Lecture 13Internet & Internet ServicesCSCS100 - Spring 2008 – Forman Christian CollegeAsher ImtiazWajeeha Akram

*Several of these slides have been adapted and modified from VU CS101 slides (Dr. Altaf A. Khan) and Peter Norton’s supplementary material.

Today’s Goal• Internet Architecture• Addressing scheme used on the Internet• To look at several services provided by

the Internet• Web• eMail• Instant messaging• VoIP

What Does the Internet Enable?• Enables users located at far-way locations

to easily share information with others located all over the world

• Enables users to easily and inexpensively communicate with others located all over the world

• Enables the users to operate and run programs on computers located all over the world

The Internet is unlike any previous human invention. It is a world-wide resource, accessible to all of the humankind.

“Cool” internet appliances

World’s smallest web serverhttp://www-ccs.cs.umass.edu/~shri/iPic.html

IP picture framehttp://www.ceiva.com/

Web-enabled toaster +weather forecaster

Internet phones

Internet Users Worldwide

673M in 2002

1B+ in 2005(48% wireless)

Key Characteristics (1)

Geographic Distribution

Global - reaches around the world

Robust Architecture

Adapts to damage and error

Speed

Data can travels at near ‘c’ on copper, fiber, airwaves

Key Characteristics (2)Universal Access

Same functionality to everyone

Growth RateThe fastest growing technology ever

Freedom of SpeechPromotes freedom of speech

The Digital AdvantageIs digital: can correct errors

Internet: Network of Networks

• A large number of networks, interconnected physically

• Capable of communicating and sharing data with each other

• From the user’s point view, Internet – a collection of interconnected networks – looks like a single, unified network

Internet ---- Web?

Internet ---- Intranet?

Internet Networking Protocols

Communications on the Internet is controlled by a set of two protocols: TCP and IP

TCP/IP (1)Transmission Control Protocol/Internet Protocol

• Networking protocol used by all computers and networks on the Internet

• Originally developed by the US DoD for Unix, but now available for most other OSes

TCP/IP (2)Transmission Control Protocol/Internet Protocol• TCP breaks down the message to be sent

over the Internet into packets

• IP routes these packets through the Internet to get them to their destination

• When the packets reach the destination computer, TCP reassembles them into the original message

Internet Addressing• Regular post cannot be delivered unless

we write a destination address on the envelope

• Same is true for the Internet

• Regular post can be delivered at the intended address even if the given address is not precise. That is not the case for Internet addressing

216.122.128.109

www.fccollege.edu.pk

IP addressDNS address

IP Address (1)

• A unique identifier for a computer on a TCP/IP network

• Format: four 8-bit numbers separated by periods. Each 8-bit number can be 0 to 255

• Example:• 216.122.128.109 (IP address of the FCC Web

server)

IP Address (2)

• Networks using TCP/IP route messages based on the IP address of the destination

• Any IP addresses (as long as they are unique) can be assigned within a PN

• However, connecting a PN to the Internet requires using unique, registered IP addresses

Domain Names• IP addresses are fine for computers, but

difficult to recognize and remember for humans

• A domain name is a meaningful, easy-to-remember ‘label’ for an IP address

• Examples:216.122.128.109

www.fccollege.edu.pk216.239.33.101 www.google.com

DNS: Domain Name System (1)

• DNS is the way that Internet domain names are located & translated into IP addresses

• Maintaining a single, central table of domain name/IP address relationships is impractical• Billions of DNS-IP translations take place

every day• The DNS-IP tables get updated continuously

DNS: Domain Name System (2)

• Tables of DNs & IP addresses are distributed throughout the Internet on numerous servers

• There is a DNS server at most ISPs. It converts the domain names in our Internet requests to actual IP addresses

• In case it does not have a particular domain name in its table, it makes a request to another DNS server on the Internet

TCP/IP Settings in a Computer

Internet Services

There are many, but we will look at only the following:

• Web• eMail• Instant messaging• VoIP

The Web

• The greatest, shared resource of information created by humankind

• A user may access any item on the Web through a URL, e.g.

http://www.fccollege.edu.pk/cs/index.html

• Before, going any further, let us dissect this URL

http://www.fcc.edu.pk/cs/index.html

ProtocolIdentifier

ServerAddress

Directory & File Name

How does the Web work?

User’sComputer

User launches the browser on his/her computer

Browser

User’sComputer

User types in the URL into the browser

User’sComputer

The browser breaks down the URL

http://www.fcc.edu.pk/cs/index.html

httpProtocolIdentifier

www.fcc.edu.pkServer’s Name

cs/index.htmlDirectory &File Name

User’sComputer

DNSServer

Browser sends server’s name to the DNS server

Domain Name

IP Address

User’sComputer

WebServer

Internet

Browser establishes a connection with the server

User’sComputer

WebServer

Browser sends a ‘GET’ request for cs/index.html

User’sComputer

WebServer

Server sends the requested file to the browser

User’sComputer

Browser displays index.html

X

eMail• Computer-to-computer messaging

• Inexpensive, and quite quick, but not instant!

• The most popular service on the Internet, even more than surfing, but soon to be overtaken by instant messaging

• Billions are sent every day

The Trouble with eMail• Slow response times

• No way of knowing if the person we are sending eMail to is there to read it

• The process of having a conversation through eMail by exchanging several short messages is too cumbersome

Instant messaging (IM) solves these problems

Instant Messaging

• The IM services available on the Internet (e.g. ICQ, GoogleTalk, MSN Messenger, Yahoo! Messenger and Skype) allow us to maintain a list of people (contacts) that we interact with regularly

• We can send an instant messages to any of the contacts in our list as long as that contact is online

Using Instant Messaging (1)

• Whenever a contact in our list comes online, the IM client informs us through an alert message and by playing a sound

• To send an instant message to a contact, just click on the contact in the IM client, and start typing the message

• The selected contact will receive that message almost immediately after you press ‘Enter’

Using Instant Messaging (2)

• When the contact’s IM client receives the message, it alerts the contact with a blinking message and by playing a sound

• That contact then can type a response to the received message, and send it instantly

• Several such conversations can be carried out simultaneously, each occupying a separate IM windows

Key Point

• Once the IM server provides the communication info to the user and his/her contact’s IM client, the two are able to communicate with each other without the IM server’s assistance

• This server-less connection is termed as a P2P connection

Question

• Why do we require the server in the first place?

• Why doesn’t my IM client look for the user’s contact’s IM client without the IM server’s help?

Answer• Many users (including almost all home

users) do not have permanent IP addresses. They are assigned temporary IP addresses by their ISP each time they connect to the Internet

• The server-based IM scheme removes the need of having permanent IP numbers

• It also gives IM users true mobility, allowing them the use of IM from any Internet-connected computer

VoIP: Voice over IP• Voice delivered from one device to another

using the Internet Protocol

• Voice is first converted into a digital form, is broken down into packets, and then transmitted over a TCP/IP network (e.g. Internet)

• Four modes:• C2C• C2T• T2C• T2T (with a TCP/IP net somewhere in between)

Pro

Much cheaper than traditional phone service

ConNoticeably poor quality of voice as

compared with land-line phone service, but not much worse than cell phone

service

Who runs the InternetWho runs the Internet??

Who owns itWho owns it??