Connections

3G• next generation of mobile communications

technology. • other countries more fully utilize mobile

phones.• increased bandwidth, up to 384 kbps when a

device is stationary or moving at pedestrian speed, 128 kbps in a car, and 5-10 mbps stationary.

• video, multimedia support.

Approaches to Networking

Client Server Model– server fulfils client requests– high speed, high capacity computer is

the server– hierarchical structure, server is

essential

Approaches to Networking

Peer 2 Peer Model– any computer can be a client or a

server.– often used on smaller networks (but not

necessarily, e.g. music sharing).– Windows & MacOS allow for P2P

networking.

Internet

• global network of networks.

• TCP / IP communication standard.

• to communicate, networks must speak the same language.

Internet Motivation

• Researchers : share computing resources, very few computers, expensive.

• Military : cold war, wanted a communication network.

Military Needs

• assume unreliability.

• decentralized : all connected computers are equal.

• most work when lines are broken, and nodes are down.

Network Must

• connect important government & research computers.

• resist point-of-failure attacks : continue to operate even if a city on the network was destroyed.

• be fault-tolerant : continue to operate even if something went wrong within the network – e.g., a computer crashed, or a transmission line was broken.

Solution

• designed to be a decentralized network of computers that could adapt the flow of traffic and to changes in the state of the overall system.

• the way that information travels on the Internet is similar to the way that traffic moves on an interconnected system of roads and highways.

Like a Highway

• detours - if a road is flooded find an alternate route.

• minimize the impact of a lost or delayed vehicle - instead of transporting groups of sixty people in buses, put each person on a motorcycle or alone in a car.

Like a Highway

• addressing - each person knows the exact address of their destination.

• traffic reports - have check points at all intersections to reassess the best route based on current traffic conditions.

Internet Protocol

• Internet Protocol - works something like the postal system, it describes how to form and address online communication packages.

• packets - messages sent over the Internet are broken into pieces equivalent to about 1500 characters.

IP Addresses

• every computer on the Internet has a unique address called an IP address.

• valid IP addresses are in the form of dotted quads : four numbers, each in the range of 0 to 255, and separated by a period (e.g. 128.233.34.18).

IP Addresses

every packet is addressed with :

• the source IP address – (e.g. from: 123.234.234.1)

• the destination IP address – (e.g. to: 231.249.3.27)

• the packet number – (e.g. number: 10 of 16)

Transmission Control Protocol

• ensures the transmission and delivery of data from source to destination.

• as packets arrive at routers or hosts (computers on the network), the routers decide the best path to send each packet on.

Transmission Control Protocol

• TCP describes how to put the packets back together (reassemble the message) once the packets reach their destination.

• if a packet is lost or damaged (corrupted) along the way, TCP allows for a "retransmit" message to be sent asking for the missing or bad packet to be resent.

Check Sums

• check if packets may have been corrupted in transit.

• apply some algorithm to add an extra number to the packet.

• if, when the packet arrives, the same algorithm does not result in the same number being calculated, we know there was a data transmission error.

TCP / IP

• Transmission Control Protocol :– establishes a connection between two

hosts. – guarantees delivery of data - packets

will arrive in the order they were sent.

• Internet Protocol :– forming and addressing packets.

TCP / IP

• Open Standard :– not owned by any one, made public. – advantage : anyone can design add-

ons. – Disadvantage : duplicated by others.

• Cross-Network Communication• Low Level Protocols – hidden from

users.

Packet-Switching

• different paths• traffic gets through even when part of the

network is down.• packets that have the same source and

destination MAY still take different routes.• Router : chooses best path.• Switch : just forwards traffic, may be

faster.

Birth and Growth

Labour Day, 1969, ARPANET is born and connects 4 host :

- U of California at L.A.

- U of California at Santa Barbara

- U of Utah

- Stanford Research Institute.

Birth and Growth

1969 : 4 hosts connected.1971 : 23 hosts connected.1974 : 62 hosts connected.1984 : more than 1000 hosts connected.1987 : more than 10 000 hosts connected.1989 : more than 100 000 hosts connected.1992 : more than 1 000 000 hosts connected.** doubling every year since mid 80's, slower

now.

How Big?

• Changing too fast to measure.

• decentralized – no one person controls and monitors the entire Internet.

• no hard boundaries – difficult to say exactly who is connected.

Connecting to the Internet

Direct Connection

Dialup Connection

Broadband Connection

Direct Connection

• devoted link from your LAN to the closest point on the Internet (phone company, cable company, university).

• computers on the LAN have IP addresses.• fast service, able to transfer large files

quickly.• using T1, T3 or fiber optic.

Dial-Up Connection• telephone lines and a modem.• email (files) stored on a host (server) and you

connect to collect them.• Limited – not all traffic can be sent this way. • ISPs - Internet Service Providers.

• various packages and services : email, web space, ect.• freenet – community access.

Broadband Connection• higher bandwidth than typical

modems.

• speed can be comparable to a direct connection.

• always connected.• DSL : phone company.• Cable Modem : cable company.• Wireless : Wi-Fi .

Traffic Direction

• Downstream – to your computer (download).

• Upstream – to the Internet (upload).

Internet & Web

• the World Wide Web and the Internet are not the same thing.

• WWW – an application of the Internet.

• Popularity :– easy to use.– easy to add– easy to search.

Internet Applications

• email & mailing lists

• FTP & file sharing

• Usenet & boards & forums

• World Wide Web

• Instant Messaging & Chat

• Remote Login & Telnet