Chapter3 Internet

8/12/2019 Chapter3 Internet

http://slidepdf.com/reader/full/chapter3-internet 1/45

Chapter 3

Internet



Physical Components of the

Internet Servers

Networks

Routers



Server

Computer that answers requests for

services.



Network

A computer system that uses

communications equipment to connect

two or more computers and theirresources.

Actual physical means for transporting

data (packets of information)



Network

Some mediums for transferring data

are:

– Copper wires -- electrical impulses. or

– Fiber-optic cables - light waves. or

– Radio Waves or

– Microwaves or – Infrared light -- invisible light that carries a

message through air.



Router

Special-purpose

computer

Computer thatdirects data

packets along the

network to their

destination by wayof thousands of

pathways.



Router

Two purposes:

1.Ensures that information does not go

where it is not needed2.Ensure that information makes it to the

intended destination



Local Area Network (LAN)

A network designed to share data and

resources among several computers,

usually personal computers in a limitedgeographical area, such as an office or

a building. (compare to WAN)



Wide Area Network (WAN)

A network of geographically distant

computers and terminals. (compare to

LAN)



Host

The central computer in a network, to whichother computers, and perhaps terminals, areattached. – Terminal - consists of a keyboard, monitor and

little or no processing capability. Processing isdone by the host computer.

A personal computer with file-transfer

software permits a user to download datafiles from the host or upload data files to thehost.



Downloading a file means toretrieve it from another

computer.



Uploading a file means tosend a file to another

computer.



Node

A device, usually a personal computer,

that is connected to a network.



Star network topology

Hub

Network is preserved if one node fails.



Ring network topology

Computers are

connected in a

circular fashion

Network is not preserved if one node fails.



Bus network topology

Network is preserved if one node fails.



Star Bus topology



Benefits of a Network

Used as a back up for files

Resources, such as printers, can be

shared

Promotes an ease of communication.



Benefits of a Network

(continued)

It costs less to use several small

computers connected to a network than

to use a large computer.

And several small computers connected

to a network can offer more computing

power than just using a single large

computer.



Packet switching

Transmitted data is divided into small

packets of information.

Each packet has the same destinationbut does not necessarily take the same

path.



Advantages of packets

Packets can be rerouted to a less

congested area of the network of a

particular area is congested. If the network experiences a failure,

packets can be rerouted.

If a packet is corrupted, only thecorrupted packet needs to be resent.



What other information is

contained in a packet? Info about the computer that sent it

Info about the computer to which it is

being sent

A sequence number - indicates how the

packets fit in the overall message



TCP / IP

Software managing the transmission ofthe individual packets.

TCP / IP - Transmission Control Protocol / Internet Protocol

Consists of many (approx. 100)different protocols

Communication between networks isbased on the TCP/IP suite.



TCP

Places the data into packets and

reassembles the packets.



IP

Handles the addressing and sees to it

that packets are routed across multiple

computers.



Transferring Data TCP/IP divides the message into packets and

sends them over the lines. The router directs the packets to their

destination.

The packets are reassembled at their

destination-computer which then responds toany request.

A message is sent from the destinationcomputer to the sending computer in order to

request that any missing or corrupt packetsbe resent.



Internet

Network of networks (or global network)

Used to:

– View web pages (WWW) – Download files (ftp)

• Files located on a remote computer can be

downloaded.

– Communicate through e-mail



Internet (another definition)

Global information system linked

together by a unique address space

(DNS).



Domain Name System (DNS)

or (Domain Name Servers)

Used to assign names to host

computers.



Domain Name

Symbolic name used to identify each

computer on the Internet.



IP Address

Numeric name used to identify each

computer on the Internet.

Consists of 32 bits (4 bytes)



Largest 8 bit number is 255.

Smallest 8 bit number is 011111111 = 28 - 1 = 255

00000000 = 0





Requesting a web page.

A URL is entered

– http://publications.UNL.edu/faculty/index.htm

The browser queries the DNS for the IP

Address of “publications.UNL.edu”

An IP address is returned

– 123.66.102.77



A TCP connection is established with

123.66.102.77

The browser then requests the “what”

part of the URL

– index.htm

The server, publications.UNL.edu,sends back the file index.htm.



The TCP connection is then closed

The browser renders the text portion of

the HTML code contained in index.htm The steps are repeated in order to

retrieve any in-line images within

index.htm. – In-line image -- Image within a document.



Who can publish on the web?

Anyone



Some material is monitored for

accuracy. Electronic Journals

Commercial presentations

Reputable authors



Be a critical judge

Who wrote it?

Is the writing quality high?

Is the document up to date?

Are there obvious errors?



Note: Pg. 126

Communication Mechanisms LOL - laughing out loud

TY - thank you

RTFM - Read The Fine Manual• Not all substitute the word “fine” for the letter

“F”.



Review



What protocol does the Web run

on? HTTP





What does HTTP transfer?

Hypertext



URL stands for ?

Uniform Resource Locator

Documents

Chapter3 Internet