INFO 203 Week #5 1

IT For EngineersIntro to Computer Networking

INFO 203Dr. Jennifer Booker

INFO 203 Week #5 2

Computer Networks A network is the structure that allows

computer applications to communicate with each other The applications could be executed by the user,

or part of the operating system Not every computer system is designed to allow

networking The Internet is our primary model for

understanding networking concepts

INFO 203 Week #5 3

The Internet Key parts of any network include

Hosts or end systems, which are the computers and other things with which most people interact End user computers, workstations, smartphones, and

servers are all considered hosts As of July 2008 there were about 600 million hosts on

the Internet, about 850 million as of July 2011, and passed a billion in January 2014

As of June 2015, 45% of the world’s population had access to the Internet

INFO 203 Week #5 4

The Internet Communication links,

which are the wired or wireless means used to connect to the network

Packet switches, which help guide information between hosts Routers and link-layer

switches are the primary types of packet switches

Graphics are taken from the text’s lecture notes

INFO 203 Week #5 5

The Internet The network sends chunks of information

called packets along a route or path to get from one host to another The speed at which it does so is the transmission

rate, typically in bits per second (bps)

INFO 203 Week #5 6

Bits and Bytes To review basic computer units

A bit is a binary digit – a 0 or 1 Typically eight bits are a byte, one character

Old ASCII text files used seven bits per byte Transmission rate of data is given in bits per

second (bps), or thousands or millions or billions of bits per second (kbps, Mbps, Gbps)

Data transfer = rate * time Which has units of: bits = bits/sec * sec

INFO 203 Week #5 7

The Internet The control over choosing the path is known

as packet switching End systems connect to the Internet through

an Internet Service Provider (ISP) ISPs provide many levels of service

Residential or business service, typically from 56kb dialup to DSL, FIOS, or cable modems

INFO 203 Week #5 8

The Internet The packets are defined and handled

according to protocols, most notably the Transmission Control Protocol (TCP) and Internet Protocol (IP)

A protocol is a language for communication

INFO 203 Week #5 9

Protocols In order for it to work, both parties (e.g. hosts,

switches, etc.) need to speak the same language oder Sie werden einander nicht verstehen or they won’t understand each other

Some protocols use a handshake concept Like saying Hi as a greeting, special messages

are defined that request a connection, and reply to accept the connection

Others don’t have a handshake

INFO 203 Week #5 10

Protocols More formally, then, protocols define

The format of messages (like the spelling of words)

The order of messages (the syntax of sentences, or else your messages like Yoda will sound)

Much of understanding networking is understanding how these protocols work

INFO 203 Week #5 11

Source of Protocols Internet protocols are defined by the Internet

Engineering Task Force (IETF) The IETF was created by the Internet Architecture

Board (IAB) and also reports to the Internet Society (ISOC)

The Request For Comments (RFCs) define the actual protocols The first RFC was dated April 1969 As of October 2015, there are over

7600 RFCs (see RFC Index)

INFO 203 Week #5 12

Internet vs Intranet The Internet (a proper noun, hence is

capitalized) is the public network of zillions of computers, toasters, etc.

An intranet (not a proper noun) is the generic term for a local private network that uses the same protocols as the Internet

INFO 203 Week #5 13

Type of Internet Service The Internet runs distributed applications

The World Wide Web, instant messaging, distributed games, etc. are all distributed applications

These applications are developed using an Application Programming Interface (API) to connect to the Internet

INFO 203 Week #5 14

Type of Internet Service There are two choices for the type of service

provided by an Internet connection A connection-oriented, reliable service A connection-less, unreliable service

Neither guarantees how fast a message will get from host A to host B

INFO 203 Week #5 15

Connection-oriented, Reliable Service This establishes a loose connection between

client and server, but not to the switches and routers between them

Key traits needed from this are Reliable data transfer – every little bit counts Flow control to keep from overwhelming hosts Congestion control to avoid Internet gridlock

TCP provides this service (RFC 793)

INFO 203 Week #5 16

Connection-less, Unreliable Service This service has no handshaking – it just

sends packets of data Don’t know if packets ever got there No flow or congestion control

Handled by the User Datagram Protocol (UDP), RFC 768

Use when speed is critical, such as video conferencing or Internet telephone

INFO 203 Week #5 17

The Edge of the Network Now we’ll examine the contents of the

Internet from the outside in – from the “edge” to the “core”

Hosts (end systems) can be divided into clients and servers Clients are computers that request services from

Servers One computer (host) can be multiple clients and

servers at once (esp. in peer-to-peer applications)

INFO 203 Week #5 18

Access Networks To get from a host to a distant part of the

Internet, you need to pass through the access network

Access networks get residential, business, and wireless users connected

Digital subscriber line (DSL) gives a dedicated connection, with different upstream and downstream rates Downstream/upstream rates are typically values like

768k/128k, 3.0M/768k, etc.

INFO 203 Week #5 19

Access Networks Cable modems use hybrid fiber-coaxial cable

(HFC) to connect to special cable modems HFC is a variant on the same cable used for cable

TV service HFC is a shared medium – if all your neighbors

are online, your connection speed will suffer! Dial-up connections are only present when

needed; DSL and cable modems are always on (we hope)

Access Networks Fiber to the home (FTTH) is fiber optic

Internet connection for residential use There are two kinds of FTTH

Active optical networks (AONs) are switched Ethernet

Passive optical networks (PONs) are used by Verizon’s FIOS service Typically up to 64 homes share a connection from the

provider’s central office (CO)

Week #5 20INFO 203

Wired access Local area networks (LANs) generally use

Ethernet for wired connections Ethernet speeds of 1000 Mbps are common,

and up to 40 Gbps for servers and routers

Week #5 21INFO 203

INFO 203 Week #5 22

Wireless Access Wireless devices connect through wireless

access points (base station) on a LAN Then the LAN uses some other access

connection to get to the Internet Wireless devices use the IEEE 802.11 family

of technologies 802.11a supports up to 54 Mbps @ 5 GHz 802.11b supports 5.5 and 11 Mbps @ 2.4 GHz 802.11g supports up to 54 Mbps @ 2.4 GHz

INFO 203 Week #5 23

Why Does Frequency Matter? Wireless signals can be interfered with by other

devices; when that occurs, they detune their speed 802.11a has seven (48, 36, 24, 18, 12, 9, and 6 Mbps) 802.11b has three lower data rates (5.5, 2, and 1 Mbps) 802.11g has a range of lower speeds

The 802.11b and 802.11g standards use the 2.4 GHz (gigahertz) frequency range This frequency range is used by other networking

technologies, microwave ovens, 2.4GHz cordless phones (a huge market), and Bluetooth devices

The 5 GHz frequency range for 802.11a is relatively clear, so it’s less likely to have interference (so far)

INFO 203 Week #5 24

Wireless Network Example

DSL Modem Gateway / DHCP server Hub

Computer 1

Computer 2

Computer 3

Phoneline

Wireless Access Point

Laptop 1

Wireless Repeater Laptop 2

Cable Modem

CoaxCable

Or could have

WiMAX The next generations of wireless

communication are a battle between advanced cell technologies (3G and 4G protocols) and WiMAX

WiMAX is IEEE 802.16, and promises 5-10 Mbps speed over ranges of tens of km

Week #5 25INFO 203

INFO 203 Week #5 26

Physical Media Physical media used for connecting networks

can be guided or unguided Guided media use something solid – wires,

coaxial cable, fiber-optic cable, etc. Unguided media use electromagnetic waves of

some kind – wireless LAN signals, satellite channels, etc.

INFO 203 Week #5 27

Physical Media Specific kinds of physical media include

Twisted pair copper wire Coaxial cable Fiber optics Terrestrial radio channels Satellite radio channels

INFO 203 Week #5 28

Twisted pair copper wire Most common physical medium, has multiple

coated wires wrapped around each other Includes phone lines, which have four thin wires

with RJ-11 plugs on the end Ethernet cables have eight wires, and RJ-45

plugs on the end, so they’re wider than phone plugs

Can handle Gbps speeds over distances of about a hundred yards

INFO 203 Week #5 29

Coaxial cable Coaxial (coax) cable has a copper wire core,

and a copper cylinder around it – they share the same axis of rotation, hence the name

Handles multiple Mbps speeds for miles There are only two conductors, which is why

it’s a shared medium – everyone shares the same resources

Copper wire and cylinder

Insulation

INFO 203 Week #5 30

Fiber optics Fiber optics use hollow fibers to guide

light pulses Handles hundreds of Gbps speeds up

to 100 km Most international phone lines, and the

Internet backbone, are fiber optic cables Used on high speed LANs – 1 to 10 Gbps

INFO 203 Week #5 31

Terrestrial radio channels These include the wireless network channels

discussed previously, plus radio signals used to beam networks between buildings

Can reach long distances with the latter, but signals can be intercepted, bounce, fade, and have interference from other signals

INFO 203 Week #5 32

Satellite radio channels Consist of geostationary satellites and

low-altitude satellites Geostationary satellites hover 24,000 miles above

the Earth’s surface, and are used to relay TV channels and parts of the Internet backbone

Low altitude satellites (LEO, low-Earth orbiting) orbit much faster, so you need several to be able to find one at any given time; are not used for networks

INFO 203 Week #5 33

Psst – what Internet Backbone? The Internet is a network of many networks

It was designed that way to be redundant in the event of war – if one part of it was no longer usable (nice euphemism!), the rest of the network would still work

At its heart are many Tier-1 ISPs Sprint, MCI, WorldCom, AT&T, etc. are all Tier-1 They run extremely fast “backbone” connections

(622 Mbps to 10 Gbps)

INFO 203 Week #5 34

Internet Backbone The Tier-2 ISPs are regional or national in

scope, and connect to Tier-1 and Tier-2 ISPs Points where ISPs connect to each other are

Points Of Presence (POPs) Don’t confuse with Post Office Protocol (POP)

They may also connect at Network Access Points (NAPs) to local telecom companies or Tier 1 ISPs

INFO 203 Week #5 35

Internet Backbone There are thousands of lower level ISPs,

Tier-3, probably including your local ISP For a packet to get from one host to another,

it may pass through a variety of Tier-1, Tier-2, and Tier-3 ISPs, NAPs, POPs, etc.

INFO 203 Week #5 36

Circuit vs Packet Switching In order to get a packet from host A to host B,

two major approaches could be used Both approaches send packets over

communication lines Circuit switching is what a traditional telephone

system does Reserve a path from A to B which is the circuit

messages will follow, until the connection is closed Packet switching is used by the Internet

Dump packets into the network with no reserved path, and make a best effort to get packet to destination

INFO 203 Week #5 37

Circuit Switching To link host A and host B, each link between

switches along the way must be reserved for the duration of that connection or circuit

There are two ways to share links with many circuits: Frequency-division multiplexing (FDM) Time-division multiplexing (TDM)

INFO 203 Week #5 38

FDM and TDM FDM acts like FM radio – it divides the link

by frequency ranges, and assigns a frequency range to each circuit Typical frequency range, or bandwidth, is 4 kHz This way one link can handle many circuits

TDM breaks the link into some number (n) of slots in a frame Each slot is dedicated to one circuit, so that

circuit has full attention of the link 100/n percent of the time

Key conversion point In dealing with prefixes k, M, G, etc., in

computer science they represent 2^(n*10) k = 2^10, M = 2^20, G = 2^30, etc.

For our purposes, treat prefixes as their base 10 equivalents k = 1000, M = 1,000,000, G = 1 billion

Week #5 39INFO 203

INFO 203 Week #5 40

TDM Example Suppose you have a 1.536 Mbps TDM

connection, and want to send a 1 Mb (megabit) file; the connection has 12 links

How long does it take? Your transmission speed is 1/12 of the

1.536 Mbps, or 0.128 Mbps Time = data / rate = 1 Mb / 0.128 Mbps =

7.8125 seconds This doesn’t include time to make the connection

INFO 203 Week #5 41

Packet Switching Messages are divided into packets before

going into the network Most packet switches must receive an entire

packet before forwarding it to the next switch This store-and-forward transmission introduces

delays while the switch waits for the entire packet to get there If a packet size is L, and the transmission rate is R,

the delay to receive one full packet is L/R

INFO 203 Week #5 42

Store and Forward Delay Assume 1) no queuing delay, 2) no time to

make a connection, and 3) no delay to propagate packets

Send a packet of L bits across a packet-switched network with Q links, all of which have a transmission rate of R bps For each link, the store and forward delay of L/R

seconds; this occurs Q times, for a total delay of Q*L/R seconds

INFO 203 Week #5 43

Packet Switching Each switch typically connects to many links For each link, there is an output buffer (or

output queue) to hold packets waiting to go on that link This introduces queuing delays, while a packet

waits its turn If the buffer is full, the packet can be lost – packet

loss isn’t good!

INFO 203 Week #5 44

Statistical Multiplexing Compare circuit to packet switching Suppose users are active 10% of the time,

sending 100 kbps of data, and not using the connection the other 90% of the time

If there’s a 1 Mbps connection available: TDM circuit switching would need 10 slots to

allow each user 100 kbps

INFO 203 Week #5 45

Statistical Multiplexing Packet switching could handle 35 users total

because the total number of active users will be 11 or more only 0.04% of the time (look up the binomial distribution for details) The remaining 99.96% of the time, the total data rate

is less than the 1 Mbps capacity of the connection Hence sharing resources on demand (which

is statistical multiplexing) allows the same performance 99.96% of the time, for over three times the number of users!

INFO 203 Week #5 46

Packet-Switched Networks There are two major kinds of packet-switched

networks – datagram networks and virtual-circuit networks

A datagram network forwards packets according to the host destination address Hence the Internet is a datagram network Routers forward packets to make a best effort to

get them to the destination address

INFO 203 Week #5 47

Virtual Circuit Networks A virtual circuit network forwards packets

according to virtual circuit numbers A virtual circuit (VC) is an imaginary connection

between the source and destination hosts Examples are X.25, frame relay, and asynchronous

transfer mode (ATM) Each packet has a VC identifier (VC ID) Each packet switch indexes its VC translation

table, and forwards the packet to the right outbound link

INFO 203 Week #5 48

Virtual Circuit Networks A key difference between datagram and VC

networks is that VC networks have to maintain state information about connections Each new VC means a new entry has to be added to

the VC translation table, and then is removed when the connection is ended

It also needs to keep a table to map VC numbers to output interface numbers

INFO 203 Week #5 49

Datagram Networks In datagram networks a packet of data is

wrapped in layers of addresses, which are used by routers and switches and hosts

Notice that datagram networks do not maintain state information about any packet – they only read the address and decide where to send it based on that address

INFO 203 Week #5 50

Datagram Networks Traceroute (in Windows, ‘tracert’; see also

RFC 1393) is an application that shows you the details of how a packet gets from one host to another

INFO 203 Week #5 51

Traceroute Output FROM www.adelphiacom.net TO www.nero.com. traceroute to www.nero.com (62.93.192.11), 64 hops max, 44 byte packets 1 i0.chi75.adelphiacom.net (66.109.10.17) 0.554 ms 0.420 ms 0.360 ms 2 g1-01-02-00.a0.chi75.adelphiacom.net (66.109.3.17) 0.561 ms 0.873 ms 0.313 ms 3 a1-00-00-00.c0.chi75.adelphiacom.net (66.109.3.1) 0.372 ms 0.355 ms 0.317 ms 4 so-00-01-00.c1.dca91.adelphiacom.net (66.109.0.82) 16.992 ms 16.940 ms 16.925

ms 5 p3-05-00-00.p0.dca90.adelphiacom.net (66.109.1.142) 17.748 ms 17.743 ms 17.740

ms 6 so-4-0-0.mpr2.iad5.us.above.net (64.124.11.225) 17.817 ms 17.812 ms 20.384 ms 7 so-7-0-0.mpr2.iad1.us.above.net (64.125.28.13) 17.832 ms 17.917 ms 17.798 ms 8 so-6-0-0.cr2.dca2.us.above.net (64.125.27.210) 18.178 ms 18.202 ms 18.211 ms 9 so-6-0-0.cr2.lhr3.uk.above.net (64.125.27.166) 90.064 ms 90.101 ms 97.132 ms 10 64.125.27.221.available.above.net (64.125.27.221) 107.404 ms 107.474 ms 107.519

ms 11 pos-9-1.mpr2.fra1.de.above.net (64.125.23.253) 113.379 ms 113.830 ms 113.340

ms 12 ge-9-7.er2a.fra1.de.above.net (64.125.23.186) 154.871 ms 117.584 ms 117.607 ms 13 62.93.192.11.insoft.fra2.de.mfnx.net (62.93.192.11) 113.757 ms 113.659 ms

113.576 ms

INFO 203 Week #5 52

Traceroute Output Each line of output gives you

The hop number (1, 2, …) The name of the server it’s passing through The IP address of that server (e.g. 66.109.1.142) And times of three attempts to “ping” that server

(say Hi to it), given in milliseconds (ms) Notice the example goes through servers in

the UK and Germany (uk, de), and the ping times go over a hundred milliseconds

INFO 203 Week #5 53

Summary of Network TypesTelecommunication

Networks

Circuit-switched networks

Packet-switched networks

Datagram Networks(Internet)

FDM TDM

Virtual-circuit Networks

(X.25, frame relay, ATM)

INFO 203 Week #5 54

Delays and Losses We’ve hinted at several kinds of things that

can delay a packet or make it get lost; now we’ll examine those concepts in more detail

After a packet leaves the host, it typically passes through several routers before getting to its destination

Each router examines the packet’s header to determine which outbound link it needs to follow, and puts it in a queue for that link

INFO 203 Week #5 55

Delays and Losses Four main causes of delay at each router:

Nodal processing delay Queuing delay Transmission delay Propagation delay

A

B

propagationtransmission

nodalprocessing queueing

A

B

propagationtransmission

nodalprocessing queueing

INFO 203 Week #5 56

Delays and Losses Nodal processing delay is the time needed for

the router to examine the packet’s header and choose the right outbound link Also may include time for error checking the packet Typically in microseconds for good routers

Queuing delay is the time for a packet waiting to be transmitted across the outbound link Depends mostly on how much traffic got to the router

which is waiting for the same link Could be microseconds or milliseconds in duration

INFO 203 Week #5 57

Delays and Losses Transmission delay is like the store-and-forward

delay mentioned earlier; it’s the time to transmit the packet onto the link The entire packet has to be pushed onto the link by

the router, so the transmission delay is L/R, or (packet size)/(transmission speed)

Propagation delay is the time for the packet to get to the next router Distance = speed * time, so the propagation delay is

distance/speed, where speed is 2 or 3x108 m/sec (the speed of light is 3x108 m/s)

INFO 203 Week #5 58

Delays and Losses So the delay at one node, the nodal delay, is

given bydnodal = dproc + dqueue + dtrans + dprop

Where dproc = Nodal processing delaydqueue = Queuing delaydtrans = Transmission delaydprop = Propagation delay

The relative magnitude of these terms can vary widely, depending on the circumstances

INFO 203 Week #5 59

Traffic Intensity Consider if all packets were the same size L

bits, and arrive at a router at a rate of ‘a’ packets per second The rate of data arriving at the router is L*a bits

per second The output rate from the router is its

transmission rate, R bits per second The traffic intensity is L*a/R

Want traffic intensity < 1 – why?

INFO 203 Week #5 60

Traffic Intensity Average queuing delay grows exponentially

as traffic intensity approaches one This is the router equivalent of gridlock!

It was assumed that the router could hold an infinite amount of packets in its queue A dropped or lost packet occurs when a packet

arrives at a router with its outbound link queue full Fraction of lost packets is a key measure

INFO 203 Week #5 61

End-to-end Delay So far we focused on one router Now consider the total delays getting from host to

host – the end-to-end delay End-to-end delay is just the sum of nodal delays

from one host to the other End-to-end delay = (dnodal)

INFO 203 Week #5 62

Internet Throughput Much of the Internet core has more capacity

than currently needed (it is over-provisioned) As a result, the limit of getting data through

the Internet is the speed of your access link (ISP connection) and your destination’s access link

INFO 203 Week #5 63

Layered Architecture As hinted at in the syllabus, the layers of

networking are a key concept Why use layers?

To solve a big problem, break it into little problems Each layer has a small, focused amount of work it

needs to accomplish; each layer provides services to the layer above it

Disadvantages are: possible duplication of work (error recovery on multiple layers), and violating the scope of a layer’s services

INFO 203 Week #5 64

Layered Architecture The layers are seen at right

The application layer is where user-visible software exists – HTTP, SMTP, FTP, etc. protocols

The transport layer is home to the TCP and UDP protocols

The network layer is home to the Internet Protocol, IP, and the protocols used by routers

application

transport

network

link

physical

application

transport

network

link

physical

INFO 203 Week #5 65

Layered Architecture The link layer is key for local routing; includes

Ethernet and Point-to-Point Protocol (PPP) The physical layer moves the bits of data

(frames, as we’ll see shortly) across the guided or unguided media discussed earlier Each medium has protocols for how data

is encoded and decoded

INFO 203 Week #5 66

But Wait Professor Booker! Aren’t we missing the Presentation and

Session layers?!? Yes, the OSI reference model has them between

the application and transport layers, but they aren’t directly relevant here The presentation layer includes coding and conversion

functions that are applied to application layer data – such as MPEG, QuickTime, JPG, GIF, TIFF

The session layer opens and closes communication sessions; AppleTalk is a typical protocol here

INFO 203 Week #5 67

Layered Architecture To make it more confusing, the packet we’ve

been discussing has different names as it descends the layers Terms may vary from vendor to vendor

A packet becomes A message in the application layer A segment in the transport layer A dataframe (or datagram) in the network layer A frame in the link and physical layers

INFO 203 Week #5 68

Layered Architecture With each layer, headers are added to the

message to describe the address information needed by that layer

This process is called encapsulation, as we put the message in bigger and bigger boxes

Routers and switches typically look at the link or network layer information Like a letter carrier, they don’t read your mail

INFO 203 Week #5 69

Layered Architecturesource

applicationtransportnetworklink

physical

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datagram

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physicalHtHnHl MHtHn MHt M

Mnetworklink

physical

linkphysical

HtHnHl MHtHn M

HtHn M

HtHnHl M

router

switch

message MHt M

Hnf rame

sourceapplicationtransportnetworklink

physical

HtHn MHtHn Msegment HtHt

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physicalHtHnHl MHtHnHl MHtHn MHtHn MHt MHt M

MMnetworklink

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linkphysicallink

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HtHnHl MHtHnHl MHtHn MHtHn M

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INFO 203 Week #5 70

Network Security Malware is a generic term for software that

does harm (malicious software) It could enroll your computer in a botnet, where it

helps distribute spam or help attack other computers

Much malware is self-replicating, so it can spread very quickly

INFO 203 Week #5 71

Network Security Viruses are malware that require the user to

activate it somehow, but it could be disguised as a web link

Worms can enter your computer without user activation

Trojan horses enter via a legitimate application, such as a simple game

INFO 203 Week #5 72

Network Security Threats can keep a host from getting

legitimate network traffic – this is a denial of service (DoS) attack Types of DoS attacks include exploiting a

vulnerability in the OS or an application, flooding the bandwidth leading to the host, or making the host establish phony network connections

Herds of computers can participate in a distributed DoS attack (DDoS)

INFO 203 Week #5 73

Network Security Network data can be read using packet

sniffers We’ll use one for our labs, WireShark

Or people can fake who they are on the network, and impersonate you (IP spoofing) or intercept a network connection (man in the middle attack)

INFO 203 Week #5 74

A Little History The concept of packet switching was

developed in the early 1960’s by MIT and the Rand Institute, in order to make it possible to share really expensive computer time efficiently

The first packet switches were called interface message processors (IMPs)

ARPAnet, the Internet predecessor, was proposed in 1967

INFO 203 Week #5 75

A Little History By 1969, four computers were on ARPAnet,

and RFCs were being published By 1972 there were 15 nodes on ARPAnet,

and it was first seen publicly The first email program was written in 1972 A microwave network was developed in

Hawaii, and various packet switching networks were developed by the mid 1970’s

INFO 203 Week #5 76

A Little History As the number of similar networks grew,

connecting them to aid researchers became an obvious direction

Vint Cerf helped establish the core Internet protocols by the end of the 1970’s – TCP, IP, and UDP

Robert Metcalfe defined Ethernet in 1976 By 1983, ARPAnet switched to TCP/IP

INFO 203 Week #5 77

A Little History The French installed Minitel, a public packet-

switched network, in the early 1980’s, a decade before the US caught on to the Internet

DNS wasn’t invented until the late 1980’s (RFC 1034)

The World Wide Web was invented between 1989 and 1991 by Tim Berners-Lee, based on work as far back as 1945

INFO 203 Week #5 78

A Little History At the end of 1992 there were ~200 web

servers in the world In 1994 Mosaic was formed, later known as

Netscape, and much of the world was introduced to the Internet

By the late 1990’s, peer-to-peer file sharing, instant messaging, email, and the Web formed the ‘killer apps’ that launched the world we see today

INFO 203 Week #5 79

A Little History The dot-Com bubble burst by 2001, but a few

companies survived Through the 1990’s, issues such as security

and handling of streaming video became urgent, as e-commerce became as common as a 7-11

Now more devices are connected – phones, PDAs – and we can’t imagine not having the Internet at our disposal