Download Internet

Chapter 3
Internet
Physical Components of the
Internet
Servers
 Networks
 Routers

Server
Computer
 Answers requests for services.

– Mail servers
– Web servers
– List servers (discussed in Ch. 10)
– News servers (discussed in Ch. 10)
Network
A computer system that uses
communications equipment to connect
two or more computers and their
resources.
 Actual physical means for transporting
data (packets of information)

Network

Uses:
– 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 that directs data packets
along the network.

Local Area Network (LAN)

A network designed to share data and
resources among several computers,
usually personal computers in a limited
geographical 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
which other computers, and perhaps
terminals, are attached.
 A personal computer with file-transfer
software permits a user to download
data files from the host or upload data
files to the host.

Downloading a file means to
retrieve it from another
computer.
Uploading a file means to
send a file to another
computer.
Node

A device, usually a personal computer,
that is connected to a network.
Star network topology
Hub Computer
Ring network topology
Computers are
connected in a
circular fashion
Bus network topology
Network is preserved if one computer fails
Benefits of a Network
Used as a back up for files
 Resources, such as printers, can be
shared
 Promotes an ease of communication
through e-mail, transferring files and
videoconferencing

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 destination
but does not necessarily take the same
path.

Advantages of packets
Packets can be rerouted to a less
congested area of the network if a
particular area is congested.
 If the network experiences a failure,
packets can be rerouted.
 If a packet is corrupted, only the
corrupted 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

TCP / IP
Software managing the transmission of
the individual packets.
 TCP / IP - Transmission Control
Protocol / Internet Protocol
 Consists of many (approx. 100)
different protocols
 Communication between networks is
based 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.
Connecting to the Internet

User connects to the ISP (Internet Service
Provider) using either a modem or an ISDN
(Integrated Services Digital Network)
– Replaces a modem with a special adaptor.

ISP connects to the NSP (Network Service
Provider) networks through leased lines
through the local phone company.
 TCP/IP then divides the message into
packets and sends them over the lines.
Connecting to the Internet
(continued)

The router directs the packets to their
destination.
 The packets are reassembled at their
destination-computer which then responds to
any request.
 A message is sent from the destination
computer to the sending computer in order to
request that any missing or corrupt packets
be resent.
Internet
Network of networks
 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)

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 0
11111111 = 28 - 1 = 255
00000000 = 0
IP Address (continued)
Consists of a network component and a
host component.
 Ex. 102.150.8.68
 01100110 = 102
 10010110 = 150
 00001000 = 8
 01000100 = 68

Review

URL entered
– http://publications.UNL.edu/faculty/index.ht
m

Browser queries the DNS for the IP
Address
– Domain Name System

IP address returned
– 123.66.102.77
TCP connection is established with
123.66.102.77
 Browser then asks for the “what” part of
the URL

– index.htm

The server, publications.UNL.edu,
sends back the file index.htm.
TCP connection is then closed
 Browser renders the text portion of the
HTML code contained in index.htm
 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”.