Communications and NetworksChapter 8 in Discovering Computers Fundamentals

Quick Overview of Some of the Main Points

Communications Uses of Communications Communication Channel/Transmission Media Transmission Characteristics Different type of lines Communication Devices Networks

Uses of Communications

Communication (in computer terms) is the process by which one computer can transfer data/information to another computer.

Telecommunications or Data Communications

Read about the Uses of Computer Communications DCF p.297

Communication is a combination of software and hardware

Network

At work, you might have a printer connected to your computer. If you were in a network, you could allow your co-workers access to your printer. The printer is the resource that you are sharing.

A network is collection of computers and devices connected together via “some method” to allow users to share resources.

Those methods are discussed in this chapter.

Internet

The internet is the world’s largest network.

When you request to see a website, the web page (the electronic document) is being sent to your computer through the internet.

How is that information being sent? Via telephone lines? Via satellites?

More on Network

VERY important to read the Networks section on page 303

It explains the advantages of a network very well!!!!!!!!!!

Networks

Know the difference between– LAN – Peer-to-peer lan network– Client/Server network– WAN– Internet peer-to-peer network– MAN

Topologies

Ok, so you are going to have a network. How are you going to physically connect them?

Make sure and read book on topologies for more information, but here are the three major ways:

Topologies of networksSEE DIAGRAMS IN BOOK

The physical layout of the hardware– Bus: consists of a single central cable to

which all devices are connected to– Ring: cable to which devices are

connected to forms a closed ring– Star: all devices on the network are

connected to a central computer, thus forming a star

Protocols

Now that the computers are physically connected, you have to make sure that they all follow the same rules … or protocols.

A protocol is a set of rules and procedures for exchanging information among computers.

More on Protocols

This is a confusing topic because some computers use many different types of protocols

Think of rules. We don’t all follow one set of rules. We follow one set of rules for driving, and another set of rules at the workplace, etc…

Computers follow different rules depending on what they are trying to do and who they are trying to communicate with.

I have two computers at home connected together in a mini-network. They use a certain protocol in order to communicate with each other. However, when they communicate on the internet, they use another protocol.

TCP/IP

Information travels on the internet in packets. Each web page, for example is broken into many packets. Each packet has the destination address, and is labeled as 1 of 3, etc… The destination computer, when it receives the packets reassembles them and then displays the information. Both computers have to follow a certain rule/protocol in order for it to work. This protocol is TCP/IP.

TCP/IP is a widely used protocol on the internet. It defines how to break the message into packets, how to reassemble the message, what to do if some of the packets get lost, etc…

A router is a device that routes these packets through the network.

Token Ring and Ethernet

These are two other protocols discussed in the book. These protocols determine how computers have access to a LAN (local area network).

For example, on a network, a computer/device cannot just send information at any given time. They basically have to take turns. There are rules that govern this and they all have to follow the same rules.

If every computer on a network sends out its information at the same time, you would probably have too many collisions and the information basically gets lost. The computers then have to resend the information.

More on Token Ring

Token Ring is a protocol that is normally used in a ring topology or star topology.

If you set up your computers in a ring, this is probably the protocol you would use.

This protocol requires that a special signal or token is passed from one device to another. The device that has the token can transmit on the network. There are few collisions since they each take turns.

More on Ethernet

Ethernet is a protocol that is normally used in a bus topology or star topology.

This protocol requires that the computers “peak” onto the network and if it senses that there is information being sent by someone else, it waits.

More on protocols

Understand that there are many protocols out there, depending on what you are trying to do.

HTTP is the protocol used for transferring web pages SMTP is a protocol used for delivering email messages Ethernet/Token Ring are protocols used to determine

when a computer has access to the network Once we figure out when the computers are going to have

access to the network, we can use TCP/IP protocol to manage the transmission of how that data gets sent from one computer to the other.

Your computer can follow TCP/IP AND ETHERNET protocols … they are for two different purposes.

Firewall

Understand what a firewall is!!!!!!!! A firewall prevents outsiders into a

network. If you use DSL or Cable Modems, you

should have a firewall program installed on your computer also … to prevent people on the internet from accessing your computer!!!

Internet vs. Intranet

This is the book!!!!!!!!!!! An Intranet looks similar to what you

see on the internet but it is limited to one particular location (a company).

A company’s intranet is a set of web pages only accessible within the company!!!!!!!!

Dial-Up Lines vs. Dedicated Lines

Dial-Up lines– Telephone lines– Only has a connection while call is in use

Dedicated lines– Always a connection (24 hours a day)– Sometimes companies don’t want to buy their own lines,

so they LEASE them.– Can use telephone lines or can use other lines (like

cable lines)– Cable Modem and DSL are dedicated– When you have dedicated lines you should think of

getting a firewall (more info in book)

Communication Devices

Types of hardware/equipment that transmits data/information onto the transmission media.

You might have the phone line plugged into your computer, but you need something to send the data out on the phone line: modem – Modem - converts the computer digital signal to an

analog signal so it can travel over the phone lines. Generally they transmit data between 28.8 Kbps and 56 Kbps

– Cable Modem - sends computer signal over cable lines. They generally transmit data between 500 Kbps and 2Mbps (2Mbps is approx. 2000Kbps).

Transfer Rates

Whenever we are referring to the speed at which a line carries data (i.e., how fast can we send info on the internet from our computer at home) … we are referring to transfer rate.

Transfer rate always uses the bps unit (bits per second). Generally we refer to it as Kbps (kilobits per second).

More on Transfer Rates

FYI: you don’t need to know how to do this, but say you have a 56 Kbps internet connection, how long does it take to download a 1MB file??

Well, 1 megabyte = approx. 1 million bytes 1 million bytes = 8 million bits 56Kbps = approx. 56000 bits per second 8,000,000/56000 = approx. 153 seconds 153 seconds = approx 2.4 minutes!

More on The Telephone Network

Dial-Up lines– Uses standard telephone lines– Remember, telephone lines require

information in analog frequencies– Modem translates digital (computer signal)

on phone line into analog frequency so that it can be sent on phone line

Even More on The Telephone Network

DSL– Uses standard telephone lines– However, it uses a different sending device (instead of a

regular modem it uses a DSL modem).– The DSL modem sends out the information digitally. Special

technique which allows us to use regular phone lines, in a digital way, which allows the information to be sent faster.

– ADSL is slower than SDSL. ISDN

– Read about it in book!!!!!!!!!!! Uses telephone lines, and also sends out info digitally. Uses and ISDN modem. This technique is older and not as fast as DSL!

And Yet Even More on The Telephone Network

Cable Lines– Does not use telephone lines– Uses cable lines– Comparable to DSL, though some say it’s faster

Read about T-carrier and ATM lines Read about modems on page 9.28-

9.29!!!!!!!!!!

Connecting Networks

The internet consists of many small networks connected together.

A hub is a device that provides a central point for cables in a network, see figure on 9.30.

A router (as stated earlier) is a device that receives packets on a network and routes them to their destination!

Communication Channel

A communication channel is the path that information takes when it is transferred from one computer to another.

For example, if you were going from Houston to Hawaii, your channel would be ALL the different ways/roads you used to get there (road to get to highway, highway to get to airport, air to get to Hawaii, road to get to hotel).

Internet Communication Channel

If you were requesting information from the www.whitehouse.gov website, that information might have to go through telephone lines, then fiber optic cables, then satellites, then back through phone lines, in order to get to your house. That is the communications channel your information traveled on.

Transmission Media

BANDWIDTH is the width of the communication channel. The higher the bandwidth, the more data and information the channel can transmit.

What can we use that will carry that information/signal from one computer to another? Cables? Satellites? What?

Transmission media consists of the materials or techniques capable of carrying a signal.

PHYSICAL TRANSMISSION MEDIA

Physical cables:– Twisted-Pair Cable (phone cables)– Coaxial Cable (cable companies use this)– Fiber-Optic Cable (Much of the internet backbone uses

this) Most companies use Twisted-Pair cables in their

buildings. Cheap, and easy to install. Most of the internet backbones use Fiber-Optic

cable. Not much noise (interference), fast, but expensive and hard to install.

Coaxial cable is in the middle.

WIRELESS TRANSMISSION MEDIA

Broadcast Radio Cellular Radio Microwaves

– Expensive to install, and not as fast as some of the other physical media, but useful when it’s too difficult to install cables

– Must have line-of-sight (read book for more info)

Satellites (Very expensive)

Recap on Transmission Media So, back to our example. If you are trying to view the www.whitehouse.gov website, the web page information must be sent through the internet to your computer.

What path (communication channel) does it take (i.e., what transmission media does it go through)?

The information probably travels on twisted pair cable out of the whitehouse.gov computer, then onto some fiber optic cable, maybe bounces off a couple of microwaves, maybe back to fiber optic cable, then back onto twisted pair cable and into your home.

Summary There are many parts to a network:

– Transmission media – physical vs. wireless• The cables or satellites that information travels through

– Communications devices – equipment that send out the info on the transmission media

– Two different networks can use the same transmission media (twisted pair cable), but depending on the communications device, software, techniques, the information can travel faster on one network than the other.

– Topologies – how do we physically connect the computers.– Protocols – rules that the computers must all follow in order

to send the information. TCP/IP is a protocol.

The End