Transcript The Internet

IT For Engineers
Intro to Computer Networking
INFO 203
Dr. Jennifer Booker
INFO 203
Week #5
1
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
2
The Internet

Key parts of any network include

Hosts or end systems, which are the computers
and other things with which most people interact



INFO 203
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
Week #5
3
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
4
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
5
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

INFO 203
Which has units of: bits = bits/sec * sec
Week #5
6
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
7
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
8
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
Some protocols use a handshake concept
or they won’t understand each other



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
9
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
10
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
11
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
12
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
13
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
14
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
15
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
16
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
17
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
18
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)
INFO 203
Week #5
19
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

INFO 203
Typically up to 64 homes share a connection from the
provider’s central office (CO)
Week #5
20
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
INFO 203
Week #5
21
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
22
Why Does Frequency Matter?

Wireless signals can be interfered with by other
devices; when that occurs, they detune their speed




The 802.11b and 802.11g standards use the 2.4
GHz (gigahertz) frequency range


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
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
23
Wireless Network Example
Computer 1
Phone
line
DSL Modem
Gateway /
DHCP server
Hub
Computer 2
Computer 3
Or could have
Coax
Cable
Wireless
Access
Point
Cable
Modem
Laptop 1
Wireless
Repeater
INFO 203
Week #5
Laptop 2
24
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
INFO 203
Week #5
25
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
26
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
27
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
28
Copper wire
and cylinder
Coaxial cable



Insulation
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
INFO 203
Week #5
29
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
30
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
31
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
32
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
33
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
34
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
35
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

INFO 203
Dump packets into the network with no reserved path,
and make a best effort to get packet to destination
Week #5
36
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
37
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
INFO 203
Week #5
38
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

INFO 203
k = 1000, M = 1,000,000, G = 1 billion
Week #5
39
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
40
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

INFO 203
If a packet size is L, and the transmission rate is R,
the delay to receive one full packet is L/R
Week #5
41
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 packetswitched 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
42
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
43
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
44
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
45
Packet-Switched Networks


There are two major kinds of packet-switched
networks – datagram networks and virtualcircuit 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
46
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
47
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
48
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
49
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
50
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
51
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
52
Summary of Network Types
Telecommunication
Networks
Circuit-switched
networks
FDM
INFO 203
Packet-switched
networks
Virtual-circuit
Networks
(X.25, frame
relay, ATM)
TDM
Week #5
Datagram
Networks
(Internet)
53
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
54
Delays and Losses

Four main causes of delay at each router:




Nodal processing delay
Queuing delay
Transmission delay
Propagation delay
transmission
A
propagation
B
INFO 203
nodal
processing
Week #5
queueing
55
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


INFO 203
Depends mostly on how much traffic got to the router
which is waiting for the same link
Could be microseconds or milliseconds in duration
Week #5
56
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

INFO 203
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)
Week #5
57
Delays and Losses

So the delay at one node, the nodal delay, is
given by
dnodal = dproc + dqueue + dtrans + dprop


Where dproc = Nodal processing delay
dqueue = Queuing delay
dtrans = Transmission delay
dprop = Propagation delay
The relative magnitude of these terms can vary
widely, depending on the circumstances
INFO 203
Week #5
58
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
59
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
60
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 = S(dnodal)
INFO 203
Week #5
61
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
62
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
63
Layered Architecture

The layers are seen at right



The application layer is where uservisible 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
INFO 203
Week #5
application
transport
network
link
physical
64
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
65
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


INFO 203
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
Week #5
66
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
67
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
68
Layered Architecture
INFO 203
Week #5
69
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
70
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
71
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
72
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
73
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
74
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
75
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
76
A Little History



The French installed Minitel, a public packetswitched 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
77
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
78
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
INFO 203
Week #5
79