ICT How Internet Works

06/02/2003 ICT Center

How The Internet Works

ICT Center University of Nairobi


Key Objectives Gain a general understanding of the technical aspects of the InternetKnow how it works Get definitions of some of the primary termsKnow what you can do with itKnow what you can’t/shouldn’t do with it


OutlineWhat is the “Internet”?Internet Infrastructure & BandwidthInternet ProtocolsInternet Addressing, DNS and RoutingPutting it all togetherURL and Web SurfingInternet Administration Issues in Internet GrowthWhat it is good for/it isn’t good for


What is the “Internet”?“An enormous global network connecting millions of computers.”

Computers connected to the Internet can “talk” to each other and access vast information resources.


What is the “Internet”?Is based on technology from the 1970’sWas conceived through one of DARPA (Defense Advanced Research Projects Agency) projects -ARPANet Project motivated by: Cold War Need for network resilient to damage

Became “commercial” in the 1980’sNowadays it’s used to transport data in vast quantities; Quite resilient to failure


What makes up the Internet?

Technologies TCP/IP, FTP, HTTP, UDP etcHardware Computers Network cards/Modems Routers Telephony/Communications equipment


NetworksThere two types of networks: Local Area Network – A network usually within a

building, department, or campus Wide Area Network – A network linking several

distributed LANs

The Internet is a global connection of such networks – an “Inter-network”


The Internet - common terms


Internet InfrastructureUser PC - A Multi-Media PC equipped to send and receive all variety of digital data, including audio and video.


Internet Infrastructure:User’s Communication Equipment

These are the communication equipment attached at the User's PC to connect the PC to the InternetUser connection can probably be one these two types: A direct connection to the Internet, through a Local

Area Network (LAN), using a network card A dial-up connection, where a Modem is used to call a

network connected to Internet using a telephone wire

Network CardMode

m


Internet Infrastructure: Local Loop Carrier

LLC Connects the User location to the Internet Service Provider's Point of Presence . Include Telephone Communication lines, Satellites, Cable TV, or Wireless

POTS, Telephone and Leased Lines

Cable TV

Satellite Wireles

s


Internet Infrastructure: ISP POP

This is the edge of the Internet Service Provider's network. Connections from the user are accepted and authenticated here before access to the Internet is granted.

User

ISP

ISP Point of Presence


Internet Infrastructure: ISP Backbone

The ISP backbone interconnects the ISP's POPs, AND interconnects the ISP to Other ISP's and online content.

ISP #2

ISP #1

NetWork Access Point:Large capacity exchange point

Large capacity routers/Switches

Large capacity Circuits


Internet Infrastructure: Online Content

These are the host sites that provide information. Have servers that user interacts with.

These servers require fast interfaces and large/fast storage.


Internet: Origins of online content

The "real-world" sources for the online information include:

Legacy Systems

BooksRecordings

Video/Movies

Scanners

Phone Financial Markets

Embedded Chips

Et cetera


Internet: BandwidthBandwidth is the maximum amount of data that can travel a communications path in a given time, usually measured in Bits Per Seconds. Measures the speed of your connection to the Internet – the higher the better. Think of the communications path as a pipe, then bandwidth represents the width of the pipe that determines how much data can flow through it all at once

Big Pipe High flow

Small Pipe Low flow


Internet ProtocolsProtocols are rules that govern the exchange of information between computer networks. Two basic Internet protocols are: Internet Protocol (IP) Transmission Control Protocol (TCP)

These two protocols are often referred to together as TCP/IP.TCP/IP is used by other Internet Protocols such as FTP, Telnet, HTTP, SMTP to communicate – it’s the lingua franca


Transmission Control Protocol (TCP)

This protocol provides a reliable flow of dataUsing this protocol transmission of Data though the net Operates as follows” Files and messages are divided into “packets” Each packet is stamped with source & destination

address Each packet is Routed or “switched” independently

through the Internet to destination (IP protocol) Destination sends acknowledge message on

receiving packets At destination packets are reassembled according to

original order


IP and Internet Addressing Internet Protocol (IP) controls how machines are addressed and how data is transferredEvery interface on an internet needs to have a unique address This is called an “Internet Address” or an “IP

Address”The standard way to show these is in “dotted-decimal” notation, which consist of four numbers separated by dots.Example:192.145.11.31


Internet AddressingAll the computers on the Internet have a unique IP address and are able to be accessed using itBut there is a limited number of “real” Internet addressesThere is NAT and Proxies which allow the “fan out” of addresses (Allow several PCs to share one “real” Internet IP)


DNS (Domain Name System)

Remembering 192.115.123.2 instead of www.uonbi.ac.ke is a little tricky for humansDNS is an application that maps a hostname to an IP addressAn application needs to convert the host name of a Server to an IP Address before it can communicate with the server

http://www.uonbi.ac.ke/



gov edu com int mil net org za au tz beke… …

.ac co org… …

The DNS Name Space is hierarchical

Generic Domains Country Domains

yahoo… cisco…

uonbi*. yahoo.com

*.uonbi.ac.ke

Unnamed root

google



So what actually happens when your application asks DNS for an IP address?

Local DNSServer

Your PC

What is the IPAddress forwww.yahoo.com?

ISP’s DNSServer

.COM DNSServer

Yahoos’DNS

Server

www.yahoo.com IP: 64.58.76.225


Routing – What is it?“The process of moving a packet of data from source to destination.”


Routing – What is it?Usually performed by a dedicated device called a “router”A key feature of the Internet because it enables messages to pass from one computer to another, possibly through many networks, and eventually reach the target machineConnecting networks allows for “internetworking” and this is how the word “Internet” came about


Routing – Why do it?Physical network distance limitations 10Base-2 Ethernet for instance has a

physical limit of 185 meters Physical network incompatibilitiesNetwork PerformanceSecurity Breaking a network in two, so machines

on one side cannot “see” what is happening on the other


Putting it all together PC

213.123.155.248

Router

213.123.155.254

www.yahoo.com64.58.76.225

Internet

213.120.62.254

Primary DNS 213.120.62.103

Secondary DNS 213.120.62.104

Router

.COM DNS 183.12.99.102

131.23.7.84

213.120.62.253

You type in http://www.yahoo.com inA web browser address lineand press [Enter] at the PC


Putting it all togetherPC

213.123.155.248

Router

213.123.155.254

www.yahoo.com 64.58.76.225

Internet

213.120.62.254

Primary DNS 213.120.62.103


Router

.COM DNS 183.12.99.102

131.23.7.84

213.120.62.253

The web browser asks Windows forthe address of www.yahoo.com…



213.123.155.248

Router

213.123.155.254


Internet

213.120.62.254

Primary DNS 213.120.62.103


Router

.COM DNS 183.12.99.102

131.23.7.84

213.120.62.253

Windows asks DNS to find theIP Address for www.yahoo.com



213.123.155.248

Router

213.123.155.254


Internet

213.120.62.254

Primary DNS 213.120.62.103


Router

.COM DNS 183.12.99.102

131.23.7.84

213.120.62.253

The DNS client on the PC knows that thePrimary DNS server is at IP Address213.120.62.103 and sends a request



213.123.155.248

Router

213.123.155.254


Internet

213.120.62.254

Primary DNS 213.120.62.103


Router

.COM DNS 183.12.99.102

131.23.7.84

213.120.62.253

The PC knows to send the packet to therouter at 213.123.155.254 by using the

“default gateway” setting.



213.123.155.248

Router

213.123.155.254


Internet

213.120.62.254

Primary DNS 213.120.62.103


Router

.COM DNS 183.12.99.102

131.23.7.84

213.120.62.253

This router knows that 213.120.62.103 ison its second network card’s network and

pushes the packet out that connection



213.123.155.248

Router

213.123.155.254


Internet

213.120.62.254

Primary DNS 213.120.62.103


Router

.COM DNS 183.12.99.102

131.23.7.84

213.120.62.253

The Primary DNS server is working andhas www.yahoo.com’s address in

its cache, so it sends it back



213.123.155.248

Router

213.123.155.254


Internet

213.120.62.254

Primary DNS 213.120.62.103


Router

.COM DNS 183.12.99.102

131.23.7.84

213.120.62.253

The web browser now knows to connectthe machine at 64.58.76.225



213.123.155.248

Router

213.123.155.254


Internet

213.120.62.254

Primary DNS 213.120.62.103


Router

.COM DNS 183.12.99.102

131.23.7.84

213.120.62.253

The packet, containing the HTTP requestinformation, is sent out to the Internet

via the 2 routers



213.123.155.248

Router

213.123.155.254


Internet

213.120.62.254

Primary DNS 213.120.62.103


Router

.COM DNS 183.12.99.102

131.23.7.84

213.120.62.253

The packet traverses the Internet and“magically” appears at the server

www.yahoo.com



213.123.155.248

Router

213.123.155.254


Internet

213.120.62.254

Primary DNS 213.120.62.103


Router

.COM DNS 183.12.99.102

131.23.7.84

213.120.62.253

The packet is processed and the twomachines have a conversation, resulting

in a web page appearing on the PC!


Other Internet ProtocolsCommon Internet Protocols HTTP: HyperText Transfer Protocol FTP : File Transfer Protocol POP3 : Post Office Protocol SMTP : Simple Mail Transport Protocol Telnet : Terminal Emulation for

NetworksAll defined by RFC’s (Request for Comment)


Hypertext Transfer Protocol “The HyperText Transfer Protocol is the de-facto standard for transferring World Wide Web documents, although it is designed to be extensible to almost any document format.”

Connected: An Internet Encyclopaedia

A web browser requests a web page from a web server using HTTP, the response may be an HTML document, it could also be an image, sound file or a PDF file


Uniform Resource Locator (URL)

Every resource on the World Wide Web has a unique address called a URL or Uniform Resource LocatorURLs that point to Web pages all begin with http:// because they are transmitted according to HTTP. URLs that reference FTP resources begin with ftp://.


Surfing: The Basic ProcessUser enters a URL (Universal Resource Locator) example: http://www.yahoo.com/Internet interprets the URL and “finds” the appropriate web server – DNS ResolutionWeb server delivers the file (HTML text with embedded objects)Browser interprets the HTML text and displays the information on your computer screen


Internet AdministrationInternet has decentralized, yet hierarchical administration

No president, CEO, BOD Instead: domain administrators

But some functions are centralized InterNIC assigns DNS names Internet Engineering Task Force (IETF)

Issues Requests for Comment (RFC) “The nice thing about standards is that there are

so many to choose from.”


Issues in Internet Growth

Bandwidth How much is needed? Affordable? The problem of the “last mile” How to address latency, etc?

Addresses DNS: how to resolve naming conflicts? Limited number of IP addresses, go to IPv6?

Security Viable for business? Viable for health care?


So – What is it good for?EmailWeb Browsing Research CollaborationCheap Communications VoIP (Voice over IP)Customer ServiceE-Commerce


So – What isn’t it good for?Applications relying on “Real-Time” information VoIP (Voice over IP)Applications needing huge bandwidth “Live” moviesGuaranteed connections/bandwidth Still better to use Leased LinesIPv6 is a possible panacea


Further Reading “Google” the net Search


Questions


Thank you for your

time.

ICT How Internet Works

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