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.htm

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”.