Internet Development What is the Internet anyway?

Colm O Suilleabhain

The Internet is short for:

• Interconnected Network

What is a network?

• From dictionary.com:– An openwork fabric or structure in which cords,

threads, or wires cross at regular intervals.– Something resembling an openwork fabric or

structure in form or concept, especially:• A system of lines or channels that cross or interconnect: a

network of railroads. • A complex, interconnected group or system: an espionage

network. • An extended group of people with similar interests or

concerns who interact and remain in informal contact for mutual assistance or support.

What is a network?

• From whatis.com• A network is a series of points or nodes connected by

communication paths. Networks can interconnect with other networks and contain subnetworks.

• Topology – Star, bus, ring• Spatial distance as local area networks (LANs), metropolitan

area networks (MANs), and wide area networks (WANs). • Type of data transmission technology in use on it (for example,

a TCP/IP or Systems Network Architecture network); • Whether it carries voice, data, or both kinds of signals• Who can use the network (public or private); • Nature of its connections (dial-up or switched, dedicated or

nonswitched, or virtual connections); • By the types of physical links (for example, optical fiber, coaxial

cable, and Unshielded Twisted Pair).

What’s the Internet NOT?

• “The web”

• Google

• Email-reachable users

• Private networks

What can it do?

• Email• WWW, Hypertext, RSS, browsers • FTP, WebDav• Voice access (VXML, SALT)• Mobile phones (WAP)• IM, IRC• Online gaming• Video conferencing• Remote backups• Remote login/admin gotomypc.com• Streaming video & audio

Where did it come from?

• Advanced Research Projects Agency (ARPA) of the U.S. government in 1969 and was first known as the ARPANET.

• Original aim was to create a network that would allow users of a research computer at one university to be able to "talk to" research computers at other universities.

• A side benefit of ARPANet's design was that, because messages could be routed or rerouted in more than one direction, the network could continue to function even if parts of it were destroyed in the event of a military attack or other disaster.

How big is the Internet?

• Assessing the size of the Internet is a somewhat difficult proposition, since it is a distributed body, and no complete index of it exists

• Do we mean how many people use the Internet? How many websites are on the Internet? How many bytes of data are contained on the Internet? How many distinct servers operate on the Internet? How much traffic runs through the Internet per second?

How big is the Internet?

• Just over a billion people used the Internet in 2008

• Of these, about 500 million use the Internet at least once a week

• There are thought to be some 155 million websites on the Internet

• All these numbers are guestimates and are nearly impossible to measure accurately

Internet Software

• Clients– A client is the requesting program or user in a

client/server relationship.

• Servers– A program that awaits and fulfills requests from client

programs in the same or other computers.

• Peers– A program may function as a client with requests for

services from other programs and also as a server of requests from other programs.

Browser

• An application program that provides a way to look at and interact with all the information on the World Wide Web.– Mosaic 1993– Opera – Firefox– Chrome– Internet Explorer

Web Server

• Using the client/server model and the World Wide Web's Hypertext Transfer Protocol (HTTP), serves the files that form Web pages to Web users (whose computers contain HTTP clients that forward their requests).

• Every computer on the Internet that contains a Web site must have a Web server program.

• Apache • Tomcat• IIS

Other clients & servers?

• Mail server/client– SendMail, Exchange, Lotus Domino– Opera, Outlook, Mozilla

• FTP Server/Client

Peer to Peer

• Gnutella

• Kazza

• Bittorrent

• Warez

• eDonkey

Internet hardware

• Edge devices - Clients, servers, peers, PC’s servers, phones, PDA’s

• Core devices – Hubs, switches, routers, gateways

• Access devices – analogue modems, 802.11 base stations, ISDN modems, network cards, cable modems, DSL modem

• Connection devices – POTS, wireless, fibre, CAT5/CAT6

Hub

• The central part of a wheel where the spokes come together.

• The term is familiar to frequent fliers who travel through airport "hubs" to make connecting flights from one point to another.

• In data communications, a hub is a place of convergence where data arrives from one or more directions and is forwarded out in one or more other directions

Switch

• A device that channels incoming data from any of multiple input ports to the specific output port that will take the data toward its intended destination.

Router

• A device or, in some cases, software in a computer, that determines the next network point to which a packet should be forwarded toward its destination.

• The router is connected to at least two networks and decides which way to send each information packet based on its current understanding of the state of the networks it is connected to.

• May create or maintain a table of the available routes and their conditions and use this information along with distance and cost algorithms to determine the best route for a given packet

Modem

• A modem modulates outgoing digital signals from a computer or other digital device to analog signals for a conventional copper twisted pair telephone line and demodulates the incoming analog signal and converts it to a digital signal for the digital device

Network card

• A network interface card (NIC) is a computer circuit board or card that is installed in a computer so that it can be connected to a network.

• A dedicated full time connection

• Wired or wireless

Wireless

• 802.11 (a,b,g)

• GPRS

• 3G

ISDN

• Standards for digital transmission over ordinary telephone copper wire as well as over other media.

• Home and business users who install an ISDN adapter (in place of a telephone modem) receive Web pages at up to 128 Kbps compared with the maximum 56 Kbps rate of a modem connection.

• Being replaced by ADSL where availible

ADSL

• Technology for transmitting digital information at a high bandwidth on existing phone lines to homes and businesses.

• Unlike regular dialup phone service, ADSL provides continously-available, "always on" connection.

• ADSL is asymmetric in that it uses most of the channel to transmit downstream to the user and only a small part to receive information from the user. ADSL simultaneously accommodates analog (voice) information on the same line.

• ADSL is generally offered at downstream data rates from 512 Kbps to about 6 Mbps.

Question?

• How can such a diverse range of hardware and software communicate?

• You can replace all the hardware with new hardware and replace all the software with new software, but its still the Internet!

• How come?– Standard Protocols

What’s a protocol?human protocols:• “what’s the time?”• “I have a question”• introductions

… specific msgs sent

… specific actions taken when msgs received, or other events

network protocols:• machines rather than

humans• all communication

activity in Internet governed by protocols

protocols define format, order of msgs sent and received

among network entities, and actions taken on msg

transmission, receipt

What’s a protocol?a human protocol and a computer network protocol:

Q: Other human protocol?

Hi

Hi

Got thetime?

2:00

TCP connection req.

TCP connectionreply.Get http://gaia.cs.umass.edu/index.htm

<file>time

What do protocols look like?

• “Binary”– Fixed-length fields, like C-structures– Type-length-value (TLV)

• “Text”– ftp: PUT foo– GET index.html HTTP/1.1

Content-Length: 100

Connection-oriented service

Goal: data transfer between end sys.

• handshaking: setup (prepare for) data transfer ahead of time– Hello, hello back human

protocol

– set up “state” in two communicating hosts

• TCP - Transmission Control Protocol – Internet’s connection-

oriented service

TCP service [RFC 793]

• reliable, in-order byte-stream data transfer– loss: acknowledgements

and retransmissions

• flow control: – sender won’t overwhelm

receiver

• congestion control: – senders “slow down sending

rate” when network congested

HTTP Protocol

Parameters

Request

QueryResults

Response

Web Server

Web Browser

Database (Optional)

E.g. A user fills in a form, which gets submitted to a web server

Port Numbers (16 bit numbers) identify the service

RFC’s:

1945

2068

2616

http://www.ietf.org/rfc/rfc1945.txt?number=1945

SMTP Protocol• Simple Mail Transfer Protocol• Protocol for sending Email• Originally designed for a secure network

Mail Client

Mail Server Mail Server Mail Server

Issues? Security & Non-repudiation

RFC’s:

821

974

1869

2821

http://www.ietf.org/rfc/rfc0821.txt?number=821

PersonShop Wholesalers

Co-opFarmer

Protocol Stacks

Internet Standardisation

• International Telecommunications Union (ITU)– United Nations treaty organization– Modem standards (V.90)– Traditional telephone services, fax

• Internet Engineering Task Force (IETF)– Core: Internet Protocol, transport (TCP)– Applications: email, HTTP, ftp, NFS– Not: HTML, APIs

• W3C– HTML, XML, XSL, …

• IEEE– WiFi

IETF

• Open membership• Meets three times a year, about 2,000+ people• Most work done on mailing lists (see www.ietf.org)• Working groups produce technology• No formal voting at WG level, but review by “area

directors”• Emphasis on interoperability and deployment• Internet drafts -> Proposed Standard (RFC)• See www.normos.org for RFC directory

RFC’sNetwork Working Group Steve CrockerRequest for Comments: 1 UCLA 7 April 1969

Title: Host Software Author: Steve Crocker Installation: UCLA Date: 7 April 1969 Network Working Group Request for Comment: 1……Introduction

The software for the ARPA Network exists partly in the IMPs and partly in the respective HOSTs. BB&N has specified the software of the IMPs and it is the responsibility of the HOST groups to agree on HOST software.

During the summer of 1968, representatives from the initial four sites met several times to discuss the HOST software and initial experiments on the network. There emerged from these meetings a working group of three, Steve Carr from Utah, Jeff Rulifson from SRI, and Steve Crocker of UCLA, who met during the fall and winter. The most recent meeting was in the last week of March in Utah. Also present was Bill Duvall of SRI who has recently started working with Jeff Rulifson.

Somewhat independently, Gerard DeLoche of UCLA has been working on the HOST-IMP interface.

I present here some of the tentative agreements reached and some of the open questions encountered. Very little of what is here is firm and reactions are expected.

http://www.ietf.org/rfc.html

What is Internet/Web development?

• Creating software that:– Runs on Internet hardware– Runs on Internet software – Uses Internet protocols