In the Beginning...

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In the Beginning... The Internet grew from a grass-roots society into a global

community.

Usenet (Users’ Network) Individual conferences organized by topics of interest such as:

World events New technology National elections Privacy issues Entertainment Computer viruses

Generates over 100 meg of new text daily Does not reside on any one computer

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Internet: Planting the Seed and Growing the Plant

Early 1960’s Packet-switching envisioned (Baran and Davies)

Divide a message into a smaller pieces called packets.

Each packet contains where they came from and the address of where they are going.

Each packet is sent to its destination separately. Provided the foundation for what became the Internet.

1966: ARPA (Advanced Research Projects Agency) Funded computer network research.

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Internet: Planting the Seed and Growing the Plant

ARPANET (Advanced Research Projects Agency NETwork) Funded by ARPA. Pooled computer scientists and resources from several

universities. In 1969, linked 4 nodes at UCLA, UC Santa Barbara, SRI

(Stanford Research Institute) and U of Utah. By mid-1970’s, linked several military sites and about 20

universities. ARPA intended to sell off the ARPANET. Transferred to the Defense Communications Agency in

1975.

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Internet: Planting the Seed and Growing the Plant

NSF (National Science Foundation) In 1980, started CSnet. Provided a resource sharing network for computer

science research at all universities. Used TCP/IP protocol. Linked 5 supercomputing centers with a very fast

connection called a backbone. Each region surrounding the centers developed their

own community network. Each community network had exclusive access to

the backbone. Became known as NSFnet.

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Internet: Planting the Seed and Growing the Plant

In 1983, ARPANET split. Part remained ARPANET: universities, research

institutes. Part became Milnet: non-classified military information. Converted from Network protocol to TCP/IP protocol. In 1989, majority of ARPANET switched to NSF’s

backbone. Became what is known as the Internet. Early 1995: “Information Superhighway.”

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UNIX, Gurus, and Gophers With the thousands of computers running the UNIX operating

system, and freely distributed TCP/IP software suite: Original access to the Internet had UNIX “feel.” Exact addresses were needed to access information.

Addresses were strings of numbers Address for UCSD: 128.54.16.1

UNIX gurus “ran the net.”

Gopher (University of Minnesota): Land of the “Golden gophers.” Introduced first improvement to accessing the Internet. Menu-driven system gave access to databases of information. Were once over 5,000 gopher servers.

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UNIX, Gurus, and Gophers Internet Gopher Information Client v2.1.3

Home Gopher server: gopher.tc.umn.edu

1. Information About Gopher/2. Computer Information/3. Discussion Groups/4. Fun & Games/5. Internet file server (ftp) sites/6. Libraries/7. News/8. Other Gopher and Information Servers/9. Phone books/10. Search Gopher Titles at the University of Minnesota <?>11. Search lots of places at the university of Minnesota <?>12. University of Minnesota Campus Information/

Press ? For Help, q to Quit, u to go up a menu

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UNIX, Gurus, and Gophers Searching for information on the Internet from Gopher:

Veronica: Very Easy Rodent-Oriented Netwide Index to

Computerized Archives. Indexed the entries of all of the known Gopher menus. Updated about twice weekly.

Archie: Searched ftp archive sites. These files were for downloading by using the Internet. Has more than 1,000,000 filenames today. Currently accessible through the WWW.

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The Internet Growing Popular Internet functions illustrate the diversity of

Internet use: Information gathering:

University sites provide class and faculty information, books, library sources, lists of government documents

Employment offices could provide vacancy notices

Governmental agencies provide informational documents

Students and academic researchers could use online bibliographies

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The Internet Growing MUDs - Multi-User Dungeons MOOs - MUDs Object-Oriented

Both are an outgrowth of Dungeons and Dragons role playing games of the 70s and 80s.

Can play with people all over the world. There are more than 500 active MUDs.

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The Internet Growing IRC - Internet Relay Chat

“Real-time” online chat facilities Communication is accomplished via typing text over a

“channel”

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Communication Basics: The Physical Topology

Types of connection - Physical connection versus wireless. Network: A Collection of computers, display terminals,

printers, and other devices linked either by physical or wireless means.

Node: Any device on a network. Each device has a unique address assigned to it by the network.

Network links: Connections between computers and other electronic devices.

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Communication Basics: The Physical Topology

The physical media used to connect the networks are: Twisted pair, coaxial cable, fiber optic cable, and space.

Three types of wireless communication commonly used in networking: Infrared, Radio frequency, Microwave.

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Communication Basics: The Physical Topology

Three physical types of links used in networks.

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Communication Basics: The Physical Topology

Wireless communication.

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Communication Basics: The Physical Topology

Properties of Transmission: Each link has common attributes

1. Type of signal communicated (analog or digital) 2. The speed at which the signal is transmitted. 3. The type of data movement allowed on the channel.

Simplex transmission - One way transmission. Half-duplex transmission - Can flow only one way at a

time. Full-duplex transmission - Two-way at the same time.

4. The method used to transport the data – Asynchronous, synchronous.

5. Single channel and multichannel transmission.

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Communication Basics: The Physical Topology

Type of signal communicated.

Analog - A continuously changing signal similar to that found on the speaker wires of a high-fidelity stereo system.

Digital - Signals consist of pulses of electrical energy that represent 0’s or 1’s.

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Communication Basics: The Physical Topology

Speed of signal. In digital systems: Speed is measured in...

Bits per second (bps).• The number of bits (0’s and 1’s) that travel down

the channel per second. Baud rate

• The number of bits that travel down the channel in a given interval.

• The number is given in signal changes per second, not necessarily bits per second.

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Communication Basics: The Physical Topology

MODEM - MOdulator DEModulator Outgoing: Converts binary data from computer (digital)

into telephone compatible signals (analog). Incoming: Converts telephone signal (analog) into

binary data for the computer (digital). Can be an external or internal device (usually a “card”).

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Communication Basics: The Physical Topology

Speed of Signal: Sample bps and baud rate speeds.300 bps (=300 baud) Painfully slow to the college-level reader1200 bps (=1200 baud) Good reader can keep up2400 bps (=2400 baud) A speed reader would get the general idea9600 bps (=9600 baud) Impossible to read14.4 K bps (not measured in baud) 14,400 bps 28.8 K bps Minimum desired for WWW

(needed for receiving images and sound)33.6 K bps56 K bps Download speed is 56 K bps.

Sending speed is much less.

These speeds are restricted to the maximum speed of the modem at theother end of the connection. If the Internet connection modem is limited to 28.8 K,then even if your modem is 56 K, it is limited to the 28.8 K speed!

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Communication Basics: The Physical Topology

Linking Computers Together - Network - 2 or more devices are linked together. Node - Individual devices on the network. Direct link networks - One whose nodes have direct

connections through either physical or wireless links. Point to point link - Simplest of networks where a

connection is made between computer systems. Ways to link the nodes of a network:

• bus, ring, star, tree, and the fully connected topology networks.

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Communication Basics: The Physical Topology

Networks not directly linked:

Internetworking - (Hybrid networks) Linking any type of direct linked networks together. Can be as small as connecting two computers together to

as large as the largest of all, the Internet. Demand special software to allow information to be

exchanged between them.

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Communication Basics: The Physical Topology

Categorizing networks according to size: DAN (Desk Area Network) LAN (Local Area Network) MAN (Metropolitan Area Network) WAN (Wide Area Network)

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The Software Architecture of the Network

Problem: Connect several different machines running different

operating systems (Windows, OS/2, MacOS, UNIX, VMS..) Now, try to: send email, data or files between them.

Solution: Create a set of rules, or protocols, that, when followed, will

allow an exchange of information. Sometimes in a collection of programs called a protocol

suite.

Network Architecture: The overall organization of the rules of the network and is implemented in a set of programs called the protocol suite.

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The Software Architecture of the Network

The Internet Architecture is based on a four-layer protocol.

FTP HTTP NV TFTP

TCP UDP

IP

Network #1

Network #2

Network N

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The Software Architecture of the Network

The Internet is referred to as a packet-switching network. Packet - The Internet chunks information into packets.

Once a file is requested, it is split into packets.• Contains information regarding content, where it came

from, where it is supposed to go.• Each packet is assigned a number.

As the packet travels through the Internet from network to network:• Each packet may not travel through the same path

through the Internet to its destination.• Each network has its own “packet-limiting” size.• Packets are often “packaged” and “repackaged.”

They are reconstructed in order when they reach the destination.

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The Software Architecture of the Network

Problem: If someone wants his own WWW site, he must find a home for it.

Solution: Server -

A dedicated computer that is part of a network. The hard drive contains files that are “served” to

whatever requests them.• Could be data, programs, or home pages for the

WWW. The server normally runs the networking software.

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The Software Architecture of the Network

Types of nodes important to networks.Hub A device that repeats or broadcasts the network stream of

information to individual nodes ( usually personal computers) Switch A device that receives packets from its input link, and then sorts

them and transmits them over the proper link that connects to the node addressed.

Bridge A link between two networks that have identical rules of communication.

GatewayA link between two different networks that have different rules of communication.

Router A node that sends network packets in one of many possible directions to get them to their destination.