

Getting CompTIA Network+ certified shows that you have knowledge in the Information Technology, or IT, industry equivalent to the skills of techs with nine months of experience in the field. CompTIA Network+ certified technicians also know their way around TCP/IP, the protocol of the Internet. CompTIA Network+ certification is one of the hottest certifications in the industry, and this course focuses on getting you CompTIA Network+ certified.

The Joys of IT Certification

Why do you need certification in the first place? Traditionally, people gain the skills for their chosen professions either by going to school or through on-the-job training. The IT industry uses both of these methods, but doesn't give employers the one thing they need: a person who can walk up to a new position and hit the ground running.

Schools provide the necessary basic, conceptual training and on-the-job training gives good practical experience, but how can an employer know that a candidate can do a certain job? How can the candidate show the employer in no uncertain terms that he or she can do the job?

The IT industry has long appreciated this problem. The best way to prove a particular skill is to pass a test that directly challenges those skills. If you pass the exam, you are then certified on that particular IT skill.

Certifications first came to prominence in the 1980s when Novell created the Certified Novell Engineer, or CNE, certification for Novell NetWare. Following Novell's lead, Microsoft created the Microsoft Certified Systems Engineer, or MCSE, for Microsoft NT. Today, almost every software package and PC manufacturer sponsors some type of certification for its hardware or software products.

These kinds of certifications are vendor-specific. They definitely prove the skills for their respective products and are highly sought-after. If you decide to work on a specific type of hardware or software, you will find employers' doors opened with one or more of these certifications.

These vendor-specific certifications, however, do not address one very important group of people: the technicians whose skills are not specific to any one hardware type or software package. These folks?the general practitioners, if you will?form the cornerstone of the IT industry.

These are people who carry screwdrivers and bootable disks in their pockets. They understand how to format hard drives. General practitioners know how to set up a system to link into a Windows network. They know how to set the TCP/IP information to access the Internet. They are, in a nutshell, Computer People?and CompTIA Network+ is one of the foundations of their credentials.

The CompTIA Network+ Exam

CompTIA Network+ is a computer-based exam composed of 100 multiple-choice questions. On a scale of 100 to 900, you need to score 720 or better to pass. You don't have to complete specific coursework for CompTIA Network+. (Once you become CompTIA Network+ certified, you have that title for life, but you will need to retest every three years to be able to demonstrate current certification status to employers.) 

CompTIA Network+ rides on the coattails of the success of the A+ Certification program and has strong support from the networking industry, as well as the IT industry as a whole. Some of the major players who helped in the development of CompTIA Network+ include 3Com Corporation, Apple, IBM, Lotus, Microsoft, Cisco, and Novell.

The demand for this certification, combined with the strong support of CompTIA, ensures that CompTIA Network+ will remain an important first certification for those pursuing a career in the networking field. Does CompTIA Network+ guarantee a job? Of course not! But it does provide a recognized certification that will catch the eye of an employer.

How to Become CompTIA Network+ Certified

The logistics of CompTIA Network+ certification are simple. When you take the test and achieve a passing score, you become CompTIA Network+ certified. There are no required courses, no CompTIA Authorized Training Centers?although CompTIA requires a technical review before any training materials can display the CompTIA Network+ logo?and no required networking experience.

CompTIA does recommend that you have nine months of networking experience?as that's what the test is geared to?and that you pass the A+ exams first.

2009 Objectives in Brief

Domain 1.0, Network Technologies: 20%
Domain 2.0, Network Media and Topologies: 20%
Domain 3.0, Network Devices: 17%
Domain 4.0, Network Management: 20%
Domain 5.0, Network Tools: 12%
Domain 6.0, Network Security: 11%

More CompTIA Network+ Information

To find out more about the CompTIA Network+ exam, you can access CompTIA's web site at www.comptia.org, or send e-mail to questions@comptia.org.
Prometric and Pearson VUE both administer the CompTIA Network+ exam.

To register for the exam, call Prometric at 800-977-3926, or Pearson VUE at 877-551-7587. You can also register online; go to www.2test.com for Prometric, or www.vue.com/comptia for Pearson VUE.





Chapter 2

Overview of Network Hardware and Software

Networking is a huge topic, so let's start at the beginning, shall we?

First of all, why do we build networks? What benefits do they provide? The simple answer is access to resources. A resource is anything that exists on another computer that a person wants to use without getting up and going to that computer. The most common network resources are files and printers.

Network designers and administrators strive to create an ideal world, where users?the people who actually sit at computers and try to get real work done?can access any information or device without getting up from their terminals.

Need to print to the printer on the other side of the hallway? No problem! Just click the Print button and it will be there. Need to look up information in a company database stored on a machine sitting in the basement of your building? No problem! Just double-click the shortcut on your desktop, and the database magically opens. In the ideal networked environment, users rise from their chairs for only two reasons: to get coffee and to answer the call of nature.

Your job as a network tech is to bring the networks you build, support, and maintain as close to that ideal as possible. Using a variety of tools with arcane names such as Ethernet, Token Ring, routers, and 10baseT, techs strive to build networks where end users can concentrate on doing whatever it is they do best.

Let Bob the accountant be the best accountant he can be! In a perfect world, the network would function so smoothly that Bob wouldn't even notice it was there. Fortunately for us network techs, this utopia does not exist; if it did, we'd all be unemployed!

As you delve into the details of computer networking, keep that goal in mind: enabling users to access resources and get work done. Of course, you have to build the network first. To accomplish this goal, you must first know what goes into building one.

What hardware do networks use?

The most obvious example of network hardware is a PC. But networks can include a lot more than just the typical Windows XP or Windows Vista PC that you find on many desks. Your network may include other operating systems, such as Linux, UNIX, Novell NetWare, or Macintosh OS X. Networks can also include different kinds of computers, like mainframe computers. And then there are all the cables, connectors, NIC cards, and other equipment.

A typical pile of network hardware
A typical pile of network hardware

Clients and servers

Networks have two categories of computers: clients?those that access and make use of shared network resources, and servers?those that provide, manage, and host the shared resources.

Client/Server Networks

Clients access resources on a server on the network
Clients access resources on a server on the network

Most medium-sized and large business networks use dedicated servers, a model of networking referred to as a client/server network or server-based network, as shown in the figure above. The server has a specific role to play and stays tucked away safely, maybe in a computer room, and left alone to get on with its job?you won't find someone sitting at the server running Microsoft Word or Call of Duty.

The only time anyone touches the server keyboard will be when an authorized person performs some administrative task, such as updating software or performing a backup. The key benefits of the client/server network model are security, performance, and centralized administration.

Using dedicated servers also provides centralized management, reducing the costs associated with the day-to-day operation of the network. Instead of roving across the building backing up every end-user system, the network tech can simply back up the server.

Peer-to-Peer Networks

Okay, so you have a PC on your desk; is it a client or a server? Ha, trick question!
You can't tell just by looking?it could be either or both! Although corporate networks typically employ dedicated servers, modern operating systems?Windows XP/Vista, Linux?enable any client system to act as a server. In a peer-to-peer network, the distinction between clients and servers becomes fuzzy because every machine on a network can be both a client and a server at the same time. So we say that they are all peers because they are all equal and you don't need a dedicated server.

A peer-to-peer network
A peer-to-peer network

Peer-to-peer networking, seen in the figure above, is ideal for small offices or groups of people who need to share a printer or two or transfer an occasional file. But it offers no centralized administration like what appears in a client/server environment. Also, computer shutdowns easily disrupt a peer-to-peer network.

Although still useful concepts, the terms client/server and peer-to-peer cannot fully capture current trends in network technology. Client/server and peer-to-peer are good terms to know for the CompTIA Network+ exam, but many real-life networks don't fit neatly into these categories.

Now how do we link it all together?

The network will need to transfer data from servers to clients. We need a way to connect our computers to the network. This section discusses the basic components required to network systems together. Later lessons will elaborate on this.

Network Wiring

The vast majority of networks you see will be in the form of copper cabling.

Network cables
Network cables

You can use a number of network wiring types, each with its own characteristics, speed, length limitations, and restrictions.

Networks can also use other forms of "wiring" such as optical fiber, infrared, and wireless. Clearly, some of these wiring types don't use wire at all, so if we want to be more precise we use the term network media to encompass all varieties. You'll learn more details about specific media standards in Lesson 2.

Network Interface Cards or NICs

A typical network interface card
A typical network interface card

An NIC is the network interface between your computer system and the network media. Physically, this interface may manifest itself as an expansion card, an integrated part of the PC motherboard, a USB device, or a PC card. Every client and server must have at least one NIC, and the NIC must be compatible with your computer hardware, the network media, and the way in which the network passes information. If it isn't, your PC isn't going to do much networking!

Network Equipment

The NICs of each PC on the network will communicate with each other using whatever network technology you choose to employ. When designing a network, you must take into account a variety of factors, including cable lengths, capacity limits, cost, and reliability.

The equipment used to build this network infrastructure, the hardware and software on which your network relies, includes devices such as repeaters, hubs, switches, bridges, and routers.

As you'll see in Lesson 4 when we discuss these devices in more detail, you can have a lot of choices, but generally the needs of your network drive your choice of equipment.

A typical network switch is used to connect all the systems together
A typical network switch is used to connect all the systems together

Overview of Network Software

Once you select your hardware, you need software to tell that hardware what to do. I've already mentioned the mainstream, server-based networking products such as Microsoft Windows Server, Linux, and Novell NetWare, and I've told you about the peer-to-peer functionality built into most desktop operating systems.

NIC Driver

Nothing happens if you can't send and receive data through the network. The NIC itself can transmit and receive streams of 1's and 0's, but it's the NIC driver's job to pass information between the operating system and the NIC.

The NIC connects to the network media, and the server or client operating system probably comes supplied with suitable drivers. If it doesn't, just reach for the CD-ROM supplied with the NIC or perhaps visit the manufacturer's website to download a suitable driver. A visit to the website is generally a good idea in any case, just to make sure you are using the latest driver.

Protocol Driver

A protocol is a standardized way of performing a specific action, such as communicating across a network or exchanging information.

Once you have installed the correct NIC driver, you need to consider the language?or protocol?that the network will use to convey the data.

Over the years, various protocols have been developed, and you need to ensure that the client and server PCs, and yes, peer-to-peer systems, all speak the same language. To complicate matters, you may need to ensure that the systems support more than one protocol?this is true when you have a mix of systems services on the network, and no common protocol fits them all.

The main communication protocols used on networks in the last few years are NetBEUI, Internet Packet Exchange/Sequenced Packet Exchange or IPX/SPX, and Transmission Control Protocol/Internet Protocol or TCP/IP; however, TCP/IP has become the dominant protocol and is the focus for the CompTIA Network+ exam. You'll find much more information about these protocols in Lessons 5 and 6.

Client and Server Software

If you're installing one of the major network operating systems, or NOS, then a lot of the files copied from the installation CD or DVD represent parts of the core NOS?the server software. Remember that to be a peer-to-peer machine, a client PC also needs to act as a server, so Windows comes with a file and printer sharing service module. This module provides the capability to act as a file and print server, even though you are using a desktop operating system!

What is a Redirector?

Client software, also known as redirector or requestor software, is responsible for intercepting requests for remote resources and redirecting the requests to the proper system.

This means, for example, enabling a network storage location that is not on your PC to appear as a driver letter, say, "S:". You simply refer to a resource by the drive letter that's not alien to the operating system, and before the OS has a chance to realize that S: doesn't actually exist, the client software has already stepped in and redirected the request to the relevant network resource. In networking terms, we call this feature redirection, or sometimes requestor.

The redirector also allows a program to treat remote resources as though they were local, even without assigning a local drive letter or port. For example, in Windows XP you can save a file directly to a remote resource simply by navigating through the My Network Places option in the Save dialog box.

In either case, the redirector functions as an intermediary, allowing you to use a remote resource the same way you would use a local one.

If you look at what's been covered to this point, you'll notice that the focus has moved from the media to the network card, to protocols, to the client/server software, and then to the operating system and applications?a clear progression in layers of functionality.

Strangely enough, there is an industry standard way of describing how networks and their hardware and software function with reference to a model that has seven layers of generic functionality?the OSI seven-layer model, which I will discuss in a moment.





Chapter 3

Data Packets and the OSI seven-layer model

In this chapter, we will take a look at data packets and the wonderful OSI seven-layer model, which is a very important part of the CompTIA Network+ exam. The model also serves well as a troubleshooting tool.

Data Packets

The fundamentals of computing are all about data: moving data, storing data, processing data, transmitting data, and receiving data. Networks rely on data, too, so before we move on, we need to talk about the facts of data life.

Data travels through network media, but you need to understand how this is accomplished for various other networking principles to make sense. Here is a breakdown of how it works.

Data packet movement
Data packet movement

Networks carry data in packets, specifically-sized and ordered groupings of data. The data in our 20 MB database is really a series of binary 1's and 0's. If we just throw all that binary information onto the network, no other machine is going to know what it is, where it came from, or where it needs to go. We need order?we need packets!

A packet contains some or all of the data we want to send across our network. Because of the way that networks operate, they can carry data packets that are only between certain sizes, with typical packet sizes ranging from 1500 to 4000 bytes, according to the network technology used. Think of a packet as an envelope into which you can stuff only so much paper. One of the things that a standard such as Ethernet or Token Ring must specify is the form of the packet so that every device on a network understands how the data is packaged.

The packet is divided into three main parts:

?The header
?The data
?The trailer information

The packet header specifies information needed to describe the type of packet, where the packet came from, and where it is going. Although the structure of the packet is different for each network protocol, the following is a general list of the types of information that are found in the packet header:

?Packets need addresses. These tell the packet where to go. In fact, a data packet contains both the source address and the destination address so that the recipient knows where the packet came from or, in case there's a problem, how to contact the sender.

?How big is that packet? Every data packet includes a note of how much data it actually contains. Among other things, this aids in error checking because the recipient can determine whether the packet just received is complete.

?What protocol is this packet using? Every basic network packet includes a protocol ID field to help devices on the network determine how to decode and understand the contents of the packet. I'll talk about these protocols?NetBEUI, IPX/SPX, and TCP/IP¬?in detail in later lessons.

After the header is the data portion of the packet, which contains the application data, or information, that needs to be delivered. For example, this could be the contents of an e-mail or web page delivered to a system.

After the data portion of the packet is the trailer information, which contains the CRC checksum value.

What is a CRC?

Your data has a hard slog through all the media from your PC to the destination device, and it may encounter electrical interference, loose connectors, power glitches, and a host of other events. To help detect dodgy data packets, each packet includes a cyclic redundancy check, or CRC, value that is the result of a complex binary mathematical calculation on the data that is performed by both the sender and the recipient of the packet.

Sometimes the CRC in the sender's packet and the locally generated CRC the receiver calculates don't match. This happens due to altered or corrupted data during delivery, and the recipient must ask the sender to resend the package.

The structure of a data packet
The structure of a data packet

For the CompTIA Network+ exam, it is important to know that packet is the term used for data at layer 3 of the OSI model, while frame is the term used to describe the data at layer 2 of the OSI model. You will learn more about the OSI model in the next section.

The OSI Seven-Layer Model

This is the part of the CompTIA Network+ studies that strikes fear into many a network technician, but I'm pretty confident that when you finish this section, you'll wonder what all the fuss is about! Honest.

A standards organization called International Organization for Standardization, or ISO, developed the Open Systems Interconnect, or OSI, seven-layer model.

ISO created a framework into which the major network hardware and software components and protocols could be placed to give every item a common reference point?a means of relating the components and their functionality to each other and a way of standardizing some of the components and protocols.

The OSI seven-layer model is a theoretical representation of how a networked device functions and helps us understand the interrelationships among hardware, software, protocols, and applications. The model provides a critical common language that network hardware and software engineers can use to communicate and ensure that their equipment will function together. Many network technicians refer to network devices by their positions in the model; for example, a repeater, a device mentioned earlier, is a layer 1 or Physical layer device.

The CompTIA Network+ exam expects you to know the layers by name, especially layers 1 through 4, how they function in relation to each other, and what they represent.

The Layers and What They Represent

Let's run through the layers and an overview of their tasks and responsibilities. The figure below summarizes the layers and their functions. Remember to study this hard for the CompTIA Network+ exam!

The seven-layer OSI model
The seven-layer OSI model

Layer 1: Physical Layer

Layer 1 of the OSI model defines the network standards relating to the electrical signals that travel the network cables, the connectors, and the media types themselves. Layer 1 of the OSI also determines which way to place the data on the network media.

For the CompTIA Network+ exam, you need to have examples of components that run at each layer of the OSI. Examples of popular network components considered layer 1 components are hubs and repeaters.

Layer 2: Data Link Layer

Layer 2 defines the rules on how to gather and complete all the elements that make up a data frame, as well as how to put the whole thing together so that it's ready to pass on to a Physical layer device and on to the network.

The exact components of the data packet depend on the Data Link protocols used but typically include the data sent, an identifier for the sending machine, an identifier for the receiving machine, and an error-correction mechanism such as a CRC, which I explained earlier in this chapter.

The Data Link layer also determines which way to place data on the wire by using an access method. An example of a popular access method is Carrier Sense Multiple Access/Collision Detection, or CSMA/CD, which Ethernet networks use.

The Data Link layer is divided into two sublayers:

? Logical Link Control or LLC: The LLC is the component layer responsible for error-correction and flow-control functions.

? Media Access Control or MAC: The MAC is responsible for addressing network devices by using a physical address known as a MAC address that is burned into the ROM chip of each network card. This physical address belongs in the layer 2 header for the sending and receiving system.

For the CompTIA Network+ exam, know that layer 2 consists of two sublayers and is responsible for physical addressing. Any devices, such as switches or bridges, that work with a physical address run at this layer.

Layer 3: Network Layer

Layer 3 is responsible for routing functions and logical addressing. Layer 3 addresses identify not only a system, but also the network on which the system resides and the router using this information to determine how to send data to the destination network. An example of a layer 3 address is the IP address; routers use this address to determine to which network to send a packet.

Examples of layer 3 components are the IP protocol and a router. For the exam, know that we consider an IP address a layer 3 address, but a MAC address is a layer 2 address.

Layer 4: Transport Layer

Fragmentation refers to breaking up data into smaller chunks. If the data sent is bigger than the packet size allowed by the lower-level protocols, the Transport layer breaks the data into smaller, manageable chunks that will fit inside two or more packets.
The Transport layer is also responsible for confirming whether transmitted packets have reached their destination intact and retransmitting them if they haven't, i.e., error correction/management. For incoming packets, the Transport layer reassembles the fragmented data, i.e., performs defragmentation, ensuring that received packets have processed in the right order. The layer also manages the flow of data to make sure to send packets at a pace that's suitable for the receiving device and for general network conditions. Sending data too quickly is like speaking too fast?you may have to keep repeating yourself to get the message understood, which is actually counterproductive.

Examples of layer 4 components are TCP and User Data Protocol or UDP that are part of the TCP/IP protocol suite.

Layer 5: Session Layer

Layer 5 is responsible for the session setup. The Session layer also manages and terminates the data connections called sessions between networked devices. These sessions enable networked systems to exchange information.

Layer 6: Presentation Layer

Layer 6 is responsible for managing and translating the information into an understandable format. Examples of functions that may occur at this layer are encryption and data compression.

Layer 7: Application Layer

Layer 7 represents the network-related program code and functions, running on a computer system, which either initiates the request on the sending system or services the request on the receiving system.

Note that the Application layer does not refer to applications such as Microsoft Outlook or WS_FTP. Instead, it refers to the protocols on which those programs rely. For example, Post Office Protocol 3 or POP3 and Simple Mail Transfer Protocol or SMTP are important Application layer protocols, but many
different end-user applications use those protocols, such as Outlook, Eudora, and Mozilla Thunderbird.

Using the Seven-Layer Model

The seven-layer model is only a theoretical representation of how networks function. Although knowing it inside-out won't change your life, it should help you pass the CompTIA Network+ exam.

The conceptual use of the model assumes that an event on one computer system, for example, a user pressing ENTER on a login screen, creates some data that sets off a chain of events. The data runs down through the layers on the sending machine and then leaves the system, traveling across the network and then up through the layers on the receiving machine, until the data arrives intact at the Application layer and the receiving system processes it.

Later lessons point out where certain key protocols and hardware fit into the model, and this can be useful stuff to know for both the CompTIA Network+ exam and real life.





Chapter 4

Real-World Networking

Enough theory! Let's get back to the real world. You have a few more terms to absorb before you're ready to be let loose on the next lesson.

Network Size

You may have heard the terms LAN and WAN before, but did you know there's a whole bunch of other *AN abbreviations that also describe the general size of a network? This section lists the main ones in order of size, with the smallest first.

By the way, network technicians often refer to every network they mention as either a LAN or a WAN. In practice, this doesn't really matter unless you feel like correcting them just to see how they react.

?Local area network or LAN : A single network confined to one building or area of a building, possibly with links to other locations at the same site, but these will be very localized.

? Campus area network or CAN : A group of interconnected LANs within a small geographical area, such as a school campus, university, hospital, or military base.

?Metropolitan area network or MAN : A group of networks with a sociopolitical boundary, such as a network of district authority offices in a town or city. Sites on a MAN are usually interconnected using fiber-optic cable or some other high-speed digital circuit rather than standard phone lines, for example, and the MAN itself may carry voice as well as data traffic.

? Wide area network or WAN : Two or more interconnected networks spread over a large geographic area, even on different continents. The Internet is the largest WAN in existence.

?Global area network or GAN A single network with connection points spread around the world. Mostly large, corporate organizations use GANs, and they consist of a series of networked, orbiting satellites.

Note the subtle difference between a WAN and a GAN: The latter is a single network, not a number of interconnected networks.

Network Performance and Bandwidth

Many factors affect network performance, but here I want to talk about just the basic speed of a standard network, how network speed is measured, and some of the terms related to performance.

We measure network data speeds in megabits per second?sometimes abbreviated Mbps. That lowercase b is important, because an uppercase B would imply megabytes. For a standard corporate network, the speed at which data travels between networked systems will typically range between 10 and 1000 Mbps, depending on the network standard used.

So what is bandwidth?

Well, the data signal traveling through the network media, which is usually some form of copper wire, is an electrical signal that's changing voltage rapidly to represent a string of binary data. Bandwidth is any signal that changes in this cyclic way and has a frequency associated with it?measured in Hertz, Hz for short.

Your network media operates across a certain range of frequencies, or bandwidths, and if you try to push data through the network at a faster rate exceeding your bandwidth, you will quickly discover that the laws of physics are not negotiable!

The bandwidth of the network closely relates to its maximum theoretical speed. So network technicians will often say things like, "Our network has a bandwidth of 100 Mbps," when they really mean, "Our network has a top speed of 100 Mbps" or "The bandwidth of our network provides a throughput of 100Mbps."

For the purposes of the CompTIA Network+ exam, we consider all these variations to be correct and to mean the same thing. Keep in mind that the stated maximum speed is usually a theoretical maximum?the real-world speed is often quite a bit slower. How much slower? That will depend on the technology used and the details of a specific network implementation. In general, the only way to determine your effective bandwidth is to test the real network.




Chapter 5

Conclusion

Overview of Network Hardware

The most obvious pieces of network hardware are the computers on the network. Each computer belongs to client or server systems unless they are desktop systems that are sharing resources, in which case we refer to them as peer-to-peer systems. Corporate networks generally use dedicated servers because they offer higher performance, greater stability, and better security than peer-to-peer options.

Your network won't be complete without some media?such as copper wiring, fiber-optics, wireless, or infrared?to interconnect your systems, as well as a network interface card, or NIC, to connect your system to the media. Other devices on the network?such as repeaters, hubs, bridges, and routers?enable you to expand the system locally or to other sites.

Overview of Network Software

The major software components of a network are the network operating system or NOS, NIC drivers, protocol drivers, and client/server services. Most of the components needed to get a network up and running are supplied as standard with your NOS or as part of your client operating system like Windows XP/Vista/2008, Linux, and so on.

Data Packets

To send a piece of data across a network, you must place it in a standard, formatted structure known as a packet or frame. These packets also state the source and destination addresses of the data, the protocol used, and the amount of data sent. A cyclic redundancy check, or CRC value, in the packet enables the receiving device to check the packet for errors. If the packet looks faulty, the recipient asks to have it resent.

The OSI Seven-Layer Model

The OSI seven-layer model describes how data flows from one networked system to another?it's a theoretical model into which many of the standards, components, and functions of a network fit. The model promotes the use of recognized network standards and helps ensure compatibility between network hardware and software from different manufacturers.

Real-World Networking

Networks come in all shapes and sizes, and a number of de facto abbreviations describe different types of networks, from small LANs to worldwide GANs.

One of the key features of a network is its performance at the desktop, i.e., the speed the client machines can send and receive data, which we measure in megabits per second. Accessing data across a network is not necessarily that fast compared to accessing the same data from a local hard disk, but the benefits of sharing data and resources, such as printers, with a large number of clients far outweighs the speed.

The term bandwidth is often used interchangeably with speed, although they are not quite the same thing.



Supplementary Material


CompTIA
http://www.comptia.org
This is the official web site for CompTIA. It provides comprehensive information about the Network+ exam objectives, testing procedures, and news, plus links to information about Prometric and Vue testing centers.

Webopedia
http://www.webopedia.com
Webopedia is a great resource for definitions of technical terms, including a broad array of networking terms.

Wikipedia
http://en.wikipedia.org/wiki/OSI_model
The Wikipedia page on the OSI model has a brief history of the OSI model and a detailed description of each of the seven layers.




FAQs

Q: I'm not sure I understand completely the purpose of MAC addresses. Are they related in any way to IP addresses, and why are they necessary?

A: MAC addresses and IP addresses are not inherently related. The MAC address is set at the manufacturer, and is completely unique in the world, just as human DNA is unique. The MAC address is included in data packets, and provides a positive identification of the machine sending the information. The IP address only needs to be unique if it's going out into the wider world of the Internet; in closed networks, there's more flexibility. Remember, too, that a NIC can have its IP address changed any number of times during its lifetime, while the MAC address is permanent.

To understand the relationship between these two types of addresses, think of how names and Social Security Numbers are related in the United States. A person can legally change his or her name, but Social Security Numbers do not change. If Mary Smith changes her name to Mary Obsequious Popinjay, her number remains the same. There's only one name associated with the number at a time, so there's always a one-to-one relationship, but the number is permanent, while the name is changeable. If you were trying to hunt Mary down after she'd changed her name, you could find her using her Social Security Number.




Assignment

Understand the ISO model and be able to walk through and explain the seven OSI layers using your own examples.


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