Mang may tinh 1

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<b>Ch.2 – Networking Fundamentals</b>

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<b>Overview</b>

Students completing this module should be able to:

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Explain the importance of bandwidth in networking.

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Use an analogy from their experience to explain bandwidth.

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Identify bps, kbps, Mbps, and Gbps as units of bandwidth.

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Explain the difference between bandwidth and throughput.

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Calculate data transfer rates.

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Explain why layered models are used to describe data communication.

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Explain the development of the Open System Interconnection model (OSI).

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List the advantages of a layered approach.

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Identify each of the seven layers of the OSI model.

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Identify the four layers of the TCP/IP model.

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Describe the similarities and differences between the two models.

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Briefly outline the history of networking.

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Identify devices used in networking.

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Understand the role of protocols in networking.

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Define LAN, WAN, MAN, and SAN.

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Explain VPNs and their advantages.

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<b>Data networks</b>

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One early solution was the creation of local-area network (LAN) standards.

Because LAN standards provided an open set of guidelines for creating

network hardware and software, the equipment from different companies

could then become compatible.

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This allowed for stability in LAN implementation.

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In a LAN system, each department of the company is a kind of electronic

island.

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<b>Data networks</b>

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What was needed was a way for information to move

efficiently and quickly, not only within a company, but also

from one business to another.

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<b>Network topology</b>

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Network topology defines the structure of the network.

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Physical topology, which is the actual layout of the wire or media.

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Logical topology, which defines how the media is accessed by the hosts for

sending data.

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The logical topology of a network is how the hosts communicate across the

medium.

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<b>Bus Topology</b>

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<b>Ring Topology</b>

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<b>Token Ring</b>

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<b>Star Topology</b>

“A star topology connects all cables to a central point of

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<b>Extended Star Topology</b>

“An extended star topology uses the star topology to be created. It links

individual stars together by linking the hubs/switches. This, as you will

learn later in the chapter, will extend the length and size of the

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<b>Hierarchical Topology</b>

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<b>Hierarchical Topology</b>

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<b>Mesh Topology</b>

“A mesh topology is used when there can be absolutely no break in

communications, for example the control systems of a nuclear power

plant. So as you can see in the graphic, each host has its own

connections to all other hosts. This also reflects the design of the

Internet, which has multiple paths to any one location.”

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<b>Network protocols</b>

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Protocol suites are collections of protocols that enable network

communication from one host through the network to another host.

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A protocol is a formal description of a set of rules and conventions that

govern a particular aspect of how devices on a network communicate.

Protocols determine the format, timing, sequencing, and error control

in data communication.

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<b>Network protocols</b>

Protocols control all aspects of data communication, which include the

following:

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How the physical network is built

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How computers connect to the network

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How the data is formatted for transmission

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How that data is sent

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How to deal with errors

Examples

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Institute of Electrical and Electronic Engineers (IEEE),

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American National Standards Institute (ANSI),

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Telecommunications Industry Association (TIA),

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Electronic Industries Alliance (EIA)

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International Telecommunications Union (ITU), formerly known as the

Comité Consultatif International Téléphonique et Télégraphique

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<b>Local-area networks (LANs)</b>

Some common LAN technologies are:

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Ethernet

•

Token Ring

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<b>Wide-area networks (WANs)</b>

Some common WAN technologies are:

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Modems

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Integrated Services Digital Network (ISDN)

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Digital Subscriber Line (DSL)

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Frame Relay

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US (T) and Europe (E) Carrier Series – T1, E1, T3, E3

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<b>Metropolitan-area networks (MANs)</b>

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A MAN is a network that spans a metropolitan area such as a city or

suburban area.

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A MAN usually consists of two or more LANs in a common geographic

area.

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<b>Storage-area networks (SANs)</b>

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A SAN is a dedicated, high-performance network used to move data between

servers and storage resources.

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SANs offer the following features:

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<b>Performance</b>

– SANs enable concurrent access of disk or tape arrays by two

or more servers at high speeds, providing enhanced system performance.

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<b>Availability</b>

– SANs have disaster tolerance built in, because data can be

mirrored using a SAN up to 10 kilometers (km) or 6.2 miles away.

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<b>Virtual private network (VPN)</b>

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VPN is a private network that is constructed within a public network

infrastructure such as the global Internet.

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Using VPN, a telecommuter can access the network of the company

headquarters through the Internet by building a secure tunnel between the

telecommuter’s PC and a VPN router in the headquarters.

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<b>Benefits of VPNs</b>

The following are the three main types of VPNs:

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<b>Access VPNs </b>– Access VPNs provide remote access to a mobile worker and small
office/home office (SOHO) to the headquarters of the Intranet or Extranet over a shared
infrastructure.

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<b>Intranet VPNs</b> – Intranet VPNs link regional and remote offices to the headquarters of
the internal network over a shared infrastructure using dedicated connections. Allow
access only to the employees of the enterprise.

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<b>Extranet VPNs</b> – Extranet VPNs link business partners to the headquarters of the

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<b>Intranets and extranets</b>

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<b>Intranets</b> are designed to permit access by users who have access privileges to the
internal LAN of the organization.

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Within an Intranet, Web servers are installed in the network.

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Browser technology is used as the common front end to access information such as
financial data or graphical, text-based data stored on those servers.

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<b>Extranets</b> refer to applications and services that are Intranet based, and use extended,
secure access to external users or enterprises.

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<b>Importance of bandwidth</b>

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Bandwidth is defined as the amount of information that can flow

through a network connection in a given period of time.

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<b>Measurement</b>

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In digital systems, the basic unit of bandwidth is bits per

second (bps).

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Bandwidth is the measure of how much information, or bits,

can flow from one place to another in a given amount of

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<b>Limitations</b>

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Bandwidth varies depending upon the type of media as well as the LAN and WAN

technologies used.

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The physics of the media account for some of the difference.

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Signals travel through twisted-pair copper wire, coaxial cable, optical fiber, and

air.

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<b>Throughput</b>

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Throughput refers to actual measured bandwidth, at a specific time of day, using

specific Internet routes, and while a specific set of data is transmitted on the network.

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Throughput is often far less than the maximum possible digital bandwidth of the
medium that is being used. Internetworking devices

The following are some of the factors that determine throughput:

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Type of data being transferred

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Network topology

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Number of users on the network

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User computer

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Server computer

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<b>Data transfer calculation</b>

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Using the formula transfer time = size of file / bandwidth (T=S/BW)

allows a network administrator to estimate several of the important

components of network performance.

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<b>Digital versus analog</b>

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Analog bandwidth is measured by how much of the electromagnetic spectrum is

occupied by each signal.

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The basic unit of analog bandwidth is hertz (Hz), or cycles per second.

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While analog signals are capable of carrying a variety of information, they have some
significant disadvantages in comparison to digital transmissions.

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The analog video signal that requires a wide frequency range for transmission cannot
be squeezed into a smaller band.

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Therefore, if the necessary analog bandwidth is not available, the signal cannot be
sent.

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In digital signaling all information is sent as bits, regardless of the kind of information it
is.

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<b>Other information</b>

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For most of this chapter we will rely on other sources.

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Comer does a good job in explaining “what happens” but

does not provide enough information to see “how it works.”

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<b>Digital and Analog Bandwidth</b>

<b>Bandwidth = The width or carrying capacity of a communications circuit.</b>

<b>Digital bandwidth = the number of bits per second (bps) the circuit can </b>

carry

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used in digital communications such as T-1 or DDS

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measure in bps

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T-1 -> 1.544 Mbps

<b>Analog bandwidth = the range of frequencies the circuit can carry</b>

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used in analog communications such as voice (telephones)

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measured in Hertz (Hz), cycles per second

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Digital and Analog Bandwidth

GOLDMAN: DATACOMM
FIG.02-14
<i><b>DTE</b></i> <i><b>DCE</b></i>
<i><b>DTE</b></i> <i><b>DCE</b></i>
<i><b>Modulation</b></i>
<i><b>Demodulation</b></i>
digital analog
digital analog
<i><b>PSTN </b></i>
Dial-up network
<i><b>PSTN </b></i>
Dial-up network

<b>Digital Signals</b>

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digital signal = a signal whose state consists of discrete elements such

as high or low, on or off

<b>Analog Signals</b>

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analog signal = a signal which is “analogous” to sound waves

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<b>Analog Signals, Modulation and Modem </b>

<b>Standards</b>

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A perfect or steady tone makes a wave with consistent height

(amplitude) and pitch (frequency) which looks like a

<i><b>sine wave.</b></i>

(Figure 4-15)

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A cycle or one complete cycle of the wave

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The frequency (the number of cycles) of the wave is measured in Hertz

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<b>Using layers to analyze problems in a flow </b>

<b>of materials </b>

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The concept of layers is used to describe communication from one computer to another.

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The OSI and TCP/IP models have layers that explain how data is communicated from
one computer to another.

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The models differ in the number and function of the layers.

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<b>Using layers to describe data </b>

<b>communication </b>

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In order for data packets to travel from a source to a

destination on a network, it is important that all the devices

on the network speak the same language or protocol.

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<b>OSI model</b>

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To address the problem of network incompatibility, the International

Organization for Standardization (ISO) researched networking models like

Digital Equipment Corporation net (DECnet), Systems Network Architecture

(SNA), and TCP/IP in order to find a generally applicable set of rules for all

networks.

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Using this research, the ISO created a network model that helps vendors

create networks that are compatible with other networks.

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The Open System Interconnection (OSI) reference model released in 1984 was

the descriptive network model that the ISO created.

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It provided vendors with a set of standards that ensured greater compatibility

and interoperability among various network technologies produced by

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<b>OSI layers</b>

• It breaks network communication into smaller, more manageable parts.

• It standardizes network components to allow multiple vendor development and
support.

• It allows different types of network hardware and software to communicate with
each other.

• It prevents changes in one layer from affecting other layers.

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<b>Peer-to-peer communications </b>

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In order for data to travel from the source to the destination, each layer of the

OSI model at the source must communicate with its peer layer at the

destination.

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This form of communication is referred to as peer-to-peer.

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During this process, the protocols of each layer exchange information, called

protocol data units (PDUs).

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<b>TCP/IP model</b>

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Unlike the proprietary networking technologies mentioned earlier,

TCP/IP was developed as an open standard.

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This meant that anyone was free to use TCP/IP. This helped speed up

the development of TCP/IP as a standard.

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Although some of the layers in the TCP/IP model have the same name

as layers in the OSI model, the layers of the two models do not

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<b>TCP/IP model</b>

Some of the common protocols specified by the TCP/IP reference model layers. Some of the
most commonly used application layer protocols include the following:

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File Transfer Protocol (FTP)

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Hypertext Transfer Protocol (HTTP)

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Simple Mail Transfer Protocol (SMTP)

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Domain Name System (DNS)

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Trivial File Transfer Protocol (TFTP)
The common transport layer

protocols include:

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Transport Control Protocol (TCP)

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User Datagram Protocol (UDP)
The primary protocol of the

Internet layer is:

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<b>TCP/IP model</b>

Networking professionals differ in their opinions on which model to use. Due to the

nature of the industry it is necessary to become familiar with both. Both the OSI

and TCP/IP models will be referred to throughout the curriculum. The focus will be

on the following:

•

TCP as an OSI Layer 4 protocol

•

IP as an OSI Layer 3 protocol

•

Ethernet as a Layer 2 and Layer 1 technology

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<b>Detailed encapsulation process </b>

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All communications on a network originate at a source, and are sent to

a destination.

•

The information sent on a network is referred to as data or data

packets. If one computer (host A) wants to send data to another

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<b>Detailed encapsulation process</b>

Networks must perform the following five conversion steps in order to

encapsulate data:

<b>1.</b>

<b>Build the data. </b>

<b>2.</b>

<b>Package the data for end-to-end transport.</b>

<b>3.</b>

<b>Add the network IP address to the header. </b>

<b>4.</b>

<b>Add the data link layer header and trailer.</b>

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<b>Application </b>

<b>Header + data</b>

Data Encapsulation Example

Let us focus on the Layer 2, Data Link, Ethernet Frame for

now.

010010100100100100111010010001101000…

<b>Application Layer</b>

<b>Layer 4: Transport Layer</b>

<b>Layer 3: Network Layer</b>

<b>Layer 2: </b>

<b>Network </b>

<b>Layer</b>

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