week3

Internet and Web Technology

Web browser orGUI

Client Tier

DatabaseManagement

Software

Data Tier

Business LogicSoftware

Application Tier

Internet or CorporateNetwork

HTTP Web Server

Presentation Tier

Data

Core technologies – where we are headed

Communication

• Communication is often defined as the exchange of information between two individuals using a common set of symbols, signs or behavior.

• More specifically, telecommunications usually involves a significant distance between the individuals and some electronic equipment for transmission and reception of the information.

• Data communications really is nothing more than the transmission of ones and zeros from one point to another.

• The Internet is the core of Internet Business and the web is the core of the Internet.

• How do they differ?• While running P&G proposed creation of

the ARPA (Advanced Research Projects Agency).

• Funding was approved by the Congress in 1958.

• The ARPA network was based on technology called packet switching and led to the development of the networking protocol called TCP/IP. (transmission control protocol/ Internet protocol)

• In the world of networking the word protocol refers to a set of rules for exchanging messages over a network.

• So think of a protocol as a set of rules computers use on a network in order to talk to each other.

• Internet can be defined as a network of computers using TCP/IP.

Computer Network Basics

• This is called a star network. • The hub at the center of this network is a very simple piece of networking hardware that takes the

data from one computer and passes them onto the other computers in the network• This is also known as a LAN (local area network). A LAN is a communications network consisting

of cables, computers and network devices confined to a very small geographic region such as a building or floor of a building.

Hub

Desktop PC Workstation

Laptop

Server

Laser Printer

A Wide Area Network

Hub

Desktop PC Workstation

Laptop

Server Laser Printer

Router Router Hub

Desktop PC Workstation

Laptop

Server

Laser Printer

Copper wireFiber

Wireless

Chicago San Antonio

When an organization’s LAN are connected together over a largergeographical region, perhaps the world, they are called Wide area network.A router sends or route packets from one LAN to another LAN

Circuit Switching

• Establishing a connection between two points using specific path on a network for the duration of a message exchange is called circuit switching.

• The problem with Circuit Switching is that the line is tied up regardless of how much information is exchanged.

• Highway example

Packet Switching

• An Alternative to circuit switching is packet switching.

• When sending a message over a network (e.g. an email) the message is usually broken up into a smaller set of messages called packets.

• Consider sending a letter from Chicago to San Antonio. Rather than sending the entire letter over a particular route we could cut the letter into a set of packets.

• These packets are cut, addressed and sent in a particular way:

Packet Switching

• Each packets are numbered so they reassembled in the correct sequence at the destination.

• Each packet contains destination and return address.• The packets are transmitted over the network as

capacity becomes available.• The packets are forwarded across the network

separately and do not necessarily follow the same route;– if a particular link of a given path is busy, some packets

might take an alternate route.

• Most packets are split into three parts:

Header

• The header contains instructions about the data carried by the packet. These instructions may include:

• Length of packet (some networks have fixed-length packets, while others rely on the header to contain this information)

• Packet number (which packet this is in a sequence of packets) • Protocol ( the protocol defines what type of packet is being

transmitted: e-mail, Web page, streaming video) • Destination address (where the packet is going) • Originating address (where the packet came from)

Payload -

• Also called the body or data of a packet. This is the actual data that the packet is delivering to the destination.

Trailer

• The trailer, sometimes called the footer, typically contains a couple of bits that tell the receiving device that it has reached the end of the packet. It may also have some type of error checking.

Packet Example

• As an example, let's look at how an e-mail message might get broken into packets. Let's say that you send an e-mail to a friend.

• The e-mail is about 3,500 bits (3.5 kilobits) in size. The network you send it over uses fixed-length packets of 1,024 bits (1 kilobit). – The header of each packet is 96 bits long and the trailer is 32 bits

long, leaving 896 bits for the payload.

• To break the 3,500 bits of message into packets, you will need four packets (divide 3,500 by 896). Three packets will contain 896 bits of payload and the fourth will have 812 bits. Here is what one of the four packets would contain:

• Each packet's header will contain the proper protocols, the originating address (the IP address of your computer), the destination address (the IP address of the computer where you are sending the e-mail) and the packet number (1, 2, 3 or 4 since there are 4 packets). Routers in the network will look at the destination address in the header and compare it to their lookup table to find out where to send the packet. Once the packet arrives at its destination, your friend's computer will strip the header and trailer off each packet and reassemble the e-mail based on the numbered sequence of the packets

Question Of The Day

• I've heard that data travels in packets on a computer network. What is a packet, and why do networks use them?

• It turns out that everything you do on the Internet involves packets. For example, every Web page that you receive comes as a series of packets, and every e-mail you send leaves as a series of packets

– Networks that ship data around in small packets are called packet switched networks

– On the Internet, the network breaks an e-mail message into parts of a certain size in bytes. These are the packets. Each packet carries the information that will help it get to its destination –

– the sender's IP address, the intended receiver's IP address, something that tells the network how many packets this e-mail message has been broken into and the number of this particular packet. The packets carry the data in the protocols that the Internet uses: Transmission Control Protocol/Internet Protocol (TCP/IP). Each packet contains part of the body of your message. A typical packet contains perhaps 1,000 or 1,500 bytes.

– Each packet is then sent off to its destination by the best available route -- a route that might be taken by all the other packets in the message or by none of the other packets in the message

• Source: www.howstuffworks.com

• TCP stands for transmission control protocol. – This is a software as the name implies responsible for

assembling the packets in the correct order and checking for missing packets.

• If packets are lost the TCP software requests new ones.

• The TCP software is responsible for establishing the session between two computers on a network.

• The TCP and IP software work together.

• TCP/IP has two major components: TCP and IP.

• IP: envelopes and addresses the data

IP enables the network to read the envelope and forward the data to its destination

defines how much data can fit in a single "envelope" (a packet)

• Computers using the internet must have IP software.

• Packets that follow the IP specification are called IP datagrams.

• The datagrams have two parts: – Header information and Data.

– Header is the information that would go on an envelope and the data as the letter that goes inside the envelope.

• The relationship between data, IP, and networks is often compared to the relationship between a letter, its addressed envelope, and the postal system.

Source: http://wwwoirm.nih.gov/15min/tcpip/sld04.html

IP Numbers

• All IP addresses have the same format. – Four sets of numbers separated by three

periods.

• Each of the four sets of numbers requires one byte (8 bits) for a total of 32 bits.

• By convention we are stating the IP address in decimal rather than binary format.

• Specifically the IP address has the following form – Network:Host – For example in the IP address 128.135.130.201

• The network address is 128.135. – This is the address that all computers in University of Chicago

share

• IP address maybe subdivided into a subnetwork and machine number. – In the host number 130.201 the 130 denotes a particular

LAN (Stuart Hall) and 201 is the machine number in that LAN.

The Web

• The standard way of reading a book is in a linear fashion starting with page one.

• The concept of hypertext is to allow a person to read or explore in a nonlinear fashion.

• By following the links the reader is not constrained to follow any particular order.

• Hypertext may contain links that do not necessarily lead to other text, but to sound or video files

• Before the web came into being there there were hypertext products in the marketplace.

• One product was guide distributed by OWL

– If you clicked on a link in Guide, a new document would be inserted in place of the link.

HTTP, URL and HTML

• All created by Tim Berners Lee

– Who is he?

• http://www.w3.org/People/Berners-Lee/

• HTTP is a high level protocol used to exchange information between a browser and a server

• HTTP protocol uses TCP/IP to locate and make a connection between the browser and the server.

• HTTP is the protocol used for document exchange in the World-Wide-Web. Everything that happens on the web, happens over HTTP transactions. TCP/IP networking and HTTP are the two essential components that make the web work.

HTTP PROTOCOL

• HTTP is a client-server protocol by which two machines can communicate over a TCP/IP connection.

• An HTTP server is a program that sits listening on a machine's port for HTTP requests.

• An HTTP client opens a TCP/IP connection to the server, transmits a request for a document, then waits for a reply from the server.

• Once the request-reply sequence is completed, the socket is closed.

• So the HTTP protocol is a transactional one. The lifetime of a connection corresponds to a single request-reply sequence. (a transaction)

• http://www.perlfect.com/articles/http.shtml

The Web

Desktop PC Server

Request:GET

/htmls/tmp/foo.htmlHTTP1.1

Header:USER_AGENT: MSIE 5.5

Body:Empty

Response:HTTP1.1/200

Header:Server: IIS 5.0

Body:<HTML>

.

.

.</HTML>1- A request line that

containing the name of the requested file 2- Header containing information such as the type of browser and OS 3- A body containing data e.g. data entered into a form

1- A response line with a code indicating that the requested file was foundOr Not found 404 error2- Header containing information such as the type of server software3- A body containing the HTML of the requested file.

HTTP Process

• There are two pieces of Software required for this process to take place.– The desktop PC must have a browser such as IE or NN.

– The server machine must have an HTTP server.

• The most common HTTP server is– APACHE

– Windows 2000 comes with IIS 20% market share

– Sun Microsystem’s iplanet

URL

• Uniform Resource Locator

• This is the address of a web page.

• There are three parts toa URL. They are:– The internet protocol used HTTP, FTP – The addrress or name of the server – The location and name of the file on the server.

Domain Name System

• Domain names must get converted or resolved into IP addresses.

• This is done through an Internet Service called the domain name system.

• This system makes use of special servers called domain name servers.

DNS ResolutionRoot server

Local DNSserver

GSB DNS server128.135.4.2

Request forgsbkip IP number

128.135.130.201

File request

File returned

Request forgsbkip.uchicago.edu

IP number128.135.130.201

128.135.4.2Request for

uchicago.eduDNS IP number Internet

Internet

Internet

Desktop Enterprise WebServer

http://www.stamey.nu/DNS/DNSHowItWorks.asp

Bandwidth

• When talking about Networks Bandwidth refers to the capacity of the network.

• Bandwidth is often measured in kilobits megabits or gigabits. The terms broadband (10MBPS) narrowband(less than 1 MBPS) and midband (1-10) are often used to describe the bandwidth.